C-doped mesoporous anatase TiO₂ comprising 10 nm crystallites

We report a C-doped mesoporous anatase TiO₂ with high surface area synthesized using multi-walled carbon nanotube (MWCNT) mat as a "rigid" template and carbon doping source. The characterization by SEM, HRTEM, X-ray diffraction and nitrogen adsorption revealed that TiO₂ samples have a porous structure which are figuratively a inverse copy of MWCNT network and pore walls are formed by interconnected TiO₂ nanoparticles with average diameter of ~10 nm. We found that annealing temperatures from 400 to 1000 °C before MWCNT template removal had very limited effect on particle size (~10 nm), surface area (112-129 m²/g) and total pore volume (0.74-0.85 m²/g) of the samples through a significantly delayed phase transition from anatase to rutile started at 800 °C, resulting in only ~9.1% conversion at 1000 °C. The pore size distribution is in mesopore range from 6 to 60 nm peaked at ~24 nm. XPS analysis showed a relatively strong C1s peak at 288.4 eV, indicating C doping at Ti sites, which is responsible for red shift of adsorption edge of UV-vis spectra and photocatalytic activity in visible-light region.