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

Abstract

Core–shell {nanocarbon-coated/TiO₂}\nhybrids (C@TiO₂) were developed through a double-nozzle\nflame spray pyrolysis\n(DN-FSP) process. By optimizing the DN-FSP parameters, we have achieved\ncontrol over the subnanometric thickness of the carbon shell as well\nas the anatase/rutile ratio within the TiO₂. A library\nof C@TiO₂ hybrids, with varying carbon contents and sp²/sp³ ratios, has been produced. These optimized\nC@TiO₂ hybrids are capable of performing efficient photocatalytic\nhydrogen production from water, exceeding 400 μmol g^–1 h^–1, without the need for any noble-metal cocatalyst.\nHR-TEM has demonstrated that the DN-FSP process facilitates the formation\nof a nanocarbon shell and carbon nanodots in close contact with the\nTiO₂ surface. XRD and Raman spectra indicate that this\nclose carbon/TiO₂ interface promotes the formation of a\nTiO₂ rutile/anatase interphase. EPR spectroscopy shows\nthat the carbon/TiO₂ nanohybrids stabilize reduced Ti³⁺ sites at the interface. Moreover, an <i>in situ</i> EPR study of the photoinduced holes/electrons demonstrates that\nthe nanocarbon moieties act as a very efficient acceptor of the photogenerated\nelectrons. In this way, the highly efficient photocatalytic performance\nof C@TiO₂ nanohybrids is attributed to the formation of\na Z-scheme assembly of {rutile/anatase/carbon} nanophases. From a\ntechnological perspective, this work highlights the potential of the\nDN-FSP process for the scalable synthesis of functional photocatalytic\n(carbon/metal oxide) nanomaterials.