Optimizing localized polarons on Co3O4 surface for photo-ozone catalysis.

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 RDCM, 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.