The effect and mechanism of Fe-modified coffee grounds hydrothermal carbon on the mass transfer efficiency of PMS and H2O2 advanced oxidation

The pore confinement environment critically restricts mass transfer efficiency in advanced oxidation process (AOPs). Hydrothermal carbons with hierarchical pore architectures significantly influence mass transfer of substances in AOPs, resulting in notable differences in performance. In this study, Fe-modified spent coffee grounds hydrothermal carbon (Fe@SCGSHC) contains Fe 2+ active sites, was synthesized using coffee grounds. We systematically compared the mass transfer and activation differences between persulfate (PMS) and hydrogen peroxide (H₂O₂) within a confinement pore environment, elucidating a micropore-mediated regulatory mechanism for performance of dual oxidizers. The diffusion constant of H₂O₂ ( K d₂  = 0.1953 mg/g·min 1/2 ) was 466 times greater than that of PMS ( K d₂  = 0.000419 mg/g·min 1/2 ). Besides, the oxidation rate constant of H₂O₂ increased from 0.026 to 8.481 (mg/L) −1 ·h −1 . 0.1 g Fe@SCGSHC achieved 100 % degradation of 5 mg/L sulfamethoxazole (SMX) within 5 min. The mechanistic study showed that the microporous structure enhances the Fe 2+ /Fe 3+ cycling within confined spaces, accelerating reaction kinetics and shifting traditional Fe-based catalysts from radical pathways (SO₄ •- , •OH) to singlet oxygen ( 1 O₂) pathways, revealing the selective advantage of micropores for H₂O₂ activation to generate 1 O₂. The stability experiments results indicated that 0.01 g Fe@SCGSHC achieved a 70.71 % removal of total organic carbon (TOC) in 5 mg/L SMX aquatic environments, exhibiting good anti-interference capability and ecological safety. In conclusion, the adoption of an appropriate pore structure can enhance the mass transfer efficiency of AOPs, leading to the effective degradation of pollutants. This study provides a scientific foundation for the preparation and modification of hydrothermal carbon and the mass transfer of substances in AOPs.