Nanodiamond–TiO2 composites for photocatalytic degradation of microcystin-LA in aqueous solutions under simulated solar light

Abstract

Titanium dioxide (TiO₂) has been under intensive investigation for photocatalytic degradation of cyanobacterial toxins. In order to develop more efficient photocatalysts, TiO₂ and oxidized nanodiamonds (ND_ox) were combined as a composite catalyst (ND_ox–TiO₂), which was tested in the photocatalytic oxidation of microcystin-LA (MC-LA), a cyanotoxin frequently found in freshwater. ND_ox–TiO₂ and neat TiO₂ photocatalysts were prepared by a liquid phase deposition method. A wide variety of analytical techniques, including physical adsorption of nitrogen, X-ray diffraction (XRD), UV-Vis and IR diffuse reflectance spectroscopies (DRUV-Vis and DRIFT), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were used to characterize the materials. The performance of the photocatalysts was studied under both simulated solar and visible light. The kinetic results show remarkable efficiency for the ND_ox–TiO₂ composite under simulated solar light irradiation with a synergistic factor of more than 15 relative to neat TiO₂, while negligible photocatalytic activity was observed for the degradation of MC-LA when ND_ox–TiO₂ was used under visible light illumination due to the wide band gap of the composite material. The photocatalytic efficiency of ND_ox–TiO₂ was ascribed to the good dispersion of both phases in the composite material, facilitating the possible electronic interaction at the heterojunction interface between ND_ox and TiO₂.