A simple method to prepare g-C3N4-TiO2/waste zeolites as visible-light responsive photocatalytic coatings for degradation of indoor formaldehyde

The indoor air quality should be highly addressed because people spend more time staying in indoor environments. Photocatalytic degradation of indoor pollutants (e.g., formaldehyde) is one of the most promising and environmental friendly technologies. In this work, a heterostructured photocatalyst combining graphitic carbon nitride (g-C3N4), TiO2 and waste zeolites (g-C3N4-TiO2/waste zeolites) is developed by a facile calcination and sol-gel method. The prepared photocatalysts exhibit the superior visible-light-responsive activities toward formaldehyde degradation (k = 0.0127 min(-1)) which is higher than g-C3N4-TiO2 (k = 0.0123 min(-1)) and P25 (k = 0.0056 min(-1)). Over 90% of low-concentration formaldehyde can be oxidized by g-C3N4-TiO2/waste zeolites under a commercial LED light within 300 min. The electron spin resonance spectra indicate that the superoxide radical anions (O-center dot(2)-) photogenerated on the g-C3N4-TiO2/waste zeolites under visible light irradiation are responsible for the decomposition of formaldehyde. The enhancement in the photocatalytic decomposition of formaldehyde in the air is possibly due to the heterojunction between g-C3N4 (the enhanced absorption of visible light) and TiO2 (fast transfer of photogenerated electrons from g-C3N4) as well as assisted adsorption of gas-phase formaldehyde via waste zeolites. This work also exemplifies the valorization of industrial silicate wastes to efficient photocatalytic coatings for indoor air purification.