Oxalic acid-assisted, metal-free light-driven activation of sodium percarbonate on kaolinite for tetracycline degradation in water: Kinetic, mechanistic, and toxicological insights.

A UV-visible-light-driven hybrid advanced oxidation system based on oxalic acid-assisted (OA) activation of sodium percarbonate (SPC) using kaolinite was developed for tetracycline (TC) degradation in aqueous environmental matrices. The hybrid SPC/Kaolinite/OA (SPC/Kao/OA) system achieved TC degradation efficiency of 91% within 50 min and exhibited an apparent pseudo-first-order rate constant of 0.0464 min-1. The integrated kinetic-statistical and machine learning (ML) analysis demonstrated robustness and physical consistency in the degradation kinetics, with ensemble models such as random forests and gradient boosting accurately reproducing experimental trends (R2 > 0.95, RMSE <0.05) and converging toward a reliable rate constant prediction. The radical scavenging, time-resolved inhibition, ESR spectroscopy, and XPS revealed a surface-mediated activation mechanism primarily involving O2•- and •OH with secondary participation of CO3•-. The oxalic acid acted as an interfacial electron-transfer mediator, promoting surface charge transfer under UV-visible light and accelerating SPC-assisted H2O2 activation without altering the aluminosilicate lattice structure of kaolinite. The system demonstrated tolerance to common inorganic ions, appreciable performance in real water matrices, and a good reusability over 4 cycles, and effective detoxification of TC intermediates as confirmed by HRMS-guided pathway elucidation and ECOSAR/TEST toxicity studies. The energy and cost analysis further established the SPC/Kao/OA system as a low-energy and economically viable alternative to conventional peroxide-based AOPs. This study provides new insights into surface-confined, metal-free SPC activation and highlights the potential of integrating classical kinetics with data-driven validation for sustainable wastewater remediation.