A broom-like tube-in-tube bundle O-doped graphitic carbon nitride nanoreactor that promotes photocatalytic hydrogen evolution

[Display omitted] •A broom-like tube-in-tube bundle g-C3N4 nanoreactor was obtained for the first time.•The unique nanoreactor enhanced light utilization and carrier separation efficiency.•Oxygen doping narrowed the band gap and expanded the range of light response.•DFT calculated that the introduction of oxygen promoted the separation of carriers.•The H2 evolution rate of O-CN-NTs nanoreactors reached up to 13.61 mmol g−1h−1. Metal-free graphite carbon nitride (g-C3N4) is an ideal catalyst in the field of photocatalytic hydrogen evolution due to its visible light response, thermochemical stability and low cost. However, limited by the high photogenerated electron-hole recombination rate and poor light trapping ability of bulk g-C3N4 prepared by thermal condensation, it remains a great challenge in boosting the photocatalytic hydrogen (H2) evolution performance. Herein, a broom-like O-doped g-C3N4 nanoreactor (O-CN-NTs) oriented by tube-in-tube was developed for the first time through the “calcination-hydrothermal-calcination” method. The tube-in-tube nanoreactor not only can facilitate the scattering of incident light inside the cavity to enhance the utilization of light, but also can reduce the transport distance of carriers from the bulk to the surface to facilitate electron-hole separation. The morphology design of the tube-in-tube nanoreactor plays a very important role in improving the performance of photocatalytic H2 production. Furthermore, the density functional theory (DFT) calculation results manifest that the charge redistribution around the doped oxygen atoms accelerates the separation of electron-hole. The doping of oxygen atoms in g-C3N4 nanoreactor further enhanced the photocatalytic H2 production performance. Attributed to above advantages, the visible-light-driven (≥420 nm) photocatalytic H2 production rate of O-CN-NTs can achieve 13.61 mmol g-1h−1, which is approximately 71.63 times that of bulk g-C3N4 (CN550).