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

Abstract

In recent years, advanced oxidation based on periodate (PI) has become a research focus for disposal of recalcitrant organics from water due to its efficient oxidizing ability. This study systematically investigated the degradation 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 a 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 the 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 k_obs values 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.