Two-dimensional/two-dimensional Z-scheme photocatalyst of graphitic carbon nitride/bismuth vanadate for visible-light-driven photocatalytic synthesis of imines

As an environmentally friendly strategy, photocatalytic synthesis of imines via selective oxidation of amines has inspired numerous interests. In comparison to conventional type-II heterojunction, the photogenerated electrons and holes on a Z-scheme photocatalyst has strong redox ability. Herein, we prepared a two-dimensional/two-dimensional (2D/2D) Z-scheme photocatalyst of graphitic carbon nitride nanosheet/bismuth vanadate (CNNS/BVO) with a large two-phase interface, which is favorable for the transfer and separation of photoexcited charge carriers. For selective oxidation of benzylamine to N-benzylidenebenzylamine under oxygen atmosphere and visible light irradiation, the CNNS/BVO showed much higher activity than the single CNNS and BVO. The optimized nanocomposite photocatalyst with a 50% CNNS/BVO mass ratio presented a high conversion (~96%) and selectivity (~99%) in 6 h oxidative coupling reaction of benzylamine. More importantly, this 2D/2D CNNS/BVO photocatalyst has good cycling stability, as well as universality for different benzylamine derivatives. Based on the experimental results, a Z-scheme mechanism was determined, where photoinduced electrons were accumulated on the conduction band (CB) of CNNS that is higher than that of BVO and holes were collected on the valence band (VB) of BVO that is lower than that of CNNS. Further, superoxide radicals and photogenerated holes are examined to the mainly active species for selective oxidation of benzylamine, and a possible reaction pathway was therefore proposed. This study demonstrates that the Z-scheme 2D/2D CNNS/BVO with high redox ability is an efficient photocatalyst for the imine synthesis.     

Facile synthesis of Y-doped graphitic carbon nitride with enhanced photocatalytic performance

Yttrium-doped graphitic carbon nitride (Y/g-C₃N₄) catalysts were prepared via a facile pyrolysis method with urea used as a precursor and yttrium nitrate as the Y source. Characterization results show that an appropriate doping ratio of Y can be embedded into in-planes of g-C₃N₄. The Y/g-C₃N₄ catalysts are characterized by hierarchical porosity, large specific surface area, and large pore volume. Introduction of Y species effectively extends the spectral response of g-C₃N₄ from ultraviolet to visible region and decelerates the recombination of photogenerated electrons and holes. Because of these properties, the Y/g-C₃N₄ catalysts show an enhanced photocatalytic performance in rhodamine B degradation under visible light.     

Zinc oxide quantum dots/graphitic carbon nitride nanosheets based visible-light photocatalyst for efficient tetracycline hydrochloride degradation

Journal of Porous Materials - A simple liquid phase self-assembly method was successfully developed to prepare 0D/2D nanocomposites based on ZnO QDs/g-C3N4 nanosheets. The structural...     

硫酸根改性g-C3N4制备与催化性能研究

采用酸水热后处理法制备了具有优异光催化合成双氧水性能的硫酸根改性石墨相氮化碳纳米棒催化剂。采用XRD、N2吸附脱附、UV-Vis、FTIR、SEM、XPS、TPD、EIS及PL对催化剂进行表征。结果显示：硫酸根的引入改变了催化剂的结构性质，光学性质和氧气吸附能力。所制备的硫酸根改性氮化碳催化剂的双氧水平衡浓度为2.7 mmol/L，是纯氮化碳的2.7倍。     

Tailoring the bandgap of N-rich graphitic carbon nitride for enhanced photocatalytic activity

Nitrogen - rich graphitic carbon nitride (Ng-C₃N₄) with improved photocatalytic activity was engineered using a facile post-annealing treatment of pristine g-C₃N₄ in N₂ atmosphere. The thermal annealing did not modify the crystal structure, vibrational modes, or morphology of the N-rich g-C₃N₄ (Ng-C₃N₄). However, it decreased the crystallinity by broadening the dominant X-ray diffraction (XRD) peak and increased the surface area and mesoporous nature because of the formation of carbon vacancies. Diffuse reflectance spectroscopy indicated that the bandgap of the annealed Ng-C₃N₄ decreased from 2.82 to 2.77 eV compared to pristine g-C₃N₄. The increase of nitrogen content in the annealed Ng-C₃N₄ was quantified by X-ray photoelectron spectroscopy (XPS), which was also used to examine the formation of carbon vacancies. Photocurrent and electrochemical impedance spectroscopy measurements showed that the annealed Ng-C₃N₄ had higher light absorption capacity than the pristine g-C₃N₄. The photocatalytic performance of the samples was investigated for the degradation of crystal violet (CV) under ultra-violet light irradiation. The annealed Ng-C₃N₄ sample exhibited superior photodegradation of CV over pristine g-C₃N₄.     

Direct microwave synthesis of graphitic C3N4 with improved visible-light photocatalytic activity

The graphitic carbon nitride (g-C₃N₄) was rapidly synthesized via direct high-energy microwave heating approach. During the preparation process, only low-cost melamine and artificial graphite powders were used, without any metal catalysts or inert protective gas. The microstructure was investigated by using X-ray diffraction (XRD), Flourier transformed infrared (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM). The spectra of XRD and HRTEM indicated that the obtained g-C₃N₄ had a high crystallinity. The optical spectra covering Photoluminescence (PL) and Ultraviolet-visible (UV–vis) were also measured at room temperature. PL peak and UV–vis absorption edge of the g-C₃N₄ were shown at 455 nm and 469 nm, respectively, indicating visible-light photocatalytic property. Finally, the photocatalytic activity of g-C₃N₄ was investigated and evaluated as photocatalyst for the photo-degradation of Rhodamine B (RhB) and Methyl Orange (MO) in aqueous solution under visible-light (λ>420 nm) irradiation, respectively. Results indicated that the g-C₃N₄ sample displayed an excellent performance of removing of RhB and MO due to the improved crystallinity and large surface area of 126 m²/g. After the visible-light photocatalytic reaction for 40 min, the decolorization ratios of RhB and MO reached up to 100% and 94.2%, respectively.     

Tetraethylorthosilicate induced preparation of mesoporous graphitic carbon nitride with improved visible light photocatalytic activity

Mesoporous graphitic carbon nitride (mg-C₃N₄) has been prepared by the in situ formed silica from tetraethylorthosilicate (TEOS) as a mesoporous template. The resultant mg-C₃N₄ possessed a large surface area (152 m² g^− 1), and enhanced photodegradation performance for Rhodamine B pollutant when energized with visible light. Moreover, mg-C₃N₄ also exhibited good stability after three recycles. The significant enhancement in photodegradation activity over mg-C₃N₄ catalyst could be ascribed to the large surface area, high adsorption ability to dye and enhanced separation efficiency of photogenerated electron-hole pairs. The simple strategy for the fabrication of mg-C₃N₄ may facilitate its wide applications in various fields.     

硫酸胍制备多孔石墨型氮化碳及其光催化降解苯酚

为了增加比表面积和提高催化活性,一种无毒和易得的前驱体硫酸胍被首次用于制备石墨型氮化碳(g-C_3N_4)。用X射线粉末衍射、红外光谱、扫描电镜、透射电镜、N_2吸附-脱附、光电子能谱、紫外-可见光吸收光谱和荧光光谱对所得多孔g-C_3N_4进行表征。与由三聚氰胺为前驱体制备的体相g-C_3N_4相比,硫酸胍为前驱体制备的多孔g-C_3N_4具有更高的比表面积、发达的孔结构和较好的光电性能。以光催化降解苯酚为模型反应考察催化剂性能,结果表明,所得多孔g-C_3N_4的催化活性明显高于体相g-C_3N_4。优异的光催化性能和简单的合成方法使硫酸胍制备的多孔g-C_3N_4可广泛用于环境和能源领域。     

Explosive thermal exfoliation of intercalated graphitic carbon nitride for enhanced photocatalytic degradation properties

Dicyandiamide derived graphitic carbon nitride (g-C₃N₄) was chemically intercalated by concentrated H₂SO₄ firstly, followed by a rapid heating treatment. Molecules between the stacking layers of g-C₃N₄ produced an explosive effect upon rapid heating to thermally exfoliate g-C₃N₄ into porous structures. The appearance color of g-C₃N₄ changed from light yellow to grey after heating treatment indicating the enhanced light absorption properties, which were identified by the UV–vis absorption test. In addition, photoluminescence intensities of porous g-C₃N₄ were obviously suppressed compared to those of bulk g-C₃N₄ samples, indicating the prevention of the recombination process of photogenerated electron-hole pairs. As a result of these simultaneous modifications in texture, optical and electronic properties, the photodegradation kinetics of crystal violet on the catalyst surface can be improved by 4.75 times.     

An investigation on the graphitic carbon nitride reinforced polyimide composite and evaluation of its tribological properties

This article presented a novel application for the graphitic carbon nitride (g‐C₃N₄), which was used as nanofillers to improve the tribological properties of polyimide (PI). The composite based on PI and g‐C₃N₄ was prepared by mechanical mixing process and hot compression molding process. The characterizations of g‐C₃N₄ and PI/g‐C₃N₄ composites were investigated by Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, and scanning electron microscopy. Friction and wear tests were carried out using UMT‐2 reciprocating tribo‐tester against stainless steel ball under dry friction. The results showed that the amount of g‐C₃N₄ was decisive to the tribological properties of PI/g‐C₃N₄ composites. The optimal tribological properties occurred when the amount of g‐C₃N₄ was 10 wt %, which showed the smallest friction coefficient and the lowest wear rate. Furthermore, this work provided an example of application for the g‐C₃N₄ as the excellent nanofiller in polymer matrix composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45403.     

Synthesis and photocatalytic H2-production activity of plasma-treated Ti3C2Tx MXene modified graphitic carbon nitride

Plasma processing technology, as a promising method to enhance photocatalytic activity of catalyst, is gradually attracting extensive interest from researchers. However, the main mechanism of plasma-treated photocatalyst on hydrogen production is not clear. In this work, 2D Ti₃C₂T_x MXene is selected as a co-catalyst of graphitic carbon nitride (g-C₃N₄), which carries out a plasma treatment (500°C) under N₂/H₂ atmosphere. Due to plasma treatment, there is a higher proportion Ti–O functional groups on surface of layered Ti₃C₂T_x MXene, especially for Ti⁴⁺. The obtained g-C₃N₄/p-Ti₃C₂T_x photocatalyst with sandwich-like structure shows an enhanced photocatalytic activity. The rate of hydrogen generation of CN/pTC3.0 sample without Pt co-catalyst is 25.4 and 2.4 times that of pure g-C₃N₄ and CN/TC3.0 samples, respectively. The improved photocatalytic activity is attributed to presence of Ti⁴⁺ due to plasma treatment, which can capture photo-induced electron from g-C₃N₄ and improve the separation of electrons and holes after visible light irradiation. The cyclic hydrogen production of the photocatalyst demonstrates good photocatalytic stability. In addition, this method of plasma treatment under N₂/H₂ atmosphere is feasible to develop a high-performance co-catalyst, which can be extended to other photocatalysts with two-dimensional structure for photocatalytic water-splitting applications.     

氨基修饰片状氮化碳的制备及光催化性能

石墨相氮化碳是一种低成本易获得的可见光响应光催化剂,但由于比表面积小、光生载流子易复合等缺点限制了其应用。为克服传统氮化碳的缺陷,本实验以尿素和三聚氰胺为原料,通过水热预处理改性前体,再用高温煅烧法成功制备出氨基修饰片状氮化碳光催化材料。并通过X射线衍射（XRD）、扫描电子显微镜（SEM）和X射线光电子能谱仪（XPS）等手段对样品的晶格结构和形貌特征等进行表征。结果表明,成功引入氨基基团的片状氮化碳,比表面积增加且光生载流子复合率显著降低。以罗丹明B和壬基酚溶液的光降解考察材料光催化性能,发现氨基修饰片状氮化碳对其去除率分别为80.69%和50.7%,分别是传统块状氮化碳的2.45倍和2.19倍,是未修饰片状氮化碳的1.26倍和1.21倍。且氨基修饰片状氮化碳材料重复使用5次后仍具有较高光催化活性,光催化性能显著提高。     

Enhanced mechanical and photocatalytic performances of epoxy nanocomposites filled with potassium-modified graphitic carbon nitride nanosheets

The unique structure and property of K⁺-modified graphitic carbon nitride (K-CN) nanosheets would be beneficial for developing advanced epoxy nanocomposites. However, the compatibility between K-CN nanosheets and epoxy matrix is a big challenge. In this study, we demonstrate a new and effective method to improve the compatibility of K-CN nanosheets and epoxy by using 1-(oxiran-2-ylmethyl)-1H-indole (IN) as surface modifier through the cation-π interaction between K⁺ on the surface of K-CN nanosheets and indole group of IN. In addition, the covalent bond between epoxy group of IN and amino group of curing agent could be used to participate in the formation of the epoxy network. When the content of K-CN nanosheets is 0.5 wt%, the tensile strength of prepared epoxy nanocomposites increases by 60.7% and extensibility of prepared epoxy nanocomposites increases by 53.4% compared to neat epoxy resin. In addition, the prepared epoxy nanocomposites are used as efficient reusable photocatalysts for degradation of methylene blue (MB). The efficiency of MB degradation is 98% within 60 min. This work opens up a new avenue to fabricate high-performance epoxy nanocomposites with multifunctional properties for advanced engineering applications.     

Controlled synthesis of high performance carbon/zeolite T composite membrane materials for gas separation

A simple approach has been developed to synthesize the carbon/zeolite T composite membrane materials with the high gas separation performance. The precursors of the composite membrane are composed of polyimide matrix and dispersed zeolite T particles. The composite membranes prepared by pyrolysis at 973 K show excellent gas (H₂, CO₂, O₂, N₂, and CH₄) permeability and selectivity (O₂/N₂, CO₂/CH₄) for both single gas and mixed-gas. The gas separation performance of the composite membranes can be controlled in a wide range by only changing the zeolite T particle size. The maximum selectivity of O₂ over N₂ (21/79 mol%) for the composite membranes with the least zeolite T particle (0.5 μm) is 15 with an O₂ permeability of 347 Barrers (1 Barrer = 7.5 × 10⁻¹⁸ m² s⁻¹ Pa⁻¹) and the selectivity of CO₂ over CH₄ (50/50 mol%) reaches a value of 179 with a CO₂ permeability of 1532 Barrers. It is believed that the increase of gas permeability is attributed to the ordered microchannels in the zeolite and the interfacial gaps formed between zeolite and carbon matrix in the composite membranes. And the gas selectivity is tuned by the size of interfacial gaps which are varied with the zeolite particle size. This technique will provide a simple and convenient route to efficiently improve the trade-off relationship between the permeability and the selectivity and enable the construction of carbon-based composite materials with novel functionalities in membrane science.     

Synthesis of Mo-doped graphitic carbon nitride catalysts and their photocatalytic activity in the reduction of CO2 with H2O

Molybdenum doped graphitic carbon nitride (g-C₃N₄) catalysts were prepared by a simple pyrolysis method using melamine and ammonium molybdate as precursors. The characterization results indicated that the obtained Mo-doped g-C₃N₄ catalysts had worm-like mesostructures with higher surface area. Introduction of Mo species can effectively extend the spectral response property and reduce the recombination rate of photogenerated electrons and holes. CO₂ photocatalytic reduction tests showed that the Mo-doped g-C₃N₄ catalysts exhibited considerably higher activity (the highest CO and CH₄ yields of 887 and 123 μmol g^− 1-cat., respectively, after 8 h of UV irradiation.) compared with pure g-C₃N₄ from melamine.     

Ag/g-C3N4 photocatalysts: Microwave-assisted synthesis and enhanced visible-light photocatalytic activity

Ag/g-C₃N₄ photocatalysts were synthesized by a rapid microwave-assisted polyol process. The characterization results showed monodisperse Ag nanoparticles with diameters of a few nanometers closely attached to the edges of g-C₃N₄. The presence of Ag nanoparticles in Ag/g-C₃N₄ photocatalysts enhanced the visible-light absorption and suppressed the recombination of photogenerated electron/hole pairs. The Ag/g-C₃N₄ photocatalysts exhibited the superior visible-light responsive photocatalytic activity for rhodamine B degradation. The mechanism of visible-light induced photocatalysis over Ag/g-C₃N₄ photocatalysts was also discussed.     

可见光催化剂N/TiO2的制备及其光催化活性

对TiO2光催化剂进行改性,提高它的可见光活性。以钛酸四丁酯为前驱物,采用水解沉淀法制备了N/TiO2光催化剂,并采用X射线衍射(XRD)、红外光谱分析(FT-IR)、紫外-可见漫反射(UV-Vis)等方法对样品进行了表征,以活性红紫为模型污染物,考察了N掺杂量、焙烧温度等制备条件对N/TiO2粉体光催化活性的影响。结果表明:当氨水投加量为20 mL时,在500℃下焙烧1 h制得的催化剂具有最高的光催化活性;同样条件下,其催化活性约为市售普通的Degussa P25 TiO2的1.5倍,N/TiO2光催化剂在可见光范围内对活性红紫的降解具有很好的应用前景。     

Novel mesoporous NiO/HTiNbO5 nanohybrids with high visible-light photocatalytic activity and good biocompatibility

Mesoporous nanohybrids of NiO nanoparticles and HTiNbO(5) nanosheets have been successfully synthesized by first exfoliating layered HTiNbO(5) in tetrabutylammonium hydroxide (TBAOH) to obtain HTiNbO(5) nanosheets, then reassembling with a nickel precursor and finally heating with urea. The resulting samples were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, photoluminescence spectroscopy (PL) and N(2) adsorption-desorption measurements. It was found that the as-prepared nanohybrids had a relatively large interlayer spacing of 1.05 nm. After calcination, the titanoniobate nanosheet was still retained and the pore size of the resulting nanohybrids became larger. Compared with the original HTiNbO(5), the obtained nanohybrids were mesoporous with a greatly expanded surface area (～75-115 m(2) g(-1)), a much strengthened absorption in the UV light region and a visible-light response. Nickel atoms were present in the form of Ni-O in the nanohybrid, and NiO nanoparticles were homogeneously distributed with an average particle size of 2-3 nm, giving rise to the visible light response. The catalytic activities of the obtained samples were evaluated by the photodegradation of RhB solution under visible light irradiation. The introduction of urea during the calcination process not only increased the thermal stability and surface area, but also decreased the rate of recombination of photogenerated holes and electrons, leading to a greatly enhanced photocatalytic activity of the resulting nanohybrids. The dye molecules were mainly degraded to aliphatic organic compounds and partially mineralized to CO(2) and/or CO, rather than being simply decolorized. In addition, cell viability results for HepG2 cells show that the as-prepared sample have good biocompatibility.     

纳米AlN增强C/C复合泡沫材料制备及机理研究

融合韧带网络型泡沫炭与微球型泡沫炭的结构特点,并结合同质复合材料与异质复合材料的互补优点,用填充了纳米AlN的酚醛树脂胶作韧带网络将酚醛树脂微球六角密排,再经过炭化、石墨化处理,成功地制备了纳米AlN/C复合泡沫样品。对该样品进行扫描电镜和X射线衍射测试,结果表明生成的直径在400～500 nm范围的炭纤维和尺寸在150～200 nm之间的纳米AlN颗粒共同增强韧带网络。同时,对纳米AlN增强C/C复合泡沫材料的机理进行了分析解释。