Facile construction of magnetic M-ZnO-Ni-RSA composite as a functional photocatalyst for tetracycline degradation: Performance and mechanism

Due to the acute contamination problem and the energy crisis, the development of high efficient, environmental-friendly, visible-light responsible photocatalyst has long been imperative to address the water pollution. Herein, we prepared a new type of magnetic catalyst (M-ZnO-Ni-RSA) via a facile combination of ultrasonic precipitation and solvothermal method. The as-prepered composite possessed high adsorption capacity, enhanced photocatalytic performance and outstanding resustability. The structural, morphological, and optical characteristics were detected by various methods, and the photocatalytic performance was systematically investigated. The results showed that the maximum removal efficiency of high initial concentration tetracycline TC (50 mg/L) over M-ZnO-Ni-RSA was up to 98.7 % within 55 min, which was faster than that of ZnO-Ni-RSA (similar to 94.07 % within 60 min). Except for removal efficiency and adsorption capacity, other novel and more dependable evaluation metrics including ratio of maximum adsorption capacity to the surface area(eS(BET)), ratio of moles of sorbents to moles in solution(q(p)), ratio of digration rate to photon flux(QY), ratio of molecules per photon to catalyst mass(SY) and the merit of product to energy consumed(FOM) were introduced to holistically assess the performance of the catalyst for TC removal.The incorporation of oxides facilitated interactions, thus increasing the oxygen traps and enhancing the segregation of photoinduced carriers, which were beneficial to promote photochemical activity. Besides, the doped magnetic Fe3O4 facilitated the easy separation and the potential of reusability. The EPR spin-trapping tests and radical substances quenching experiments highlighted the vital participation of O-1(2), O-2(-) and OH in TC removal. The initial pH, light source, catalyst dosage on the removal of TC were investigated. As expected, the M-ZnO-Ni-RSA exhibited consistent stability after five runs of TC photodegradation. Above all, the possible photocatalytic mechanism was proposed. The showed that the downstream intermediates possessed no toxicity and mutagenicity through QSAR and T.E.S.T. results. This study basically proposed a facile strategy for synthesis of efficient and stable catalyst for TC removal, thus paving the way for a promising green remediation of actual wastewater.