Oxidation of organic compounds by PMS/CuO system: The significant discrepancy in borate and phosphate buffer

Peroxymonosulfate (PMS)-based advanced oxidation process are widely used in the degradation of organic pollutants. The degradation of the electron-rich azo dye Acid Orange 7 (AO7) through a PMS/CuO heterogeneous system in borate and phosphate buffer were systematically investigated. The CuO was characterized via X-ray diffraction, scanning electron microscopy, fourier-transform infrared spectra, X-ray photoelectron spectroscopy and energy dispersive spectroscopy (SEM-EDS) techniques. The difference of AO7 degradation by PMS/CuO system in borate and phosphate buffer varied with the buffer concentration, PMS concentration, CuO dosage and pH. AO7 degradation fitted well with the pseudo-first order kinetics in these two buffer solutions, the reaction rate constant (kobs) of AO7 degradation in phosphate buffer increased with the increase of phosphate concentration firstly and then reached the maximum value of 0.0123 min−1 at 0.2 M, but it decreased obviously with the increase of borate concentration. It was found that the kobs in two buffers increased linearly with the increase of PMS concentration, and increased with the increase of CuO dosage in borate, while the reaction in phosphate buffer was slightly affected by CuO dosage. Additionally, the kobs increased from 0.0057 min−1 to 0.0487 min−1 with the increase of pH value in phosphate, but decreased gradually with the increase of pH value from 7.0 to 8.5 in borate due to the deprotonation of PMS. Fewer reactive species were produced in phosphate including SO4•–, •OH and 1O2. The conversion between Cu(Ⅱ) and Cu(Ⅰ) was a crucial process for the activation of PMS by CuO in borate, which was hindered in phosphate. This study will provide a reference for the application of different types of buffers in heterogeneous catalysis of PMS.