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.