Photocatalytic deactivation mechanism and regeneration for TiO₂/Bi₁₂O₁₇Cl₂ heterojunctions

The stability of photocatalysts is currently a crucial technical bottleneck that restricts its widespread industrial application. Photocatalytic deactivation and activity recovery are the essential indicators of photocatalytic stability. Researchers have made remarkable progress in improving photocatalytic activity and selectivity,however, little attention has been paid on the deactivation and regeneration of photocatalysts. Herein, we focus on the TiO₂/Bi₁₂O₁₇Cl₂ heterojunction with excellent visible-light response photocatalytic activity, aiming to purify wastewater in a solid-liquid multiphase photocatalytic system. The deactivation mechanism of TiO₂/Bi₁₂O₁₇Cl₂ heterojunction was investigated, and an effective regeneration strategy was proposed to restore its activity subsequently. The initial deactivation of TiO₂/Bi₁₂O₁₇Cl₂ heterojunction occurs due to the surface adsorption of intermediate phase resulting from incomplete degradation, which hinders the transfer and separation of photo-generated charge carriers. With the extension of irradiation time, the interface of TiO₂/Bi₁₂O₁₇Cl₂ heterojunction dissociates, leading to the agglomeration of TiO₂ nanospheres and the preferential recrystallization of Bi₁₂O₁₇Cl₂ nanosheets. As a result, the concentration of oxygen vacancies on the photocatalyst surface decreases. This reduction lowers the yield rate of \bullet \mathrmO_2^- , and diminishes the separation efficiency of photogenerated \mathrme^- and \mathrmh^+ pairs. These are the primary reasons for the persistantand rapid deactivation of TiO₂/Bi₁₂O₁₇Cl₂ heterojunction. Based on the results, \mathrmC\mathrml^- was employed as a medium to repair the microstructure of deactivated samples using solvothermal method. The regenerated TiO₂/Bi_xO_yCl_z heterojunction achieved a 100% recovery rate of photocatalytic activity compared to the deactivated samples.