The effects of activated carbon surface features on the reactive adsorption of carbamazepine and sulfamethoxazole

© 2014 Elsevier Ltd. All rights reserved.Two commercial carbons, coconut shell- and wood-based were chosen to evaluate the mechanisms of carbamazepine (CBZ) and sulfamethoxazole (SMX) adsorption from a low (ppm level) concentration of these pharmaceuticals. The initial sample and those after adsorption were extensively characterized using potentiometric titration, thermal analysis combined with mass spectroscopy, FTIR, and XPS. It was found that not only porosity but also surface chemistry plays an important role in the adsorption process. The results show that extensive surface reactions take place during adsorption and adsorbates undergo significant transformations in the pore system. The ability of carbon surfaces to form superoxide ions results in the oxidation of CBZ and SMX, and their partial decomposition. Surface chemistry also promotes dimerization of the latter species. Moreover, functional groups of CBZ and SMX, mainly amines, react with oxygen groups of the carbon surface. Thus not only microporous carbons with sizes of pores similar to those of adsorbate molecules, but the carbons with large pores, rich in oxygen groups, can efficiently remove these pharmaceuticals following the reactive adsorption mechanism

Oxygen reduction on chemically heterogeneous iron-containing nanoporous carbon: the effects of specific surface functionalities

Synthetic activated carbon containing iron and sulfur heteroatoms, obtained from polystyrene sulfonic acid-based organic salt, and commercial wood-based carbon containing phosphorous were tested as catalysts for oxygen reduction reactions. The carbons were characterized using adsorption of nitrogen, TA-MS, FTIR, XRD, XPS, potentiometric titration, SEM/EDX, and HR-TEM microscopy. The introduction of iron to the carbon resulted a marked electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline medium. A current density was higher than that on commonly used platinum modified carbon and number of electron transfer (~4e-) indicated a high ORR efficiency. This was accompanied by a high tolerance to methanol oxidation and a good long-term stability after 1500 potential cycles. The extensive surface characterization indicated the fast O2 adsorption and charge transfer was owed to the surface hydrophobicity, small pores and conductivity. The synergistic effect of porosity and specific iron species containing sulfur lead to high ORR activity and high kinetic current densities

Highly Efficient Air Desulfurization on Self-Assembled Bundles of Copper Hydroxide Nanorods

Copper hydroxide and copper hydroxyl nitrate were successfully synthesized from copper nitrate. A slight alteration of a base addition pathway led to entirely different chemical and crystal structures. Structural, morphological, and surface chemical features were analyzed using various physical and chemical methods. The copper hydroxide texture consists of self-assembled bundles of nanorods with a diameter between 15 and 40 nm. They are stack together forming platelet-like particles. In the case of the copper hydroxyl nitrate, platelet-like particles with a smooth surface were detected. The fully hydroxylated sample showed a considerably higher surface area and mesoporous volume than those of copper hydroxyl nitrate. Both synthesized materials were used as air desulfurization media at moist or dry conditions. The results indicate a supreme chemical adsorption of H₂S on copper hydroxide. Moisture in air has a positive effect on the adsorption performance. In humid conditions, almost 0.9 mol H₂S/mol of Cu­(OH)₂ was adsorbed. CuS with almost a stoichiometric ratio was a product of surface reactions. The color change of the powder from sapphire blue to dark brown during the adsorption can be used as a fast indication of the adsorbent exhaustion level

Desulfurization of Model Diesel Fuel on Activated Carbon Modified with Iron Oxyhydroxide Nanoparticles: Effect of <i>tert</i>-Butylbenzene and Naphthalene Concentrations

Commercially activated carbon Filtrasorb 400 (F400) was modified with iron oxyhydroxide nanoparticles and tested, in a continuous process, as a diesel fuel desulfurization medium. Model diesel fuel (MDF) was prepared as a mixture of decane and hexadecane, with 20 ppm of sulfur from dibenzothiophenes (dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT)), and different concentrations of <i>tert</i>-butylbenzene and naphthalene. The calculated selectivities and adsorption capacities for DBT and DMDBT were analyzed at different concentration of aromatics. The results indicate that, while the concentration of naphthalene greatly affects the adsorption capacity of both DBT and DMDBT, the concentration of <i>tert</i>-butylbenzene only affects DMDBT uptake. At low concentration of aromatics, iron-containing carbon performs better than unmodified carbon and further oxidized species were identified on the surface of the iron-modified activated carbon. This indicates that iron is acting as an acidic center, attracting basic DBT and DMDBT, and is acting as an oxidant for the adsorbed species. With an increase in the content of aromatics in MDF, the difference in the desulfurization performance between the studied materials diminishes. After thermal regeneration of the iron-containing sample, 95% of the pore volume is recovered and only a 10% loss in the DBT and DMDBT adsorption capacity is observed

Superior Performance of Copper Based MOF and Aminated Graphite Oxide Composites as CO₂ Adsorbents at Room Temperature

New composites Cu-BTC MOF and graphite oxide modified with urea (GO-U) are developed and tested as CO₂ adsorbents at room temperature. The composite containing GO-U with the highest nitrogen content exhibits an excellent CO₂ uptake (4.23 mmol/g) at dynamic conditions. The incorporation of GO-U into MOF changes the chemistry and microstructure of the parent MOF and results in synergistic features beneficial for CO₂ retention on the surface. To identify these features the initial and exhausted materials were extensively characterized from the points of view of their porosity and chemistry. Although the adsorption forces are relatively strong, the results indicate that CO₂ is mainly physisorbed on the composites at dry dynamic conditions at ambient temperature and pressure. The primary adsorption sites include small micropores specific for the composites, open Cu sites, and cage window sites

A New Generation of Surface Active Carbon Textiles As Reactive Adsorbents of Indoor Formaldehyde

Highly porous carbon textiles were modified by impregnation with urea, thiourea, dicyandiamide, or penicillin G, followed by heat treatment at 800 °C. This resulted in an incorporation of nitrogen or nitrogen and sulfur heteroatoms in various configurations to the carbon surface. The volume of pores and, especially, ultramicropores was also affected to various extents. The modified textiles were then used as adsorbents of formaldehyde (1 ppmv) in dynamic conditions. The modifications applied significantly improved the adsorptive performance. For the majority of samples, formaldehyde adsorption resulted in a decrease in the volume of ultramicropores. The enhancement in the adsorption was linked not only to the physical adsorption of formaldehyde in small pores but also to its reactivity with sulfonic groups and amines present on the surface. Water on the surface and in challenge gas decreased the adsorptive performance owing to the competition with formaldehyde for polar centers. The results collected show that the S- and N-modified textiles can work as efficient media for indoor formaldehyde removal

Carbon Textiles Modified with Copper-Based Reactive Adsorbents as Efficient Media for Detoxification of Chemical Warfare Agents

Carbon textile swatch was oxidized and impregnated with copper hydroxynitrate. A subsample was then further heated at 280 °C to form copper oxide. The swatches preserved their integrity through the treatments. As final products, they exhibited remarkable detoxification properties for the nerve agent surrogate dimethyl chlorophosphate (DMCP). Based on the amount of reactive copper phases deposited on the fibers, their adsorption capacities were higher than those of the bulk powders. After 1 day exposure to DMCP (1:1 weight ratio adsorbent/DMCP), 99% of the initial amount of DMCP was eliminated. A synergistic effect of the composite components was clearly seen. GC-MS results showed that the main surface reaction product was chloromethane. Its formation indicated hydrolysis as a detoxification path. Surface analyses showed phosphate bonding to the fibers and formation of copper chloride. The appearance of the latter species results in a clear textile color change, which suggests the application of these fabrics not only as catalytic protection agents but also as sensors of nerve agents

Electrochemical Reduction of Oxygen on Hydrophobic Ultramicroporous PolyHIPE Carbon

A new kind of polyHIPE (polymerized high internal phase emulsion)-based carbon derived from coreacted furfuryl alcohol and tannin was tested as an ORR catalyst. To understand the reduction process, the surface was extensively characterized from the point of view of texture and chemistry. The prepared materials show subtle differences in the chemistry but marked differences in the porosity. The best-performing sample had a very high volume of ultramicropores and the highest degree of defects on the surface. The oxygen was present on the surface mainly in epoxy and ether configurations. Those oxygen groups located in large pores promoted transfer of O₂ dissolved in water/electrolyte to small pores of the hydrophobic surface. There, a strong adsorption of oxygen was energetically favorable. This led to weakening of O–O bonds, subsequent dissociation of oxygen, and its reduction/protonation. The presented polyHIPE carbons show high electrochemical stability and better tolerance to methanol than Pt/C. High kinetic current density was measured on them

Role of Surface Chemistry and Morphology in the Reactive Adsorption of H₂S on Iron (Hydr)Oxide/Graphite Oxide Composites

Composites of magnetite and two-line ferrihydrite with graphite oxide (GO) were synthesized and tested as hydrogen sulfide adsorbents. Exhausted and initial composites were characterized by the adsorption of nitrogen, X-ray diffraction, potentiometric titration, thermal analysis, and FTIR. The addition of GO increased the surface area of the composites due to the formation of new micropores. The extent of the increase depended on the nature of the iron (hydr)­oxide and the content of GO. The addition of GO did not considerably change the crystal structure but increased the number of acidic functional groups. While for the magnetite composites an increase in the H₂S adsorption capacity after GO addition was found, the opposite effect was recorded for the ferrihydrite composites. That increase in the adsorption capacity was linked to the affinity of the composites to adsorb water in mesopores of specific sizes in which the reaction with basic surface groups takes place. Elemental sulfur and ferric and ferrous sulfates were detected on the surface of the exhausted samples. A redox reactive adsorption mechanism is proposed to govern the retention of hydrogen sulfide on the surface of the composites. The incorporation of GO enhances the chemical retention of H₂S due to the incorporation of OH reactive groups and an increase in surface heterogeneity

Cu-BTC/Aminated Graphite Oxide Composites As High-Efficiency CO₂ Capture Media

CO₂ adsorption isotherms on Cu-BTC/aminated graphite oxide composites were measured in the pressure range up to 1.5 MPa at three different temperatures close to ambient. Adsorption capacity, isosteric heat of adsorption, and regenerability were investigated. They are considered as significant factors determining the practical application of materials for CO₂ capture. The results indicate a significant improvement in the performance of the composites as CO₂ adsorbents in comparison with the parent Cu-BTC MOF. Among all samples analyzed, the composite of Cu-BTC and modified graphite oxide with the highest N content (MOF/GO-U3) is the best performing sample. On its surface 13.41 mmol/g CO₂ was adsorbed at room temperature and 1.5 MPa. A high selectivity for CO₂ adsorption over that of CH₄ was found. The selectivities for CO₂ adsorption over N₂ are governed by the properties of the MOF phase. A relatively low heat of CO₂ adsorption and the high degree of surface homogeneity cause that the composites can be fully regenerated and used in multicycle adsorption with the minimum energy demand