The practical feasibility of bismuth oxyhalide semiconductors with controlled surface defects in photocatalytic degradation of toluene in air

The photocatalytic degradation (PCD) of toluene (as model aromatic volatile organic compound (VOC)) is studied using two-dimensional semiconductors (bismuth oxyhalides (BiOX (X = Cl and Br)) synthesized with surface defects (BiOX-R (R = reduction)) through a solvothermal-induced reduction process. The PCD efficiency of BiOCl-R against 5 ppm toluene (20 % relative humidity (RH)) is 98.6 % under ultraviolet light irradiation with the quantum yield and clean air delivery rate of 1.04E-03 molecules photon^-1 and 3 L/h, respectively. A combined evaluation of catalyst properties, experimental data, and density functional theory simulations consistently indicates that the formation of surface defects should promote the adsorption and activation of toluene, molecular oxygen (O₂), and water (H₂O) molecules. Meanwhile, the geometric and electronic structure of defective BiOX favorably generates superoxide anion ([rad]O₂^–) and hydroxyl ([rad]OH) radicals through electron (e^-)-assisted O₂ activation and hole (h⁺)-mediated H₂O oxidation, respectively. Notably, the BiOCl-R surface becomes more advantageous to reduce the reaction energy barrier in the ring-opening processes of intermediate forms like benzaldehyde and benzoic acid. Overall, the results of this study offer practical guidelines for the design of advanced photocatalysts with controlled surface defects for the efficient PCD of aromatic VOCs in air.