Developing a photocatalyst with the necessary characteristics of being cheap, efficient and robust for visible-light-driven water splitting remains a serious challenge within the photocatalysis field. Herein, an effective strategy, deprotonating g-C3N4 with Na ions from low-cost precursors, is reported. The deprotonated g-C3N4 exhibits a stable and reproducible H2 and O2 evolution rate of 31.5 and 15.2 μmol h−1 from pure water over 24 h. Our findings reveal that the extraordinary photoreactivity comes from the enhanced optical absorption, the promoted charge transfer, and the completely inhibited H2O2 intermediate due to the deprotonation.

•g-C3N4 hexagonal microprisms were synthesized via molecular self-assembly.•The H2-evolution rate is 16.8 times higher than that on the bulk.•The microprisms feature large surface area for efficient charge separation.Graphitic carbon nitride (C3N4) hexagonal microprisms were synthesized via a self-assembly route using (NH4)2CO3 as a structure-directing reagent. It shows that the extraordinary hierarchical structure is favorable to improving the photocatalytic activity of C3N4 toward water splitting under visible light irradiation (λ>420 nm). The photocatalytic H2-evolution rate on the microprisms is 185 µmol/h, 16.8 times higher than that over bulk C3N4. The enhanced photocatalytic performance of the as-prepared microprisms mainly originates from the characteristic micro-nanostructure, possessing enlarged surface area for efficient charge separation.

•S-doped and N-deficient g-C3N4 with porous framework was prepared by a facile method.•The H2-evolution rate is 12 times as high as that on g-C3N4 under visible light.•The structural and electronic reconstruction contributes to the enhanced activity.A highly photoactive sulfur-doped and nitrogen-deficient g-C3N4 photocatalyst with porous framework has been prepared by a one-step approach using trithiocyanuric acid as the precursor. It is found that the as-synthesized catalyst exhibits an enhanced visible-light photocatalytic activity for H2 production. The H2-evolution rate on the modified g-C3N4 is 121 μmol/h, which is ca. 12 times as high as that over pristine g-C3N4. Characterization results show that the sulfur doping induces nitrogen vacancies and hierarchical microspores in g-C3N4. Such a structural reconstruction is beneficial for improving optical absorption and hindering photoinduced charge recombination on g-C3N4, resulting in the enhanced photocatalytic activity.

Graphitic carbon nitride (g-C3N4) hybridized with a small number of multi-walled carbon nanotubes (CNT) was synthesized using cyanamide as precursor. The optimal CNT content is found to be ∼0.2 wt% in the composite, which displays a 2.4-fold enhancement in photocatalytic water splitting over pure g-C3N4. Characterizations by a series of joint techniques including Raman spectra, UV/vis diffuse reflectance spectra, steady and time-resolved fluorescence emission spectra, and photocurrent responses were carried out, aiming to reveal the determinative factor for the improved visible-light response. Our results indicate that the increased photoactivity originates from the enhanced charge-transfer effect due to the intimate interactions between g-C3N4 and conjugated CNT. The presence of CNT in the hybrids is beneficial for improving electron–hole separation on the excited g-C3N4 by prolonging the lifetimes of charge carriers and improving the population distribution of short-lived and long-lived charge carriers.

•Porous g-C3N4 with 3D hierarchical structure was prepared by a temple-free method.•Porous g-C3N4 features large surface area and low charge carrier recombination.•Porous g-C3N4 exhibits superior visible-light photocatalytic H2-evolution activity.Porous graphitic carbon nitride (g-C3N4) with three-dimensional (3D) hierarchical structure was fabricated via a template-free approach by using cyanuric acid as a polymerization inhibitor. The hierarchical porous structure has a remarkable effect on the surface properties and photocatalytic performance of g-C3N4 for photocatalytic H2 production under visible light irradiation (λ >420 nm). The photocatalytic H2-evolution rate over the hierarchical porous g-C3N4 is 68.5 μmol/h, which is about 4.8 times higher than that of pristine g-C3N4. Characterization results show that the formation of the 3D hierarchical porous structure results in the enlarged specific surface area, enhanced redox potential, and decreased recombination of photoinduced charge carriers of g-C3N4, contributing to the enhanced photocatalytic activity.

Nitrogen-deficient graphitic carbon nitride (g-C3N4−x) was synthesized by a hydrothermal treatment using ammonium thiosulfate as an oxidant. The as-prepared photocatalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption–desorption, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), electron paramagnetic resonance (EPR), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence (PL) spectroscopy. The visible-light-driven photocurrent measurement was performed by several on–off cycles of intermittent irradiation. The photocatalytic activity of catalysts was evaluated by splitting water under visible-light irradiation (λ > 420 nm). Results demonstrated that the photoactivity of g-C3N4−x was enhanced greatly by the deficiency of the terminal amino species on the catalysts. The average H2 evolution rate on g-C3N4−x was 31.6 μmol h−1, which was ca. 3 times higher than that on pristine g-C3N4. It was revealed that the unique nitrogen-deficient structure of g-C3N4−x played an important role in broadened visible-light absorption and efficient electron–hole separation, mainly accounting for the improved photocatalytic activity.

N-doped and oxygen-deficient TiO2 photocatalysts were fabricated by a two-step calcination method using dicyandiamide and commercial TiO2 as starting materials. Photocatalytic activity was tested by decomposing gas-phase benzene under visible light irradiation. The nitrogen dopants and oxygen defects in TiO2 played important roles in benzene photodegradation. It was found that the optimum doping dosages of nitrogen and defects (Ti3+/Titotal) were 0.23 wt% and 26 at%, respectively. After photooxidation for 5 h, the benzene conversion rate and CO2 yielded over the as-doped TiO2 were 72% and 190 ppmv, respectively, which were much higher than the sum on NH3-treated TiO2 and H2-treated TiO2. It suggests that the visible-light activity of the modified TiO2 is attributed to a synergistic effect between substitutional N dopants and oxygen defects in TiO2.Highlights► N-doped and oxygen-deficient TiO2 was synthesized by a two-step calcination method using dicyandiamide as a N-containing and reductive reagent. ► Comparative study of NH3-treated TiO2 and H2-treated TiO2 were implemented. ► The sum of the benzene conversion rates or CO2 yields over NH3-treated TiO2 and H2-treated TiO2 was much lower than that on the co-doped catalyst. ► A synergistic effect between N dopants and oxygen vacancies in TiO2 was found.

O-doped g-C3N4 was synthesized for the first time by a facile H2O2 hydrothermal approach. The O-doping in the g-C3N4 lattice could induce intrinsic electronic and band structure modulation, resulting in its absorbance edge up to 498 nm and enhanced visible-light photoactivity, consequently.

Bi2WO6-coated carbon (Bi2WO6@C) microspheres were prepared by a two-step hydrothermal method using glucose as a carbon source. The physicochemical properties of the prepared microspheres were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller (BET), and UV/Vis diffuse reflectance spectrum (DRS). The photocatalytic activity of the as-prepared sample was determined by degradation of gas-phase benzene under visible-light irradiation, and was compared to N-doped TiO2. It was revealed that the photocatalytic performance of the Bi2WO6 was enhanced greatly by the doping of carbon microspheres. The photocatalytic conversion rate and mineralization rate of benzene over the Bi2WO6@C microspheres were 42.6% and 80.0% respectively, which were much higher than that of N-doped TiO2.Download full-size imageResearch highlights►Photocatalyst with controllable morphology and structure. ►Well-dispersed Bi2WO6 on carbon microspheres. ►Carbon microspheres promote Bi2WO6 performance towards benzene photodegradation.

Nitrogen-deficient graphitic carbon nitride (g-C3N4−x) was synthesized by a hydrothermal treatment using ammonium thiosulfate as an oxidant. The as-prepared photocatalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption–desorption, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), electron paramagnetic resonance (EPR), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence (PL) spectroscopy. The visible-light-driven photocurrent measurement was performed by several on–off cycles of intermittent irradiation. The photocatalytic activity of catalysts was evaluated by splitting water under visible-light irradiation (λ > 420 nm). Results demonstrated that the photoactivity of g-C3N4−x was enhanced greatly by the deficiency of the terminal amino species on the catalysts. The average H2 evolution rate on g-C3N4−x was 31.6 μmol h−1, which was ca. 3 times higher than that on pristine g-C3N4. It was revealed that the unique nitrogen-deficient structure of g-C3N4−x played an important role in broadened visible-light absorption and efficient electron–hole separation, mainly accounting for the improved photocatalytic activity.

Developing a photocatalyst with the necessary characteristics of being cheap, efficient and robust for visible-light-driven water splitting remains a serious challenge within the photocatalysis field. Herein, an effective strategy, deprotonating g-C3N4 with Na ions from low-cost precursors, is reported. The deprotonated g-C3N4 exhibits a stable and reproducible H2 and O2 evolution rate of 31.5 and 15.2 μmol h−1 from pure water over 24 h. Our findings reveal that the extraordinary photoreactivity comes from the enhanced optical absorption, the promoted charge transfer, and the completely inhibited H2O2 intermediate due to the deprotonation.

O-doped g-C3N4 was synthesized for the first time by a facile H2O2 hydrothermal approach. The O-doping in the g-C3N4 lattice could induce intrinsic electronic and band structure modulation, resulting in its absorbance edge up to 498 nm and enhanced visible-light photoactivity, consequently.