The Construction of Au/Carbon Nanocomposite Material,Characterization and Their Application in Catalytic Reaction of Styrene Epoxidation

The composite nanofibers from Au nanoparticles/carbon nanofibers (Au/CNFs) were fabricated through electrospinning, chemical reduction and high-temperature calcination methods. The polyacrylonitrile acted as the carbon precursor polymer. A series of characterization methods, which include UV–Vis diffuses reflectance spectra, UV–Vis spectra, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction respectively, were used to investigate the morphology and properties of catalysts. The result showed that the gold nanoparticles were well-distributed in/on the CNFs. In the end, the composite material was applied to epoxidation of styrene to investigate its catalytic activity.     

Functionalization of carbon nanofibers (CNFs) through atom transfer radical polymerization for the preparation of poly(tert‐butyl acrylate)/CNF materials: Spectroscopic,thermal, morphological,and physical characterizations

Vapor‐grown carbon nanofibers (CNFs) were oxidized and functionalized for atom transfer radical polymerization (ATRP) of tert‐butyl acrylate (t‐BA) from the surface of the CNFs. The materials were characterized by solubility tests, Fourier‐transform infrared (FTIR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and scanning electron microscopy. The FTIR and electron microscopy results suggest that ATRP process was successfully used to graft poly(tert‐butyl acrylate) (poly(t‐BA)) chains from the surface of the fibers. Raman results strongly indicate the partial degradation of the graphitic layer of CNFs because of the chemical treatments. TGA results suggest that the presence of poly(t‐BA) leads to a decrease of the initial degradation temperature of the fibers. XRD and electron microscopy results indicate that the microstructure of fibers was not destroyed because of the oxidation and functionalization processes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3326–3335, 2008     

Nanosized anatase titanium dioxide loaded porous carbon nanofiber webs as anode materials for lithium-ion batteries

Nanosized anatase titanium dioxide loaded porous carbon nanofibers (TiO₂/PCNFs) were prepared from electrospun TiO(OAc)₂/PAN/PMMA composite precursor fibers with different amount of PMMA porogen, which were sequentially heat-treated in different environments. Electrochemical measurement results show that these as-prepared TiO₂/PCNFs present higher cyclic reversible capacity than the TiO₂/CNFs counterpart (without PMMA porogen in its precursor fibers). Among the as-prepared TiO₂/PCNFs samples, the representative TiO₂/PCNFs (the mass ratio of PAN to PMMA is 3:1) exhibits the best high-rate performance with a high stable capacity retention about 200 mAhg^{− 1} at a current density as high as 800 mAg^{− 1}. This novel TiO₂/PCNFs composite material opens up a promising application in high-power lithium-ion batteries.     

Disordered carbon nanofibers/LiCoPO<Subscript>4</Subscript> composites as cathode materials for lithium ion batteries

LiCoPO₄-coated disordered carbon nanofibers (CNFs/LiCoPO₄) were obtained by a sol–gel method, using triethyl phosphite or triethyl phosphate as the phosphorous source. The crystal structure of the products was analyzed by X-ray powder diffraction, while morphology was studied using scanning electron microscopy, transmission electron microscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy. Optimal synthesis conditions for the CNFs/LiCoPO₄ in light of the best electrochemical performance are discussed. The best discharge capacity 105 mAh/g (or ca. 63% of the theoretical capacity) shows the material with 40% CNFs/LiCoPO₄ and addition coating by carbon black. This composition has a best purity of active materials and point coverage of CNFs. The X-ray photoelectron C1s spectra of the CNFs surface without and with sputter erosion show enhancement of C–O bonds at the fiber surface, which does not influence significantly electrochemical behavior of the composite materials.     

Enhanced Conductivity and mechanical properties of polyimide based nanocomposite materials with carbon nanofibers via carbonization of electrospun polyimide fibers

Carbon nanofibers (CNF) have been obtained by the thermal treatment of the electrospun polyimide fibers in our present work. The carbon structure and surface morphology of the as-received CNFs were investigated using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Investigations of the nanocomposite materials fabricated using these CNFs as conductive fillers and polyimide as matrix show that the presence of CNFs can improve both the mechanical and electrical properties of the material. The conductivity of the nanocomposite films increases with increases in the CNF content and a percolation threshold of about 6.3 vol % (0.0785 in weight fraction) is calculated according to percolation theory.     

Electrochemical performance of Li4Ti5O12/carbon nanofibers composite prepared by an in situ route for Li-ion batteries

A Li₄Ti₅O₁₂/carbon nanofibers (LTO/CNFs) composite has been synthesized by solid-state reaction with the in situ growth of CNFs using the chemical vapor deposition method in N₂/C₂H₂. The nanocomposite is characterized by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, Raman spectrum, and nitrogen adsorption/desorption isotherms, and is investigated as an anode material for lithium-ion (Li-ion) batteries. The underlying mechanism for the improvement is analyzed by cyclic voltammetry and electrochemical impedance spectroscopy. The in situ synthesized composite shows better electrochemical performance than the bare LTO. The in situ formation of CNFs not only supply an efficient electronic conductive network but also reduce the particle size of LTO and increase in specific surface area, leading to increased electrical conductivity and rapider Li-ion diffusion in electrode/electrolyte interface and bulk electrode.     

Preparation and characterization of porous TiO_2/ZnO composite nanofibers via electrospinning

<正>Porous TiO_2/ZnO composite nanofibers have been successfully prepared by electrospinning technique for the first time.It was generated by calcining TiO_2/ZnCl_2/PVP[PVP:polyvinyl pyrrolidone)]nanofibers,which were electrospun from a mixture solution of TiO_2,ZnCl_2 and PVP.Transmission electron microscopy(TEM) and X-ray diffraction(XRD) analyses were used to identify the morphology of the TiO_2/ZnO nanofibers and a formation of inorganic TiO_2/ZnO fibers.The porous structure of the TiO_2/ZnO fibers was characterized by N_2 adsoption/desorption isotherm.Surface photovoltage spectroscopy(SPS) and photocatalytic activity measurements revealed advance properties of the porous TiO_2/ZnO composite nanofibers and the results were compared with pure TiO_2 nanofibers,pure ZnO nanofibers and TiO_2/ZnO nanoparticles.     

The controllable preparation of electrospun carbon fibers supported Pd nanoparticles catalyst and its application in Suzuki and Heck reactions

The palladium nanoparticles/carbon nanofibers(Pd NPs/CNFs) catalyst was prepared by the electrospinning method, the hydrazine hydrate solution reduction in an ice bath environment, the high temperature carbonization. The catalyst was characterized by X-ray diffraction(XRD), fieldemission scanning electron microscope(FE-SEM), and transmission electron microscopy(TEM). The nanofibers are not cross-linked and arranged in order. The surface of Pd NPs/CNFs is smooth, and it can be observed that a large number of particles were loaded and well-dispersed in carbon fiber matrix, and the particle distribution is uniform. The activity center of catalyst is Pd(0). The Pd NPs/CNFs exhibited a high efficiency, good reusability and stability in the Suzuki and Heck reactions. It can be used for at least five consecutive runs without significant loss of its catalytic activity. The good recyclability of Pd NPs/CNFs provides a way to greatly reduce the cost of the catalyst.     

Effect of needle diameter on nanofiber diameter and thermal properties of electrospun poly(methyl methacrylate)

The effect of needle diameter on the resulting electrospun poly(methyl methacrylate) (PMMA) average nanofiber diameter has been evaluated for three different needle gauges. The resulting nanofibers were observed and analyzed by scanning electron microscopy (SEM), suggesting a lack of correlation between the needle diameter used and the resulting average nanofiber diameter. Thermogravimetric analysis (TGA) indicated an increase in the thermal stability of PMMA nanofibers when compared to powdered PMMA, while differential scanning calorimetry (DSC) studies evidenced lower glass transition temperatures (Tg) for PMMA nanofibers in the first heating cycle. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of cellulose nanofibers on induced polymerization of aniline and formation of nanostructured conducting composite

Cellulose nanofibers (CNFs), derived from the most abundant and renewable biopolymer, are known as natural one-dimensional nanomaterials because of their high aspect ratio. CNFs also are rich in hydroxyl groups, offering opportunities for functionalization toward development of high-value nanostructured composites. Herein, CNFs were extracted from poplar wood powder by chemical pretreatment combined with high-intensity ultrasonication, and then coated with polyaniline (PANI) through in situ polymerization. The PANI-coated CNFs formed nanostructured frameworks around PANI, thereby conferring the CNF/PANI composite with stability and higher charge transport. The optimum PANI content to achieve maximum conductivity of CNF/PANI composites was determined. The morphology, crystall structure, chemical composition, and conductivity of the samples were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and four-point probe method, respectivily. Our results demonstrated that CNFs can be effective as a template for a flexible and stable conducting polymer to form higher-order nanostructures.     

Topochemistry of cellulose nanofibers resulting from molecular and polymer grafting

The aim of this study was to synthesize hydrophobic cellulose nanofibers (CNFs) using different chemical treatments including polymer and molecular grafting. For polymer grafting, immobilizing poly (butyl acrylate) (PBA) and poly (methyl methacrylate) (PMMA) on CNFs were implemented by the free radical method. Also, acetyl groups were introduced directly onto the CNFs surface by acetic anhydride for molecular grafting. The gravimetric and X-ray photoelectron spectroscopy analysis showed the high grafting density of PMMA on the surface of CNFs. AFM results revealed that molecular grafting created non-uniformity on the CNFs surface, as compared to polymer brushes. In addition, thermodynamic work of adhesion and work of cohesion for the modified CNFs were reduced in water and diiodomethane solvents. Dispersion factor was studied to indicate the dispersibility of CNFs in polar and non-polar media. Dispersion energy was reduced after modification as a result of decreasing interfacial tension and the dispersibility of modified CNFs was improved in diiodomethane.     

Catalytic graphitization of bacterial cellulose–derived carbon nanofibers for stable and enhanced anodic performance of lithium-ion batteries

Bacterial cellulose (BC) produced through microbial fermentation has emerged as a viable precursor for carbon nanofibers (CNF) anode used in lithium-ion batteries. However, the low capacity and fading behavior of BC-derived CNFs render their usage in its pure form. Tuning the microstructure of CNFs in such cases plays an essential role in overcoming these negative ramifications and improves battery performance. In this study, the fermentation media used for BC production is modified by the addition of an iron catalyst, which can induce graphitization in the derived CNFs. Pure BC and catalyst-incorporated BC are pyrolyzed at 900 °C and 1800 °C to obtain CNFs, and the properties of derived CNFs are compared for understanding the role of incorporated catalyst. The structural, morphological, and electrochemical properties of CNFs are analyzed through X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, impedance spectroscopy, galvanostatic charge-discharge studies, and cyclic voltammogram studies. By possessing a higher graphitic content, catalyst-incorporated BC–derived CNFs exhibit an enhanced rate performance with a reversible capacity of 529 mAh g^?1 after 100 continuous charge/discharge cycles at a current density of 0.2C.     

Isolation and characterization of cellulose nanofibers from four plant cellulose fibers using a chemical-ultrasonic process

Cellulose nanofibers (CNFs) were isolated from four kinds of plant cellulose fibers by a chemical-ultrasonic treatment. The chemical composition, morphology, crystalline behavior, and thermal properties of the nanofibers and their intermediate products were characterized and compared. The CNFs extracted from wood, bamboo, and wheat straw fibers had uniform diameters of 10–40 nm, whereas the flax fibers were not uniformly nanofibrillated because of their initially high cellulose content. The chemical composition of each kind of nanofibers was mainly cellulose because hemicelluloses and lignin were significantly removed during chemical process. The crystallinity of the nanofibers increased as the chemical treatments were applied. The degradation temperature of each kind of nanofiber reached beyond 330 °C. Based on the properties of the CNFs, we expect that they will be suitable for use in green nanocomposites, filtration media and optically transparent films.     

金纳米棒负载的静电纺丝纤维的制备及其表面增强拉曼光谱性能

为简单有效地制备高活性表面增强拉曼光谱(Surface-enhanced Raman Spectroscopy,SERS)基底。本文采用静电纺丝聚乙烯醇(PVA)/聚丙烯酸(PAA)纳米纤维为支撑材料,通过直接浸泡的方法,利用金纳米棒与电纺纤维之间的静电力,使纳米棒在纤维表面自组装,得到了性能优异的SERS基底。通过透射电子显微镜、扫描电子显微镜对金纳米棒以及不同状态下的电纺纤维的形貌进行表征,结果表明,金纳米棒均匀且密集地负载在纤维表面。通过设置不同的浸泡时间确定了金纳米棒组装平衡的时间为12 h,并通过调控纺丝时间和金纳米棒的浓度发现随着纺丝时间和金纳米棒浓度的增加,复合纤维膜SERS增强效果随之提升。该复合纤维膜具有优异的SERS均匀性,并且能够检测到浓度低至10~(-10)mol/L的4-氨基苯硫酚的存在。     

Acicular Nickel on Carbon Nanofiber as Electrochemical Sensor Electrode for the Rapid Detection of Aqueous and Gaseous Formaldehyde at Room Temperature

The rapid and straightforward detection of formaldehyde (FA) in the environment is crucial for preventing the accidental inhalation of FA and limiting skin exposure to FA. In this study, we developed a simple nickel-based electrocatalytic electrode on carbon nanofibers (CNFs−Ni), which is suitable for rapidly detecting FA at room temperature. Centrifugal electrospinning was used to obtain polyacrylonitrile (PAN) nanofibers, which was subsequently stabilized and carbonized to fabricate the CNFs. Carbonization of the CNFs occurred at various temperatures (T_c=1200, 1300, 1400, and 1500 °C). PAN CNFs served as a highly conductive template for electroless plating under a magnetic field of 500 G to grow acicular nickel. The amperometric responses of the CNFs−Ni to aqueous FA were then measured. A lab-built amperometric gas sensor (CNFs−Ni 1–8), which comprised CNFs with a reduced Ni loading, was used as the electrode for detecting gaseous FA. Scanning electron microscopy (SEM), linear sweep voltammetry (LSV), cyclic voltammetry (CV), and chronoamperometry were used to evaluate the sensitivities of the electrodes. Within the linear range of 0.05–91.5 mM, the CNFs1400-Ni electrode was highly sensitive for detecting aqueous FA (2592 μA mM⁻¹ cm⁻²), as evidenced by the fast response time (6 s). At a low concentration of gaseous FA (0.5 ppm), the laboratory-built FA gas sensor was stable (98.3 %) and had a fast response time (5 s) after 9 h of continuous operation.     

Decorating silver nanoparticles on electrospun cellulose nanofibers through a facile method by dopamine and ultraviolet irradiation

In this paper, a new method is introduced for producing multi-functional cellulose nanofibers in order to achieve the biodegradable materials for various applications with a minimal amount of potentially toxic materials. Cellulose nanofibers (CNFs) were fabricated by electrospinning cellulose acetate solution followed by deacetylation. The CNFs were then treated with silver nitrate, ammonia, and sodium hydroxide and subsequently with dopamine as reducing and adhesive agent. Ag ions on the CNF surface were photo-reduced to Ag nanoparticles (NPs) using UVA irradiation to produce a dense layer of silver nanoparticles on the nanofibers. This is based on the simultaneous formation of polydopamine and Ag NPs on CNFs. Overall, this is a fast, simple, and efficient procedure that takes place in a conventional method at ambient temperature. The crystalline structure of CNFs decorated with AgNPs was studied by X-ray diffraction. Field-emission scanning electron microscopy and energy-dispersive X-ray patterns showed uniform distribution of silver nanoparticles on the CNF surface. Incorporation of AgNPs on the CNF surface via dopamine improved the electrical conductivity and also the tensile strength of the nanomat. The CNFs decorated with AgNPs exhibited a low electrical resistivity around 35 KΩ/square and a tensile strength of 87% higher than untreated CNFs.     

三元Ho3+-TiO2/Bi等离子体复合纤维制备及其可见光催化产氢性能

以电纺Ho³⁺-TiO₂纳米纤维为基质,葡萄糖酸钠为还原剂,采用水热法制备Ho³⁺-TiO₂/Bi等离子体复合纤维光催化剂。 利用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)、紫外可见漫反射光谱(UV-Vis DRS)和瞬时光电流(IP)等分析测试手段对样品的物相、形貌和光电性能等进行表征。 以三乙醇胺为电子给体,研究了Ho³⁺-TiO₂/Bi光催化分解水产氢的反应过程。 结果表明:在水热过程中,Bi³⁺被葡萄糖酸钠还原成单质Bi纳米颗粒,复合在Ho³⁺-TiO₂纳米纤维表面形成肖特基结。 金属Bi通过局域表面等离子体共振效应结合稀土元素丰富的能级结构和4f电子跃迁特性,对TiO₂进行双重修饰改性,有效提高了TiO₂的光催化活性和稳定性,可见光下产氢速率最大为43.6 μmol/(g·h)。     

Surface decoration and dispersibility of carbon nanofibers in aqueous surfactant solution

As a novel functional nanomaterial, the dispersion effect of carbon nanofibers (CNFs) has a significant influence on the application of CNFs in the composites. Two effective surfactants, methylcellulose (MC) and polycarboxylate superplasticizer, were used to analyze the dispersion of CNFs in aqueous solution. A method utilizing ultrasonic processing was employed to achieve a homogenous CNF suspension, and the dispersion effect was further characterized by the method of measuring ultraviolet absorbency (UV absorbency), zeta potential, surface tension and transmission electron microscopy (TEM) micrographs. The results show that the zeta potential and surface tension reach the saturation plateau at MC concentration and polycarboxylate superplasticizer concentration of about 0.4 and 0.8 g/L, respectively, which reflects that the optimum concentration ratio of MC to CNFs is 2: 1, and the optimum dispersing polycarboxylate superplasticizer to CNFs ratio of 4: 1 is required to achieve dispersions with maximum achievable dispersion of CNFs.     

The direct architecture of carbon fiber‐carbon nanofiber hierarchical reinforcements for superior interfacial properties of CF/epoxy composites

A simple and efficient chemical method was developed to graft directly carbon nanofibers (CNFs) onto carbon fiber (CF) surface to construct a CF‐CNF hierarchical reinforcing structure. The grafted CF reinforcements via covalent ester linkage at low temperature without any usage of dendrimer or catalyst was investigated by FTIR, X‐ray photoelectron spectroscopy, Raman, scanning electron microscopy, atomic force microscopy, dynamic contact angle analysis, and single fiber tensile testing. The results indicated that the CNFs with high density could effectively increase the polarity, wettability, and roughness of the CF surface. Simultaneous enhancements of the interfacial shear strength, flexural strength, and dynamic mechanical properties as well as the tensile strength of CFs were achieved, for an increase of 75.8%, 21.9%, 21.7%, and 0.5%, respectively. We believe the facile and effective method may provide a novel and promising interface design strategy for next‐generation advanced composite structures.     

Highly Porous Amidoximed Carbon Nanofibers Supported Palladium(0) Nanoparticle Catalyzed Heck Reaction

Highly porous amidoximed carbon nanofibers(AOCNFs), which were fabricated via a conventional electrospinning technique followed by chemically modification, impregnation-reduction and carbonization process, had been used for the immobilization of palladium nanoparticles(Pd NPs) catalyst. During the carbonization process, polystyrene(PS) was selectively decomposed from bicomponent fibers, generating porous fibers. Fourier transform infrared spectroscopy(FTIR) result revealed the functional groups on PAN-PS fibers(PAN=polyacrylonitrile), AOPAN-PS fibers and AOCNFs; scanning electron microscopy(SEM) was used to observe the morphology of all stages of nanofibers; transmission electron microscopy(TEM) result gave the structure of through-hole morphology clearly visible and the dispersion of Pd NPs on the surface of nanofibers; and X-ray photoelectron spectra(XPS) confirmed that Pd nanoparticles on the surface of AOCNFs was of the metallic state. Moreover, the as-prepared catalyst exhibited high catalytic activity and efficient recycle for Heck coupling reactions between iodobenzene and acrylates.