Synergistic activation of peroxydisulfate by photothermal and FeS₂-loaded air-laid cloth in a shallow continuous flow reactor

Synergistic activation of persulfate by photothermal and solid catalysts is an effective method for degrading organic pollutants. However, the batch reaction mode not only fails to fully utilize photothermal, but also makes it hard to separate the solid catalysts from the reaction solution. In this work, a shallow continuous flow way of effluent was set up for synergistic activation of peroxydisulfate (PDS) by photothermal and FeS₂-loaded air-laid cloth (FeS₂-ALC). The degradation efficiency of carbamazepine (CBZ) was significantly enhanced with a pseudo-first-order kinetic constant of 0.0359 min^-1, which is 180, 40 and 10 times higher than that of the photothermal/ALC, photothermal/FeS₂-ALC and photothermal/PDS processes, respectively. The enhanced efficiency was partly due to the absorption of sunlight by FeS₂-ALC to heat up the reaction solution which in turn can use photothermal to activate PDS, and partly due to the activation of the PDS by Fe²⁺ from FeS₂-ALC and the promotion of Fe³⁺/Fe²⁺ cycling via S₂^-. Parameters such as reaction conditions, hydraulic conditions and water quality parameters affecting degradation efficiency were investigated. A possible degradation pathway was proposed and the toxicities of byproducts were tested. Finally, cycling experiments and outdoor experiments demonstrated that the photothermal/FeS₂-ALC/PDS process has potential for practical wastewater treatment.