Energy band engineering of hydroxyethyl group grafted on the edge of 3D g-C3N4 nanotubes for enhanced photocatalytic H2 production

The reduction of H2O into H2 through solar energy has attracted great attention of renewable energy research. However, the rapid recombination of photogenerated electrons and holes limits its application. In this paper, the hydroxyethyl group (-CH2CH2OH) was edge grafted on the g-C3N4 nanotubes (NTs) (named g-C3N4 NTs-CCO) by the one-pot solvothermal for photocatalytic hydrogen evolution, enhancing the light absorption and the transport of carriers, and improving the energy band structure for photocatalytic hydrogen evolution. The g-C3N4 NTs-CCO exhibited greatly improved photocatalytic hydrogen evolution activity (2521 μmol h−1 g−1), about 4.90 times of bulk g-C3N4/Pt and 2.71 times of the g-C3N4 NTs/Pt. Meanwhile, the apparent quantum yield (AQE) value of g-C3N4 NTs-CCO using 50 mg photocatalyst is 6.45% under light at λ = 370 nm. The experimental tests and DFT calculation have shown that g-C3N4 NTs-CCO have the benefits as follows: 1) The unique ordered and well-crystallized array structure could form the potential difference after photoexcitation which promotes charge transfer and mass transfer and increases the active sites for the hydrogen evolution reaction; 2) the edge grafting of hydroxyethyl group improves the energy band structure of the catalyst, provides an intermediate band at the 0 eV Fermi level which acts as the transition sites for photogenerated carriers and the energy level (H+/H2) of reaction, and provides a more thermodynamically favorable active site N3, thus facilitates photogenerated carrier migration and reaction processes; 3) the unique ordered well-crystallized array structure and the improvement of energy band structure enhance the light absorption and the transport of carriers and provide the active sites, thereby promoting the excitation, migration and surface reaction process of carriers for the improved photocatalytic hydrogen evolution performance.