Surface Oxygen Functionalities Research Articles

Evolution of the complex surface chemistry in mesoporous carbons obtained from polyaramide precursors

Chemical evolution of micro/mesoporous ordered carbons containing nitrogen, oxygen and phosphorus surface functionalities was investigated by XPS. Nanocasting was selected as synthetic route: SBA-15 mesoporous silica was the solid template, 3-aminobenzoic acid was used as carbon, nitrogen and oxygen precursor, and phosphoric acid was selected to achieve doping with phosphorus. The evolution of the surface chemistry as a function of phosphoric acid concentration and carbonization temperature was studied, and carbons with a wide range of type and number of surface functional groups were identified. Thus, we show an easy way to successfully design ordered carbons exhibiting a specific surface composition by selecting certain experimental conditions.

Catalytic Oxidation of Aqueous Sulfide Promoted by Oxygen Functionalities on the Surface of Activated Carbon Briquettes Produced from Viticulture Wastes

In this work, the catalytic oxidation of the hazardous and unpleasant aqueous sulfide contaminant was investigated by activated carbon in the form of mechanically resistant and versatile briquettes produced from two different wastes of the wine industry, i.e., lex and stalk. Characterization by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), surface area Brunauer-Emmett-Teller (BET), Raman, thermogravimetry (TG), X-ray diffractometry (XRD) and potentiometric titration showed that the materials have high mesoporous area with a large number of surface oxygen functionalities. These briquettes showed high efficiency for the oxidation of sulfides in aqueous medium, which is discussed in terms of two effects: the relatively high concentrations of quinone/hydroquinone surface redox groups formed from the grape must binder and the macro/mesoporosity, which facilitates the diffusion of the different species during the reaction.

MD simulation of organics adsorption from aqueous solution in carbon slit-like pores. Foundations of the pore blocking effect

The results of systematic studies of organics adsorption from aqueous solutions (at the neutral pH level) in a system of slit-like carbon pores having different sizes and oxygen groups located at the pore mouth are reported. Using molecular dynamics simulations (GROMACS package) the properties of adsorbent–adsorbate (benzene, phenol or paracetamol) as well as adsorbent–water systems are discussed. After the introduction of surface oxygen functionalities, adsorption of organic compounds decreases (in accordance with experimental data) and this is caused by the accumulation of water molecules at pore entrances. The pore blocking effect decreases with the diameter of slits and practically vanishes for widths larger than approx. 0.68 nm. We observed the increase in phenol adsorption with the rise in temperature. Moreover, adsorbed molecules occupy the external surface of the slit pores (the entrances) in the case of oxidized adsorbents. Among the studied molecules benzene, phenol and paracetamol prefer an almost flat orientation and with the rise in the pore width the number of molecules oriented in parallel decreases. The decrease or increase in temperature (with respect to 298 K) leads to insignificant changes of angular orientation of adsorbed molecules.

Effect of UV-C on pre-oxidation prior amination for preparation of a selective CO2 adsorbent

In order to enhance the selectivity of activated carbon (AC) toward CO2, surface modification was carried out in a two-step approach viz. pre-oxidation and amination. First, the most suitable oxidation was determined by using O3 and H2O2 with or without UV-C (λ≈253.7nm), to impregnate surface oxygen functionalities (SOFs) on the AC surface, followed by optimization of the most efficient technique. Chemical characterization showed that pre-oxidation increased the total amount of SOFs tethered on the AC surface. However, it was reduced when the oxidation was carried out under the influence of UV-C. Upon amination, less thermally refractory SOFs such as ether, carbonyl and carboxylic groups, tend to favor the formation of surface nitrogen functionalities such as pyridine and pyrrole-N types, which showed comparatively higher affinity toward CO2. Pre-oxidation and amination parameters of AC treatment with O3 in the presence of UV-C (ROUV), which exhibited most favorable condition for CO2 low-level selectivity, were optimized. The intrinsic capture affinity of AC for low and high levels CO2 was ultimately enhanced from 0.016 and 0.46 to 0.36 and 0.9mmol/g respectively. Conclusively, UV-C inhibits the formation of recalcitrant SOFs during oxidation, thereby reducing steric hindrance and promoting amination and eventual CO2 adsorption.

Free Standing Reduced Graphene Oxide Film Cathodes for Lithium Ion Batteries

We report the fabrication and electrochemical activity of free-standing reduced graphene oxide (RGO) films as cathode materials for lithium ion batteries. The conducting additive and binder-free RGO electrodes with different oxygen contents were assembled by a simple vacuum filtration process from aqueous RGO colloids prepared with the aid of cationic surfactants. The gravimetric capacity of RGO film cathodes showed clear dependence on the oxygen contents controlled by the thermal reduction process. The capacity increased with the increase of the amount of oxygen functional groups, indicating that the main lithium capturing mechanism of RGO cathodes is Li(+) ion interaction with the surface oxygen functionalities. The hydroxyl groups (C-OH) as well as carbon-oxygen double bonds have been identified as the lithiation-active species. The RGO cathodes achieved excellent rate capability due to the fast surface Faradaic reaction, suggesting that self-supported RGO films are promising cathodes for high power application. The graphene oxide (GO)/RGO composite films showed inferior performance to those of RGO only. The poor electronic conductivity of GO might result in inefficient utilization of redox active oxygen functional groups despite the higher oxygen content and higher theoretical capacity of GO/RGO composite films. Further optimization on the amount of oxygen functional groups for higher capacity and better electronic conductivity would lead to the development of RGO based high energy-high power cathodes.

Surface oxidation of activated carbon pellets by hydrogen peroxide for preparation of CO2 adsorbent

This work attempted to use H2O2 as an oxidant for the incorporation of surface oxygen functionalities (SOFs) on activated carbon in the preparation of a CO2 adsorbent. Experimental results showed that oxidation at lowered temperature improved both structural and chemical properties more than those at ambient temperature, although oxidation at this temperature with 30% H2O2 incorporated the highest amount of useful SOFs for amination purpose. pHpzc value was most significantly reduced by altering the temperature either way while dilution seemed to have positive impact regarding this property. Pre-treatment ultimately enhanced the selectivity for CO2 adsorption as well as its capacity.

Graphene composites containing chemically bonded metal oxides

Composites of graphene involving chemically bonded nano films of metal oxides have been prepared by reacting graphene containing surface oxygen functionalities with metal halide vapours followed by exposure to water vapour. The composites have been characterized by electron microscopy, atomic force microscopy and other techniques. Magnetite particles chemically bonded to graphene dispersible in various solvents have been prepared and they exhibit fairly high magnetization.

Microwave deposition of Pt catalysts on carbon nanotubes with different oxidation levels for formic acid oxidation

Platinum (Pt) nanoparticles are uniformly deposited on carbon nanotubes (CNTs) with different oxidation levels using a pulse microwave-assisted polyol (MP) method. The CNTs are chemically oxidized using nitric acid for different periods of time (1−3 h). The MP route is capable of depositing uniform Pt nanoparticles with grain size of 2.67–2.95 nm over the surface of CNTs, forming Pt@CNT catalysts for formic acid electro-oxidation. The oxygen functionalities assist in the deposition of Pt crystals over the oxidized CNTs. The Pt@CNT catalyst with high oxidation level shows positive effects on the ratio of direct (dehydrogenation) to indirect (dehydration) oxidation, CO tolerance, and long-term stability. The improved anti-poisoning ability is attributed to the facts that the surface oxygen functionalities facilitate the direct pathway of HCOOH oxidation and strip the Pt-COads occupied sites.

Influence of activated carbon surface oxygen functionalities on SO2 physisorption – Simulation and experiment

The influence of the gradual oxidation of carbons on SO2 physisorption was studied, by comparison of experimental and simulated SO2 adsorption isotherms. The results confirmed a significant impact of surface groups on the SO2 adsorption. The simulations also revealed a similar, to that observed experimentally, effect of the increase in the percentage of the smallest micropores on adsorption isotherms. The isotherms were analysed using the CMMS model. The conclusion is that this model seems to be a good and sensitive tool for studying SO2 physisorption mechanism since a very good qualitative agreement between the experimental and simulated data was observed.

Synthesis and Functionalization of Nitrogen-doped Carbon Nanotube Cups with Gold Nanoparticles as Cork Stoppers

Nitrogen-doped carbon nanotubes consist of many cup-shaped graphitic compartments termed as nitrogen-doped carbon nanotube cups (NCNCs). These as-synthesized graphitic nanocups from chemical vapor deposition (CVD) method were stacked in a head-to-tail fashion held only through noncovalent interactions. Individual NCNCs can be isolated out of their stacking structure through a series of chemical and physical separation processes. First, as-synthesized NCNCs were oxidized in a mixture of strong acids to introduce oxygen-containing defects on the graphitic walls. The oxidized NCNCs were then processed using high-intensity probe-tip sonication which effectively separated the stacked NCNCs into individual graphitic nanocups. Owing to their abundant oxygen and nitrogen surface functionalities, the resulted individual NCNCs are highly hydrophilic and can be effectively functionalized with gold nanoparticles (GNPs), which preferentially fit in the opening of the cups as cork stoppers. These graphitic nanocups corked with GNPs may find promising applications as nanoscale containers and drug carriers.

Synthesis and Functionalization of Nitrogen-doped Carbon Nanotube Cups with Gold Nanoparticles as Cork Stoppers

Nitrogen-doped carbon nanotubes consist of many cup-shaped graphitic compartments termed as nitrogen-doped carbon nanotube cups (NCNCs). These as-synthesized graphitic nanocups from chemical vapor deposition (CVD) method were stacked in a head-to-tail fashion held only through noncovalent interactions. Individual NCNCs can be isolated out of their stacking structure through a series of chemical and physical separation processes. First, as-synthesized NCNCs were oxidized in a mixture of strong acids to introduce oxygen-containing defects on the graphitic walls. The oxidized NCNCs were then processed using high-intensity probe-tip sonication which effectively separated the stacked NCNCs into individual graphitic nanocups. Owing to their abundant oxygen and nitrogen surface functionalities, the resulted individual NCNCs are highly hydrophilic and can be effectively functionalized with gold nanoparticles (GNPs), which preferentially fit in the opening of the cups as cork stoppers. These graphitic nanocups corked with GNPs may find promising applications as nanoscale containers and drug carriers.

Electron Cyclotron Resonance-Sputtered Nanocarbon Film Electrode Compared with Diamond-Like Carbon and Glassy Carbon Electrodes as Regards Electrochemical Properties and Biomolecule Adsorption

The electrochemical properties and biocompatible characteristics at an electron cyclotron resonance (ECR)-sputtered nanocarbon film electrode, a diamond-like carbon (DLC) electrode and a glassy carbon (GC) electrode have been studied. The three carbon electrodes show significant current reductions with increased peak separations as a result of protein fouling before oxygen plasma treatment, but the current reductions of the ECR-sputtered nanocarbon and DLC film electrodes are smaller than that of the GC electrode due to their superior surface flatness. The oxygen plasma pretreated ECR-sputtered nanocarbon film electrode exhibits a significant improvement in anti-fouling performance with an improved electron transfer. This is because the pretreated ECR-sputtered nanocarbon film enabled the surface to introduce surface oxygen functionalities that not only improve the interaction between the analytes and the electrode surface but also make the film surface more hydrophilic, which is important for the suppression of biomolecule adsorption. At the same time, the pretreated ECR-sputtered nanocarbon film also retained an ultraflat surface even after pretreatment as a result of the low background current. This excellent performance can only be achieved with our ECR-sputtered nanocarbon film, indicating that our film is promising for application to electrochemical detectors for various biomolecular analytes.

Dye-sensitized solar cells equipped with graphene-based counter electrodes with different oxidation levels

This study examines the performance of dye-sensitized solar cells (DSCs) equipped with graphene nanosheet (GN) counter electrodes having different oxidation levels. A thermal deposition is adopted to adjust the O/C atomic ratio and surface oxygen functionalities on graphene sheets. By decreasing the O/C ratio, the GN electrode displays high catalytic activity toward the I3−/I− redox reaction and lower charge-transfer resistance, as analyzed by cyclic voltammetry and electrochemical impedance spectroscopy. The DSC fabricated with the GN counter electrode also offers an improved incident photon-to-current efficiency and power conversion efficiency, in comparison with that equipped with graphene oxide electrodes. This improvement of cell performance could be attributed to the fact that the GN electrode, with a two-dimensional crystal of sp2 carbon, serves as a semi-metal or a zero-bandgap semiconductor with remarkable high electron mobility.

Potential of powdered activated mustard cake for decolorising raw sugar

Carbon decolorisation has become customary in the food processing industries; however, it is not economical. Extensive research has therefore been directed towards investigating potential substitutes for commercial activated carbons which might have the advantage of offering an effective, lower-cost replacement for existing bone char or coal-based granular activated carbon (GAC). The physical (bulk density and hardness), chemical (pH and mineral content) and adsorption characteristics (iodine test, molasses test and raw sugar decolorisation efficiency) of powdered activated mustard cake (PAMC) made from de-oiled mustard cake were determined and compared to commercial adsorbents. Although the colour removal efficiency of the PAMC is lower than that of commercial materials, it is cost effective and eco-friendly compared to the existing decolorisation/refining processes. To reduce the load on GAC/activated carbon/charcoal, PAMC could be used on an industrial scale. A decolorisation mechanism has been postulated on the basis of oxygen surface functionalities and surface charge of the PAMC and, accordingly, charge transfer interaction seems to be responsible for the decolorisation mechanism. In addition, a complex interplay of electrostatics and dispersive interaction seem to be involved during the decolorisation process. A low-cost agricultural waste product in the form of de-oiled mustard cake was converted to an efficient adsorbent, PAMC, for use in decolorising raw as well as coloured sugar solutions. The physical, chemical, adsorption characteristics and raw sugar decolorisation efficiency of PAMC were determined and compared to those of commercial adsorbents. The colour removal efficiency of the PAMC is lower than that of commercial materials but it is cost effective and eco-friendly as compared to existing decolorisation/refining processes. The availability of the raw material for the production of PAMC further demands its use on an industrial scale.

Surface characterisation of oxygen plasma treated electrospun polyurethane fibres and their interaction with red blood cells

In this work, the effects of oxygen plasma surface modification have been studied on electrospun polyether-based polyurethane in order to investigate the imposed limitations and possibilities to improve surface characteristics on fibrous assemblies. The evolution of induced changes in surface morphology, chemistry and wettability by the plasma treatment has been characterised for increasing plasma exposure time using scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Significant reduction in fibre diameter concomitant with progressing rough surface textures are found on the fibres in surface layers during early treatment phases while extended exposure eventually causes the fibre structure to deteriorate. Surface oxygen content and functionalities such as carbonyl and carboxyl increase slightly with longer treatments until loss of material integrity occurs. The results have also shown that oxygen plasma rapidly alters the initially strong hydrophobic character of the non-woven fibres to hydrophilic behaviour, allowing water penetration into the network, but without significant changes for increased exposure time. In addition, the response of red blood cell shape to pristine and oxygen plasma treated fibres were found to be similar. In both cases, a population of cells having fibre contact displayed protrusions while measurements showed that the cell function remain intact and indicated that the adhesion was non-specific. The reported findings yield useful process knowledge that can support the formation of well-defined fibre architectures and are valuable in the designs of electrospun polyurethane material systems utilising oxygen plasma surface modification.

Synthesis and characterisation of nanoporous carbon–metal composites for hydrogen storage

Metal–carbon composites have nowadays received much attention as potential hydrogen stores, since nanosized metal particles seem to catalytically enhance hydrogen sorption at room temperature. In the present work a series of ordered mesoporous carbon materials of CMK-3 type are modified, either by heat treatment or mild oxidation in order to induce varying amounts of oxygen surface functionalities, and doped with Pd nanoparticles in an attempt to elucidate the associated hydrogen storage process. Although the measured hydrogen storage capacities are far below the desirable targets for practical applications, the obtained results demonstrate clearly the synergy between the carbon support and the dispersed metal nanoparticles towards a significant enhancement of hydrogen adsorption.

Physicochemical and Toxicological Properties of Commercial Carbon Blacks Modified by Reaction with Ozone

Ozonation of two commercial carbon blacks (CBs), Printex 90 (P90) and Flammruss 101 (F101), was carried out and changes in their morphology, physical properties, and cytotoxicity were examined. The hypothesis examined was that different methods of manufacture of CBs influence their chemical reactivity and toxicological properties. Structural changes were examined by X-ray photoelectron spectroscopy, infrared spectroscopy, Raman spectroscopy, and electron paramagnetic resonance spectroscopy (EPR). Introduction of surface oxygen functionality upon ozonation led to changes in surface charge, aggregation characteristics, and free radical content of the CBs. However, these changes in surface functionality did not alter the cytotoxicity and release of inflammation markers upon exposure of the CBs to murine macrophages. Interaction of macrophages with F101 resulted in higher levels of inflammatory markers than P90, and the only structural correlation was with the higher persistent radical concentration on the F101.

Effect of potassium permanganate pretreatment of pitch on the textural properties of pitch-based activated carbons

Petroleum pitch-based activated carbons (ACs) were obtained in this work from a combination of pretreatment with different amounts of potassium permanganate (KMnO4) and chemical activation with potassium hydroxide. The surface characteristics of the pitch after the KMnO4 pretreatment were characterized by means of Fourier transform infrared spectroscopy (FT-IR). The structural characteristics of the pitch after the KMnO4 pretreatment were determined by means of X-ray diffraction. The influence of the KMnO4 treatment on the textural properties of the petroleum pitch-based ACs was investigated by means of N2/77 K adsorption isotherms. The investigation also involved the use of the Brunauer-Emmett- Teller equation and the Dubinin-Radushkevich method. The FT-IR results show that the pretreatment promotes the formation of surface oxygen functionalities and leads to an increase of the interplanar distance (d002) of the functional groups induced between carbon layers. Moreover, the specific surface area of the pitch-based ACs increases in proportion to the amount of KMnO4 pretreatment and reaches its highest value of 2334 m2/g with 2 g of KMnO4 because the surface oxygen groups of the pitch act as an active site during chemical activation.

Oxygen-doped activated carbon fiber cloth as electrode material for electrochemical capacitor

Novel oxygen-doped activated carbon fiber cloths (OACFC), with different compositions of surface oxygen functionalities, have been prepared by direct electrooxidative/reductive methods in an undivided electrolytic cell filled with high purity water without a supporting electrolyte under high voltage conditions. The morphology and surface chemical composition of the materials have been investigated by SEM, Raman and XPS spectroscopies. They revealed an electrochemical erosion of the CF surface upon activation, concomitant with a strong change of the D/G ratio of characteristic Raman bands and the surface O/C atomic ratio, respectively. Thus pretreated material was tested as electrodes for an electrochemical capacitor by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements in 3.75 M H 2SO 4. The performance of the electrochemical capacitor based on modified carbon electrodes was compared to that of an analogous device with unmodified carbon. The measurements revealed altered electrochemical behavior of the OACFC in terms of the determined capacitances. The proposed activation method is also superior to other electrochemical activation procedures, since it uses much less energy per CF surface or mass.

Synthesis of submicron carbon spheres by the ultrasonic spray pyrolysis method

Submicron carbon spherical particles were obtained by polycondensation of resorcinol and formaldehyde in a solution and subsequent ultrasonic spray pyrolysis of the prepared sol. Microscopic characterization indicates the regular spherical shape of the obtained particles and sphere diameters in 200–700 nm range. The carbon spheres are amorphous as confirmed by electron diffraction, EELS, XRD and HREM characterization. Activation procedure was performed with H 2O in a nitrogen flow for 15 and 30 min at 800 °C. The activation procedure preserved the initial spherical shapes of the particles while the particle porosity and specific surface area were increased. The amount of surface oxygen functionalities was also increased by activation procedure as indicated by FTIR analysis.