Copper Oxide Enhances the Ability of Zero-Valent Iron for Persulfate Activation and Subsequent Dye Degradation

Abstract

Methyl orange (MO) wastewater, a complex and refractory dye effluent, poses significant environmental risks when discharged in large quantities due to its persistence in aquatic systems. Transition metal-activated persulfate has emerged as an effective advanced oxidation process for treating recalcitrant printing and dyeing wastewater, particularly for representative pollutants such as MO. This study developed a novel catalytic system utilizing low-concentration copper oxide coupled with zero-valent iron to activate persulfate (PDS) for generating sulfate radicals (SO₄^•−), and systematically investigated its degradation performance and mechanism. In addition, the optimized system achieved an MO degradation efficiency of 86.84% under the following conditions: pH = 4, [PDS] = 1 mmol/L, [CuO] = 0.2 g/L, and [Fe⁰] = 0.2 g/L. Furthermore, mechanistic studies revealed that sulfate radicals played a dominant role in the degradation process, with the resulting byproducts exhibiting minimal biotoxicity. Besides, compared with the conventional Fe⁰/PDS system, the CuO/Fe⁰/PDS system demonstrated superior performance, including enhanced degradation kinetics and broader pH adaptability. While the system’s efficiency was compromised in tap and river water matrices, but acidification to pH 4 significantly alleviated these inhibitory effects. Additionally, this work provides valuable insights into the application of sulfate radical-based advanced oxidation processes for the treatment of printing and dyeing wastewater, offering a promising strategy for addressing complex organic pollutants in aquatic environments.