Temperature dependent photocatalysis of g-C₃N₄, TiO₂ and ZnO: Differences in photoactive mechanism

Photocatalysis has been believed as one of the green and sustainable avenues to address energy and environmental crises by converting solar energy to chemical energy via reactions. Temperature is usually a vital factor controlling kinetics and thermodynamics of a reaction, but it has been less investigated in photocatalysis. In this work, the effect of reaction temperature on photocatalysis was investigated in a simple process, photocatalytic degradation of Congo Red (CR) on three typical catalysts, g-C₃N₄, TiO₂ and ZnO, to differentiate the interfacial radical generation and reaction mechanism. The results showed that the temperature has a positive effect on the photocatalytic activity of the three catalysts. The scavenger experiments at various temperatures indicated that the generation of reactive species from the three photocatalysts is different and that the free radicals can be produced more quickly at higher temperatures, causing improved activities in photocatalysis. However, photocurrent analysis and EIS at various temperatures showed that the temperature had a different effect on recombination rate and transfer barriers of the charge carriers from each catalyst. Therefore, the dramatic enhancement in photodegradation activities probably originated from a novel mechanism of the photothermocatalytic oxidation. The interfacial reaction and mechanism from the influence of reaction temperature on the photocatalytic process was proposed.