Synergy of radical and nonradical degradations triggered by self-floating MnO2/cotton hydrogels with photothermal effect and oxygen vacancy

Persulfate-based advanced oxidation process is a promising technology for the water purification. While the synergy of radical and nonradical degradations are still unfeasible during persulfate activation, which process consumes a large amount of external energy. The self-floating manganese dioxide (MnO2)/cotton hydrogels (MCH) was developed, which achieves solar energy capture and wastewater treatment. In this study, a meticulously designed MCH enables simultaneous interface heating and persulfate activation. The MCH exhibited an excellent photothermal conversion capability with an evaporation rate of 2.89 kg/(m2·h) under 1 sun. The MCH coupled with peroxydisulfate (PDS) achieved a tetracycline (TC) degradation efficiency of 74.53 % under a visible light irradiation in 120 min. Furthermore, the result of TC evaporation experiment showed that 99.43 % of TC can be removed from the evaporated water. Interestingly, it was found that the singlet oxygen (1O2) increased with the concentration of Vo in the MCH during PDS activation process. In contrast to the conventional view, the thermal effect increases the concentration of Vo thus promoting the conversion of superoxide radicals (O2−) to 1O2 in the presence of Mn4+. Additionally, the polyvinyl alcohol/polyvinylpyrrolidone (PVA/PVP) hydrogel with porous structure that provided the oxygen for MnO2, promoting the production of reactive oxygen species. This study provides a new model for simultaneous evaporation and degradation, which deepens the understanding of synergy of radical and nonradical degradations.