Effect of Bi/Cl atomic ratio on the photocatalytic activities of TiO₂/Bi_xO_yCl_z composites

TiO₂/Bi_xO_yCl_z composite is one of the highest photocatalytic semiconductor. Herein, the competitive reaction between anions is utilized to control the Bi/Cl atomic ratio of TiO₂/Bi_xO_yCl_z composites during solution-phase synthesis, and the effect of Bi/Cl ratio on their absorption band edge and photocatalytic activity are further studied. With increasing the Bi/Cl ratio of Bi_xO_yCl_z, its conduction-band potential becomes more positive, and results narrow down of band gap energy. Accordingly, the adsorption edge of TiO₂/Bi₁₂O₁₇Cl₂ is red-shifted to about 505 nm. Moreover, It leads to the formation of S-scheme TiO₂/Bi₁₂O₁₇Cl₂ heterojuntion, and the photogenerated \mathrme^- and h⁺ retain strong redox ability. Under sunlight, the photodegradation rate constant k of TiO₂/Bi₁₂O₁₇Cl₂ heterojunction is 5.30 and 3.24 times higher than that of TiO₂/BiOCl and TiO₂/Bi₃O₄Cl toward phenol, respectively. After irradiation for 75 min, the photodegradation rate of phenol is about 100% using TiO₂/Bi₁₂O₁₇Cl₂ heterojunction as photocatalyst. However, TiO₂/BiOCl exhibits higher photocatalytic activity than TiO₂/Bi₁₂O₁₇Cl₂ and TiO₂/Bi₃O₄Cl for the degradation of rhodamine B (RhB). It is due to that TiO₂/BiOCl is a type II heterojunction, and the main active species of TiO₂/BiOCl heterojunction is photogenerated \mathrmh^+ , \mathrmh^+ is the predominant active substance in RhB photodegradation.