Developing highly effective photocatalytic hydrogen production in graphitic carbon nitride (g-C3N4) is still a challenging issue. Herein, for the first time, the structural engineering of g-C3N4 nanosheets with Co atoms...

Developing high-efficiency, stable, and low-cost catalysts is essential for water splitting to generate hydrogen. Herein, an abundant material, g-C3N4 nanosheet, modified with a moderate amount of Cu atoms to form a special Cu-N3 structure exhibits excellent performance of photocatalytic hydrogen generation under visible light illumination. The structure of Cu-N3 is formed through Cu-atom-substituted C atoms in g-C3N4. X-ray absorption fine structure spectroscopy (XAFS) was employed to confirm the Cu coordination and the special structure of Cu-N3. Doping of Cu atoms not only regulates the energy band structure but also enhances the visible light absorption of g-C3N4 as confirmed by the UV–vis diffuse reflectance spectroscopy and Mott–Schottky test, and significantly improves the separation and transfer of photogenerated charges confirmed by the electrochemical test. Therefore, the catalyst exhibits a superior photocatalytic hydrogen production rate of 3774.35 μmol·g–1·h–1 and an apparent quantum efficiency (AQE) of 1.34% under visible light illumination (at 427 nm), which are both more than 3 times those of pure g-C3N4 nanosheets (1116.07 μmol·g–1·h–1 and 0.40%, respectively).

Two physical models, the replacing model and the filling model, have been proposed to explain the mechanism of the effective-refractive-index change of photonic crystals (PCs). Theoretically, the photonic bandgap (PBG) would shift when PCs are exposed to different environments, which leads to a change of the effective refractive index of PCs. However, the mechanism of effective-refractive-index change is distinct when PCs are placed in different gases or vapors. Here, silica PCs were successfully fabricated by a self-assembly method. The PBG of silica PCs exhibit similar redshifts in volatile organic compounds (VOCs) and in small-molecule gases. We propose a replacing model to elaborate silica PCs exposed to VOCs and a filling model to explain silica PCs exposed to small-molecule gases. Additionally, the redshift of PBG was transformed into the volume fraction of adsorbed gas in order to achieve selective sensing of silica PCs. The approach could be exploited for applications in sensing.

It is commonly believed that active oxygen species over ABO 3 perovskite play an important role in improving catalytic activity. In this paper, SrTiO 3 (STO) was prepared and doped with an extremely low concentration of NiP. By adjusting the doping process, the content of three kinds of oxygen species can be transformed accordingly, which consequently influences the catalytic activity in water splitting under visible light irradiation. The transformation of oxygen species and the improvement mechanism of hydrogen generation were investigated. X-ray absorption fine structure (XAFS), X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculation confirmed that Ni occupied the Ti sites and P coordinated with lattice oxygen on the STO surface. Structural evolution not only forms reactive lattice oxygen but also regulates oxygen vacancies and adsorbed oxygen. Reactive lattice oxygen serves as the reaction site during the hydrogen evolution reaction. In summary, constructing reactive lattice oxygen and adjusting the ratio of different oxygen species are effective ways to fabricate high-performance photocatalysts for H 2 evolution.