Structural and photocatalytic properties of precious metals modified TiO2-BEA zeolite composites

Abstract

The nanosized beta zeolite (BEA) prepared using organic precursors was used to synthesize TiO2-BEA composite by a simple impregnation of titanium isopropoxide (15 wt% TiO2) with uncalcined BEA sample. Then, the Ti-BEA composite was modified with different precious metals (0.25 wt% of Ag, Pd and Au) to obtain photocatalysts, which could work under visible light irradiation. The physico-chemical properties of the synthesized composites were analyzed by powder XRD, FTIR, TEM, DRS UV–vis, XPS and N2-physisorption methods The modification of precious metals reinforced the formation of pure anatase phase. The XRD and TEM results demonstrated that, in combination of BEA and TiO2 retarded the formation of large size crystals of Pd and Ag with a grain size (∼5 nm), however formation of Au nanoparticles in Au modified Ti-BEA composite was observed. The photocatalytic efficiency of the samples was evaluated using malachite green under visible light irradiation. Au modified Ti-BEA sample was found to exhibit higher photocatalytic activity than Pd and Ag modified samples, bare Ti-BEA and Degussa anatase. The observed high photocatalytic activity under visible light is due to the low band gap energy calculated for Au-Ti-BEA sample (2.27 eV) in comparison with 2.54 eV and 3.46 eV for Pd-Ti-BEA and Ag-Ti-BEA samples respectively. Additionally, the presence of relatively big crystalline Au metal particles on the surface to suppress the electron-hole recombination during the reaction. The synthesized composite catalysts can be easily separable and reused for six cycles without losing any photocatalytic activity.