Surface Oxygen Groups Research Articles

Understanding the Influence of Surface Oxygen Groups on the Electrochemical Behavior of Porous Carbons as Anodes for Lithium-Ion Batteries.

The present study elucidates the role of surface oxygen functional groups on the electrochemical behavior of porous carbons when used as anodes for Li-ion batteries. To achieve this objective, a carbon xerogel (CX) obtained by pyrolysis of a resorcinol-formaldehyde gel, was modified by different postsynthesis treatments in order to modulate its surface chemistry while maintaining its external surface constant. Various surface modifications were obtained by oxidation in air, in situ polymerization of dopamine, and finally by grafting of a polyethylene oxide layer on the polydopamine coating. While oxidation in air did not affect the pore texture of the CX, modifications by coating techniques substantially decreased the micropore fraction. Detailed electrochemical characterizations of the materials processed as electrodes were performed by capacitance measurements and galvanostatic cycling. Surface chemistry results, from X-ray photoelectron spectroscopy, show that the accessibility and the capacity increase when carbonyl (R-C═O) groups are formed on the CX, but not with oxides and hydroxyls. The amount of surface carbonyls, and in particular, aldehyde (O═CH) groups, is found to be the key parameter because it is directly correlated with the modified CX electrochemical behavior. Overall, the explored surface coatings tend to reduce the micropore volume and add mainly hydroxyl functional groups but hardly change the Li+ insertion/deinsertion capacities, while oxidation in air adds carbonyl groups, increasing the Li+ ion storage capacity, thanks to an improved accessibility to the carbon network, which is not caused by any textural change.

Investigation on Deactivation of K‐promoted Ru Catalyst for Ammonia Synthesis by CO Formation

AbstractThe prevailing view of the deactivation of carbon‐supported Ru catalyst in ammonia synthesis is carbon methanation, but those strategies focusing on inhibiting carbon methanation cannot effectively solve the challenge of Ru/C catalysts. Herein we prepared four K‐promoted Ru catalysts with different Ru loadings and treated the samples at 450 or 500 °C under 1 MPa during ammonia synthesis reaction. The result showed that the presence of a larger amount of Ru species enhanced methane formation at the reaction temperature, which was irrelevant to the loss in activity of ammonia synthesis. On the contrary, CO formation along with a great decline in catalytic activity can be observed when Ru catalysts are heated at 500 °C. The characterization results indicated that the severe depletion of surface oxygen groups following the CO‐formation pathway, resulting in the notable decrease in the amount of gas adsorption, contributed to the deactivation of carbon‐supported Ru catalyst.

Biomass-derived furfural conversion over Ni/CNT catalysts at the interface of water-oil emulsion droplets

Carbon nanotubes-supported Ni catalysts were investigated for the hydrogenation of furfural as a biomass-derived furanic model compound at the liquid-liquid interface of Pickering emulsions in a batch reactor at 200 °C and 2.0 MPa of H2 pressure. The catalysts were characterized by N2 physisorption, He-TPD/MS, NH3-TPD/MS, TEM, CO chemisorption, H2-TPR, contact angle and optical/fluorescent microscopy. It was found that an increase of surface oxygen groups allows for the formation of amphiphilic particles. The amphiphilic 10%Ni/CNTox particles were homogeneous dispersed at the water-oil interface of the emulsion droplets thus enhancing the catalytic activity in furfural conversion.

Influence of Loading a Tertiary Amine on Activated Carbons and Effect of CO2 on Adsorptive H2S Removal from Biogas

This work studied the influence of loading a tertiary amine on activated carbons (ACs) and the effect of CO2 on adsorptive H2S removal from biogas. After loading a tertiary amine, tetramethyl hexanediamine (THMDA), the H2S adsorption capacity increased for all ACs but with different levels. Detailed characterization results (TGA-MS, TGA/DTG, and in situ FT-IR) demonstrate the TMHDA-induced changes of surface oxygen or nitrogen functional groups, pH value, and textural properties and their impacts on H2S adsorption performance, which also varied with CO2 concentrations. On bare AC adsorbents, the H2S adsorption is attributed to the surface oxygen functional groups, whereas on tertiary amine-loaded ACs, the H2S adsorption is due to the interaction between H in H2S and N in the amine group. The presence of CO2 can promote H2S adsorption on some ACs and THMDA-loaded ACs. The formation of solid sulfur and CH4 was observed for the H2S adsorption in the presence of CO2.

Microporous 3D Graphene-like Zeolite-Templated Carbons for Preferential Adsorption of Ethane

Microporous 3D graphene-like carbons were synthesized in Faujasite (FAU)-, EMT-, and beta-zeolite templates using the recently developed Ca2+ ion-catalyzed synthesis method. The microporous carbons liberated from these large-pore zeolites (0.7-0.9 nm) retain the structural regularity of zeolite. FAU-, EMT-, and beta zeolite-templated carbons (ZTCs) with faithfully constructed pore diameters of 1.2, 1.1, and 0.9 nm, respectively, and very large Brunauer-Emmet-Teller areas (2700-3200 m2 g-1) were obtained. We have discovered that these schwarzite-like carbons exhibit preferential adsorption of ethane over ethylene at pressures in the range of 1-10 bar. The curved graphene structure, consisting of a diverse range of carbon polygons with a narrow pore size of ∼1 nm, provides abundant adsorption sites in micropores and retains its ethane selectivity at pressures up to 10 bar. After varying the oxygen content in the beta ZTC, the ethane and ethylene adsorption isotherms show that the separation ability is not significantly affected by surface oxygen groups. Based on these adsorption results, a breakthrough separation procedure using a C2H4/C2H6 gas mixture (9:1 molar ratio) is demonstrated to produce ethylene with a purity of 99.9%.

Understanding the rate performance of microporous carbons in aqueous electrolytes

Variation of specific capacitance versus current density is studied for microporous carbons. Although literature states that capacitance retention is higher for macro/mesoporous than for microporous carbons, the results reported here show that high capacitance retention can be reached for microporous carbons in combination with aqueous electrolytes (2M H2SO4, 1M KOH and 6M KOH). Six carbon monoliths are studied; three pristine ones and those three heat-treated, so as to reduce their content of surface oxygen groups and develops porosity. The capacitance retention is analyzed based on five parameters: electronic conductivity, surface chemistry and porosity of the monoliths, ionic conductivity and type of electrolyte. The capacitance retention is higher for the monoliths working as negative (H3O+ and K+) electrodes than as positive (HSO4− and OH−) ones, being these results of interest for the use of carbon monoliths in asymmetric and hybrid supercapacitors. The highest capacitance retention is obtained by combining (i) monolith electronic conductivity of 11–14 Scm−1 and micropore size of 0.6–0.8 nm for H3O+, K+ and HSO4−, and of 0.85–0.95 nm for OH−; (ii) electrolyte ionic conductivity above 600 mScm−1 and 6M KOH electrolyte, since this electrolyte performs better than 2M H2SO4 and 1M KOH.

The interaction of metallic ions onto activated carbon surface using computational chemistry software

Activated carbon was prepared from the seeds of aguaje palm ( Mauritia flexuosa L.f.) by a chemical activation with phosphoric acid. This activated carbon was used for adsorbing metal ions: Pb(II), Cd(II), and Cr(III). To understand the mechanism of adsorption of these heavy metals (Cr, Cd, and Pb), the activated carbon surface was oxidized with nitric acid (1 M) increasing the oxygenated surface groups showing an increasing in their adsorption capacities of these metals. The oxidized activated carbon slightly increased the maximum adsorption capacity to 5–7%. The order of adsorption for unoxidized and oxidized activated carbons was Pb> Cd> Cr. This experimental information was corroborated by molecular modeling program Hyperchem 8 based adsorption mainly on two factors: the electron density and orbitals—highest occupied molecular orbital and lowest unoccupied molecular orbital.Activated carbons were characterized by adsorption/desorption of N2, obtaining an increase of microporous surface area for oxidized activated carbon. An increase of surface acidity and a reduction of isoelectric points were observed in oxidized activated carbon. According to these results, the adsorption of metal ions is favored in contact with an oxidized activated carbon, which has more amount of phenolic and carboxylic functional groups. Similarly, decreasing the isoelectric point indicates that the surface has a higher negative charge. The surface information was corroborated by Hyperchem, which indicates that the surface of the oxidized activated carbon has a higher electron density, indicating a larger amount of electrons on its surface, which means the surface of oxidized activated carbon charges negatively and thereby attracts metal ions.

(Invited) The Relationship of Morphology and Catalytic Activity: A Case Study of Iron Corrole Incorporated in High Surface Area Carbon Supports

In the past several years we have been thoroughly studying the performance of molecular catalysts for oxygen reduction based on metallo-corrole. We studied the effect of the metal center, substituents in their meso and beta positions and ORR mechanism at a wide pH range. The most influential factor was found to be the metal center while the effect of electro-negative substituents seems to diminish once these molecular catalysts were incorporated in porous carbon supports. Moreover, the overall activity and reaction selectivity has increased dramatically after this incorporation, and was found to be dependent on the carbon support. Specifically, metallo-corroles have shown to have unique catalytic properties for oxygen reduction when adsorbed on a high surface area carbon: BP2000. The nature of the interaction between carbon surfaces and metallo-corroles was identified in this work. The results suggests that the catalytic activity lays not in a bond between the carbon surface and the corrole molecule, but rather in the arrangement of corrole molecules within the porous structure of the carbon surface. This hypothesis was studied here using Electron Paramagnetic Resonance (EPR), X-ray diffraction (XRD), UV-VIS spectroscopy, elemental analysis, N2 adsorption and several electrochemical methods. BP2000 carbon was compared to four other carbons with different properties (oxygen surface groups, surface area, porous structure and crystallinity). All of these show that the Fe-corrole that was incorporated in BP2000 tends to adsorb in pores of 20-25 nm in diameter, which allow synergistic effects to take place, and enhance the electrocatalysis of oxygen reduction reaction.

Effect of surface oxygen groups in the electrochemical modification of multi-walled carbon nanotubes by 4-amino phenyl phosphonic acid

Electrochemical functionalization of pristine Multi-walled Carbon Nanotubes (MWCNTs) and oxidized MWCNTs by nitric acid with 4-aminophenyl phosphonic acid (4-APPA) has been studied. Electrochemical modification has been carried out by cyclic voltammetry using different upper potential limits, what results in the incorporation of N and P functionalities through oligomerization and covalent attachment. The electrochemical characterization shows that there are important differences among the functionalized materials derived from the pristine MWCNTs or the oxidized materials. For the pristine MWCNTs, well-defined redox processes are observed. Characterization by X-Ray photoelectron spectroscopy, Raman spectroscopy and electron microscopy, show that oligomerization is easier for the pristine MWCNTs and the presence of oligomer chains are clearly distinguished for the lowest oxidation potentials. However, the presence of surface oxygen groups in the oxidized MWCNTs modify the interaction of the 4-APPA with the surface promoting mainly covalent attachment.

Amphiphilic acid carbon catalysts produced by bio-oil sulfonation for solvent-free glycerol ketalization

Herein, an efficient amphiphilic carbon catalyst produced by the reaction of bio-oil with sulfuric acid was used for the first time for the solvent-free glycerol ketalization with 2-propanone for solketal production (2,2-dimethyl-1,3-dioxolane-4-methanol) at room temperature. The catalyst synthesis, described previously, led to an amphiphilic carbon due to hydrophobic nanostructures, e.g. graphene, nanotube, nano-onions, nanographite, embedded in an amorphous carbon containing high concentration of hydrophilic oxygen and sulfonic surface groups with strong acid sites (ca. 0.3 mmol g−1). The amphiphilic catalyst promoted the formation of an emulsion from the two immiscible phases, glycerol and 2-propanone, which had a strong effect on the reaction interface and solketal yield. Glycerol ketalization at 25 °C and solvent-free showed conversions higher than 90%, using 0.6 wt% catalyst, 1:10 glycerol:2-propanone after 2 h. The catalyst can be recovered and reused four times without any significant activity loss.

Review on Activated Carbons by Chemical Activation with FeCl3

This study reviews the most relevant results on the synthesis, characterization, and applications of activated carbons obtained by novel chemical activation with FeCl3. The text includes a description of the activation mechanism, which compromises three different stages: (1) intense de-polymerization of the carbon precursor (up to 300 °C), (2) devolatilization and formation of the inner porosity (between 300 and 700 °C), and (3) dehydrogenation of the fixed carbon structure (>700 °C). Among the different synthesis conditions, the activation temperature, and, to a lesser extent, the impregnation ratio (i.e., mass ratio of FeCl3 to carbon precursor), are the most relevant parameters controlling the final properties of the resulting activated carbons. The characteristics of the carbons in terms of porosity, surface chemistry, and magnetic properties are analyzed in detail. These carbons showed a well-developed porous texture mainly in the micropore size range, an acidic surface with an abundance of oxygen surface groups, and a superparamagnetic character due to the presence of well-distributed iron species. These properties convert these carbons into promising candidates for different applications. They are widely analyzed as adsorbents in aqueous phase applications due to their porosity, surface acidity, and ease of separation. The presence of stable and well-distributed iron species on the carbons’ surface makes them promising catalysts for different applications. Finally, the presence of iron compounds has been shown to improve the graphitization degree and conductivity of the carbons; these are consequently being analyzed in energy storage applications.

Adsorption of DBT and 4,6-DMDBTon nanoporous activated carbons: the role of surface chemistry and the solvent.

Adsorption of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) from solutions in hexane and hexadecane respectively as well as in acetonitrile for both thiophenic compounds was investigated with sorbents of three activated carbons and their oxidized counterparts. The raw sorbents were of different surface acidity. Oxygen surface groups created after oxidation increased the adsorption of thiophenic compounds via polar interactions.

Characterization of Chemically Activated Carbons Prepared from Miscanthus and Switchgrass Biomass.

Lignocellulosic biomass, including that of energy crops, can be an alternative source to produce activated carbons (ACs). Miscanthus and switchgrass straw were used to produce ACs in a two-step process. Crushed plant material was carbonized at 600 °C and then obtained carbon was activated using NaOH or KOH at 750 °C. The content of surface oxygen groups was determined using Boehm’s method. The porosity of ACs was assayed using the nitrogen adsorption/desorption technique, while their thermal resistance using the thermogravimetric method. The ACs derived from miscanthus and switchgrass were characterized by surfaces rich in chemical groups and a highly developed porous structure. The highest specific surface areas, over 1600 m2/g, were obtained after carbon treatment with NaOH. High values of iodine number, 1200–1240 mg/g, indicate an extensive system of micropores and their good adsorption properties. The type of activator affected the contents of oxygen functional groups and some porosity parameters as well as thermal stability ranges of the ACs. Among obtained carbons, the highest quality was found for these derived from M. sacchariflorus followed by switchgrass, after activation with NaOH. Hence, while these crop species are not as effective biomass sources as other energy grasses, they can become valuable feedstocks for ACs.

Efficient adsorbent based on construction and demolition wastes functionalized with 3-aminopropyltriethoxysilane (APTES) for the removal ciprofloxacin from hospital synthetic effluents

An inorganic sludge from construction and demolition wastes (ICDW) was grafted with APTES to obtain an inorganic-organic modified adsorbent ICDW-APTES. This adsorbent was successfully employed for ciprofloxacin (CFX) adsorption and treatment of synthetic hospital effluent. The chemical composition of ICDW presented large quantities of SiO2 and Al2O3, which supports its application for being functionalized by APTES that occurred through a chemical reaction between the surface oxygen groups of oxides with the silanol groups of the APTES. The characterization data suggested that APTES was successfully grafted on the ICDW structure. The kinetic studies showed that the general-order provided the best fitness for CFX adsorption on ICDW-APTES. Liu isotherm model presented the best fitness for the equilibrium studies, and it provided a Qmax of 138.0 mg g−1 at 40.0 °C. Electrostatic interaction was the primary mechanism involved in the adsorption process. The ICDW-APTES also exhibited a good percentage of removal of the two synthetic effluents (71.0 % and 69.0 %).

Impact of Carbon Porosity on the Performance of Cathode Microporous Layers in Proton Exchange Membrane Fuel Cells

AbstractAcetylene black carbons were activated under flowing CO2 atmosphere at 900 °C for different treatment times. The impact of this heat treatment on the porosity, hydrophilicity, and surface oxygen groups was carefully examined. Longer periods of activation led to increases in the surface area and porosity of the samples. Pore size distributions of the samples showed an increase in micropores, followed by a rise in mesopores, which indicated the occurrence of pore widening with a longer activation period. When used as a microporous layer for H2/air fuel cells, samples with higher levels of porosity showed, in general, reduced mass transport performance due to the formation of pooling locations for water. These results highlight the importance of textural pores in carbon structures on the water management in hydrogen fuel cell when operating under high humidity conditions.

Highly sensitive and reproducible quantification of oxygenated surface groups on carbon nanomaterials

The quantification of surface groups is a key characterization for different carbon materials as their behavior in colloidal dispersion, their interaction with proteins, drugs or polymers as well as their aggregation behavior strongly depend on the type and number of surface groups. Some of the most challenging groups are those containing oxygen as the typical characterization methods do not allow for a highly sensitive and reproducible quantification of carboxylic, lactonic and alcoholic groups. The only known wet-chemical method that is able to yield quantitative results is the Boehm titration. However, this method is also known to be extremely demanding regarding procedure compliance, requires large amounts of sample, and leads to rather large standard deviations. Here we report on a significantly improved titration method for the quantification of oxygen containing surface groups. All methodical aspects like sample preparation, reaction time, filtration medium, volumetric and gravimetric methods have been optimized, leading to the detection of carboxylic, lactonic and alcoholic groups with a standard deviation of ±1 μmol/g while using only small amounts of sample material. The method has been successfully applied on a broad variety of hydrophilic and hydrophobic carbon materials including nanodiamond, partially graphitized nanodiamond, multiwall carbon nanotubes and acetylene black.

Reasonable design and sifting of microporous carbon nanosphere-based surface molecularly imprinted polymer for selective removal of phenol from wastewater

Highly selective surface molecularly imprinted polymer (SMIP) was prepared on glucose-derived microporous carbon nanospheres (GMCNs) by surface molecular imprinting technology for the removal of phenol from wastewater. GMCNs with rich pore structure and surface oxygenic functional groups were adopted as support materials, on which the active layers were constructed by grafting silane coupling agent 3-(methacryloyloxy) propyltrimethoxysilane. Then with phenol as template molecule, different types and amounts of functional monomer (including methacrylic acid and 4-vinylpyridine (4-VP)) were screened for optimizing imprinting conditions suitable for phenol adsorption, and a series of SMIP was obtained through crosslinking polymerization. The adsorption behaviors of SMIP were evaluated by UV spectrophotometry. The results show that, when 4-VP is used as functional monomer, the resultant 4-VP/SMIP exhibites an excellent adsorption capacity of 85.72 mg g−1. The relative selectivity factor for phenol against hydroquinone, p-nitrophenol and p-tert-butylphenol is 8.38, 7.96 and 6.67, respectively, indicating outstanding adsorption capacity and selectivity of 4-VP/SMIP. The pseudo-second-order model and Langmuir‒Freundlich model fit better than other models for the adsorption of phenol. 4-VP/SMIP is promising for selective removal and enrichment recovery towards phenol in wastewater.

Adsorption of ampicillin sodium on activated carbons with different surface chemistries

BACKGROUND: The adsorption of ampicillin from aqueous solution by three types of activated carbon was investigated. The first was a commercial activated carbon (AC), the second (AAC) was AC modified by HNO3 oxidation and the third (HAAC) was AAC modified through thermal treatment. The surface properties of the activated carbon samples were characterized and the effects of pH and contact time on the adsorption were determined. The adsorption isotherms, adsorption kinetics and adsorption mechanism are discussed. RESULTS: Compared to AC, HNO3 oxidation increased the number of acid functional groups on the surface of AAC, which hindered the adsorption of ampicillin. For HAAC, thermal treatment removed surface oxygen groups and then improved the adsorption ability. The adsorption processes was greatly affected by pH and acidic conditions were favorable for adsorption. With an initial ampicillin sodium concentration of 200 mg/L, 9 h was needed for adsorption to reach equilibrium. The Langmuir isotherm provides a better fit for the adsorption than the Freundlich isotherm and the maximum adsorption capacities for AC, AAC and HAAC were 90.6, 59.8, 140.9 mg/g, respectively. The sorption kinetics can be described by a pseudo-second order model. CONCLUSION: The functional groups on activated carbon greatly affect its adsorption ability. The adsorption of ampicillin can be improved by increasing the number of basic functional groups on the activated carbon. Chemisorption was the dominant adsorption process and pH was an important factor affecting ampicillin adsorption.

Thermal Modification Effect on Supported Cu-Based Activated Carbon Catalyst in Hydrogenolysis of Glycerol.

Glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO) was performed over activated carbon supported copper-based catalysts. The catalysts were prepared by impregnation using a pristine carbon support and thermally-treated carbon supports (450, 600, 750, and 1000 °C). The final hydrogen adsorption capacity, porous structure, and total acidity of the catalysts were found to be important descriptors to understand catalytic performance. Oxygen surface groups on the support controlled copper dispersion by modifying acidic and adsorption properties. The amount of oxygen species of thermally modified carbon supports was also found to be a function of its specific surface area. Carbon supports with high specific surface areas contained large amount of oxygen surface species, inducing homogeneous distribution of Cu species on the carbon support during impregnation. The oxygen surface groups likely acted as anchorage centers, whereby the more stable oxygen surface groups after the reduction treatment produced an increase in the interaction of the copper species with the carbon support, and determined catalytic performances.

Ageing remarkably alters the toxicity of carbon black particles towards susceptible cells: determined by differential changes of surface oxygen groups

Ageing process remarkably alters the toxicity of carbon black particles towards susceptible cells via changing the species of their surface oxygen groups.