Electrochemical catalytic modification of activated carbon fabrics by ruthenium chloride for supercapacitors

A novel method, electrochemical catalytic oxidation via a ruthenium redox couple in an aqueous RuCl₃ · xH₂O solution rather than the anodic deposition of Ru oxides, was developed to modify the microstructure and electrochemical properties of activated carbon fabrics (ACFs). The variation in microstructures (i.e., specific surface area and mean pore size) for the modified ACFs was examined by means of nitrogen gas adsorption isotherms. The distribution of oxygen-containing functional groups within the modified ACFs was identified by temperature programmed desorption (TPD) and X-ray photoelectron (XPS) spectra. Effects of the electrochemical catalytic modification on the electrochemical characteristics and reversibility of ACFs were investigated systematically by means of cyclic voltammetry (CV) and chronopotentiometry (CP) in 0.5 M H₂SO₄. The total specific capacitance of ACFs reached a maximum (ca. 180 F/g measured at 10 mA/cm²) when they were catalytically modified at 1.15 V with a passed charge density of 5 C/cm². These modified ACFs were demonstrated to be an excellent candidate for the supercapacitor application.     

Functionalization of carbon nanotubes using a silane coupling agent

A new method is developed to chemically functionalize multi-walled carbon nanotubes (MWCNTs) based on silanization reaction for use as the reinforcement for polymer matrix composites. To oxidize and create active moieties on the MWCNTs, the samples were exposed to UV light within the ozone chamber, followed by silanization using 3-glycidoxypropyltrimethoxy silane after the oxidized MWCNTs were reduced by lithium aluminum hydride. FT-IR, TEM and XPS were employed to characterize the changes in carbon nanotubes surface morphology, chemistry and physical conditions at different processing stages. The results indicate improved dispersion and attachment of silane molecules on the surface of the MWCNTs.     

Pore structure modification of pitch-based activated carbon by NaOCl and air oxidation/pyrolysis cycles

Two complementary wearing off cycling methods based on an initial wet oxidation in a sodium hypochlorite solution or an initial dry oxidation under air, both followed by a thermal pyrolysis under nitrogen, have been applied to a same carbon molecular sieve to study its gradual pore structure modifications. The changes in microporous properties resulting from these cycles were studied by N₂ physisorption at 77 K and analyzed by using the Dubinin–Radushkevich equation. The observed textural behaviour is different from those usually observed using conventional activation processes. The surface complexes created on the surface of carbon by each NaOCl oxidation were characterized by temperature-programmed desorption (TG-TPD-MS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Corresponding surface functional species have been identified and quantified.

Each of the two methods leads to the formation of two distinct microporous domains developed on the obtained modified CMS series. The gradual mean pore size values of one of those domains are common to the two series while the others are much more enlarged by the oxygen than by the NaOCl treatments. Therefore, the two methods lead to complementary data allowing experimental differentiation of the different porosities encountered in activated carbons. Such series of materials of common origin and surface chemistry but different gradual textural properties are of great interest for activated carbons structural studies as well as for characterization technique improvements.     

Enhancement of adsorption on graphite (HOPG) by modification of surface chemical functionality and morphology

The effects of chemical functional groups and surface morphology on the adsorption/desorption behavior of a model non-polar organic adsorbate (propane) on model carbonaceous surfaces [air-cleaved highly oriented pyrolytic graphite (HOPG) and plasma-oxidized HOPG], were investigated using temperature-programmed desorption (TPD). Oxygen- and hydrogen-containing functional groups exist on both air-cleaved HOPG and plasma-oxidized HOPG. The presence of these groups almost completely suppresses propane adsorption at 90 K. However, these groups can be removed from both air-cleaved and plasma-oxidized HOPG by thermal treatment (>500 K), leading to more than an order of magnitude increase in adsorption capacity. It is essential for both air-cleaved HOPG and plasma-oxidized HOPG to be outgassed at over 1273 K for all the adsorption sites to be chemically accessible for propane molecules. The effect of morphological heterogeneity is evident for plasma-oxidized HOPG as this substrate provides greater surface area available for adsorption, as well as higher energy binding sites.     

Surface modification of PEEK by UV irradiation for direct co-curing with carbon fibre reinforced epoxy prepregs

Adding a layer of thermoplastic resin on the surface of thermoset composites enables welding as a possible joining method for thermoset composites. Adhesion at the thermoset/thermoplastic interface was achieved by direct co-curing of an UV irradiation treated PEEK film with aerospace grade carbon/epoxy prepregs. The effectiveness of UV irradiation for surface modification of PEEK was characterized using Fourier-Transformed InfraRed (FTIR) spectroscopy and contact angle measurement. The adhesion quality at the thermoset/thermoplastic interface was evaluated using a double cantilever beam test and Atomic Force Microscopy (AFM). UV treatment was found to effectively modify the chemical structure of PEEK surface and improve the wettability, which enables the development of a thermoset/thermoplastic interface by direct co-curing.     

Modified carbon nanotubes: an effective way to selective attachment of gold nanoparticles

Through various modifications of carbon nanotubes (CNTs), gold nanoparticles were selectively attached to the nanotube and the locations of functional groups were further confirmed. Using cationic polyethyleneamine or anionic citric acid as the dispersant, the surface properties of CNTs could be changed to yield a basic or acidic surface. By electrostatic interaction, the CNTs could be successfully coated with about 10 nm gold nanoparticles. After heat treatment in NH₃, about 1–2 nm gold nanocluster-filled nanotubes were achieved. This shows that the heat treatment with NH₃ could make CNTs open-ended and generate functional basic groups on the inner wall of the nanotubes.     

Surface modification and characterisation of a coal-based activated carbon

Surface modification of a coal-based activated carbon (F400) was performed using thermal and chemical methods. Nitric acid oxidation of the conventional sample produced samples with weakly acidic functional groups and the presence of such groups was confirmed by Fourier transform infra red (FTIR) spectroscopy, pH titration, zeta potential measurements and sodium uptake capacity results. There was a significant loss in microporosity of the oxidised samples which was caused by humic substances that were formed as a by-product during the oxidation process. Thermal treatment produced a carbon with some basic character while amination of the thermally treated carbon gave a sample containing some amino (–NH₂) groups and these groups were detected by X-ray photoelectron spectroscopy (XPS) analysis.     

Voltammetric quantification of the spontaneous chemical modification of carbon black by diazonium coupling

Surface coverage limits obtained through the spontaneous and reductive reaction of 1-diazo-anthraquinone ions with Vulcan XC72 carbon black have been studied using cyclic voltammetry. The effect of modifying the surface structure of the carbon, varying reaction conditions and time, and the use of sequential reactions were studied. The maximum loading of AQ that could be obtained was 1.0 × 10⁻⁴ mol g⁻¹, consisting in the best case of a 3:1 ratio of covalently bound to adsorbed species. Based on literature specific area values for the carbons and measured specific capacitances, it is concluded that only ca. 25% of the BET area of the pristine Vulcan XC72 is accessible to the diazonium ions, and that a loosely packed monolayer of bound and adsorbed species is formed on this accessible area. Carboxylic acid groups on the carbon surface were not found to limit the total loading of AQ, but did significantly favor covalent bonding over adsorption.     

Surface properties of oxyfluorinated PAN-based carbon fibers

In this study, the oxyfluorination of PAN-based carbon fibers was undertaken at room temperature using fluorine-oxygen mixtures, and the influence of oxyfluorination on properties such as wettability, surface polarity, surface free energy, conductivity and tensile strength was investigated. As the oxyfluorination time increased at a total pressure of 5 kPa, both the fluorine/carbon and oxygen/carbon ratios increased. The contribution of semicovalent C-F bond to F1s spectra is considerably decreased with increasing total pressure from 5 to 80 kPa, and at the same time, the contribution of covalent C-F bond is increased. As the total pressure of fluorine-oxygen mixtures increased, the contact angle of water significantly decreased and again increased to a similar value to that of as-received carbon fiber. A short oxyfluorination of carbon fibers considerably increased the wettability, that is, hydrophilicity.The electrical conductivity of oxyfluorinated carbon fiber is larger than that of the as-received fiber. This is because the surface region of carbon fiber is fluorinated. An increase in the tensile strength of about 18% after oxyfluorination is observed. The increase in tensile strength of oxyfluorinated carbon fibers can be understood as being due to a decrease in the diameter of the fiber.     

A new method for the preparation of stable carbon nanotube organogels

Single-walled carbon nanotubes (SWNTs) functionalized by ferrocene-grafted poly(p-phenyleneethynylene)s can gelate common organic solvents such as chloroform to form a freestanding carbon nanotube organogel that cannot be redispersed in any organic solvents, indicating the robustness of 3D nanotube network. The drying of SWNT gel on silicon wafer in the air gives a highly convoluted film that is composed of numerous bumps and grooves at multiple length scales. In addition, we report a method for the preparation of an insoluble, homogeneous, electroactive SWNT film from a fresh SWNT solution, which may find applications in nanotube coatings and thin films that require both uniformity and solvent-resistance.     

NOx adsorption-temperature programmed desorption and surface molecular ions distribution by activated carbon with chemical modification

Activated carbon, the surface of which has been modified with KOH, was used in this study. The study examined adsorption and desorption behaviors and the accompanied surface reaction mechanism as well as the distribution of molecular ions on the surface. The peaks of NO_x desorption behavior may be classified into three bond categories depending on adsorption strength. NO desorption occurs at the earliest stage as chemical adsorption occurs earlier, in a sort of competition, than physical adsorption due to strong basic OH⁻ ion of surface. It was confirmed that the adequate temperature for NO_x desorption was near 390 °C. The potassium that existed on the surface remained without being consumed even with complete desorption of NO_x.     

Analysis of the microporous texture of a glassy carbon by adsorption measurements and Monte Carlo simulation. Evolution with chemical and physical activation

A mesoporous glassy carbon has been chemically (KOH) and physically (CO₂) activated in order to improve its micropore volume while preserving the well-defined mesopore network. The microporosity of the glassy carbon and the evolution of the micropore texture with activation have been studied by means of Monte Carlo simulation and gas adsorption. Micropore size distributions obtained from simulated adsorption isotherms on slit-shaped pores revealed different accessibilities of methane and nitrogen to the microporous texture of the original sample, indicating the presence of constrictions in the micropore network. Both activating agents are able to increase the micropore volume generating new micropores, although KOH showed to be more effective. While CO₂ treatment preserved some hindrances to the access of nitrogen molecules to the micropores, KOH activation generates a more accessible micropore network. Therefore, chemical activation by KOH is a suitable way to increase the adsorption capacity of glassy carbons while preserving the mesoporous structure. Molecular simulation of adsorption linked to experimental adsorption of different gases, has proven to give very satisfactory results in analysing the evolution of the micropore texture and accessibility of carbon materials by different activation treatments.     

Biomimetic surface modification on polyacrylonitrile-based asymmetric membranes via direct formation of phospholipid moieties

To improve the antifouling property and biocompatibility for polyacrylonitrile-based asymmetric membranes, phospholipid moieties were directly anchored on the poly(acrylonitrile-co-2-hydroxyethyl methacrylate) (PANCHEMA) membrane surface through the reaction of hydroxyl groups and 2-chloro-2-oxo-1,3,2-dioxaphospholane (COP) followed by the ring-opening of COP with trimethylamine. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and water contact angle measurement were employed to confirm the conducted surface modification. Water and protein solution filtration tests plus cell adhesion measurement were used to evaluate the antifouling property and the biocompatibility of the membranes. It was found that the content of the phospholipid moieties on the membrane surface, which can be mainly modulated by the content of reactive hydroxyl groups in PANCHEMA, has a great influence on the performances of the studied membranes. With the increase in the phospholipid moieties content at the modified membrane surface, the hydrophilicity and biocompatibility on the basis of water contact angle and macrophage adhesion can be improved significantly. Furthermore, the modified membranes show higher water and protein solution fluxes, and better flux recovery after cleaning than those of the original PANCHEMA membranes. All these results reveal that the antifouling property and biocompatibility of PANCHEMA membrane could be enhanced obviously by the introduction of phospholipid moieties on the membrane surface.     

Enhanced mass transport to a reticulated vitreous carbon rotating cylinder electrode using jet flow

The mass transport characteristics of a porous, rotating cylinder electrode (RCE, 1.0 cm diameter; 0.5, 0.9 or 1.2 cm long; 1.25, 2.25, 3.00 cm³ overall volume; 250-2000 rpm speed) fabricated from reticulated vitreous carbon (RVC, 60 ppi or 100 ppi) were investigated. The deposition of copper from an acid sulfate electrolyte (typically, deoxygenated 1 mM CuSO₄ in pH 2, 0.5 M Na₂SO₄ at 298 K) was used as a test reaction. The effect of a jet flow of electrolyte towards the electrode and the introduction of polypropylene baffles in the electrochemical cell were studied at controlled rotation rates of the RCE. The product of mass transport coefficient and volumetric electrode area (k_mA_e) is related to the rotation speed of the electrode. For the 60 ppi RVC RCE, the jet electrolyte flow (3.5 cm³ s⁻¹) enhanced the mass transport rates by a factor of 1.46 at low rotation speeds; this factor was reduced to 1.08 at high rotation speeds. For a 100 ppi electrode, the enhanced mass transport decreased from 1.26 to 1.03 at low and high rotation rates, respectively. Under the experimental conditions, baffles showed little effect on the mass transport rates to the RVC RCE. Mass transport to jet flow at an RVC RCE is compared to other RCEs using dimensionless group correlation.     

Ordered mesoporous carbons: Implication of surface chemistry, pore structure and adsorption of methyl mercaptan

Three ordered mesoporous carbon materials (OMC) were prepared by pyrolysis of sucrose filled in the mesoporous channels of SBA-15 at three different temperatures of 600 °C (OMC-600), 850 °C (OMC-850) and 1100 °C (OMC-1100), and followed by dissolution of the silica matrix in hydrofluoric acid. The pore structures and surface characteristics of the OMC materials were evaluated using XRD, nitrogen adsorption, FTIR spectroscopy, pH of carbon surface, and the amount of acidic surface groups from Boehm titration, respectively. The increase of the pyrolysis temperature resulted in an increase in surface pH, but a decrease in the amount of acidic surface groups. The surface area and micro- and mesopore volumes increased by increasing the pyrolysis temperature from 600 °C to 850 °C, but there were no significant changes in these properties above 850 °C. In this paper, adsorption characteristics of methyl mercaptan on the OMC materials were studied using a dynamic adsorption method in a fixed bed. The results showed that the adsorption of methyl mercaptan was strongly influenced by pore structure and surface chemistry of the OMC.     

Characterization of oxidized reticulated vitreous carbon electrode for oxygen reduction reaction in acid solutions

The oxidation of reticulated vitreous carbon (RVC) and its impact on the oxygen reduction reaction (ORR) in H₂SO₄ solutions has been studied. The results are compared with that of a planar glassy carbon (GC) electrode. The oxidation process was characterized by using different electrode configurations, GC (planar) and RVC electrodes both with flooded (batch process) and flow-through assembly. Cyclic voltammetry, potentiodynamic and rotating ring-disk electrode voltammetry were used for the characterization of the ORR. Anodically oxidized GC and flooded RVC are similar in that the ORR on both electrodes gave a more defined limiting current plateau. For the flow-through porous electrode, the oxidation process caused a distribution of the oxidation extent within the bed thickness, as evident from the SEM images, and only about half of the porous electrode was utilized in the oxidation process. X-ray photoelectron spectroscopy (XPS) measurements confirmed the above distribution and a gradient of the oxygen-to-carbon ratio was obtained within the porous bed. Oxidation of RVC led to an enhancement of its electrocatalytic properties towards ORR. H₂O₂ production was tested at the oxidized RVC from flowing acid solutions. The oxidation of RVC resulted in higher current efficiencies and higher outlet concentrations of the H₂O₂ acid solutions.     

Sensitivity of single wall carbon nanotubes to oxidative processing: structural modification, intercalation and functionalisation

The effect of oxidation on modification of single wall carbon nanotubes (SWCNTs) through successive purification steps has been studied. The efficient elimination of metal impurities has been followed by induced coupled plasma spectroscopy. Upon acid treatment, Raman spectroscopy clearly proofed that HNO₃ molecules were intercalated into the bundles of SWCNTs. At the same time, SWCNTs also have suffered a high degree of degradation and defects were introduced. The subsequent thermal processes led to the removal of further defect carbon materials and to the almost complete de-intercalation of the HNO₃ molecules. Changes in the structure of the SWCNT bundles have been observed by transmission electron microscopy. While bundles tend to separate upon acid treatment, after the complete purification process, the remaining SWCNTs tend to form thick bundles again. The existence of functional groups in the raw single wall carbon nanotubes material and their modification and almost complete removal after the final annealing step has been studied by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and temperature programmed desorption. Nitrogen adsorption isotherms analysed according to Brunauer-Emmet-Teller showed important changes in the pore volume and surface area through the purification steps.     

Surface modification of a granular activated carbon by citric acid for enhancement of copper adsorption

In this study, citric acid was used to modify a commercially available activated carbon to improve copper ion adsorption from aqueous solutions. The carbon was modified with 1.0 M citric acid, followed by an optional step of reaction with 1.0 M sodium hydroxide. It was found that the surface modification reduced the specific surface area by 34% and point of zero charge (pH_pzc) of the carbon by 0.5 units. Equilibrium results showed that citric acid modification increased the adsorption capacity to 14.92 mg Cu/g, which was 140% higher than the unmodified carbon. Higher initial solution pH resulted in higher copper adsorption. The chemical surface modification adversely affected the copper adsorption rate. Adsorption kinetic mechanisms were investigated with an intraparticle diffusion model. It was found that the modification did not change both external diffusion and intraparticle diffusion.     

Removal of ionic substances from dilute solution using activated carbon electrodes

Removal of various electrolytes from aqueous solution and a recycling operation were carried out using a flow-through capacitor. The amount of ions removed corresponds to the surface area and especially the micropore volume of the activated carbon electrode. Introduction of acidic functional groups on the surface of the carbon promoted ion removal (i.e. increase in rate and capacity), but there is a limit to the amount of functional groups that can be introduced with good effect. The adsorption-desorption properties of various alkali, alkaline earth and heavy metal sulfates were investigated. It was found that removal characteristics were different for the different types of ions. Depletion of the electrode also differed depending on the electrolyte that was removed. When copper and zinc ions were removed, the surface area of the cathode was reduced by a small amount.     

Measurement of functionalised carbon nanotube carboxylic acid groups using a simple chemical process

Chemically functionalised single-walled carbon nanotubes were formed using sonication in a mixture of concentrated sulphuric and nitric acids for varying lengths of time which resulted in carboxylic acid group functionalisation, predominantly at the ends. The carboxylic acid groups were used to form an ionic bond with dodecylamine. The weight of this complex was used to monitor the number of carboxylic acid groups present in the cut SWNT.