Facet tailoring and Cu doping promoted photo-assisted peroxymonosulfate activation by oxygen-deficient α-MnO2 for efficient mineralization of bisphenol a

Revealing the synergistic mechanism between facets and metal doping during catalytic processes is an efficient approach to improve the catalytic performance. Herein, the synergetic effects between Cu doping and crystal facets over α-MnO2 on the peroxymonosulfate (PMS) activation towards bisphenol A (BPA) degradation under full-spectrum light irradiation were studied in details for the first time. The Cu-doped α-MnO2 with (1 0 0), (1 1 0), and (3 1 0) facets were synthesized by hydrothermal method. The Cu-doped (1 1 0)/PMS/Light system presented the highest BPA removal efficiency with high 1O2 generation and selectivity, being superior over the Cu-doped (1 0 0), Cu-doped (3 1 0) and pristine (1 1 0) counterparts. The corresponding mechanism showed that Cu doping for α-MnO2 enhanced the absorption of light, the formation of oxygen vacancies and electronic conductivity as well as PMS activation, especially for the (1 1 0) facet, as compared to the (1 0 0) and (3 1 0) facets. In addition, density functional theory (DFT) calculations and characterizations indicated that the synergetic effect between facet and oxygen vacancies played an important role in 1O2 generation. Moreover, oxygen vacancies accelerated the complexation of PMS with surface Mn(IV) and improved the generation of 1O2, different to that due to Mn(III). Toxicity assessment showed that BPA was partially decomposed into highly toxic intermediates during the degradation process. However, Cu doping and light synergistically improved the mineralization rate of pollutants, removing 95% of the total organic carbon (TOC) and reducing the toxicity of the intermediates. The ultrahigh TOC removal was attributed to the joint effect of 1O2, O2− and electron transfer. This work therefore provides an efficient and highly selective PMS catalyst for 1O2 generation, and reveals the synergistic mechanism between metal doping and crystal facets of the catalyst in advanced oxidation processes.