Flame retardant and visible light-activated Fe-doped TiO2 thin films anchored to wood surfaces for the photocatalytic degradation of gaseous formaldehyde

Flame retardant and visible light-activated Fe-doped TiO2 thin films were anchored to wood surfaces by a facile precipitation method for the photocatalytic degradation of gaseous formaldehyde. All of the as-prepared TiO2 thin films exhibited the anatase crystal structure and grew on the wood surfaces by the aggregation of nanoparticles with diameters ranging from 11 to 16 nm. The UV-vis diffuse reflectance spectroscopy (UV-vis DRS) results showed that the presence of a small amount of iron ions in the TiO2 matrix could significantly extend the optical responses in the UV to visible region. Compared to the pure TiO2/wood samples, the Fe-doped TiO2/wood samples exhibited higher photocatalytic activities under visible light irradiation. The optimum nFe/nTi molar ratio was 2.0 at. %. The electron spin resonance (ESR) tests further confirmed that the active oxygen species of OH and O2- that were generated on the Fe-doped TiO2/wood samples under visible light irradiation are responsible for the degradation of formaldehyde. The Fe-doped TiO2 samples also exhibited high stability and reusability after 6 cycles. Additionally, the limiting oxygen index of the original wood increased from 24.8% to 33.9% after it was coated with Fe-doped TiO2 thin films, indicating a significant improvement in its flame resistance.