Construction of covalent bonding oxygen-doped carbon nitride/graphitic carbon nitride Z-scheme heterojunction for enhanced visible-light-driven H2 evolution

Photocatalytic water splitting for hydrogen production is a brilliant method for utilization of solar energy. Herein, a series of covalent bonding oxygen-doped carbon nitride/graphitic carbon nitride hybrids (O-CN/CN) have been synthesized via solvothermal treatment using cyanuric chloride, cyanuric acid (derived from hydrolysis of cyanuric chloride) and urea-derived graphitic carbon nitride as precursors. In O-CN/CN hybrids, guest O-CN was covalently bonded with incomplete polycondensation –NHx derived from the host CN surface as verified by XRD, FT-IR, XPS and solid-state 13C MAS NMR spectra. With assistance of Pt co-catalyst, the most efficient O-CN/CN-3 photocatalyst showed the highest H2 generation rate at 6.97 mmol g−1h−1 under visible light irradiation (λ > 420 nm) by 12.4 times as that of pristine CN (0.56 mmol g−1h−1). Moreover, the apparent quantum yield (AQY) was estimated as 21.4% at 425 nm irradiation for O-CN/CN-3. The improved photocatalytic performance was ascribed to the extended visible light absorption, the inhibited photo-induced charge carrier recombination and rapid charge carriers transfer that were confirmed by UV–vis diffuse reflectance spectra, photoluminescence spectra, transient photocurrent responses, electrochemical impedance spectroscopy and time-resolved photoluminescence. Moreover, the photocatalytic activity displayed unnoticeable deactivation within five recycles, further verifying that O-CN/CN hybrids were stable for visible-light-driven H2 evolution. This present work promotes new insights into Z-scheme heterojunction engineering for graphitic carbon nitride.