Visible light-activated N-F-codoped TiO2 nanoparticles for the photocatalytic degradation of microcystin-LR in water

In this study, we developed nonmetal-doped TiO2 nanoparticles (N-F-TiO2) by a novel synthesis route employing a simple sol–gel method containing a nonionic fluorosurfactant as pore template material to tailor-design the structural properties of TiO2 and fluorine dopant as well as ethylenediamine as nitrogen source for the photocatalytic response towards visible light. The synthesized photocatalyst was characterized by XRD, UV–vis spectroscopy, XPS, HR-TEM, ESEM and porosimetry measurements. The resulting nanoparticles exhibited enhanced structural properties such as high surface area (141 m2/g), high porosity (49%), mesoporous structure (2–10 nm pore size) and low degree of agglomeration (1.07). A reduction in the effective band gap (2.75 eV) was observed compared with reference TiO2 (3.00 eV) due to the red-shift in the optical absorption spectrum of the nonmetal-doped TiO2 photocatalyst. We also focused on the environmental application of the prepared nanoparticles for the destruction of microcystin-LR (MC-LR) under visible light irradiation (λ > 420 nm). Under acidic conditions (pH 3.0 ± 0.1), the highest MC-LR degradation rate was achieved with N-F-TiO2. The electrostatic interactions between the toxin and the N-F-codoped TiO2 favored the photocatalytic degradation. Beneficial effects induced by codoping with nitrogen and fluorine are responsible for higher photocatalytic activity than TiO2 nanoparticles with only fluorine or nitrogen doping. Also, commercially available visible light-activated TiO2 showed lower degradation rate per unit surface area of the material.