Sol–gel preparation of metal and nonmetal-codoped TiO2–graphene nanophotocatalyst for photodegradation of MO under UV and visible-light irradiation

Abstract

To improve the photocatalytic activity of TiO2 nanoparticles in the visible area, different metal/nonmetal co-doped TiO2 crystals (Cu, C, N, S/TiO2-x wt%) were grown on graphene (GR) by means of a sol–gel procedure using cysteine (Cys) (C3H6O2NS), Cu(NO3).3H2O, and titanium (IV) isopropoxide (Ti{OCH(CH3)2}4) as precursors. The products were used for degrading methyl orange (MO) in water. The qualities, surface morphology, band gap energy, and composition of the photocatalyst were evaluated through scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and UV–vis diffuse reflectance spectroscopy (UV–Vis DRS). Based on the XRD results, the samples x%Cu/1.5%Cys/TiO2-x wt% GR and x%Cu/1.5%Cys/TiO2 were found to be mainly composed of anatase and some rutile phases. The x%Cu/1.5%Cys/TiO2-x wt% GR nanocomposites revealed to have a red shift in its light absorption wavelength, reflecting the narrowing of the band gap, which was not the case with x%Cu/1.5%Cys/TiO2. The nanocomposite containing 0.5 mol% Cu/1.5 mol% Cys/TiO2-15 wt% GR was found to be a very efficient photocatalyst for degrading MO under UV and visible light, which can be due to the presence of GR nanosheets and the resulting enhancement in the lifetime of the photogenerated electron–hole pairs, as well as the faster interfacial charge transfer rates.