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.     

ZIF衍生多孔碳纳米纤维用于高效电容去离子的研究

作为一种环保节能的新兴脱盐技术,电容去离子技术正在成为替代反渗透脱盐和电渗析脱盐的一项重要的脱盐技术。各种碳基材料被广泛地应用于电容去离子电极材料的研究,然而大多数碳基材料为粉末状材料,需要添加黏结剂,这必将导致电极材料电吸附能力的下降。利用静电纺丝技术,将ZIF纳米颗粒和聚丙烯腈混纺,并通过分段高温热处理过程,成功合成了具有柔性结构的整体性多孔碳纳米纤维。由于其具有孔道结构的分级分布和较强的亲水性等优良特性,所制得的多孔碳纳米纤维在1.2 V电压下于500 mg/L NaCl溶液中表现出良好的电吸附性能,脱盐量达到了19.92 mg/g,比普通碳纳米纤维提高了一倍以上。     

Graphitic carbon nanofibers developed from bundles of aligned electrospun polyacrylonitrile nanofibers containing phosphoric acid

Graphitic carbon nanofibers (GCNFs) with diameters of approximately 300 nm were developed using bundles of aligned electrospun polyacrylonitrile (PAN) nanofibers containing phosphoric acid (PA) as the innovative precursors through thermal treatments of stabilization, carbonization, and graphitization. The morphological, structural, and mechanical properties of GCNFs were systematically characterized and/or evaluated. The GCNFs made from the electrospun PAN precursor nanofibers containing 1.5 wt.% of PA exhibited mechanical strength that was 62.3% higher than that of the GCNFs made from the precursor nanofibers without PA. The molecules of PA in the electrospun PAN precursor nanofibers initiated the cyclization and induced the aromatization during stabilization, as indicated by the FT-IR and TGA results. The stabilized PAN nanofibers possessed regularly oriented ladder structures, which facilitated the further formation of ordered graphitic structures in GCNFs during carbonization and graphitization, as indicated by the TEM, XRD, and Raman results.     

Towards high purity graphene/single-walled carbon nanotube hybrids with improved electrochemical capacitive performance

CoMgAl layered double hydroxides were prepared as catalysts for the in situ synchronous growth of graphene and single-walled carbon nanotubes (SWCNTs) from methane by chemical vapor deposition. The as-calcined CoMgAl layered double oxide (LDO) flakes served as the template for the deposition of graphene, and Co nanoparticles (NPs) embedded on the LDOs catalyzed the growth of SWCNTs. After the removal of CoMgAl LDO flakes, graphene (G)/SWCNT/Co₃O₄ hybrids with SWCNTs directly grown on the surface of graphene and 27.3 wt.% Co₃O₄ NPs encapsulated in graphene layers were available. Further removal of the Co₃O₄ NPs by a CO₂-oxidation assistant purification method induced the formation of G/SWCNT hybrids with a high carbon purity of 98.4 wt.% and a high specific surface area of 807.0 m²/g. The G/SWCNT/Co₃O₄ hybrids exhibited good electrochemical performance for pseudo-capacitors due to their high Co₃O₄ concentration and the high electrical conductivity of SWCNTs and graphene. In another aspect, the G/SWCNT hybrids can be used as excellent electrode materials for double-layer capacitors. A high capacity of 98.5 F/g_electrode was obtained at a scan rate of 10 mV/s, 78.2% of which was retained even when the scan rate increased to 500 mV/s.     

Enhanced capacitive deionization of graphene/mesoporous carbon composites

Capacitive deionization (CDI) with low-energy consumption and no secondary waste is emerging as a novel desalination technology. Graphene/mesoporous carbon (GE/MC) composites have been prepared via a direct triblock-copolymer-templating method and used as CDI electrodes for the first time. The influences of GE content on the textural properties and electrochemical performance were studied. The transmission electron microscopy and nitrogen adsorption-desorption analysis indicate that mesoporous structures are well retained and the composites display improved specific surface area and pore size distribution, as well as pore volume. Well dispersed GE nanosheets are deduced to be beneficial for enhanced electrical conductivity. The electrochemical performance of electrodes in an NaCl aqueous solution was characterized by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements. The composite electrodes perform better on the capacitance values, conductive behaviour, rate performance and cyclic stability. The desalination capacity of the electrodes was evaluated by a batch mode electrosorptive experiment and the amount of adsorbed ions can reach 731 μg g(-1) for the GE/MC composite electrode with a GE content of 5 wt%, which is much higher than that of MC alone (590 μg g(-1)). The enhanced CDI performance of the composite electrodes can be attributed to the better conductive behaviour and higher specific surface area.     

聚合氮化碳的制备、改性及光催化还原二氧化碳性能研究

由过量二氧化碳（CO₂）排放导致的温室效应使得全球气候变暖问题日益紧迫,在“双碳”背景下,如何资源化利用CO₂尤为重要。光催化还原CO₂生成化学品和燃料是有望同时解决能源危机和环境问题的途径。非金属半导体聚合氮化碳（PCN）具有可见光响应、化学稳定性高、易于制备等优点,在光催化领域备受关注,但由传统热聚合方法得到的PCN存在比表面积小、电子-空穴对复合严重、对可见光吸收范围窄等不足之处。介绍了光还原CO₂的反应机理和PCN的结构,总结了PCN的制备方法以及提升其光还原CO₂性能的手段,包括形貌调控、异原子掺杂、缺陷工程和构建异质结等。最后,对目前PCN材料在CO₂光还原反应研究中存在的问题进行了分析,并对未来发展方向进行了展望。     

石墨相氮化碳的可控制备及其在能源催化中的应用

石墨相氮化碳（g-C₃N₄）具有独特的电子结构和化学特性,作为非金属催化剂,近年来尤其在清洁和可持续能源领域显示了光明的应用前景,引起了相关领域研究人员的广泛关注。综述了g-C₃N₄纳米材料的可控制备及其在氧还原、光催化分解水制氢、二氧化碳还原、光固氮等能源催化重要方面的国内外近期进展,并讨论了此领域中的关键问题和未来的发展趋势。     

The characterization and application of p-type semiconducting mesoporous carbon nanofibers

The microstructures of mesoporous carbon nanofibers were characterized by scanning electron microscopy, transmission electron microscopy, nano-Raman, nitrogen adsorption-desorption and optical transmission. They possessed a high specific surface area 840 m² g⁻¹ and a 1.07 eV band gap. All mesoporous carbon nanofiber network can act as the channel material in p-type field-effect transistor devices with field-effect mobilities over 10 cm²/V s. Furthermore, mesoporous carbon nanofiber network exhibits better sensitivity and faster response to NO₂ gas than that of carbon nanotubes, which makes it a promising candidate as poisonous gas sensing nanodevices.     

Selective silver ion adsorption onto mesoporous graphitic carbon nitride

A 3D cubic structure of mesoporous graphitic carbon nitride (3D-g-CN) was fabricated by nano casting using the mesoporous silica hard template KIT-6. The abundant intrinsic amine functionalities of 3D-g-CN were applied as a selective adsorbent for silver ions using the unique affinity of silver and amine functionalities. The large surface area of 3D-g-CN resulted in increased amine functionalities at the surface and enabled it to form complexes with silver ions. As a result, almost 400 mg/g of silver ion could be removed from 100 mM of initial solution at 293.15 K. The isotherm of silver ion adsorption onto 3D-g-CN was described by the Freundlich and Sips models and indicated heterogeneity of the adsorbent surface. Thermodynamic parameters determined from temperature dependent isotherms were verified by the endothermic silver ion adsorption process of 3D-g-CN. The adsorption capacity of silver ion on 3D-g-CN was maintained during several reuses without a significant decrease in capacity. Overall, the results indicate that 3D-g-CN has intrinsic amine functional groups with a large surface area and could therefore be utilized as an efficient selective adsorbent of silver ions for water purification.     

Graphitic carbon nitride materials synthesized via reactive pyrolysis routes and their properties

The present article describes the large-scale powder syntheses of high nitrogen-content graphitic carbon nitride materials with unique belt-like or tubular morphologies via reactive pyrolysis of two molecular precursors, melamine and cyanuric chloride. The structural characterizations based on XRD indicate the presence of turbostratic ordering in the graphene layers of carbon nitride. Spectroscopic analyses via FTIR technique are consistent with the layered structure with sp²-hybridized bonding features. Morphological investigations via SEM and TEM reveal the elaboration of micron-sized tubular hollow vessels. The optical properties of the prepared samples are investigated via UV absorption and PL spectroscopy, which exhibit the semiconductor-like absorption edge at 2.7 to 2.8 eV and a well-defined PL emission band at 425 nm.     

Porous boron nitride nanofibers/PVA hydrogels with improved mechanical property and thermal stability

Polyvinyl alcohol (PVA) hydrogel is a promising material possessing good chemical stability, high water absorption, excellent biocompatibility and biological aging resistant. However, the poor mechanical performance of PVA hydrogel limits its applications. Here we report the utilization of one-dimensional (1D) BN nanofibers (BNNFs) as nanofillers into PVA matrix to prepare a novel kind of BNNFs/PVA composite hydrogel via a cyclic freezing and thawing method. For comparison, the composite hydrogels using spherical BN nanoparticles i.e. BN nanospheres (BNNSs) as fillers were also prepared. The mechanical properties, thermal stabilities and swelling behaviors of the composite hydrogels were investigated in detail. Our study indicates that the mechanical properties of the hydrogels can be improved by adding of BNNFs. After loading of BNNFs into PVA with content of 0.5?wt%, the compressive strength of the composite hydrogel increases by 252% compared with that of pure PVA hydrogel. The tensile performance of BNNFs/PVA composite hydrogels has also been improved. Impressive 87.8% increases in tensile strengths can be obtained with 1?wt% BNNFs added. In addition, with the increase of BNNFs content, the thermal stability and the swelling ratio of hydrogels are increased gradually. The swelling ratio of hydrogel increases by 56.3% with only 1?wt% BNNFs added. In comparison, the improvement effects of the BNNS fillers on the mechanical strengths and swelling ratios are much weaker. The enhanced effects of BNNFs can be ascribed to the strong hydrogen bond interaction between BNNFs and PVA. The high aspect ratios of the nanofibers should also be took into account.     

Graphitic mesoporous carbon as a support of promoted Rh catalysts for hydrogenation of carbon monoxide to ethanol

Graphitic mesoporous carbon (GMC), prepared through high-temperature graphitization of soft-templated amorphous mesoporous carbon (AMC), was used as the support for Mn, Li, and Fe triple-promoted Rh catalysts for CO hydrogenation to ethanol. The use of GMC results in C₂H₅OH selectivity and formation rate comparable to nonporous SiO₂ support along with a significant inhibition on the formation of undesired CH₄ and light hydrocarbons at the expense of appreciable amounts of CO₂ produced. The better catalytic performance of promoted-Rh/GMC than those supported on other carbon allotropes (AMC and non-porous graphitic carbon black) seems to be associated with the specific graphitic structure and mesoporosity of GMC. The surface modification of GMC by wet oxidation leads to considerable increases in C₂H₅OH selectivity and formation rate. The modified GMC as a support shows substantially greater CO₂-free selectivity for C₂H₅OH than the SiO₂.     

Carbon/carbon-boron nitride composites with improved wear resistance compared to carbon/carbon

This paper describes the fabrication of a carbon fiber reinforced/carbon-boron nitride (C/C-BN) hybrid matrix composite for possible use in aircraft brakes. These composites were fabricated via liquid infiltration of a liquid crystalline borazine oligomer into a low-density carbon fiber/carbon matrix (C/C) composite. The friction and wear properties of the C/C-BN were explored over the entire energy spectrum for aircraft braking using an inertial brake dynamometer. The C/C-BN composites with densities of 1.55 g/cc displayed wear rates 50% lower than values observed with C/C samples with densities of approximately 1.75-1.8 g/cc. This includes the near elimination of wear from 300 to 600 kJ/kg, which represents the normal landing regime for aircraft brakes. This encouraging behavior is attributed in part to the improved oxidation resistance of the BN at high energy levels and the ability of the BN to facilitate formation of a stable wear film at lower energy levels. The coefficient of friction, while being slightly lower than the values for C/C, appeared much less sensitive to changes in energy level.     

Amorphous SiCNO hollow nanofibers with mesoporous walls

In this work, for the first time, we reported the fabrication of polymer-derived amorphous SiCNO ceramics via electrospinning of tetraethoxysilane (TBOS), polyvinylpyrrolidone (PVP), cetrimonium bromide (CTAB), and urea combined with subsequent air calcination. The resultant products exhibited a well-defined one-dimensional (1D) hollow fiber nanostructure with mesoporous walls. The BET surface area of SiCNO hollow nanofibers is ~95.6 m²/g, and the average pore diameter is sized in ~9 nm. The movement of urea within the core of the as-spun polymeric fibers accounted for the formation of hollow nanofibers, and the thermal decomposition of polymers such as PVP, TEOS, and urea responded for the formation of mesopores within the walls. In addition, it was found that the contents of urea within the raw materials played a critically important role in the formation of SiCNO mesoporous hollow nanofibers, making their growth in a controlled manner.     

Chemical preparation and characterization of nitrogen-rich carbon nitride powders

Creamy white powders were obtained by the chemical vapor reaction of carbon tetrachloride and ammonia at 1000 °C, followed by washing with boiling water. The composition of the material was C₃N_5.5O_0.5H_5.4, having a nitrogen content greater than that of the hypothetical hard material C₃N₄. The powders were harder than quartz whose Mohs hardness is 7, but were not as hard as sapphire (Mohs hardness: 9). The hardness could be explained by the C-N single bond observed in the ESCA C1s spectrum. The material washed with boiling water showed photoluminescence, which was mostly bright and white-blue in color to the naked eye.     

The improved electrical conductivity of carbon nanofibers by fluorinated MWCNTs

In order to increase the conductivity of carbon nanofiber sheet, conductive multi wall carbon nanotubes (MWCNTs) was added into the carbon fibers. The dispersion of MWCNTs into the fibers and adhesion between carbon fibers and MWCNTs were improved through fluorine modification on surface of MWCNTs. By fluorination treatment, hydrophobic functional group was introduced on the surface of MWCNTs improving the affinity on interface between two carbon materials. These nanofibers made by electrospinning method were treated at different temperature in order to investigate the effect of temperature. According to the increment of temperature, the better conductivity of carbon nanofibers sheet was obtained due to the better oriented carbon structure. Eventually, the improved conductivity of carbon nanofiber sheet was resulted showing 27 S/cm.