The effects of Au species and surfactant on the catalytic reduction of 4-nitrophenol by Au@SiO2

Abstract

Au-based nanocatalysts are usually capped with surfactant and cannot be directly used. Thermal annealing is an effective method for surface cleaning. However, the effect of Au species on activity in the thermal annealing process has not previously been researched. We studied the effects of surfactant and Au species on catalytic performance using Au@porous SiO₂ (Au@pSiO₂). It was found that Au@pSiO₂ annealed at different temperatures showed different performances toward the reduction of 4-nitrophenol even though the size of Au was maintained. The activity of the annealed Au@pSiO₂ was higher than that of the untreated sample. The sample annealed at 500 °C had the best performance, and the catalytic activity was higher than that of the Au-based catalysts reported in the literature. It was concluded that the cationic Au species and the surfactant poly(vinyl pyrrolidone) (PVP) had a combined effect on catalytic performance. The removal of the surfactant PVP from the surface of the Au NPs during the thermal annealing process enhanced the activity, and the cationic Au species played a vital role in catalytic performance. The results are important in relation to surface cleaning and the determination of the pre-treatment conditions of catalysts. Surprisingly, there was an induction period for the untreated Au@pSiO₂ in the catalytic process because PVP blocked the adsorption and migration of 4-nitrophenol on the surface of the Au. The disappearance of the induction period for the annealed samples can be attributed to the removal of PVP.