Green Synthesis of Au-Ni Bimetallic Nanoparticles using Aqueous Extract of Coccinia grandis (L.) Voigt and their Catalytic Activity in Oxidation of Alcohols

Background: In recent years, bimetallic nanoparticles have gained remarkable attention due to their excellent physical and chemical properties. Especially, bimetallic nanoparticles are found to be highly efficient as catalysts in many important organic transformations. Objective: The objective of the present work involves green synthesis of Au-Ni bimetallic nanoparticles using plant extract as the bio-reductant and to evaluate their catalytic efficiency in oxidation of alcohols. Methods: The experiment involves a simple and eco-friendly protocol for synthesis of Au-Ni bimetallic as well as their corresponding monometallic nanoparticles that involves the use of aqueous fruit seed extract of Coccinia grandis(L.) Voigt as the bio-reductant and tannic acid as the bio-stabilizer. The synthesized nanoparticles were characterized by using XRD, TEM, FTIR, TGA etc., and their catalytic activity was evaluated for oxidation of alcohols. Results: The synthesized bimetallic nanoparticles have shown excellent catalytic activity towards aqueous phase oxidation of alcohols to aldehydes under ambient reaction conditions. Furthermore, the results have revealed better effective performance of the bimetallic nanoparticles over the corresponding monometallic nanoparticles of gold and nickel, establishing the synergic influence of the two metals. Another attractive feature of this work is that the Au-Ni bimetallic nanoparticles could be recycled and reused up to four catalytic cycles without any significant decline in product yield. Conclusion: The green synthesized bimetallic Au-Ni nanoparticles have shown excellent catalytic activity toward the oxidation of alcohols in aqueous media under ambient reaction conditions. In addition, the nanoparticles are found to be successfully recyclable upto four catalytic cycles.