Peroxymonosulfate activation by mesoporous CuO nanocage for organic pollutants degradation via a singlet oxygen-dominated pathway

Cupric oxide (CuO) is reported to be an effective catalyst for peroxymonosulfate (PMS) based advanced oxidation process for degrading refractory organic pollutants. In this work, mesoporous CuO nanocage was prepared via calcination of metal-phenolic coordination polymer (Cu-TA). The CuO nanocage exhibited high catalytic activity for PMS activation to degrade bisphenol A (BPA) with a high kinetic rate constant (0.17 min⁻¹). The high catalytic activity was attributed to the unique hollow mesoporous structure which renders high specific surface area, high-level exposure of active sites and efficient mass diffusion of pollutants and PMS. Systematic evaluation on BPA removal under different experimental conditions indicated that the mesoporous CuO nanocage was highly active in a wide pH range and resistant to inorganic ions and background organic constituents. Electron paramagnetic resonance tests and chemical scavenging experiments implied that the degradation of BPA was mainly ascribed to singlet oxygen (¹O₂) with a small contribution from hydroxyl radicals (OH^•). A redox cycle of surface Cu(II)-Cu(I)-Cu(II) was responsible for the production of reactive oxygen species (i.e., ¹O₂ and OH^•). The possible degradation pathway of BPA was proposed according to the intermediates (such as hydroxylated BPA, quinones, phenol, etc.) identified by ultra-performance liquid chromatography-Quadrupole-time of flight mass spectrometer. This work provides a new prospect for engineering the nanostructure of CuO catalyst to maximize its catalytic activity for water purification.