Chemoselective Hydrogenation of Functionalized Nitroarenes and Imines by Using Carbon Nanofiber‐Supported Iridium Nanoparticles

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF‐P, tubular: CNF‐T, herringbone: CNF‐H) with Ir₄(CO)₁₂ in mesitylene at 165 °C provided the corresponding CNF‐supported iridium nanoparticles, Ir/CNFs (Ir content=2.3–2.6 wt. %). Transmission electron microscopy (TEM) studies of these Ir/CNF samples revealed that size‐controlled Ir nanoparticles (average particle size of 1.1–1.5 nm) existed on the CNFs. Among the three Ir/CNF samples, Ir/CNF‐T showed an excellent catalytic activity and chemoselectivity towards hydrogenation of functionalized nitroarenes and imines; the corresponding aniline derivatives were obtained with high turnover numbers at ambient temperature under 10 atm of H₂, and the catalyst is reusable. Ir/CNF‐T was also effective for the reductive N‐alkylation of anilines with carbonyl compounds.     

Ruthenium Nanoparticles on Nano‐Level‐Controlled Carbon Supports as Highly Effective Catalysts for Arene Hydrogenation

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF‐P, tubular: CNF‐T, herringbone: CNF‐H) with [Ru₃(CO)₁₂] in toluene heated at reflux provided the corresponding CNF‐supported ruthenium nanoparticles, Ru/CNFs (Ru content=1.1–3.8 wt %). TEM studies of these Ru/CNFs revealed that size‐controlled Ru nanoparticles (2–4 nm) exist on the CNFs, and that their location was dependent on the surface nanostructures of the CNFs: on the edge of the graphite layers (CNF‐P), in the tubes and on the surface (CNF‐T), and between the layers and on the edge (CNF‐H). Among these Ru/CNFs, Ru/CNF‐P showed excellent catalytic activity towards hydrogenation of toluene with high reproducibility; the reaction proceeded without leaching of the Ru species, and the catalyst was reusable. The total turnover number of the five recycling experiments for toluene hydrogenation reached over 180 000 (mol toluene) (mol Ru)^?1. Ru/CNF‐P was also effective for the hydrogenation of functionalized benzene derivatives and pyridine. Hydrogenolysis of benzylic C? O and C? N bonds has not yet been observed. Use of poly(ethylene glycol)s (PEGs) as a solvent made possible the biphasic catalytic hydrogenation of toluene. After the reaction, the methylcyclohexane formed was separated by decantation without contamination of the ruthenium species and PEG. The insoluble PEG phase containing all of the Ru/CNF was recoverable and reusable as the catalyst without loss of activity.     

Effect of carbon nanofiber microstructure on oxygen reduction activity of supported palladium electrocatalyst

Palladium electrocatalysts supported on carbon nanofibers (CNFs) with controlled microstructure or on activated carbon (AC) are prepared, and the effects of the carbon materials microstructure on the oxygen reduction reaction (ORR) properties of the electrocatalysts are investigated. The physical properties of the CNFs with different microstructure, i.e. platelet CNF (p-CNF) and fish-bone CNF (f-CNF), are characterized by high resolution transmission electron microscope and N₂ physisorption. From cyclic voltammetric studies, it is found that Pd/p-CNF and Pd/f-CNF are more active than Pd/AC. The effects of CNF microstructure on the ORR activities of Pd/f-CNF and Pd/p-CNF are discussed. The p-CNF has a higher ratio of edge atoms to basal atoms, and therefore Pd/p-CNF has more positive ORR onset reduction potential and ORR peak potential than Pd/f-CNF. The supports also have influences on the reaction process. The ORR is surface reaction controlled when Pd/AC is used, while it becomes diffusion control when Pd/f-CNF is used.     

Supercritical CO2-driven, periodic patterning on one-dimensionals carbon nanomaterials

One-dimensional carbon nano-materials, in particular carbon nanotubes (CNTs) and carbon nanofibers (CNFs), are of scientific and technological interest due to their satisfactory properties and ability to serve as templates for directed assembly. In this work, linear high density polyethylene (PE) was periodically decorated on CNTs and CNFs using a supercritical carbon dioxide (scCO₂)antisolvent-induced polymer epitaxy (SAIPE) method, leading to nano-hybrid shish-kebab (NHSK) structures. The formation mechanism of different morphologies of PE lamellae on CNTs and CNFs has been discussed. Palladium nanoparticles were synthesized and immobilized on the PE/CNF NHSK structure with the assistance of scCO₂. The obtained hierarchical nano-hybrid architecture may find applications in microfabrication and other related fields.     

Complete nanofibrillation of cellulose prepared by phosphorylation

In this work, we prepared phosphorylated pulp with a phosphorous content of 1.23 mmol/g by adding an aqueous solution of NH₄H₂PO₄ and urea to softwood pulp sheets followed by drying and curing with hot air and obtained cellulose nanofibers (CNFs) with a uniform width of 3–4 nm in approximately 100% gravimetric yield by high-pressure homogenization of the phosphorylated pulp slurry. After phosphorylation, no significant decrease in the pulp recovery ratio was observed, and the viscosity-average degree of polymerization of phosphorylated pulp was almost equal to that of the original pulp. In addition, the crystal structure and crystallinity index were almost unchanged during phosphorylation. The obtained phosphorylated CNF dispersion was highly transparent, and the maximum total light transmittance was nearly 100% when the CNF content was 0.2 wt%. The maximum viscosity of the CNF dispersions was nearly 10–100 times greater than that of conventional thickeners. Furthermore, we found that not only insufficient but also excessive phosphorylation negatively affected the gravimetric yield, transparency and viscosity.     

Carbon nanofibers–SiO<Subscript>2</Subscript> composites: Preparation and characterization

A method has been developed for preparing carbon fibers–SiO₂ composites using oligomethylhydridesiloxane (OMHS) as the precursor for SiO₂. The presence of active hydrogen in OMHS made it possible to attain chemical interaction between the surface of carbon nanofibers (CNFs) and the applied silicon oxide layer. The oxidation rate of CNF–SiO₂ composite is found to be lower by about one order of magnitude compared to that of the as-synthesized CNF. The thermal stability of CNF–SiO₂ composites has been studied. Under an inert atmosphere, CNF–SiO₂ composite has thermal stability up to 1300°C. At temperatures above 1350°C, silicon carbide (SiC) fibers are formed as a result of the carbothermal reduction of silicon oxide.     

纳米碳纤维的表面性质和微结构对氧还原催化活性的影响

采用超声处理的方法分别对管式纳米碳纤维(t-CNF)和鱼骨式纳米碳纤维(f-CNF)进行了表面化学处理. XPS结果表明, 在混酸(浓硫酸+浓硝酸)和氨水中进行超声化学处理可以在CNF表面分别引入含氧官能团和含氮官能团. 电化学测试结果表明, 2种不同微结构CNF的氧还原催化活性都遵循相同的趋势, 即CNF-P相似文献   

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.     

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.     

Structure characterization of cellulose nanofiber hydrogel as functions of concentration and ionic strength

Carboxylated cellulose nanofibers (CNFs), having an average width of 7 nm and thickness of 1.5 nm, were produced by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation method. The fiber cross-sectional dimensions were determined using small-angle X-ray scattering (SAXS), transmission electron microscopy and atomic force microscopy techniques, where the rheological properties under different concentration and ionic strength were also investigated. The formation of hydrogel was evidenced by increasing the CNF concentration or ionic strength of the solvent (water), while the gel structure in ion-induced CNF hydrogels was found to be relatively inhomogeneous. The gelation behavior was closely related to the segmental aggregation of charged CNF, which could be quantitatively characterized by the correlation length (ξ) from the low-angle scattering profile and the scattering invariant (Q) in SAXS.     

In-Vitro Cytotoxicity Study: Cell Viability and Cell Morphology of Carbon Nanofibrous Scaffold/Hydroxyapatite Nanocomposites

Electrospun carbon nanofibers (CNFs), which were modified with hydroxyapatite, were fabricated to be used as a substrate for bone cell proliferation. The CNFs were derived from electrospun polyacrylonitrile (PAN) nanofibers after two steps of heat treatment: stabilization and carbonization. Carbon nanofibrous (CNF)/hydroxyapatite (HA) nanocomposites were prepared by two different methods; one of them being modification during electrospinning (CNF-8HA) and the second method being hydrothermal modification after carbonization (CNF-8HA; hydrothermally) to be used as a platform for bone tissue engineering. The biological investigations were performed using in-vitro cell counting, WST cell viability and cell morphology after three and seven days. L929 mouse fibroblasts were found to be more viable on the hydrothermally-modified CNF scaffolds than on the unmodified CNF scaffolds. The biological characterizations of the synthesized CNF/HA nanofibrous composites indicated higher capability of bone regeneration.     

Cellulose nanofibril-reinforced biodegradable polymer composites obtained via a Pickering emulsion approach

Preparation of cellulose nanofibril (CNF)-reinforced, biodegradable polymer composites is challenging in that it’s hard to achieve good dispersion of the hydrophilic cellulose fibers in a hydrophobic polymer matrix. In this work, we developed a surfactant-free and efficient process to prepare CNF-reinforced poly (lactic acid) (PLA) composites from an aqueous dichloromethane Pickering emulsion self-emulsified by CNFs. CNF/PLA composites of homogeneous dispersion were obtained upon evaporation of CH₂Cl₂, filtration, drying and hot-pressing. Differential scanning calorimetry measurement revealed an enhanced crystallization capacity of the CNF/PLA composites. Thermogravimetric analysis indicated an increase of onset degradation temperature. The composites displayed an enhanced storage modulus compared with neat PLA throughout the testing temperature range, and especially in the high-temperature region (>70 °C). Enhancements of the flexural modulus and strength were also achieved.     

Effects of microstructure of carbon nanofibers for amperometric detection of hydrogen peroxide

Carbon nanofibers (CNFs) with three microstructures, including platelet-carbon nanofibers (PCNFs), fish-bone-carbon nanofibers (FCNFs), and tube-carbon nanofibers (TCNFs), were synthesized, characterized, and evaluated for electrochemical sensing of hydrogen peroxide. The CNFs studied here show microstructures with various stacked morphologies. The sizes and graphite-layer ordering of the CNFs can be well controlled. Glassy carbon (GC) electrodes modified by CNFs were fabricated and compared for amperometric detection of hydrogen peroxide. Sensors based on PCNFs/GC, FCNFs/GC, and TCNFs/GC were used in the amperometric detection of H₂O₂ in solution by applying a potential of +0.65 V versus Ag/AgCl at the working electrode. The highest electrocatalytic performance was observed for PCNFs/GC among the three types of hydrogen peroxide sensors. The amperometric response of PCNFs/GC retained over 90% of the initial current of the first day up to 21 days. The linear range is from 1.80 × 10⁻⁴ to 2.62 × 10⁻³ M with a correlation coefficient larger than 0.999 and with a detection limit of 4.0 μM H₂O₂ (S/N = 3). The relative standard deviation for detecting 1.80 × 10⁻⁴ M H₂O₂ (N = 8) is 2.1% with an average response of 0.64 μA. The significant diversity of electrocatalytic activity of the CNFs toward the oxidation of hydrogen peroxide may result from the difference of morphologies, textural properties, and crystalline structures.     

Effects of poly(ethylene glycol) on the morphology and properties of biocomposites based on polylactide and cellulose nanofibers

Polylactide (PLA)/cellulose nanofiber (CNF) biocomposites were prepared via solution casting and direct melt mixing. To improve the compatibility, a masterbatch of CNFs and poly(ethylene glycol) (PEG) (1:2) was also prepared. The effects of PEG on the morphology and properties of the biocomposites were investigated. The dispersion/distribution of nanofibers in PLA was improved when the masterbatch was used and the composites were prepared in solution. Substantial effects on the rheological properties of solution-prepared PLA/CNF/PEG composites were observed compared to composites containing no PEG, whereas for melt-prepared composites no significant changes were detected. Increased crystalline content and crystallization temperature were observed for the composites prepared via the masterbatch and solvent casting. The storage modulus of PLA was increased by 42 and 553% at 25 and at 80 °C, respectively, for the solution-based PEG-compatibilized composite containing 2 wt% nanofibers. Also, a better light transmittance was measured for the PLA/CNF/PEG composites prepared in solution.     

Ionic liquid immobilization on carbon nanofibers and zeolites: Catalyst design for the liquid-phase toluene chlorination

The environmental-friendly chlorination reaction of toluene by trichloroisocyanuric acid (TCCA, C₃N₃O₃Cl₃) was investigated applying immobilized ionic liquids (ILs) on different supports. Ionic liquids were grafted either on carbon nanofibers (CNF) or encapsulated in zeolites. Their influence on the chlorination activity as well as on the selectivity in different chlorinated products was studied. An unusually high selectivity toward meta-chlorotoluene was achieved, up to 36%. Hence, the selectivity could be tuned to produce either expected ortho-/para-chlorotoluene or meta-chlorotoluene with a proper support choice.     

In situ synthesis of Pt/carbon nanofiber nanocomposites with enhanced electrocatalytic activity toward methanol oxidation

Pt/carbon nanofiber (Pt/CNF) nanocomposites were facilely synthesized by the reduction of hexachloroplatinic acid (H(2)PtCl(6)) using formic acid (HCOOH) in aqueous solution containing electrospun carbon nanofibers at room temperature. The obtained Pt/CNF nanocomposites were characterized by TEM and EDX. The Pt nanoparticles could in situ grow on the surface of CNFs with small particle size, high loading density, and uniform dispersion by adjusting the concentration of H(2)PtCl(6) precursor. The electrocatalytic activities of the Pt/CNF nanocomposites were also studied. These Pt/CNF nanocomposites exhibited higher electrocatalytic activity toward methanol oxidation reaction compared with commercial E-TEK Pt/C catalyst. The results presented may offer a new approach to facilely synthesize direct methanol fuel cells (DMFCs) catalyst with enhanced electrocatalytic activity and low cost.     

Ru/CNFs 催化剂催化氨分解制氢

 研究了鱼骨式碳纤维 (CNFs) 和管式碳纤维 (CNTs) 负载 Ru 催化剂的氨分解反应活性. 结果表明, Ru/CNFs 催化剂上氨分解活性高于 Ru/CNTs 催化剂. 通过改变 Ru 负载量或载体表面的含氧基团来调节 Ru 的粒径. Ru 的活性位随着 Ru 颗粒尺寸的增大而增加. CNFs 上的含氧基团对 Ru 颗粒的氨分解活性影响很大. 在相同粒径的 Ru 颗粒上, CNFs 表面的含氧基团增加了 Ru 的活性.     

Non Thermal Plasma Functionalized 2D Carbon–Carbon Composites as Supports for Co Nanoparticles

Novel two-dimensional carbon–carbon composites made of carbon nanofibers (CNFs) supported on a carbon preform were functionalized by non thermal plasma treatment (room temperature, atmospheric pressure, humid air), before being used as supports for metallic cobalt nanoparticles. It was shown that the degree of functionalization of the carbon nanofibers depends on the plasma power input, the treatment time and the CNF loading. The size of the cobalt nanoparticles generated after subsequent reduction of the Co-containing plasma treated CNF/C composites under hydrogen flow seems to be independent of the amount of supported cobalt. Changes in surface characteristics were analyzed using thermogravimetric analyses coupled to a mass spectrometer, X-ray photoelectron spectroscopy analyses and Raman spectroscopy. Transmission electron microscopy was used to complementary characterize the final size, dispersion and location of the so generated Co nanoparticles.     

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.     

Fe–N/C nanofiber electrocatalysts with improved activity and stability for oxygen reduction in alkaline and acid solutions

Fe–N/C nanofiber (Fe–N/CNF) electrocatalysts were prepared by impregnating electrospun polyacrylonitrile nanofibers with iron nitrate (Fe(NO₃)₃) solution and subsequent heat treatment, exhibiting improved activity and stability during oxygen reduction reaction (ORR) both in 0.1 M KOH (pH?=?13) and 0.5 M H₂SO₄ (pH?=?0) electrolyte solutions. Higher treatment temperature and NH₃ atmosphere were preferred by the Fe–N/CNF catalysts, and especially the concentration of Fe(NO₃)₃ solution exerted great effects on the surface morphology, structure, and thus electrocatalytic performance of the catalysts. The Fe–N/CNFs prepared using 0.5 wt% Fe(NO₃)₃ solution showed relatively higher ORR activity in alkaline and acid solutions and better stability especially in 0.5 M H₂SO₄ solution than the catalyst without Fe, probably because Fe could promote the graphitization of the polymer-converted carbon species, enhancing the resistance to electrochemical oxidation and thus the stability of the Fe–N/CNF catalysts.