Composition Dependence of TiO2:(Nb,N)-x Compounds on the Rate of Photocatalytic Methylene Blue Dye Degradation

Visible-light-absorbing compounds that generate active oxygen species in water are needed to maximize the rate of organic dye degradation under incident solar radiation. In this study, a series of Ti 1–(5 x /4) Nb x O 2– y –δ N y compounds, herein denoted as TiO 2:(Nb,N)- x, with varying mole percentage of niobium substituting for titanium ( x = 1–30) was prepared by a sol–gel process followed by nitridation under flowing ammonia. All compositions crystallized in the anatase structure, as determined by powder X-ray diffraction, and diffuse reflectance UV–vis spectroscopy showed that the indirect band gap ranged from 2.37 eV ( x = 1) to 2.20 eV ( x = 30). X-ray photoelectron spectroscopy revealed that the mole percentage of substitutional nitrogen in the compounds was a linear function of the mole percentage of niobium present. NbN-25 and -30 compounds exhibited a 6-fold increase in the rate of methylene blue dye degradation ( k = 0.779 and 0.759 h –1, respectively) compared to lower-mole-percentage niobium samples NbN-1 and -5 ( k = 0.115 and 0.146 h –1, respectively).