Porous g-C3N4/TiO2 foam photocatalytic filter for treating NO indoor gas

g-C3N4/TiO2 heterojunction functional foams were constructed as gas purification filters for treating NO indoor gas with a high removal rate (>65%) and high stability under visible-light (λ ≥ 400 nm) illumination. The skeletons of the 3D foams consisted of g-C3N4 and TiO2 quantum dots (QDs). Such 3D porous foamy filters provided a large surface area and continuous pores for trapping and oxidizing NO molecules owing to their excellent adsorption and activation capability. The embedded g-C3N4/TiO2 QD heterojunctions in the foam skeletons effectively promoted the separation of photo-generated carriers, allowing the generation of more active species (holes and ·OH) for oxidizing NO molecules. An oxidation pathway (NO → NO+ → NO2− or NO3−) was proposed based on in situ FTIR spectroscopy, which suggested the important role of NO+ for removing NO gas. This work provides an efficient and stable air-purification filter for indoor air treatment.