Adsorption of volatile organic compounds onto carbon nanotubes, carbon nanofibers, and high-surface-area graphites

The adsorption of different alkanes (linear and cyclic), aromatics, and chlorohydrocarbons onto different nonmicroporous carbons--multiwalled carbon nanotubes (CNTs), carbon nanofibers (CNFs), and high-surface-area graphites (HSAGs)--is studied in this work by inverse gas chromatography (IGC). Capacity of adsorption was derived from the isotherms of adsorption, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined from chromatographic retention data. HSAGs present the highest adsorption capacity, followed by CNTs and CNFs (although CNTs present an intermediate surface area between the two HSAG studied). Among the different adsorbates tested, benzene exhibits the highest adsorption capacity, and the same trend is observed in the enthalpy of adsorption. From surface free energy data, enthalpies of adsorption of polar compounds were divided into dispersive and specific contributions. The interactions of cyclic (benzene and cyclohexane) and chlorinated compounds (trichloroethylene, tetrachloroethylene, and chloroform) with the surfaces are mainly dispersive over all the carbons tested, CNTs being the material with the highest dispersive contribution, as was deduced also from the entropy parameter. Adsorption parameters were correlated with morphological and chemical properties of the materials.     

Tuning the Functionality of a Carbon Nanofiber-Pt-RuO(2) System from Charge Storage to Electrocatalysis

Chemical-functionalization-induced switching in the property of a hybrid system composed of a hollow carbon nanofiber (CNF) and Pt and RuO(2) nanoparticles from charge storage to electrocatalysis is presented. The results of this study show how important it is to have a clear understanding of the nature of surface functionalities in the processes involving dispersion of more than one component on various substrates including carbon nanomorphologies. When pristine CNF is used to decorate Pt and RuO(2) nanoparticles, random dispersion occurs on the CNF surface (C-PtRuO(2)). This results in mainly phase-separated nanoparticles rich in RuO(2) characteristics. In contrast to this, upon moving from the pristine CNF to those activated by a simple H(2)O(2) treatment to create oxygen-containing surface functional groups, a material rich in Pt features on the surface is obtained (F-PtRuO(2)). This is achieved because of the preferential adsorption of RuO(2) by the functionalized surface of CNF. A better affinity of the oxygen-containing functional groups on CNF toward RuO(2) mobilizes relatively faster adsorption of this moiety, leading to a well-controlled segregation of Pt nanoparticles toward the surface. Further reorganization of Pt nanoparticles leads to the formation of a Pt nanosheet structure on the surface. The electrochemical properties of these materials are initially evaluated using cyclic voltammetric analysis. The cyclic voltammetric results indicate that C-PtRuO(2) shows a charge storage property, a typical characteristic of hydrous RuO(2), whereas F-PtRuO(2) shows an oxygen reduction property, which is the characteristic feature of Pt. This clear switch in the behavior from charge storage to electrocatalysis is further confirmed by galvanostatic charge-discharge and rotating-disk-electrode studies.     

Polycarbonate carbon nanofiber composites

Carbon nanofiber (CNF) composites have the potential for creating inexpensive, semiconducting polymers. These composites require a homogeneous dispersion within the polymer. Many groups have focused on high shear methods such as twin screw extrusion. Although high shear methods produce a homogeneous dispersion, the aspect ratio of the nanofibers is reduced by the mechanical force. In this report, we present results for low shear composite formation via in situ polymerization of cyclic oligomeric carbonates. The composites were characterized by thermal gravimetric analysis, electrical conductivity, scanning electron microscopy and transmission electron microscopy. The composites exhibit minimal aggregation of the carbon nanofibers even at high weight percents. The polycarbonate/CNF composites exhibit an electrical conductivity percolation threshold of 6.3 wt% which is higher compared with similar CNF composites. The composites also show an increase in thermal stability of 40 °C as the CNF loading increases from 0 to 9 wt%.     

Carbon Nanofiber–Polystyrene Composite Electrodes for Electroanalytical Processes

Carbon nanofibers provide an active and well‐defined high surface area material for electroanalytical processes. In this study a novel procedure is suggested for compacting carbon nanofiber (CNF) materials (diameter typically 100–200 nm) with a polystyrene (PS) binder and additives into highly conducting and re‐polishable CNF‐PS composite electrodes. Three types of carbon nanofibers (Pyrograf III, 70–200 nm diameter) and a range of compositions are surveyed. A 33 wt% carbon nanofibers in polystyrene electrode provides optimum electrical conductivity and reactivity.     

Thin, bendable electrodes consisting of porous carbon nanofibers via the electrospinning of polyacrylonitrile containing tetraethoxy orthosilicate for supercapacitor

In the present study, electrically conducting carbon nanofiber (CNF) mats were produced by incorporating tetraethoxy orthosilicate (TEOS) into polyacrylonitrile (PAN) via electrospinning. A simple thermal treatment was applied to the electrospun nanofibers to create ultramicropores that could accommodate a large number of ions were formed on the surface of the CNFs, removing the need for a time-consuming activation step. The Si/CNF composites showed high capacitance and energy/power density values due to the formation of ultramicropores and the introduction of heteroatoms.     

Synthesis, characterization and formation process of transition metal oxide nanotubes using carbon nanofibers as templates

Mono and binary transition metal oxide nanotubes could be synthesized by the immersion of carbon nanofiber templates into metal nitrate solutions and removal of the templates by heat treatment in air. The transition metal oxide nanotubes were composed of nano-crystallites of metal oxides. The functional groups on the carbon nanofiber templates were essential for the coating of these templates: they acted as adsorption sites for the metal nitrates, ensuring a uniform metal oxide coating. During the removal of the carbon nanofiber templates by calcination in air, the metal oxide coatings promoted the combustion reaction between the carbon nanofibers and oxygen.     

Adsorption and redox processes at carbon nanofiber electrodes grown onto a ceramic fiber backbone

The adsorption of aromatic compounds onto activated carbons and carbon nanofibers is of considerable technical importance and beneficial in electroanalytical procedures. Here, effects due to the strong adsorption of hydroquinone, benzoquinone, and phenol onto carbon nanofiber electrodes immersed in aqueous media are reported. Carbon nanofiber materials (fiber diameter approximately 100 nm) are grown onto ceramic fiber substrates by employing an ambient pressure chemical vapour deposition process. The resulting composite electrode material is sufficiently electrically conducting due to the high carbon content and mechanically robust due to the ceramic backbone. It is shown that the voltammetric signal obtained for the one electron reduction of Ru(NH₃)₆³⁺ is dominated by solution trapped in the three-dimensional electrode structure. In contrast, for the hydroquinone/benzoquinone redox system in aqueous phosphate buffer (pH 7) strong adsorption onto the carbon nanofiber material is observed. In the presence of phenol also strong adsorption is detected. In the course of the chemically irreversible oxidation of phenol in aqueous phosphate buffer (pH 7), the formation of multi-electron oxidation products related to benzoquinone is observed. The pathway for the oxidation process is attributed to (i) the high surface area of the carbon nanofiber electrode and (ii) the adsorption of intermediates.     

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.     

Adsorbents based on carbon microfibers and carbon nanofibers for the removal of phenol and lead from water

This paper describes the production, characteristics, and efficacy of carbon microfibers and carbon nanofibers for the removal of phenol and Pb(2+) from water by adsorption. The first adsorbent produced in the current investigation contained the ammonia (NH(3)) functionalized micron-sized activated carbon fibers (ACF). Alternatively, the second adsorbent consisted of a multiscale web of ACF/CNF, which was prepared by growing carbon nanofibers (CNFs) on activated ACFs via catalytic chemical vapor deposition (CVD) and sonication, which was conducted to remove catalytic particles from the CNF tips and open the pores of the CNFs. The two adsorbents prepared in the present study, ACF and ACF/CNF, were characterized by several analytical techniques, including SEM-EDX and FT-IR. Moreover, the chemical composition, BET surface area, and pore-size distribution of the materials were determined. The hierarchal web of carbon microfibers and nanofibers displayed a greater adsorption capacity for Pb(2+) than ACF. Interestingly, the adsorption capacity of ammonia (NH(3)) functionalized ACFs for phenol was somewhat larger than that of the multiscale ACF/CNF web. Difference in the adsorption capacity of the adsorbents was attributed to differences in the size of the solutes and their reactivity towards ACF and ACF/CNF. The results indicated that ACF-based materials were efficient adsorbents for the removal of inorganic and organic solutes from wastewater.     

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   

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.     

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.     

纳米碳纤维负载钯催化剂在Heck反应中的应用——载体相互作用的影响

使用多元醇还原法制备了均匀分散的钯纳米颗粒.将钯纳米颗粒负载于板式、鱼骨式和管式纳米碳纤维,得到稳定、可重复使用的非均相催化剂.实验结果表明,钯纳米胶粒同载体之间的电位差对钯在载体上的负载量、粒子大小以及Heck反应中钯的溶失量有很大的影响.在制备过程中,增加钯纳米胶粒同纳米碳纤维表面的电位差能够大大降低钯在Heck反应中的流失.催化剂的反应活性随钯粒子的增大而降低.     

A composite made from palladium nanoparticles and carbon nanofibers for superior electrocatalytic oxidation of formic acid

We report on a novel type of nanocomposite for use in the electrooxidation of formic acid in fuel cells. The material is composed of palladium nanoparticles (Pd-NPs) and carbon nanofibers (CNFs) and was prepared by electrospinning of the precursors Pd(acac)₂ and polyacrylonitrile, respectively, followed by thermal treatment to generate in-situ Pd-NPs that are well dispersed within the CNF framework. The nanocomposite was characterized by TEM, high-resolution TEM, SEM, XRD, Raman spectroscopy, and XPS. The size of the Pd-NPs ranges from 12 to 82 nm, depending on the temperature for carbonization (700–1,000 °C). The length and width of the CNF is in the order of tens of micrometers and 300 to 500 nm, respectively. TEM and XPS studies indicate that the Pd-NPs are firmly embedded in the CNF, resulting in a good electrochemical stability of the composite. The electrocatalytic properties of the composite with respect to the oxidation of formic acid were studied by cyclic voltammetry and chronoamperometry. They showed a distinctly improved electrocatalytic activity and stability compared to a commercial Pd-on-carbon catalyst. The Pd/CNF composite carbonized at 900 °C was found to display the best performance.

Onion-like graphitic nanoshell structured Fe–N/C nanofibers derived from electrospinning for oxygen reduction reaction in acid media

Hollow onion-like graphitic nanoshell structured Fe–N/C nanofiber (Fe–N/CNF) catalyst with porous morphology was prepared by heat treating as-spun polyacrylonitrile/ferrous oxalate composite nanofibers in ammonia atmosphere for the first time. These porous electrocatalyst showed both excellent catalytic activity for oxygen reduction reaction (ORR) and much better stability than commercial Pt/C catalyst in acid solution. The Fe–N/CNF catalysts developed here could be easily fabricated on a large scale and show high potential in proton exchange membrane fuel cells (PEMFCs).     

Electrochemistry of perfluorinated fullerenes: the case of three isomers of C60F36

1-Naphthol has been used as an in situ fluorescent probe to characterize the surface physicochemical properties of carbon nanofibers (CNFs). The fluorescence of 1-naphthol adsorbed on untreated CNFs originates from the ¹L_b state and its peaks are shifted by the polarity of the surrounding media, indicating that there is a relatively non-polar area on the CNF surface. 1-Naphthol interacting with oxidized sites on the surface of nitric acid-treated CNFs exhibited an ion-pair fluorescence. This shows that there are some functional groups, interacting with 1-naphthol, on the treated CNF surface. The surface physicochemical properties of the CNFs can be characterized by this fluorescent probe.     

dsDNA modified carbon nanofiber—solidified paste electrodes: probing Ni(II)—dsDNA interactions

In order to develop a renewable electrode surface, carbon nanofibers (CNF) were embedded into solidified paste electrodes using a composite of paraffin wax and paraffin oil. A range of different compositions was surveyed and the optimal composition of the paste for electroanalysis was found to be 43% of CNF, 41% of paraffin wax, and 16% of paraffin oil. The electrochemical properties of the novel composite electrode were investigated using cyclic voltammetry and electrochemical impedance spectroscopy and compared to those of similar graphite—solidified paste electrodes. The carbon nanofibers enhance the activity of the surface of the electrode and provide a good substrate for the adsorption and voltammetric detection of dsDNA. Responses of dsDNA bases and Ni²⁺ ions accumulated from ammonium buffer pH 8.5 (with a Langmuirian binding constant of 10⁵ mol^?1 L) were investigated and a limit of detection of 7 nmol L^?1 (at 3σ) was obtained using “nucleation stripping voltammetry”. Interferences by other metal cations are examined and discussed.     

Effect of carbon nanofibers on mechanical and electrical behaviors of acrylonitrile‐butadiene rubber composites

Recently, carbon nanofibers have become an innovative reinforcing filler that has drawn increased attention from researchers. In this work, the reinforcement of acrylonitrile butadiene rubber (NBR) with carbon nanofibers (CNFs) was studied to determine the potential of carbon nanofibers as reinforcing filler in rubber technology. Furthermore, the performance of NBR compounds filled with carbon nanofibers was compared with the composites containing carbon black characterized by spherical particle type. Filler dispersion in elastomer matrix plays an essential role in polymer reinforcement, so we also analyzed the influence of dispersing agents on the performance of NBR composites. We applied several types of dispersing agents: anionic, cationic, nonionic, and ionic liquids. The fillers were characterized by dibutylphtalate absorption analysis, aggregate size, and rheological properties of filler suspensions. The vulcanization kinetics of rubber compounds, crosslink density, mechanical properties, hysteresis, and conductive properties of vulcanizates were also investigated. Moreover, scanning electron microscopy images were used to determine the filler dispersion in the elastomer matrix. The incorporation of the carbon nanofibers has a superior influence on the tensile strength of NBR compared with the samples containing carbon black. It was observed that addition of studied dispersing agents affected the performance of NBR/CNF and NBR/carbon black materials. Especially, the application of nonylphenyl poly(ethylene glycol) ether and 1‐butyl‐3‐methylimidazolium tetrafluoroborate contributed to enhanced mechanical properties and electrical conductivity of NBR/CNF composites.     

Ligand adsorption on an activated carbon for the removal of chromate ions from aqueous solutions

The results presented in this work are related to the design of a guideline to develop specific properties at the surface of an activated carbon (AC). For this, two model aromatic compounds have been synthesized and their electrolytic behavior in aqueous solutions was studied by a potentiometric method. The textural characteristics of the activated carbon were determined by porosimetry methods. The nature of oxygen-carrying functions and the acid-base behavior of the AC surface were characterized by TPD and potentiometric titration methods, respectively. The adsorption and desorption equilibria of the aromatic compounds on activated carbon were measured in aqueous solutions, and the hysteresis between adsorption and desorption, which reveals irreversible adsorption, was discussed on the basis of the frontier orbital theory. HOMO and LUMO orbitals of the adsorbent and adsorbates were calculated, and irreversible adsorption was attributed to the small energy difference between HOMO and LUMO of the aromatic adsorbates and the adsorbent. Adsorption equilibria of K2CrO4 in aqueous solution on the AC alone and on the AC-aromatic ligand adsorbents, respectively, prove the efficient development of specific chemical functions at the carbon surface provided by the adsorbed aromatic compounds.     

Carbon nanofiber electrode array for electrochemical detection of dopamine using fast scan cyclic voltammetry

A carbon nanofiber (CNF) electrode array was integrated with the Wireless Instantaneous Neurotransmitter Concentration Sensor System (WINCS) for the detection of dopamine using fast scan cyclic voltammetry (FSCV). Dopamine detection performance by CNF arrays was comparable to that of traditional carbon fiber microelectrodes (CFMs), demonstrating that CNF arrays can be utilized as an alternative carbon electrode for neurochemical monitoring.