In-situ fabrication of CuS/g-C3N4 nanocomposites with enhanced photocatalytic H2-production activity via photoinduced interfacial charge transfer

In this work, novel CuS/g-C₃N₄ composite photocatalysts were successfully prepared via a simple in-situ growth method. CuS nanoparticles, with an average diameter of ca.10 nm, were well dispersed on the surface of g-C₃N₄, revealing that g-C₃N₄ nanosheets were promising support for in-situ growth of nanosize materials. The CuS/g-C₃N₄ composites exhibited highly enhanced visible light photocatalytic H₂ evolution from water-splitting compared to pure g-C₃N₄. The optimum photocatalytic activity of 2 wt% CuS/g-C₃N₄ composite photocatalytic H₂ evolution was about 13.76 times higher than pure g-C₃N₄. The enhanced photocatalytic activity is attributed to the interfacial charge transfer (IFCT). In this system, electrons in the valence band (VB) of g-C₃N₄ can transfer directly to CuS clusters, causing the reduction of partial CuS to Cu₂S, which can act as an electron sink and co-catalyst to promote the separation and transfer of photo-generated electrons. The accumulated photoinduced electrons in CuS/Cu₂S clusters could effectively reduce H⁺ to produce H₂. This work provides a possibility for constructing low-cost CuS as a substitute for noble metals in the photocatalytic production of H₂ via a facile method based on g-C₃N₄.     

Redox couple mediated charge carrier separation in g-C3N4/CuO photocatalyst for enhanced photocatalytic H2 production

Graphitic carbon nitride (g-C₃N₄) is one of the promising two-dimensional metal-free photocatalysts for solar water splitting. Regrettably, the fast electron-hole pair recombination of g-C₃N₄ reduces their photocatalytic water splitting efficiency. In this work, we have synthesized the CuO/g-C₃N₄ heterojunction via wet impregnation followed by a calcination method for photocatalytic H₂ production. The formation of CuO/g-C₃N₄ heterojunction was confirmed by XRD, UV–vis and PL studies. Notably, the formation of heterojunction not only improved the optical absorption towards visible region and also enhanced the carrier generation and separation as confirmed by PL and photocurrent studies. The photocatalytic H₂ production results revealed that CuO/g-C₃N₄ photocatalyst demonstrated the increased photocatalytic H₂ production rate than bare g-C₃N₄. The maximum H₂ production rate was obtained with 4 wt % CuO loaded g-C₃N₄ photocatalyst. Importantly, the rate of H₂ production was further improved by introducing simple redox couple Co²⁺/Co³⁺. Addition of Co²⁺ during photocatalytic H₂ production shuttled the photogenerated holes by a reversible conversion of Co²⁺ to Co³⁺ with accomplishing water oxidation. The effective shuttling of photogenerated holes decreased the election-hole pair recombination and thereby enhancing the photocatalytic H₂ production rate. It is worth to mention that the addition of Co²⁺ with 4 wt % CuO/g-C₃N₄ photocatalyst showed ∼7.5 and ∼2.0 folds enhanced photocatalytic H₂ production rate than bare g-C₃N₄/Co²⁺ and CuO/g-C₃N₄ photocatalysts. Thus, we strongly believe that the present simple redox couple mediated charge carrier separation without using noble metals may provide a new idea to reduce the recombination rate.     

Investigation of Photo(electro)catalytic water splitting to evolve H2 on Pt-g-C3N4 nanosheets

g-C₃N₄ has shown great potentials in photocatalytic water splitting to produce hydrogen. Herein, we successfully synthesized g-C₃N₄ nanosheets via exfoliating bulk g-C₃N₄. And different metal nanoparticles were photo-deposited onto the surface of g-C₃N₄ nanosheets. The photocatalytic H₂ production activity of g-C₃N₄ nanosheets increased from 0 to 11.2 μmol/h/g_cat. The Pt loaded g-C₃N₄ nanosheets manifested the highest H₂ production activity with a rate of 589.4 μmol/h/g_cat. In addition, the hydrogen evolution rate was further enhanced with addition of external bias to fabricate a photoelectrocatalytic (PEC) system. And the maximum hydrogen production rate (23.1 mmol/h/m²) was obtained at a voltage of 0.6 V (vs. Ag/AgCl). The enhancement in H₂ production may be due to the following reasons: (1) Two-dimensional atomic flakes is beneficial to increase the specific surface area of g-C₃N₄, enhance the mobility of carriers, and improve the energy band structure, (2) Pt nanoparticles play an important role in g-C₃N₄ electron transport, (3) the g-C₃N₄ nanosheets loaded with Pt nanoparticles exhibited significant enhancement in photoelectrocatalytic performance, which may be attributed to its enhanced electronic conductivity and photoelectrochemical surface area, (4) Pt inhibited the recombination of photogenerated carriers and significantly improved the photocatalytic performance. The enhancement mechanism was deeply discussed and explained in this work.     

WO3/g-C3N4 two-dimensional composites for visible-light driven photocatalytic hydrogen production

WO₃/g-C₃N₄ two-dimensional (2D) composite photocatalysts were prepared through a simple hydrothermal method followed by a post thermal treatment. The H₂ generation activity of these photocatalysts in the visible light was evaluated. The photocatalysts were characterized by X-ray powder diffraction, Fourier transform infrared spectra, transmission electron microscopy and UV–vis diffuse reflectance spectroscopy et al. These results show that the orthorhombic-phase WO₃ nanoparticles with a grain size from 5 to 80 nm were successfully anchored on g-C₃N₄ nanosheets surface with intimate contact. Furthermore, the charge separation mechanisms of photo-generated charge carriers of the 2D WO₃/g-C₃N₄ photocatalysts were further studied by photoelectrochemical response and electrochemical impedance spectroscopy. The result shows that the 2D WO₃/g-C₃N₄ photocatalyst with 10 wt% WO₃ possesses the maximum photocatalytic performance for H₂ generation, as high as of 1853 μmol h^?1 g^?1, which is about 6.5 times higher than that of bare g-C₃N₄, indicating the fast injection of interface interaction between 2D g-C₃N₄ and WO₃. The increased photocatalytic performance of the composite photocatalyst can be attributed to the enhanced absorption of visible light, the higher photo-generated electrons and holes separation efficiency and low recombination rate of electrons and holes generated by photoexcitation.     

Influence of the nitrogen pots from graphitic carbon nitride with the presence of wrinkled silica-titania for photodegradation enhancement of 2-chlorophenol

An interlayer structure hybrid wrinkled silica titania (WST) loaded on graphitic carbon nitride (g-C₃N₄) was successfully constructed using facile microwave-assisted solid-state technique. The as-prepared materials were characterized using N₂ adsorption-desorption, XRD, FESEM, UV–Vis DRS, FTIR, and TEM analysis. The photocatalytic degradation of 2-chlorophenol (2-CP) towards visible light illumination (150 mW/cm²) is following the sequence: 10 wt% WST@CN (91%) > 5 wt% WST@CN (65%) > g-C₃N₄ (63%) > 15 wt% WST@CN (58%) ? WST (50%). The supreme photocatalytic performance of 10 wt% WST@CN was owing to the WST morphology that more concealed between stacked layer of g-C₃N₄, as a consequence of the stronger interaction between “nitrogen pots” of the g-C₃N₄ and Si/Ti species of the 10 wt% WST, and thus, enhanced the efficiency of charge separation. These criteria provide better charge carrier mobility for enhanced visible light driven photocatalytic performance. The kinetic studies revealed that the photocatalytic degradation of 2-CP using 10 wt% WST@CN obeyed a model of pseudo-first order, with the surface reaction being the rate determining step. Subsequently, the scavenger study confirmed that hydroxyl radicals that absorbed on the catalyst surface play a major role over 10 wt% WST@CN as emerged from the mechanism of Z-scheme. It is notable that the interfacial of WST@CN composite could appear as an excellent catalyst for its useful application for endocrine disruptive wastewater treatment.     

1D/2D carbon-doped nanowire/ultra-thin nanosheet g-C3N4 isotype heterojunction for effective and durable photocatalytic H2 evolution

It is still challenging to design effective g-C₃N₄ photocatalysts with high separation efficiency of photo-generated charges and strong visible light absorption. Herein, a simple, template-free and “bottom-up” strategy has been developed to prepare 1D/2D g-C₃N₄ isotype heterojunction composed of carbon-doped nanowires and ultra-thin nanosheets. The ethanediamine (EE) grafted on melamine ensures the growth of 1D g-C₃N₄ nanowires with high carbon doping, and the ultra-thin g-C₃N₄ nanosheets were produced through HCl-assisted hydrothermal strategy. The apparent grain boundary between 2D nanosheets and 1D carbon-doped nanowires manifested the formation of the isotype heterojunction. The built-in electric field provide strong driving force for photogenerated carriers separation. Meanwhile, the doping carbon in g-C₃N₄ nanowires promotes visible light absorption. As a result, the photocatalytic H₂ evolution activity of 1D/2D g-C₃N₄ isotype heterojunction is 8.2 time that of the pristine g-C₃N₄, and an excellent stability is also obtained. This work provides a promising strategy to construct isotype heterojunction with different morphologies for effective photocatalytic H₂ evolution.     

In-situ synthesis of ternary heterojunctions via g-C3N4 coupling with noble-metal-free NiS and CdS with efficient visible-light-induced photocatalytic H2 evolution and mechanism insight

The two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) nanosheets based composites are prepared in the form of the NiS/g-C₃N₄, CdS/g-C₃N₄ and CdS/NiS/g-C₃N₄ using a facile and reliable method of chemical deposition. The TEM and HRTEM images demonstrated a spectacular representation of the 2D lamellar microstructure of the g-C₃N₄ with adequately attached CdS and NiS nanoparticles. The changes in crystallinity and the surface elemental valence states of composites with the incorporation of two metal sulphides are studied, which confirmed the formation of composites. The photocatalytic response of the composites was estimated by photodegradation of Rhodamine B (C₂₈H₃₁ClN₂O₃–RhB), and the ternary composite CdS/NiS/g-C₃N₄ samples exhibited the superior photocatalytic performance. Further, the free radical capture and electron paramagnetic resonance (EPR) spectroscopy experiments identified the main active species that contributed to the photocatalytic reaction. Besides, the samples’ photocatalytic performance was evaluated by photocatalytic hydrogen production. The stability of the performance-optimized composite was determined by employing cyclic experiments over five cycles. The CdS/NiS/g-C₃N₄ showed the highest efficiency of hydrogen production i.e. about 423.37 μmol.g^?1.h^?1, which is 2.89 times that of the pristine g-C₃N₄. Finally, two types of heterojunction structures were proposed to interpret the enhanced photocatalytic efficiency.     

Mo incorporated Ni nanosheet as high-efficiency co-catalyst for enhancing the photocatalytic hydrogen production of g-C3N4

The design and development of noble metal-free, low-cost and stable co-catalyst are of great significance to the practical application of photocatalysts. In this work, the Mo incorporated Ni nanosheets (MoNi NSs) are successfully prepared and loaded onto g-C₃N₄ via a simple and controllable method. The controlled loading of MoNi NSs with an optimal Mo intake can greatly enhance the photocatalytic H₂-evolution property of g-C₃N₄ (Mo_0.25Ni_0.75/CN5). Specifically, the Mo_0.25Ni_0.75/CN5 exhibits the highest photocatalytic H₂-evolution rate of 273.2 μmol h⁻¹ (5464 μmol h⁻¹ g⁻¹), which is the highest rate under one-solar light in the g-C₃N₄ systems coupled with noble-metal-free co-catalysts. The greatly enhanced photocatalytic H₂-evolution activity of MoNi/g-C₃N₄ is attributed to the role of MoNi as an outstanding co-catalyst to promote the carriers’ separation and transfer, and accelerate the surface H₂ evolution reaction (HER).     

Multiphase TiO2 surface coating g-C3N4 formed a sea urchin like structure with interface effects and improved visible-light photocatalytic performance for the degradation of ibuprofen

In this research, we did not use any template, but a prickly structure urchin like morphology made of composite TiO₂/g-C₃N₄ was synthesized by a one-step solvothermal method. It is generally reported that TiO₂ is a pure phase, besides, the photocatalytic effect of multiphase TiO₂ will be better. After the g-C₃N₄ was successfully loaded on the TiO₂ surface, the morphology did not change. The special sea urchin morphology provides more active sites for catalysis. The band gap becomes smaller, because two materials were combined to form an interface effect. Meanwhile, it could effectively separate electron hole pairs, and promote charge transfer efficiency. More active substances were produced under visible light, such as superoxide radicals and holes. The scavenging experiment further confirms that superoxide radicals and holes play an important role in the catalytic process. The photocatalytic degradation of ibuprofen under visible light was improved. A possible enhanced photocatalytic mechanism of g-C₃N₄/TiO₂ heterojunction photocatalysts was proposed.     

g-C3N4 coated SrTiO3 as an efficient photocatalyst for H2 production in aqueous solution under visible light irradiation

A highly active photocatalyst based on g-C₃N₄ coated SrTiO₃ has been synthesized simply by decomposing urea in the presence of SrTiO₃ at 400 °C. The catalyst demonstrates a high H₂ production rate ∼440 μmol h⁻¹/g catalyst in aqueous solution under visible light irradiation, which is much higher than conventional anion doped SrTiO₃ or physical mixtures of g-C₃N₄ and SrTiO₃. The improved photocatalytic activity can be ascribed to the close interfacial connections between g-C₃N₄ and SrTiO₃ where photo-generated electron and holes are effectively separated. The newly synthesized catalyst also exhibited a stable performance in the repeated experiments.     

Photo-assisted splitting of water into hydrogen using visible-light activated silver doped g-C3N4 & CNTs hybrids

Herein, highly efficient and cost effective solar photocatalytic water splitting for hydrogen (H₂) generation was achieved by modified g-C₃N₄. Visible light absorption of g-C₃N₄ was enhanced by decorating g-C₃N₄ matrix with silver nanoparticles (Ag). Moreover, incorporation of carbon nanotubes (CNTs) in Ag/g-C₃N₄ facilitated photocatalytic performance through efficient separation and transfer of photogenerated e-h pairs (charges) in Ag/g-C₃N₄ that consequently generated very pure and significant H₂. Among several tested ratios (wt. %) of Ag/g-C₃N₄/CNTs, 1.82 (Ag/g-C₃N₄) and 2.00 (and Ag/g-C₃N₄/CNTs) were found to be highly efficient that harvested maximum visible-light and produced H₂ @1.48 mmol h⁻¹ and 1.78 mmol h⁻¹. We witnessed distinctive role of CNTs as an electron collector and carrier to separate photogenerated e-h pairs to facilitate photocatalysis for H₂ generation together with possible utility of Ag and CNTs doped materials with regard to energy transformation.     

Rationally designed ternary CdSe/WS2/g-C3N4 hybrid photocatalysts with significantly enhanced hydrogen evolution activity and mechanism insight

Excellent light harvest, efficient charge separation and sufficiently exposed surface active sites are crucial for a given photocatalyst to obtain excellent photocatalytic performances. The construction of two-dimensional/two-dimensional (2D/2D) or zero-dimensional/2D (0D/2D) binary heterojunctions is one of the effective ways to address these crucial issues. Herein, a ternary CdSe/WS₂/g-C₃N₄ composite photocatalyst through decorating WS₂/g-C₃N₄ 2D/2D nanosheets (NSs) with CdSe quantum dots (QDs) was developed to further increase the light harvest and accelerate the separation and migration of photogenerated electron-hole pairs and thus enhance the solar to hydrogen conversion efficiency. As expected, a remarkably enhanced photocatalytic hydrogen evolution rate of 1.29 mmol g⁻¹ h⁻¹ was obtained for such a specially designed CdSe/WS₂/g-C₃N₄ composite photocatalyst, which was about 3.0, 1.7 and 1.3 times greater than those of the pristine g-C₃N₄ NSs (0.43 mmol g⁻¹ h⁻¹), WS₂/g-C₃N₄ 2D/2D NSs (0.74 mmol g⁻¹ h⁻¹) and CdSe/g-C₃N₄ 0D/2D composites (0.96 mmol g⁻¹ h⁻¹), respectively. The superior photocatalytic performance of the prepared ternary CdSe/WS₂/g-C₃N₄ composite could be mainly attributed to the effective charge separation and migration as well as the suppressed photogenerated charge recombination induced by the constructed type-II/type-II heterojunction at the interfaces between g-C₃N₄ NSs, CdSe QDs and WS₂ NSs. Thus, the developed 0D/2D/2D ternary type-II/type-II heterojunction in this work opens up a new insight in designing novel heterogeneous photocatalysts for highly efficient photocatalytic hydrogen evolution.     

Cobalt phosphate hydroxide loaded g-C3N4 photocatalysts and its hydrogen production activity

To overcome the low photocatalytic efficiency of bulk g-C₃N₄, herein, we have designed a novel cobalt phosphate hydroxide loaded graphitic carbon nitride photocatalysts by co-precipitation route. The FESEM and HRTEM analysis revealed that in the presence of the phosphorus compound, the g-C₃N₄ sheets tend to fold and form a rod-like morphology. The loading of cobalt phosphate hydroxide in g-C₃N₄ resulted in the redshift of the absorption edge. XRD, FTIR and XPS analysis revealed that cobalt phosphate hydroxide is bonded to g-C₃N₄ via electrostatic interaction. The cobalt phosphate hydroxide/g-C₃N₄ photocatalysts was used for photocatalytic hydrogen evolution and produced nearly 1016 μmol/g of hydrogen in 4 h of reaction time under direct solar light irradiation. This significantly higher activity was accredited to the effective charge carrier separation by cobalt phosphate hydroxide in the photocatalysts, as shown by the photoluminescence and time-resolved photoluminescence (TRPL) measurements. TRPL measurements have shown that Co₂PO₄OH incorporation in g-C₃N₄ leads to a 42% higher lifetime of photogenerated charge carriers. In addition, the Co₂PO₄OH loaded g-C₃N₄ photocatalysts retains its photostability even after four cycles of reaction without any significant drop in hydrogen production activity. This work provides a facile approach to synthesize highly stable and efficient visible light active cobalt phosphate hydroxide loaded graphitic carbon nitride photocatalysts for solar energy conversion applications.     

Construction of ternary hybrid layered reduced graphene oxide supported g-C3N4-TiO2 nanocomposite and its photocatalytic hydrogen production activity

Reduced graphene oxide (rGO) supported g-C₃N₄-TiO₂ ternary hybrid layered photocatalyst was prepared via ultrasound assisted simple wet impregnation method with different mass ratios of g-C₃N₄ to TiO₂. The synthesized composite was investigated by various characterization techniques, such as XRD, FTIR, Raman Spectra, FE-SEM, HR-TEM, UV vis DRS Spectra, XPS Spectra and PL Spectra. The optical band gap of g-C₃N₄-TiO₂/rGO nanocomposite was found to be red shifted to 2.56 eV from 2.70 eV for bare g-C₃N₄. It was found that g-C₃N₄ and TiO₂ in a mass ratio of 70:30 in the g-C₃N₄-TiO₂/rGO nanocomposite, exhibits the highest hydrogen production activity of 23,143 μmol g^?1h^?1 through photocatalytic water splitting. The observed hydrogen production rate from glycerol-water mixture using g-C₃N₄-TiO₂/rGO was found to be 78 and 2.5 times higher than g-C₃N₄ (296 μmol g^?1 h^?1) and TiO₂ (11,954 μmol g^?1 h^?1), respectively. A direct contact between TiO₂ and rGO in the g-C₃N₄-TiO₂/rGO nanocomposite produces an additional 10,500 μmol g^?1h^?1 of hydrogen in 4 h of photocatalytic reaction than the direct contact between g-C₃N₄ and rGO. The enhanced photocatalytic hydrogen production activity of the resultant nanocomposite can be ascribed to the increased visible light absorption and an effective separation of photogenerated electron-hole pairs at the interface of g-C₃N₄-TiO₂/rGO nanocomposite. The effective separation and transportation of photogenerated charge carriers in the presence of rGO sheet was further confirmed by a significant quenching of photoluminescence intensity of the g-C₃N₄-TiO₂/rGO nanocomposite. The photocatalytic hydrogen production rate reported in this work is significantly higher than the previously reported work on g-C₃N₄ and TiO₂ based photocatalysts.     

Increased photocatalytic hydrogen evolution and stability over nano-sheet g-C3N4 hybridized CdS core@shell structure

A novel visible-light-active CdS@g-C₃N₄ photocatalyst was synthesized via a chemisorption method. This core@shell structure catalyst exhibited enhanced photocatalytic H₂ production activity under visible-light (λ ≥ 420 nm) irradiation. The nano-sheet g-C₃N₄ was successfully coated on CdS nanoparticles with intimate contact. When the content of g-C₃N₄ in the hybridized composite is 3 wt. %, the hydrogen-production rate of the CdS@g-C₃N₄ is 2.5 and 2.2 times faster than pure CdS and bulk g-C₃N₄, respectively. Superior stability was also observed in the cyclic runs. The improvement in stability and activity result from the ability of the π-conjugated g-C₃N₄ material in transporting photo-induced holes. The core@shell structure promoted separation of the photo-generated electron-hole pair and accelerated the emigration speed of the hole from the valence band of CdS. This effect also results in a greatly improved amount of hydrogen production. The possible mechanism for the photocatalytic activity and stability of CdS@g-C₃N₄ are tentatively proposed.     

Largely elevated photocatalytic hydrogen generation over Eu doped g-C3N4 photocatalyst

Graphitic carbon nitrides (g-C₃N₄) have come into researchists’ horizons for their diversified merits, such as the especial graphite-phase 2D laminar framework, competitive price, innoxious, eligible bandgap (∼2.7 eV) and acceptable consistency. Whereas limited by the disadvantages of inferior specific surface area and fast recombination of photo-generated charge pairs, the pragmatic applicability of g-C₃N₄ turns out to be still lacking. In our work, g-C₃N₄ (GCN) and Eu-doped g-C₃N₄ (Eu/CN) with different Eu/g-C₃N₄ molar ratios (1%, 2%, 3%, 4%) were synthesized by an impregnating method and characterized through a series of measurements. Photocatalytic activities of Eu/CN catalysts manifest preeminent H₂ generation capacity and stability excited by solar light. The highest H₂ generation rate without any co-catalyst is 128.8 μmol g⁻¹ h⁻¹ over the 3% Eu/CN, achieving 117.1-fold as high as that of GCN (1.1 μmol g⁻¹ h⁻¹). Eu doping is proven to slightly widen the bandgap of the samples, resulting in the conduction band of samples more negative and the reduction reaction more effortlessly. Simultaneously, Eu doping changes the molecular structure of g-C₃N₄ and forms more nitrogen defects. Photo-excited electrons can be captured by the defective sites derived from the defect levels, and the recombination rate of photoinduced carriers will be significantly inhibited, accordingly facilitating the high-efficiency separation of photo-induced carriers and improving photocatalytic efficiency. This study provides an advantageous instruction for the implementation of rare earth metals application in improving the separation and transfer rate of photo-induced electrons (e⁻) and holes (h⁺) over g-C₃N₄.     

The charge transfer pathway of g-C3N4 decorated Au/Bi(VO4) composites for highly efficient photocatalytic hydrogen evolution

In this report, a novel g-C₃N₄/Au/BiVO₄ photocatalyst has been prepared successfully by assembling gold nanoparticles on the interface of super-thin porous g-C₃N₄ and BiVO₄, which exhibits outstanding photocatalytic performance toward hydrogen evolution and durable stability in the absence of cocatalyst. FESEM micrograph analysis suggested that the intimate contact between Au, BiVO₄, and g-C₃N₄ in the as-developed photocatalyst allows a smooth migration and separation of photogenerated charge carriers. In addition, the XRD, EDX and XPS analysis further confirmed the successful formation of the as-prepared g-C₃N₄/Au/BiVO₄ photocatalyst. The photocatalytic hydrogen production activity of the developed photocatalyst was evaluated under visible-light irradiation (λ > 420 nm) using methanol as a sacrificial reagent. By optimizing the 5-CN/Au/BiVO₄ composite shows the highest H₂ evolution rate (2986 μmolg⁻¹h⁻¹), which is 15 times higher than that of g-C₃N₄ (199 μmolg⁻¹h⁻¹) and 10 time better than bare BiVO₄ (297 μmolg⁻¹h⁻¹). The enhancement in photocatalytic activity is attributed to efficient separation of the photoexcited charges due to the anisotropic junction in the g-C₃N₄/Au/BiVO₄ system. The enhancement in photocatalytic activity is attributed to efficient separation of the photoexcited charges due to the anisotropic junction in the g-C₃N₄/Au/BiVO₄ system.     

Direct Z-scheme CoS/g-C3N4 heterojunction with NiS co-catalyst for efficient photocatalytic hydrogen generation

Facilitating the separation of photoexcited electron-hole pairs and enhancing the migration of photogenerated carriers are essential in photocatalytic reaction. CoS/g-C₃N₄/NiS ternary photocatalyst was prepared by hydrothermal and physical stirring methods. The optimized ternary composite achieved a hydrogen yield of 1.93 mmol g^?1 h^?1, 12.8 times that of bare g-C₃N₄, with an AQE of 16.4% at 420 nm. The enhanced photocatalytic activity of CoS/g-C₃N₄/NiS was mainly ascribed to the synergistic interaction between the Z-scheme heterojunction constructed by CoS and g-C₃N₄ and the NiS co-catalyst featuring a large amount of hydrogen precipitation sites, which realized the efficient separation and migration of photogenerated carriers. In addition, the CoS/g-C₃N₄/NiS heterojunction-co-catalyst system exhibited excellent photocatalytic stability and recyclability.     

Facile construction of phosphate incorporated graphitic carbon nitride with mesoporous structure and superior performance for H2 production

Novel mesoporous phosphate incorporated g-C₃N₄ (CNM-Px) polymeric material was synthesized via a facile hydrothermal-calcination method, using melamine as precursor and phosphoric acid as dopant. The successful incorporation of phosphate into the framework of g-C₃N₄ nanosheets was verified by XRD, FT-IR and XPS characterizations and the possible formation mechanism was put forward. The as-fabricated CNM-Px samples were applied to photocatalytic hydrogen evolution reaction and exhibited remarkably improved photocatalytic performance both under simulated sunlight and visible light irradiation. The concentration of phosphoric acid was also well tuned and the optimal concentration was 2.5 mol L^?1. The hydrogen evolution rate of the optimized sample CNM-P2.5 (the concentration of treating phosphoric acid was 2.5 mol L^?1) reached 8163 μmol g^?1 h^?1 under simulated sunlight irradiation, which is 3.7 times higher than that of pristine g-C₃N₄ (CNM). It also showed dramatically improved hydrogen evolution rate under visible light irradiation, which was 2105 μmol g^?1 h^?1, about 6.7 times higher than that of CNM. The excellent photocatalytic activity of CNM-Px samples is due to the synergic advantages of larger surface area and reduced recombination of photo-generated electrons and holes. This study paves the way for tailoring design and synthesis of highly active metal-free carbon nitride materials for photocatalytic hydrogen evolution.     

In situ fabrication of CDs/g-C3N4 hybrids with enhanced interface connection via calcination of the precursors for photocatalytic H2 evolution

Novel carbon dots (CDs)/graphitic carbon nitride (g-C₃N₄) hybrids were fabricated via an in situ thermal polymerization of the precursors, urea and glucose. This heterojunction catalyst exhibited enhanced photocatalytic H₂ evolution activity under visible-light (λ > 420). A sample of CDs/g-C₃N₄ hybrids, CN/G0.5, which was prepared from 0.5 mg of glucose in 6.0 g of urea (8.3 × 10^?3 wt% glucose), exhibited the best photocatalytic performance for hydrogen production from water under visible light irradiation, which is about 4.55 times of that of the bulk g-C₃N₄ (BCN). The improvement of photocatalytic activity was mainly attributed to the construction of built-in electric field at the interface of CDs and g-C₃N₄, which could improve the separation of photogenerated electron-hole pair. Moreover, the tight connection of CDs with g-C₃N₄ would serve as a well electron transport channel, which could promote the photocatalytic H₂ evolution ability.