Boosting transformation of dissolved oxygen to superoxide radical: Function of P25

TiO₂ (P25) could significantly accelerate the degradation of carbon tetrachloride (CT) in the UV/K₂ S₂ O₈ system by about 4 times, and 88.5% of the CT was dechlorinated. The presence of dissolved oxygen (DO) could delay the degradation process. The addition of P25 produced •O₂ ^- through the transformation of DO, so as to prevent the inhibitory effect. In this work, it was proved that P25 could not enhance the persulfate (PS) activation. The presence of P25 delayed the CT degradation in the absence of DO. Furthermore, the results of electron paramagnetic resonance (EPR) and quenching experiments demonstrated that the presence of P25 could produce •O₂ ^- , which could remove CT. Therefore, this work highlights the function of •O₂ ^- during the reaction and excludes the possibility that the presence of P25 could activate PS under the UV illumination. Then, the pathway of the CT degradation is discussed. Heterogeneous photocatalysis could provide a new method to deal with the problems caused by DO. PRACTITIONER POINTS: The main reason of the improvement in P25-PS-UV-EtOH system is transformation of dissolved oxygen into superoxide radical in presence of P25. The addition of P25 could not accelerate PS activation in P25-PS-UV-EtOH system. Photo-induced electron, superoxide radical, alcohol radical and •SO₄ ^- could all contribute to CT degradation, and the pathway is discussed.