Catalytic reduction of 4-nitrophenol over biostabilized gold nanoparticles supported onto thioctic acid functionalized silica-coated magnetite nanoparticles and optimization using response surface methodology

An environmentally benign magnetic gold nanoparticles (AuNPs) catalyst supported onto thioctic acid functionalized silica-coated magnetite nanoparticles, Au–RS–SR–NH–SiO2–Fe3O4,without employing any toxic reductant or capping agent was successfully synthesized. The Phaleria macrocarpa (Scheff.) Boerl (P. macrocarpa) fruit aqueous extract was used as the reducing and stabilizing agents for the biosynthesis of AuNPs. The catalytic performance of the magnetic AuNPs catalyst was evaluated for the reduction of 4-nitrophenol into 4-aminophenol in the presence of NaBH4. A three-factor Box–Behnken design coupled with response surface methodology was applied to evaluate the effects of several operating parameters, namely, volume of NaBH4, 4-nitrophenol concentration, and weight of Au–RS–SR–NH–SiO2–Fe3O4 on the conversion of 4-nitrophenol. The reduction of 4-nitrophenol using Au–RS–SR–NH–SiO2–Fe3O4 was welldescribed by a quadratic polynomial model. A significant quadratic model with p value ˂.0001 and R2 = 0.9958 was achieved using the analysis of variance (ANOVA). The conversion of 4-nitrophenol to 4-aminophenol was maintained at 90% after five cycles