Starch-mediated green synthesis of bismuth/reduced graphene oxide nanocomposites: A recyclable nanocatalyst for nitro compound reduction towards wastewater treatment

This study offers a green synthesis of bismuth/reduced graphene oxide (Bi/rGO) nanocomposites in a simple, environmentally friendly, and economically feasible one-step process using soluble starch as a safe and inexpensive novel reducing agent. As demonstrated by ultraviolet-visible, Fourier-transform infrared, Raman, and energy-dispersive X-ray spectroscopic studies and X-ray diffraction analysis, starch efficiently and concurrently reduces GO and the Bi 3+ ion to produce Bi/rGO nanocomposite. In addition, scanning electron microscopy and transmission electron microscopy analysis showed that the nano bismuth, with plate-like nanostructure with a diagonal length of 100–300 nm, depending on the Bi/GO feeding ratio, was affixed to the exfoliated rGO sheets. This Bi/rGO nanocomposite showed an efficient catalytic performance in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of NaBH₄. This reduction was completed in 18 min, which is faster than those catalyzed by bare nano-Bi (25 min) and the mixture of the bare Bi with rGO (22 min). Furthermore, the Bi/rGO nanocomposite also exhibited notable reusability. The enhanced catalytic activity is attributed to the synergistic properties of uniformly dispersed Bi nanoplates over the rGO sheets, which facilitate efficient electron transport and add the substrate adsorption. This 'green' synthesis of nanocatalysts, which utilizes starch, provides an ecofriendly strategy for the reduction of nitroaromatics in wastewater treatment and organic synthesis.