Comparative Study on Oxidative Removal of Acid Orange 7 from Water by Iron-Modified Corn Straw Biochar Activated Urea-Hydrogen Peroxide and Its Mechanisms

• • Fe-CSB300, Fe-CSB500, and Fe-CSB700 achieved AO7 degradation rates of 98.54%, 97.38%, and 98.54%, respectively, within 60 min under optimal conditions (0.2 g·L−1 UHP, 0.2 g·L−1 Fe-CSB, 20 mg·L−1 AO7, pH 3), demonstrating high efficacy for dye removal. • • Coexisting CO3^2− and HCO3^− significantly inhibited AO7 degradation, while Cl^− had no effect, indicating the need for pre-treatment in carbonate-rich wastewaters. • • Quenching experiments identified ·OH and ^1O2 as the dominant reactive species, providing mechanistic insight for optimizing UHP activation. • • LC-MS analysis revealed that AO7 degradation proceeds via azo bond cleavage, leading to benzene-containing intermediates and eventual mineralization to CO2 and H2O, confirming complete detoxification potential.