Performance, mechanism, and ecotoxicity assessment of sulfamethoxazole degradation by coupling visible-light photocatalysis with persulphate activation over Fe₃O₄/ZnO composites

ABSTRACT

To probe the efficient and ecofriendly treatment of emerging pollutants, a magnetically separable Fe₃O₄/ZnO composite was facilely synthesised and utilised to establish a combined oxidation process by coupling photocatalysis with persulphate activation (Fe₃O₄/ZnO-PS). As proved by various characterisations, the Fe₃O₄/ZnO composite was constituted of highly dispersed Fe₃O₄ nanoparticles with ZnO nanorods as the support, and it showed the increased visible-light harvesting and facilitated charge transfer. The Fe₃O₄/ZnO-PS process significantly enhanced sulfamethoxazole (SMX) degradation under visible light irradiation, and the degradation rate constant and synergy coefficient approached 0.222 h⁻¹ and 1.98, respectively. The enhancement mechanism of Fe₃O₄/ZnO-PS process for SMX degradation was resulted from the promotion of reactive oxygen species formation. Electron spin resonance and fluorescence measurements indicated that •OH and SO₄•^‒ majorly contribute to the SMX degradation. In addition, the effects of catalyst dosage, PS dosage, solution pH and inorganic anions were systematically investigated. Based on liquid chromatography – mass spectrometry (LC/MS) identification, there were totally 12 products of SMX degradation found in the Fe₃O₄/ZnO-PS process, the degradation pathways of which involve hydroxylation, S‒N bond cleavage, and SO₂ abstraction. The ecotoxicities of these degradation products were predicted by quantitative structure-activity relationship software and were verified by actual experiments using Vibrio fischeri. The ecotoxicity assessment results indicated that although the Fe₃O₄/ZnO-PS process degraded SMX effectively, more toxic intermediates appeared and accordingly increased the ecological risk, which should be deeply concerned.

KEYWORDS:

• Fe₃O₄/ZnO composite
• visible-light photocatalysis
• persulphate activation
• sulfamethoxazole
• degradation products
• ecotoxicity assessment

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/03067319.2024.2368258.

Additional information

Funding

This study was financially supported by the Young and Middle-aged Teachers’ Educational Research Project of Fujian Province [Grant No. JAT220222].