Preparation of wood functional coatings with carbon dots grafted TiO₂ for its photocatalytic degradation of formaldehyde gas

  Objective  In order to broaden the photocatalytic degradation ability of titanium dioxide (TiO₂) for formaldehyde gas pollutants, carbon dots (CDs) with excellent light absorption and electron transfer were used to modify the TiO₂, which greatly improves the performance of pure TiO₂ photocatalyst.

  Method  The surface of TiO₂ nanoparticles was modified by (3-aminopropyl) trimethoxysilane (APTMS) and integrated with CDs, which was synthesized from plant biomass of switchgrass. The resulted TiO₂-CDs composites were then coated on wood to construct a photocatalytic coating. Multiple characterizations such as high-resolution transmission electron microscopy (HRTEM), infrared spectroscopy (FTIR), thermo-gravimetric analysis (TG), ultraviolet-visible spectroscopy (UV-Vis), fluorescence spectroscopy were applied to characterize the CDs and their loading TiO₂ photocatalysts. The photocatalytic experiments were also carried out with formaldehyde gas as a typical pollutant.

  Result  The synthesized fluorescent CDs had a good graphite phase structure with a particle size of 3−6 nm, which also showed strong excitation dependence. TiO₂-CDs composites not only had strong absorption under UV light, but also had a wider absorption band in the wavelength range of 400−500 nm. TiO₂-CDs wood coatings can achieve 68.26% and 81.63% degradation efficiency of formaldehyde gas under UV light and UV combined with visible light source, which was 35.55% and 38.71% higher than that of unmodified TiO₂ coating under the same condition. In addition, TiO₂-CDs coating significantly reduced the wettability of wood surface with a water contact angle of 96.4°, which was 54.24% higher than that of the pure wood (62.5°). Moreover, surface coating had little effect on the apparent color of wood. Surface brightness of functional wood was slightly lower than that of the pure wood by 5.22%, and the color difference was only 11.03 compared with the uncoated wood. Furthermore, the TiO₂-CDs photocatalytic wood coating showed good recyclability with a degradation efficiency decrease of 2.56% and 3.54%, respectively after 7 cycles.

  Conclusion  The utilization of CDs doping could broaden the degradation ability of formaldehyde gas for TiO₂ photocatalyst in the visible light region, reduce the wettability of wood surface and has little effect on the apparent color of wood, which would be useful for the development of wood functional materials for degradation of formaldehyde gas pollutants.