Number Of Surface Oxygen Groups Research Articles

Eco-friendly biosorbent for lead removal: Activated carbon produced from grape wood

This study looked into the removal of heavy metals from aqueous systems using carbon obtained from grape wood, an agricultural waste. Activated carbon was created by pyrolyzing and activating grape wood. Characterization of the material showed a highly porous structure with a large number of surface oxygen groups. In batch investigations, optimal conditions (pH 5, 25 °C, 100 mg L−1 starting Pb2+) resulted in an all-out lead uptake capability of 135.7 mg g−1. In 60 min, over 90% of the material was removed at a pseudo-second-order rate of 1.894 × 10−4 g mg-1 min-1. Adsorption had an all-out capability of 293.7 mg g−1, which was in line with the Sips model. Positive enthalpy (70.88 kJ mol−1) and entropy (0.2546 kJK−1mol−1) values from the thermodynamic analysis suggested chemisorption. Using HCl, the adsorbent could be renewed up to five times.

Contribution of surface roughness and oxygen-containing groups to the interfacial shear strength of carbon fiber/epoxy resin composites

The interfacial shear strength (IFSS) between carbon fibers (CFs) and the matrix is crucial to the performance of CF-reinforced polymer composites. To evaluate the contribution of mechanical interlocking and chemical anchoring at the interfaces of a polyacrylonitrile-based CF (TORAYCA T800SC-12000-10E)-reinforced epoxy resin (EP: bisphenol A type epoxy resin and tetrafunctional epoxy resin) composites, the surface roughness and content of oxygen-containing functional groups of the CFs were respectively altered by ammonia treatment and electrochemical oxidation. The results showed that ammonia treatment increased the surface roughness without much change to the surface elemental composition, while electrochemical oxidation increased the number of surface oxygen groups without changing the surface roughness. The IFSS of CF/EP composites was tested by the micro-droplet method. The relationships between IFSS, and surface roughness and oxygen content were obtained by linear fitting. The results showed that in the interfacial bonding of CF to epoxy resin, the contribution of chemical anchoring to the IFSS is larger than that of mechanical interlocking.

Enhancement of the Electrode Activity of the Vanadium Redox Flow Battery by Higher Crystallinity of Carbon Matrix Using Seamless and Consecutive-porous Carbon Materials

The crystallinity of the carbon matrix and the surface oxygen groups of the electrode materials for vanadium redox flow batteries (VRFBs) are considered to be important for enhancing the activity of the electrochemical reactions. We applied seamless carbon materials with consecutive macropores as a novel electrode material for the VRFB. We heat-treated the seamless carbon materials from 1200 °C to 2200 °C in an Ar atmosphere, then oxidized them in air at the appropriate temperature. Although the number of surface oxygen groups, which are believed to be the active sites, decreased at the higher crystallinity of the carbon matrix, the electrode activity was simply increased at the higher crystallinity of the carbon matrix. This result suggests the increased π electron density enhanced the ion exchange between the active materials and protons at the active sites due to the higher pK a value. Next, we examined the necessity of the surface oxygen groups for the material by the thermal decomposition in the Ar atmosphere. The current density significantly decreased after the thermal decomposition of the surface oxygen groups. Hence, the surface oxygen groups are believed to be essential for the electrochemical reactions.

Functionalization of graphenic surfaces by oxygen plasma toward enhanced wettability and cell adhesion: experiments corroborated by molecular modelling.

Graphenic materials attract huge attention because of their outstanding properties, and have a wide range of applications as, i.e., components of biomaterials. Due to their hydrophobic nature, however, the surfaces need to be functionalized to improve wettability and biocompatibility. In this study, we investigate the functionalization of graphenic surfaces by oxygen plasma treatment, introducing surface functional groups in a controlled way. The AFM images and LDI-MS results clearly show that the graphenic surface exposed to plasma is decorated with -OH groups, whereas the surface topography remains intact. The measured water contact angle decreases significantly after oxygen plasma treatment from 99° to ca. 5°, making the surface hydrophilic. It is also reflected in the surface free energy values which increase from 48.18 mJ m-2 to 74.53 mJ m-2 when the number of surface oxygen groups reaches 4 -OH/84 Å2. The DFT (VASP) molecular models of unmodified and oxygen-functionalized graphenic surfaces were constructed and used for molecular interpretation of water-graphenic surface interactions. The computational models were validated by comparison of the theoretically determined water contact angle (based on the Young-Dupré equation) to the experimentally determined values. Additionally, the VASPsol (implicit water environment) results were calibrated against the explicit water models that can be used in further research. Finally, the biological role of functional groups on the graphenic surface was examined in terms of cell adhesion with the use of mouse fibroblast cell line (NIH/3T3). The obtained results illustrate the correlation between surface oxygen groups, wettability, and biocompatibility providing the guidelines for the molecular level-driven design of carbon materials for various applications.

Beech sawdust based adsorbents for solid-phase extraction of pesticides and pharmaceuticals

Carbonaceous solid-phase extraction (SPE) sorbent, efficient in isolation and enrichment of multiclass pesticides and pharmaceuticals from water, was synthesized starting from cheap waste beech sawdust and using KOH as the activated agent. The first step in carbon material preparation was hydrothermal carbonization of the waste beech sawdust. Following hydrothermal treatment, the obtained material was activated, using different amounts of KOH. It was found that applied activation leads to changes in material structure, an increase in specific surface area, and a decrease in the number of surface oxygen groups compared to carbonized sample. SPE procedure of multiclass pesticides and pharmaceuticals from water using activated carbonized beech sawdust (AcSD) was optimized by selecting the appropriate elution solvents, the sample pH, and the sample volume to obtain the highest enrichment efficiency. The optimized SPE procedure was applied for water analysis using different AcSD samples as a sorbent for analyte preconcentration. Activated carbon sorbent, obtained with the highest amount of KOH, showed the highest recoveries regarding the most analytes, which were comparable with the recoveries obtained by commercial cartridges.

Adsorption of Single and Multiple Graphene-Oxide Nanoparticles at a Water-Vapor Interface.

The adsorption of graphene-oxide (GO) nanoparticles at the interface between water and vapor was analyzed using all-atom molecular simulations for single and multiple particles. For a single GO particle, our results indicate that the adsorption energy does not scale linearly with the surface coverage of oxygen groups, unlike typically assumed for Janus colloids. Our results also show that the surface activity of the particle depends on the number of surface oxygen groups as well as on their distribution: for a given number of oxygen groups, a GO particle with a patched surface was found to be more surface active than a particle with evenly distributed groups. Then, to understand what sets the thickness of GO layers at interfaces, the adsorption energy of a test GO particle was measured in the presence of multiple GO particles already adsorbed at the interface. Our results indicate that in the case of high degree of oxidation, particle-particle interactions at the water-vapor interface hinder the adsorption of the test particle. In the case of a low degree of oxidation, however, clustering and stacking of GO particles dominate the adsorption behavior, and particle-particle interactions favor the adsorption of the test particle. These results highlight the complexity of multiple particle adsorption and the limitations of single-particle adsorption models when applied to GO at a relatively high surface concentration.

Feasibility of electrochemical regeneration of activated carbon used in drinking water treatment plant. Reactor configuration design at a pilot scale

This work evaluates the feasibility of electrochemical regeneration of granular activated carbon used in drinking water treatment plants as a real alternative to thermal regeneration. Two pilot-plant-scale reactors, with a capacity of 10−15 kg, have been designed using two different configurations, parallel plate electrodes and concentric cylindrical electrodes. The optimization of the anode material has also been studied and Pt/Ti, RuO2/Ti and IrO2/Ti have been used. After the regeneration and, thus, recovery of the porosity the samples were tested in the adsorption of bisphenol A. In the electrochemical regeneration, recovery of the porosity of spent activated carbon until 100 % and 96 % with respect to the pristine activated carbon using Pt/Ti anode after 3 h of treatment, has been achieved. The regeneration process produces a small increase in the number of surface oxygen groups. No important differences have been observed among the tested anodes and RuO2/Ti and IrO2/Ti can be an economic alternative to Pt/Ti. Bisphenol A adsorption kinetics was slower in regenerated activated carbons probably due to the formation of surface oxygen groups. However, the adsorption capacity was similar in the regenerated samples and the pristine one.

Highly Active Electrode With Efficiently Added Surface Oxygen Groups for a Vanadium Redox Flow Battery

AbstractHigher power output by a lower kinetic resistance of the vanadium redox flow battery is needed for its commercialization. In this study, we focused on the air oxidation conditions of carbon paper, which is the electrode material, to reduce the kinetic resistance. The air oxidation is considered to affect the number of surface oxygen groups such as the phenol-type hydroxyl group due to oxidation of the carbon fiber. The surface oxygen groups may correspond to the active sites for the charge/discharge reaction. We quantitatively evaluated the number of surface oxygen groups by temperature-programmed desorption. In addition, we measured the double-layer capacitances of the carbon papers, which may reflect the surface area of the carbon fiber. The single-cell performances, i.e., current–voltage curves and charge–discharge profile, of the electrodes were studied. The air oxidized carbon paper, heat-treated at 500 °C for 3 h (8.4% mass decrease from the pristine sample), showed the highest power density (960 mW cm−2) in this study with thin electrode material (ca., 0.2 mm for one sheet). The negative half-reaction was enhanced by air oxidation. This result could be explained by the reduction of the kinetic resistance by increasing the number of phenol groups, and this power output was relatively high as the vanadium redox flow battery by using a commercial carbon paper and the standard flow field.

Interaction between carbon fibers and polymer sizing: Influence of fiber surface chemistry and sizing reactivity

Different aspects of the interaction of carbon fibers and epoxy-based polymer sizings are investigated, e.g. the wetting behavior, the strength of adhesion between fiber and sizing, and the thermal stability of the sizing layer. The influence of carbon fiber surface chemistry and sizing reactivity is investigated using fibers of different degree of anodic oxidation and sizings with different number of reactive epoxy groups per molecule. Wetting of the carbon fibers by the sizing dispersion is found to be specified by both, the degree of fiber activation and the sizing reactivity. In contrast, adhesion strength between fibers and sizing is dominated by the surface chemistry of the carbon fibers. Here, the number of surface oxygen groups seems to be the limiting factor. We also find that the sizing and the additional functionalities induced by anodic oxidation are removed by thermal treatment at 600 °C, leaving the carbon fiber in its original state after carbonization.

Carbon support surface effects in the catalytic performance of Ba-promoted Ru catalyst for ammonia synthesis

Carbon-supported Ru catalyst is arguably the most promising applications of Ru catalysts in ammonia synthesis. However, the insufficient stability of Ru/C catalyst greatly limits its applications, and the elimination of surface oxygen species by carbon preactivation has been imagined to be an efficient method for preparing Ru/C catalyst with high stability. However, herein we demonstrate that the presence of some oxygen functional groups in carbon support of Ba-promoted Ru/C catalyst was beneficial not only to the dispersion of Ru particles, but also to the low-temperature hydrogen adsorption. Furthermore, the formation of CO during heat treatment, which was closely related to oxygen groups, enhanced the ammonia synthesis activities of carbon-supported Ru catalyst with Ba promoter. Therefore, Ru catalyst supported on carbon with a large number of surface oxygen groups showed higher activity. Understanding the effect of carbon support surface on the activity and stability of Ru/C provides a basis for the rational design of the optimal carbon-supported metal catalyst for ammonia synthesis and related reactions.

Thermal and physicochemical properties of phosphorus-containing activated carbons obtained from biomass

Abstract The phosphorus-containing activated carbons have been obtained by activation of the low quality hay and the chars obtained by its pyrolysis with 50% phosphoric acid at 600 °C in a stream of nitrogen. Furthermore, the study was performed on two series of carbonaceous materials prepared from hay using different heating methods – microwave and conventional heating. These two groups of materials were compared, moreover the impact of microwave radiation on their physicochemical properties was checked. The samples obtained were characterized by ICP-OES, elemental analysisas well as determination of pH and the number of surface oxygen groups by the Boehm method. The porous structures of activated carbons were characterised by nitrogen adsorption using BET methods. Thermal properties of the samples were investigated by thermogravimetric (TG) analysis and differential thermogravimetry (DTG). The final products were activated carbons of well-developed surface area varying from 212 to 1300 m 2 /g, total pore volumes of 0.17–0.78 cm 3 /g. More favourable textural parameters have shown activated carbons obtained with the use microwave radiation, especially via one step activation. H 3 PO 4 activation of the low quality hay gave carbon materials containing 2–6% of phosphorus and surfaces showing acidic character. Results of the study suggest the feasibility of phosphoric acid activation of biomass, which leads to high quality activated carbons with high fractions of micropores. High content of phosphorusin the activated carbons studied offers the opportunities for the application of these materials for specific adsorption and catalytic processes used in environmental engineering.

Thermal analysis of activated carbon obtained from residue after supercritical extraction of hops

Activated carbons have been obtained by physical activation of residue left after supercritical extraction of hops. The effect of pyrolysis temperature on the physicochemical properties of the adsorbents prepared was tested. The carbonaceous materials were characterised by low-temperature nitrogen sorption, determination of pH and the number of surface oxygen groups. The thermal properties of the chars and activated carbons were identified by thermogravimetric analysis and differential thermogravimetry. The products of thermochemical treatment of the starting hops were carbonaceous adsorbents of specific surface area ranging from 2 to 416 m2 g−1, showing definitely basic character of the surface and moderate thermal stability as evidenced by a considerable mass loss at about 300–400 °C. The results obtained in our study have proved that residue left after supercritical extraction of hops (or similar plant materials) can be cheap, easily accessible and promising precursor for activated carbons. The results have also shown that future research should be aimed at the optimum choice of the temperature of carbonation and activation in order to significantly improve the textural parameters of the activated carbons as well as their thermal stability.

Activated Carbons from Residue after Supercritical Extraction for Removal of Nitrogen Dioxide

The aim of this study was to obtain activated carbons by physical activation of the waste left after supercritical extraction of marigold and hops, provided by the Institute of New Chemical Syntheses in Pulawy (Poland). The precursors were first subjected to carbonisation at 500oC in nitrogen atmosphere. The chars were next subjected to physical activation at 700 and 800oC in carbon dioxide atmosphere. The effect of activation temperature on the physicochemical properties of the adsorbents prepared has been tested. The carbonaceous materials were characterised by low-temperature nitrogen sorption as well as determination of the number of surface oxygen groups. The sorption properties of the chars and activated carbons obtained were characterised by nitrogen dioxide adsorption. The results have shown that activated carbons are characterised by low developed surface area varying from 2 to 413 m2/g and show alkaline character of the surface. It has been proved that appropriate choice of the activation parameters and the presence of steam have a positive effect on adsorption of nitrogen dioxide by activated carbons obtained. The highest sorption capacity toward nitrogen dioxide in wet conditions was 72.1 mg/gads, while in dry conditions it was 38.7 mg/gads. The results have also shown that future research should be aimed at the optimum choice of the temperature of activation or activating agent in order to significantly improve the textural parameters of the activated carbons.

Effect of heat treatment on the physicochemical properties of nitrogen-enriched activated carbons

A series of functionalized carbonaceous adsorbents were prepared by means of reaction with urea and chemical activation of Polish brown coal. In order to obtain nitrogen groups bonded in different ways to the carbon structure, the reaction with urea was performed at two different stages of processing, with precursor or char. Additionally, the influence of annealing under nitrogen atmosphere at 600 and 800 °C or in hydrogen/nitrogen mixture at 600 °C on the textural, acid–base and thermal properties of activated carbons prepared was tested. The resulting materials were characterized by elemental analysis, low-temperature nitrogen sorption, determination of the number of surface oxygen groups as well as by thermogravimetric study in helium atmosphere. The final products were microporous nitrogen-enriched activated carbons of very well-developed surface area reaching from 1303 to 2004 m2 g−1, showing different content of nitrogen (from 0.5 to 2.3 mass%) and different chemical character of the surface (from weakly acidic to intermediate acidic–basic), depending on the sequence of particular processes and variant of further thermochemical treatment. According to the results of thermal study, the nitrogen functional groups introduced into the carbon structure by the reaction with urea (especially at the char stage) show moderate thermal and chemical stability. Under the effect of high temperature, some of these groups underwent decomposition or transformation into more thermally stable nitrogen species. It was also proved that the thermochemical treatment of modified activated carbons led to considerable deterioration of their textural parameters as well as caused significant changes in the acid–base character of their surface.

The use of microwave radiation for obtaining carbonaceous adsorbents from biomass and their use in elimination of inorganic pollutants

A new technology of obtaining activated carbons by physical and direct activation of biomass with the use of microwave radiation is described. The effect of activation temperature (700 and 800 °C) and two periods of time (15 and 30 min) on the textural parameters, acid–base character of the surface and sorption properties of activated carbons was tested. The resulting carbons were characterized by low-temperature nitrogen sorption and determination of pH as well as the number of surface oxygen groups. The sorption properties of the activated carbons obtained were characterized by determination of nitrogen dioxide and hydrogen sulphide adsorption in dry and wet conditions as well as by iodine removal from aqueous solution. The final products were adsorbents of surface area ranging from 291 to 368 m2/g and pore volume from 0.20 to 0.26 cm3/g, showing basic character of the surface. The results obtained in our study have proved that suitable choice of the pyrolysis and activation procedure for hay with the use of microwave radiation permit producing adsorbents with good capacity toward toxic gases of acidic character as well as inorganic pollutants of molecules of size similar to that of iodine molecules.

The use of microwave radiation for obtaining activated carbons from sawdust and their potential application in removal of NO2 and H2S

Activated carbons obtained from sawdust pellets from coniferous wood were used as adsorbents of nitrogen dioxide and hydrogen sulphide. The precursor was subjected to pyrolysis at 400°C in nitrogen atmosphere and next to physical activation at 600 and 700°C by CO2. Some part of the precursor was also subjected to direct activation at 600°C by CO2. The effect of activation temperature on the textural parameters, acid–base character of the surface and sorption properties of activated carbons was analysed. The resulting carbons were characterized by low-temperature nitrogen sorption, determination of pH and the number of surface oxygen groups by Boehm method. The adsorption of NO2 and H2S was carried out from dry or moist (70% humidity) air.The results have shown that NO2 and H2S sorption properties of activated carbons depend on the temperature of activation and the conditions of adsorption. The results obtained in our study have proved that a suitable choice of the pyrolysis and activation procedure of sawdust can give adsorbents with high capacity of nitrogen dioxide, reaching to 54.7 and 28.8mgNO2/g in dry and wet conditions, respectively and low capacity of hydrogen sulphide of 4.1 and 6.2mgH2S/g in dry and wet conditions, respectively.

Nitrogen-enriched activated carbons prepared by the activation of coniferous tree sawdust and their application in the removal of Nitrogen dioxide

A technology of obtaining nitrogen-enriched activated carbons from coniferous tree sawdust by direct activation of the precursor and physical activation with CO2 is described. The effect of activation time, pyrolysis temperature as well as modification with urea on the textural parameters, acid–base character of the surface and sorption properties of activated carbons has been tested. The resulting carbons were characterised by low-temperature nitrogen sorption and determination of the number of surface oxygen groups. The sorption properties of the materials obtained were characterised by nitrogen dioxide adsorption in dry and wet conditions. The final products were nitrogen-enriched microporous activated carbons of medium-developed surface, showing very diverse nitrogen content and acidic–basic character of the surface. The results obtained in our study have proved that through suitable choice of the activation and modification procedure of coniferous tree sawdust, activated carbons can be produced with high capacity towards nitrogen dioxide adsorption, reaching to 69 and 46 mg NO2/g in dry and wet conditions, respectively. The results of our study have also shown that the adsorption ability of carbonaceous adsorbents depends both on the method of preparation as well as on the textural parameters and acid–base properties of the adsorbents surface.

NO2 removal on adsorbents prepared from coffee industry waste materials

A technology for obtaining carbonaceous adsorbents by physical and chemical activation of waste materials from coffee industry is described. The effect of pyrolysis temperature and type of activation procedure on the textural parameters, acid–base character of the surface and sorption properties of activated carbons has been tested. The resulting carbons were characterized by low-temperature nitrogen sorption, determination of pH and the number of surface oxygen groups. The sorption properties of the activated carbons obtained were characterized by evaluation of nitrogen dioxide adsorption in dry and wet conditions. The final products were adsorbents of specific surface area ranging from 5 to 2,076 m2/g and pore volume from 0.03 to 1.25 cm3/g, showing very diverse acidic–basic character of the surface. The results obtained in our study have proved that a suitable choice of the pyrolysis and activation procedure for coffee industry wastes permits production of adsorbents with high sorption capacity of nitrogen dioxide, reaching to 44.5 and 84.1 mg NO2/g in dry and wet conditions, respectively.

The influence of the carbon surface chemical composition on Dubinin–Astakhov equation parameters calculated from SF6 adsorption data—grand canonical Monte Carlo simulation

Using grand canonical Monte Carlo simulation we show, for the first time, the influence of the carbon porosity and surface oxidation on the parameters of the Dubinin–Astakhov (DA) adsorption isotherm equation. We conclude that upon carbon surface oxidation, the adsorption decreases for all carbons studied. Moreover, the parameters of the DA model depend on the number of surface oxygen groups. That is why in the case of carbons containing surface polar groups, SF6 adsorption isotherm data cannot be used for characterization of the porosity.

First Molecular Dynamics simulation insight into the mechanism of organics adsorption from aqueous solutions on microporous carbons

The results of 84 MD simulations showing the influence of porosity and carbon surface oxidation on adsorption of three organic compounds from aqueous solutions on carbons are reported. Based on a model of ‘soft’ activated carbon, three carbon structures with gradually changed microporosity were created. Next, different number of surface oxygen groups was introduced. We observe quantitative agreement between simulation and experiment i.e. the decrease in adsorption from benzene down to paracetamol. Simulation results clearly demonstrate that the balance between porosity and carbon surface chemical composition in organics adsorption on carbons, and the pore blocking determine adsorption properties of carbons.