Optimization of sol-immobilized bimetallic Au-Pd/TiO2 catalysts: reduction of 4-nitrophenol to 4-aminophenol for wastewater remediation.

A sol-immobilization method is used to synthesize a series of highly active and stable AuxPd1-x/TiO2 catalysts (where x = 0, 0.13, 0.25, 0.5, 0.75, 0.87 and 1) for wastewater remediation. The catalytic performance of the materials was evaluated for the catalytic reduction of 4-nitrophenol, a model wastewater contaminant, using NaBH4 as the reducing agent under mild reaction conditions. Reaction parameters such as substrate/metal and substrate/reducing agent molar ratios, reaction temperature and stirring rate were investigated. Structure-activity correlations were studied using a number of complementary techniques including X-ray powder diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. The sol-immobilization route provides very small Au-Pd alloyed nanoparticles, with the highest catalytic performance shown by the Au0.5Pd0.5/TiO2 catalyst. This article is part of a discussion meeting issue 'Science to enable the circular economy'.