Natural reducing agents for electroless nanoparticle deposition: Mild synthesis of metal/carbon nanostructured microspheres

Abstract

Composite materials are of interest because they can potentially combine the properties of their respective components in a manner that is useful for specific applications. Here, we report on the use of coffee as a low-cost, green reductant for the room temperature formation of catalytically active, supported metal nanoparticles. Specifically, we have leveraged the reduction potential of coffee in order to grow Pd and Ag nanoparticles at the surface of porous carbon microspheres synthesized via ultraspray pyrolysis. The metal nanoparticle-on-carbon microsphere composites were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA). To demonstrate the catalytic activity of Pd/C and Ag/C materials, Suzuki coupling reactions and nitroaromatic reduction reactions were employed, respectively.3

Green Synthesis of Metal Nanoparticles via Natural Extracts: The Biogenic Nanoparticle Corona and Its Effects on Reactivity

“…Carbon microspheres (CMs) were synthesized using ultrasonic spray pyrolysis as reported previously. 28 Briefly, a 1.5 M solution of potassium dichloroacetate or sodium dichloroacetate was converted into droplets using a 1. A similar process was used for the synthesis of silver nanoparticle/carbon microsphere composites (Ag/CMs), as previously reported.…”

“…Figure 1c shows a Raman spectrum of the CMs in Figure 1a; the spectrum displays peaks at 1364 and 1590 cm -1 which are characteristic of the D and G bands, respectively, of amorphous carbon. 28,36 Figure 1d shows the corresponding FTIR absorbance spectrum of CMs; the spectrum displays two broad peaks in the region 1800-1000 cm -1 with maxima at 1591 and 1270 cm -1 .…”

“…We synthesized metal nanoparticles on CMs using a three-step method used previously and outlined in Scheme 1. 28 Briefly, CMs were first sensitized in a Sn 2+ solution, then activated in a Pd 2+ solution and finally immersed in a coffee solution yielding Pd/CM composite particles. Previous studies on sensitization of carbon substrates using the same protocol show that Sn 2+ adsorption leads to the formation of tin carboxylates at the carbon surface 40 and that this step is required for the formation of supported metal nanoparticles.…”

“…Previous studies on sensitization of carbon substrates using the same protocol show that Sn 2+ adsorption leads to the formation of tin carboxylates at the carbon surface 40 and that this step is required for the formation of supported metal nanoparticles. 28 After activation in PdCl Coffee solutions have been shown by us and other groups to act as effective reductants for the formation of palladium nanoparticles from palladium complexes in solution. 14,28 Here, the coffee was found to reduce palladium ions onto the surface-bound nucleation sites, resulting in the formation of Pd/CM composites.…”

“…28 After activation in PdCl Coffee solutions have been shown by us and other groups to act as effective reductants for the formation of palladium nanoparticles from palladium complexes in solution. 14,28 Here, the coffee was found to reduce palladium ions onto the surface-bound nucleation sites, resulting in the formation of Pd/CM composites. The composites were collected by centrifugation and washed multiple times by suspension in clean solvent followed by centrifugation.…”