Enhanced visible light photocatalytic VOC oxidation via Ag‑loaded TiO2/SiO2 materials

Abstract

Ag-TiO2/SiO2 materials were synthesized with 1, 3, 5, and 10 wt% Ag contents and extensively characterized by different techniques, including XRD, SEM, TEM, XPS, BET, UV–VIS, EPR, and PL spectroscopy. Subsequently, the activity of these materials in the degradation of a model volatile organic compound (n-hexane) was compared by testing in a continuous gas–solid photoreactor. Loading with Ag induced stabilization of the brookite phase and crystal growth. TEM images showed d-spacing values corresponding to anatase and metallic silver. The specific surface area was lower in the Ag-modified catalysts, probably due to the blocking of the silica gel pores by Ag nanoparticles, whose size (~ 20 nm) was larger than the silica pores (~ 1.98 nm). SEM–EDS images showed heterogeneous distribution of Ag on the surface of the materials. XPS spectra showed bands referring to Ag+ and Ag0 3d, and Ti4+ and Ti3+ 2p. EPR analyses showed that silver loading of TiO2/SiO2 greatly increased the occurrence of oxygen vacancies in the material. Finally, the band gap energies calculated from the UV–VIS spectra were lower in the silver-containing catalysts, dropping from 3.25 to 3.17 eV in the optimal material. Under visible light, while TiO2/SiO2 showed no photoactivity, the Ag-modified materials presented satisfactory steady-state performance (46.4% n-hexane removal).