Optimizing localized polarons on Co3O4 surface for photo-ozone catalysis

Abstract

Photothermal conversion-induced increase in temperature enhances the recombination of charge carriers, thereby limiting solar energy utilization for catalysis. Herein, we developed a freeze-straw-capillary-action method for synthesizing N-doped Co₃O₄ (Co₃O₄-FC) to enhance the photo-induced nonthermal effect on the catalytic ozonation of dichloromethane (DCM). The N doped in Co₃O₄-FC generated localized polarons under light irradiation through d-d transitions. The polarons remained stable over the test temperature range (25–70 °C) and converted some surface Co²⁺ sites to Co³⁺ sites. Co³⁺ ions were formed under light irradiation and served as adsorption and activation sites for DCM. Given this unique property, Co₃O₄-FC exhibited a strong synergistic effect between photothermal and photocarrier processes. At 70 °C, illumination increased the R_DCM, mineralization efficiency, and ozone utilization of Co₃O₄-FC by 37.8 %, 163.6 %, and 73.7 %, respectively, whereas the those of Co₃O₄-blank presented no significantly change under illumination. To our knowledge, the photo-induced nonthermal effect observed in this work has not been previously reported. This newly identified pathway has the potential to lower the temperatures required for thermocatalysis or to alter reaction selectivity via light irradiation.