Tungsten disulfide and reduced graphene oxide composite as efficient catalyst for the reduction of picric acid in aqueous media

Nitroaromatic compounds, recognized as principal organic pollutants, are a grieving concern now a days. Herein, we report the use of tungsten disulfide/reduced graphene oxide (WS₂/rGO) composites as new catalysts for the reduction of picric acid by NaBH₄ in aqueous media. Unlike the conventional methods, the required WS₂ nanosheets were prepared via mechanical grinding devoid of using large volumes of solvents. For assessing the effect of composition towards the catalysis, we have prepared WS₂/rGO composites with 1:1, 1:2 and 2:1 weight ratios and WS₂/GO with 1:1 weight ratio, followed by characterization using Fourier transform infrared, X-ray diffraction, scanning electron microscopy and UV–visible spectroscopy. Among the composites, WS₂/rGO (1:1) exhibits superior catalytic properties than WS₂/GO (1:1) due to the high electron relay of rGO. In the presence of WS₂/rGO as a catalyst, a 96% reduction of picric acid was achieved within 10 min. Experimental data indicate the existence of a synergistic phenomenon involving both adsorption of the analyte onto the catalyst surface and its subsequent chemical reduction which attributes to the fact of enhanced catalytic behavior. The reduction reaction follows pseudo-first-order kinetics, with a rate constant K = 3.1 × 10^–1 min⁻¹ which is about tenfold higher than that of using the composite WS₂/GO, rGO and WS₂. The reusability of the catalyst is good as the catalytic efficiency does not significantly decrease after 10 catalytic cycles.