Large Scale Methodology for Preparation of Carbon Supported Metallic Nanoparticles

Silver and other metallic nanoparticles are of significant research interest due to their intriguing properties for applications in optoelectronics, catalysts and fuel cells, and antimicrobial surfaces. Wang, et. al., offer a scalable approach to forming supported metallic nanoparticle compositions through a straightforward manufacturing process.

Reviewed by Jeff Morse, Ph.D., National Nanomanufacturing Network

• Wang, B., Tian, C., Zheng, C., Wang, L., and Fu, H., "A simple and large-scale strategy for the preparation of Ag nanoparticles supported on resin-derived carbon and their antibacterial properties," Nanotechnology 20 (2009) 025603. DOI: 10.1088/0957-4484/20/2/025603 

Silver and other metallic nanoparticles are of significant research interest due to their intriguing properties for applications in optoelectronics, catalysts and fuel cells, surface enhanced Raman spectroscopy (SERS) substrates, and antimicrobial surfaces. Since the physical and chemical properties of the particles are determined by their size and morphology, a scalable process to synthesize controlled nanoparticles is highly desirable. In the case of Ag nanoparticles, stability remains a critical issue for many applications, as the high surface energy of the nanoparticles render them reactive, with a tendency to oxidize under atmospheric conditions causing a loss of novel properties.

Typical methods to create stabilized Ag nanoparticles include utilizing organic molecules precipitated from solution as a capping layer, or depositing nanoparticles on host materials forming core-shell nanostructures, thereby preventing oxidation and aggregation during synthesis. In either case, a hybrid material is produced with improved electrical, optical, or catalytic properties, for example, or enhanced biochemical activity. Nominally, assembly of metallic particles on specified support materials enhances their stability, with carbon providing a promising choice because it is chemically stable, low-cost, non-toxic, and biocompatible. Limitations on the large-scale production of hybrid supported nanoparticles include typically low yield, and lack of cost-effective process scaling.

In a recent issue of Nanotechnology, Wang et. al., report the preparation of carbon supported Ag nanoparticles derived from acrylic acid-based ion exchange macroporous resins. The authors chose ion exchange resins as the carbon source in this work for their high pore density and ability to tune pore size. The resin composition can be controlled to include various functional groups capable of forming complexes with different metal ions from solution. In this case, a carboxyl acrylic acid cation-exchange resin was dipped in an aqueous solution of AgNO3 to create an Ag+/resin complex. The resin had an initial pore size in the 10-100 nm range. The authors then heated the resin complex in a ceramic tube furnace under a N2 atmosphere to carbonize the resin and reduce the silver ion to metallic form, creating an Ag/C nanocomposite. By varying the temperature of the furnace from 400-1000°C, the size of the nanoparticles can be controlled. X-Ray diffraction and UV-vis spectroscopy analysis showed that the Ag nanoparticle size increased with increasing temperature. At higher temperatures the larger nanoparticles melted to form smaller diameter particles. Thus, within certain temperature ranges, the nanoparticle size can be well controlled.

Additionally, the authors characterized the antibacterial characteristics of the Ag nanocomposites for a range of bacteria exposures.  Under a set of controlled experiments, they found that the lower temperature and higher temperature treated nanoparticles both possessed strong antibacterial properties, demonstrating a dependence on the size of the Ag nanoparticles.

Overall, this technique offers a scalable approach to forming supported metallic nanoparticle compositions through a straightforward manufacturing process. By altering the ion-exchange resin type and functional group, additional supported metal composites are possible, thereby providing a simple method for controlling the physical, chemical, and size distribution of these materials structures.

Image reproduced with permission from Wang, B., Tian, C., Zheng, C., Wang, L., and Fu, H., "A simple and large-scale strategy for the preparation of Ag nanoparticles supported on resin-derived carbon and their antibacterial properties," Nanotechnology 20 (2009) 025603.