A scalable route to mixed and layered sandwich-structured carbonaceous–anatase TiO2 coatings with bi-functional photocatalytic activity for air pollution remediation and solar water splitting

This study showcases how carbonaceous materials, including graphene (G), fullerene (F), and multi-walled carbon nanotubes (MWCNTs), can be integrated within titanium dioxide (TiO 2 ) films as either: (i) mixed or (ii) layered sandwich structures (TiO 2 /carbonaceous material/TiO 2 ) and show bifunctional photocatalytic activity. Our composites are engineered to address both NO x pollution and water splitting within the same platform. In the mixed composite (TGmix), graphene's high conductivity and electron-accepting ability enhance the photo-oxidation of NO x , where under UVA light 17.6 % NO and 9.6 % total NO x removal was seen, which was significantly higher than TiO 2 alone, which showed 6.8 % NO and 1.3 % total NO x removal. Whereas in the sandwich-layered composite (TGT), the architecture promotes hole accumulation on the surface, favouring water splitting, with incident-photon-to-current efficiency (IPCE) reaching 68 % at 1.23 V RHE (pH = 7) under 250 nm illumination; a factor of ∼2 increase compared to TiO 2 alone. Transient photocurrent (TPC) and diffuse reflectance transient absorption spectroscopy (DR-TAS) were employed operando to probe the kinetics of electron extraction and hole-mediated water oxidation. At 1.23 V RHE , the TGT sample showed slightly faster electron extract kinetics to T (TGT: t 50 % –0.25 ms and T: t 50 % –0.268 ms), along with a significantly higher long-lived hole carrier population that drove water oxidation, which were found to linearly correlate with the observed photocurrent density. Our wholistic study, including in operando investigations, informs the rational design of active carbonaceous composite coatings within anatase TiO 2 that can be grown at scale for applications in NO x air pollution remediation and solar water splitting. • Bi-functional coatings for air pollution remediation and solar fuel production. • Coatings produced using a novel and scalable chemical vapour deposition method. • Composite films incorporate graphene, fullerene, or carbon nanotubes. • Intimately mixed graphene with titania boost light-driven nitrogen oxide (NO x ) pollution remediation. • Layered titania and graphene structures show more efficient solar water splitting activity.