Photocatalytic degradation of microcystin-LR with a nanostructured photocatalyst based on upconversion nanoparticles@TiO 2 composite under simulated solar lights.

In this work, we prepared advanced upconversion nanoparticle coated with TiO2 photocatalysts (NaYF4 :Yb,Tm@TiO2 ) to utilize not only UV energy but also the large portion of NIR energy in order to improve the utilization efficiency of solar lights. The MC-LR (10 μg/mL) degradation rate can be approached 100% within 30 min at the concentration of NaYF4 :Yb,Tm@TiO2 0.4 mg/mL and initial pH value 4, while 61%, using pure TiO2 (P25) under simulated solar lights. The reaction processes were studied and fitted with the pseudo-first-order kinetic model. Highly reactive hydroxyl radicals (•OH) were found to be the major reactive species. Meanwhile, seven degradation intermediates of MC-LR were examined by liquid chromatography/mass spectrometry and the degradation mechanism was analyzed. The main degradation pathways were proposed based on the molecular weight of the intermediates and the reaction mechanism are hydroxylation on the diene bonds and the aromatic ring of Adda. The products were evaluated to be nontoxic based on the construction of the intermediates. This study demonstrated that the NIR energy can be used as the driving source for photocatalysis besides the UV and the NIR-responsed photocatalysis had a high-efficiency and potential for MC-LR degradation.