Improved thermochromic and photocatalytic activities of F–VO₂/Nb–TiO₂ multifunctional coating films

Multifunctional photocatalytic and thermochromic composites consisting of fluorine-doped vanadium dioxide (F–VO₂) and niobium-doped TiO₂ (NTO) were prepared by a simple physical mixing. The composites exhibited a higher thermochromic activity and nitrogen oxide (NO_x) decomposition activity than that of pristine VO₂/NTO. Both VO₂ and NTO materials were synthesized using an environmentally friendly soft chemical solvothermal/hydrothermal process, which produced NTO nanoparticles with a controllable morphology and particle size by changing the ratio of ethanol and acetic acid solvent. F–VO₂/NTO showed a better multifunctionality of thermochromic and photocatalytic activities than those of VO₂/NTO samples. The coexistence coating films showed a better effect on thermochromic and deNO_x (NO_x reduction) activity than those of double-sided films for F–VO₂/NTO samples. The best thermochromic and photocatalytic activities obtained from sample F–VO₂/NTO 60 showed the ΔT_{1500 nm} [difference of transmittance (ΔT) at the wavelength of 1500 nm under 25 °C and 95 °C] of up to 29.5% and deNO_x activity of up to 40% at λ > 290 nm under mercury lamp irradiation. The use of F–VO₂/NTO coexistence coating films showed the appropriateness for multifunctional materials.