TiO2@g-C3N4/SiO2 with superior visible-light degradation of formaldehyde for indoor humidity control coatings

Indoor air quality is a critical concern in people's daily life due to the adverse effects of formaldehyde and humidity on human health. The development of multifunctional indoor coatings which can photodegrade formaldehyde and regulate humidity is desirable. In this study, we use a simple route to synthesize a heterostructure photocatalyst (denoted as TiO2@g-C3N4/SiO2-x%) via combining TiO2, graphitic carbon nitride (g-C3N4), and enhancement silica fume (SiO2). The results indicate that the prepared TiO2@g-C3N4/SiO2-12% photocatalyst is capable of degrading formaldehyde with a removal efficiency of 83.5%, which is higher than those of pure TiO2 (10.8%) and g-C3N4 (67.8%) after 3 h of visible-light irradiation. The above findings may be attributed to the enhanced visible light absorption and the fast transfer of photogenerated electrons. Electron paramagnetic resonance spectra and Mott-Schottky plots show that the generation of ･O2− and ･OH active species via Z-scheme route on TiO2@g-C3N4/SiO2-12% are responsible for the decomposition of formaldehyde under visible light. For practical applications, the TiO2@g-C3N4/SiO2-12% photocatalyst is further employed to fabricate the sustainable coating (denoted as TGS coating), which exhibits a formaldehyde removal efficiency of 85.0% with outstanding humidity control performance over ten times higher than commercial coatings. The remarkable improvement of humidity control performance on TGS coatings is due to the effect of better textural properties. More importantly, this study demonstrates the valorization of waste silicas to fabricate sustainable TGS coatings with great stability, which may provide the practical applications in the indoor environment.