Use of Invasive Weed to Synthesize Shape-Tunable Gold Nanoparticles and Evaluation of their Catalytic Activities in Dye Reduction

Background: Gold nanoparticles (GNPs) of different sizes and shapes are very important for technological applications. They possess unique catalytic behavior under mild conditions and also they are considered catalysts of choice due to higher stability and negligible poisoning as compared to other metal nanoparticles (NPs). Objective: The main aim of the work is to synthesize GNPs using the flower extract of the harmful invasive wild growing plant, Lantana camara as a reducing and stabilizing agent under ambient conditions and use them for catalytic applications. Methods: The as-synthesized GNPs were characterized using various spectroscopic, microscopic and diffractometric techniques. UV-vis spectroscopy was used to monitor the progress of the catalytic dye reduction reactions. Results: UV-vis spectroscopic results indicated that optical properties of GNPs can be tuned by varying the concentration of extract in the reaction medium. Zeta potential measurement confirmed that the surfaces of these GNPs are negatively charged which imparts stability to the colloids. Microscopic results confirmed that varying the concentration of flower extract; size and shape of the formed GNPs can be systematically tuned. Selected area electron diffraction analysis of spherical and polygonal GNPs indicated that spherical GNPs are mainly polycrystalline in nature whereas polygonal GNPs are single crystalline. X-ray diffraction analyses confirmed the formation of pure face-centered cubic gold. These GNPs showed excellent catalytic activity in the borohydride reduction of organic dye molecules. Conclusion: At higher extract concentration, spherical GNPs are formed predominantly. But when the concentration of extract is lowered, GNPs of mixed morphology are formed. Further lowering in the concentration of extract resulted in polygonal GNPs only. These gold nanoparticles can be used as an efficient catalyst for borohydride reduction of toxic organic dyes in an aqueous medium.