C,N-Codoped TiO2 with a Nitrogen-Doped Carbon Coating Derived from 2,6-Diaminopyridine for Visible Light-Induced Photocatalytic Hydrogen Evolution

Nitrogen-doped carbon-wrapped C,N-codoped TiO2 (CN@C,N-TiO2) was successfully prepared using a facile and efficient method involving hydrolysis and calcination under Ar using tetrabutyl titanate and 2,6-diaminopyridine as the precursors. X-ray photoelectron spectroscopy (XPS) and valence band XPS measurements reveal the successful codoping of interstitial carbon and nitrogen into TiO2, which leads to a visible-light absorption of up to ∼550 nm in the UV–vis diffuse reflectance spectra. Raman spectra and high-resolution transmission electron microscopy results show that N-doped carbon exists on the surface of C,N-TiO2, which gives rise to the efficient separation of photoexcited charge carriers, as determined by photoluminescence and electrochemical impedance spectroscopy. Benefiting from the combined effects of a surface-coated N-doped carbon layer and C,N-codoping, the photocatalyst calcined at 450 °C exhibits remarkable visible-light activity toward the hydrogen evolution reaction in the water splitting process with a H2 production rate of 833.2 μmol h–1 g–1 under 94 mW cm–2 visible-light illumination (λ > 420 nm). Moreover, the representative CN@C,N-TiO2 sample can maintain its activity for at least 40 h.