Synthesis and properties of nanocomposites of WO3 and exfoliated g-C3N4

The nanocomposites of WO₃ nanoparticles and exfoliated graphitized C₃N₄ (g-C₃N₄) particles were prepared and their properties were studied. For this purpose, common methods used for characterization of solid samples were completed with dynamic light scattering (DLS) method and photocatalysis, which are suitable for study of aqueous dispersions.The WO₃ nanoparticles of monoclinic structures were prepared by a hydrothermal method from sodium tungstate and g-C₃N₄ particles were prepared by calcination of melamine forming bulk g-C₃N₄, which was further thermally exfoliated. Its specific surface area (SSA) was 115 m² g⁻¹.The nanocomposites were prepared by mixing of WO₃ nanoparticles and g-C₃N₄ structures in aqueous dispersions acidified by hydrochloric acid at pH = 2 followed by their separation and calcination at 450 °C. The real content of WO₃ was determined at 19 wt%, 52 wt% and 63 wt%. It was found by the DLS analysis that the g-C₃N₄ particles were covered by the WO₃ nanoparticles or their agglomerates creating the nanocomposites that were stable in aqueous dispersions even under intensive ultrasonic field. Using transmission electron microscopy (TEM) the average size of the pure WO₃ nanoparticles and those in the nanocomposites was 73 nm and 72 nm, respectively.The formation of heterojunction between both components was investigated by UV–Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photocatalysis and photocurrent measurements. The photocatalytic decomposition of phenol under the LED source of 416 nm identified the formation of Z-scheme heterojunction, which was confirmed by the photocurrents measurements. The photocatalytic activity of the nanocomposites decreased with the increasing content of WO₃, which was explained by shielding of the g-C₃N₄ surface by bigger WO₃ agglomerates. This study also demonstrates a unique combination of various characterization techniques working in solid and liquid phase.     

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.     

Rational design of MoS2/g-C3N4/ZnIn2S4 hierarchical heterostructures with efficient charge transfer for significantly enhanced photocatalytic H2 production

The rational design of hierarchical heterojunction photocatalysts with efficient spatial charge separation remains an intense challenge in hydrogen generation from photocatalytic water splitting. Herein, a noble-metal-free MoS₂/g-C₃N₄/ZnIn₂S₄ ternary heterostructure with a hierarchical flower-like architecture was developed by in situ growth of 3D flower-like ZnIn₂S₄ nanospheres on 2D MoS₂ and 2D g-C₃N₄ nanosheets. Benefiting from the favorable 2D-2D-3D hierarchical heterojunction structure, the resultant MoS₂/g-C₃N₄/ZnIn₂S₄ nanocomposite loaded with 3 wt% g-C₃N₄ and 1.5 wt% MoS₂ displayed the optimal hydrogen evolution activity (6291 μmol g^?1 h^?1), which was a 6.96-fold and 2.54-fold enhancement compared to bare ZnIn₂S₄ and binary g-C₃N₄/ZnIn₂S₄, respectively. Structural characterizations reveal that the significantly boosted photoactivity is closely associated with the multichannel charge transfer among ZnIn₂S₄, MoS₂, and g-C₃N₄ components with suitable band-edge alignments in the composites, where the photogenerated electrons migrate from g-C₃N₄ to ZnIn₂S₄ and MoS₂ through the intimate heterojunction interfaces, thus enabling efficient electron-hole separation and high photoactivity for hydrogen evolution. In addition, the introduction of MoS₂ nanosheets highly benefits the improved light-harvesting capacity and the reduced H₂-evolution overpotential, further promoting the photocatalytic H₂-evolution performance. Moreover, the MoS₂/g-C₃N₄/ZnIn₂S₄ ternary heterostructure possesses prominent stability during the photoreaction process owing to the migration of photoinduced holes from ZnIn₂S₄ to g-C₃N₄, which is deemed to be central to practical applications in solar hydrogen production.     

构建Bi2O2CO3/g-C3N4异质结光催化完全氧化苯甲醇至苯甲醛

在保证选择性的前提下高效光催化氧化苯甲醇为苯甲醛仍然是当下面临的一个巨大挑战。g-C₃N₄的价带位置适中,具有温和的氧化能力,已被开发用来光催化氧化苯甲醇以保证反应的选择性,但由于其电子空穴复合率高导致反应的转化率难以提升。由于Bi₂O₂CO₃的超薄片层结构不仅可以增加催化剂的比表面积形成更多的活性中心,同时可以形成局部电场,更有效地分离光生电子-空穴对,因此通过构建Bi₂O₂CO₃/g-C₃N₄异质结来加快光生载流子分离进而提升反应速率。其中最优的催化剂可以在反应9 h后使苯甲醇完全氧化为苯甲醛,降低了分离成本。     

S-scheme g-C3N4/TiO2/CFs heterojunction composites with multi-dimensional through-holes and enhanced visible-light photocatalytic activity

A novel multi-dimensional through-holes structure of g-C₃N₄ with adjustable pore size was prepared by controlling the mass ratio of oxamide (OA, structure guiding agent) to urea during one-step calcination process, and a break-rearrangement mechanism was explored. Then, a series of porous g-C₃N₄/TiO₂ (CT) composites with uniformly deposited TiO₂ nanoparticles were prepared based on the multi-dimensional framework by a facile hydrothermal method. The results show that a new S-scheme heterojunction with multi-dimensional through-channel structure was obtained, which is particularly desired for enhancing the visible-light utilization, reducing the carrier recombination rate and enhancing redox capacity. The CT composite obtained at hydrothermal treatment time of 2 h has a specific surface area of 180.15 m² g^-1, which shows high degradation capability (99.99%) for tetracycline hydrochloride (TC·HCl) under 350 W Xe lamp irradiation for 90 min. In addition, CT nanostructures was in-situ growth on carbon fiber (CFs), the degradation rate constant is 0.1566 min^-1, and 90% of the degradation efficiency can be maintained even after 5 consecutive cycles. It is expected to provide an effective reference for solving the problems of recovery difficulty and low reuse rate of powder photocatalytic materials.     

Synthesis and photocatalytic activity of g-C3N4/ZnO composite microspheres under visible light exposure

In this paper, a novel g-C₃N₄/ZnO composite microspheres (CZCM) with enhanced photocatalytic activity under visible light exposure were successfully prepared by a self-assembly method followed by calcination in the air. A hierarchical structure in which ZnO microspheres were closely covered with g-C₃N₄ nanosheets was constructed. The microstructure and photocatalytic activities of the CZCM were characterized. The photocatalytic property of CZCM was evaluated by degrading solution Methyl Orange (MO) and Tetracycline (TC). The effects of varied contents of g-C₃N₄ on the photocatalytic capability of CZCM were systematically investigated and the results show that the optimized CZ-15% sample exhibit much higher photocatalytic degradation efficiency than that of bare g-C₃N₄ or ZnO under identical conditions. The analysis of Photoluminescence (PL) and photocurrent (PC) independently conformed that the photo-induced electron-hole (e^?-h⁺) pairs in the CZCM were effectively generated and responsible for the observed photocatalysis. The enhanced adsorption of visible-light and the effective charge separation on the surface of CZCM enabled significant improvement of photocatalytic performance. According to the experimental results and relative energy band levels of the two semiconductors, a possible photocatalysis mechanism for the reaction process is proposed.     

Construction of g-C3N4 nanotube/Ag3PO4 S-scheme heterojunction for enhanced photocatalytic oxygen generation

Heterojunction engineering is considered as a hopeful approach to ameliorate the separation of photogenerated carriers of photocatalysts, realizing efficient water-splitting performance. In this study, an organic-inorganic S-scheme of a one-dimensional g-C₃N₄ nanotube (TCN)/Ag₃PO₄ photocatalytic system with high photocatalytic water oxidation activity was designed by coupling g-C₃N₄ nanotubes over Ag₃PO₄ particles through a chemical coprecipitation method. The TCN/Ag₃PO₄ heterojunction demonstrated excellent photocatalytic O₂ production with an O₂ evolution rate of up to 370.2 μmol·L^?1·h^?1. X-ray photoelectron spectroscopy analysis showed that electron migration between TCN and Ag₃PO₄ led to the formation of an internal electric field pointing from TCN to Ag₃PO₄, which drove the S-scheme charge transfer mode between TCN and Ag₃PO₄. Accordingly, the TCN/Ag₃PO₄ heterojunction possessed fast charge separation and high redox ability, leading to high photoactivity and photostability. This research provides a new strategy for fabricating highly efficient inorganic-organic S-scheme photocatalysts for O₂ production.     

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.     

Facile one-step synthesis of pellet-press-assisted saddle-curl-edge-like g-C3N4 nanosheets for improved visible-light photocatalytic activity

Graphitic carbon nitride (g-C₃N₄) has attracted increasing interest as a visible-light-active photocatalyst. In this study, saddle-curl-edge-like g-C₃N₄ nanosheets were prepared using a pellet presser (referred to as g-CN P nanosheets). Urea was used as the precursor for the preparation of g-C₃N₄. Thermal polymerization of urea in a pellet form significantly affected the properties of g-C₃N₄. Systematic investigations were performed, and the results for the modified g-C₃N₄ nanosheets are presented herein. These results were compared with those for pristine g-C₃N₄ to identify the factors that affected the fundamental properties. X-ray diffraction analysis and high-resolution transmission electron microscopy revealed a crystallinity improvement in the g-CN P nanosheets. Fourier-transform infrared spectroscopy provided clear information regarding the fundamental modes of g-C₃N₄, and X-ray photoelectron spectroscopy (XPS) peak-fitting investigations revealed the variations of C and N in detail. The light-harvesting property and separation efficiency of the photogenerated charge carriers were examined via optical absorption and photoluminescence studies. The valence band edge and conduction band edge potentials were calculated using XPS, and the results indicated a significant reduction in the bandgap for the g-CN P nanosheets. The Brunauer–Emmett–Teller surface area increased for the g-CN P nanosheets. The photocatalytic degradation performance of the g-CN P nanosheets was tested by applying a potential and using the classical dye Rhodamine B (RhB). The RhB dye solution was almost completely degraded within 28 min. The rate constant of the g-CN P nanosheets was increased by a factor of 3.8 compared with the pristine g-C₃N₄ nanosheets. The high crystallinity, enhanced light absorption, reduced bandgap, and increased surface area of the saddle-curl-edge-like morphology boosted the photocatalytic performance of the g-CN P nanosheets.     

Enhanced photocatalytic hydrogen evolution over TiO2/g-C3N4 2D heterojunction coupled with plasmon Ag nanoparticles

2D heterojunction based on g-C₃N₄ nanosheets with other semiconductor nanosheets is a promising way to improve photocatalytic hydrogen evolution (PHE) activity over g-C₃N₄. However, current 2D heterojunction based on g-C₃N₄ are unsatisfactory due to their insufficient absorption of visible light and inefficient charge separation. In this work, Ag/TiO₂/g-C₃N₄ nanocomposites based on 2D heterojunction coupling with Ag surface plasmon resonance (SPR) were synthesized by a method combining facile wetness impregnation calcination. The PHE activity of Ag/TiO₂/g-C₃N₄ nanocomposites is attributed to the TiO₂/g-C₃N₄ 2D heterojunction and bare g-C₃N₄ nanosheet under visible light irradiation, indicating a cooperative effect between Ag and TiO₂/g-C₃N₄ 2D heterojunction. As a result of SPR effect, the composites strongly absorb visible light. In addition, the oscillating hot electrons from Ag can easily transfer to 2D heterojunction. This synergistic effect lead to sufficient visible light absorption and efficient charge separation of 2D heterojunction, which improved the PHE activity of g-C₃N₄. This work indicates that loading metal nanoparticles on 2D heterojunction as metal SPR-2D heterojunction nanocomposites may be a potential method for harvesting visible light for PHE.     

g-C3N4/ZnCo2O4微球的制备及光催化降解四环素

以ZnCo2O4微球材料为基础材料,采用溶液分散吸附和100 oC下恒温12 h方法制备了g-C3N4负载的ZnCo2O4复合材料,并采用X-射线衍射(XRD)、扫描电镜(SEM)、光电子能谱(XPS)和固体紫外漫反射(Uv-DRS)技术对其进行了表征。ZnCo2O4与g-C3N4之间形成异质结结构,禁带宽度值为1.73 eV。在可见光的照射下,ZnCo2O4的光生电子(e‒)在异质结处的C3N4的离域π键所捕获,有效的促进了ZnCo2O4的光生电子(e‒)和光生空穴(h+)分离,ZnCo2O4的光生空穴(h+)是光催化降解四环素水溶液的主要因素。在可见光下,初始浓度为10 mg/L的四环素水溶液(C22H24N2O8)最高降解率可达到90.02 %。     

BiOCl/g-C3N4异质结催化剂可见光催化还原CO2

以KCl、Bi（NO₃）₃和类石墨氮化碳（g-C₃N₄）为前体,采用水热法成功制备了BiOCl/g-C₃N₄异质结光催化剂,并进行可见光催化还原CO₂,考察了催化剂的活性及稳定性,同时研究BiOCl：g-C₃N₄（摩尔比）、催化剂用量和光照强度对光催化还原CO₂的影响。结果表明,在水蒸气的存在下,BiOCl/g-C₃N₄较纯BiOCl和g-C₃N₄具有更高的光催化还原CO₂活性,在催化剂用量为0.1 g,光照强度为2.413×10^-6 einstein·min^-1·cm^-2,BiOCl：g-C₃N₄摩尔比为1：1的异质结催化剂显示了最高的光催化还原CO₂活性,且可见光催化剂在5次套用实验后其活性基本不变。基于X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、X射线光电子能谱（XPS）、比表面积测试（BET）和紫外-可见（UV-vis）吸收光谱表征,可以推断BiOCl和g-C₃N₄之间形成的p-n结能有效分离光生电子和空穴,是增强光催化剂活性的主要原因。     

Synthesis of novel p-n heterojunction Cu2SnS3/Ti3+-TiO2 for the complete tetracycline degradation in few minutes and photocatalytic activity under simulated solar irradiation

In this research work, p-n heterojunction Cu₂SnS₃/Ti³⁺-TiO₂ photocatalysts were synthesized by using a facile hydrothermal method to degrade tetracycline and produce hydrogen energy. The properties of Cu₂SnS₃/Ti³⁺-TiO₂ was analyzed by using XRD, SEM, TEM, HRTEM, BET, PL and UV–vis characterization. The HPLC-MS and TOC analyzer systems were used to analyze the intermediate products during the photocatalysis deprivation and total organic carbon. The characterizations showed that the addition of self-doped Ti³⁺ and Cu₂SnS₃ into TiO₂ enhanced the material's crystallinity, increased the absorption region from 450 nm to 750 nm, increased the surface area of the material from 234 to 583 m²/g and reduced the recombination of charge carriers. Under visible light irradiation, Cu₂SnS₃/Ti³⁺-TiO₂ exhibited excellent degradation performance and stability. The increase in the efficiency of the material is due to the creation of an internal electric field induced by the p-n heterojunction and reduction in the bandgap of the material, which efficiently reduced the rate of recombination, increased the surface area for light absorption and increased the transfer of charge carriers. The Cu₂SnS₃/Ti³⁺-TiO₂ photocatalyst degraded 100 % tetracycline and produced 510 μmol/hg hydrogen energy. The Cu₂SnS₃/Ti³⁺-TiO₂ composite exhibited good stability even after six cycles Cu₂SnS₃/Ti³⁺-TiO₂ degraded 98–99 % TC under visible light irridiation. The efficiency of Cu₂SnS₃/Ti³⁺-TiO₂ was also analyzed in the outdoor environment, confirming that this material can be effectively used in practical applications.     

g-C_3N_4/BiVO_4复合光催化剂的制备与光催化性能研究

通过原位复合的方法制备不同配比的g-C3N4/BiVO4复合光催化剂,利用傅里叶红外光谱(FTIR)、X-射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、紫外-可见光漫反射光谱(UV-Vis DRS)和N2吸附-脱附对所制备的材料进行表征。并通过光催化降解有机染料罗丹明B对其光催化活性进行测试。结果表明,部分g-C3N4附着在BiVO4表面,g-C3N4/BiVO4复合光催化剂比纯的BiVO4光催化效果要好,并且确定了最佳复合比例,同时对复合光催化剂性能提高的机理进行了讨论。     

Investigation of g-C3N4/ZnAl2O4 and ZnO/ZnAl2O4 nanocomposites: From synthesis to photocatalytic activity of pollutant dye model

The fabrication of nanocomposite photocatalytsts with excellent photocatalytic activity is an important step in the improved degradation of organic dyes. A series of nanocomposite photocatalysts was synthesized with g-C₃N₄ and ZnO loading contents of 10, 20 and 30%. The nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). The optical band gaps of g-C₃N₄, ZnO and ZnAl₂O₄ were about 2.79, 3.21 and 3.55 eV, respectively. Methylene blue (MB) was degraded over the prepared photocatalysts under UV irradiation. Photocatalytic activity was about 9.1 and 9.6 times higher, respectively, on 20%g-C₃N₄/ZnAl₂O₄ and 20%ZnO/ZnAl₂O₄ nanocomposite photocatalysts than on pure ZnAl₂O₄ spinel powders. Recycling experiments showed that 20%g-C₃N₄/ZnAl₂O₄ and 20%ZnO/ZnAl₂O₄ nanocomposite photocatalysts exhibited good stability after five cycles of use.     

g-C3N4-CdS-NiS2复合纳米管的制备及可见光催化分解水制氢

光生电子-空穴对的快速复合是导致半导体光催化剂性能不佳的重要因素之一,构建异质结是分离光生电子-空穴对的有效方法。结合热缩合和两步水热反应构建了g-C₃N₄-CdS-NiS₂复合纳米管,并进一步研究了在可见光照射下不同CdS含量的g-C₃N₄-CdS-NiS₂分解水制氢的光催化性能。结果表明,当CdS含量为10%(质量)时,三元复合物的产氢速率最高(50.9 μmol·h^-1),是纯g-C₃N₄纳米管的25倍,是g-C₃N₄-CdS和g-C₃N₄-NiS₂二元复合物的11倍。而且,经过五次循环光催化反应后,产氢速率保持不变。光催化制氢性能的提高主要源于g-C₃N₄、CdS与NiS₂形成的异质结促进光生电子和空穴的迁移及电子-空穴对的分离。     

Preparation and photocatalytic activity of g-C3N4/TiO2 heterojunctions under solar light illumination

The solar light sensitive g-C₃N₄/TiO₂ heterojunction photocatalysts containing 20, 50, 80, and 90 wt% graphitic carbon nitride (g-C₃N₄) were prepared by growing Titania (TiO₂) nanoparticles on the surfaces of g-C₃N₄ particles via one step hydrothermal process. The hydrothermal reactions were allowed to take place at 110 °C at autogenous pressure for 1 h. Raman spectroscopy analyses confirmed that an interface developed between the surfaces of TiO₂ and g-C₃N₄ nanoparticles. The photocatalyst containing 80 wt% g-C₃N₄ was subsequently heat treated 1 h at temperatures between 350 and 500 °C to improve the photocatalytic efficiency. Structural and optical properties of the prepared g-C₃N₄/TiO₂ heterojunction nanocomposites were compared with those of the pristine TiO₂ and pristine g-C₃N₄ powders. Photocatalytic activity of all the nanocomposites and the pristine TiO₂ and g-C₃N₄ powders were assessed by the Methylene Blue (MB) degradation test under solar light illumination. g-C₃N₄/TiO₂ heterojunction photocatalysts exhibited better photocatalytic activity for the degradation of MB than both pristine TiO₂ and g-C₃N₄. The photocatalytic efficiency of the g-C₃N₄/TiO₂ heterojunction photocatalyst heat treated at 400 °C for 1 h is 1.45 times better than that of the pristine TiO₂ powder, 2.20 times better than that of the pristine g-C₃N₄ powder, and 1.24 times better than that of the commercially available TiO₂ powder (Degussa P25). The improvement in photocatalytic efficiency was related to i) the generation of reactive oxidation species induced by photogenerated electrons, ii) the reduced recombination rate for electron-hole pairs, and iii) large specific surface area.