Regenerating hazardous waste: enhancing photocatalytic performance through heterojunctions and oxygen vacancy-driven charge transport

Abstract

The improper disposal of hazardous electric arc furnace dust (EAFD) poses significant environmental risks, with limited strategies for effective resource utilization. In this study, a high-performance ZnFe₂O₄/ZnO heterojunction photocatalyst with oxygen vacancies (OVs) was fabricated from hazardous EAFD (EAFD-HOVs). Fermi-level alignment between ZnFe₂O₄ and ZnO leads to interfacial charge redistribution and creates a built-in electric field that directs a Z-scheme charge transfer pathway. Interfacial OVs optimize the local electronic environment by introducing trap states, thereby promoting interfacial recombination of low-energy carriers while maintaining spatially separated, strongly oxidizing holes (h⁺) in ZnO and strongly reducing electrons in ZnFe₂O₄. As a result, the EAFD-HOVs catalyst exhibited exceptional photocatalytic activity, achieving 98% tetracycline degradation in 120 min with a rate constant of 0.040 min⁻¹, which was 6.1, 1.2, and 1.5 times higher than those of synthetic ZnFe₂O₄, ZnO, and their physical mixture, respectively. Radical quenching experiments, electron paramagnetic resonance (EPR) analyses, and in situ X-ray photoelectron spectroscopy (in situ XPS) measurements indicated a direct Z-scheme mechanism, with ˙O₂⁻ and h⁺ serving as the dominant reactive species. The catalyst also exhibited robust adaptability to complex aqueous environments typical of real applications, efficiently degrading multiple pollutants and showing sustained activity after five consecutive recycling cycles. This work introduces a novel paradigm for repurposing industrial solid waste into high-performance photocatalytic materials, combining metallurgical waste management and wastewater treatment through a sustainable and scalable strategy.