Structural and Photocatalytic Activity of Mesoporous N-Doped TiO2 with Band-to-Band Visible Light Absorption Ability

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White colored N-doped TiO2 and a neat TiO2 powder were synthesized via sol–gel method. Prepared samples were characterized by means of x-ray diffractions, Brunauer–Emmet–Teller and Barrett–Joyner–Halenda methods, x-ray photoelectron spectroscopy, ultraviolet-visible analysis, scanning electron microscopy, and energy dispersive x-ray spectroscopy. Both of the N-doped TiO2 and neat TiO2 consisted of anatase phase of titania with mesoporous nature and according to XPS analysis prepared N-doped TiO2 is a substitutional nitrogen containing sample. The band gap of N-doped TiO2 and neat TiO2 were estimated from ultraviolet-visible spectroscopy data to be 2.7 and 3.2 eV, respectively. Prepared substitutional N-doped TiO2 featured steep light absorption edge with an approximately parallel characteristic of its absorption edge to that neat TiO2. This is due to its band-to-band visible light absorption ability. Synthesized N-doped TiO2 had a large surface area value of 193 m2/g and high photon absorption ability causing superior photocatalytic properties towards Congo red azo dye compared to neat TiO2 either under ultraviolet or visible light illumination.