Boosting hydroxyl radical production via floatable S-scheme heterojunction-integrated polyacrylic acid hydrogels as a photo-self-Fenton catalyst for pollutant removal

Abstract

Non-homogeneous photocatalysis-self-Fenton technology offers a highly efficient approach to pollutant degradation. However, conventional catalysts suffer from limited light absorption and challenging separation processes. In this study, BaFe₁₂O₁₉ (BFO) was integrated into iron–carbon-dot-modified resorcinol-formaldehyde (FRF) to construct an S-scheme heterojunction (BFR), which was subsequently embedded into a cross-linked polyacrylic acid-based hydrogel (PAA) matrix to obtain a floating composite gel catalyst. Under visible light irradiation, this catalyst achieved complete degradation of 20 mg L⁻¹ chloroquine phosphate within 30 minutes, exhibiting a reaction rate constant 10-fold higher than that achieved by the BFR powder catalyst. The in situ generation rate of H₂O₂ (30.05 mmol g⁻¹ h⁻¹) increased by a factor of 11, enhancing hydroxyl radical (˙OH) production. This substantial improvement was attributed to the superior adsorption capacity of the PAA hydrogel (124.2 mg g⁻¹), its enhanced near-infrared absorption, and the photothermal effects of the BFR heterojunction. The underlying mechanisms, including internal electric field formation between FRF and BFO and the construction of the S-scheme heterojunction, were elucidated using in situ XPS and Kelvin probe force microscopy. Additionally, reactive species analysis, potential chloroquine phosphate (CQ) degradation pathways, and toxicity assessments of degradation products were conducted. The proposed floating photocatalyst design presents an innovative strategy for developing efficient and recyclable photo-self-Fenton systems.