Facile synthesis of carbon self-doped g-C3N4 for enhanced photocatalytic hydrogen evolution

Graphite carbon nitride (g-C₃N₄) is an appealing metal-free photocatalyst for hydrogen evolution, but the potential has been limited by its poor visible-light absorption and unsatisfactory separation of photo-induced carriers. Herein, a facile one-pot strategy to fabricate carbon self-doped g-C₃N₄ composite through the calcination of dicyanamide and trace amounts of dimethylformamide is presented. The as-obtained carbon self-doped catalyst is investigated by X-ray photoelectron spectroscopy (XPS), confirming the substitution of carbon atoms in original sites of bridging nitrogen. We demonstrate that the as-prepared materials display remarkably improved visible-light absorption and optimized electronic structure under the premise of principally maintaining the tri-s-triazine based crystal framework and surface properties. Furthermore, the carbon doped g-C₃N₄ composite simultaneously weakens the transportation barrier of charge carriers, suppresses charge recombination and raises the separated efficiency of photoinduced holes and electrons on account of the extension of pi conjugated system. As a result, carbon self-doped g-C₃N₄ exhibits 4.3 times greater photocurrent density and 5.2 times higher hydrogen evolution rate compared with its bulk counterpart under visible light irradiation.     

Fabrication of g-C3N4/TiO2 heterojunction composite for enhanced photocatalytic hydrogen production

In this study, graphitic carbon nitride (g-C₃N₄) was successfully coupled with TiO₂ using hydrothermal method, to develop an advanced heterojunction photocatalyst. The interaction between g-C₃N₄ and TiO₂ was confirmed through analysis of X-Ray spectroscopy (XPS) C 1s, N 1s, O 1s high resolution core level spectra of g-C₃N₄, TiO₂ and g–C₃N₄–TiO₂ heterojucntion. Further, through valence band spectra analysis, conduction band offset (0.12 eV) and valence band offset (0.28 eV) of g–C₃N₄–TiO₂ heterojunction were estimated. Also, composite material was identified as type II heterojunction between g-C₃N₄ and TiO₂. XRD, UV–vis, BET and HRTEM were employed to understand the changes in physicochemical properties. Photocatalytic hydrogen production rates were evaluated through water splitting experiments. Under visible light irradiation highest hydrogen production rate was achieved for g–C₃N₄–TiO₂ heterojunction sample with high content of TiO₂, and was about 1041 μmol/g.h. The improved photocatalytic activity of the heterojunction material was explained in detail.     

Facile synthesis of WO3 nanorods/g-C3N4 composites with enhanced photocatalytic activity

In this paper, WO₃ nanorods (NRs)/g-C₃N₄ composite photocatalysts were constructed by assembling WO₃ NRs with sheet-like g-C₃N₄. The as-synthesized photocatalysts were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, UV–vis diffuse reflectance spectroscopy and photoluminescence. The photocatalytic activity of the photocatalysts was evaluated by degradation of Rhodamine B (RhB) under simulated sunlight irradiation. Compared to pristine WO₃ NRs and g-C₃N₄, WO₃ NRs/g-C₃N₄ composites exhibit greatly enhanced photocatalytic activities. The enhanced performance of WO₃ NRs/g-C₃N₄ composite photocatalysts was mainly ascribed to the synergistic effect between WO₃ NRs and g-C₃N₄, which improved the photogenerated carrier separation. A possible degradation mechanism of RhB over the WO₃ NRs/g-C₃N₄ composite photocatalysts was proposed.     

Manifestation of enhanced and durable photocatalytic H2 production using hierarchically structured Pt@Co3O4/TiO2 ternary nanocomposite

A hierarchical structure composed of Pt@Co₃O₄/TiO₂ (CTP) ternary nanocomposite was synthesized and demonstrated for its enhanced and durable production of hydrogen from glycerol under simulated solar light irradiation. The rate of hydrogen production over the optimized composition was found to be 19.2 mmol h^?1 g^?1_cat. The obtained XRD and XPS results revealed the facile formation of the composite. The heterojunction formed in the ternary system remarkably enhanced the visible light absorption properties and charge separation in CTP as evidenced from their UV–visible absorption and PL spectra, respectively. The optimized union of the materials with specific properties and their intimate physical contacts might be the origin for the manifested, improved and durable photocatalytic efficiency towards hydrogen production.     

Controlled preparation of P-doped g-C3N4 nanosheets for efficient photocatalytic hydrogen production

Hydrogen production by photolysis of water by sunlight is an environmentally-friendly preparation technology for renewable energy. Graphitic carbon nitride (g-C₃N₄), despite with obvious catalytic effect, is still unsatisfactory for hydrogen production. In this work, phosphorus element is incorporated to tune g-C₃N₄'s property through calcinating the mixture of g-C₃N₄ and NaH₂PO_2, sacrificial agent and co-catalyst also been supplied to help efficient photocatalytic hydrogen production. Phosphorus (P) doped g-C₃N₄ samples (PCN-S) were prepared, and their catalytic properties were studied. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and ultraviolet diffuse reflection (UV-DRS) were used to study their structures and morphologies. The results show that the reaction rate of PCN-S is 318 μmol h⁻¹ g⁻¹, which is 2.98 times as high as pure carbon nitride nanosheets (CN) can do. Our study paves a new avenue, which is simple, environment-friendly and sustainable, to synthesize highly efficient P doping g-C₃N₄ nanosheets for solar energy conversion.     

关于解决g-C3N4在光催化制氢领域的两个局限的研究进展

随着工业的发展，化石燃料消耗巨大，环境问题也日益突出，寻找一种绿色新型能源已成为一个被广泛讨论的问题。氢气是一种清洁、可再生燃料，利用光催化剂分解水制氢气是一种制取氢气的有效途径。石墨碳氮化物（g-C3N4）作为光催化剂不仅成本低、反应稳定，而且其尺寸、厚度、结构、形貌等可控，在众多光催化剂中脱颖而出。但g-C3N4目前在光催化领域主要存在两个局限：g-C3N4不能有效地吸收光来产生足够多的光生电子-空穴对；g-C3N4不能有效的运输及分离光生电子-空穴对，以至于电子与空穴的复合率较高。文章综述了g-C3N4在光催化制氢领域的进展成果，分析了g-C3N4存在的问题并总结了其改进方法，最后对g-C3N4进行了展望，以期为设计高效、稳定的光催化制氢材料提供参考。     

Novel spindle-shaped nanoporous TiO2 coupled graphitic g-C3N4 nanosheets with enhanced visible-light photocatalytic activity

Highly efficient visible-light-driven heterojunction photocatalysts, spindle-shaped nanoporous TiO₂ coupled with graphitic g-C₃N₄ nanosheets have been synthesized by a facile one-step solvothermal method. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption analysis and UV–vis diffuse reflectance spectrometry (DRS), proving a successful modification of TiO₂ with g-C₃N₄. The results showed spindle-shaped nanoporous TiO₂ microspheres with a uniform diameter of about 200 nm dispersed uniformly on the surface of graphitic g-C₃N₄ nanosheets. The g-C₃N₄/TiO₂ hybrid materials exhibited higher photocatalytic activity than either pure g-C₃N₄ or nanoporous TiO₂ towards degradation of typical rhodamine B (RhB), methyl blue (MB) and methyl orange (MO) dyes under visible light (>420 nm), which can be largely ascribed to the increased light absorption, larger BET surface area and higher efficient separation of photogenerated electron–hole pairs due to the formation of heterostructure. In addition, the possible transferred and separated behavior of electron–hole pairs and photocatalytic mechanisms on basis of the experimental results are also proposed in detail.     

Well-designed ZnIn2S4/TiO2 Z-type heterojunction for efficient photocatalytic reduction of Cr(VI)

ZnIn₂S₄/TiO₂ photocatalyst was obtained by a facile hydrothermal method. Various techniques were used to characterize the ZnIn₂S₄/TiO₂, crystal structure and optical properties of ZnIn₂S₄/TiO₂. Cr (Ⅵ) as highly-toxic pollutant was used as the target reduction product to evaluate the catalytic performance of ZnIn₂S₄/TiO₂ under visible light irradiation. According to the experiment results, the reduction rate of Cr(VI) in the presence of ZnIn₂S₄/TiO₂ reaches 99% within 60 min, which is much better than ZnIn₂S₄ and TiO₂, respectively. At the same time, ZnIn₂S₄/TiO₂ also performs good stability for reduction rate hardly changes after 5 recycling experiments.     

Facile construction Z-scheme anatase/rutile TiO2/g-C3N4 hybrid for efficient photocatalytic H2 evolution under visible-light irradiation

Z-scheme anatase/rutile TiO₂/g-C₃N₄ hybrids (denoted as LTARCN-x, x represents calcination temperature) were designed and synthesized by growing TiO₂ nanorods on the surface of g-C₃N₄ utilizing impregnation-calcination method. Furthermore, through the etched effect of hydrochloric acid and calcination treatment, the as-prepared LTARCN-x possessed abundant pore structure and larger surface area, and the surface area of LTARCN-425 was 8.5 times than that of bulk g-C₃N₄. Meanwhile, the g-C₃N₄ would play a role of carrier to prevent from the aggregation of TiO₂ nanorods. In addition, under visible light irradiation, the Z-scheme heterostructure would be constructed between the rutile TiO₂ nanorod and g-C₃N₄ nanosheet, respectively. The optimized photocatalyst LTARCN-425 exhibited a preferable activity, the photocatalytic hydrogen production rate of LTARCN-425 was about 1031 μmol g^?1 h^?1, and it was about 6.3 and 13.6 times than that of g-C₃N₄ and TiO₂, respectively. Moreover, the photocatalytic mechanism of the hydrogen production was studied intensively via designing fluorescent probe, Pt and PbO₂ deposition experiment, and the characterizations of EPR, TEM, HRTEM and XPS.     

Significantly enhanced charge transfer efficiency and surface reaction on NiP2/g-C3N4 heterojunction for photocatalytic hydrogen evolution

In this work, a novel NiP₂/g-C₃N₄ heterojunction via homogeneous precipitation method assisted by thermal phosphorization reaction was designed and constructed, and the optimized sample showed the excellent photocatalytic H₂ evolution activity under visible-light irradiation, which was nearly 112 times higher than that of pristine g-C₃N₄ sample. Experimental characterizations and DFT calculations demonstrated that the NiP₂ nanoparticles covered on the g-C₃N₄ surface can form a built-in electric field at the interface to accelerate the transfer of photoexcited electrons from g-C₃N₄ to NiP₂, crucial for hindering the recombination of electron-hole pairs. Moreover, the energy barrier of hydrogen evolution reaction can also vastly reduce when combined NiP₂ and g-C₃N₄ to construct NiP₂/g-C₃N₄ heterojunction. This work represents a method through combing experimental and theoretical tools to thoroughly investigate the mechanism of photocatalytic process.     

Facile fabrication of 3D interconnected porous boron doped polymeric g-C3N4 with enhanced visible light photocatalytic hydrogen evolution and dye contaminant elimination

Researchers have attempted to developing high-efficiency catalysts for photocatalytic hydrogen evolution and organic pollution elimination simultaneously to alleviate the issues of energy shortage and water pollution. In this work, we fabricated 3D interconnected porous boron doped polymeric g-C₃N₄ catalysts with efficient photocatalytic activity for hydrogen evolution and dye contaminant elimination under visible-light irradiation. The as-fabricated catalysts exhibited significantly enhanced hydrogen evolution (4.37 mmol g ^?1 h^?1) and RhB contaminant elimination (96.37%) activity. Based on characterization and photocatalytic tests, an enhanced mechanism of the superior photocatalytic performance was proposed: 3D interconnected porous structure and B-doping have a synergistic effect on the greatly improved photocatalytic activity. The 3D interconnected structures endowed g-C₃N₄ with a higher specific surface area and abundant active sites and improved the capacity of rapid absorption to facilitate the photocatalytic process. B doping provided enhanced visible-light absorption capacity and a narrowed bandgap and served as a “highway” for electron-hole pairs to facilitate migration and separation and suppress the combination of photogenerated carriers. Besides, the possible mechanism of enhanced photocatalytic performance was elucidated according to the results of characterization measurements and active species analysis.     

S-scheme bimetallic sulfide ZnCo2S4/g-C3N4 heterojunction for photocatalytic H2 evolution

Transition bimetallic sulfides have attracted widespread attention because of their superior electrochemical characteristics compared to their parent materials. Herein, ternary ZnCo₂S₄ was deposited on g-C₃N₄ (CN) to enhance the photocatalytic water splitting reactivity of CN. The hydrogen (H₂) evolution rate of 25 wt%-ZnCo₂S₄/CN reached 6619 μmol h⁻¹ g⁻¹, which was 55.2 times higher than that of CN alone. Under the same conditions, ZnS/CN and Co₃S₄/CN were also synthesized, and their H₂ evolution rates were both inferior to that of ZnCo₂S₄/CN. Investigations showed that the presence of both zinc and cobalt ions in ZnCo₂S₄ lowered the H₂ evolution overpotential and charge recombination rate, leading to excellent H₂ release activity. In addition, the composite maintained its activity even after reacting for 20 h, and the charge transfer mechanism between ZnCo₂S₄ and CN was subject to the S-scheme charge transfer route according to trapping experiments for active species. This work revealed a promising and efficient bimetallic sulfide heterojunction to enhance H₂ evolution during water splitting and thus achieved improved conversion efficiency for solar energy applications.     

Ionic liquid-assisted preparation of g-C3N4/RGO co-intercalated CuBi2O4 hierarchical nanoflower and enhancement of the photocatalytic activity

A new p-n type CBO/CN/RGO ternary heterojunction photocatalyst combining three-dimensional multi-stage rosette CuBi₂O₄ and two-dimensional g-C₃N₄ and RGO flakes was successfully prepared by ionic liquid-assisted hydrothermal method. The successful construction of p-n heterojunctions of CBO/CN/RGO composites was verified by means of UV–vis diffuse reflection, Mott Schottky curves and TEM, and construction the heterojunctions significantly improved that of the transfer and transport speed of photogenerated carriers. The photocatalytic degradation of MO by CBO/CN/RGO-6% reached 91.83% within 150 min, while the kinetic constants of degradation k were 9.7 and 7.9 times greater than those of single-phase CBO and g-C₃N₄, respectively. Three cycles of experiments demonstrated that the degradation efficiency of CBO/CN/RGO-6% composites remained above 88% for RhB, which fully proved that the CBO/CN/RGO-6% composites possessed good chemical stability. Based on its excellent photocatalytic performance and good stability, CBO/CN/RGO-6% is expected to be the preferred material for environmental wastewater treatment.     

氮化碳的梯度热分解法制备与产氢研究

以三聚氰胺为原料,采用梯度升温热解法制备了石墨状氮化碳(g-C_3N_4),采用XRD、XPS、FTIR、SEM及UV-Vis、PL等技术手段对氮化碳材料的微观结构和光学性能进行了表征,并分析其光解水产氢性能。结果表明:采用梯度升温热解法制备的g-C_3N_4结构良好;620°C才开始快速分解,对热稳定性良好;几乎不溶于常见试剂,化学稳定性较好;在400~550 nm的可见光波长范围内对可见光有着明显吸收,禁带宽度达到2.42 e V,具有较高的光催化分解水制氢能力(18.95μmol/h).     

One-pot-solid preparation of novel three-dimensional FexS1-x/g-C3N4 heterostructures for efficient photocatalytic mixed-pollutants removal

In order to overcome the problem of low photocatalytic rate of g-C₃N₄, the 3D Fe_xS_1-x/g-C₃N₄ heterojunction was prepared via a simple one-pot solid method. The X-Ray Diffraction (XRD) and scanning electron microscope (SEM) results demonstrated that the Fe_xS_1-x/g-C₃N₄ heterojunction was established and a g-C₃N₄ nanosheet was tightly bound to Fe_xS_1-x. Compared with g-C₃N₄ samples, Fe_xS_1-x coupling resulted in substantial enhancement of visible light absorption, moreover, the bandwidth of heterojunction was also expanded. In addition to effectively degrading RhB and reducing Cr(VI), the redox performance of Fe_xS_1-x/g-C₃N₄ was also increased in the Cr(VI)/RhB mixed system. Based on a variety of experimental results, the enhanced synergistic photocatalytic activity of the 3D Fe_xS_1-x/g-C₃N₄ heterojunction was attributed to enhancement of the separation of e^- and h⁺ in FeS_2, which resulted from the effective conversion of FeS into FeS₂ under UV-light irradiation. The type II heterojunction structure that was produced via one-pot solid fabrication also inhibited the recombination of electron/hole pairs. Fe_xS_1-x doping and heterojunction building improve the photocatalysis capacity of g-C₃N₄ and broaden the visible-light response of pure g-C₃N₄.     

MoS2/g-C3N4复合光催化剂催化降解H2S的研究

采用热处理法合成了g-C3N4,通过光照沉积法将MoS2原位沉积到g-C3N4表面的活性位点,制备了MoS2/g-C3N4复合光催化剂,采用XRD、XPS和BET对MoS2/g-C3N4复合光催化剂的结构进行了表征:MoS2负载到g-C3N4表面,且未改变g-C3N4的晶体结构,同时具有较大的比表面积.考察了MoS2负...     

Construction of sandwich structured photocatalyst using monolayer WS2 embedded g-C3N4 for highly efficient H2 production

The construction of sandwich structured binary composite can enlarge its specific surface and strengthen the contact of binary interface. This can enhance H₂ generation efficiency of the photocatalyst. In this study, two-step strategy for the preparation of novel sandwich-structured g-C₃N₄/WS₂ is proposed. Step one is hydrothermal process producing the layered WO₃, which is used as the precursor for monolayer WS₂. While step two involves one-pot calcination process that generates sandwich structured g-C₃N₄/WS₂. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometry (ICP-OES), Brunauer Emmett Teller method (BET), and transmission electron microscopy (TEM) are employed to characterize the composition, structure and morphology of g-C₃N₄/WS₂. Photocatalytic H₂ generation tests show that the optimal H₂ generation rate of g-C₃N₄/WS₂ is 599.7 μmol h^-1 g^-1 (20 mg of photocatalyst), which is about 25 times higher than that of bare g-C₃N₄. Moreover, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), photoluminescence (PL) and electrochemical tests are employ to establish possible mechanism of photocatalytic H₂ evolution in sandwich-structured g-C₃N₄/WS₂.     

Controlled preparation of P-doped g-C3N4 nanosheets for efficient photocatalytic hydrogen production

Hydrogen production by photolysis of water by sunlight is an environmentally-friendly preparation technology for renewable energy. Graphitic carbon nitride (g-C₃N₄), despite with obvious catalytic effect, is still unsatisfactory for hydrogen production. In this work, phosphorus element is incorporated to tune g-C₃N₄'s property through calcinating the mixture of g-C₃N₄ and NaH₂PO₂, sacrificial agent and co-catalyst also been supplied to help efficient photocatalytic hydrogen production. Phosphorus (P) doped g-C₃N₄ samples (PCN-S) were prepared, and their catalytic properties were studied. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and ultraviolet diffuse reflection (UV-DRS) were used to study their structures and morphologies. The results show that the reaction rate of PCN-S is 318 μmol·h^-1·g^-1, which is 2.98 times as high as pure carbon nitride nanosheets (CN) can do. Our study paves a new avenue, which is simple, environment-friendly and sustainable, to synthesize highly efficient P doping g-C₃N₄ nanosheets for solar energy conversion.