Composition Dependence of TiO₂:(Nb,N)-<i>x</i> 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 Ti1–(5x/4)NbxO2–y–δNy compounds, herein denoted as TiO2:(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).

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