Efficient degradation of Orange IV by an ultraviolet/sulfite system: Influencing factors, degradation mechanisms and response surface analysis.

Schematic diagram of UV/sulfite system for Orange Ⅳ degradation. [Display omitted] • Influencing factors for Orange IV degradation in the UV/SO 3 ²⁻ system were studied. • The degradation effect was better under neutral and alkaline conditions. • The dominant reactive species were SO 4 ^•− and ¹O 2. • A possible pathway for indirect photolysis has been proposed to clarify the mechanism for Orange IV degradation. • Response surface analysis is used to optimize the ultraviolet/sulfite system's operational parameters. In this study, experiments on Orange IV degradation in simulated dyeing wastewater were conducted using an ultraviolet/sodium sulfite (UV/SO 3 ²⁻) method. The results showed that Orange IV degradation accorded with first-order kinetic reaction, and the degradation efficiency was positively correlated with the SO 3 ²⁻ concentration, temperature, and light power. Based on the results of radical scavengers and electron paramagnetic resonance, the sulfate radical and single-line oxygen were regarded as the primary reactive oxidants for decolorization of Orange IV, whereas the hydrogen radical was regarded as the reducing agent. Additionally, using the intermediates discovered by Liquid Chromatography-tandem Mass Spectrometry (LC-MS) and the active sites estimated by Density Functional Theory (DFT), it may be possible to infer a pathway for indirect photolysis to clarify the mechanism underlying the degradation of Orange IV via reactive species. After performing the response surface methodology (RSM), optimizing the reaction parameters, building the RSM model (R² = 0.9882), and using the model with SO 3 ²⁻ concentration of 11.26 mmol/L, pH of 7.2, and light power of 25 W, the best experimental conditions were discovered. [ABSTRACT FROM AUTHOR]