Carbon-Coated TiO₂ Nanoparticles for Noble-Metal-Free Photocatalytic H₂ Production from H₂O

Core–shell {nanocarbon-coated/TiO2} hybrids (C@TiO2) were developed through a double-nozzle flame spray pyrolysis (DN-FSP) process. By optimizing the DN-FSP parameters, we have achieved control over the subnanometric thickness of the carbon shell as well as the anatase/rutile ratio within the TiO2. A library of C@TiO2 hybrids, with varying carbon contents and sp2/sp3 ratios, has been produced. These optimized C@TiO2 hybrids are capable of performing efficient photocatalytic hydrogen production from water, exceeding 400 μmol g–1 h–1, without the need for any noble-metal cocatalyst. HR-TEM has demonstrated that the DN-FSP process facilitates the formation of a nanocarbon shell and carbon nanodots in close contact with the TiO2 surface. XRD and Raman spectra indicate that this close carbon/TiO2 interface promotes the formation of a TiO2 rutile/anatase interphase. EPR spectroscopy shows that the carbon/TiO2 nanohybrids stabilize reduced Ti3+ sites at the interface. Moreover, an in situ EPR study of the photoinduced holes/electrons demonstrates that the nanocarbon moieties act as a very efficient acceptor of the photogenerated electrons. In this way, the highly efficient photocatalytic performance of C@TiO2 nanohybrids is attributed to the formation of a Z-scheme assembly of {rutile/anatase/carbon} nanophases. From a technological perspective, this work highlights the potential of the DN-FSP process for the scalable synthesis of functional photocatalytic (carbon/metal oxide) nanomaterials.