It is classified as bottom-up manufacturing which involves building up of the atom or molecular constituents as against the top method which involves making smaller and smaller structures through etching from the bulk material as exemplified by the semiconductor industry.
Gas condensation was the first technique used to synthesize nanocrystalline metals and alloys. In this technique, a metallic or inorganic material is vaporized using thermal evaporation sources such as a Joule heated refractory crucibles, electron beam evaporation devices, in an atmosphere of 1-50 m bar. In gas evaporation, a high residual gas pressure causes the formation of ultra fine particles (100 nm) by gas phase collision. The ultrafiine particles are formed by collision of evaporated atoms with residual gas molecules. Gas pressures greater than 3 mPa (10 torr) are required. Vaporization sources may be resistive heating, high energy electron beams, low energy electron beam and inducting heating. Clusters form in the vicinity of the source by homogenous nucleation in the gas phase grew by incorporation by atoms in the gas phase. It comprises of a ultra high vacuum (UHV) system fitted evaporation source, a cluster collection device of liquid nitrogen filled cold finger scrapper assembly and compaction device. During heating, atoms condense in the supersaturation zone close to Joule heating device. The nanoparticles are removed by scrapper in the form of a metallic plate. Evaporation is to be done from W, Ta or Mo refractory metal crucibles. If the metals react with crucibles, electron beam evaporation technique is to be used. The method is extremely slow. The method suffers from limitations such as a source-precursor incompatibility, temperature ranges and dissimilar evaporation rates in an alloy. Alternative sources have been developed over the years. For instance, Fe is evaporated into an inert gas atmosphere (He). Through collision with the atoms the evaporated Fe atoms loose kinetic energy and condense in the form of small crystallite crystals, which accumulate as a loose powder. Sputtering or laser evaporation may be used instead of thermal evaporation. Sputtering is a non-thermal process in which surface atoms are physically ejected from the surface by momentum transfer from an energetic bombarding species of atomic/molecular size. Typical sputtering uses a glow discharge or ion beam. Interaction events which occur at and near the target surface during the sputtering process in magnetron sputtering has advantage over diode and triode sputtering. In magnetron sputtering, most of the plasma is confined to the near target region. Other alternate energy sources which have been successfully used to produce clusters or ultra fine particles are sputtering electron beam heating and plasma methods. Sputtering has been used in low pressure environment to produce a variety of clusters including Ag, Fe and Si.
Before proceeding to the other methods, it is important to understand the terms vacuum deposition and vaporization or vacuum evaporation. In vacuum deposition process, elements, alloys or compounds are vaporized and deposited in a vacuum . The vaporization source is the one that vaporizes materials by thermal processes. The process is carried out at pressure of less than 0.1 Pa (1 m Torr) and in vacuum levels of 10 to 0.1 MPa. The substrate temperature ranges from ambient to 500C. The saturation or equilibrium vapor pressure of a material is defined as the vapor pressure of the material in equilibrium with the solid or liquid surface. For vacuum deposition, a reasonable deposition rate can be obtained if the vaporization rate is fairly high. A useful deposition rate is obtained at a vapor pressure of 1.3 Pa (0.01 Torr).
Vapor phase nucleation can occur in dense vapor cloud by multibody collisions, The atoms are passed through a gas to provide necessary collision and cooling for nucleation. These particles are in the range of 1 to 100 nm and are called ultra fine particles or clusters. The advantages associated with vacuum deposition process are high deposition rates and economy. However, the deposition of many compounds is difficult. Nanoparticles produced from a supersaturated vapor are usually longer than the cluster.
CVD is a well known process in which a solid is deposited on a heated surface via a chemical reaction from the vapor or gas phase. CVC reaction requires activation energy to proceed. This energy can be provided by several methods. In thermal CVD the reaction is activated by a high temperature above 900oC. A typical apparatus comprises of gas supply system, deposition chamber and an exhaust system. In plasma CVD, the reaction is activated by plasma at temperatures between 300 and 700C. In laser CVD, pyrolysis occurs when laser thermal energy heats an absorbing substrate. In photo-laser CVD, the chemical reaction is induced by ultra violet radiation which has sufficient photon energy, to break the chemical bond in the reactant molecules. In this process, the reaction is photon activated and deposition occurs at room temperature. Nano composite powders have been prepared by CVD. SiC/Si3N composite powder was prepared using SiH4, CH4, WF6 and H2 as a source of gas at 1400C. Another process called chemical vapor condensation (CVC) was developed in Germany in 1994. It involves pyrolysis of vapors of metal organic precursors in a reduced pressure atmosphere. Particles of ZrO2, Y2O3 and nanowhiskers have been produced by CVC method. A metalorganic precursor is introduced in the hot zone of the reactor using mass flow controller. For instance, hexamethyldisilazane (CH3)3 Si NHSi (CH3)3 was used to produce SiCxNyOz powder by CVC technique. The reactor allows synthesis of mixtures of nanoparticles of two phases or doped nanoparticles by supplying two precursors at the front end of reactor and coated nanoparticles, n-ZrO2, coated with n-Al2O3 by supplying a second precursor in a second stage of reactor. The process yields quantities in excess of 20 g/hr. The yield can be further improved by enlarging the diameter of hot wall reactor and mass of fluid through the reactor. Typical nanocrystalline materials which have been synthesized are shown in Table 1.
Unlike many of the methods mentioned above, mechanical attrition produces its nanostructures not by cluster assembly but by the structural decomposition of coarser grained structures as a result of plastic deformation. Elemental powders of Al and -SiC were prepared in a high energy ball mill. More recently, ceramic/ceramic nanocomposite WC-14% MgO material has been fabricated. The ball milling and rod milling techniques belong to the mechanical alloying process which has received much attention as a powerful tool for the fabrication of several advanced materials. Mechanical alloying is a unique process, which can be carried out at room temperature. The process can be performed on both high energy mills, centrifugal type mill and vibratory type mill, and low energy tumbling mill.
The milling procedure takes place by a stirring action of a agitator which has a vertical rotator central shaft with horizontal arms (impellers). The rotation speed was later increased to 500 rpm. Also, the milling temperature was in greater control.
Centrifugal forces are caused by rotation of the supporting disc and autonomous turning of the vial. The milling media and charge powder alternatively roll on the inner wall of the vial and are thrown off across the bowl at high speed (360 rpm).
They have been used for successful preparation of mechanically alloyed powder. They are simple to operate with low operation costs. A laboratory scale rod mill was used to prepare homogenous amorphous Al30Ta70 powder by using S.S. cylinder rods. Single-phase amorphous powder of AlxTm100-x with low iron concentration can be formed by this technique.
High-energy ball milling is an already established technology, however, it has been considered dirty because of contamination problems with iron. However, the use of tungsten carbide component and inert atmosphere and /or high vacuum processes has reduced impurity levels to within acceptable limits. Common drawbacks include low surface, highly poly disperse size distribution, and partially amorphous state of the powder. These powders are highly reactive with oxygen, hydrogen and nitrogen. Mechanical alloying leads to the fabrication of alloys, which cannot be produced by conventional techniques. It would not be possible to produce an alloy of Al-Ta, because of the difference in melting points of Al (933 K) and Ta (3293 K) by any conventional process. However, it can be fabricated by mechanical alloying using ball milling process.
Several other processes such as hydrodynamic cavitation micro emulsion and sonochemical processing techniques have also been used. In cavitation process nanoparticles are generated through creation and release of gas bubbles inside the sol-gel solution. By pressurizing in super critical drying chamber and exposing to cavitational disturbances and high temperature heating, the sol-gel is mixed. Te erupted hydrodynamic bubbles cause the nucleation, growth and quenching of nanoparticles. Particle size can be controlled by adjusting pressure and solution retention times.
In addition to techniques mentioned above, the sol-gel processing techniques have also been extensively used. Colloidal particles are much larger than normal molecules or nanoparticles. However, upon mixing with a liquid colloids appear bulky whereas the nanosized molecules always look clear. It involves the evolution of networks through the formation of colloidal suspension (sol) and gelatin to form a network in continuous liquid phase (gel). The precursor for synthesizing these colloids consists of ions of metal alkoxides and aloxysilanes. The most widely used are tetramethoxysilane (TMOS), and tetraethoxysilanes (TEOS) which form silica gels. Alkoxides are immiscible in water. They are organo metallic precursors for silica, aluminum, titanium, zirconium and many others. Mutual solvent alcohol is used. The sol gel process involves initially a homogeneous solution of one or more selected alkoxides. These are organic precursors for silica, alumina, titania, zirconia, among others. A catalyst is used to start reaction and control pH. Sol-gel formation occurs in four stages.
During hydrolysis, addition of water results in the replacement of [OR] group with [OH-] group. Hydrolysis occurs by attack of oxygen on silicon atoms in silica gel. Hydrolysis can be accelerated by adding a catalyst such as HCl and NH3. Hydrolysis continues until all alkoxy groups are replaced by hydroxyl groups. Subsequent condensation involving silanol group (Si-OH) produced siloxane bonds (Si-O-Si) and alcohol and water. Hydrolysis occurs by attack of oxygen contained in the water on the silicon atom.
Polymerization to form siloxane bond occurs by either a water producing or alcohol producing condensation reaction. The end result of condensation products is the formation of monomer, dimer, cyclic tetramer, and high order rings. The rate of hydrolysis is affected by pH, reagent concentration and H2O/Si molar ratio (in case of silica gels). Also ageing and drying are important. By control of these factors, it is possible to vary the structure and properties of sol-gel derived inorganic networks.
As the number of siloxane bonds increase, the molecules aggregate in the solution, where they form a network, a gel is formed upon drying. The water and alcohol are driven off and the network shrinks. At values of pH of greater then 7, and H2O/Si value ranging from 7 to 5. Spherical nano-particles are formed. Polymerization to form siloxane bonds by either an alcohol producing or water producing condensate occurs.
Above pH of 7, Silica is more soluble and silica particles grow in size. Growth stops when the difference in solubility between the smallest and largest particles becomes indistinguishable. Larger particles are formed at higher temperatures. Zirconium and Yttrium gels can be similarly produced.
Despite improvements in both chemical and physical methods of synthesis, there remain some problems and limitations. Laser vaporization technique has offered several advantages over other heating techniques. A high energy pulsed laser with an intensity flux of 106 - 107 W/cm2 is forced on target material. The plasma causes high vaporization and high temperature (10,000C). Typical yields are 1014-1015 atoms from the surface area of 0.01 cm2 in a 10-8 s pulse. Thus a high density of vapor is produced in a very short time (10-8 s), which is useful for direct deposition of particles.
Nanostructured materials can also be produced by electrodeposition. These films are mechanically strong, uniform and strong. Substantial progress has been made in nanostructured coatings applied either by DVD or CVD. Many other non-conventional processes such as hypersonic plasma particle deposition (HPPD) have been used to synthesize and deposit nanoparticles. The significant potential of nanomaterial synthesis and their applications is virtually unexplored. They offer numerous challenges to overcome. Understanding more of synthesis would help in designing better materials. It has been shown that certain properties of nanostructured deposits such as hardness, wear resistance and electrical resistivity are strongly affected by grain size. A combination of increased hardness and wear resistance results in a superior coating performance.
SE5133/SE5134: These are graphene-based filler compounds that function for both corrosion protection and heat dissipation. It is the perfect choice for any corrosion-weak equipment that requires a great deal of heat dissipation.
The synthesis of gold and silver nanoparticles was evaluated using green chemistry metrics, with an emphasis on process mass intensity (PMI). Opportunities for improving synthetic methods were identified based on these metrics. Solvent usage was identified as the biggest challenge among nanoparticle syntheses, including those otherwise deemed as green, with PMIs that were typically in the thousands. The synthesis of ligated metal nanoparticles by arrested precipitation was identified as the best opportunity for making impactful improvements, since they are the most industrially relevant but the least green. Although this review focuses on gold and silver nanoparticles, much of the discussion also pertains to inorganic nanomaterials synthesis in general.
O. J. Gbadeyan, S. Adali, G. Bright, B. Sithole, S. Onwubu, "Optimization of Milling Procedures for Synthesizing Nano-CaCO3 from Achatina fulica Shell through Mechanochemical Techniques", Journal of Nanomaterials, vol. 2020, Article ID 4370172, 9 pages, 2020. https://doi.org/10.1155/2020/4370172
The possibility of obtaining calcium carbonate nanoparticles from Achatina fulica shell through mechanochemical synthesis to be used as a modifying filler for polymer materials has been studied. The process of obtaining calcium carbonate nanopowders includes two stages: dry and wet milling processes. At the first stage, the collected shell was dry milled and undergone mechanical sieving to 50m. The shell particles were wet milled afterward with four different solvents (water, methanol, ethylene glycol, and ethanol) and washed using the decantation method. The particle size and shape were investigated on transmission electron microscopy, and twenty-three particle counts were examined using an iTEM image analyzer. Significantly, nanoparticle sizes ranging from 11.56 to 180.06nm of calcium carbonate was achieved after the dry and wet milling processes. The size particles collected vary with the different solvents used, and calcium carbonate synthesis with ethanol offered the smallest organic particle size with the average size ranging within 13.48-42.90nm. The effect of the solvent on the chemical characteristics such as the functional group, elemental composition, and carbonate ion of calcium carbonate nanopowders obtained from Achatina fulica shell was investigated. The chemical characterization was analyzed using Fourier transform infrared (FTIR) and a scanning electron microscope (SEM) equipped with an energy-dispersive spectroscope (EDX). The effect of milling procedures on the mechanical properties such as tensile strength, stiffness, and hardness of prepared nanocomposites was also determined. This technique has shown that calcium carbonate nanoparticles can be produced at low cost, with low agglomeration, uniformity of crystal morphology, and structure from Achatina fulica shell. It also proved that the solvents used for milling have no adverse effect on the chemical properties of the nano-CaCO3 produced. The loading of calcium carbonate nanoparticles, wet milled with different solvents, exhibited different mechanical properties, and nanocomposites filled with methanol-milled nano-CaCO3 offered superior mechanical properties.
Nanosized calcium carbonate (CaCO3) has received noteworthy consideration for several applications due to its availability, advantageous mechanical strength, and thermal stability . It is commonly used as filler or reinforcement for polymeric materials, papers, and paints. This carbon-based material is obtained from several resources such as rock, humans, and animal waste through different methods. Over many decades, montmorillonite and kaolinite with a high concentration of CaCO3 commonly referred to as nanoclay are commonly used and soured from rock and synthesized using either gas pressure blasting or explosion method . Studies conducted confirmed the effectiveness of nanoclay in improving several composite properties [5, 6]. However, it has been discovered that the end-of-life of the composite produced with nanoclays tends to have negative impacts on human health, and, at times, the composite is more expensive when compared to naturally sourced fillers . These drawbacks consequently have reduced the use of this filler in some countries.
The harmful impact of the abovementioned fillers and factors such as climate change compelled materials scientist to source for alternative filler material. The fillers are sourced from natural resources that not only offer suitable filler material properties but also meet societal needs and support global sustainability. Consequently, in recent decades, calcium carbonate (CaCO3) of different particle sizes extracted from natural resources such as bones, horns, and animal shells is used as reinforcement to enhance thermal stability, degradation, strength, and physical properties of polymeric materials .
Several types of research have investigated the functional group, elemental composition, and minerals present in eggshell, mollusk shell, and animal bone . These natural resources were discovered to have a higher content of calcium carbonate (CaCO3), especially eggshell, which was confirmed to have about 95% of CaCO3 . Furthermore, mollusk shell, oyster shell, and animal bone have been investigated for CaCO3, and they were found to have adequate filler-appropriate properties for different applications. Consequently, calcium carbonate produced from animal waste has been suggested to be used as an alternative to commercial CaCO3 for some applications, which include but not limited to the dental and medical applications [8, 9, 1518]. The mechanism behind the physical properties of shell structure has been studied [19, 20]. Filetin et al.  investigated microhardness of Pinna pectinata (Pinnidae), with the Adriatic Sea mollusk shell structure as a function of the indentation load. The result proved that the microhardness of the shell depends on the load for the nacreous (inner layer of the shell) and prismatic (outer layer of the shell) structures. Furthermore, the microhardness value measure for the outer layer was higher than that for the inner layer with a lesser margin. Besides, a notable aragonite platelet structure was seen in between the nacreous and prismatic predominant normal stress, preventing interlamellar sliding/plastic deformation of the shell. This study was consistent with our previous investigation on the physical and morphological study of Achatina fulica shell. The layer of aragonite was referred to as reinforcement and served as the main functional mechanism that prevents plastic deformation which resulted in high resistance to indentation, resulting in relatively high microhardness and tensile strength properties . However, there is limited literature about CaCO3, synthesized from these natural resources, being used either as a filler material to fabricate composite or as polymer material reinforcement. This output may be because milling a large quantity of these materials to smaller particle sizes comes with many challenges, which include but not limited to particle agglomeration.
Despite the availability of numerous milling techniques used for small organic particle synthesis, the mechanochemical technique has been found to be most effective [4, 21]. This organic synthesis mechanism has been regarded as a significant change towards achieving the sustainable and efficient process of producing small molecular sizes of grains . Numerous researchers confirmed that mechanochemical techniques are a branch of chemistry that covers any chemical transformations induced mechanically or physiochemical changes of the material of any state of combination due to the influence of mechanical energy such as friction, compression, or shear [15, 2326]. A mechanochemical procedure such as hand grinding or ball milling has been reported to influence the structure and composition of materials. Consequently, it brings about an opportunity for the preparation and fabrication of nanomaterial particles using top-down tactics .
Ball mill is a high-energy mill process especially used for an energy-intensive process like mechanical alloying, mechanochemistry, or mechanical activation. Planetary ball mill is used to determine the dependence of process efficiency using milling parameters such as ball size and number, mill geometry, and velocity of the rotating parts. However, the maximum efficiency of the grinding process achieved with high-density balls, and higher rotation speed seems to provide materials with higher impact energy in comparison with small, low-density balls and lower rotation speed [28, 29].
The planetary ball mill theory and its efficient procedure for producing small molecular sizes of grains achieved using the mechanochemical technique made it a promising candidate for solvent-free synthesis [21, 30, 31]. However, solvent-free synthesis may not apply to all materials, especially calcium carbonate-based materials, where the agglomeration of particles is dominant. Research studies have proved that dry milling technique causes a large agglomeration of the particles during synthesis. Most times, this results in a bimodal size distribution, which weakens the bond in nanocomposites . Having this in mind, this present study deals with the optimization of milling procedures for synthesizing nano-CaCO3 from Achatina fulica shell through mechanochemical (wet milling) techniques using different solvents. It further investigates the consequence of the solvent on the reinforcement effect of the nano-CaCO3 on polymeric material.
Achatina fulica snail shells collected from the University of Kwazulu-Natal, Westville campus soccer pitch, were washed and disinfected. Snail shells were soaked in a solution of water and 5% diluted household sodium hypochlorite for seven hours. Afterward, they were rinsed with distilled water and dried in the oven at 150C for 20mins to ensure absolute dehydration.
The clean shells were kept under room temperature for 24 hours to dry before milling. The milling process was done in two stages. The first stage was dry milling, and the second was wet milling. At the first stage, 30g of dried Achatina fulica snail shells was measured and dry milled in a planetary ball mill (Retsch PM 100) to obtain fine particles [12, 36]. The milling setup comprises 50 stainless steel balls of 10mm diameter and a 500mL stainless steel jar (inner diameter of 100mm). The snail shells were milled at 450rpm for 30 minutes in a clockwise direction. The shell powder after the milling process was sieved using a mechanical sieving shaker (Retsch, AS 200 basics, Germany) to a particle size of 50m. In the second stage, the collected snail shell powder was wet milled to achieve nanoparticles. Accordingly, 30g of snail shell particle size of 50m was measured into the 500mL stainless steel jar. After that, 100mL of a different solvent such as water, methanol, ethylene glycol, and ethanol was added differently and wet milled at 450rpm for 258mins in a clockwise direction. Subsequently, mixtures of fine particles and solvent were separated by removing the liquid layer that is free of a precipitate using the decantation method. To ensure the total removal of the solvent, settled particles were washed by adding distilled water and separated using the decantation method. This process was repeated five times to ensure the cleanness of fine particles. Then, particles were dried in the oven at 35C for 72 hours. The fine powders obtained after that were characterized to establish the successful synthesis of the CaCO3.
The particle size, shape, and distribution of snail shell particles milled with different solvents were observed under a transmission electron microscope (TEM). The investigation was conducted on JEM Jeol 2100 (Japan). Before this investigation, a small amount of snail shell powder was dispersed in 10mL of ethanol and sonicated at 10kV for 10mins. Afterward, a thin cross section of cryomicrotomed specimens was prepared using a Leica microtome and placed on carbon copper grids. The TEM image was further analyzed on iTEM analyzer software, version 5.0.1 (Japan), to determine the range of particle sizes.
The Fourier transform infrared (FTIR) spectra were measured to identify the functional group constituents of snail shell particles milled with different solvents. A PerkinElmer Universal ATR spectrometer was used for investigation. A small quantity of each sample was placed in the sample pouch. Subsequently, an initial background check was conducted before scanning within the range of 550-4000cm1 at a resolution of 4cm1.
The chemical composition of the shell was determined on the Zeiss Ultra FEG-SEM field emission scanning electron microscope (SEM) equipped with an energy-dispersive spectroscope (EDX). Before SEM (field emission, Carl Zeiss) observation, the surface was coated with a thin, electric conductive gold film to prevent a buildup of electrostatic charge.
Nanocomposites were prepared using the conventional resin casting method. To facilitate shell particle dispersion and to reduce matrix viscosity, 100wt.% of epoxy resin was measured into the beaker using a Snowrex digital electronic scale with 0.1g and heated up to 70C. Subsequently, 2wt.% of CaCO3 nanoparticles from shell particles was slowly incorporated into the matrix and mixed using a mechanical stirrer at 500rpm for one hour to ensure homogeneous dispersion of shell particles. Nanocomposites were taken off the stirrer and were allowed to cool down to room temperature. Then, the catalyst was added to nanocomposites at a mixing ratio of 100-30wt.%. The blend was thereafter poured into an open mold to have a composite panel and allowed to cure for two days. To facilitate the easy removal of the nanocomposite panel, the wax was applied to the inner surface of the plastic mold before pouring. The mechanical strength of the fabricated nanocomposite panel was investigated after 15 days.
The tensile strength and stiffness of nanocomposite were determined according to the ASTM D3039 test standard. The test was carried out on samples using a Lloyd universal testing machine (Model 43) fitted with a 30kN load cell. Five samples were tested at ambient temperature, and the constant crosshead speed of testing used was 1.3mm/min. The mean value of the five samples was reported.
The Barcol impressor hardness tester commonly used for composite material was used to determine the hardness property of composite panel samples. The test was performed according to the ASTM D2583 test standard. A standard impressor with a steel truncated cone (6.82 height and a tip diameter of 0.55mm) was used at an angle of 26. This intender was positioned on the surface of the composite panel, and a uniform downward press was applied by hand, and readings were collected directly from the dial indicator. Twenty-five indentation readings were randomly collected on the sample, and the mean values were used for graphical illustration and discussion.
Figure 1 presents the FTIR spectra of the raw snail shell (Achatina fulica) powder and CaCO3 nanoparticle obtained through ball milling mechanochemical techniques using different solvents. Numerous bands were seen within the range of 550cm1-4000cm1.
Noticeably, the spectra for the raw shell and synthesized nano-CaCO3 are quite different within the functional group region. On the contrary, insignificant different FTIR spectra peaks and bends were observed between nano-CaCO3 wet milled and synthesized with different solvents such as ethylene glycol, ethanol, water, and methanol. Furthermore, the raw shell FTIR spectra display absorption peaks of calcite at about 713cm1 and 873cm1, while nano-CaCO3 synthesized with different solvents such as ethylene glycol, ethanol, water, and methanol shows the absorption peaks of aragonite at around 712cm1, 854cm1, and 1083cm1. The peaks of calcite displayed at 713cm1 and 873cm1 were accredited to the out-of-plane bending and in-of-plane bending vibration modes, asymmetric and symmetric stretching for calcium carbonate (CO32) molecules.
Furthermore, a very close prominent absorption peak is observed for both the raw shell powder and the synthesized CaCO3 nanoparticle (1474cm1 and 1448cm1) at the functional group region. These were associated with the presence of carbonate ions in both materials. The FTIR spectra observed for the raw shell powder were consistent with the literature for calcite [12, 16, 37, 38]. The absorption peaks of aragonite displayed at around 1083cm1 of CaCO3 nanoparticles synthesized with different solvents such as ethylene glycol, ethanol, water, and methanol could be attributed to symmetric carbonate stretching vibration, and the absorption peaks of aragonite displayed at around 854cm1 were accredited to carbonate out-of-plane bending vibrations . Additionally, the carbonyl group C=O bending identified around 1788cm1 was attributed to solvent (ethylene glycol, ethanol, water, and methanol) used for mechanochemical processes. Similarly, the tiny slope of carboxyl group O-H stretching is observed at around 2533cm1. This is associated with traces of water molecules. This suggests that CaCO3 nanoparticles can be obtained from snail shell Achatina fulica using wet milling with ethylene glycol, ethanol, water, or methanol using mechanochemical procedures.
The elemental composition of the raw snail shell and CaCO3 nanoparticle synthesized with different solvents such as ethylene glycol, ethanol, water, and methanol is shown in Table 1. An elemental composition such as carbon, oxygen, and calcium dominated different weight percentages in both raw snail shells and the synthesized nano-CaCO3. It was observed that the raw snail contains a high volume of CaCO3 of about 99.4wt.% and other metal oxides of about 6wt.%. However, this was lesser compared to the synthesized nano-CaCO3 that has 100wt.% CaCO3 irrespective of the solvent used for the wet milling process. This may suggest that the mechanochemical procedure used to synthesize helps in achieving small molecular nanoparticles and the decantation method adopted also helps in purification of the nanoparticle, resulting in clean 100wt.% CaCO3.
This performance may be a result of the milling period and solvent used. Among the nano-CaCO3 synthesized with different solvents and raw snail shells, water-synthesized nano-CaCO3 contains the highest amount of carbon, which eventually reduces the weight percentage of oxygen and calcium present in the material. The weight percentage of these components suggests that the use of water increases the carbon content in the synthesized CaCO3, which make it harder than others; this fact can be related to the mechanical property improvement observed in Figures 24.
Table 2 presents particle sizes of the synthesized CaCO3 nanoparticles that were investigated using iTEM Jeol 2100 HR (high resolution). To determine the appropriate solvent for optimizing the wet milling method for producing nano-CaCO3, TEM images were further analyzed under TEM image analyzer software version 5.0.1 on volume base. Significantly, 28 counts of CaCO3 particle sizes randomly selected were investigated against each solvent used. Figure 5 shows the TEM image analysis for CaCO3 powder obtained, and the means of the powder consisted of 25.35nm63.68nm sizes of a particle having semisphere morphology.
The particle size of ethanol-synthesized CaCO3 ranges from 13.43nm to 42.56nm, ethylene glycol-synthesized CaCO3 ranges from 11.56nm to 65.78nm, methanol-synthesized CaCO3 ranges from 12.57nm to 98.66nm, and water-synthesized CaCO3 ranges from 24.29nm to 180.06nm. Notably, nanosized particles within the range of 100nm were observed for all synthesized CaCO3. However, water-synthesized CaCO3 has the biggest particle size of 63.68nm, considering the mean of the 25 counts, as shown in Table 2. This particle size is consistent with figure observed in Table 1, where water-synthesized CaCO3 powder has high carbon content.
The presence of water mixtures has been confirmed to affect CaCO3 polymorphs and morphology . This fact suggests that the inclusion of water before the milling process affected polymorphs and morphology of the shell powder, which eventually prevents the effectiveness of the ball milling process, resulting in larger particle sizes. Furthermore, ethanol-synthesized nano-CaCO3 has the smallest range of particle sizes. This outcome proved the effect of ethanol on breaking CaCO3 molecules into small sizes. Additionally, a low standard deviation was observed for 28 counts of CaCO3 particle sizes randomly selected. This consequence depicts the effectiveness of ball milling in providing uniform particle sizes that are very close to the mean value of the particle sizes.
The reinforcement effect of synthesized nano-CaCO3 using different solvents through mechanochemical was investigated. Table 3 shows that the loading of the manufactured nanoparticle enhanced the mechanical properties of the epoxy composite. This trend is consistent with previous findings.
This performance may be attributed to the good dispersion and interconnecting networked structure of the particles incorporated in the matrix that formed a tougher, strengthened, and stronger structure than neat epoxy. This trend is consistent with pieces of literature where filler loading enhances mechanical properties [3, 8, 41]. The mechanical property results shown in Table 3 are higher compared with those reported in some available literature where CaCO3 synthesized from other shells are used to improved mechanical properties . The loading of CaCO3 synthesized from a shell such as eggshell and mollusk and milled to microparticles improved the mechanical properties; however, loading of Achatina fulica shell offered superior properties . This performance may be attributed to excellent dispersion of particles in the polymeric material shown in Figure 6, which was facilitated by the small particle sizes of the synthesized calcium carbonate particles.
Nano-CaCO3 produced with ethanol- and methanol-filled composites exhibited almost the same tensile strength and hardness properties, as shown in Figures 2 and 4. The loading of nano-CaCO3 synthesized with ethanol improved the strength of epoxy by 22.42%, and incorporation of nano-CaCO3 manufactured by methanol enhanced tensile strength by 21.34%. This improvement may be attributed to the particle size and shape of the synthesized nano-CaCO3 incorporated.
Tensile strength values for the epoxy composite filled with nano-CaCO3 synthesized with ethanol glycol and water are on the lower side compared to nano-CaCO3 produced with the ethanol- and methanol-filled composites. On the contrary, hardness properties for nano-CaCO3 synthesized with ethanol glycol- and water-filled composites were superior to those of nano-CaCO3 produced with ethanol- and methanol-filled composites as represented in Figure 4. This confirmed that the loading of nano-CaCO3 synthesized with ethanol glycol and water increases hardness, which makes it brittles. The brittleness of this material is the reflection of low tensile strength offered by this composite, as shown in Figure 2.
Figure 3 shows that the loading of synthesized nano-CaCO3 is not only an efficient way to improve the mechanical strength of polymeric material but also enhances stiffness. The incorporation of synthesized nano-CaCO3 improved the stiffness of epoxy nanocomposite irrespective of the solvent used for synthesizing the nanoparticles. The addition of nano-CaCO3 synthesized with ethanol through mechanochemical techniques increased epoxy stiffness by 57.7%, and incorporation of nano-CaCO3 produced with the addition of ethanol glycol enhanced the stiffness of epoxy by 56.8%. The addition of nano-CaCO3 synthesized with water through mechanochemical techniques increased epoxy stiffness by 10.65%, and the loading of nano-CaCO3 wet milled with methanol improved stiffness by 84.65%. Although loading of synthesized nano-CaCO3 improved stiffness, the epoxy composite filled with nano-CaCO3 wet milled with methanol offered superior stiffness.
TEM images presented in Figure 6 are for the epoxy polymer filled with nano-CaCO3 milled using different solvents. The dark phase of the image signifies the nano-CaCO3, and the lighter phase of the image signifies the polymer matrix. The TEM micrograph not only shows the well-dispersed nano-CaCO3 in the matrix but also shows that the size of the nanoparticles is slightly different. This trend complements different particle sizes of synthesized nano-CaCO3 shown in Table 2. Furthermore, the homogeneous dispersion of the nanoparticle shown in the TEM image formed an interlocking structure that strengthened the epoxy composite, which eventually led to the improved mechanical properties observed in Table 3.
Nano-CaCO3 was successfully synthesized from Achatina fulica shell. The reinforcement effect of the produced nanocalcium carbonate particles, wet milled with different solvents using the mechanochemical technique, was investigated. High-speed (450rpm) balling milling machine was used to synthesize nanoparticle sizes. The mixture of 100mL of different solvents and 30g of raw snail powder of particle was wet milled at 450rpm for 258mins in a clockwise direction to produce nano-CaCO3. It was discovered that nanoparticle particle sizes (25.35nm63.68nm) of calcium carbonate could be synthesized from Achatina fulica shell using the mechanochemical wet milling technique.
FTIR spectra for the raw shell display absorption peaks of calcite at about 713cm1 and 873cm1 and were accredited to out-of-plane bending and in-of-plane bending vibration modes, asymmetric and symmetric stretching for calcium carbonate (CO32) molecules. On the other hand, nano-CaCO3 synthesized with different solvents such as ethylene glycol, ethanol, water, and methanol shows the absorption peaks of aragonite at around 712cm1, 854cm1, and 1083cm1. The observed absorption peaks were attributed to carbonate out-of-plane bending vibrations. This bending vibration proves that milling Achatina fulica shell to nanoparticles changed the polymorphs of the shell powder at microsize from calcite to aragonite.
The energy-dispersive spectroscope (EDX) confirmed that the mechanochemical procedure used to synthesize nano-CaCO3 from Achatina fulica shell helped not only in achieving small molecular nanoparticles but also in purification, resulting in unsoiled 100wt.% CaCO3. TEM image analyzer results evidenced that the CaCO3 powder obtained consisted of a particle size range of 25.35nm63.68nm with semisphere morphology. The mechanical property results show that the loading of nano-CaCO3 synthesized from Achatina fulica shell through the mechanochemical procedure was an effective way of modifying mechanical strength. Although loading of synthesized nano-CaCO3 improved strength and stiffness polymetric material however, the epoxy composite filled with nano-CaCO3 wet milled with methanol offered superior stiffness.
The completion of this study brought forward some limitations that opened up opportunities for future work. The drawback included but not limited to the long milling period of the shells. Thus, the reduction of the milling process for synthesizing nano-CaCO3 from Achatina fulica shell shall be a potential area for future work.
The author would like to acknowledge the scholarship support towards the remission of school fees from the University of Kwazulu-Natal and financial assistance received from the CSIR and the Department of Science and Innovation (General Business Support Treasury funding).
Copyright 2020 O. J. Gbadeyan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Nanotechnology is the study, application, and engineering of materials, devices and systems on a very small scale: by definition, it involves the manipulation of matter with at least one dimension sized from 1 to 100 nanometers, deemed nanomaterials. At this scale, sometimes referred to as the quantum realm, quantum mechanical effects play a large role in the properties and interactions of matter. These quantum effects generate unique phenomena, and the exploitation of this reality allows for the production of an enormously greater range of possible material characteristics than are achievable through conventional, macro or even micro scale engineering.
American Elements nanoscience products have found uses in fields such as medicine, electronics, green technology, defense, and water purification. New products and applications for nanotechnology are being invented every day. As products continually become more and more dependent upon nanotechnology, nanomaterials will become ever more important to our daily lives.
In his famous talk entitled Theres Plenty of Room at the Bottom, Richard Feynman set the stage for research into applied nanoscience. The speech, which was delivered on December 29th, 1959 at the annual meeting of the American Physical Society at the California Institute of Technology, marked a revolution in the way the scientists looked at materials and is widely credited as one of the turning points in the history of materials science that spurred nanotechnology research. At the time, many engineers were interested in miniaturizing devices. For example, engineers of the era talked about making electric motors the size of a fingernail. However, while some scientists were working on devices that could write the Lords Prayer on the head of a pin, Feynman was asking why we couldnt write the entire Encyclopedia Britannica on the head of a pin. Feynman proposed engineering on a radically smaller scale, millions of times smaller than the popular trend at the time, and challenged researchers to achieve that goal.
Manipulation of matter atom by atom was realized in 1986 with the groundbreaking work by Don Eigler of IBM. The research is immortalized in Eiglers famous I-B-M image. His experiment utilized a machine known as a scanning tunneling microscope (STM), the discovery of which earned its inventors a Nobel Prize. An STM is a device that has the ability to map the surface of a material at the atomic level using a needle. Working with an STM that he built, Eigler showed that when he cooled his material to very low temperatures, he was able to use the needle to position individual atoms producing dramatic results. Pursuant to this discovery, an explosion of research has led to a better understanding of nanoscience and its practical application through nanomaterials. American Elements's high purity silica has been used in the production of nanotransistors which are a recent technology inspired by this research.
Nanomaterials have wide ranging and diverse applications in optoelectronics, renewable energy, environmental remediation, chemical catalysis, medical devices, consumer products, and biomedicine. Select applications are briefly discussed below.
Nanostructured metallic and ceramic particles for vastly improve the performance of solid-state alternative energy sources such as fuel cells and batteries, and researchers are actively investigating novel means of utilizing these materials in electrodes, electrolytes, and catalysts that improve on current technologies.
Silicon nanoparticles have been shown to dramatically expand the storage capacity of lithium ion batteries without degrading the silicon during the expansion-contraction cycle that occurs as power is charged and discharged. Silicon has long been known to have an excellent affinity for storage of positively charged lithium cations, making them ideal candidates for next generation lithium ion batteries. However, the quick degradation of silicon storage units has made them commercially unfeasible for most applications. Silicon nanowires, however, cycle without significant degradation and present the potential for use in batteries with greatly expanded storage times.
Rare earth nanoparticles have become particularly important in the development of both cost-effective solid oxide fuel cells (SOFCs) and hydrogen storage technologies based on metal hydrides, including nickel metal-hydride (NiMH) batteries. Materials such as LSM, strontium carbonate nanoparticles, manganese nanoparticles, Manganese oxide nanoparticles, nickel oxide nanoparticles, and several other nanomaterials are finding application in the development of small cost-effective solid oxide fuel cells (SOFCs). Platinum nanoparticles are being used to develop small proton exchange membrane fuel cells (PEM).
Ultra high purity silicon nanoparticles are being used in new forms of solar energy cells. Thin film deposition of silicon quantum dots on the polycrystalline silicon substrate of a photovoltaic (solar) cell increases voltage output as much as 60% by fluorescing the incoming light prior to capture.
Certain nanomaterials serve as effective products for environmental remediation. For example, nickel nanocrystals are a reagent for the dehalogenation of trichloroethylene (TCE) , a common groundwater contaminant. A team of researchers from Singapore and the United States developed a lightweight, porous gel embedded with silver nanoparticles that effectively kill bacteria in tainted water, leaving it purified and potable.
Nanoparticles can be applied directly or as an additive to coatings to produce a number of effects on a given surface such as anti-reflective, hydrophobic, adhesive, or anti-microbial properties. For example, liquid repellant coatings are used for numerous applications such as consumer products, vehicles, textiles and more.
Zinc oxide nanoparticles, zinc nanoparticles and silver nanoparticles are often used as anti-microbial, anti-bacterial, anti-biotic and anti-fungal agents when incorporated in coatings, fibers, polymers, first aid bandages, plastics, soap and textiles. For detailed product information on the uses and applications of our Zinc Oxide products, Z-MITE, see the Z-MITE Product Data Sheet.
For a given amount of material, as particle size decreases, surface area increases. American Elements cerium oxide nanoparticles, platinum nanoparticles, gold nanoparticles, palladium nanoparticles, molybdenum nanoparticles, nickel nanoparticles and iridium nanoparticles have extremely high surface areas which increase their effectiveness as catalysts in a range of chemical synthesis, chemical treatment and petrochemical cracking applications.
The biomedical and bioscience fields have found near limitless uses for nanoparticles. Nanoparticles made of peroxalate ester polymers with a fluorescent dye (pentacene) encapsulated into the polymer have shown to be capable of detecting cancer since hydrogen peroxide is generated by pre-cancerous cells. The dye-bound nanoparticles fluoresce upon coming into contact with hydrogen peroxide which is then detected using medical imaging equipment. When bound to organic molecules, gold and silver nanoparticles have proven to be effective in delivering pharmaceutical drugs to the bodies of cancer patients.
Artificial bone composites are now being manufactured from calcium phosphate nanocrystals. These composites are made of the same mineral as natural bone, yet have strength in compression equal to stainless steel. Tungsten oxide nanoparticles are being used in dental imaging because they are sufficiently radiopaque (impervious to radiation) for high quality X-ray resolution. The group of magnetic nanoparticles discussed above is being used to both kill cancer cells in malignant tumors and in MRI medical imaging. Coating tungsten particles with DNA and injecting them into plant cells or plant embryos allows for the transformation of plant plastids with lower transformation efficiency than in agro bacterial mediated transformation. The anti-bacterial and anti-microbial effects of many nanoparticles such as silver are well understood technology. Fluorescent nanoparticles are being used by biologists to stain and label cellular components. By changing the particle size of quantum dots the specific color emitted can be controlled. With a single light source, one can see the entire range of visible colors, presenting an advantage over traditional organic dyes.
Nanoscale Z-MITE ZnO is being used for its UV absorbing properties to create transparent but highly effective sunscreen. The small size of these particles makes them invisible to the naked eye resulting in a clear lotion.
Nanorobots are engineered nanoscale mechanical devices or machines that can be used for applications in medicine, environmental remediation, renewable energy, or computing. Most of these applications are in research and development stages with medical applications, also known as nanomedicine, showing particular promise. Medical researchers at Johns Hopkins University have studied the uses of nanobots for drug delivery, diagnostics and surgical procedures. Another application of nanobots is in developing nanoscale molecular positions systems or conveyor belt-like systems using nanoscale molecules that act like motors when attached to macroscopic surfaces.
Nanotechnology is a powerful tool in the fabrication of metamaterials: artificial materials designed to exhibit properties not previously found in nature. The potential to tune materials with precise properties for different applications can have a profound impact on nearly every industry.
As researchers continue to learn more and more about the potential applications of nanomaterials, health officials are also learning about their potential toxicological effects. Indeed, the new field of nanotoxicologya subfield of particle toxicologyhas arisen in order to address the public health concerns related to nanotechnology. The unique dimensions of nanomaterials do present safety and environmental issues that should be addressed responsibly by industry at least in the same manner as fine particulate materials are currently handled under existing health and safety guidelines. Nanomaterials are classified by size ranges for the purposes of regulatory bodies and investigative studies pertaining to their risks, both to environmental and health outcomes. Numerous articles have been published warning of the dangers presented by unregulated nanotechnologies. Perhaps the most publicized of which is the threat of "Gray Goo," a hypothesized substance resulting from the runaway dissolution of the earth by self-replicating nanobots. While many of these concerns are being studied, the very scale range of these materials do present safety and environmental issues that should be addressed responsibly by industry in at least the same manner as fine particulate materials are currently handled under existing health and safety guidelines.
Nanomaterials are classified by size ranges for the purposes of regulatory bodies and investigative studies pertaining to their risks, both to environmental and health outcomes. Numerous articles have been published warning of the dangers presented by unregulated nanotechnologies. Perhaps the most publicized of which is the threat of "Gray Goo," a hypothesized substance resulting from the runaway dissolution of the earth by self-replicating nanobots. While many of these concerns are being studied, the very scale range of these materials do present safety and environmental issues that should be addressed responsibly by industry in at least the same manner as fine particulate materials are currently handled under existing health and safety guidelines.
Nanotechnology is expected to have an impact on nearly every industry. The research community is actively pursuing hundreds of applications in nanomaterials, nanoelectronics, and bionanotechnology. Most current developments in nanotechnology are in the shape and composition of nanomaterials themselves. Researchers are beginning to understand how to assemble complicated nanostructures and accurately predict their behavior, in addition to experimenting with composites of multiple nanomaterials (like graphene and graphene oxide) and fabricating nanoscale structures of materials never created at that size before. Advanced nanodevices and nanoelectronics that utilize these materials are on the horizon, such as nanorobot drug delivery systems, faster computers, and in sensors.
American Elements is actively involved in pursuing promising research to develop equipment and procedures to manipulate single atoms or molecules at a time. In addition, we support the industrial, commercial and academic efforts by supplying the ultra-pure, advanced materials required to perform nanotechnology research.
Nanopowders are powders consisting of nanoparticles: particles with all dimensions less than 100nm. They are used in a variety of material fabrication processes, and many of our materials are available in this form. Nanoparticles can exhibit a variety of morphologies, including spheres, rods, fibers, cups, and stars. Nanoparticles can even be porous, as in the case of mesoporous silica nanoparticles. Materials sold as nanopowders typically contain particles with some degree of variation in morphology or size while still falling within the 1-100nm range. Nanoparticles with specific, uniform morphologies are often sold under a name that characterizes this morphology, and single-crystal nanomaterials are typically referred to as nanocrystals.
Nanoparticles can be provided as suspensions in various carrier liquids. Nanofluids are generally defined as suspended nanoparticles in solution either using surfactant or surface charge technology. Nanoparticle inks are suspensions of nanoparticles in dense liquid media such as ethylene glycol. These inks are finding applications in printed electronics, photovoltaics, battery technologies and other renewable energy solutions.
Surface functionalized materials such as dodecanethiol-functionalized gold nanoparticles have controlled surface chemistries which can provide novel methods to change the adhesion (wetting) properties of the particles, re-order their interfacial region, or enhance the dispersion properties of the nanopowder in polymers, plastics and coatings for improved magnetic, fluorescent, dielectric, and catalytic properties. Surface functionalized nanoparticles have particular application in LEDs, drug delivery systems, sensors and electronics.
Nanowires are nanomaterials with length-to-width ratios greater than 1000 and diameters on the order of nanometers. Common nanowires may be composed of pure metals such as platinum or gold, semiconducting elements and compounds such as silicon and gallium nitride, or insulating materials such as silicon dioxide. Additionally, moleular nanowires are nanowires composed of repeating molecular units; DNA can be considered an organic nanowire. Nanowires can be produced using suspension techniques, vapor-liquid-solid growth (VLS), or solution-phase synthesis. Most applications for nanowires remain experimental, but ultimately these materials may be used in electronics devices, including in next-generation computing devices and sophisticated chemical sensors.
Nanofoils (or nano-foils) are ultra thin foils as thin as only 20 nm up to 1000 nm, 1 micron, 2 micron, and up to a few microns thick. Nanofoil can also be plated or produced on a substrate with a parting agent to permit removal by floating and can then be mounted on frames.
Nanorods are nanoparticles with rod-like morphology, and each of their dimensions falls within the range of 1-100nm. Most commonly, they are about 3-5 times as long as they are wide, though this can vary with material and synthesis conditions. Nanorods are synthesized from metals or semiconducting compounds.
Nanotubes are materials which exhibit a cylindrical nanostructure. The first nanotubes described were carbon nanotubes, cylindrical tubes of carbon that are members of the fullerene structural family. Carbon nanotubes have a number of unusual properties including high strength, and have a wide variety of applications. Other nanotubes now produced include silicon nanotubes, which have potential applications in hydrogen storage, battery technology, and boron nitride nanotubes, which show promise in aerospace applications due to their strength and radiation-shielding properties.
In the past decade, carbon-based nanomaterials have become increasingly important in research, industrial and commercial applications. Graphene, a flat one-atom thick sheet of carbon atoms densely packed in a honeycomb crystal lattice structure, is a unique material that exhibits extremely high strength, electrical conductivity and is one of the most opaque materials known. The discovery of graphene has greatly expanded the possibilities for improvement and development of advanced technologies, from microelectronics and nanomedicine to spintronics-based computing. Research into graphene and graphene oxide have led scientists to synthesize other two-dimensional materials like hexagonal boron nitride (hBN), molybdenum diselenide (MoSe2), molybdenum disulfide (MoS2), tungsten diselenide, (WSe2) tungsten disulfide (WS2), and others which may have the ability to outperform graphene for applications such as photovoltaic panels.
Fullerenes, spherical cage-like carbon structures known as "buckeyballs", have found applications in lithography and medicine. Carbon nanotubes are among the stiffest and strongest fibers known to man and have unique electrical properties. When used as reinforcement fibers, carbon nanotubes can improve the quality and properties of metal, polymers and ceramics. Carbon nanotubes are found in flat screen displays, needles for scanning probe microscopes, brushes for commercial electric motors, and in sensing devices.
Carbon nanotubes are extraordinary materials which come in several variations and exhibit highly unique properties. These materials are effectively rolled tubes of graphene, and contain only sp2 bonds, which are even stronger than the sp3 found in diamond. These bonds, arranged in the cage like structure of the nanotube, give these unique materials their considerable strength. Currently they are widely used to enhance the strength of structural materials, as tips for atomic force microscope probes, and as scaffolds in tissue engineering, but dozens of additional applications are areas of active research.
Quantum dots are crystalline semiconductor materials with diameters ranging from 2-10 nanometers, making them small enough to exhibit quantum mechanical properties. Specifically, in quantum dots the crystals diameter is smaller than the size of the materials exciton Bohr radius, leading to quantum confinement. The materials therefore exhibit electronic and optical properties that are tunable based on manipulation of the precise particle size. One common phenomena seen in quantum dots is fluorescence, which has been exploited in light-emitting devices such as LEDs and diode lasers. Additionally, quantum dots are being investigated as labeling agents for medical imaging, light absorbing materials for solar cells, and quibits in quantum computing.
Fluorescent nanoparticles are promising tools for technical applications in optical data storage, renewable energy solutions and biomedical fields. Quantum dots, for example, can be tuned to emit specific wavelengths of light through careful control of their particle size. Numerous biomedical assays utilize fluorescent nanoparticles as tools to bind biomolecules for diagnostics, analytics, and biochemical studies. Immunoassays, microarrays, intracellular sensing and medical diagnostics are areas that have found particularly beneficial uses of fluorescent nanoparticles.
Magnetic nanoparticles such as iron oxide are nanoparticles that exhibit magnetic properties and can be manipulated by a magnetic field. Studies in the application of these magnetic nanoparticles have led to new research areas in medicine, renewable energy and computing.
Semiconductor materials have long been used in the electronic and computing industry. Nanoscale semiconductors are now being implemented into circuit components and devices to produce next generation products and processes. Nanowires are used by to produce a new generation of transistors and antennas. In addition to this, a host of research is ongoing in the uses of nanowires as a means of energy harvesting and storage.
Nanoporous nanostructures increase surface area of a given 2D nanoparticle and in turn can be useful for membrane applications. Controlling pore sizes in nanoparticle production is a key aspect to nanoporous materials and their uses. This research holds promising applications for electronic devices.
A wide range of methods are used to synthesize nanomaterials and can be categorized as either one of two general approaches, top-down synthesis or bottom-up synthesis. Top-down synthesis methods begin with macroscopic structures or materials that undergo processing to form nanostructured materials. Bottom-up synthesis of nanomaterials starts with atoms or small molecules that can undergo self-assembly to form new nanostructures. Common examples of the bottom-up method include quantum dot formation during epitaxial growth and nanoparticle formation from colloidal dispersion.
American Elements can "grow" larger than typical particle sizes for materials for various purposes; for example, to create particle distributions in the 20 to 70 micron range for materials that are naturally produced in the 2 to 8 micron range. This allows our customers to use them in plasma spray guns and in other deposition technologies that can be blocked by particles that are either too small or too large for the delivery system. Other materials processing techniques include ink jet, spin coating, screen printing, slot-die, and doctor blading. We can also achieve very high surface area ranges up to 130 square meters per gram for products used in environmental groundwater remediation, electronics, batteries, dielectric and magnetic and fuel cell applications, and optical, imaging and catalyst functions.
Our expertise in formulation engineering enables us to produce nanomaterials tailored to customer specifications at commercial-scale volumes up to multi-ton batches. American Elements physical morphology capabilities include aerosol, thermal and sol-gel methods, attrition, ball and jet milling, atomization, particle growth by fusion and sintering, and co-precipitation and screening classification. Analysis and certification include particle distribution by laser diffraction, BET surface area analysis, phase analysis by X-ray diffraction and SEM.
Below is only a limited selection of the full catalog of nanomaterials that American Elements manufactures. If you do not see a material you're looking for listed, please search the website or contact [email protected]
American Elements is a global manufacturer of numerous nanoscale materials including nanoparticles, nanopowder, nanotubes, nanowire, quantum dots, submicron, -325 mesh, and high surface area metal powders with particle distribution and size controlled and certified. We also produce larger -40 mesh, -100 mesh, -200 mesh range sizes and <0.5 mm, 2 mm, 5 mm and other mm sizes of shot, granules, lump, flake and pieces. Our technical teams are experts in not only the chemical properties of advanced materials, but also their physical properties and morphology.
American Elements is capable of producing most compounds, metals, and alloys in the submicron and nanopowder range and atomized metallic powders in sizes as low as -325 mesh to ultrafine particle. Surface areas as high as 140 m2/g have been achieved. We can also produce certain metallic catalytic powders (such as platinum) in the submicron and nanoparticle range. Even if a customer requires a particular material in the submicron or nanoparticle that is not in our catalog, we can probably produce it.
Herein, we report an environmentally benign method for the preparation of Pt, Au and Pd NPs in water. Water insoluble alkali lignin (AL) and hemicellulose was used soly as the reducing and protecting agents. Both of the AL and hemicellulose show excellent reduce ability in the metal precursor reduce process. The solid AL could support the obtained metal NPs. The metal particles reduced by hemicellulose are aggregated and the extent of aggregation increased along with the time.
Nowadays, noble metal nanoparticles (NPs) are at a leading edge of the rapidly developing field of nanomaterials [1-3]. Preparation of noble metal NPs, such as platinum, gold and palladium, have been studied intensively based on their wide usefulness in magnetic, electronic, catalytic and mechanic technologies [4,5] Various methods have been developed for their preparation, including citrate reduction, sodium borohydride reduction, polyol process and physical radiolytic synthesis etc [6-9]. However, in those cases, harmful or petroleum-derived chemical reduce agents or dispersant were used to prepare stable metal NPs. Under the growing concern over the depleting of fossil fuels and the excessive emission of greenhouse gases, "green processes" in terms of eco-friendly reducing and stabilizing agents, "green" solvent and rout are attracting increasing attention to the production of metal NPs. Biomass with abundant availability and renewable nature plays an important role in the preparation of metal NPs . Biomass such as vitamin B1, vitamin B2 and Honey et al. has been reported widely for the formation of noble metal NPs [11-15].
Lignin is the second-most-abundant biopolymer on the Earth, second only to cellulose. Furthermore, lignin is the only biomass constituent that is based on aromatic units which have strong anti-oxidant property. It has been studied in the reduction of metal cations to metal NPs based on its reducibility of phenolic hydroxyl groups . Coccia et al. illustrated a one-pot synthesis method for lignin-stabilized platinum and palladium NPs using water soluble lignin and fulvic acid . For most plant resource, lignin exist in solid state mixing with cellulose and hemicellulose. The phenol hydroxyl groups on the surface of solid lignin possess reducibility. The three-dimensional network of the solid phase could be used as support of the metal NPs. Preparation of noble metal NPs with solid lignin remains an important goal with significant industrial consequences.
Hemicelluloses are heterogeneously branched polymer of pentoses and hexoses, mainly xylose, arabinose, mannose, galactose, and glucose. It has been reported that water-soluble primary alcohols, secondary alcohols and diethers are available as reductants for preparation of metal colloidal dispersions . Hemicellulose is a heterogeneous biopolymer composed of several different types of monosaccharides which have secondary alcohol and ethers in structure. Therefore, hemicellulose could be considered as a reducing agent to prepare metal NPs. Peng et.al. have reported the preparation of Ag NPs with hemicelluloses and glucose . Synthesizing other noble metal NPs such as Pt, Pd and Au NPs using hemicellulose reagents remains an important task which will allow us to utilize our renewable resources to a greater extent.
In this study, preparation of Pt, Pd and Au NPs with solid lignin and hemicelluloses in water at ambient pressure has been investigated. The reduce ability as well as the stabilize ability of solid lignin and hemicellulose in the formation of noble metal NPs were evaluated. This is the first time that Au, Pt and Pa NPs were successfully formed using solid lignin and water soluble hemicelluloses. This research would provide useful information for the utility of natural biomass which contains lignin or hemicelluloses.
Lignin (Sigma-Aldrich 370959) powder was crushed by ball milling method (Fritsch Pulverisette 7) in water. Hemicellulose powder (Xylanase, BR) was used as received. The structures of these compounds are shown in Figure s1. The specific surface area of the solid lignin was determined by nitrogen adsorption (BET analysis).
A desired amount of the metal precursor, H2PtCl6, HAuCl4 or PdCl2, was added to 10 ml of aq. suspension (0.5 wt% for lignin and 1.0 wt% for hemicellulose) contained in a glass bottle equipped with a reflux condenser. The mixture was stirred for 2 h at 100C under atmospheric pressure.
Lignin is a heterogeneous aromatic polymer containing various biologically stable carbon-to-carbon and ether linkages interspersing with hemicelluloses surrounding cellulose microfibrils. Because of the unstable chemical structure and complex connection with cellulose and hemicellulose, it is difficult to extract lignin from plant while keep its body structure. The specific structures of lignin vary with the extraction method. In this paper, water insoluble alkali lignin (AL) was employed; its molecular structure is shown in Figure s1. The main functional group of AL is phenolic hydroxyl group, tertiary hydroxyl group, mercapto group and ether. Since the AL does not dissolve in water, the functional groups that capable of contacting the metal ions are on the surface of AL totally. Increasing the specific surface area of AL would greatly improve the utilization of the functional groups. In addition, higher specific surface area of AL can also provide more loading location for metal particles. This effect is based on the strong interaction between metal particles and phenolic hydroxyl and mercapto group on the AL. We used the ball milling method to crush lignin and the specific surface area of AL is increased from 1.9 to 10.9 m2/g (based on BET test). TEM and FTIR were taken to the AL before and after ball milling which are shown in Figures 1 and 2 respectively. From Figure 1 we can see that the AL is woody powder with three-dimension irregular network. After milling the diameter of the powder would be decrease to nanometer-scale which is coincidence with its specific surface area changes. Figure 2 shows the FTIR of lignin before and after ball-milling, there is no significant signal change in the region of 3000 cm-1 and 1271 cm-1 which could attribute to phenol peak and -C-O stretching peak, respectively. The AL after milling with the specific surface area of 10.9 m2/g was used to reduce metal ions in this paper.
Figure 2: (a) photograph of bare lignin suspension and the Au, Pt NPs and Pd NPs suspention after reaction. (b-d): TEM of Au, Pt and Pd NPs obtained by reduction of 10 mM metal precursor for 1 h with 0.1% wt. lignin suspension. For (a-c) the scale bar is 100 nm.
The color of the AL suspension was brown. The suspension was used to biosynthesis Pt NPs directly. After reaction, the suspension turned to black. From the TEM we can see that Pt particles are formed and supported on the surface of the AL with slightly aggregation. HRTEM was used to characterize the Pt NPs reduced by AL. The image of the obtained Pt NPs shows the clear lattice with average lattice spacing of 0.23 nm (Figure 3d), which matches the d-spacing of (111) plane of face-centred cubic (fcc) Pt and confirms formation of Pt NPs crystals.
HAuCl4 was used as precursor to synthesis Au NPs. The color of the suspension deepened as soon as the Au3+ was added. After a reaction time of 2 h, the color of the suspension turned to purple. From the TEM we can see that Au particles with triangle, pentagon, rodlike and circle shapes are formed (Figure 2). All the particles are supported on the surface of the AL without apparent aggregation. HRTEM was used to characterize the Au NPs reduced by AL. We can see that the particles are polycrystalline with multiple grain zone (Figure 3). The image of the obtained Au NPs shows the clear lattice with average lattice spacing of 0.23 nm (Figure 3), which matches the d-spacing of (111) plane of face-centred cubic (fcc) Au and confirms formation of Au NPs crystals. Moreover, Pd NPs were also synthesized by AL at the same reaction conditions. From the TEM we can see that Pd particles are formed and supported on the surface of the AL. The HRTEM image shows the clear lattice of Pd NPs with average lattice spacing of 0.22 nm (Figure 3), which matches the d-spacing of (111) plane of face-centred cubic (fcc) Pd and confirms formation of Pd NPs crystals. It has been reported that the morphologies of metal NPs are determined by reaction conditions such as reaction temperature, time, concentration and pH value of the system. Further work about the morphologies of metal NPs reduced by lignin under different reaction condition is required to clarify this phenomenon.
Xylanase, known as a kind of hemicellulose, had been chosen to illustrate the reduce ability of hemicellulose towards metal ions. Firstly colorless xylanase solutions of 1% wt. were prepared, and then metal precursors were added to the solution. Within an hour, the solutions became purple, yellow and brown corresponding to Au, Pt and Pd NPs solution respectively (Figure 4). TEM images of the samples are shown in Figure 4. The images of the obtained Au, Pt and Pd NPs show that the majority of metal particles appear with irregular shape and the particles tend to aggregate. This result illustrates that the xylanase can be employed as efficient reduces agent to prepare metal NPs. However, water soluble hemicellulose could not prevent migration and secondary aggregation of metal NPs under the tested conditions. After keep for 5 days, the color of the aqueous solution changed significantly. The color of Pt and Pd NPs deepened and the violet color of Au NPs solution changed to blue (Figure 4). UV-vis was taken to exam the stabilization of xylanase based on the Au NPs aggregating process (left top of Figure 4). The Au NPs freshly prepared by xylanase show an absorption peak at 530 nm on the spectrum. For the sample that placed for 5 days, this absorption peak red shift to 536 nm. Meantime an absorption peak at 644 nm is shown indicating the further aggregation of Au NPs.
Figure 4: Top left: UV-vis absorption spectrum of Au NPs stabilizing by xylanase. insert: photograph of the Au, Pt and Pd NPs stabilizing by xylanase and after keeping for 5 days. (a-c) TEM of the Au, Pt and Pd NPs samples obtained immediately after reduce reaction. For (a) the scale bar is 50 nm. For (b) and (c) the scale bar is 20 nm.
It is well documented that the surface energy of nanoparticles is significantly higher as compared to that of the bulk. In the two-phase reduce process, it can be inferred that the particles incline to load on the surface of the solid phase to decrease surface energy. The phenolic hydroxyl and mercapto group on the surface of AL could reduce the metal ions and supply the supporting points to fix the nanoparticles through the electrostatic interaction. On the other hand, since water soluble hemicellulose are inclined to acid hydrolysis, our results illustrate that xylanase solution could reduce Pt, Au and Pd ions but could not prevent migration and secondary aggregation of metal NPs under the tested conditions.
We analysis the effect of solid lignin and hemicelluloses in the chemical reduce of kinds of metal NPs. Both of AL and hemicellulose show excellent reaction ability in the metal precursor reduce process. The presence of the solid phase enables the fabrication of metal NPs with the matrix. The metal particles reduced by hemicellulose are aggregated obviously and the extent of aggregation increased along with the time. This paper illustrated that AL and hemicellulose could be used as efficient reduce agents to prepare Pt, Au and Pd NPs, at the same time, the AL could be considered as useful stabilizing agent to disperse the obtained metal NPs.
This work was supported by the National Program on Key Basic Research Project (973Program, No. 2011CB933700), the National Natural Science Foundation of China (51172247, 51043003, 50773086), Natural Science Foundation of Hebei Province (E2014210054), the Chinese Academy of Sciences Visiting Professorships, and Hebei Key Discipline Construction Project.
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Monreal-Prez, P.; Isasi, J.R.; Gonzlez-Benito, J.; Olmos, D.; Gonzlez-Gaitano, G. Cyclodextrin-Grafted TiO2 Nanoparticles: Synthesis, Complexation Capacity, and Dispersion in Polymeric Matrices. Nanomaterials 2018, 8, 642. https://doi.org/10.3390/nano8090642
Monreal-Prez P, Isasi JR, Gonzlez-Benito J, Olmos D, Gonzlez-Gaitano G. Cyclodextrin-Grafted TiO2 Nanoparticles: Synthesis, Complexation Capacity, and Dispersion in Polymeric Matrices. Nanomaterials. 2018; 8(9):642. https://doi.org/10.3390/nano8090642
Monreal-Prez, Pablo, Jos R. Isasi, Javier Gonzlez-Benito, Dania Olmos, and Gustavo Gonzlez-Gaitano. 2018. "Cyclodextrin-Grafted TiO2 Nanoparticles: Synthesis, Complexation Capacity, and Dispersion in Polymeric Matrices" Nanomaterials 8, no. 9: 642. https://doi.org/10.3390/nano8090642
Kar Xin Lee, Kamyar Shameli, Mikio Miyake, Noriyuki Kuwano, Nurul Bahiyah Bt Ahmad Khairudin, Shaza Eva Bt Mohamad, Yen Pin Yew, "Green Synthesis of Gold Nanoparticles Using Aqueous Extract of Garcinia mangostana Fruit Peels", Journal of Nanomaterials, vol. 2016, Article ID 8489094, 7 pages, 2016. https://doi.org/10.1155/2016/8489094
The synthesis of gold nanoparticles (Au-NPs) is performed by the reduction of aqueous gold metal ions in contact with the aqueous peel extract of plant, Garcinia mangostana (G. mangostana). An absorption peak of the gold nanoparticles is observed at the range of 540550nm using UV-visible spectroscopy. All the diffraction peaks at 2 = 38.48, 44.85, 66.05, and 78.00 that index to (111), (200), (220), and (311) planes confirm the successful synthesis of Au-NPs. Mostly spherical shape particles with size range of 32.96 5.25nm are measured using transmission electron microscopy (TEM). From the FTIR results, the peaks obtained are closely related to phenols, flavonoids, benzophenones, and anthocyanins which suggest that they may act as the reducing agent. This method is environmentally safe without the usage of synthetic materials which is highly potential in biomedical applications.
Nanotechnology is technology that deals with nanoscale materials range from 1 to 100nm and their applications . Among different type of nanomaterials, noble metal nanoparticles gained considerable attention due to their special catalytic, electronic, and optical properties . Gold nanoparticles (Au-NPs) have been widely investigated due to their uniqueness especially in biomedication . The multiple surface functionality of Au-NPs ease nanobiological attachment of Au-NPs with drug , oligonucleotides , antibodies , and protein . The optical property of Au-NPs also enables them to play a role in bioimaging by acting as marking agent .
Despite the popularity and development of synthesizing nanoparticles using chemical and physical methods, the need to establish environmental friendly methods that do not involve the usage of toxic chemicals is crucial especially in medical purpose . Synthesis method that uses natural products as reducing agents need more focus to reduce the hazards on environment and human. Greener substrates such as enzyme , fungus , and algae [12, 13] were reported successfully in the production of Au-NPs. However, as compared to the difficulties faced in microbe assisted synthesis , plant mediated synthesis is developing due to the ease to handle and to control the size and shape of nanoparticles. Plant-based synthesis is relatively fast, safe, and light and works under room condition without the needs of high physical requirements . Every part of the plant is proved to be useful especially the leaves , but few reports are targeted on the fruit peels .
Garcinia mangostana (G. mangostana) which is commonly known as mangosteen belong to the family of Guttiferae. It can grow up to 625m in height and is mainly cultivated in Southeast Asian countries such as Indonesia, Malaysia, Thailand, Philippines, and Sri Lanka. Traditionally, mangosteen has been used as medicine to treat abdominal pain, dysentery, diarrhoea, infected wound, and chronic ulcer . Secondary metabolites such as phenolic acid, flavonoids, alkaloids, and terpenoids that are contained in plant crude extract are involved in the reduction of nanoparticles . G. mangostana here contains high level of phenolic compound, namely, xanthone, especially in its pericarp (peels) . There are more than 30 xanthones isolated from G. mangostana where the major constituents are -mangostin and -mangostin . This phenolic compound possesses antioxidant, antitumour, antiallergic, and antiviral properties where there are researches that shows that -mangostin and -mangostin are high potential antioxidants  which are believed to take part in the synthesis reaction of Au-NPs . Also, different kind of flavonoids, benzophenones, and anthocyanins present in the plant may be involved closely in the reduction of nanoparticles .
To the best of our knowledge, there is no work reported on adopting G. mangostana in the synthesis of Au-NPs or any other metal nanoparticles. Here, we demonstrate the biosynthesis and characterization of Au-NPs by using tetrachloroaurate and aqueous extract of G. mangostana fruit peel.
G. mangostana fruits were collected from Terengganu, Malaysia. Analytical grade tetrachloroaurate salt (HAuCl4, 99.98%) was purchased from Sigma-Aldrich, USA, and used as gold precursor. All reagents used were of analytical grade. All aqueous solutions were prepared using distilled water. All glassware used was cleaned and washed with distilled water and dried before used.
The peels were washed thoroughly with tap water to remove dirt and washed again with distilled water before being dried in oven (Esco Isotherm Forced Convection Laboratory Oven) at 40C. All the peels were ground into fine powder using an electric blender (Panasonic) and stored at room temperature for further use. The extract was prepared by taking 0.50g of the fine powder with 20mL distilled water and boiled at 60C for 30mins. The crude extract was filtered with Filtres Fioroni 601 filter paper.
In a conical flask, 20mL of the peel extract was reacted with 10mM of tetrachloroaurate at room temperature under static conditions. The colour change of the reaction was observed and the time taken for the changes was noted. The solution colour changes immediately from pale brownish to purple colour indicating the formation of [Au/G. mangostana]. The Au-NPs nanoparticles emulsion obtained was kept at 4C.
The reduction of Au-NPs was confirmed by using UV-vis spectroscopy at regular intervals in the range of 300 to 1000nm (Shimadzu, UV-1800 UV-VIS Spectrometer). The nanoparticles emulsion was oven dried at 40C for one day. The dried sample was collected and examined for the structure and composition using powder X-ray diffraction spectroscopy. The data was recorded using PANalyticXPert Pro ( = 0.15406nm) at 45kV and 20mA. The dried sample was scanned in the range of 2 = 1080 with 2/min. Transmission electron microscopy (TECNAI, G2 F20) was used to investigate the size and morphology of the Au-NPs using SC1000 Orius CCD camera. The stability of Au-NPs was measured using Particulate Systems Nano-Plus Zeta/Nano Particle Analyser, Japan. The bioreduction compounds that are responsible for the reaction were determined using Fourier Transform Infrared spectroscopy. The spectrum was obtained by Thermo Scientific Nicolet 6700 system with 16 scans per sample at the range of 5504000cm1.
G. mangostana peel extract (0.50g, 20mL) acts as both the reducing and stabilizing agent and HAuCl4 (10mM) acts as the gold precursor. The reduction of HAuCl4 was indicated by the colour changes of G. mangostana extract as shown in Figure 1. The reaction was rapid as the pale brownish colour of the G. mangostana peels extract turns into purple colour within 3min indicating formation of Au-NPs .
The possible chemical equations for synthesizing the Au-NPs areAfter dispersion of HAuCl4 in the G. mangostana aqueous solution matrix, the extract was reacted with the functional groups of G. mangostana components to form [Au/G. mangostana] .
The presence of Au-NPs is confirmed by UV-vis spectra in Figure 2. The results showed that there is no obvious peak for G. mangostana peel extract. However, after the addition of tetrachloroaurate, a sharp peak appears at the range of 540550nm . It is further confirmed by other characterizations that this peak indicates the formation of monodispersed spherical shape Au-NPs. The reaction takes place within 3 minutes with obvious colour change.
Powder X-ray diffraction pattern in Figure 3 shows that the Au-NPs synthesized is in crystalline structure. The spectrum gives an intense peak at 2 = 38.47, 44.84, 66.05, and 78.00 which correspond to the (111), (200), (220), and (311) plane proving the structure of Au-NPs to be face center cubic (fcc). The crystallinity of Au-NPs is pure by comparing its XRD pattern with the database; JCPDS file number 00-004-0784 . However, there is shifting of the peaks with database where crystal structure of pure metallic Au-NPs is present . The particle size of Au-NPs can be estimated using the Debye-Scherrer equation, where is the average crystallite size, is the Scherrer constant (0.9), is the X-ray wavelength (0.154nm), is the line broadening in radians, and is the Bragg angle . By using the Scherrer equation, 16nm is calculated to be the average crystallite size of the Au-NPs.
The size and the morphology of the Au-NPs synthesized was investigated using the TEM which is represented by Figure 4. The Au-NPs is well dispersed with G. mangostana matrix surrounding it indicating that G. mangostana matrix acts as the capping agent to separate the Au-NPs from aggregation. The average size of the Au-NPs synthesized is 32.96 5.25nm with mostly spherical and some hexagonal and triangular shape. The dispersity of Au-NPs is further supported by the FESEM where no aggregation occurs and also the nanoparticles produced are encapsulated by the matrix of G. mangostana.
The stability of Au-NPs was performed using zeta potential. A zeta value of 30mV is needed for a suspension to be physically stable while 20mV is necessary for a combined electrostatic and steric condition . The zeta potential results for pure G. mangostana peel extract are 14.68mV, whereas the reading of Au-NPs formed using the extract reduced to 20.82mV (Figure 5). Thus, Au-NPs formed show an acceptable stability with reading not less than the required stable expression.
FTIR spectroscopy was carried out to determine the potential functional groups that are responsible for the reduction of Au-NPs. Figure 6 shows the spectra obtained from pure G. mangostana peel extract and Au-NPs synthesized using the G. mangostana peels extract. The major stretching appearing at 30003500cm1 indicates the presence of O-H stretch which signifies the presence of phenols, flavonoids, benzophenones and anthocyanins . A little shifting occurs here, suggesting that the carbonyl group in the peel extract capped and stabilized the Au-NPs . Aside the O-H stretching, at the region of 2919cm1 and 2914cm1 the presence of C-H bond in xanthone  and other compounds in the peel extract is significant. Bands of C-H bond from G. mangostana peel extract split into two, 2914cm1 and 2845cm1, suggest that, after the formation of Au-NPs, the transmittance changed , while at the region of 1700cm1 it shows the presence of C=O stretching . At the region of 16001500cm1, C-C in ring aromatic bond also suggests the presence of aromatics structure exists in the G. mangostana extract. The C-C aromatics stretch is observed for both spectra at the region of 15001400cm1 which is relevant to the aromatic backbone that can be found mainly in the pericarp of G. mangostana. Finally, C-O-C stretch can be found in the range of 13001000cm1 where shifting occurs from 1279cm1 to 1234cm1 after capping with Au-NPs . All the above results are matching with xanthone , flavonoids , and other compounds that derived from the pericarp of G. mangostana as shown in Figure 7 suggesting that they are involved closely in the reduction and stabilization of HAuCl4 to Au-NPs where the presence of oxygen atoms helped in absorption of compounds on Au-NPs [24, 39, 40].
This study gives an environmental favourable approach of the synthesis of Au-NPs using G. mangostana peel extract. The extract demonstrates that the properties of both reducing and stabilizing agent owe to the presence of different compounds in the pericarp of G. mangostana. The usage of peels from the plant takes full advantage of unwanted waste material which is economically friendly, efficient, and safe. No study is established before with the usage of G. mangostana for the production of Au-NPs. The synthesized Au-NPs are potential to be applied in biomedical and other applications where nontoxicity is crucial.
This research was supported by the grant funded by the Ministry of Education (Reference Grant no. PY/2015/05547 under FRGS grant). Also, the authors would like to express their gratitude to the Research Management Centre (RMC) of UTM for providing a conducive environment to carry out this research.
Copyright 2016 Kar Xin Lee et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.