Facile synthesis of mesoporous titanium dioxide doped by Ag-coated graphene with enhanced visible-light photocatalytic performance for methylene blue degradation

Abstract

A highly efficient and elaborately structured visible-light-driven catalyst composed of mesoporous TiO₂ (MT) doped with Ag⁺-coated graphene (MT-Ag/GR) has been successfully fabricated by a sol–gel and solvothermal method. The as-prepared catalyst has been investigated by X-ray diffraction (XRD), photoluminescence spectroscopy (PL), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and transmission electron microscopy (TEM). Inexpensive, stable MT was coupled with hole-accepting graphene (GR) and electron-trapping silver induced higher activities than those achieved with pure MT, MT-Ag, and MT/GR in the degradation of methylene blue (MB) in solution. Although the Ag dopant and graphene support were responsible for narrowing the band gap of TiO₂ and shifting its optical response, respectively, they acted synergistically in shifting absorbance from the ultraviolet (UV) to the visible-light region with a smaller band-gap energy. Meanwhile, they also served to lower the photo-induced electron and hole recombination rate, and increased the specific surface area and the concentrations of Ti³⁺ ions and hydroxyl groups. In degradation studies, the effects of catalyst amount, pH, and initial MB concentration have been examined as operational parameters. A photocatalytic mechanism for the action of MT-Ag/GR is proposed, and possible reasons for the enhancement in visible-light photocatalytic efficiency are discussed.