Transition metal-doped mesoporous TiO₂ films fabricated through cellulose nanocrystal template synthesis: studies of physicochemical, spectrophotometric properties, and photocatalytic degradation activity

The effects of CNC (cellulose nanocrystal) templating and transition metal (TM) doping on the preparation and photocatalytic activity of TiO₂ (titania) films were investigated. CNC-templated TiO₂ film has superior physical and crystalline properties (crystallite size: 9.95 nm, surface area: 102.6 m²/g) when compared to pure TiO₂ film (crystallite size: 12.78 nm, surface area: 76.7 m²/g) due to the CNC template effect. The formation of a mesoporous slit-like pore channel by CNC self-combustion during calcination and an increase in the heterogeneous nucleation rate of the anatase phase are the improvements in the aforementioned properties, which ascribed to the CNC template effect. The CNC template also effectively stabilizes the anatase phase when compared to the mixed anatase/rutile phases found in pure TiO₂ film. Further, the prepared CNC-TiO₂ was doped with the low (electron acceptor of Co²⁺) and high (electron donor of Mo⁵⁺, Nb⁵⁺, and W⁶⁺) valence group of TMs into Ti⁴⁺ lattice in TiO₂. The XPS analysis was used to investigate how low and high valence cations affect the properties of the Ti⁴⁺ lattice in TiO₂. The photocatalytic performance was evaluated using trichloroethylene (TCE) degradation under a fluorescent light source, which confirmed that TCE conversion was more efficient in the case of high valence cation doping than low valence cation doping. Greater adsorption result was observed in the UV–Vis region for the Mo doped CNC-TiO₂ film, demonstrating an excellent photocatalytic activity. This excellent activity is mainly attributed to a highly efficient photoexcited electrons transfer between the conduction and valence bands. Furthermore, the pentad (Mo, Nb) and hexad (W) TMs act as electron donors to TiO₂, allowing visible light absorption and creating trap/recombination sites within the TiO₂ bands, extending the life of photoinduced charge carriers.