Synthesis of sandwich-structured AgBr@Ag@TiO2 composite photocatalyst and study of its photocatalytic performance for the oxidation of benzyl alcohols to benzaldehydes

Abstract

Silver halide-based photocatalytic materials have been successfully used in organic contaminant degradation and disinfection, but their application in the oxidation of alcohols to aldehydes has never been reported. Herein, we fabricated sandwich-structured AgBr@Ag@TiO2 composite photocatalyst by a facile multistep route and for the first time studied its photocatalytic performance for the oxidation of benzyl alcohols to benzaldehydes. It was found that the porous TiO2 shell layer can be successfully anchored on the surface of AgBr core by a kinetics-controlled hydrolysis process and the thickness of TiO2 shell layer can be conveniently tuned by adjusting the addition amount of ammonia water during titanium source hydrolysis. The control experiments indicated that the O2 plays a vital role in promoting the oxidation of benzyl alcohols while non-aqueous solvents are favorable to improving the reaction selectivity from alcohol to aldehyde. Compared to blank TiO2 and AgBr@Ag, sandwich-structured AgBr@Ag@TiO2 exhibited a drastically enhanced photocatalytic activity in terms of benzyl alcohol oxidation under visible light irradiation. The transient photocurrent and photoluminescence (PL) spectrum analyses confirmed that the core-shell structure can effectively promote the separation of photo-generated electrons and holes. The radical scavenging experiments revealed that superoxide radical (O2−) and hole (h+) are the main reactive species responsible for the transformation from benzyl alcohols to benzaldehydes.