ZnCr LDH nanosheets modified graphitic carbon nitride for enhanced photocatalytic hydrogen production

ZnCr layered double hydroxides (ZnCr LDH) nanosheets modified graphitic carbon nitride (g-C₃N₄) nanohybrids were fabricated via a self-assembly procedure through electrostatic interaction between these two components. Such 2D-2D inorganic-organic hybrid material was employed for photocatalytic hydrogen production under visible light for the first time. The physical and photophysical properties of the hybrid nanocomposites were investigated to reveal the effect of ZnCr LDH nanosheets on the photocatalytic activities of g-C₃N₄. It was found that 1 wt% ZnCr LDH nanosheets modified g-C₃N₄ was optimal for the formation of intimate interfacial contact. The visible light photocatalytic H₂ production activity over g-C₃N₄ was enhanced about 2.8 times after ZnCr LDH nanosheets modification. The significant enhancement in photocatalytic performance for ZnCr LDH/g-C₃N₄ heterojunction should be attributed to the promoted charge transfer and separation efficiency, resulting from the intimate interfacial contact and Type II band alignment between ZnCr LDH and g-C₃N₄.     

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.     

Mesoporous g-C3N4/Zn–Ti LDH laminated van der Waals heterojunction nanosheets as remarkable visible-light-driven photocatalysts

Mesoporous g-C₃N₄/Zn–Ti layered double hydroxide (LDH)-laminated van der Waals heterojunction nanosheets were prepared by a facile one-step in situ hydrothermal method. Due to the strong electrostatic interactions between the positively charged Zn–Ti LDH and negatively charged g-C₃N₄ nanocrystal, a laminated van der Waals heterostructure was successfully formed between Zn–Ti LDH and g-C₃N₄. The mesoporous g-C₃N₄/Zn–Ti LDH-laminated van der Waals heterojunction, which had a narrow bandgap of 2.41 eV extended the photoresponse to the visible light region. The obtained heterojunctions showed excellent visible-light-driven photocatalytic performance for the complete removal of ceftriaxone sodium (up to ∼97%) and a high hydrogen production rate (∼161.87 μmol h⁻¹ g⁻¹). This was mainly attributed to the formation of the laminated van der Waals heterojunctions, which favoured charge separation and the absorption of visible light, and the mesoporous structure, which provided more surface active sites. This facile strategy for preparing mesoporous g-C₃N₄/Zn–Ti LDH-laminated van der Waals heterojunctions offers new insights for the fabrication of high-performance van der Waals heterojunction photocatalytic materials.     

In situ W/O Co-doped hollow carbon nitride tubular structures with enhanced visible-light-driven photocatalytic performance for hydrogen evolution

Heteroatom co-doping has been considered as an effective strategy to simultaneously overcome intrinsic shortcomings of g-C₃N₄ to achieve enhanced photocatalytic properties, in which the involved dopants could play its role in altering electronic structure, optical absorption and charge separation of the catalyst. Herein, W/O co-doped hollow g-C₃N₄ tubular structures are successfully obtained for the first time via a one-step thermal decomposition. By W/O co-doping, architecture of g-C₃N₄ is able to be modulated with enhanced optical absorption towards visible region. In addition, narrowed band gap and restrained charge recombination are conducive for the excitation of electron-hole pairs and transportation. Photocatalytic water splitting tests indicate that the co-doped hollow tubular g-C₃N₄ structures enable superior activity for generating hydrogen up to 403.57 μmol g^?1 h^?1 driven by visible light, nearly 2.5 times as high as that of pristine g-C₃N₄. This work presents a rational strategy to design co-doped g-C₃N₄ as an efficient visible-light-driven photocatalyst.     

Two dimensional N-doped ZnO-graphitic carbon nitride nanosheets heterojunctions with enhanced photocatalytic hydrogen evolution

The effective separation of photogenerated charge carriers, their transport and interfacial contact is of great significance for excellent performance of semiconductor based photocatalysts. Herein, we report the fabrication of two dimensional (2D) nanosheets heterojunction comprising of N-doped ZnO nanosheets loaded over graphitic carbon nitride (g-C₃N₄) nanosheets for enhanced photocatalytic hydrogen evolution. The prepared 2D-2D heterojunctions with varying amount of g-C₃N₄ nanosheets have been characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) techniques. The optimized heterojunction photocatalyst with 30 wt% of g-C₃N₄ nanosheets (NZCN30) exhibit hydrogen evolution rate of 18836 μmol h^?1 g_cat^?1 in presence of Na₂S and Na₂SO₃ as sacrificial agents under simulated solar light irradiation. The enhanced photocatalytic performance of NZCN30 heterojunction has been supported well by photoluminescence and photoelectrochemical investigations, which shows the minimum recombination rate and high photoinduced current density, respectively. In addition, the existence of 2D-2D interfacial contact plays a major role in enhanced H₂ evolution by high face-to-face contact surface area for separation of photogenerated charge carriers in space which facilitate their transfer for H₂ generation. This work paves way for the development of 2D-2D heterojunctions for diverse applications.     

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.     

Active-center-enriched Ni0.85Se/g-C3N4 S-scheme heterojunction for efficient photocatalytic H2 generation

Photocatalysts with abundant active sites are essential for photocatalytic H₂ evolution from water. Herein, Ni_0.85Se-deposited g-C₃N₄ was obtained by a physical solvent evaporation method. The investigation shows that Ni_0.85Se with unsaturated active Se atoms can significantly improve the photocatalytic activity of g-C₃N₄, and the H₂ production rate of Ni_0.85Se/g-C₃N₄ can reach 8780.3 μmol g^?1 h^?1, which is 3.5 and 92.9 times higher than that of Ni_0.85+xSe/g-C₃N₄ (2497.9 μmol g^?1 h^?1) and pure g-C₃N₄ (94.5 μmol g^?1 h^?1), respectively. This improvement can be attributed to the quick charge transfer between Ni_0.85Se and g-C₃N₄ with S-scheme heterojunction feature based on a series of trapping experiments and photoelectrochemical analysis. Moreover, abundant unsaturated Se atoms could provide more H₂ evolution active sites. This work sheds light on the construction of heterojunctions with abundant active sites for H₂ production.     

Synthesis of mesoporous g-C3N4/S-PAN π-conjugation heterojunction via sulfur-induced cyclization reaction for enhanced photocatalytic H2 production

Simultaneously extended π-conjugated system and provide abundant pore structure of semiconductor photocatalysts for hydrogen (H₂) production is highly desirable. Hence, a novel mesoporous sulfurized polyacrylonitrile modified g-C₃N₄ (g-C₃N₄/S-PAN) π-conjugation heterojunction is firstly fabricated by one-step strategy under the sulfur-induced cyclization reaction and pore-creating effect. Excitedly, the g-C₃N₄/S-PAN π-conjugation heterojunction extends the π-conjugated system in favor of speeding up the photogenerated electron transfer, which is due to strengthen the π-π interactions between the S-PAN and g-C₃N₄ and S-PAN is more apt to accept electrons. And the obtained g-C₃N₄/S-PAN π-conjugation heterojunction with mesoporous structure also provide abundant active sites for proton reduction. Accordingly, the g-C₃N₄/S-PAN-2 π-conjugation heterojunction shows the optimal photocatalytic H₂ evolution (PHE) activity (736.24 μmol h⁻¹g⁻¹), which is approximately 2.15 times higher than pristine g-C₃N₄. In addition, the relationships of the optical and photoelectrochemical properties with photocatalytic activity are revealed in depth based on the first-principles calculations of band structure and density of states (DOS). This work provides a new one-step strategy to obtain g-C₃N₄-based π-conjugation heterojunction with the unique microstructure for improving PHE activity.     

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.     

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.     

A BiOCl/β‐FeOOH heterojunction for HER photocatalytic performance under visible‐light illumination

β‐iron oxide hydroxide (β‐FeOOH) had been proven to be an effective co‐catalyst during H₂ evolution reaction (HER) process. In this research, a BiOCl/β‐FeOOH heterojunction was successfully synthesized by a solid‐state doping method. Then, the structure, composition, and photo‐electrochemical properties of the prepared photocatalysts were studied. For the superior HER photocatalytic activity of ultrasmall β‐FeOOH nanoparticles (NPs) and the formation of the BiOCl/β‐FeOOH heterojunction, this heterojunction photocatalyst exhibited very superior photocatalytic performance in the HER process. Especially, when the amount of incorporated β‐FeOOH NPs was appropriate, the BFOH‐2 possessed the highest photocatalytic activity in HER process, and the HER rate was about 16.64 mmol·g^?1·h^?1 during illuminated time of 6 hours under visible light. When appropriate, ultrasmall β‐FeOOH NPs were implanted into the structure of BiOCl, the BiOCl/β‐FeOOH heterojunction interfaces would form for the existence of interfacial interactions. Therefore, this BiOCl/β‐FeOOH heterojunction exhibited superior visible‐light response, fast photo‐carrier migration, and high‐efficient separation of photo‐carriers, so that the BFOH‐2 heterojunction possessed high‐efficient hydrogen evolution reaction (HER) photocatalytic activity.     

Preparation,structure and application of g-C3N4/BiOX composite photocatalyst

Graphite-like carbon nitride (g-C₃N₄) has attracted great attention for pollutant degradation and clean energy production. The heterojunctions of bismuth halide (BiOX, X = Cl, Br, I) and g-C₃N₄ are proposed to overcome the shortcomings of the g-C₃N₄ photocatalyst, such as low charge separation rate and high charge recombination rate. This review paper systematically discusses the progress in synthesis, structure, and applications of heterojunction photocatalytic composites made of g-C₃N₄ and BiOX based on the understanding of their photocatalytic reaction mechanism. We clarify and summarize structural mechanisms of a single and compound semiconductor to reveal the factors that affect photocatalytic performances. We discuss and compare advantages and disadvantages of versatile preparation processes. Particularly, we focus on the understanding of the structure and characteristics of type II, Z-type, n-n, and p-n heterojunctions and their applications, specifically in pollutant degradation, H₂ production by water splitting, CO₂ reduction, and medical sterilization. The future prospects of g-C₃N₄/BiOX composites are also discussed from aspects of their preparation, application, and research methods. This work may offer a good avenue and data reference to develop novel g-C₃N₄ photocatalytic materials to meet the ever-increasing environmental pollution and energy shortage.     

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.     

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.     

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.     

Heterojunction composites of g-C3N4/KNbO3 enhanced photocatalytic properties for water splitting

In this paper, g-C₃N₄/KNbO₃ heterojunction composites were prepared and used to water splitting for hydrogen production under simulated sunlight. The morphology and structure of the composites were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-Ray spectroscopy and high resolution transmission electron microscopy. The g-C₃N₄/KNbO₃ composites exhibited the better photocatalytic performance for water splitting more than 2 and 1.8 times of the pure g-C₃N₄ and KNbO₃. Meanwhile, the Pt nanoparticles as a co-catalyst were deposited on the surface of g-C₃N₄/KNbO₃ as Pt-g-C₃N₄/KNbO₃ composites for water splitting which enhanced photocatalytic properties almost 74 and 14 times than that of Pt-KNbO₃ and Pt-g-C₃N₄. Such a significant improvement of the photocatalytic activity was mainly ascribed to the photoinduced electron-holes in the interface of g-C₃N₄/KNbO₃ composites rapid separation and the co-catalysis effect of Pt nanoparticles. These present study work may provide a useful method for water splitting using an effective composites photocatalysts.     

CoCO3 hierarchical structure embedded on g-C3N4 nanosheets to assemble 3D/2D Z-scheme heterojunction towards efficiently and stably photocatalytic hydrogen production

Structure and interface control of heterojunction is usually a challenging issue to improve the photocatalytic performance. Herein, a new 3D/2D CoCO₃/g-C₃N₄ heterojunction is assembled by embedding hexahedral CoCO₃ on g-C₃N₄ nanosheets. The unique step-like hierarchical structure of CoCO₃, the formed built-in electric field and Z-scheme charge transfer behavior at the interface jointly drive the high-efficient separation of photogenerated carriers to boost the photocatalytic H₂ production. It achieves the optimal H₂ production rate that is almost 2.6 times than g-C₃N₄, apparent quantum efficiency (AQE) of 10.1% at 400 nm and continuous running of 60 h over the 3D/2D CoCO₃/g-C₃N₄ heterojunction. This work endows a fresh structural control strategy for the fabrication of 3D/2D Z-scheme heterojunction to improve the photocatalytic H₂ production performance.     

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.     

Electron transfer via a carbon channel for efficient Z-scheme solar hydrogen production

Z-scheme photocatalysis provides a promising solution to photocatalytic solar water splitting, yet restricted by inferior interfacial charge transfer. Here, we demonstrate a Z-scheme composite photocatalyst made of Fe₂O₃, a carbon layer, and g-C₃N₄ that can achieve efficient hydrogen generation from solar water decomposition. The success relies on in-situ preparation of core-shell Fe₂O₃@C structure at the surface of g-C₃N₄. Carbon as an intermediate layer thus acts as a bridge that significantly accelerates the migration of photogenerated electrons from Fe₂O₃ conduction band to g-C₃N₄ valence band. As a result, the highest rate of H₂ generation reaches 5.26 mmol h⁻¹g⁻¹. This activity is approximately 33-time greater than that achieved over pristine g-C₃N₄ and about 4-time larger than that obtained over a Fe₂O₃/g-C₃N₄ heterojunction without internal carbon layer. This work explicates the potential insight of the composite and paves a promising way to engineer the charge transfer behavior.     

Potassium doped and nitrogen defect modified graphitic carbon nitride for boosted photocatalytic hydrogen production

Controlling the structure of semiconductors to tailor are physicochemical and photoelectronic structure features. Graphitic carbon nitride has triggered a new impetus in the field of photocatalysis. However, the rapid recombination of charge carriers limited its photocatalytic activity. Herein, we demonstrate that potassium doped and nitrogen defects into graphitic carbon nitride (KCN_x) framework are favorable for visible light harvesting, charge separation and have highly efficient photocatalytic behavior for water splitting. It exhibits a high hydrogen evolution activity of 59.9 mmol·g^?1·h^?1 (66.6 times much higher than that of pristine g-C₃N₄), and remarkable apparent quantum efficiency of 57.17% at 420 nm. The superior photocatalytic performance of the KCNx sample was attributed to the less recombination rate of photogenerated electron and hole, and enhanced conductivity, which was proven by photoelectrochemical and PL. This work reveals the synergistic mechanism of introducing foreign elements and defects into the framework of graphitic carbon nitride to improve its photocatalytic activity.