Two-Dimensional Ultrathin Graphic Carbon Nitrides with Extended pi-Conjugation as Extraordinary Efficient Hydrogen Evolution Photocatalyst

Construction of 2D graphic carbon nitrides (g-CNx) with wide visible light adsorption range and high charge separation efficiency concurrently is of great urgent demand and still very challenging for developing highly efficient photocatalysts for hydrogen evolution. To achieve this goal, a two-step pyrolytic strategy has been applied here to create ultrathin 2D g-CNx with extended the pi-conjugation. It is experimentally proven that the extension of pi-conjugation in g-CNx is not only beneficial to narrowing the bandgap, but also improving the charge separation efficiency of the g-CNx. As an integral result, extraordinary apparent quantum efficiencies (AQEs) of 57.3% and 7.0% at short (380 nm) and long (520 nm) wavelength, respectively, are achieved. The formation process of the extended pi-conjugated structures in the ultrathin 2D g-CNx has been investigated using XRD, FT-IR, Raman, XPS, and EPR. Additionally, it has been illustrated that the two-step pyrolytic strategy is critical for creating ultrathin g-CNx nanosheets with extended pi-conjugation by control experiments. This work shows a feasible and effective strategy to simultaneously expand the light adsorption range, enhance charge carrier mobility and depress electron-hole recombination of g-CNx for high-efficient photocatalytic hydrogen evolution.