CoO crystal plane regulation to efficiently activate peroxymonosulfate in water: The role of oxygen vacancies.

Crystal plane effect has attracted remarkable attention in the process of peroxymonosulfate (PMS) activation in water. In this work, nanocube-CoO (CoO-NC), nanoplate-CoO (CoO-NP) and nanorod-like CoO (CoO-NR) with (100), (111) and (110) plane predominant exposure is prepared by a facile hydrothermal method. CoO-NR with (110) plane exposed possesses more lattice defects (oxygen vacancies, Ov) and low oxidation state Co (Co), consequently, it exhibits a superior activity for PMS activation to efficiently remove bisphenol A (BPA) in water. Furthermore, it could be used in a widely water pH values ranging from 5.0 to 9.0 with an excellent PMS activited effects. During CoO-NR/PMS oxidation process, it is found that singlet oxygen (O) plays a dominant role in BPA degradation. However, CoO-NR treated by HO shows a poor PMS activation performance, confirming Ov acting as the active site during such oxidation process. The important effect of dissolved oxygen is tested by Ar introduction into the reaction system and the Ov-O* metastable intermediate is proposed. In situ Raman proves the interaction between dissolved oxygen and Ov and then the intermediate activates PMS to degrade BPA. This work not only explores the effect of different crystal plane exposures on PMS activation in CoO/PMS system, but investigates the evolution of Ov during the PMS activation.