N-doped mesoporous TiO2 nanoparticles synthesized by using biological renewable nanocrystalline cellulose as template for the degradation of pollutants under visible and sun light

• Nanocrystalline cellulose (NCC) as template for preparing N-doped mesoporous TiO2.
• Few reports on the NCC-templated and N-doped TiO2 (TiO2-NT).
• TiO2-NT showed good photodegradation for pollutants under visible and solar light.
• Defects of VO2+ and NO1− led to visible light-induced electronic transition.
• Optimization of N-doping is to tune electrical properties of TiO2 with acceptor.

Yellow-colored N-doped mesoporous TiO2 photocatalyst (TiO2-NT) with visible-light response was prepared by a hydrolysis–precipitation method at different urea contents with the use of nanocrystalline cellulose (NCC) as template. The photocatalytic activity was investigated through the degradation of phenol, nitrobenzene, and methyl orange (MO) under artificial visible and sun light irradiation. X-ray photoelectron spectroscopy (XPS), UV–Vis diffuse spectroscopy (DRS), X-ray diffraction (XRD), thermogravimetry–differential thermal analysis (TG/DSC), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and N2 adsorption–desorption isotherms were used for catalyst characterization. The results showed that NCC-templated TiO2 with a suitable N-doping content (TiO2-NT) exhibited higher activity under visible and sun light irradiation than N-doped TiO2 synthesized without NCC template (TiO2-N). Affected by the hydroxyl groups of NCC macromolecule and the Ti precursor, the growth and aggregation of TiO2 precursor before calcination were inhibited. The NCC template led to high dispersion, small grain size, and high specific surface area of TiO2-NT. Nitrogen doping was proposed to adjust band gap and electrical properties of TiO2 by establishing acceptor defect. N-doped TiO2 with the intrinsic donor defect of oxygen vacancy and the nitrogen-to-oxygen acceptor defect could be excited by visible irradiation for efficient pollutant degradation.