Acidic Oxygen-containing Groups Research Articles

Preparation and performance evaluation of resin-derived carbon spheres for desulfurization of fuels

A polystyrene-based ion-exchange resin was employed as the precursor for preparation of resin-derived carbon spheres (RCSs) through KOH activation with various impregnation ratios. Pore structure, yield and hardness, surface functional groups of the samples and their adsorption performance towards dibenzothiophene (DBT) were investigated. The RCSs with large surface areas (up to 2696 m2/g) and total pore volumes (up to 1.46 cm3/g) exhibited larger adsorption capacities than a commercial activated carbon, F400. Polanyi-Dubinin-Mane (PDM) model was applied to fit the adsorption data, which proved that micropore filling was involved during the adsorption process. Moreover, a good linear relationship was observed between the extra-micropore volume and adsorption capacity. Intra-particle diffusion (IPD) model was used to describe the kinetic data of DBT onto the adsorbents. The adsorption processes were divided into three stages according to the different diffusion parameter. The selective adsorption towards DBT in the presence of competing compounds was also investigated and the high selectivity of the RSCs towards DBT may be attributed to the large quantity of acidic oxygen-containing groups.

Biodegradability enhancement of coking wastewater by catalytic wet air oxidation using aminated activated carbon as catalyst

The catalytic wet oxidation (CWO) under mild conditions was employed for pre-treatment of low-biodegradable coking wastewater. The catalysts were a commercial activated carbon (AC) and its ammonia-treated samples at various temperatures and were characterized by N2 adsorption/desorption and X-ray photoelectron spectroscopy. The CWO experiments and pilot tests were performed in fixed bed reactors at 140–160°C and 0.2–1MPa of oxygen partial pressure. The amination introduced nitrogen-containing functional groups into the AC surface and decreased acid oxygen-containing functional groups. The ACs aminated at 450 and 650°C showed higher activity than their parent counterpart. It was suggested that nitrogen-containing functional groups contributed to the enhanced activities compared the activities, surface chemistry and porosity of ACs with and without amination. The BOD/COD ratio increased from 0.23 of the untreated wastewater up to 0.84 of the effluents of pilot tests. Higher COD removal of anoxic digestion experiments also indicated the biodegradability enhancement of coking wastewater after the CWO treatment.

Effect of Modification with Nitric Acid and Hydrogen Peroxide on Chromium (VI) Adsorption by Activated Carbon Fiber

The activated carbon fiber (ACF) was treated by different concentration nitric acid (HNO3) and hydrogen peroxide (H2O2) oxidization to enhance its adsorption capacity to hexavalent chromium (Cr6+) ion. The adsorption amount and adsorption kinetics of Cr6+ ion on ACFs, and the surface chemical groups were investigated. The results showed that the modified ACFs with 1% HNO3 and 10% H2O2 had a better adsorption capacity, respectively. The adsorption amount of ACFs was affected strongly solution pH value, and decreased significantly with increasing of the pH value. The adsorption kinetics indicated that the adsorption rates of Cr6+ ion on different modified ACFs were well fitted with the pseudo-second-order kinetic model. After 1% HNO3 and 10% H2O2 modification, respectively, the total acidic oxygen-containing groups on ACFs surface had an increase obviously, which might be enhance the adsorption amount of Cr6+ ion on ACFs.

Functionalization of textiles with multi-walled carbon nanotubes by a novel dyeing-like process

Multi-walled carbon nanotubes (MWCNTs) were functionalized with oxygen-containing surface groups and subsequently incorporated in cotton and polyester fabrics by a process that mimics the traditional industrial dyeing process. The washing fastness, hydrophobicity and flame retardancy of the functional textiles were evaluated. The MWCNTs surface chemistry was modified by three different routes: (i) liquid phase oxidation with nitric acid, in order to introduce acidic oxygen-containing groups, (ii) thermal treatment of the sample oxidized in (i), in order to remove the carboxylic acid functionalities and (iii) gas phase oxidation with 5% oxygen in nitrogen to incorporate basic and neutral groups. All samples were characterized by temperature programmed desorption, pH at the point of zero charge and N2 adsorption–desorption isotherms at −196 °C. The effect of the MWCNTs acidity/basicity and of the type of substrate in the nanomaterials incorporation efficiencies and in the performance of the final textile materials was assessed. The scanning electron microscopy images and the whiteness degree values of the functional textiles before and after washing indicated that the incorporation efficiency was higher for the textiles containing the most acidic MWCNTs, especially for the polyester textiles. The immobilization of the less acidic MWCNTs in polyester imparted hydrophobic properties to the fabrics surface; in particular, the polyester samples functionalized with unmodified and O2-oxidized MWCNTs presented an almost superhydrophobic behaviour. In the case of the cotton-based samples, a hydrophobic behaviour was not achieved. Finally, the flame-retardant properties of both substrates improved upon the MWCNTs immobilization.

Synthesis and characterization of ruthenium supported on carbon nanofibers with different graphitic plane arrangements

Ruthenium supported on carbon nanofibers with different structures with respect to the arrangement of the graphitic planes (platelet, fishbone and tubular) have been prepared by wet impregnation method. On the other hand, the CNFs were prepared by CVD method at different temperatures using C 2H 4 as the carbon precursor and Ni/SiO 2 as the catalyst. Different techniques have been employed to characterize both the supports and the final Ru catalysts: N 2 adsorption–desorption analyses, XRD, TEM, elemental analyses, TPD, TPR, H 2 chemisorption, TPO, atomic absorption spectrophotometry and titration analyses. The results show that, depending on the orientation of the graphitic plane, the amount of acidic oxygen-containing groups can change significantly when the Ru was added to the CNFs. Thus, the specific surface area of CNF tubular was increased when Ru particles were impregnated. It was due to the oxygen groups were increased in comparison with other CNF types. In turn, the Ru particle size, its dispersion and its interaction with the support were clearly influenced by these oxygen-containing groups. Therefore, it was demonstrated that the presence of more acidic groups stabilizes the Ru particles during reduction.

Optimization Conditions of Modified Activated Carbon and the Adsorption of Phenol

To optimize the conditions of modification and understand the absorption mechanism of activated carbon, the orthogonal test was used to select the best conditions of ammonia-modified activated carbon. The changes of activated carbon’s specific surface area, pore volume and surface acidic oxygen-containing functional groups were determined before and after modification by ammonia, and the equilibrium adsorption model for phenol was also explored. The results show that under the conditions of ammonia concentration of 10%, soaking time of 2h, activation time of 2.5h and activation temperature of 500°C, the best removal rate could be obtained. The specific surface area and pore volume of modified activated carbon were increased, whereas the acidic oxygen-containing groups of its surface were significantly reduced by 57.88% after modification. It means the surface polarity of carbon was decreased, and which was conducive to the adsorption of phenol, since phenol was a weakly polar substance. Both Freundlich and Langmuir model could reflect the adsorption behavior of modified activated carbon for phenol, while the Freundlich model was more properly, but for the unmodified activated carbon, Freundlich model was more suited to describe the adsorption behavior of phenol than Langmuir model.

Modified activated carbon with an enhanced nitrobenzene adsorption capacity

To enhance nitrobenzene removal from aqueous solution, commercial activated carbon (AC) was modified by oxidation with HNO3 followed by heat treatment in a nitrogen atmosphere. The modification process introduced oxygen-containing functional groups and changed the charge properties of the AC surface. The effects of surface chemical properties and pore structure on the adsorption of nitrobenzene by the AC were investigated through kinetics and equilibrium isotherms. HNO3 oxidation modified the surface chemical properties and increased the number of acidic oxygen-containing surface groups, but had an almost negligible effect on the pore structure. Subsequent heat treatment caused decomposition of oxygen-containing functional groups on the AC surface, increased the pH point of zero charge (pHPZC) and increased the number of mesopores. The maximum adsorption capacity achieved by the modified AC was 1,443.53 mg g−1, 3.33 times of that unmodified AC. HNO3 oxidation combined with heat treatment was an effective method for the preparation of AC with high nitrobenzene adsorption capacity and fast adsorption kinetics. An appropriate pHPZC, amount of surface oxygen groups and the presence of well-developed mesopores together with micropores were the main reasons for the high nitrobenzene adsorption capacity of the modified AC.

Preparation of polystyrene-based activated carbon spheres with high surface area and their adsorption to dibenzothiophene

Polystyrene-based activated carbon spheres (PACS K) with high surface area were prepared through KOH activation. Effects of the carbonization temperature and the ratio of KOH to carbon spheres (CS) on the textural structure, hardness and yield of the resultant PACS K were studied, and their adsorption to dibenzothiophene (DBT) were investigated. The as-prepared PACS K exhibited a high surface area (up to 2022 m 2/g), large total pore volume (≥ 0.78 cm 3/g), superior mechanical hardness and high adsorption capacity (ca. 153 mg/g). With the increase of the KOH/CS ratio from 2:1 to 4:1, the surface area, total pore volume, volume of micropores, and volume of mesopores, increase, whereas the volume of small-micropores (< 0.8 nm) decreases from 0.36 to 0.31 cm 3/g. The adsorption capacity has a good linear correlation with the volume of small-micropores rather than the surface area. In addition, the large quantity of acidic oxygen-containing groups of PACS K may also be responsible for their higher adsorption capacity and selectivity of DBT. The PACS K saturated by DBT can be regenerated by a washing process in a shaking bath or using ultrasonic with toluene at 80 °C.

Effects of oxidative modification of carbon surface on the adsorption of sulfur compounds in diesel fuel

This work examines the effects of modification of activated carbons (ACs) by HNO3 oxidation and gas-phase O2 oxidation, respectively, on the liquid-phase adsorption of sulfur compounds in diesel fuel. The adsorption characteristics of the oxidized and the original AC samples were evaluated in a fixed-bed flow system by using a model diesel fuel containing 400 parts per million by weight (ppmw) of sulfur as thiophenic compounds and 10wt% of aromatics in a paraffinic solvent. The pore structure and surface properties of the AC samples were characterized by N2 adsorption, SEM, FTIR, XPS and surface pH measurements. The adsorptive selectivity factor of the AC samples increases in the order of benzothiophene (BT)≈naphthalene (Nap)<2-methyl naphthalene (2-MNap)<dibenzothiophene (DBT)<4-methyldibenzothiophene (4-MDBT)<4,6-dimethyldibenzothiophene (4,6-DMDBT). It was found that the HNO3 oxidation was an efficient method in improvement of the adsorption performance of the AC for sulfur compounds. The improved adsorption performance upon the HNO3 oxidation can be attributed mainly to an increase in the acidic oxygen-containing functional groups. However, the improved adsorption capacity upon oxidation is unlikely due to an increase in mesoporous or microporous surface/volume, although such attribution might have been inferred from the literature. An excellent correlation between the concentration of the surface oxygen-containing functional groups and the adsorption capacity per unit area as well as a good relationship between the adsorption capacity and the surface pH value were observed in this work, which suggest that the adsorption of the sulfur compounds over AC from the liquid hydrocarbon fuel may involve an interaction of the acidic oxygen-containing groups on AC with the sulfur compounds.

Effect of thermal oxidation of activated carbon surface on its adsorption towards dibenzothiophene

Abstract The effect of thermal oxidation of activated carbon (AC) on adsorption capacity of dibenzothiophene (DBT) was investigated. ACs were treated in air by thermal oxidation at different temperature 473, 573 and 673 K and thus modified ACs, AC473, AC573 and AC673 were separately available. The oxygen functional groups on the surfaces of the ACs were determined separately by diffuse reflectance infrared Fourier transform spectroscopy and Boehm titration. The influence of the surface chemistry of the ACs on its adsorption towards DBT was discussed. The results showed that after the thermal oxidation of carbon surfaces, its total basicity decreased, while its total acidity increased. The higher the oxidation temperature was, the more the amounts of surface acidic oxygen-containing groups were, and thus the higher the amounts adsorbed of DBT on corresponding carbon were. For the original AC, AC473, AC573 and AC673, the breakthrough amount of the treat fuel with containing 320 mg S l−1 was 35.5, 45, 52.5 and 61 ml fuel g−1 A−1, respectively, corresponding to the breakthrough capacity of 11.4, 14.5, 16.8 and 19.5 mg of sulfur per gram of adsorbent (mg S g−1 A−1). The adsorption capacity of the AC473, AC573 and AC673 for DBT increased separately by 27.2%, 47.4% and 70.2% compared to the original AC.

The effect of graphitic platelet orientation on the properties of carbon nanofiber supported Pd catalysts prepared by ion exchange

Carbon nanofibers with different nanostructures are prepared by catalytic CVD at 873 K using different catalysts and carbon-containing gases. As-grown carbon nanofibers are treated in concentrated nitric acid to introduce oxygen-containing groups, and therefore, to anchor palladium. The TPD-MS method is used to determine the number of acidic oxygen-containing groups and the results show that the number of oxygen-containing groups was strongly dependent on the graphitic platelet orientation. TEM, CO pulse chemisorption, and ICP-AES are used to characterize carbon nanofiber supported palladium catalysts. The results show that palladium particle sizes and palladium loading are dependent on the amounts of oxygen-containing groups on carbon nanofibers. TPR results show that the interaction between the palladium and the oxidized carbon nanofibers can be tailored by the variation of graphitic platelet orientation. A linear correlation between the amount of acidic groups and the palladium loading are observed.

Preparation of Carbon Nanofiber Supported Platinum and Ruthenium Catalysts: Comparison of Ion Adsorption and Homogeneous Deposition Precipitation

Carbon nanofiber (CNF) supported platinum catalysts have been prepared using Pt(NH3)4(NO3)2 as a precursor by two different ion adsorption techniques, one at a constant pH and one in which the pH is gradually and homogeneously increased from 3 to 6 by hydrolysis of urea. The latter method resembles the procedure of homogeneous deposition precipitation (HDP). Characterization of the CNF support was performed by acid−base titration, thermogravimetric mass spectrometry, and X-ray photoelectron spectroscopy, and for the various platinum catalysts, transmission electron microscopy, H2-chemisorption, and X-ray fluorescence/inductively coupled plasma-atomic emission spectrometry were utilized. With both synthesis techniques from diluted precursor solutions homogeneously distributed, highly dispersed and thermally stable metal particles were obtained with an average particle size of 1−2 nm. With the HDP method for the Pt/CNF catalysts, a linear relationship between the number of acidic oxygen-containing groups on...

Adsorption of dyes on activated carbons: influence of surface chemical groups

The surface chemistry of a commercial activated carbon has been selectively modified, without changing significantly its textural properties, by means of chemical treatments, using HNO 3, H 2O 2, NH 3, and thermal treatments under a flow of H 2 or N 2. The resultant samples were characterized in terms of their surface chemistry and textural properties, and subsequently tested in the removal of different classes of dyes. It was shown that the surface chemistry of the activated carbon plays a key role in dye adsorption performance. The basic sample obtained by thermal treatment under H 2 flow at 700 °C is the best material for the adsorption of most of the dyes tested. For anionic dyes (reactive, direct and acid) a close relationship between the surface basicity of the adsorbents and dye adsorption was shown, the interaction between the oxygen-free Lewis basic sites and the free electrons of the dye molecule being the main adsorption mechanism. For cationic dyes (basic) the acid oxygen-containing surface groups show a positive effect but thermally treated samples still present good performances, showing the existence of two parallel adsorption mechanisms involving electrostatic and dispersive interactions. The conclusions obtained for each dye individually were confirmed in the colour removal from a real textile process effluent.

Mercury and Cadmium Sorption Performance of a Fibrous Ion Exchanger and Granular Activated Carbon

A commercially available wood-based granular activated carbon (WHK) and a weak acid fibrous ion exchanger (K-4) were evaluated for the removal of mercury and cadmium from aqueous solution. As-received granular WHK was modified electrochemically to enhance cation sorption capacity for comparison with K-4. Granular carbon samples were characterized by direct titration, X-ray photoelectron spectroscopy (XPS), elemental analysis, surface area, electrophoretic mobility measurements, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The sodium sorption capacity of K-4 was 4.28 mmol g−1 compared to l.27 mmol g−1 for as-received WHK. Electrochemical oxidation for 3 h increased the ion exchange capacity of WHK to 2.57 mmol g−1. Elemental analysis and XPS showed a noticeable increase in the oxygen content of electrochemically modified WHK, which was reflected in a higher content of acidic oxygen-containing groups and a shift of the isoelectric point to lower pH values compared to as-received WHK. Batch sorption experiments showed that K-4 is more effective for the removal of cadmium than mercury when compared to modified WHK. The effect of pH on sorption isotherms indicated that metal uptake increased with increasing pH. Small-scale studies indicated that breakthrough occurred at 20 and 75 bed volumes for mercury and cadmium respectively when a 1 mM mixed cadmium and mercury feed solution at pH 6 was passed through a column packed with modified WHK. This indicated that modified WHK is more selective for cadmium than for mercury.

Influence of thermooxidative treatment on the surface properties of anthracite

The chemical nature of oxidized anthracite, obtained by oxidation with air of Bulgarian anthracite at different temperatures was studied by EPR spectroscopy, 13C NMR solid state, EPR and chemical methods. The X-ray analysis reveals that the oxidation process is confined to the surface of the particles and does not cause considerable change in the internal structure of the material. The 13C NMR solid state data show that up to 200°C no change occurs in the anthracite composition. Only at 300°C the oxidation process leads to noticeable changes, which become considerable at 400°C. The 13C NMR spectroscopic data reveal an increase in the amount of the oxygen-containing groups with acid character after oxidation of anthracite at 400°C. EPR investigations show that oxidation of anthracite with air to 300°C does not change the EPR parameters. It was found that the decrease of PMC concentration up to 400°C depends on formation of stable acid oxygen-containing groups, which cannot be removed in the conditions of deep vacuum. The 13C NMR and EPR data were confirmed by determination of oxygen-containing groups on the oxidation anthracite surface with chemical methods. It was found that a thermooxidation treatment with air at 400°C leads to considerable enhancement of the quantity of oxygen-containing groups on the anthracite surface. These groups were mainly of acidic character and variable chemical nature and have different dissociation strength in aqueous suspension. The pH of oxidized at 400°C anthracite is 4.3.