Reduced porous 2D Co3O4 enhanced peroxymonosulfate activation to form multi-reactive oxygen species: The key role of oxygen vacancies

The introduction of oxygen vacancies (O-v) into Co-based metal oxides has been considered a promising strategy for activating peroxymonosulfate (PMS) to effectively degrade refractory organic contaminants. However, the types of reactive oxygen species (ROS) generated in O-v-catalyst/PMS systems exhibited variability. Therefore, the effect of the interaction between O-v and PMS on ROS generation required further research. Herein, the O-v-tuned 2D porous Co3O4 catalysts were easily constructed by simply controlling the NaBH4 concentration. The as-prepared 2D Co3O4-1.6 had the highest O-v content (2.88 x 10(14) spins/g, delta = 0.726), and its catalytic activity for benzotriazole (BTA) degradation (k = 0.032 min(-1)) was three times higher than that of pristine 2D Co3O4 (k = 0.011 min(-1)). A series of characterizations and DFT calculations demonstrated that the major active site was Co(II), with O-v serving as an localized electron-rich co-site. These dual sites synergistically improved the adsorption capacity for PMS, enabling rapidly electrons transfer to PMS while promoting the dissociation of O-O bond in PMS to form multiple ROS. Compared to the pristine 2D Co3O4/PMS system, which was dominated only by SO4-, the key ROS in the 2D Co3O4-1.6/PMS system were found to be O-1(2) (3.56 mu M) and SO4- (2.53 mu M), while both O-2(-) (0.72 mu M) and OH (0.65 mu M) were involved in the activation reaction, the contributions of these four ROS were as follows: O-1(2) (36.8%) > SO4- (25.4%) >O-2(-) (9.5%) > OH (6.3%). Finally, three possible degradation pathways of BTA were proposed, and the toxicity of BTA degradation decreased with time, which was consistent with the toxicity prediction results of eleven intermediates. This study provides new insights into the key role of O-v in the heterogeneous catalytic system of PMS-based advanced oxidation processes.