Hydrogen storage in scandium decorated triazine based g-C3N4: Insights from DFT simulations

Hydrogen is being considered a ‘fuel of the future,’ a viable alternative to fossil fuels in fuel cell vehicles. Using Density Functional Theory simulations, reversible, onboard hydrogen storage in Sc-decorated triazine-based graphitic carbon nitride (g-C₃N₄) has been explored. Sc atom binds strongly on the g-C₃N₄ structure with a binding energy of ?7.13 eV. Each Sc atom can reversibly bind 7 molecules of hydrogen, giving a net gravimetric storage capacity of 8.55 wt%, an average binding energy of ?0.394 eV per H₂, and a corresponding desorption temperature of 458.28 K, fulfilling the criteria prescribed by the US Department of Energy. The issue of transition metal clustering has been investigated by computing the diffusion energy barrier (2.79 eV), which may be large enough to hinder the clustering tendencies. The structural integrity of Sc-g-C₃N₄ has been verified through ab-initio Molecular Dynamics simulations. The interaction mechanism of Sc over g-C₃N₄ and H₂ over Sc-g-C₃N₄ has been explored using density of states and charge transfer analysis. A flow of charge from valence 3d orbitals of Sc towards vacant orbitals of g-C₃N₄ during the binding of Sc over g-C₃N₄ is observed. The binding of H₂ on Sc-g-C₃N₄ may be via Kubas type of interactions which is stronger than physisorption due to net charge gain by H 1s orbital from Sc 3d orbital. Our systematic investigations indicate that Sc-decorated g-C₃N₄ may be a high-performance material for reversible hydrogen storage applications.     

Novel ReS2/g-C3N4 heterojunction photocatalyst formed by electrostatic self-assembly with increased H2 production

Binary heterostructures (named as CN@Re) composed of ReS₂ nanospheres and g-C₃N₄ nanosheets are constructed by electrostatic self-assembly method. The ReS₂ nanospheres were prepared by hydrothermal method and the g-C₃N₄ nanosheets were treated with surface charge modification. Hydrogen production efficiency of modified CN and CN@Re nanostructures was evaluated in a simulated solar environment. To our surprise, CN5@Re5% exhibits the highest H₂ production up to 1823 μmol g^?1h^?1 of CN5@Rey, which is 3.2 times as high as CN. The improvement of the photocatalytic hydrogen production efficiency of modified CN is attributed to its interaction with the hole sacrificing agent lactic acid, while the improvement of the photocatalytic activity of CN@Re nanostructure is attributed to the efficient electron transfer efficiency between CN and ReS₂ and the enhanced light absorption capacity brought by ReS₂. In addition, the photocatalytic stability of CN5@Re5% has been studied, which can maintain a stable rate of hydrogen production over four cycles. The apparent quantum efficiency is as high as 4.10% at 365 nm and 2.82% at 420 nm.     

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.     

A visible-light-driven heterojunction for enhanced photocatalytic water splitting over Ta2O5 modified g-C3N4 photocatalyst

The photocatalytic water splitting for generation of clean hydrogen energy has received increasingly attention in the field of photocatalysis. In this study, the Ta₂O₅/g-C₃N₄ heterojunctions were successfully fabricated via a simple one-step heating strategy. The photocatalytic activity of as-prepared photocatalysts were evaluated by water splitting for hydrogen evolution under visible-light irradiation (λ > 420 nm). Compared to the pristine g-C₃N₄, the obtained heterojunctions exhibited remarkably improved hydrogen production performance. It was found that the 7.5%TO/CN heterojunction presented the best photocatalytic hydrogen evolution efficiency, which was about 4.2 times higher than that of pure g-C₃N₄. Moreover, the 7.5%TO/CN sample also displayed excellent photochemical stability even after 20 h photocatalytic test. By further experimental study, the enhanced photocatalytic activity is mainly attributed to the significantly improve the interfacial charge separation in the heterojunction between g-C₃N₄ and Ta₂O₅. This work provides a facile approach to design g-C₃N₄-based photocatalyst and develops an efficient visible-light-driven heterojunction for application in solar energy conversion.     

Computational exploration of magnesium-decorated carbon nitride (g-C3N4) monolayer as advanced energy storage materials

Density functional theory (DFT) computational studies were conducted to explore the hydrogen storage performance of a monolayer material that is built on the base of carbon nitride (g-C₃N₄, heptazine structure) with decoration by magnesium (Mg). We found that a 2 × 2 supercell can bind with four Mg atoms. The electronic charges of Mg atoms were transferred to the g-C₃N₄ monolayer, and thus a partial electropositivity on each adsorbed Mg atom was formed, indicating a potential improvement in conductivity. This subsequently causes the hydrogen molecules’ polarization, so that these hydrogen molecules can be efficiently adsorbed via both van der Waals and electrostatic interactions. To note, the configurations of the adsorbed hydrogen molecules were also elucidated, and we found that most adsorbed hydrogen molecules tend to be vertical to the sheet plane. Such a phenomenon is due to the electronic potential distribution. In average, each adsorbed Mg atom can adsorb 1–9 hydrogen molecules with adsorption energies that are ranged from ?0.25 eV to ?0.1 eV. Moreover, we realised that the nitrogen atom can also serve as an active site for hydrogen adsorption. The hydrogen storage capacity of this Mg-decorated g-C₃N₄ is close to 7.96 wt %, which is much higher than the target value of 5.5 wt % proposed by the U.S. department of energy (DOE) in 2020 [1]. The finding in this study indicates a promising carbon-based material for energy storage, and in the future, we hope to develop more advanced materials along this direction.     

Nickel–cobalt layered double hydroxide/NiCo2S4/g-C3N4 nanohybrid for high performance asymmetric supercapacitor

Graphitic carbon nitride (g-C₃N₄) with semiconducting nature can be considered for energy storage system by modifying its electrical conductivity and structural properties through formation of hybrid with materials such as bimetallic metal sulfide and nickel-cobalt layered double hydroxide (LDH). g-C₃N₄ as a N-rich compound with basic surface sites can change the surface properties of nanohybrid and impress the charge transfer. In this study, a nanohybrid based on nickel-cobalt LDH and sulfide and graphitic carbon nitride (NiCo LDH/NiCo₂S₄/g-C₃N₄) was synthesized through a three-step method. At first, Ni doped ZIF-67 was formed at the surface of g-C₃N₄ nanosheets and then the product was calcined in a furnace to form NiCo₂O₄/g-C₃N₄. At next step, the sample was hydrothermally converted to NiCo₂S₄/g-C₃N₄ using thioacetamide and finally modified with NiCo LDH nanoplates to form porous structure with high surface area. The NiCo LDH/NiCo₂S₄/g-C₃N₄ nanohybrid showed high specific capacitance of 1610 F g^?1 at current density of 1 A g^?1 and also excellent stability of 108.8% after 5000 cycles at potential scan rate of 50 mV s^?1, which makes it promising candidate for energy storage. An asymmetric system was prepared using nickel foams modified with NiCo LDH/NiCo₂S₄/g-C₃N₄ and g-C₃N₄ as positive and negative electrodes, respectively. The specific capacitance of 246.0 F g^?1 was obtained at 1 A g^?1 in 6 M KOH solution and system maintained 90.8% cyclic stability after 5000 cycles at potential scan rate of 50 mV s^?1. The maximum energy density and power density of the system were calculated as 82.0 Wh kg^?1 and 12,000 W kg^?1, respectively, which demonstrate its capability for energy storage.     

Construction of heterostructured g-C3N4@TiATA/Pt composites for efficacious photocatalytic hydrogen evolution

Construction of heterostructured photocatalysts is a feasible method for improving hydrogen production from water splitting because of its good charge transport efficiency. Herein, we coupled the Ti-MOFs (TiATA) with metal-free graphitic carbon nitride (g-C₃N₄) to synthesize composites, g-C₃N₄@TiATA, in which a heterostructure was formed between g-C₃N₄ and TiATA. The establishment of heterojunctions not only broadens the light absorption range of g-C₃N₄@TiATA (490 nm) by contrast with g-C₃N₄ (456 nm), but also greatly accelerates charge migration. Photocatalytic studies present that the construction of heterostructure steering the charges flow from g-C₃N₄ to TiATA and then delivery to the cocatalyst of Pt nanoparticles, exhibiting an impressively photocatalytic hydrogen production rate (265.8 μmol·h⁻¹) in assistance of 300 W Xenon lamp, which is about 3.4 times as much as g-C₃N₄/Pt.     

Photo-assisted electrolysis of urea using Ni-modified WO3/g-C3N4 as a bifunctional catalyst

Urea splitting to produce H₂ is as an energy-saving alternative to water electrolysis. However, efficient catalysts are required for the practical implementation of urea splitting because of the high overpotentials of the urea oxidation reaction and the hydrogen evolution reaction. Herein, a Ni-modified direct Z-scheme photocatalyst for the urea oxidation and hydrogen evolution reactions was synthesized by electroplating a WO₃/g-C₃N₄ nanocomposite on Ni-decorated carbon felt (WO/CN–Ni@CF). The 2D/2D nanostructure of the as-synthesized WO₃/g-C₃N₄ composite was confirmed by SEM and TEM. The WO/CN–Ni@CF catalyst electrode exhibited excellent bifunctional photocatalytic activity for the urea oxidation and hydrogen evolution reactions. Consequently, the potential required to generate 100 mA cm^?2 in an illuminated photoelectrochemical cell using WO/CN–Ni@CF as the anode and the cathode was reduced from 1.80 to 1.50 V. The photoelectrochemical cell exhibited good stability for 18 h with stable H₂ generation.     

The synergy of thermal exfoliation and phosphorus doping in g-C3N4 for improved photocatalytic H2 generation

Photocatalytic H₂ generation has been believed to be a hopeful technology to deal with the current energy shortage issue. Among multifarious photocatalysts, graphitic carbon nitride (g-C₃N₄) has acquired enormous interests in virtue of its numerous advantages, such as peculiar physicochemical stability, favorable energy band structure and easy preparation. However, the insufficient light response range, low specific surface area, and inferior charge separation efficiency make its photocatalytic activity still unsatisfactory. In this work, the thermal exfoliation method was taken to prepare the thin g-C₃N₄ nanosheets with significantly improved specific surface area, which can afford more reaction sites and shorten the charge migration distance. Moreover, phosphorus (P) doping in g-C₃N₄ nanosheets can greatly expand its light absorption, improve the conductivity and charge-transfer capability. Due to the synergistic effect of these two strategies, the optimal H₂ generation performance of P-doped g-C₃N₄ nanosheets came up to 1146.8 μmol g^?1 h^?1, which improved 15, 2.94 and 2.62 times compared to those of original bulk g-C₃N₄, thermally exfoliated g-C₃N₄ and P-doped bulk g-C₃N₄, respectively. The synergistic effect will inspire the design of other photocatalytic systems to achieve the efficient photocatalytic H₂ generation activity.     

Heterostructured thin LaFeO3/g-C3N4 films for efficient photoelectrochemical hydrogen evolution

The deposition of LaFeO₃ at the surface of a graphitic carbon nitride (g-C₃N₄) film via magnetron sputtering followed by oxidation for photoelectrochemical (PEC) water splitting is reported. The LaFeO₃/g-C₃N₄ film was investigated by various characterization techniques including SEM, XRD, Raman spectroscopy, XPS and photo-electrochemical measurements. Our results show that the hydrogen production rate of a g-C₃N₄ film covered by a LaFeO₃ film, exhibiting both a thickness of ca. 50 nm, is of 10.8 μmol h⁻¹ cm⁻² under visible light irradiation. This value is ca. 70% higher than that measured for pure LaFeO₃ and g-C₃N₄ films and confirms the effective separation of electron-hole pairs at the interface of LaFeO₃/g-C₃N₄ films. Moreover, the LaFeO₃/g-C₃N₄ films were demonstrated to be stable and retained a high activity (ca. 70%) after the third reuse.     

Computational Evaluation of Li-doped g-C2N Monolayer as Advanced Hydrogen Storage Media

The emerging 2D g-C₂N obtained increasingly more popularity in functional materials design, and its natural porosity can easily accommodate metal atoms, making itself more suitable for energy gases storage. In this study, we employed DFT computational studies to systematically solve the electronic structure of Li-doped g-C₂N monolayer, and evaluate its performance in hydrogen storage. In our calculations, we found that each pore of g-C₂N can adsorb at most three Li atoms that bind with pyridinic N atoms. We also noticed that considerable amount of charges were transferred from the adsorbed Li to the pristine materials, potentially enhancing its overall conductivity. The change of electronic structure also leads to its improved performance in H₂ adsorption, due to the fact that the electrostatic interactions between the adsorbed H₂ and Li can be largely enhanced. The optimised configurations of the Li-doped g-C₂N with multiple adsorbed H₂ molecules were presented, and the fundamental mechanisms of adsorption were also investigated in details. The highest storage capacity of hydrogen by Li-doped g-C₂N can reach to 7.8 wt%, much higher than the target value of 5.5 wt %, defined by the U.S department of energy (DOE). Moreover, except Li, we also found that the nitrogen atoms or the N-C bonds can also serve as active adsorption sites. The computational explorations conducted in this study actually indicates a promising prospect of alkali metals decorated 2D materials in the area of hydrogen storage; and we believe the performance of these kinds of novel materials can be further enhanced via more decent modifications.     

Sustainable hydrogen production by CdO/exfoliated g-C3N4 via photoreforming of formaldehyde containing wastewater

Graphitic carbon nitride (g-C₃N₄) has been well-known as an appealing semiconducting material for photocatalytic hydrogen production despite its restricted active sites and poor electronic properties. In this work, exfoliated g-C₃N₄ nanosheets were synthesised by chemical treatment of the bulk graphitic carbon nitride (gCN) and the nanosheets were further doped with CdO. The photocatalysts produced were extensively characterized by diverse analysis including XRD, BET, XPS, TEM, FESEM, UV-Vis spectroscopy and PL analysis. The BET surface area of CdO/exfoliated g-C₃N₄, 40.1 m² g⁻¹ was doubled in comparison to the exfoliated g-C₃N₄. Numerous electrochemical analyses such as Mott-Schottky, linear weep voltammetry and chronoamperometry were also performed in a standard photoelectrochemical system with three-electrode cell. The hydrothermally synthesised CdO/exfoliated g-C₃N₄ resulted higher amount of hydrogen evolution (145 μmol/g) for the photoreforming of aqueous formaldehyde than the CdO (20 μmol/g), bulk gCN (58 μmol/g) and exfoliated g-C₃N₄ (87 μmol/g). The excellent hydrogen production rate using CdO/exfoliated g-C₃N₄ nanocomposite could be ascribed by higher number of active sites as well as shorter path of the charge carries to the reaction surface. The anticipated Z-Scheme mechanism has demonstrated a synergistic impact between the CdO and exfoliated g-C₃N₄ where the organic compounds acting as hole scavenger as well as contribute protons, H⁺ for the effective hydrogen production. Thus, it is clearly confirmed that the newly formulated CdO/exfoliated g-C₃N₄ has an outstanding potentiality for environmental remediation and conversion sectors.     

The heterojunction construction of hybrid B-doped g-C3N4 nanosheets and ZIF67 by simple mechanical grinding for improved photocatalytic hydrogen evolution

In this study, B-doped g-C₃N₄ nanosheets (BCN) were prepared using a thermal-oxidative etching method, resulting in a semiconductor with a large specific surface area. The B-doping enhances the light absorption of graphitic carbon nitride(g-C₃N₄) and improves the photogenerated carrier lifetime. The optimal B-containing amount resuled in a hydrogen production rate of 1297 μmol g⁻¹ h⁻¹ for g-C₃N₄ nanosheets. Furthermore, zeolitic imidazolate framework (ZIF)67/BCN heterostructures were successfully obtained through simple mechanical grinding approaches. The BCN provided abundant active sites and contributed to excellent encapsulation on the surface of ZIF67. The obtained ZIF67/BCN photocatalyst displayed an H₂ evolution rate of 3392 μmol g⁻¹ h⁻¹, attributed to forming type-II heterojunctions between ZIF67 and BCN. Moreover, the BCN exhibited a higher conduction band (CB) potential with ZIF67 than CN, resulting in more efficient light-driven charge separation between ZIF67 and BCN and enhanced photocatalytic performance. This work provides a meaningful reference for improving the activity of g-C₃N₄ photocatalysts.     

Facile synthesis of CeO2/g-C3N4 nanocomposites with significantly improved visible-light photocatalytic activity for hydrogen evolution

Ceria dioxide supported on graphitic carbon nitride (CeO₂/g-C₃N₄) composites were facilely synthesized to be application for photocatalytic hydrogen (H₂) generation in this present work. The physical and chemical properties of CeO₂/g-C₃N₄ nanocomposites were determined via a series of characterizations. The CeO₂/g-C₃N₄ composites prepared by facile thermal annealing and rotation-evaporation method exhibit excellent photocatalytic H₂ evolution with visible-light illumination. The best hydrogen generation rate of CeO₂/g-C₃N₄ composite with 1.5 wt% Pt is 0.83 mmol h⁻¹ g⁻¹, which is almost same as that of composite with 3 wt% Pt prepared by simple physical mixing method. The significantly developed photocatalytic activity of CeO₂/g-C₃N₄ composite is majorly ascribed to the stronger interfacial effects with the more visible-light absorbance and faster electron transfer. This work reveals that construction of the CeO₂/g-C₃N₄ composite with high disperse and close knit by the facile thermal annealing and rotation-evaporation method could be an effective method to achieve excellent photocatalytic hydrogen evolution performance.     

Facile construction of composition-tuned ruthenium-nickel nanoparticles on g-C3N4 for enhanced hydrolysis of ammonia borane without base additives

Developing high-efficiency and low-cost catalysts for hydrogen evolution from hydrolysis of ammonia borane (AB) is significant and critical for the exploitation and utilization of hydrogen energy. Herein, the in-situ fabrication of well-dispersed and small bimetallic RuNi alloy nanoparticles (NPs) with tuned compositions and concomitant hydrolysis of AB are successfully achieved by using graphitic carbon nitride (g-C₃N₄) as a NP support without additional stabilizing ligands. The optimized Ru₁Ni_7.5/g-C₃N₄ catalyst exhibits an excellent catalytic activity with a high turnover frequency of 901 min^?1 and an activation energy of 28.46 kJ mol^?1 without any base additives, overtaking the activities of many previously reported catalysts for AB hydrolysis. The kinetic studies indicate that the AB hydrolysis over Ru₁Ni_7.5/g-C₃N₄ is first-order and zero-order reactions with respect to the catalyst and AB concentrations, respectively. Ru₁Ni_7.5/g-C₃N₄ has a good recyclability with 46% of the initial catalytic activity retained even after five runs. The high performance of Ru₁Ni_7.5/g-C₃N₄ should be assigned to the small-sized alloy NPs with abundant accessible active sites and the synergistic effect between the composition-tuned Ru–Ni bimetals. This work highlights a potentially powerful and simple strategy for preparing highly active bimetallic alloy catalysts for AB hydrolysis to generate hydrogen.     

Effective solar driven H2 production by Mn0.5Cd0.5Se/g-C3N4 S-scheme heterojunction photocatalysts

Photocatalytic technology offers a practical way to solve the energy crisis by producing hydrogen under sunlight but its performance is encumbered by the fast recombination of photoinduced electron-hole pairs. Constructing heterojunctions to form built-in electric fields could separate these electrons and holes, finally enhancing the photocatalytic efficiency. Herein, a Mn_0.5Cd_0.5Se/g-C₃N₄ (MCS/CN) heterojunction was fabricated by a facile method to tap into this advantage. 2%MCS/CN shows a hydrogen evolution rate of up to 354.5 μmol in 3 h, which is 4.49 and 126.6 times that of pure g-C₃N₄ and Mn_0.5Cd_0.5Se, respectively. Its photocatalytic stability is proved by six cycling tests. Photocurrent, EIS, along with PL spectra, prove that the recombination of photoinduced electron-hole pairs is inhibited by constructing a heterojunction between Mn_0.5Cd_0.5Se and g-C₃N₄. In summary, this work demonstrates the enhancement of photocatalysis by constructing a S-scheme heterojunction and offers a feasible way to develop other effective photocatalysts.     

Construction of MOFs/g-C3N4 composite for accelerating visible-light-driven hydrogen evolution

In this work, we researched the effect of PCN-222 (M = Ni, Fe, Co) (PM) with different metal ligands on their photocatalytic performance. Compared with PFe and PCo, PNi has the highest photocatalytic hydrogen evolution efficiency due to the narrowest bandgap and the highest conduction band (CB) position. Furthermore, PCN-222(M)/g-C₃N₄ (PM/CN) heterojunctions was synthesized by one-pot solvothermal method in which PNi/CN displayed the most outstanding photocatalytic activity for H₂ evolution. PNi/CN-1 displayed the highest photocatalytic activity. Its hydrogen evolution rate is 19.3 and 3.7 times higher than that of PNi and CN, respectively. A mechanism is proposed to expound the roles of PNi and the enhancement of visible-light photocatalytic performance of the PNi/CN. This work presents a new perspective for the development of high performance photocatalysts for hydrogen production under visible-light driven.     

g-C3N4 particles with boron and oxygen dopants/carbon vacancies for efficient dehydrogenation in sodium borohydride methanolysis

In the study, metal-free boron and oxygen incorporated graphitic carbon nitride (B and O doped g-C₃N₄) with carbon vacancy was successfully prepared and applied as a catalyst to the dehydrogenation of sodium borohydride (NaBH₄) in methanol for the first time. The hydrogen generation rate (HGR) value was found to be 11,600 mL min^?1g^?1 by NaBH₄ of 2.5%. This is 2.53 times higher than the g-C₃N₄ catalyst without the addition of B and O. The obtained activation energy was 25.46 kJ mol^?1. X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), energy dispersive X-Ray analyser (EDX), Transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR) analyses for characterization were performed. A possible mechanism of H₂ production from the reaction using metal-free B and O doped g-C₃N₄ catalyst with carbon vacancy has been proposed. This study showed that g-C₃N₄ and its composites with doping atoms can be used effectively in H₂ production by NaBH₄ methanolysis.     

Constructing g-C3N4 quantum dots modified g-C3N4/GO nanosheet aerogel for UV-Vis-NIR driven highly efficient photocatalytic H2 production

The development of ultraviolet to near-infrared (UV-Vis-NIR) responsive photocatalysts offers a unique opportunity for the full use of solar energy to solve the energy and the environmental problems. Here, successful preparation of a three-dimensional (3D) porous photocatalyst of graphitic carbon nitride quantum dot (CNQDs) modified g-C₃N₄/graphene oxide composite aerogel (CNGO/CNQDs) via hydrothermal and vacuum injection method was reported. In this unique ternary 3D photocatalyst, graphene oxide could improve the separation of photogenerated electrons and holes and promote the charge separation, while the aerogel's 3D network structure provided a rich active site. Simultaneously, due to the appropriate up-conversion performance of the nitrogen carbide quantum dots, CNGO/CNQDs achieved a light response from ultraviolet (UV) to near-infrared (NIR). These properties endow it with a good photocatalytic performance. The hydrogen production efficiency of CNGO/CNQDs reached 1231 μmol h⁻¹, which was 16 times more than that of matrix material. In addition, the apparent quantum yields (AQY) of CNGO/CNQDs at wavelengths of 420 nm and 700 nm were 13% and 0.116%, respectively.     

Ag2CO3-derived Ag/g-C3N4 composite with enhanced visible-light photocatalytic activity for hydrogen production from water splitting

In this paper, Ag-based g-C₃N₄ composites have been successfully fabricated through two deferent synthetic methods: (i) a facile and efficient precipitation-calcination strategy (denoted as D–CN–xAg, x represents the dosage of Ag₂CO₃, the same below), (ii) a calcination method (denoted as Z–CN–xAg). All Ag-based g-C₃N₄ composites exhibit the enhanced photocatalytic activities under visible-light irradiation. Moreover, the optimal dosage of Ag₂CO₃ in the D–CN–xAg composite is found to be 5%, the corresponding hydrogen production capacity is 153.33 μmol g⁻¹ h⁻¹, which is 4.6 times higher than that of Z–CN–5%Ag composite. This might be attributed to appropriate content of metallic Ag and more active sites exposed on the surface of D–CN–5%Ag composite. Meanwhile, combining with photoelectrochemical results, it could be inferred that LSPR effect and the intimate interfacial between metallic Ag and g-C₃N₄ in the system play also important role for the improvement of photocatalytic activity. These results demonstrate that the appropriate loading of metallic Ag originated from Ag₂CO₃ into g-C₃N₄ could accelerate the separation and transfer of photogenerated electron-hole pairs, leading to the improvement of photocatalytic activity for hydrogen production from water splitting. Finally, a possible photocatalytic mechanism is proposed.