3D spherical CuO@g-C3N4 composites activating peroxymonosulfate for high efficient degradation of 2,4,6-trichlorophenol: The mechanism of 1O2 generation

A series of CuO@g-C3N4 composites with different contents of g-C3N4 and different morphologies of CuO have been designed and prepared by hydrothermal method and applied to activate peroxymonosulfate (PMS) for the removal 2,4,6-trichlorophenol (2,4,6-TCP). The results showed that 3D spherical shape CuO-1@g-C3N4-3, being able to activate PMS to produce a large amount of singlet oxygen (1O2), not only had good catalytic performance, but also reduced the dissolution of Cu2+. By comparing the morphological characteristics, catalytic performance, free radical species, decomposition rate of PMS and surface properties of three kinds of CuO, the generation mechanism of 1O2 and key reasons of CuO for producing 1O2 were deeply explored and finally deduced. Besides, under the conditions of initial pH 7.0, catalyst dosage 50 mg·L−1, PMS dosage 0.3 mmol·L−1 and initial concentration of 2,4,6-TCP 10 mg·L−1, the removal rate of 2,4,6,-TCP reached 94 % at 25 min in the first cycle, and 85 % in the fifth cycle. When CuO-1@g-C3N4 was applied in actual water samples, 65 % of 2,4,6-TCP was removed in the Yangtze River, and 60 % of 2,4,6-TCP in Xuanwu and Yueya Lake in 40 min. Quenching experiments and electron paramagnetic resonance (EPR) were used to indentify active species during degradation process and the degradation intermediates of 2,4,6-TCP and possible degradation pathways were determined and proposed by high performance liquid chromatography-time of flight-mass spectrometry (HPLC-TOF-MS2). This study shed light on the 1O2 generation mechanism of catalyst and provided theoretical basis and guidance for the design of 1O2 catalysts rich in non-radical active species.