Directionally inducing non-radical pathways for peroxymonosulfate activation by regulating the exposed crystal plane of MnO2

Persulfate activation based on non-radical pathways has unique advantages in wastewater treatment. A precise design for inducing non-radical pathways by regulating the exposed crystal plane of metal oxides was proposed. Manganese dioxide (MnO2) with (310) and (110) as the main exposed planes (310-M and 110-M) were designed and synthesized for inducing different non-radical pathways. The performance of PMS activation by 310-M and 110-M for phenol degradation was investigated. The quenching experiments, EPR tests and premix experiments implied the absence of radical (SO4•- and •OH) in 310-M/PMS and 110-M/PMS systems. Combined with the results of XPS and electrochemical analysis, electron transfer process (ETP) was the dominant mechanism in the 310-M/PMS system, and Mn (III) was the active site for combining with PMS to form the MnO2-PMS* complex with strong oxidation capacity, which directly extracted the electrons from phenol. While in the 110-M/PMS system, the 1O2 oxidation pathway played a major role in phenol degradation. And the 1O2 was proved to originate from the released lattice oxygen and the single electron reduction of O2. In addition, both 310-M and 110-M exhibited high performance on phenol degradation even in the presence of inorganic ions (Cl-, NO3- and SO42-) and humic acid (HA), and showed good stability in five cycle experiments. This study highlights a novel route for precisely inducing non-radical pathways by regulating the exposed crystal planes of metal oxide catalyst on persulfate activation and improving the performance on wastewater treatment.