Degradation of reactive black 5 via Cu(II)/NaIO₄ advanced oxidation process: response surface methodology optimization, kinetic simulation and performance enhancement

Abstract

In recent years, advanced oxidation based on periodate has become a research focus in disposing of recalcitrant organics from water due to its efficient oxidizing ability. This study systematically investigated the degradation result of Reactive Black 5 (RB5) by the Cu(II)-activated sodium periodate (NaIO₄, SPI) system. The optimal reaction conditions were determined via Box-Behnken response surface methodology as [Cu(II)] = 1.013 ± 0.021 g L⁻¹, [SPI] = 45 ± 2 μM, and pH = 5.7 ± 0.3, achieving an RB5 removal rate of 91.98% (R² = 0.9901, prediction error < 1%). The free radical quenching experiment confirmed that the dominant ROS in the system were •OH, 1O2, and IO3•, and their contribution was IO3• > 1O2 > •OH. The coexistence anion experiments showed that Cl⁻ (0.1-5.0 mM) and SO₄²⁻ (0.1-5.0 mM) had almost no effect on the RB5 degradation efficiency, with inhibition rates lower than 1.99% and 3.58%, respectively, while CO₃²⁻ (1.0 mM) and HCO₃⁻ (1.0 mM) led to a decrease of 20.8% and 14.17% in RB5 degradation rate. In the presence of HA, the degradation efficiency of RB5 was maintained at 89.88%-92.66%. The system maintained a removal rate of 73.33-87.66% for RB5 in the simulated actual water bodies (tap water/river water/brewery wastewater). Energy-assisted experiments showed that the activation energy of the reaction was significantly reduced and the kobs were increased by 10.3 times when the temperature was increased to 40°C, and the reaction time could be shortened to 2 min (removal rate > 98%) after ultraviolet (365 nm, 20 W) coupling. In summary, this study is expected to support the related PI-based advanced oxidation process in stubborn pollutant treatment.