Influence of Lignin units on the properties of Lignin/PAN-derived carbon fibers

Lignin was proposed to an attractive precursor for making carbon fibers (CFs) owing to its high carbon yield, low-cost, and renewable sourcing. In this work, Lignin/polyacrylonitrile (PAN)-derived CFs were prepared and characterized to investigate the effects of Lignin units on their porous texture and surface chemistry. The results showed that the LP20-CF prepared from PAN with 20% Lignin had higher surface areas than that of the pristine LP0-CF, and it possessed interconnected multidimensional network with fiber bonding. Moreover, Lignin/PAN-derived CFs contained more oxygen functional groups of CO, COOR, and nitrogen functional groups of N-6, N Q than the pristine CFs. These results indicated that the Lignin could be beneficial to achieve CFs with special structure, developed porosity and rich surface chemistry without activation. Therefore, the utilization of Lignin to produce pores and improve surface chemistry of CFs was a simple and effective strategy for preparing the low-cost and high-performance functional carbon materials.     

A facile and scalable coating technique of carbon fibers with carbon nanoparticles for surface adhesion enhancement of fibers and resin in 2D C/C composites

In order to improve mechanical properties of 2D carbon-carbon composite via increasing fiber/matrix interfacial adhesion, we have developed a simple, low cost and scalable method for carbon fibers (CFs) coating. This method is inspired to ink printing process in which pigments/dyes are transferred and set on the different surfaces via proper chemical bindings. For this purpose, we have used colloidal suspension of carbon nanoparticles in printing ink solution and coated the surfaces through dip-coating procedure. The results of SEM observations showed that colloidal suspension of nano-carbon particles in ink solution could be successfully used as a coating solution for preparing a uniform, well distributed and defect-free coating. Also water wettability measurement test has been conducted in order to evaluate the carbon coating on the surface chemistry of carbon nanofibers. The results revealed significant improvement on wettability of CFs after coating owing to abundant hydrophilic groups introduced from ink solution onto the surface of CFs (approved by FTIR spectroscopy). Finally, the mechanical properties of 2D C/C composites prepared by as-received and nano-coated CFs have been evaluated. The result of mechanical properties showed remarkable improvement in both flexural and shear strength of final composite by 15% and 18%, respectively.     

氨气处理碳纤维 第I报 表面组成和反应机理

采用原位漫反射红外光谱(FT-IR)在线分析碳纤维表面谱图变化。结果发现,当温度升至500℃后,3260cm-1处吸收峰减弱,在3157cm-1、3048cm-1、2829cm-1和1405cm-1处新增吸收峰。用X-射线光电子能谱(XPS)对未处理与在氨气气氛中600℃处理30s后碳纤维的表面官能团组成进行分析对比发现,处理后的碳纤维表面氮元素显著增加,而氧含量降低。由FT-IR和XPS的谱图变化推测出在高温时,碳纤维表面的羟基和羧基与氨气发生反应,形成了氨基官能团。     

Fabrication of the carbon paper by wet-laying of ozone-treated carbon fibers with hydrophilic functional groups

Carbon papers (CPs) have been widely investigated as a gas diffusion layer for high performance fuel cells. Herein we report the fabrication of the CP by wet-laying of ozone-treated carbon fibers (CFs) with hydrophilic functional groups. To improve the dispersion of CFs in water, the surface of the CFs was modified by the ozone treatment. The surface of the ozone-treated CFs contains hydrophilic functional groups such as C–O, CO and O–CO, which have been characterized by X-ray photoelectron spectroscopy. The negative charge of CFs determined by zeta potential was significantly increased after the ozone treatment, and the value was linearly decreased upon increasing ozone-treated time. Since ozone-treated CFs were better dispersed in aqueous solution than bare CFs, the CP prepared by a wet-laying process of ozone-treated CFs have higher porosity and gas permeability than that from bare CFs. In addition, the prepared CP from ozone-treated CFs showed better performance in I–V measurement of the single cell than those from bare CFs because of their high gas permeability.     

Increasing the interfacial strength in carbon fiber/epoxy composites by controlling the orientation and length of carbon nanotubes grown on the fibers

Multi-walled carbon nanotubes (MWCNTs) were grafted onto carbon fibers (CFs) using an injection chemical vapor deposition method. The orientation and length (16.6–108.6 μm) of the MWCNTs were controlled by the surface treatment of the CFs and the growth time, respectively. The interface between the MWCNTs and the CFs indicated the grafted CNTs were immobilized by embedding catalyst on CFs. Two orders of magnitude increase in the specific surface areas of CFs was obtained by grafting the MWCNT. MWCNT–CF hybrids exhibited good wettability with the epoxy resin due to the surface roughness and capillary action. Single-fiber composite fragmentation tests revealed an remarkable improvement of interfacial shear strength (IFSS) controlled by the orientation and length of MWCNTs. MWCNTs with an perpendicular alignment and long length showed a high IFSS in epoxy composites due to better wettability and a large contact interface between the hybrids and the resin. Hybrids with an optimum length (47.2 μm) of aligned MWCNTs showed a dramatic improvement of IFSS up to 175% compared to that of pristine CFs.     

Controllable synthesis of nitrogen-doped graphene and its effect on the simultaneous electrochemical determination of ascorbic acid,dopamine, and uric acid

A simple, low-cost method for fabricating nitrogen-doped graphene (NG) is demonstrated by combining the ultrafast thermal exfoliation and covalent transformation from the melamine (MA)–graphene oxide (GO) mixture. NGs prepared at 300, 600, and 900 °C were systematically characterized by X-ray photoelectron spectroscopy (XPS), in which pyridinic-N, pyrrolic-N and graphitic-N are the main nitrogen-doped structures in various ratios. These NGs possess large specific surface area and porous microstructures, confirmed by the N₂ adsorption–desorption isotherms. The NG-modified screen-printed carbon electrodes (SPCEs) were fabricated to detect ascorbic acid (AA), dopamine (DA) and uric acid (UA) simultaneously by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Due to the large specific surface area, mesoporous structures and nitrogen-doped sites, these NGs show highly electrochemical sensitivity for AA, DA and UA. Notably, the pyrrolic-N structure makes the negative shift in the oxidation peak potential of these biomolecules, showing the better catalytic activity than pyridinic-N and graphitic-N structures. The large surface area of NGs provides more nitrogen-doped sites to oxidize bio-compounds and enhances the corresponding currents. The good sensitivity of NG-modified SPCEs makes them become effective sensors for determining AA, DA and UA simultaneously. The discrimination to peak potential and current among these NGs can be observed.     

碳载Sb-Pb-Pt电催化纳米材料的制备与结构表征

:通过电化学方法在玻碳表面沉积催化物质研制Sb Pb Pt合金纳米材料。运用循环伏安(CV)、石英晶体微天平 (EQCM)、扫描隧道显微镜 (STM)和X 光电子能谱 (XPS)等技术对其进行表征。结果指出 ,碳载Sb Pb Pt电催化纳米材料的稳定性明显高于电有机合成中常用的Pb和Sb等电极。在酸性介质中碳载Sb Pb Pt电催化纳米材料电极上氢的析出电位负移至 - 0 45V ,有较高的电还原应用价值。通过EQCM技术对纳米薄膜合金电极的形成过程进行原位跟踪和STM观察 ,表明所研制的Sb Pb Pt纳米材料是由粒度均匀的纳米颗粒组成的合金薄膜。     

On the flame synthesis of carbon nanotubes grafted onto carbon fibers and the bonding force between them

A simple one-step method of the synthesis of carbon nanotubes (CNTs) grafted onto carbon fibers (CFs) was developed using catalysts formed in an ethanol flame, where the reducing atmosphere prevents the CFs from combustion and reduces the catalyst precursor to catalyst particles on the fibers. The growth process was studied and both the type and concentration of catalyst ions were found to affect CNT growth on CFs. The peeling force to separate the interfacial bonding between a CNT and a CF substrate was also measured by an instrumented tip of an atomic force microscope.     

氨气处理碳纤维 第II报 碳纤维表面和复合材料的性能

常压下,使碳纤维通过以氨气为气体介质的600℃热反应炉,反应停留时间为30s。采用三点短梁法和界面评价装置研究处理前后复合材料的层间剪切强度(ILSS)和界面剪切强度(IFSS),经氨气处理后二者分别提高了13.2%和32.1%。接触角测试结果表明:处理后碳纤维与水和环氧树脂的浸润性得到很大改善。采用扫描电子显微镜(SEM)研究处理前后碳纤维表面和复合材料断裂面形貌的变化,发现氨气处理对碳纤维表面形貌没有影响。力学性能测试数据表明,氨气处理不影响碳纤维的强度。     

Unipolar resistive switching behavior of amorphous SrMoO4 thin films deposited at room temperature

Amorphous SrMoO₄ (SMO) thin films were deposited on Pt/Ti/SiO₂/Si substrates at room temperature by pulsed laser deposition and the resistive switching (RS) behavior of the Au/SMO/Pt devices was investigated. The Au/SMO/Pt devices exhibit typical unipolar RS behavior with excellent switching parameters as follows: high resistance ratio (~10⁵) between the low resistance state (LRS) and high resistance state (HRS), non-overlapping switching voltages, and good endurance and retention characteristics. Detailed analysis of their current-voltage characteristics reveals that the conduction mechanisms are Ohmic conduction in the LRS and lower voltage region of HRS, and Poole-Frenkel emission in the higher voltage region of the HRS. Temperature dependent resistance measurements, combined with x-ray photoelectron spectroscopy and model analysis indicate that the unipolar RS behavior of the Au/SMO/Pt devices could be understood by a conical conducting filaments (CFs) model in which the conical CFs are composed of oxygen vacancies. The conical CFs extend from the cathode to anode during the forming process and the observed RS behavior occurs in the localized region near the anode. These results suggest that the room-temperature- deposited amorphous SMO thin films could find potential application in nonvolatile RS memory.     

Metal deposition onto a thiol-covered gold surface: A new approach

In this study, we report on details of a new technique for depositing metal on top of a self-assembled monolayer (SAM). The experiments were performed with 4,4′-dithiodipyridine (4-PySSPy) SAMs on Au(1 1 1) electrodes, which were immersed without potential control into a Pd(II)-containing solution, where Pd(II) adsorbs on the surface by forming a complex with the pyridine nitrogen. The complexed Pd(II) ions were reduced electrochemically to Pd(0) after transferring the electrode to a Pd ion-free solution. Upon reduction, monoatomic high Pd islands were observed in STM. From cyclic voltammetry, in situ STM and ex situ angle-resolved XPS we conclude that these islands reside on top of the SAM, not underneath. It is shown that palladium complexation and deposition on self-assembled monolayers of 2-mercaptopyridine is not possible.     

ZnO nanowires decoration on carbon fiber via hydrothermal synthesis for paper-based friction materials with improved friction and wear properties

Two-step growth of ZnO nanowires (NWs) on carbon fiber (CF) surface via hydrothermal synthesis was studied and their application in the preparation of paper-based friction materials by wet-forming process was also investigated. SEM and EDS results showed a dense and uniform ZnO NWs layer with vertical alignment was well established on surface of CFs. UV–vis spectra and XRD characterization further confirmed the formation of ZnO NWs on CFs surface. In comparison with control sample (paper-based friction material containing pristine CFs), the modified sample (paper-based friction material containing modified CFs) exhibited higher and more stable dynamic friction coefficient and greater wear resistance. It was concluded that the CFs@ZnO NWs had excellent tribological properties and was highly promising for wet paper-based friction material.     

Improved interfacial adhesion in carbon fiber/epoxy composites through a waterborne epoxy resin sizing agent

A series of self‐emulsified waterborne epoxy resin (WEP) emulsions were used as surface sizing for carbon fibers (CFs) to improve the interfacial adhesion between the CF and epoxy matrix. In this work, the hydrogenated bisphenol‐A epoxy resin (HBPAE) was modified by polyethylene glycol (PEG) with molecular weights of 400, 800, 1000, 1500, 2000, 4000, and 6000 g/mol. The properties of the WEP emulsion were examined by Fourier transform infrared spectroscopy, dynamic light scattering, and transmission electron microscopy. The surface characteristics of sized CFs were evaluated using scanning electron microscopy, atomic force microscopy, and X‐ray photoelectron spectroscopy. Afterwards, CF/EP composites were prepared and their fracture surface and interlaminar shear strength (ILSS) were examined. The results indicated that PEG2000 modified HBPAE sizing had the optimum emulsion stability and film‐forming ability. Meanwhile, the results also demonstrated that a continuous and uniform sizing layer was formed on the surface of CFs and the surface sizing was excellent in improving the chemical activity of CFs. Compared with unsized CFs, the O1s/C1s composition ratio was observed to increase from 11.51% to 33.17% and the ILSS of CF/EP composites increased from 81.2 to 89.7 MPa, exhibiting better mechanical property than that of commercial Takemoto S64 sized CFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44757.     

Development of multiwalled‐carbon‐nanotube‐welded carbon fibers and evaluation of the interfacial strength in epoxy composites

Multiwalled carbon nanotube (MWCNT)‐welded carbon fibers (CFs) were prepared by a three‐step process, which included polyacrylonitrile (PAN) coating, MWCNT absorption, and heat treatment. The structure of these materials was characterized by scanning electron microscopy, Fourier‐transform infrared spectroscopy, and Raman spectroscopy. The MWCNTs were uniformly assembled on the surface of the PAN‐coated CFs and welded by a PAN‐based carbon layer after heat treatment. The contact angle of the MWCNT‐welded CFs in the epoxy resins was 41.70°; this was 22.35% smaller than that of the unsized CFs. The interfacial shear strength (IFSS) of the MWCNT‐welded CF–epoxy composite was 83.15 MPa; this was 28.89% higher than that of the unsized CF–epoxy composite. The increase in the IFSS was attributed to the enhancement of adhesions between the CFs and polymer matrix through the welding of the MWCNTs on the CFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45027.     

Iron phthalocyanine coatings on the surface of carbon fibers and their improved interfacial interactions with poly(arylene ether)nitrile

Riveted carbon fibers (CFs) were fabricated via in situ thermopolymerization. Iron phthalocyanine was like rivets distributed on the surface of the acidulated CFs. The rivets were characterized by scanning electron microscopy (SEM) and distributed uniformly on the surface of the CFs with a uniform microsphere size of 120 nm. Next, the pristine and riveted CFs were used to prepare fiber‐reinforced poly(arylene ether)nitrile (PEN)‐based composites with a hot‐press molding technique. The creep behaviors of PEN on the pristine and riveted CFs were investigated by dynamic rheological measurements. Among the samples, the viscosities changed with the frequency, and the stress relaxation and Cole–Cole plots are presented and discussed in detail. These results indicated better interlocking between the PEN chains and the rivets on the surface of the CFs. The dynamic mechanical properties of the composites were examined in three‐point bending mode with a dynamic mechanical analyzer. The results indicate that the reduction of the tan δ peak height may have been due to the improved interfacial adhesion between the CFs and PEN. Additionally, the interfacial morphologies of the CF‐reinforced PEN composites were monitored; this also confirmed the improved adhesion between the PEN chains and the riveted CFs in comparison with that of the pristine CFs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46466.     

Continuous and rapid stabilization of polyacrylonitrile fiber bundles assisted by atmospheric pressure plasma for fabricating large-tow carbon fibers

A bundle of carbon fibers (CFs) with 24,000 filaments was prepared using atmospheric pressure plasma and heat simultaneously for only 30 min, followed by the carbonization process. Conventional thermal stabilization process takes more than few hours to prevent the ignition of the polyacrylonitrile (PAN) fiber when large-tow PAN fibers are stabilized. The CFs produced using the plasma stabilization process had a tensile strength as high as 2.6 GPa. This strength level, which is slightly higher than that of CFs stabilized by the conventional process for 120 min, satisfies the demands in automobile applications. It is believed that the plasma-based stabilization process provides a potential solution not only for shortening the process time but also for providing continuous stabilization of large-tow carbon fibers.     

Improved tensile strength of carbon fibers undergoing catalytic growth of carbon nanotubes on their surface

We demonstrate that the tensile strength of carbon fibers (CFs) can be increased by more than 14% by the catalytic growth of carbon nanotubes (CNTs) onto their surface. Repair to some of the damage incurred during the formation of catalyst nanoparticles, an increase in the carbon crystal size, and the formation of crosslinks of neighboring crystals by CNTs all occur during the chemical vapor deposition process, and are the main reasons for the improvement. The interfacial shear strength of the CFs is also shown to be significantly improved due to the CNTs grown on the CF surface.     

Graphene growth on Pt(111) and Au(111) using a MBE carbon solid-source

In this work we present a Molecular Beam Epitaxy (MBE) growth method to obtain graphene on noble metals using evaporation of carbon atoms from a carbon solid-source in ultra-high vacuum conditions. We have synthesized graphene (G) on different metal surfaces: from a well studied substrate as platinum, to a substrate where it can only be formed using innovative methods, as is the case of gold. For the characterization of the graphene layers we have used in situ surface science techniques as low energy electron diffraction (LEED), auger electron spectroscopy (AES) and scanning tunneling microscopy (STM).One of the main advantages of our methodology is that low surface temperatures are required to form graphene. Thus, by annealing Pt(111) and Au(111) substrates up to 650 °C and 550 °C respectively during carbon evaporation, we have obtained the characteristic LEED diagrams commonly attributed to graphene on these surfaces. STM results further prove the formation of graphene. For the case of G on Pt(111), STM images show a long range ordering associated with moiré patterns that correspond to a monolayer of graphene on (111) platinum surface. On the other hand, G/Au(111) STM results reveal the formation of dendritic islands pinned to atomic step edges. This method opens up new possibilities for the formation of graphene on many different substrates with potential technological applications.     

Synthesis of multiscale reinforcement fabric by electrophoretic deposition of amine-functionalized carbon nanofibers onto carbon fiber layers

Deposition of amine-functionalized carbon nanofibers (CNFs) on the surface of carbon fibers (CFs) using water as dispersive medium was achieved by a two-stage scalable electrophoretic process. The resulting hybrid CNF-CF layers showed uniform distribution and microfiber wrapping of amidized-CNFs not seen when depositing oxidized-CNFs on the same substrate. Such layers provide potential for improving the mechanical properties of advanced composites by covalent bonding between amine and epoxide groups of the CNFs and matrix, respectively.     

碳纤维增强聚合物组织工程支架的制备及表征

以碳纤维（CF）作为增强材料,将CF有序排列于聚乳酸羟基乙酸（PLGA）多孔结构中,制备性能优良的CF/PLGA复合支架,并对其力学性能及细胞生物学性能进行表征.对增强体CF进行有序排列以提高支架的力学性能,扫描电子显微镜（SEM）观察CF/PLGA复合支架的微观形貌,可以看出CF在聚合物基体内部是呈有序结构并且二者结合情况良好.为了提高CF的生物相容性,利用对氨基苯甲酸对CF进行表面修饰,细胞生长在支架上的SEM照片反映了成纤维细胞对PLGA及CF/PLGA复合支架的黏附性能良好;通过细胞毒性测试,发现表面修饰的CF对细胞的生长没有负面作用,且在一定程度上促进了细胞的生长.研究结果表明,制备的CF/PLGA支架具有良好的力学性能和生物相容性,在骨组织工程支架的应用中具有一定的潜力.