Amount Of Surface Oxygen Groups Research Articles

3D/2D MnO/MXene heterostructure with high efficiency for adsorbing uranium

An innovative MnO/Ti3C2 MXene heterostructure, consisting of three-dimensional (3D) MnO nanosheet array directly assembled on two-dimensional (2D) Ti3C2 MXene nanosheets, was synthesized via a simple hydrothermal-annealing strategy for uranium elimination. This unique 3D/2D heterostructure derived substantially high specific surface area (311.9 m2/g) and exposed considerable amount of surface oxygen groups, including surface lattice M–O and adsorbed –OH. Through a comprehensive exploration encompassing adsorbent dosage, pH, ionic strength, initial U(VI) concentration, and environmental conditions, the MnO/Ti3C2 MXene heterostructure demonstrated an extraordinary proficiency and specificity in the removal of U(VI). This composite exhibited an outstanding adsorption capacity of 862.1 mg/g, with a removal efficiency of 99.7 % and rapid kinetics (above 90 % within 20 s). The kinetic study indicated the adsorption process followed chemisorption dynamics and single-layer adsorption behavior. Comprehensive analyses validated the structural integrity and confirmed the successful uranium adsorption via strong interaction between UO22+ and surface unsaturated oxygen groups. Notably, the MnO/Ti3C2 MXene maintained excellent recyclability, highlighting its potential for large-scale applications. It emerges as a promising candidate for uranium removal, offering insights for optimizing composite materials in diverse environmental conditions and fostering advancements in water purification technologies.

Influence of boron doping on characteristics of glucose-based hydrothermal carbons

In this study, the influence of boron doping on structural and surface properties of carbon material synthesized by a hydrothermal method was investigated, and the obtained results were compared with the previously published influence that boron has on characteristics of carbonized boron-doped hydrothermal carbons (CHTCB). Hydrothermal carbons doped with boron (HTCB) were obtained by the hydrothermal synthesis of glucose solutions with different nominal concentrations of boric acid. It was found that glucose based hydrothermal carbon does not have developed porosity, and the presence of boron in their structure has insignificant influence on it. On the contrary, additional carbonization increases the specific surface area of the undoped sample, while an increase in boron content drastically decreases the specific surface area. Boron doping leads to a decrease in the amount of surface oxygen groups, for both, hydrothermally synthesized and additionally carbonized materials. Raman analysis showed that the boron content does not affect a structural arrangement of the HTCB samples, and Raman structural parameters show a higher degree of disorder, compared to the CHTCB samples. Comparison of structural and surface characteristics of hydrothermal carbons and carbonized materials contributes to the study of the so far, insufficiently clarified influence that boron incorporation has on the material characteristics.

Disinfection by-product formation and toxicity evaluation for chlorination with powered activated carbon

With the deterioration of source water quality, pre-chlorination and pre-addition of powdered activated carbon (PAC) have been widely applied to improve water treatment efficiency, which would lead to PAC exposure to chlorine. Although previous studies reported that some emerging carbon materials (e.g., graphene) could potentially act as disinfection by-product (DBP) precursors, there were few studies paying attention to the interaction between chlorine and the most commonly used carbon material-PAC on the DBP formation. In this study, the DBPs formed by chlorination with and without PAC were investigated, and the DBP toxicities in different systems were evaluated. The results showed that the PAC could react with chlorine and form trihalomethanes (THMs) and haloacetic acids (HAAs). The amount of surface oxygen groups of the PAC increased during the chlorination, with these oxygen groups, especially the meta-positioned –OH groups, facilitating the formation of THMs and HAAs. In the presence of NOM, lower concentrations of THMs and HAAs were observed in the systems with PAC than in those without PAC, demonstrating the critical role of PAC adsorption towards DBP control. The cytotoxicity evaluation indicated that more toxic reaction products between PAC and chlorine were formed besides conventional DBPs. Moreover, the PAC with higher BET surface area and more lactonic function groups formed less toxic DBPs during chlorination, which might reduce health risk for treatment processes with pre-chlorination.

Electrochemical modification of activated carbon fiber as 3-D particle electrodes: characterization and enhancement for the degradation of m-cresol.

Commercial activated carbon fiber (ACF) has been employed as particle electrodes to degrade aqueous m-cresol in 3-D electrode systems. To enhance the electrooxidation performance, three types of new ACF modification modes (anodic oxidation, cathodic reduction, and aqueous oxidation with concentrated HNO3) were introduced in this paper. These pretreated samples were characterized by N2 adsorption, scanning electron microscopy (SEM), cyclic voltammetry (CV), temperature-programmed desorption mass (TPD-MS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). It was revealed that the two new modification methods could efficiently modify the surface morphology as well as the chemical property. Eight types of surface oxygen groups (SOGs) were identified on the surface of ACF, and the types and amount of SOGs might be related to the oxidation effect of ACF on the 3-D electrodes. The effect and mechanism of these SOGs on electrooxidation performance were discussed with the aid of the frontier molecular orbital theory. It was demonstrated that the H2O2-·OH reaction mechanism was improved in the 3-D electrode system and the mechanism was elucidated.

Adsorption of toluene vapours on micro–meso hierarchical porous carbon

This work reports the synthesis of micro–meso hierarchical porous carbons prepared with sucrose as a carbon source. With properties characterised, dynamic adsorption performances of toluene on carbons were investigated at various initial concentrations. Results showed that adsorption capacities as high as 687.60 mg/g toluene/1 cm modified carbon can be achieved. Thus, large surface area, large volume of narrow microporosity and proper average pore size are the desired parameters to achieve strong toluene adsorption capacities. Moderate amounts of surface oxygen groups can also improve the adsorbents performance.

Solid-phase extraction of multi-class pharmaceuticals from environmental water samples onto modified multi-walled carbon nanotubes followed by LC-MS/MS

In this paper, pristine and chemically treated multi-walled carbon nanotubes (MWCNTs) were employed as solid-phase extraction sorbents for the isolation and enrichment of multi-class pharmaceuticals from the surface water and groundwater, prior to liquid chromatography-tandem mass spectrometry analysis. Thirteen pharmaceuticals that belong to different therapeutical classes (erythromycin, azithromycin, sulfamethoxazole, diazepam, lorazepam, carbamazepine, metoprolol, bisoprolol, enalapril, cilazapril, simvastatin, clopidogrel, diclofenac) and two metabolites of metamizole (4-acetylaminoantipyrine and 4-formylaminoantipyrine) were selected for this study. The influence of chemical treatment on MWCNT surface characteristics and extraction efficiency was studied, and it was shown that HCl treatment of MWCNT leads to a decrease in the amount of surface oxygen groups and at the same time favorably affects the efficiency toward extraction of selected pharmaceuticals. After the optimization of the SPE procedure, the following conditions were chosen: 50mg of HCl-treated MCWNT as a sorbent, 100mL of water sample at pH6, and 15mL of the methanol-dichloromethane mixture (1:1, v/v) as eluent. Under optimal conditions, high recoveries (79-119%), as well as low detection (0.2 to 103ngL-1) and quantitation (0.5-345ngL-1) limits, were obtained. The optimized method was applied to the analysis of five surface water and two groundwater samples, and three pharmaceuticals were detected, the antiepileptic drug carbamazepine and two metabolites of antipyretic metamizole.

Introducing sulphur surface groups in microporous carbons: A mechanistic study on carbide derived carbons

The mechanisms of introducing sulphur surface groups in porous carbons was deduced from the model carbon material carbide derived carbon (CDC) based on titanium carbide. The electrophilic substitution reaction at the aromatic ring system was identified as the predominant mechanism, even in highly amorphous carbons. The finding was deduced from TG–MS and XPS analysis. Upon varying the aromaticity and the amount of oxygen surface groups of the porous carbons, no change in mechanism was observed. This neglects an effect of spatial hindrance of the electrophilic substitution reaction within micropores. The introduced sulphur groups were found to be highly acidic sulphonic acid groups, which enable the functionalized carbons to be used as solid acid catalysts. The performance evaluation of the functionalized carbons catalyst in the esterification reaction of levulinic acid with ethanol supported the mechanistic findings. The activity correlated with the amount of sulphuric acid groups. The maximum amount of 0.86mmolm−2 and, thus, the highest activity was determined for the most graphitic porous carbon material.

Determination of the Surface Oxidation Degree of the Carbonaceous Materials by Quantitative TG-MS Analysis.

The developed quantitative TG-MS analysis was used for the determination of the surface oxidation degree of activated carbon cryogels. The surface chemistry of a prepared carbon cryogels pyrolyzed at 400 and 500 °C was modified using H3PO4, Fenton-like reaction, (NH4)2S2O8 with H2SO4 and HNO3 with H2O2 into a different surface oxidation degree. The influence of activation method and the amount of oxygen surface groups were characterized by elemental analysis, immersion calorimetry, water vapor adsorption, and Boehm titration. The obtained results from these methods were compared with the amount of surface oxygen determined by TG-MS. It was found out, that with the more intensive oxidation method (Fenton < (NH4)2S2O8 with H2SO4 < HNO3 with H2O2) the concentration of oxygen-containing surface groups increases, which lead to considerably higher parameters of immersion heat, amount of adsorbed water and acidity of the sample surface. The H3PO4 treatment of carbon cryogels causes no significant changes in the surface chemistry. The results obtained from the TG-MS analysis imply the good agreement with the results obtained from other used methods. It was proved that the quantitative TG-MS analysis could be a useful tool for the characterization of the surface of the carbonaceous materials.

Influence of the precursor chemical composition on heavy metal adsorption properties of hemp (Cannabis Sativa) fibers based biocarbon

Waste hemp (Cannabis sativa) fibers were used as sustainable and renewable raw materials for production of low-cost biocarbon sorbent for heavy metals removal. Carbon precursors of different chemical composition were obtained by oxidative and alkaline treatments of hemp fibers. Influence of lignocellulosic precursor chemical composition on hemp fibers-based biocarbon (HFB) characteristics was examined by BET surface area measurement, scanning electron microscopy and mass titration. It was found that lignin content and polymorphic transformation of cellulose increase the SBET of microporous HFBs, while hemicelluloses induce more homogeneous distribution of adsorption active sites. Heavy metal ions adsorption onto HFBs is primarily influenced by the amount of surface oxygen groups, while specific surface area plays a secondary role. Equilibrium data obtained for lead ions adsorption were analyzed by different nonlinear adsorption isotherms, and the best fitting model was chosen using standard deviation and Akaike information criterion (AICC). The maximum adsorption capacities of HFBs ranged from 103.1 to 116.3 mg Pb/g. Thermodynamic parameters showed that Pb2+ adsorption onto HFBs is a spontaneous and complex endothermic process, suggesting the coexistence of physisorption and chemisorption mechanisms.

Bio-oil upgrading in supercritical water using Ni-Co catalysts supported on carbon nanofibres

This work addresses the preparation, characterisation and screening of different Ni-Co catalysts supported on carbon nanofibres (CNFs) for use in the upgrading of bio-oil in supercritical water. The aim is to improve the physicochemical properties of bio-oil so that it can be used as a fuel. The CNFs were firstly oxidised in HNO3 and afterwards subjected to a thermal treatment to selectively modify their surface chemistry prior to the incorporation of the metal active phase (Ni-Co). The CNFs and the supported catalysts were thoroughly characterised by several techniques, which allowed a relationship to be established between the catalyst properties and the upgrading results. The use of Ni-Co/CNFs for bio-oil upgrading in supercritical water (SCW) significantly improved the properties of the original feedstock. In addition, the thermal treatment to which the fibres were subjected exerted a significant influence on their catalytic properties. An increase in the severity of the thermal treatment led to a substantial reduction in the oxygen content of the CNFs, mainly due to the removal of the less stable oxygen surface groups, which allowed their surface polarity to decrease. This decrease resulted in less formation of solid products. However, it also reduced the H/C and increased the O/C ratios of the upgraded liquid. Therefore, a compromise between the yield and the properties of the upgraded bio-oil was achieved with a Ni-Co supported on a CNF with a moderate amount of oxygen surface groups.

Adsorption of carbon dioxide using activated carbon impregnated with Cu promoted by zinc

In the present study, modified activated carbon (AC) was used in a fixed-bed column for CO2 adsorption of gaseous mixtures. The adsorbents were prepared by impregnation two metals Cu and Zn on the surface of the acid modified AC using a two-stage modification. At the first stage, the samples of AC were pretreated by oxidizing agent (nitric acid) to increase the amount of oxygen surface groups and at the second stage, the acid modified AC were impregnated by two metal salts Cu and Zn on the surface to produce a superior CO2 adsorbent. Metal-loaded acid modified AC was prepared by using different ratios of Cu/Zn ranging from 4 to 20%. The CO2 adsorbed have been measured over the temperature range of (30–50 °C), pressure (100–200 kPa) and CO2 concentrations from 5 to 50%. An increase of 49% CO2 adsorbed was resulted by using modified activated carbon. The breakthrough curves indicated that the breakthrough time increased with increasing the operating pressure, and decreased with increasing the temperature from 30 to 50 °C and CO2 concentration from 5 to 50%. The deactivation model was successfully applied to analyze the breakthrough curves under various operating conditions.

Applications for CO2‐Activated Carbon Monoliths: II. EDLC Electrodes

The use of high‐density carbon monoliths (CM) for preparing supercapacitor electrodes is analyzed. The starting CMs, produced by ATMI Co, were treated as follows: (1) under a N2 flow at 1073 K to modify the carbon surface chemistry and (2) activated with CO2 at the same temperature, using different activation times, to increase their porosity. Electrochemical measurements were performed on disks of 1–2 mm thickness which are suitable for direct use in practical devices. Two‐ and three‐electrode cells were used with 2 M H2SO4 solution as electrolyte. The contents of surface oxygen groups were measured by temperature‐programmed desorption (TPD) and X‐ray photoelectron spectroscopy (XPS). The porosity of the starting monolith is increased by physical activation with CO2, the BET surface area increasing from 957 to 1684 m2/g. Upon heat treatments, both, the high density (1.2 g/cm3), as well as the high amount of surface oxygen groups (2411 μmol CO/g) of the starting monolith are reduced; however, the densities of the treated monoliths remain higher than values reported for other porous carbon monoliths. The performance of the CMs as supercapacitor electrodes show as follows: (1) high specific and exceptionally high volumetric capacitances (up to 292 F/g and 342 F/cm3, respectively) due to their appropriate structure, porosity, and density, (2) a long and stable cyclability, (3) a decrease of power density with disk thickness, and (4) a decrease of pseudocapacitance with activation time.

Photocatalytic Performance of Carbon Monolith/TiO2Composite

The new and simple approach for deposition of catalytically active TiO2coating on carbon monolith (CM) carrier was presented. CM photocatalysts were impregnated with TiO2using titanium solution and thermal treatment, and their photocatalytic activity was investigated in the process of methylene blue (MB) photodegradation. For the purpose of comparison, CM composite photocatalysts were prepared by dip-coating method, which implies binder usage. The presence of TiO2on CM carrier was confirmed by Raman spectroscopy and scanning electron microscopy. The sorption characteristics of CM and the role of adsorption in the overall process of MB removal were evaluated through amount of surface oxygen groups obtained by temperature-programmed desorption and specific surface area determined by BET method. CM has shown good adsorption properties toward MB due to high amount of surface oxygen groups and relatively high specific surface area. It was concluded that photocatalytic activity increases with CM disc thickness due to increase of MB adsorption and amount of deposited TiO2. Good photocatalytic activity achieved for samples obtained by thermal treatment is the result of better accessibility of MB solution to the TiO2particles induced by binder absence.

Modification process optimization, characterization and adsorption property of granular fir-based activated carbon

Abstract Granular fir-based activated carbon (GFAC) was modified with H 2 O 2 , and orthogonal array experimental design method was used to optimize the process. The properties of the original and modified GFAC were characterized by N 2 adsorption–desorption isotherms, Brunauer–Emmett–Teller (BET) equation, Barett–Joyner–Halenda (BJH) equation, field emission scanning electron microscopy (FESEM), and Fourier transform infrared spectroscopy (FT-IR) analysis, etc. When 10.00 g of GFAC with particle size of 0.25–0.85 mm was modified by 150.0 ml of aqueous H 2 O 2 solution, the optimized conditions were found to be as follows: aqueous H 2 O 2 solution concentration 1.0 mol·l −1 , modification temperature 30.0 °C, modification time 4.0 h. Modified under the optimized conditions, decolonization of caramel, methylene blue adsorption, phenol adsorption and iodine number of the modified GFAC increased by 500.0%, 59.7%, 32.5%, and 15.1%, respectively. The original and optimally modified GFAC exhibited adsorption isotherms of hybrid Type I–IV isotherms with H4 hysteresis. BET surface area, micropore area, total pore volume, micropore volume, and microporosity of the modified GFAC increased by 7.33%, 11.25%, 3.89%, 14.23%, 9.91%, respectively. Whereas the average pore width decreased by 3.16%. In addition, the amount of surface oxygen groups (such as carbonyl or carboxyl) increased in the modified GFAC.

Tailoring the Surface Chemistry of Activated Carbon Cloth by Electrochemical Methods

This paper presents a systematic study of the effect of the electrochemical treatment (galvanostatic electrolysis in a filter-press electrochemical cell) on the surface chemistry and porous texture of commercial activated carbon cloth. The same treatments have been conducted over a granular activated carbon in order to clarify the effect of morphology. The influence of different electrochemical variables, such as the electrode polarity (anodic or cathodic), the applied current (between 0.2 and 1.0 A) and the type of electrolyte (HNO3 and NaCl) have also been analyzed. The anodic treatment of both activated carbons causes an increase in the amount of surface oxygen groups, whereas the cathodic treatment does not produce any relevant modification of the surface chemistry. The HNO3 electrolyte produced a lower generation of oxygen groups than the NaCl one, but differences in the achieved distribution of surface groups can be benefitial to selectively tune the surface chemistry. The porous texture seems to be unaltered after the electro-oxidation treatment. The validity of this method to introduce surface oxygen groups with a pseudocapacitive behavior has been corroborated by cyclic voltammetry. As a conclusion, the electrochemical treatment can be easily implemented to selectively and quantitatively modify the surface chemistry of activated carbons with different shapes and morphologies.

Palladium supported on carbon nanofiber coated monoliths for three-phase nitrobenzene hydrogenation: Influence of reduction temperature and oxidation pre-treatment

Carbon nanofiber (CNF) coated monoliths with a homogeneous and consistent layer were prepared by catalytic decomposition of ethane on Ni particles, and the CNF coated monolith supports were oxidized using different agents to get different oxidation degrees. The as-prepared catalysts were characterized by SEM, TG, Raman spectra, FT-IR, TPD, TPR, CO pulsar and TEM, while the behavior of Pd supported on CNF coated monoliths were tested by liquid phase of nitrobenzene hydrogenation in a continuous flow reactor. For comparison Pd/Al2O3/cordierite was also prepared. It was found that the reduction temperature controlled Pd dispersion, which in turn was responsible for the catalytic activity. A good linear relationship between nitrobenzene conversion and Pd dispersion was observed. Furthermore, Pd/CNF/cordierite showed higher nitrobenzene conversion compared with Pd/Al2O3/cordierite, indicating CNF was a superior support. The aniline selectivity was related to the amount of surface oxygen groups (SOCs) formed during the oxidation pre-treatment. SOCs, especially carboxylic acid groups, increased as the degree of oxidation deepened, and more amounts of SOCs on CNF surface were responsible for the lower aniline selectivity.

Electrochemical Performance of Hierarchical Porous Carbon Materials Obtained from the Infiltration of Lignin into Zeolite Templates

Hierarchical porous carbon materials prepared by the direct carbonization of lignin/zeolite mixtures and the subsequent basic etching of the inorganic template have been electrochemically characterized in acidic media. These lignin-based templated carbons have interesting surface chemistry features, such as a variety of surface oxygen groups and also pyridone and pyridinic groups, which results in a high capacitance enhancement compared to petroleum-pitch-based carbons obtained by the same procedure. Furthermore, they are easily electro-oxidized in a sulfuric acid electrolyte under positive polarization to produce a large amount of surface oxygen groups that boosts the pseudocapacitance. The lignin-based templated carbons showed a specific capacitance as high as 250 F g(-1) at 50 mA g(-1) , with a capacitance retention of 50 % and volumetric capacitance of 75 F cm(-3) at current densities higher than 20 A g(-1) thanks to their suitable porous texture. These results indicate the potential use of inexpensive biomass byproducts, such as lignin, as carbon precursors in the production of hierarchical carbon materials for electrodes in electrochemical capacitors.

New insights on electrochemical hydrogen storage in nanoporous carbons by in situ Raman spectroscopy

In situ Raman spectroscopy was exploited to analyze the interaction between carbon and hydrogen during electrochemical hydrogen storage at cathodic conditions. Two different activated carbons were used and characterized by different electrochemical techniques in two electrolytes (6MKOH and 0.5MNa2SO4). The in situ Raman spectra collected showed that, in addition to the D and G bands associated to the graphitic carbons, two bands appear simultaneously at about 1110 and 1500cm−1 under cathodic conditions, and then they disappear when the potential increases to more positive values. This indicates that carbon–hydrogen bonds are formed reversibly in both electrolytes during cathodic conditions. Comparing the two activated carbons, it was confirmed that, in both electrolytes, the hydrogenation of carbon atoms is produced more easily for the sample with lower amount of surface oxygen groups. In KOH medium, for the two samples, the formation of carbon–hydrogen bonds proceeds at more positive potential with respect to the thermodynamic potential value for hydrogen evolution. Furthermore, changes in the shape of the D band (due to an intensity increase of the D1 band) during the formation of carbon–hydrogen bonds suggest that hydrogenation of the carbon atoms increases the number of edge planes.

Effects of multiwalled carbon nanotube morphology on the synthesis and electrocatalytic performance of Pt supported by multiwalled carbon nanotubes

The effect of the diameter of multiwalled carbon nanotubes (CNTs) during the synthesis of CNT-supported Pt (Pt/CNT) has been studied. Three different CNTs with mean diameters of 10, 20 and 60nm were chemically treated in acidic media and used as supports for Pt nanoparticles. Features such as specific surface area and the degree of surface modification during the chemical treatment are strongly influenced by the diameter of the CNT. Those features are key aspects that determine the size and loading of the Pt particles immobilized onto the nanotubes. Therefore, the catalysts prepared using nanotubes with smaller diameters exhibit both higher Pt loading and dispersion. Consequently, the performance of the catalysts during the electrooxidation of CO and oxygen reduction reaction in acidic media varies with the diameter of the CNTs. Remarkably, the catalyst prepared on 60-nm diameter CNTs is the most stable during long-term use. This higher stability arises from both the superior stability of the larger Pt particles and the stronger anchorage of the Pt onto the CNTs with higher amounts of surface oxygen groups. The groups increase in number with increased CNT diameters.

Surface Modification of Activated Carbon and its Effects on Methane Adsorption

In this work, one activated carbon (AC) was modified with H2O2, (NH4)2S2O8 saturated solution and H2SO4/(NH4)2S2O8 mixture respectively. The oxygen groups on ACs surface were characterized by Boehm titration. The textures of the ACs were investigated by N2 adsorption at 77 K. The influence of surface oxygen groups on methane adsorption on ACs has been studied. The results of Boehm titration showed that the concentration of acidic oxygen functional groups on the AC surface increased after modification. N2 adsorption data showed that the specific surface area SBET and the micropore volume Vmic of AC were changed lightly after modification. It was observed that there was, in general, a positive correlation between the methane saturated adsorption capacity and the SBET of ACs while a negative correlation between methane saturated adsorption capacity and the total surface acidic groups. The methane saturated adsorption capacity was determined by the ACs surface chemistry when the microporosity parameters of two samples were similar. AC with a higher amount of oxygen surface groups, and consequently with a less hydrophobic character, had lower methane adsorption capacity.