Facile synthesis of dispersed Ag nanoparticles on chitosan-TiO 2 composites as recyclable nanocatalysts for 4-nitrophenol reduction

This paper presents a facile, rapid, and controllable procedure for the recovery of trace Ag + ions and in situ assembly of well dispersed Ag nanoparticles on chitosan-TiO 2 composites through bioaffinity adsorption followed by photocatalytic reduction. The prepared Ag nanoparticles are proven to be efficient and recyclable nanocatalysts for the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH 4 . Well dispersed quasi-spherical Ag NPs are synthesized in 20 min in the designed inner-irradiated photocatalytic system under a wide range of Ag + concentrations (50–200 mg l −1 ), temperatures (10 °C–25 °C) conditions, and UV or visible light irradiation. The synthesized Ag NPs can catalyze the reduction of 4-nitrophenol by NaBH 4 at 100% conversion in 120 min and preserve the catalytic activity in five successive cycles. This procedure for trace Ag + ions recovery and Ag NPs assembly has the potential to be scaled up for the mass production of recyclable Ag nanocatalysts. The present work provides a green and efficient procedure for the conversion of hazardous 4-nitrophenol to industrially important 4-aminophenol and also sheds a light on designing scaled-up procedures for treating high volumes of wastewater with dilute heavy metals to produce recyclable metallic nanocatalysts in aqueous systems.