S doping in CoOHS modified hollow fiber membranes boosting electron transfer between activated PMS and pollutants in a continuous flow reactor

The surface-sulfurized CoAl-LDH (CoOHS) modified hollow fiber membranes (HFM@(PDA/PEI)@CoOHS) demonstrated excellent peroxymonosulfate (PMS) activation for oxytetracycline (OTC) degradation, with high removal efficiency and detoxification capacities, thanks to the coexistence of S-doping species, flower-like microstructures, and hollow fiber membrane support. Meanwhile, the hollow tube morphology of HFM@(PDA/PEI)@CoOHS is easily separated for recycling. With the combination of competitive radical quenching experiments, EPR, and electrochemical analysis, the 1O2 and enhanced electron transfer can be accounted for OTC oxidation. Therein, S doping species are able to promote the Co(III)/Co(II) redox cycle by forming more metastable catalyst/PMS* complexes to enhance electron transfer between OTC and PMS* complexes. A continuous flow reactor with hollow fiber membranes was used to evaluate the OTC removal in practice. Using computational fluid dynamics (CFD), the flow within the modified hollow fiber membrane was modeled. Additionally, HFM@(PDA/PEI)@CoOHS is recyclable after 5 cycles with a degradation efficiency of 86.17%. This research paves the way for an innovative strategy for designing continuous flow reactors functioning as PMS activators, opening up possibilities for practical applications in organic pollutant removal.