Comparative mechanisms of PDS-activated antibiotic remediation in groundwater via controlled-release materials with different mesoporous catalysts

In situ chemical oxidation (ISCO) using controlled-release oxidants materials (CRMs) is an effective method for the long-term removal of organic pollutants from groundwater. However, the complex hydrodynamic characteristics of groundwater make it extremely challenging to elucidate the mechanisms of pollutant degradation through CRMs. This study aims to construct persulfate-based CRMs using mesoporous MnO₂ (Mn-CRMs) and TiO₂ (Ti-CRMs) as catalysts to degrade tetracycline (TC) under static and dynamic groundwater. The types and contributions of active species, stoichiometric efficiency of the reactions, TC degradation pathways of the CRMs were compared in the static and dynamic groundwater. The results revealed the active species in the CRMs-based TC degradation depending on the structures of the powder catalysts. In the static and dynamic groundwater, the contribution rate of ·OH and SO₄^·- in the Mn-CRMs-based TC degradation was nearly 100 %, indicating a complete radical-based degradation pathway. TiO₂ with abundant oxygen vacancies produced abundant ¹O₂ during the PDS activation process. Ti-CRMs showed a contribution rate of ¹O₂ to the TC degradation of up to 32.05 %, which indicated the co-action of ·OH and ¹O₂ for degrading TC. The RSE values of the CRMs-based TC degradation were similar to those of TC degradation using powder catalysts. Since the groundwater flow and PDS release, lower PDS concentrations were maintained around the CRMs in the dynamic groundwater, resulting in a higher RSE value. The results in this study provide insights into the removal mechanisms of pollutants in different groundwater and expand the application of ISCO to groundwater remediation.