g-C3N4 doping TiO2 recovered from spent catalyst for H2 evolution from water

Spent catalysts of selective catalytic reduction (SCR) contain a high content of TiO₂ (>70 wt%). The effective recovery of TiO₂ from spent SCR catalysts and its reuse in photocatalytic hydrogen production is of great importance for environmental protection. In this study, the recovered TiO₂ from the spent SCR catalyst was recovered by the alkali washing method, and the purity of the recovered TiO₂ reached 94.7%. g-C₃N₄ as a co-catalyst and enhanced the separation efficiency of the photogenerated electron-hole pairs of the TiO₂ photocatalyst. The composite photocatalyst R–TiO₂/g-C₃N₄ prepared by directly mixing the recovered TiO₂ with g-C₃N₄ significantly improved the photocatalytic activity. The experimental design of the photocatalyst synthesis was optimized using the Design Expert software. The results showed that the recovered TiO₂ was 0.334 g when the g-C₃N₄ was 0.046 g and the ultrasonic time was 163 min. Moreover, the hydrogen production rate reached 443.105 μmol g⁻¹ h⁻¹ within 4 h.     

Hierarchical TiO2 spheroids decorated g-C3N4 nanocomposite for solar driven hydrogen production and water depollution

A novel hierarchical TiO₂ spheroids embellished with g-C₃N₄ nanosheets has been successfully developed via thermal condensation process for efficient solar-driven hydrogen evolution and water depollution photocatalyst. The photocatalytic behaviour of the as-prepared nanocomposite is experimented in water splitting and organic pollutant degradation under solar light irradiation. The optimal ratio of TiO₂ spheroids with g-C₃N₄ in the nanocomposite was found to be 1:10 and the resulting composite exhibits excellent photocatalytic hydrogen production of about 286 μmol h^?1g^?1, which is a factor of 3.4 and 2.3 times higher than that of pure TiO₂ and g-C₃N₄, respectively. The outstanding photocatalytic performance in this composite could be ascribed as an efficient electron-hole pair's separation and interfacial contact between TiO₂ spheroids with g-C₃N₄ nanosheets in the formed TiO₂/g-C₃N₄ nanocomposite. This work provide new insight for constructing an efficient Z-scheme TiO₂/g-C₃N₄ nanocomposites for solar light photocatlyst towards solar energy conversion, solar fuels and other environmental applications.     

Direct Z-scheme anatase/rutile bi-phase nanocomposite TiO2 nanofiber photocatalyst with enhanced photocatalytic H2-production activity

Design and preparation of direct Z-scheme anatase/rutile TiO₂ nanofiber photocatalyst to enhance photocatalytic H₂-production activity via water splitting is of great importance from both theoretical and practical viewpoints. Herein, we develop a facile method for preparing anatase and rutile bi-phase TiO₂ nanofibers with changing rutile content via a slow and rapid cooling of calcined electrospun TiO₂ nanofibers. The phase structure and composition, surface morphology, specific surface area, surface chemical composition and element chemical states of TiO₂ nanofibers were analyzed by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), nitrogen adsorption and X-ray photoelectron spectroscopy (XPS). By a rapid cooling of 500 °C-calcined electrospun TiO₂ precursor, anatase/rutile bi-phase TiO₂ nanofibers with a roughly equal weight ratio of 55 wt.% anatase and 45 wt.% rutile were prepared. The enhanced H₂ production performance was observed in the above obtained anatase/rutile composite TiO₂ nanofibers. A Z-scheme photocatalytic mechanism is first proposed to explain the enhanced photocatalytic H₂-production activity of anatase/rutile bi-phase TiO₂ nanofibers, which is different from the traditional heterojunction electron–hole separation mechanism. This report highlights the importance of phase structure and composition on optimizing photocatalytic activity of TiO₂-based material.     

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.     

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.     

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.     

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.     

In situ tuning of band gap of Sn doped composite for sustained photocatalytic hydrogen generation under visible light irradiation

The significance of Sn dopant on the photocatalytic performance of Iron/Titanium nanocomposite towards photocatalytic hydrogen generation by water splitting reaction is investigated. Iron/Titanium nanocomposite modified by Sn⁴⁺ dopant acts as a suitable photocatalyst for induced visible light absorption facilitating pronounced charge separation efficiency. Various characterization techniques reveal the heterojunction formation of hematite Fe₂O₃ with anatase - rutile mixed phase of TiO₂ employing Sn doping, where Sn⁴⁺ dopant accomplishes the phase transformation of anatase to rutile, entering into the TiO₂ lattice. This extended the lifetime of photogenerated charge carriers and enhanced the quantum efficiency of the photocatalyst. The band gap of the nanocomposite is tuned to ~2.4 eV, favoring visible light absorption. A hydrogen generation activity of 1102.8 μmol, approximately five times higher than the lone system (216.5 μmol) is achieved for the 5% Sn doped system for an average of 5 h. Heterojunctions of hematite with anatase-rutile mixed phase, generated as a consequence of tin doping facilitated the enhanced hydrogen generation activity of photocatalyst.     

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.     

Fabrication of hollow g-C3N4@α-Fe2O3/Co-Pi heterojunction spheres with enhanced visible-light photocatalytic water splitting activity

For the first time, g-C₃N₄@α-Fe₂O₃/Co-Pi heterojunctional hollow spheres were successfully fabricated via thermal condensation method followed by solvothermal and photo-deposition treatment, which showed excellent photocatalytical property. Except for the Z-scheme charge transfer between α-Fe₂O₃ and g-C₃N₄, the Co-Pi could further reduce the combination of photogenerated electrons and holes as a hole storage agent, resulting in remarkably enhanced visible-light photocatalytic water splitting activity with the H₂ production rate of 450 μmol h⁻¹g⁻¹, which is 15.7 times higher than that of g-C₃N₄. Moreover, the photocatalytic activity of the prepared ternary hollow photocatalysts showed almost no significant weakness after five cycles, which indicated their good performance stability. The as-prepared g-C₃N₄@α-Fe₂O₃/Co-Pi also possessed good activity for overall water splitting with the hydrogen production rate reaching 9.8 μmol h⁻¹g⁻¹. This synthesized g-C₃N₄@α-Fe₂O₃/Co-Pi composite is expected to be a promising candidate for water splitting.     

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.     

In-situ synthesis of Pd nanocrystals with exposed surface-active facets on g-C3N4 for photocatalytic hydrogen generation

Engineering surface-active facets of metal cocatalysts is one of the most widely explored strategies to develop advanced photocatalysts and promote photocatalytic solar energy conversion. Here, the surface-active facets of Pd nanocrystals in Pd/g-C₃N₄ photocatalyst was related to the injection flow rate of PdCl₂. When PdCl₂ was injected at a low flow rate of 7.5 mL/h (7.5-Pd/g-C₃N₄), the Pd nanocrystals were uniformly dispersed onto the g-C₃N₄ with exposed low-index {100} and {111} surface-active facets. However, increasing the injection flow rate to 150 mL/h (150-Pd/g-C₃N₄) formed Pd nanocrystals where only the {100} surface-active facet was exposed. Under visible light irradiation, the 7.5-Pd/g-C₃N₄ nanocomposite exhibited excellent water splitting activity for hydrogen production (7.61 mmol g⁻¹ h⁻¹), which was significantly better than with the 150-Pd/g-C₃N₄ nanocomposite (3.3 mmol g⁻¹ h⁻¹). Theoretical calculations and experimental results confirm the importance of the {111} surface-active facets in the 7.5-Pd/g-C₃N₄ nanocomposite for promoting photocatalytic activity.     

A facile one-step strategy to construct 0D/2D SnO2/g-C3N4 heterojunction photocatalyst for high-efficiency hydrogen production performance from water splitting

Fabricating 0D/2D heterojunctions is considered to be an efficient mean to improve the photocatalytic activity of g-C₃N₄, whereas their applications are usually restricted by complex preparation process. Here, the 0D/2D SnO₂/g-C₃N₄ heterojunction photocatalyst is prepared by a simple one-step polymerization strategy, in which SnO₂ nanodots in-situ grow on the surface of g-C₃N₄ nanosheets. It shows the outstanding photocatalytic H₂ production activity relative to g-C₃N₄ under the visible light, which is due to the formation of 0D/2D heterojunction significantly contributing to the separation of photogenerated charge carriers. In particular, the H₂ production rate over the optimal SnO₂/g–C₃N₄–1 sample is 1389.2 μmol h⁻¹ g⁻¹, which is 6.06 times higher than that of g-C₃N₄ (230.8 μmol h⁻¹ g⁻¹). Meanwhile, the AQE value of H₂ production over the SnO₂/g–C₃N₄–1 sample reaches up to a maximum of 4.5% at 420 nm. This work develops a simple approach to design and fabricate g–C₃N₄–based 0D/2D heterojunctions for the high-efficiency H₂ production from water splitting.     

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.     

Facile strategy to fabricate Ni2P/g-C3N4 heterojunction with excellent photocatalytic hydrogen evolution activity

Transition metal phosphides are considered as the most prospective replacements for noble metal cocatalysts used for H₂ evolution during photocatalytic water splitting. In this work, Ni₂P/g-C₃N₄ composite photocatalyst was synthesized using a simple in-situ hydrothermal method by one step. Benefiting from the excellent light trapping, efficient transfer of charge carriers and strong stability of Ni₂P nanoparticles, as well as the stable interface contact between Ni₂P and g-C₃N₄, the Ni₂P/g-C₃N₄ exhibit greatly enhanced H₂ evolution performance during photocatalytic water splitting. The optimized H₂ evolution rate can reach 3344 μmol h^?1 g^?1 over 17.5 wt% Ni₂P/g-C₃N₄, which is 68.2 times greater than that of pure g-C₃N₄ and even much greater than that of 15 wt% Pt/g-C₃N₄. The apparent quantum efficiency (QE) is about 9.1% under 420 nm monochromatic. The enhancement mechanism was demonstrated in detail by transient photocurrent responses, photoluminescence spectra and electrochemical impedance spectroscopy. This work develops a facile strategy to fabricate transition metal phosphide/semiconductor heterojunction systems with potential application for photocatalytic H₂ evolution.     

Enhanced visible-light-assisted photocatalytic hydrogen generation by MoS2/g-C3N4 nanocomposites

A facile, one-pot, solvothermal synthesis of MoS₂ microflowers (S1) and the heterostructures MoS₂/g-C₃N₄ with varying ratios of 1:1 (S2), 1:2 (S3) and 1:3 (S4) exhibiting enhanced visible-light-assisted H₂ generation by water splitting has been reported. The compounds were thoroughly characterized by PXRD, FESEM, HRTEM, EDS, UV–vis and XPS techniques. FESEM and HRTEM analyses showed the presence of microflowers composed of nano-sized petals in case of pure MoS₂ (S1), while the MoS₂ microflowers covered with g-C₃N₄ nanosheets in case of MoS₂/g-C₃N₄ heterostructure, S4. XPS analysis of S2 showed the presence of 2H phase of MoS₂ with g-C₃N₄. The Eosin-Y/dye-sensitized visible-light-assisted photocatalytic investigation of the samples in the absence of any noble metal co-catalyst revealed very good water splitting activity of MoS₂/g-C₃N₄ heterostructure, S2 with hydrogen generation rate of 1787 μmol h⁻¹g⁻¹ which is about 6 and 40 times higher than pure MoS₂ and g-C₃N₄ respectively. The relatively higher catalytic activity of the heterostructure, S2 has been ascribed to the efficient spatial separation of photo-induced charge carriers owing to the synergistic interaction between MoS₂ and g-C₃N₄. A possible mechanism for the Eosin-Y-sensitized photocatalytic H₂ generation activity of MoS₂/g-C₃N₄ heterostructures has also been presented. The enhanced activity of S2 was further supported by fluorescence measurements. Thus, the present study highlights the importance of non-noble metal based MoS₂/g-C₃N₄ heterojunction photocatalysts for efficient visible-light-driven H₂ production from water splitting.     

Influence of Rh nanoparticle size and composition on the photocatalytic water splitting performance of Rh/graphitic carbon nitride

The effect of Rh co-catalyst nanoparticle size for photocatalytic water splitting using graphitic carbon nitride (g-C₃N₄) as light absorber was investigated. Rh nanoparticles with sizes in the 4–9 nm range were synthesized and deposited on g-C₃N₄. The light-absorption properties of the g-C₃N₄ and the particle size of Rh supported on g-C₃N₄ were also not influenced by the catalyst synthesis procedures. Rh/C₃N₄ is active in the photocatalytic splitting of water using visible light. The activity for H₂ generation does not depend on Rh particle size. The results obtained point to two important design criteria for a successful photocatalyst: firstly, the surface of the semiconductor should support a sufficient number of Rh nanoparticles to remove the photogenerated electrons before their recombination with holes; secondly, the nanoparticles should be metallic in nature to catalyze the proton-electron transfer reaction to generate adsorbed H atoms. Surface oxidation of the Rh nanoparticles substantially lowers their photocatalytic activity.     

Interfacially bonded Co-N boosts photocatalytic H2 evolution in a closely coupled CoFe2O4/g-C3N4 composite structure

To create hybrid composites for highly effective photocatalytic hydrogen evolution reactions, the photogenerated charge separation efficiency at the hybrid interface and the surface reaction kinetics at the reactive sites are key factors. In this work, CoFe hydroxide nanosheets prepared by dealloying were first mixed with graphitic carbon nitride (g-C₃N₄) to synthesize a CoFe₂O₄/g-C₃N₄ composite with strong Co-N bonds at the interface by a simple hydrothermal method. It was found that the presence of Co-N bonds between the components in the composites enhances the separation and transfer by photogenerated carriers at the composite interface. Furthermore, the presence of Co-N bonds enhanced the synergistic effect of the hybrid, which significantly boosts their photocatalytic performance in comparison to their counterparts. Under full-spectrum light, the composite photocatalyst has a greater efficiency of photocatalytic water H₂ evolution (6.793 mmol/g⁻¹·h⁻¹) and exceptional stability when compared to pure g-C₃N₄ (0.236 mmol/g⁻¹·h⁻¹) and CoFe₂O₄ (0.088 mmol/g⁻¹·h⁻¹). Under visible irradiation, the photocatalytic activity of the composite (0.556 mmol/g⁻¹·h⁻¹) for H₂ evolution increased by factors of 28.37 and 75.8 when compared to pure g-C₃N₄ and CoFe₂O₄, respectively.     

High-efficiency hydrogen evolution reaction photocatalyst for water splitting of Type-II β-AsP/g-C3N4 van der Waals heterostructure

Photocatalytic for water splitting to produce hydrogen is recognized as a low-cost, promising and attractive method to solve environmental problems and energy crises, but finding a high-performance photocatalyst is a big challenge. In this work, we designed a type-II β-AsP/g-C₃N₄ van der Waals heterostructure as an efficient photocatalyst and had the first principles calculations to analyze its stability, electronic properties, and photocatalytic performance. The results showed that the photocatalyst of β-AsP/g-C₃N₄ heterostructure met the proper band gap and band edge of the redox potential of water splitting, had effective charge separation of photogenerated electronic holes, and efficient visible light response. Importantly, our research showed that the β-AsP/g-C₃N₄ heterostructure could proceed spontaneously in thermodynamics and had an excellent photocatalytic performance in further study. It had quite good hydrogen evolution performance with the Gibbs free energy of ?0.02 eV, which is closer to zero than ?0.09 eV of Pt (111). The overpotential of its oxygen evolution reaction is as low as 0.57 V. This work showed excellent development prospects for β-AsP/g-C₃N₄ heterostructure in the field of photocatalysts, which will promote the development of g–C₃N₄–based photocatalytic for water splitting.     

In- situ solid-phase fabrication of Ag/AgX (X=Cl,Br, I)/g-C3N4 composites for enhanced visible-light hydrogen evolution

In this work, a series of Ag/AgX (X = Cl, Br, I)/g-C₃N₄ (Ag/AgX/CN) composites were successfully fabricated by an in-situ solid phase method. The morphology and structure, photoluminescence and photoelectrochemical properties of composites were investigated in detail. The as-prepared Ag/AgX/CN composites were used as H₂ evolution photocatalysts under visible-light irradiation with a sacrificial agent. The experimental results revealed that Ag/AgI/CN-4 composite possesses highest-H₂ evolution rate (up to 59.22 μmol g⁻¹ h⁻¹) which are approximately 31 times higher than that of pure g-C₃N₄ (1.94 μmol g⁻¹ h⁻¹). In addition, Ag/AgCl/CN-4 and Ag/AgBr/CN-4 composites also present high photocatalytic activities yielding, 26.39 and 18.05 μmol_H2 g⁻¹ h⁻¹_, respectively. The enhanced photocatalytic activities of Ag/AgI/CN-4 composite might be attributed to the synergistic effect between Ag/AgI nanoparticles and g-C₃N₄ and the localized surface plasmon resonance effect of metallic Ag. Moreover, Ag/AgI/CN-4 composite showed excellent recyclability and stability after five cycling photocatalytic tests (about 25 h). Furthermore, the possible photocatalytic mechanism of Ag/AgI/CN composites is proposed.