Phenol adsorption on active carbon by means of thin-layer chromatography

Summary The effect of the acidity of the media on the adsorption of phenol and creasols was investigated using TLC and using the R_F-values as a measure of the adsorption ability of active carbon. Three types of chromatographic layers were employed: silica gel, silica gel containing 3% of active carbon and silica gel containing 6% of active carbon. Standard solutions of phenol, m-cresol and o-cresol were used as the samples. The acetic acid content of the solvent mixture significantly influences the adsorption of phenol and cresols on the active carbon layer. An increase in the acetic acid content results in a decrease of the adsorption of phenols. However, under specific conditions [81∶5∶7 hexane-diethyl ether-acetic acid, and 48∶2∶8 benzene-acetone-acetic acid developers] the competitive adsorption of phenols and acetic acid may take place, which has been observed by a steep increase in the adsorption of phenol and cresols.     

Anew technique for determining the adsorption energy of terminally adsorbed polymer

Using a new experimental technique, “Continuous Elution Method”, the desorption behavior of polystyrene(PS) and polystyrene (PS-X) functionalized by a terminal iminium ion (-X) from α-Al₂O₃ and γ-Al₂O₃ surface were investigated, and found that PS-X is forming a terminally adsorbed polymer layer on α-Al₂O₃, surface. Furthermore, it was found that the adsorption force of terminally adsorbed polymer is balanced with the desorption force which is contributed from the osmotic pressure in the adsorption layer. Based on this concept, the adsorption energy of the end-functionalized polystyrene terminally adsorbed on the α-Al₂O₃, surface was evaluated to be 4.2 ˜4.3 kT.     

Adsorption of benzene and perfluorobenzene vapor from a flow of moist air by a layer of equilibrium moistened active carbon

The equilibrium adsorption of benzene and perfluorobenzene vapor from a flow of moist air by a layer of active carbon (AC) hydrated to equilibrium were considered. It was ascertained that these organic substances partly displace the water from the adsorptive micropore volume of AC. The equilibrium adsorption values of benzene, perfluorobenzene, and water vapors on AC were calculated. The adsorption of benzene and perfluorobenzene from a flow of moist air by a layer of AC is characterized by volume filling of the micropore adsorption space. This work is part of the research devoted to the study of the dynamics of the adsorption of organic substances from a flow of moist air by a layer of AC hydrated to equilibrium.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1398–1401, August, 1994.     

Functions of moments in the elution dynamics of adsorption

An exact solution obtained for the direct problem concerning the elution dynamics of adsorption in terms of the model of an equilibrium adsorption layer using the gamma function is analyzed. Analytical expressions derived for the functions of moments comprise adsorbent layer lengths, mobile phase velocities, and adsorption constants. The functions are found to be interrelated via the slope coefficients of linear equations. The correctness of the results obtained is confirmed by good agreement between the theory and experimental data presented as tabulated values of the moments measured previously for the elution dynamics of Freon 13B1 adsorption on active carbon layers of different lengths.     

Thermodynamics of adsorption of acetone on active carbon supported metal adsorbents

Adsorption of acetone on active carbon and active carbon supported metals (Ni, Cu, Zn and Cd) have been studied as a function of temperature. Thermodynamic parameters such as G ⁰, H ⁰, and S ⁰ are calculated from virial and Langmuir isotherm expressions. It is observed that active carbon supported metals have more adsorption affinity for acetone as compared to active carbon. Results show that the increase in adsorption affinity for active carbon supported metals is not due to configurational factors affecting the entropy of adsorption, but because of enhanced enthalpy of adsorption. XRD spectra show that active carbon supported metals adsorbents are amorphous and metal residues are present on the surface of active carbon in its reduced form. From adsorption data, isosteric heats and molar entropies of adsorption were calculated as a function of coverages and temperature. The values of isosteric heats of adsorption were found to be higher for active carbon supported metals, which may be due to the chemisorption of adsorbate molecules with metal sites present on the surface of active carbon. The extent of coordination of adsorbate molecules with metal sites is discussed on the basis of the acidic character of metal.     

Specific Features of the Adsorption and Nuclear Magnetic Relaxation of the Water Molecules in Active Carbons: 2. The State of Water in Active Carbon with Relatively Large Pores According to the NMR Relaxation Data

The state of water upon adsorption on FAS-3 active carbon with relatively large micropores is studied by the NMR relaxation method. The dependences of the times of spin–lattice (T ₁) and spin–spin (T ₂) NMR relaxation of adsorbed water molecules on the adsorption value are established. The character of the dependences of T ₁ and T ₂ on the number of adsorbed water molecules per primary adsorption site reflects the specific features of the volume filling of micropores and the formation of a continuous adsorption layer on the mesopore surface due to cluster coalescence on the one wall of a pore. The results obtained are compared with the data for typical microporous active carbons, as well as with the data obtained by the adsorption method.     

Composite electrodes of electrochemical capacitors based on carbon materials with different structure

For composite electrodes based on active carbon DCL Supra 30, ordered mesoporous carbon, and synthetic carbon material Sibunit, the electrical double layer capacitance is studied. The original carbon samples are characterized by the methods of gas adsorption, X-ray diffraction, and transmission electron microscopy. The mesoporous structure of the material synthesized by the template method provides the maximum rate of ion transport in pores and demonstrates an insignificant decrease in the specific capacitance (9.5% in an aqueous electrolyte and 1.1% in an nonaqueous electrolyte) with an increase in the polarizing current.     

Synthesis, performance, and modeling of immobilized nano-sized magnetite layer for phosphate removal

A homogeneous layer of nano-sized magnetite particles (<4 nm) was synthesized by impregnation of modified granular activated carbon (GAC) with ferric chloride, for effective removal of phosphate. A proposed mechanism for the modification and formation of magnetite onto the GAC is specified. BET results showed a significant increase in the surface area of the matrix following iron loading, implying that a porous nanomagnetite layer was formed. Batch adsorption experiments revealed high efficiency of phosphate removal, by the newly developed adsorbent, attaining maximum adsorption capacity of 435 mg PO(4)/g Fe (corresponding to 1.1 mol PO(4)/mol Fe(3)O(4)). It was concluded that initially phosphate was adsorbed by the active sites on the magnetite surface, and then it diffused into the interior pores of the nanomagnetite layer. It was demonstrated that the latter is the rate-determining step for the process. Innovative correlation of the diffusion mechanism with the unique adsorption properties of the synthesized adsorbent is presented.     

Estimation of the energetic nonhomogeneity of the surface of oxide and carbon materials

The molecular statistical method for evaluating the distribution of active sites of various adsorbents relative to their energies has been improved. This method is used not only for the treatment of experimental data on the adsorption of hydrocarbons on various adsorbents, which is the usual procedure, but also data on the adsorption of polar water and methanol molecules on the active sites of adsorbent surfaces. Two types of active sites differing in energy have been shown to exist on the surface of graphitized carbon black, the complex shungite carbon/mineral adsorbent, and modified Silochrom. Chromatographic, calorimetric, and structural adsorption data were used to establish the relationship between the observed maxima of the energy distribution function of the adsorption sites with concrete adsorption sites or pores of the surface, on which the molecules are adsorbed. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 5, pp. 315–320, September–October, 2008.     

Adsorption kinetics of catalase to thin films of carbon nanotubes

The adsorption conditions used to immobilize catalase onto thin films of carbon nanotubes were investigated to elucidate the conditions that produced films with maximum amounts of active catalase. The adsorption kinetics were monitored by spectroscopic ellipsometry, and the immobilized catalase films were then assayed for catalytic activity. The development of a volumetric optical model used to interpret the ellipsometric data is discussed. According to the results herein discussed, not only the adsorbed amount but also the initial adsorption rates determine the final catalytic activity of the adsorbed layer. The results described in this paper have direct implications on the rational design and analytical performance of enzymatic biosensors.     

Computer simulation of active layers in double-layer supercapacitors: Galvanostatics,determination of effective coefficients,and calculation of overall characteristics

A computer simulation of the structure and modes of functioning of biporous active layers (activated carbon) in double-layer capacitors (DLCs) was performed. The charging of DLCs in a galvanostatic mode was studied. The main characteristics of DLCs (charging time, specific capacity, stored energy, and power) were calculated. DLCs with aqueous electrolyte of different types were studied: active layer with the “ideal” structure (type 1), active layer with a monoporous structure (2), and biporous active layer (3). A computer simulation of biporous active layers of DLCs involves the formulation of a model of the structure of the active layer, percolation evaluation, and calculation of the effective ion conductivities of both highly porous carbon grains and the whole active layer. When calculating the characteristics of the active layers of DLC, we analyzed the effect of the main parameters (charge current density and active layer thickness) on the charging process and overall characteristics. The central problem of calculation of a DLC with a real, nonmonoporos structure was formulated. In active layers generally having pores of three types (micro-, meso-, and macropores) in the galvanostatic mode of DLC charging, the wide pores are polarized first. In this case, the limiting acceptable potential is achieved, and galvanostatic charging should be stopped and changed to potentiostatic charging. As a result, a large number of micropores can remain unpolarized. Therefore, it is important to perform a theoretical search for means to carry out complete adsorption of ions in micropores and obtain high specific capacities of DLCs.     

The recovery of gold from thiourea solutions with open-cell polyurethane foams

The recovery of the gold-thiourea complex from aqueous solutions with TBP-loaded and unloaded polyurethane foams was investigated in batch experiments. The rates of adsorption of the gold complex on various types of loaded and unloaded foams were studied in detail and compared with the rate of adsorption on active carbon. Loaded and unloaded polyurethane foams of the polyether or polyester type behaved similarly to active carbon. The adsorption capacity of the foams was lower than that of active carbon but the use of foam simplifies the procedure by eliminating the filtration process which is necessary with carbon.     

Kinetics of the adsorption of polystyrene macromolecules from dilute solutions in methyl ethyl ketone on carbon black

The kinetics of the adsorption of a mixture of three polystyrenes (the weight-average molecular weight M _w = 8300, 34000, and 195000) on nonporous carbon (carbon black pretreated in the argon flow at 3800 K) from dilute solutions in methyl ethyl ketone at 298 K is studied. The kinetic dependences of the adsorption of polystyrenes on carbon black nanoparticles from solutions in methyl ethyl ketone are described by adsorption kinetics equations previously used for describing the adsorption of aromatic hydrocarbons from aqueous solutions by active carbon. The correlation between the kinetic coefficients and the molecular weights of polystyrenes is discussed.     

ADSORPTION CHARACTERISTICS OF L-HISTIDINE ON ACTIVE CARBON

Adsorption properties of L-histidine on active carbon were studied in the paper, which are affected by the main parameters, such as the quantity percent of active carbon, pH value of the solution, the time of adsorption equilibrium and adsorption temperature. The results indicate that adsorption equilibrium time of L-his on active carbon is about 80 minutes. With the increasing of the quantity percent of active carbon, the adsorbance of L-his decreases sharply, and increases lighter after that. When the quantity percent of active carbon is 10%, the adsorbance reaches the minimum.pH value of solution and extraction temperature have great affection on the adsorption. When the pH value is higher or lower than the pI of L-his, the adsorbance is small, even zero. It is proven that the experimental equilibrium data which are obtained under the conditions of 80 ℃and pH=1.0, are fitted with the Freundlich equation: q=2.5914c0.8097. The results can provide certain references in L-his adsorption process of industrial operation.     

Adsorption of long-chain aliphatic amines—components of corrosion inhibitors

Adsorption of certain long-chain aliphatic amines with 6–18 carbon atoms is studied on a stationary mercury drop electrode using the impedance method. It is found that adsorption of amines with C₆–C₁₂ results in the formation of an adsorption layer with the limiting capacitance of about 5 μF/cm². In the case of amines with C₁₄–C₁₆, the limiting capacitance is approximately 0.5–0.7 μF/cm². The most probable reason for such abrupt decrease in the adsorption layer capacitance is the formation of condensed layers of adsorbate molecules at the electrode surface. The adsorption parameters are calculated for hexylamine. The surface activity is estimated for amines with 10–14 carbon atoms in their chains.     

3,5-Dinitrosalicylic Acid Adsorption Using Granulated and Powdered Activated Carbons

Some nitroaromatic compounds are found in wastewater from industries such as the weapons industry or the wine industry. One of these compounds is 3,5-dinitrosalicylic acid (DNS), widely used in various tests and frequently found as an emerging pollutant in wastewater and to which the required attention has not been given, even though it may cause serious diseases due to its high toxicity. This study investigated the adsorption of DNS using granulated activated carbon (GAC) and powdered activated carbon (PAC) at different temperatures. The results show that in equilibrium, the adsorption takes place in more than one layer and is favorable for the removal of DNS in both GAC and PAC; The maximum adsorption capacity was obtained at 45 °C, with values of 6.97 mg/g and 11.57 mg/g, respectively. The process is spontaneous and exothermic. In addition, there was a greater disorder in the solid-liquid interface during the desorption process. The predominant kinetics using GAC (7.14 mg/g) as an adsorbent is Elovich, indicating that there are heterogeneous active sites, and when PAC (10.72 mg/g) is used, Pseudo-second order kinetics predominate, requiring two active sites for DNS removal. External mass transfer limitations are only significant in GAC, and ATR-FTIR studies in PAC demonstrated the participation of functional groups present on the adsorbent surface for DNS adsorption.     

Analytical methods for airborne arsine,silane and dichlorosilane by adsorption sampling and AA spectrophotometry

Analytical methods for arsine, silane and dichlorosilane by adsorption sampling and elemental analysis with graphite furnace AA were studied to establish convenient methods for atmospheric contamination surveys. This study included the following five items: (1) primary selection of adsorbents applicable to adsorption sampling; (2) examination of the adsorption capacities of the adsorbents for the gases; (3) improvement of the adsorbents by chemical modification; (4) desorption of the gases adsorbed on the adsorbents with solvents; and (5) quantitative analysis of arsenic and silicon in the solutions. Experimental results showed that active carbon made from synthetic thermosetting resin beads contained no aresenic and little silicon as impurities. This active carbon by itself was proved to adsorb arsine and dichlorosilane, but not silane. Impregnation with sodium hydroxide of the active carbon improved the adsorption capacity for all three gases. Refined silica gel, free from arsenic contamination, did not adsorb arsine by itself but potassium permanganate impregnation produced an adsorption capacity for arsine. The adsorbed arsine on the active carbon was desorbed into a hot dilute nitric acid solution with high efficiency (over 90%), but arsine adsorbed on sodium hydroxide impregnated active carbon or on potassium permanganate impregnated silica gel was dissolved into various solutions only at lower efficiencies. Silane adsorbed on sodium hydroxide-impregnated active carbon was desorbed with hot water with an efficiency higher than 90%. Dichlorosilane adsorbed on the active carbon with or without sodium hydroxide impregnation was desorbed with a nitric acid solution with efficiency of 85%. The lower determination limit for arsine able to discriminate from background interference of arsenie was 0.005 ppm, and those for silane and dichlorosilane were each 0.05 ppm for 3-dm³ air samples.     

Water‐Induced Growth of a Highly Oriented Mesoporous Graphitic Carbon Nanospring for Fast Potassium‐Ion Adsorption/Intercalation Storage

A highly oriented mesoporous graphitic carbon nanospring (OGCS) with graphitic layers that are perpendicular to the axis is prepared by hydrothermal treatment of epoxy resin at 500 °C and annealing at 1400 °C. Water plays an important role in not only forming the graphitic carbon nanospring with a high [002] orientation and a large amount of active edge‐plane sites, but also in the generation of the mesoporous structure, which facilitate fast K‐ion adsorption and diffusion. In situ and ex situ measurements confirm that OGCS undergoes K‐adsorption in mesopores and then K‐intercalation in the graphite layer to form KC₈ with a low discharge voltage. The spring‐like nanostructure can expand one‐dimensionally along the axial direction to accommodate the volume variation. The OGCS electrode thus shows a much better K‐storage performance than that of unoriented graphitic carbon.     

硅烷化活性炭的表面性质

测定了活性炭经三甲基氯硅烷蒸气处理后比表面、比孔容、平均孔径等的变化;研究了硅烷化炭表面的润湿性质和吸附性质.结果表明,随活性炭与三甲基氯硅烷反应时间的延长,其比表面和比孔容急剧减小,而孔径分布和平均孔径无明显变化;硅烷化后炭表面的疏水性明显增强;硅烷化炭自水中对正丁醇的吸附量增大.     

Supercapacitive Swing Adsorption of Carbon Dioxide

An electrical effect, the supercapacitive swing adsorption (SSA) effect is reported, which allows for reversible adsorption and desorption of carbon dioxide by capacitive charge and discharge of electrically conducting porous carbon materials. The SSA effect can be observed when an electrically conducting, nanoporous carbon material is brought into contact with carbon dioxide gas and an aqueous electrolyte. Charging the supercapacitor electrodes initiates the spontaneous organization of electrolyte ions into an electric double layer at the surface of each porous electrode. The presence of this double layer leads to reversible, selective uptake and release of the CO₂ as the supercapacitor is charged and discharged.