Mechanism study on photocatalytic purification of low-concentration gaseous benzene over germanium & graphene quantum dot-doped titanium dioxide: An experimental and theoretical study

Benzene (C 6 H 6 ) is a typical gaseous pollutant in newly-decorated buildings, which is harmful to people's health. For fast and complete purification of C 6 H 6 , photocatalysis has been widely applied. However, effectively purifying low-concentration but still detrimental C 6 H 6 remains troublesome. To address this issue, this study aims to investigate the commonly-detected concentration of C 6 H 6 and prepares germanium & graphene quantum dots-doped titanium dioxide (Ge-GQDs/TiO 2 ) via the hydrothermal impregnation method for its purification. In the meantime, density functional theory (DFT) calculations are used to uncover the microscopic mechanisms in the above experiments. The characterization results reveal that replacing Ti 4+ with Ge 4+ generates lattice distortion (thereby producing oxygen vacancies and Ge-O-Ti for wider visible-light absorption) and functional groups of dopant GQDs achieve π → π ⁎ conjugation (thereby preventing nanoparticle aggregation and constructing hierarchical porosity). The experimental results demonstrate that 0.2 wt% Ge-0.3 wt% GQDs/TiO 2 achieves 100 % purification efficiency of 15 ppm C 6 H 6 within 2 h at 25 °C and RH 5 % with its losses being less than 15 % after 20 purification-regeneration cycles. The DFT calculation results disclose that doping of both Ge and GQDs enhances the adsorption intensity of C 6 H 6 and lowers the transition-state (TS) energy barriers of first-order decomposition of C 6 H 6 , making the purification process easier. This study provides a systematic comprehension of low-concentration C 6 H 6 purification in buildings.