Defect engineering of transition metal oxides and synergistic interaction of two-dimensional conducting metal–organic frameworks for efficient photocatalytic hydrogen evolution

[Display omitted] •A new visible light catalyst Ni3(HITP)2/TiO2-x is synthesized by solvothermal method.•The existence of oxygen defects adjusts the band gap structure of TiO2.•The S-scheme heterojunction enhances the redox capability of photogenerated carriers.•Ni3(HITP)2/TiO2-x exhibits enhanced photocatalytic performance.•The mechanism of photocatalytic hydrogen evolution is proposed. S-scheme heterojunctions demonstrate exceptional hydrogen evolution property due to their unique charge transfer mechanism and robust redox potential. In this study, oxygen-deficient titanium dioxide (TiO2-x) was prepared with a band gap narrowed from 3.2 eV to 2.8 eV. Meanwhile, TiO2-x exhibits oxygen vacancy concentration-dependent hydrogen evolution rate, in which TiO2-x-2 with appropriate oxygen vacancy concentration displays significantly higher H2 evolution efficiency than matrix TiO2. Subsequently, Ni3(HITP)2/TiO2-x was synthesized using mechano-solvothermal approach. The experiments show that the material possesses excellent catalytic activity and stability and can effectively produce hydrogen by photocatalytic water splitting after undergoing five cycles. The hydrogen evolution rate of 3 wt% Ni3(HITP)2/TiO2-x-2 reaches 5.804 mmol/g/h, exhibiting a 6.64-fold increase compared to TiO2. The proposed enhanced photocatalytic capacity of Ni3(HITP)2/TiO2-x-2 can be ascribed to the creation of S-scheme heterojunctions, Ni3(HITP) 2′s full-spectrum light absorption ability, excellent conductivity, and a large specific surface area. In support, in situ X-ray photoelectron spectroscopy and surface photovoltage spectroscopy, along with radical capture experiments confirmed the charge transport mechanism of Ni3(HITP)2/TiO2-x following the S-scheme heterojunction. In general, this study offers significant contributions to the understanding of the cooperative application of conductive MOFs and defect engineering in photocatalysis.