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1.
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 gcat?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.  相似文献   

2.
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.  相似文献   

3.
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.  相似文献   

4.
Photocatalytic H2 production is a hopeful technology to solving the environment problems and global energy. Consequently, it is essential to develop high efficient, nonprecious and stable photocatalysts. Graphitic carbon nitride (g-C3N4) was fascinated much concentration owed to this metal free n-type semiconductor possesses appropriate bandgap, unique two dimensional (2D) layered structures, low toxicity, high thermal and chemical stability, lowcost, facile preparation and visible light response. Moreover, the g-C3N4 composites are having huge promise on photocatalytic H2 production but, the efficiency of pure g-C3N4 is at present limited by its poor visible light absorption and suffers from high recombination rate of g-C3N4 photogenerated electron/hole pairs resulting in low photocatalytic performance. Furthermore, the g-C3N4 has unique electronic structure, therefore renowned candidates have been coupled with different functional components to improve photocatalytic activity. In this contribution, we review the recent research progresses of transition metals, non metals, noble metals, semiconductor compounds, graphene, carbon nanotubes (CNTs), carbon dots and quantum dots, supported on g-C3N4 nanosheets, which were applied to photocatalytic H2 production. In addition, different techniques used to synthesis the g-C3N4 based photocatalyst including with their corresponding examples have been described. We hope that this review will encourage the readers to extend the applications of g-C3N4 based heterostructure in the field of H2 production in a green manner.  相似文献   

5.
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.  相似文献   

6.
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.  相似文献   

7.
AuPd bimetallic nanoparticle (NP) modified ultra-thin graphitic carbon nitride nanosheet photocatalysts were synthesized via photochemical deposition-precipitation followed by hydrogen reduction. The crystal structure, chemical properties, and charge carrier behavior of these photocatalysts were characterized by X-ray diffraction (XRD), surface photovoltage spectroscopy (SPS), transient photovoltage spectroscopy (TPV), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and UV-Vis diffuse-reflectance spectroscopy (DRS). Photocatalytic H2 evolution experiments indicate that the hydrogen treated AuPd nanoparticles can effectively promote the separation efficiency of electron-hole pairs photo-excited in the g-C3N4 photocatalyst, which consequently promotes photocatalytic H2 evolution. The 1.0 wt% AuPd/g-C3N4 (H2) composite photocatalyst showed the best performance with a corresponding photocatalytic H2 evolution rate of 107 μmol h?1. The photocatalyst can maintain most of its photocatalytic activity after four photocatalytic experiment cycles. These results demonstrate that the synergistic effect of light reduction and hydrogen reduction of AuPd and g-C3N4 help to greatly improve the photocatalytic activity of the composite photocatalyst.  相似文献   

8.
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.  相似文献   

9.
In this paper, a novel Au/g-C3N4/ZnIn2S4 plasma photocatalyst heterojunction composite with 3D hierarchical microarchitecture has been successfully constructed by integrating Au/g-C3N4 plasmonic photocatalyst composite with 3D ZnIn2S4 nanosheet through a simple hydrothermal process. The Au nanoparticles were firstly anchored on the surface of pristine g-C3N4 material to get Au/g-C3N4 plasmonic photocatalyst. Ascribing to the surface plasmon resonance of Au nanoparticles, the obtained Au/g-C3N4 plasmonic photocatalyst shows a significant improved photocatalytic activity toward hydrogen production from water with visible light response comparing with pristine g-C3N4. Further combining Au/g-C3N4 plasmonic photocatalyst with 3D ZnIn2S4 nanosheet to construct a heterojunction composite. Owing to the synergistic effect of the surface plasmon resonance of Au nanoparticles in Au/g-C3N4 and the heterojunction structure in the interface of Au/g-C3N4 and ZnIn2S4, the prepared Au/g-C3N4/ZnIn2S4 plasma photocatalyst heterojunction composite shows an excellent photocatalytic activity toward hydrogen production from water with visible light response, which is around 7.0 and 6.3 times higher than that of the pristine C3N4 and Znln2S4 nanosheet, respectively. The present work might provide some insights for exploring other efficient heterojunction photocatalysts with excellent properties.  相似文献   

10.
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.  相似文献   

11.
As an increasing number of photocatalysis are developed, non-noble metal photocatalysts that can be synthesized from earth-abundant and low-cost materials have received a great deal of attention. In this study, non-noble metal WS2/g-C3N4 photocatalysts were prepared by a facile one-pot synthesis. Varying masses of tungsten disulfide (WS2) were successfully loaded onto g-C3N4 and characterized by X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). These results indicated that the WS2 was successfully synthesized and immobilized closely on the surface of g-C3N4 to form a sheet-like nanostructure. The H2 generation results showed that the optimal photocatalyst was 0.3-WCN because it had the highest photocatalytic H2 production of 154 μmol h−1g−1, which is 34 times higher than bare g-C3N4 and even higher than 0.3 wt% platinum-loaded g-C3N4. Additionally, the possible mechanism of the photocatalyst was studied by photoluminescence (PL), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and photoelectrochemical tests, which showed that the WS2 played a key role in improving the efficiency of separation and migration of the photogenerated carriers in g-C3N4.  相似文献   

12.
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.  相似文献   

13.
In previous studies, it has been shown that phosphorus and phosphate can improve the conductivity, change the electronic structure, and accept electrons from catalysts. In this study, we obtained phosphorylated NiAl-layered double hydroxide (P-LDH) nanosheets and used them as a novel cocatalyst in photocatalytic hydrogen evolution. After assembly with g-C3N4 via an in situ process, these noble-metal-free composite photocatalysts showed superior photocatalytic hydrogen evolution activity. It was also found that the efficiency of H2 production on the optimal composite was 1.5 times that of Pt-modified g-C3N4. Characterization of the photocatalysts revealed that the effects of P-LDH were different from those of other bimetallic LDHs, showing a lower overpotential and faster reaction kinetics of H2 evolution. Moreover, it was found that P-LDH has a higher surface work function than that of g-C3N4, leading to the formation of an interfacial electric field from CN toward P-LDH. Therefore, modifying P-LDH can efficiently improve the interfacial charge transfer rate, suppress photogenerated charge recombination, and lower the surface overpotential of g-C3N4. This study serves as guidance on the design of more effective cocatalysts for photocatalytic hydrogen evolution reactions.  相似文献   

14.
Highly efficient and direct photocatalytic H2 evolution from water via water splitting without using sacrificial reagents is a challenging approach to convert solar energy into renewable and storable chemical energy. Herein, by amalgamating the architecture recommendations and energy band engineering principles into the design formulation, a novel Ag@CoFe2O4/g-C3N4 plasmonic p-n heterojunction photocatalytic system is designed and constructed for the first time. The Ag@CoFe2O4/g-C3N4 photocatalyst so designed, under the illumination of the visible-light (λ > 420 nm), produced H2 and O2 in 2:1 stoichiometric amount at the rates of 335 μmol h?1 and 186 μmol h?1, respectively, with an apparent quantum yield reaching 3.35% at 420 nm, demonstrating that Ag@CoFe2O4 dimer colloids are responsible for oxidation and g-C3N4 for reduction. Moreover, in the presence of triethanolamine, the apparent quantum yield achieved by Ag@CoFe2O4/g-C3N4 is 16.47% with hydrogen produced at the rate 3.5 times higher than the CoFe2O4/g-C3N4 heterojunction photocatalyst with AQY of 5.49%. The combination of Ag plasmonic effect and internal electric field established at the interface of p-type CoFe2O4 and n-type g-C3N4 boosts the separation efficiency of photoexcitons from CoFe2O4 to g-C3N4, extending the visible-light absorption capacity of the systems. The generation of optimum amount of defects like oxygen vacancies at the p-n heterojunction interface due to the structural distortion of CoFe2O4 also plays a prominent photocatalytic enhancement by providing active sites for the adsorption of water molecules for the light driven catalytic reactions. Our work introduces a potential avenue to design efficient photocatalysts by constructing several other suitable p-n heterojunction semiconductor photocatalysts toward practical application in solar energy conversion.  相似文献   

15.
Photocatalytic hydrogen production is considered as an ideal approach to solve global energy crisis and environmental pollution. Graphitic carbon nitride (g-C3N4) has received extensive consideration due to its facile synthesis, stable physicochemical properties, and easy functionalization. However, the pristine g-C3N4 usually shows unsatisfactory photocatalytic activity due to the limited separation efficiency of photogenerated charge carriers. Generally, introducing semiconductors or co-catalysts to construct g–C3N4–based heterojunction photocatalysts is recognized as an effective method to solve this bottleneck. In this review, the advantages and characteristics of various types of g–C3N4–based heterojunction are analyzed. Subsequently, the recent progress of highly efficient g–C3N4–based heterojunction photocatalysts in the field of photocatalytic water splitting is emphatically introduced. Finally, a vision of future perspectives and challenges of g–C3N4–based heterojunction photocatalysts in hydrogen production are presented. Predictably, this timely review will provide valuable reference for the design of efficient heterojunctions towards photocatalytic water splitting and other photoredox reactions.  相似文献   

16.
Small surface area, deficient reaction sites, and poor visible-light harvest ability of the original graphitic carbon nitride (g-C3N4) severely restrict its photocatalytic H2 production activity. Here, an ultrathin porous and N vacancies rich g-C3N4 (VN-UP-CN) was fabricated by thermal oxidation exfoliation and high-temperature calcination under the Ar atmosphere. The ultrathin porous morphology increases the surface area and reaction sites of original g-C3N4, moreover, the produced N vacancies greatly broaden the light harvest ability of ultrathin porous g-C3N4 (UP–CN). Therefore, VN-UP-CN displays the maximal H2 production rate of 2856.7 μmol g?1 h?1 in triethanolamine solution under visible-light, and adding 0.5 M of K2HPO4 can further improve its H2 production rate to 4043.9 μmol g?1 h?1. Importantly, VN-UP-CN also shows good performance in simultaneous photocatalytic H2 production and benzyl alcohol oxidation to benzaldehyde with the activities of 196.08 and 198.28 μmol g?1 h?1, respectively, which avoids the waste of sacrificial agent and photogenerated holes. This work affords an achievable way to design the efficient g-C3N4 photocatalyst by morphology and defect regulation, which can effectively utilize both photogenerated electrons and holes for H2 and value-added chemical production.  相似文献   

17.
Rational design of high-efficiency heterostructure photocatalyst is an effective strategy to realize photocatalytic H2 evolution from pure water, but remains still a considerable challenge. Herein, an anatase/rutile TiO2/g-C3N4 (A/R/CN) multi-heterostructure photocatalyst was prepared by a facile thermoset hybrid method. The combination of two type-II semiconductor heterostructures (i.e., A/R and R/CN) significantly improve the separation and transfer efficiency of photogenerated carriers of anatase TiO2, rutile TiO2 and g-C3N4, and A/R/CN photocatalyst with high activity is obtained. The optimal A/R/CN photocatalyst exhibits significantly increased photocatalytic overall water splitting activity with a rate of H2 evolution of 374.2 μmol g−1h−1, which is about 8 and 4 times that of pure g-C3N4 and P25. Moreover, it is demonstrated to be stable and retained a high activity (ca. 91.2%) after the fourth recycling experiment. This work comes up with an innovative perspective on the construction of multi-heterostructure interfaces to improve the overall photocatalytic water splitting performance.  相似文献   

18.
To achieve low-cost photocatalytic hydrogen (H2) production, it is necessary to develop low-priced transition metal co-catalysts to replace the roles of noble metals for photocatalytic H2 evolution. Herein, a co-catalyst of Mo-doped CoSx (Mo-CoSx) was synthesized by using the hydrothermal procedure, then attached to g-C3N4 to construct a composite photocatalyst. As a co-catalyst, Mo-CoSx can work as an electron acceptor, it is utilized to receive electrons generated by g-C3N4 photocatalyst on the surface of the catalyst, and inhibit the recombination of those electrons, thus showing enhanced charge transfer ability as well as reduction ability. The optimized Mo-CoSx/g-C3N4 delivered a prominent photocatalytic H2 evolution rate of 2062.4 μmol h?1 g?1, which was ~193 times higher than g-C3N4. Its AQE at 400 nm and 420 nm were 11.05% and 6.83%, respectively. This work provides a novel non-precious metal co-catalyst/g-C3N4 photocatalyst that is expected to be an acceptable cost route to solar energy conversion.  相似文献   

19.
Free-standing carbon nanotube films (CNTF) with entangled carbon nanotubes (CNT) were used as conductive supports for the preparation of CuS–ZnS/CNTF composite as immobilized photocatalysts for H2 production. The surface morphology, crystalline property, surface chemistry, and optical properties of the CuS–ZnS/CNTF photocatalysts were investigated. The effects of forming CuS–ZnS heterojunction and conductive CNTF on the separation of photogenerated charges and photocatalytic hydrogen production activity of CuS–ZnS/CNTF photocatalysts were evaluated by the photocatalytic hydrogen production tests. Conductive CNT films can prevent the recombination of photogenerated electron–hole pairs. The deposition of CuS nanoparticles on the ZnS/CNTF leads to higher photocatalytic activity which can be attributed to the effective electron–hole separation. Introducing ZnS and CuS makes the photocatalyst surface more hydrophilic. The porous structure contributed to the effective contact between the sacrificing agents and the photocatalysts, leading to enhanced H2 production activity.  相似文献   

20.
Vacancies engineering was widely reported as the promising strategy for the improvement of the photocatalytic performance of semiconductor photocatalysts. In current work, carbon vacancies are constructed successfully in graphitic carbon nitride (g-C3N4) photocatalyst via magnesium vapor etching. Experimental results show that the formed carbon vacancies in g-C3N4 photocatalyst can significantly improve the photocatalytic H2 generation performance. XRD, FTIR, SEM/TEM, XPS and PL characterization data are employed to evidence the construction of carbon vacancies, which are revealed to be the reason for the enhancement of photocatalytic H2 evolution. This work develops an alternative route to construct carbon vacancies in g-C3N4 materials and gives an insight into the influence of vacancies on the photocatalytic performance of photocatalysts.  相似文献   

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