Enhanced degradation of tetracycline under natural sunlight through the synergistic effect of Ag3PO4/MIL-101(Fe) photocatalysis and Fenton catalysis: Mechanism, pathway, and toxicity assessment.

Here, we show that the adverse environmental and health effects of tetracycline (TC) can be efficiently reduced by encapsulating Ag3PO4 into MIL-101(Fe) to construct a Ag3PO4/MIL-101(Fe) heterojunction composite through advanced oxidation processes, such as Fenton catalysis, photocatalysis, and photo-Fenton catalysis. Notably, the reaction can be driven by natural sunlight and does not require any artificial energy source. Remarkably, the optimal degradation of TC can be achieved under different compositions of the composite system through photocatalysis and photo-Fenton catalysis. For photo-Fenton catalysis, the maximum degradation rate of TC (2.5730 min-1) is achieved when the mass ratio of MIL-101(Fe) to Ag3PO4 in the composite is 5:1, which is 31.65- and 3.12-fold of that in the Ag3PO4 + PDS + Sunlight and MIL-101(Fe) + PDS+ Sunlight catalyst systems, respectively. Moreover, the internal conversion of matrix during photocatalysis and Fenton catalysis processes inhibits the photocorrosion of Ag3PO4 and improves the reusability of the composite. Furthermore, it is found that both radical and non-radical species participate in the TC degradation. Besides, the degradation products and catalytic mechanism of Ag3PO4 and Ag3PO4/MIL-101(Fe) systems are explored. The toxicity evaluation results suggest that the intermediates produced during Ag3PO4/MIL-101(Fe) catalysis have a lower biotoxicity than those produced during Ag3PO4 catalysis. Overall, this work provides an effective strategy to inhibit the inherent photocorrosion of Ag3PO4 and establishes an efficient catalytic system for the treatment of organic-contaminated wastewater under natural sunlight conditions.

Green photocatalytic disinfection of real sewage: efficiency evaluation and toxicity assessment of eco-friendly TiO2-based magnetic photocatalyst under solar light.

To evaluate the green photocatalytic disinfection for practical applications, disinfection of different types of real sewage using magnetic photocatalyst RGO/Fe,N-TiO2/Fe3O4@SiO2 (RGOFeNTFS) under simulated solar light was investigated: low-salinity sewage after tertiary treatment, low-salinity sewage after secondary biological treatment, high-salinity sewage after secondary biological treatment, and high-salinity sewage after chemically enhanced primary treatment. The classification of the sewage as high and low-salinity is based on the regions of sewage source that use seawater and freshwater for toilet flushing, respectively. It shows potential of solar-light-driven photocatalytic disinfection in low-salinity sewage: around 20 min (for sewage after tertiary treatment) and 45 min (for sewage after secondary treatment) of photocatalytic disinfection are required for sewage to meet the discharge standard, and no bacterial regrowth is observed in the treated sewage after 48 h. However, due to the poorer water quality, the high-salinity sewage requires a relatively long reaction time (more than 240 min) to meet the discharge standard, showing minimal practical significance. Further, the complex characteristics of real sewage, such as organic matter, suspended matter, multivalent-ions, pH and DO level significantly influence photocatalytic disinfection, and should be carefully reviewed in evaluating the photocatalytic disinfection of sewage. Besides, RGOFeNTFS shows a good reusability over three cycles for photocatalytic disinfection of low-salinity sewage samples. Moreover, the non-toxicity, indicated by phytoplankton in seawater, of both RGOFeNTFS (<= 3 g/L) and treated low-salinity sewage demonstrates the feasibility of the practical application of photocatalytic disinfection using RGOFeNTFS under irradiation of solar light.