High photocatalytic activity over starfish-like La-doped ZnO/SiO2 photocatalyst for malachite green degradation under visible light

In this work,the unique starlike La-doped ZnO-SiO2 photocatalysts were constructed by an evaporation and calcination method and characterized in detail.UV-vis reflectance and DFT calculation confirm that the doping with La allows to obtain a decrease of band gap of ZnO/SiO2,which enhances visible light absorbance and oxidizing ability.The photoluminescence intensity reduces greatly,indicating more effective separation of the photo generated carriers of La-doped ZnO-SiO2.Photocatalytic activities of Ladoped ZnO-SiO2 with different doping ratios under simulated visible light irradiation were evaluated with malachite green(MG) as a model pollutant.Under optimized conditions including solution pH of 8,15 mg/L of MG solution and 15 mg of catalyst dosage,0.2% La-ZnO-SiO2 exhibits the best catalytic activity in photodegradations of MG in water.The removal and mineralization efficiency of MG can reach 96.1%and 70.9% in 140 min,respectively.The as-prepared catalysts present superior stability and recyclability after four times reuse.Moreover,selective quenching experiments indicate that hydroxyl radical(·OH),hole(h~+) and superoxide radical(·O2~-) are the main reactive species responsible for MG degradation.Possible mechanism for photocatalytic elimination of MG over La-doped ZnO/SiO2photocatalyst is finally proposed.