Guar gum mediated synthesis of NiO nanoparticles: An efficient catalyst for reduction of nitroarenes with sodium borohydride.

An excellent catalyst (GNiOc) for reduction of nitroarenes with sodium borohydride is being reported. The synthesis of GNiOc was carried out by direct precipitation method using guar gum (GG) as the modifier. The nanostructures have been characterized using UV-visible spectroscopy (UV-vis), Fourier transformation infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) surface area analysis, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Thermal (TGA and DTA) analysis. TEM analysis revealed that GNiOc sample is crystalline in nature (similar to cubic NiO) and had an average particle size of ~3 nm. The reduction of 4‑nitrophenol (4‑NP) (2 mM) using sodium borohydride (0.1 M) was completed within 2 min when GNiOc (5 mg) was used as catalyst. GNiOc could be successfully recovered and reused for six repetitive cycles and even in the sixth cycle; the reduction was completed in 18 min time. The reduction followed zero order kinetics, the rate constant being 8 × 10-3 mmol L-1 min.-1 Under identical experimental conditions, GNiOc catalyzed reductions (with sodium borohydride) of 4‑nitroaniline (4‑NA) and 4‑nitro benzoic acid (4‑NBA) were completed in 6 and 7 min respectively, while NiO required >15 min time for reducing all the three nitroarenes.