Amoxicillin degradation in persulfate activation system induced by concrete-based hydrotalcites: Efficiency, mechanism, and degradation pathway

Concrete-based hydrotalcites (CLDHs) was synthesized from concrete to activate peroxysulphate (PDS) for amoxicillin (AMX) degradation. The proportion of Fe2+ in CLDHs was optimized, the effects of initial pH, CLDHs/PDS ratio and PDS dosage on AMX degradation were investigated. To clarify the removal mechanism and degradation pathway of AMX, a quenching test was conducted to identify the active species in the system, the reactive sites of AMX were predicted by density functional theory (DFT) calculation, and the degradation intermediates of AMX were analyzed by liquid chromatography-mass spectrometry (LC-MS). Furthermore, the toxicity of AMX and its degradation intermediates were evaluated based on quantitative structure-activity relationship (QSAR). The results showed that when the molar ratio of M2+/M3+ in CLDHs was 2:1, the optimal mole proportion of Fe2+ in M2+ was 33 %. The activation system obtained better AMX removal as pH value ranged in 4-6, and the optimum CLDHs/PDS mass ratio was 2.6. The removal of AMX by CLDHs-PDS system was the coordination of SO4 center dot- and HO center dot, and the contribution of SO4 center dot- was slightly higher than that of HO center dot. Based on DFT calculations and intermediates identification, the degradation pathway of AMX in CLDHs-PDS system was proposed, including quaternary ring opening reaction and hydroxylation reaction. The ecotoxicological assessment showed a slight increase in toxicity of intermediates during AMX degradation. Therefore, appropriate time extension is required to ensure the full mineralization of AMX.