Sol-gel synthesis of carbon-doped TiO2 nanoparticles based on microcrystalline cellulose for efficient photocatalytic degradation of methylene blue under visible light.

Carbon-doped titanium dioxide photocatalyst with improved performance in visible light was prepared via the typical sol-gel method. Microcrystalline cellulose (MCC) was used as carbon elements source. The prepared pure and carbon-doped TiO2 samples were calcined at 400-650°C in air and the effect of annealing temperature on the stability of carbon ions was investigated. EDX analysis showed the presence of 5.66 wt.% carbon atoms in TiO2 nanoparticles formed on MCC, which was attributed to the doping of carbon atoms in TiO2 lattice. Carbon doping was also confirmed by Raman spectroscopy. According to the UV-VIS DRS analysis, the band gap of TiO2 particles decreased from 2.96 to 2.71 eV in pure and carbon-doped TiO2, respectively. Therefore the visible light absorbance increased to 15.05% compared to 0% absorbance in pure TiO2. The heat treatment of carbon-doped TiO2 nanostructures showed that carbon element could escape from the O-Ti-O lattice at temperatures higher than 600°C. According to the SEM images, synthesis of TiO2 in presence of MCC also limited the growth of TiO2 nanoparticles and controlled the morphology and aggregation of nanoparticles. Carbon doping improved the photocatalytic performance of TiO2 photocatalyst compared to the pure nanoparticles in degradation of methylene blue in the aqueous phase. Carbon-doped TiO2 attained the efficiency of 56.25%, 51.18% and 62.95% under UV, visible and solar lights, respectively, compared to 28.43%, 6.36% and 33.65% related to the pure TiO2.