Search

Sulfonation of nanoporous activated carbon (NAC) was performed in the different ways available within the synthetic organic chemistry armory for preparing solid acid catalysts of isopropyl alcohol ...

In this study, we considered changes in the surface chemistry after introducing fluorine into the surface layer of nanoporous activated carbon (BAU) produced from the birch wood. Here, we examined the BAU treated with 1,1,1,2-tetrafluoroethane at the selected temperature in the range of 400–800 °C. Diverse methods, including chemical analysis, nitrogen adsorption–desorption, SEM–EDS, XPS, and 19F solid-state NMR, were used for the characterization of the prepared materials. It was found that one can introduce from 0.17 to 0.42 mmol of F per gram of BAU using fluoroalkylation at 400–500 °C. Increasing the temperature to 600 °C increases the fluorination efficiency, and the relatively high fluorine content of 1.86 mmol of F per gram of BAU can be reached. At least three group types, namely, C–F, CF2, and CF3 groups, were found by XPS and 19F solid-state NMR after such treatment. The content of “semi-ionic” fluorine drastically increases in the surface layer after high-temperature fluoroalkylation at 700 °C and 800 °C. This “semi-ionic” fluorine, in the form of C–F and CF2 groups, is directly conjugated with the π-electron system of the carbon matrix.

Nanoporous activated carbon (NAC) beads that prepared by carbonization of microporous polymer 2,6-di-tert-butyl pyridine beads were subjected to bromination followed by amination to synthesize the ...

Here, we have examined the nanoporous activated carbon fibers (ACFs) sulfonated using the direct sulfonation and the staged method that included bromination, followed by sulfidation and oxidation. TEM confirmed the nanoporous structure of the prepared sulfonated ACFs. Nitrogen porometry and 2D nonlocal DFT simulations showed the nanoporosity reduction and variations of the pore size distribution because of the functionalization. Comparison of parameters of the SO3H groups confined in nanopores, e.g., the thermal stability and catalytic potential, showed that the most efficient acid sites, in the catalytic 2-propanol dehydration to propylene, are the SO3H groups grafted by the staged Houben–Weil methods. From the productivity of reactions used at the preparation stage, and in contrast to the one-staged aromatic substitution, the bromine addition to π sites of the edges of carbon matrix supplies enough active sites and is a reason for further high yields of the grafted thermostable SO3H groups. Hydrolysis of the grafted bromine and the surface oxidation of nanopores walls are parallel reactions that lowered the SO3H-related acidity, increasing the total acidity to 1.5 mmol g−1. The reported nanoporous sulfonated ACFs are effective to be used in the dehydration reactions catalyzed by solid acids.

The production of propylene by dehydration of 2-propanol at solid-vapor interfaces, as an example of the acidcatalyzed surface reaction, was explored by using sulfonated polyacrylonitrile-derived activated carbon fibers (PAN-ACFs). To prepare these catalysts, the PAN-ACFs obtained by onestep carbonation-activation were modified with a surface coverage of high acidity. The surface of PAN-ACFs was sulfurated with sulfur vapors at high temperatures followed by oxidation, to yield the corresponding sulfonates. The chemical analysis showed that the carbon surface layer contains from 1.28 to 6.10 mmol$\mathrm{g}^{-1}$ of sulfur, including the contribution of sulfonic $(\mathrm{S}\mathrm{O}{}_{3}\mathrm{H})$ groups. In addition to sulfonic groups, the obtained catalysts contain carboxyl, lactone, and phenolic groups, which are formed as a result of oxidation treatment. In order to understand the changes in surface chemistry and the results of sulfuration and oxidation, the sulfonated PAN-ACFs were characterized by a variety of techniques including TPD MS, TGA, SEM, and FTIR ATR. During a typical temperature mode screening at catalyst testing, it was found that the sulfonated PAN-ACFs prepared by treatment with sulfur vapor at low temperature, at $400\circ \mathrm{c}$ and $500\circ \mathrm{c}$, are very efficient at dehydrating 2-propanol. A weighed mass of 100 mg of each of these catalysts was operated at 165-175°C in 12 hours, and the catalysts were characterized by high conversion of 2-propanol and high selectivity to propylene, with a propylene yield of about 100%. Furthermore, the solid acid catalysts have high stability and strong acidity and can be reused with no significant loss in the activity after the third cycle in the subsequent 20 cycles. The preparation of solid acid catalysts from PAN-ACFs affords a novel strategy for producing propylene through alternative green and sustainable technologies.

Fluorination of nanoporous activated carbon and its subsequent modification with sodium sulfide, which leads to the introduction of sulfur-containing groups in the carbon matrix containing fluorine, was carried out. After oxidation with hydrogen peroxide, sulfo groups are formed in the surface layer of activated carbon, i.e., in this way, it is possible to obtain samples that have both fluorine-and sulfur-containing functional groups. As a result of this work, active and stable catalysts of the reactions catalyzed by acids were obtained. They have a fairly high catalytic activity and thermal stability. When testing the obtained samples in the temperature range up to 250°C under the catalytic 2-propanol dehydration, the yield of propylene remains unchanged for each cycle, the temperature of the dehydration reaction does not change, the activity remains stable for at the least three catalysis cycles, with no deactivation of catalysts.

We proposed the brominated carbon cloth that made of polyacrylonitrile-based activated carbon fibers (PAN-ACFs) as a precursor to chemically and uniformly graft SO3H groups to prepare the solid acid catalyst. The thermal and catalytic properties of the sulfonated PAN-ACFs were examined by IR controlled catalytic measurements and thermal analysis. The catalytic test results showed that the sulfonated surface remarkably improved the operating efficiency in isopropanol dehydration by decreasing the reaction temperature. All PAN-ACFs with grafted SO3H groups prepared through brominated precursors can converse 100% of isopropanol into propylene at moderate temperature. They showed the highest catalytic activity compared to PAN-ACFs sulfonated with oleum and chlorosulfonic acid, which conversed only 40% and 70% of isopropanol into propylene and deactivated at the higher temperatures in the reaction medium.

The functionalization of activated carbon (AC) by P-containing groups was conducted, and their thermal desorption was studied. Depending on the used method, the functionalized AC contains 0.5–1.45 mmol/g of acidic groups acting in catalytic 2-propanol dehydration. All catalysts showed 100% conversion of 2-propanol to propylene. The catalytic activity does not change with time under isothermal conditions and during their repeated use in catalysis, for 3 cycles of heating-cooling. In fact, the yield of propylene remains stable; it does not decrease with each cycle. Preliminary oxidation with nitric acid causes a small increase in the catalytic activity.

Oxidation of activated carbon (AC) with nitric acid was carried out, and the resulting AC/HNO 3 showed high capacity when used as supercapacitor electrode material operated in the KOH electrolyte. Oxidation caused different structural changes in the AC, reducing the specific surface area and the total pore volume. After oxidation, the content of all types of oxygen-containing groups and, especially, carboxyl groups showed a significant increase. Despite the significant reduction of the specific surface area, the specific capacitance of the oxidized AC in symmetric supercapacitor electrodes is 1.4 times larger than that for the pristine AC.

Nanoporous activated carbon fibers (BusofitTM, BACF) showed effective adsorption of carbon tetrachloride (CTC) vapors. About 2.50 mmol × g−1 of chlorine, in the form of trichloromethyl and ...

In this work, the adsorption of copper ions onto activated carbons that oxidatively modified with H 2 O 2 and HNO 3 was studied. The prepared sorbents with the surface area of 275–780 m 2 /g contain 0.53–3.77 mmol/g of oxygen-containing groups. It was found that the oxidized activated carbon effectively adsorbs Cu 2+ ions from aqueous solutions. For the most efficient activated carbon–HNO 3 –30 sorbent, the percentage removal of copper ions from solutions of varying concentration is high. In the concentration range from 1.5 to 6 × 10 −4 M of Cu 2+ , it reaches >55%. At the concentrations lower than 1.5 × 10 −4 M, the expected removal is above 80%. The experimental equilibrium adsorption data were modeled with 2- and 3-parameter isotherms. The analysis of adsorption modeling results accounting for the surface heterogeneity effect was provided. The data fit well to the Dubinin–Radushkevich model. Presumably, the complexation of Cu 2+ with oxygen-containing groups passes within micropores. We found the correlation between the sorption capacity for Cu 2+ and the concentration of surface groups. The presence of the carboxyl, anhydride, and lactone groups make a major impact on the adsorption.

Here we report on the phosphorylation of activated carbon (AC) at 500–800 °C. From thermal, titrimetric, and catalytic data, high surface acidity of the prepared solids is attributed to the total concentration of the protogenic groups. Transmission electron microscopy and nitrogen physisorption measurements showed a chemisorption-induced contraction of microporosity. The most active catalysts prepared at 700 °C contain 1.04 mmol g−1 of the phosphonic groups and supports dehydration of isopropanol with about 100% conversion and 100% selectivity to propylene at 170–180 °C.

Here we report on the preparation of effective aminated sorbents based on activated carbon (AC), which was produced from natural raw material (Apricot pits) for the removal of heavy metal ions from wastewaters. For effective functionalization, bromination and following amination were carried out. At the amination stage, the grafted bromine groups were substituted by amino groups. Amination by ethylenediamine and monoethanolamine alcohol solutions can replace 0.52 mmol of bromine groups by 0.51–0.57 mmol of amino groups per gram of sorbent. We showed that the aminated ACs could remove 90% of Cu(II) ions from aqueous solutions containing from 4×10−5 to 1×10−3 mol/L of Cu2+. The regeneration of used sorbents and the recovery of copper were also studied to evaluate the reusability of the sorbents.

The thermal resistivity method, which is a convenient and sensitive to electrical resistance changes, was proposed for control of chemical modification of nanoporous activated carbon fibers (NACF) with hydrofluorocarbons (HFC). The surface state changes could be monitored by measuring Ohmic resistance during heating, physisorption, and chemical reaction between the activated carbon material and HFC. Thus, we found a correlation between the fluorine content in the resulted carbon material and electrical resistance, measured from the room temperature to 900 °C. It was shown that in this way the temperature of the beginning of a chemical reaction and the temperature of the most effective chemical modification could be determined. The thermal grafting of fluororganic groups onto NACF is assumed to be the reason for the changed electrical resistivity of the initial NACF.

The adsorption remediation behavior of nanoporous activated carbon (NAC) was studied towards toluene, heptane, water, and 2-propanol. Besides, NACs tailored with acidic treatment were prepared and selected as catalysts to examine their potential in the reaction of 2-propanol dehydration to propylene. It was shown that depending on the used modification method, the surface layers of carbons contain from 0.30 up to 0.98 mmol/g of SO 3 H groups. Thermal stability, adsorption of 2-propanol and catalytic behavior of the resulted samples were characterized. Thermoprogrammed desorption studies presented the positive correlation of catalytic efficiency with the temperature range of desorption of 2-propanol and propylene. The lowest temperatures at the desorption maxima had the sample of NAC modified with the sulfonated poly(α-methylstyrene). It showed the highest catalytic performance and relatively low temperatures and could completely dehydrate alcohol at 140 °C, while the pristine NAC has no catalytic activity for 2-propanol dehydration at that temperature.

Activated carbon fibers originated from viscose was brominated in the dibromine solution. An active surface precursor with 1.0 mmol of bromine per gram of carbon fibers was obtained. The bromine groups are capable for a further replacement, e.g. for amines residues. The thermochemical properties of the synthesized samples were studied. The rules of the surface layer bromination were discussed within the results of the thermal and chemical analysis. Two types of bromine groups on the carbon fiber surface were determined by the thermal desorption. These groups were associated with different centers situated on the accessible surface or placed in tight nanoscale pores. The reason of such distribution was the bromination that producing groups which binding strength varies and the effect of configuration factor. This factor limits the thermal desorption of various gaseous molecules which were formed and released during the thermal decomposition of grafted functionalities and sorbed by the samples with small nanosized pores. The use of the precursor route shows that the interface covered with from 0.62 to 0.95 mmol/g of the residual amine functional groups can be prepared.

Activated carbon fibers (ACFs) made from polyacrylonitrile and viscose were treated with the sulfur vapor at the temperatures of 500–800 °C in an argon flow. Obtained materials were oxidized by 30% H 2 O 2 water solution in order to convert S-containing surface moieties into SO 3 H-groups. The samples were studied using Boehm titration, thermogravimetric analysis and temperature-programmed desorption with a mass spectrometric registration of gaseous desorption products. According to obtained data, the surface layer of synthesized samples contains grafted SO 3 H-groups and different functional groups formed at the carbon oxidation. The decomposition of SO 3 H-groups occurs in the temperature range of 75–590 °C. Two peak maxima at 200±30 °C and 300±30 °C were registered on all SO 2 desorption profiles. These maxima are assigned to two forms of surface SO 3 H groups having a different chemical environment. Testing of the catalytic activity shows that SO 3 H-functionalized carbon fibers are high active in the model reaction of propan-2-ol dehydration. The total conversion of propan-2-ol to propene is observed at 145–220 °C. The lowest temperature of total conversion was registered for the ACFs prepared from polyacrylonitrile being treated with the sulfur vapor at 500 °C. All SO 3 H-functionalized samples maintain their activity after repeated use.

Halogenated activated carbons (AC–Hal, Hal = F, Br and Cl) used as precursors were functionalized with SO 3 H groups to prepare (AC–Hal–S) solid acid catalysts. ACs obtained were subjected to chemical and elemental analysis, characterized by miscellaneous physicochemical techniques and were tested in the propan-2-ol dehydration. The high catalytic activity of AC–Hal–S (Hal = F, Cl) is attributed to the presence of F and Cl affect on the catalysts performance and stability at the operation conditions.

The paper addresses the thermal stability of fruit-stone activated carbon impregnated with the Cu-Co-Fe oxide catalyst. The nature and concentration of the oxygen-containing surface groups are determined. The kinetic investigation of the process of oxidation of fruit-stone activated carbon reveals a high catalytic activity of the Cu-Co-Fe oxide catalyst. It is shown that the nitric-acid treatment of fruit-stone activated carbon leads to an increase in the concentration of carboxyl groups which are the binding centers for Cu-Co-Fe oxide system with subsequent formation of the active center for the low-temperature oxidation. This gives rise to a great number of active centers of oxidation in the surface layer of fruit-stone activated carbon, resulting in a decrease of the temperature of the oxidation reaction of activated carbon by almost 100°C.

The present study is objected to develop an analytical remote optical diagnostics of the functionalized carbons surface. Carbon composites with up to 1 mmol g−1 of irreversibly adsorbed bromine were produced by the room temperature plasma treatment of an activated carbon fabric (ACF) derived from polyacrylonitrile textile. The brominated ACF (BrACF) was studied by elastic optical scattering indicatrix analysis at wavelength 532 nm. The obtained data were interpreted within results of the thermogravimetric analysis, X-ray photoelectron spectroscopy and temperature programmed desorption mass spectrometry. The bromination dramatically reduces the microporosity producing practically non-porous material, while the incorporated into the micropores bromine induces the dielectric and structural impact on surface polarizability and conductivity due to the charging effect. We have found that the elastic optical scattering in proper solid angles in the forward and the backward hemispheres is sensitive to the kind of the bromine bonding, e.g., physical adsorption or chemisorption, and the bromination level, respectively, that can be utilized for the express remote fabrication control of the nanoscale carbons with given interfaces. Electronic supplementary material The online version of this article (doi:10.1186/s11671-017-1873-7) contains supplementary material, which is available to authorized users.