Abstract
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.
Highlights
Cyanobacterial blooms pose a serious threat to aquatic ecosystems due to the liberation of cyanotoxins into water sources
The as-prepared UCNP were modified by cetyltrimethyl ammonium bromide (CTAB) to form the hydrophilic UCNP
The sunlight photocatalytic activity of composite photocatalysts was approximately 3 times than pure TiO2 and approaching 100% of MC-LR was photodegraded within 30 min
Summary
Cyanobacterial blooms pose a serious threat to aquatic ecosystems due to the liberation of cyanotoxins into water sources. Among various photocatalysts reported so far, titanium dioxide (TiO2) is undoubtedly the most widely used in the degradation of inorganic or organic pollutants due to its strong oxidizing power, extraordinary chemical stability, low cost and non-toxicity toward both human and environment[23,24,25]. This photocatalyst requires ultraviolet (UV) light to be activated because of its large bandgap of ∼3.2 eV. After absorbing NIR light, transfers energy to TiO2 to generate strongly oxidative holes (h+) and reductive electrons (e-) which are powerful oxidizing agents for environmental pollutants
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