Photothermocatalytic performance of ACo2O4 type spinel with light-enhanced mobilizable active oxygen species for toluene oxidation

Recently, photo-thermocatalysis has been intensively motivated since it is beneficial for both relieving energy consumption and using the full solar spectrum energy. In this work, efficient photo-promoted thermocatalytic removal of VOCs has been investigated on ACo(2)O(4) (A = Ni, Cu, Fe, Mn) spinel by harvesting inexhaustible solar energy to provide thermal energy. ACo(2)O(4) was synthesized by co-precipitation method, which exhibits strong light absorption in the entire solar spectrum (200-2500 nm) and high solar heating effect, providing enough thermal energy for catalytic degradation of toluene. The photo-thermocatalytic performance of ACo(2)O(4) catalysts follows the sequence: ACo(2)O(4) > CuCo2O4 > FeCo2O4 > MnCo2O4, in which NiCo2O4 exhibits the highest photo-thermocatalytic activity (93% for toluene conversion and 80% for CO2 yield) and good stability (at least for 20 h) for toluene oxidation under irradiation. And such excellent light-driven catalytic performance over NiCo2O4 can be mainly explained by its strong light absorption, high photo-thermal conversion, more active oxygen species, enlarged surface area and the better OCS. Besides, a novel light-enhanced effect is revealed to considerably increase the photo-thermocatalytic activity for toluene oxidation, which is quite different from the traditional photocatalysis. By combining CO temperature-programmed reduction (CO-TPR) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), it is revealed that the irradiation is able to enhance the mobility of active oxygen species, resulting in a significant improvement of photo-thermocatalytic activity over NiCo2O4.