Improved tetracycline degradation via integrated peroxymonosulfate activation and photocatalytic self-Fenton using hybrid Type-II/Z-scheme Se/g-C3N4/Bi2WO6 carboxymethyl cellulose hydrogels

Abstract

Developing efficient integrated advanced oxidation processes (AOPs) is vital for sustainable treatment of antibiotic-contaminated water. In this work, a novel 3D photocatalyst was engineered by embedding a ternary Se/g-C₃N₄/Bi₂WO₆ (SGB) heterojunction into a carboxymethyl cellulose hydrogel, yielding a stable and reusable SGB hydrogel system. Structural, optical, electrochemical, and photoelectrochemical analyses confirmed a hybrid Type-II/Z-scheme heterojunction, reducing the bandgap to 1.74 eV and enhancing charge separation. The synergistic effects of the ternary interface and hydrogel matrix enabled efficient in situ H₂O₂ generation (716 μM in water; 958 μM with isopropanol), facilitating a self-Fenton-like reaction. Upon coupling with peroxymonosulfate (PMS) activation, the system achieved 93.86% tetracycline degradation within 30 minutes. Radical scavenging and trapping experiments revealed a multi-radical degradation pathway involving ˙OH, SO₄˙⁻, O₂˙⁻, and ¹O₂, with their roles modulated by pH. At higher pH, PMS activation via O₂˙⁻/e⁻ favored SO₄˙⁻ and ¹O₂ generation, while lower pH conditions promoted H₂O₂/˙OH production and hole oxidation. LC-MS analysis confirmed the stepwise degradation of tetracycline into low-mass intermediates, supporting the proposed mechanism. Toxicity analysis further demonstrated that the transformation products exhibited reduced ecological risk, confirming the environmental safety of the process. The SGB hydrogels exhibited excellent stability and reusability, retaining 72.14% degradation efficiency after 12 cycles and retaining performance across a broad pH range. This study introduces a novel photocatalytic platform integrating Type-II/Z-scheme charge transfer, photoelectrochemical performance, multiple AOP pathways, and progressive detoxification within a hydrogel matrix for sustainable pharmaceutical pollutant remediation.