Visible light-induced activation of persulfates in MgFe-LDH and toluidine blue system

Although numerous studies on peroxydisulfate (PS) activation with catalysts, organic pollutants acting as photosensitizers to activate peroxydisulfate in heterogeneous systems are rare. In this study, a visible light-induced activation system was developed for persulfates, using toluidine blue as a photosensitizer and MgFe-LDH as a heterogeneous catalyst. The results showed that toluidine blue can be photoexcited by visible light to produce photoelectrons, while MgFe-LDH acts as a photoelectron acceptor to promote persulfates synergistically. Non-radical O-1(2) is the dominant active species in these systems, although its generation pathway is different when the oxidants are peroxymonosulfate and peroxodisulfate, respectively. As a result, >98 % self-degradation of toluidine blue was achieved within 60 min. Toluidine blue sensitization can provide electrons for the heterogeneous catalytic process and reduce metal precipitation, thus MgFe-LDH can show high catalytic stability in persulfates activation processes. In addition, the feasibility of photosensitized toluidine blue activated persulfates for the degradation of organic pollutants was explored using tetracycline hydrochloride as a model pollutant. The removal efficiencies of tetracycline hydrochloride were 75.7 % and 76.0 % in the PMS and PDS systems, respectively, after reaction time at 60 min under laboratory visible light. When the system was exposed to sunlight, these removal efficiencies were 70.1 % and 73.4 % for tetracycline hydrochloride, respectively.