Effect of temperature and a weakly polar organic medium on water localization in slit-like pores of various sizes in microporous activated carbon

The joint adsorption of water and methane in pores of the synthetic carbon adsorbent with specific surface area of 3463 m²/g was studied by ¹H NMR spectroscopy. It was shown that during adsorption of water and methane in pores of activated carbon AC86 under conditions of low surface filling the adsorbate molecules are localized not only in micropores, but in mesopores as well, and are revealed in the spectra as several signals with different values of the chemical shift. A substantial drop in the magnetic shielding effect of the carbon surface was detected upon a reduction in temperature; this is explained by the presence of two energy minima on the curves of the adsorption potential energy (close to the walls and in the center of pores) and allows the migration of adsorbed molecules from the walls to the center of pores, which are characterized by a lower shielding effect.     

Accessible area and hydrophobicity of activated carbons obtained from the enthalpy characterization

Were determined the immersion enthalpy in benzene and water for 24 carbonaceous materials, granular activated carbon and activated carbon monoliths prepared from African palm stone by chemical activation with H₃PO₄, ZnCl₂ and CaCl₂ solutions. The immersion enthalpies in benzene and water were exothermic, in accordance with a surface process that takes place between the solid and liquid. Benzene enthalpies for this set of solids were ?20.26 and ?181.1 J g^?1 and water enthalpies were between ?7.42 and ?67.01 J g^?1. The textural and chemical surface properties of the activated carbons were related to the immersion enthalpies. Since the evaluation of the porous structure was made with non-polar liquids with which the solid does not have a specific interaction, immersion enthalpy was proportional to the surface area accessible to liquid molecules, which was calculated from the enthalpic determinations based on the assumption of the existence of a direct relationship between the immersion enthalpy and the total area of the solid accessible to liquid molecules. The hydrophobic factor was calculated by dividing the immersion enthalpy in benzene and the immersion enthalpy in water; this is related to the acidity, basicity and hydrophobicity of the activated carbons.     

Mucoadhesive vaginal film of fluconazole using cross-linked chitosan and pectin

A series of silica gels (Si-40, Si-60, Si-100) and related carbon–silica gels, prepared by carbonization of CH₂Cl₂ at a surface of silica gels at 550 °C, characterized using FTIR/PAS, SEM/EDX, and nitrogen adsorption, was investigated upon interactions with polar (water, dimethylsulfoxide), weakly polar (chloroform), and nonpolar (n-hexane, n-decane, benzene, toluene) adsorbates using adsorption and differential scanning calorimetry methods. Features of confined space effects, such as freezing/melting point depression and melting delay, depend strongly on pore sizes, pore wall structure, type and amount of adsorbates, and the degree of pore filling. Melting curves of both polar and nonpolar adsorbates bound in broad pores (Si-60 and Si-100 based materials) can include two–three peaks around melting point, but for Si-40-based materials, a number of similar peaks is smaller. This occurs due to step-by-step melting of frozen structures located in broader pores and the absence of similar effects in narrower pores. The present study shows that complex carbon–silica gel adsorbents can be more effective adsorbents than simple silica gels due to the presence of a number of surface sites of various polarity and structure.

     

Calorimetric evaluation of activated carbons modified for phenol and 2,4-dinitrophenol adsorption

Two commercial activated carbons with differences in their superficial chemistry, one granular and the other pelletised, were modified for use in phenol and 2,4-dinitrophenol adsorption. In this paper, changes to the activated carbon surface will be evaluated from their immersion calorimetry in water and benzene, and they will then be compared with Area BET, chemical parameters, micropore size distributions and hydrophobicity factors of the modified activated carbons. The activated carbons were modified using 60 % solutions of phosphoric acid (H₃PO₄), nitric acid (HNO₃), zinc chloride (ZnCl₂) and potassium hydroxide (KOH); the activated carbon/solution ratio was 1:3 and impregnation was conducted 291 K for a period of 72 h before samples were washed until a constant pH was obtained. Water immersion calorimetry showed that the best results were obtained from activated carbons modified with nitric acid, which increased from ?10.6 to ?29.8 J g^?1 for modified granular activated carbon, and ?30.9 to ?129.3 J g^?1 for pelletised activated carbon. Additionally, they showed the best results in phenol and 2.4-dititrophenol adsorption. Those results indicate that impregnation with nitric acid under the employed conditions could generate a greater presence of oxygenated groups on their surface, which favours hydrogen bond formation and the increased adsorption of polar compounds. It should also be noted that immersion enthalpy in benzene for modified activated carbon with nitric acid is the method with the lowest value, which is consistent with the increased presence of polar groups on its surface. Regarding hydrophobicity factors, it was observed that granular carbons modified with nitric acid and potassium hydroxide have the lowest ratios, indicating greater interaction with water.     

Behaviour of pure water and water mixture with benzene or chloroform adsorbed onto ordered mesoporous silicas

Structural characteristics of synthesized ordered mesoporous silicas MCM-41, MCM-48 and SBA-15 were studied using XRD, nitrogen adsorption and FTIR methods. Pure water and mixtures with water/benzene and water/chloroform-d adsorbed onto silicas were studied by ¹H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial liquids. Concentrated aqueous suspensions of MCM-48 and SBA-15 were studied by thermally stimulated depolarization current (TSDC) method. Benzene and chloroform-d can displace a portion of water to broad pores from the pore walls and from narrower pores, especially in the case of a large excess of an organic solvent. This process is accompanied by diminution of both interaction energy of water with an adsorbent surface and freezing temperature depression of adsorbed water. The effect of nonpolar benzene on pore water is much stronger than that of weakly polar chloroform-d. Modifications of the Gibbs-Thomson relation to describe the freezing point depression of mixtures of immiscible liquids confined in pores allow us to determine distribution functions of sizes of structures with unfrozen pore water and benzene. Former address: Pisarzhevskii Institute of Physical Chemistry, 31 Prospect Nauki, Kiev, Ukraine     

单壁碳纳米管上毒性苯气体净化的分子模拟

采用巨正则系综蒙特卡罗(GCMC)方法研究了空气中微量苯组分在单臂碳纳米管(SWNTs)上的吸附净化. 模拟表明, 具有较大孔径的(20,20)纳米管比较适合吸附纯苯蒸汽, 而对于移除空气中的毒性苯物质, 苯的吸附选择性分别在(12,12)纳米管及4.0 MPa时和(18,18)纳米管及0.1 MPa时出现最小值和最大值. 为了解释这一异常行为, 我们进一步分析了N₂-O₂-C₆H₆混合物的局部密度分布、吸附分子构型和概率密度分布, 发现(18,18)纳米管内外完全被苯分子占据, 而对于(12,12)纳米管, 由于存在更强的吸附质-吸附剂相互作用, 空气分子更倾向于吸附在管与管之间的间隙. 此外, 吸附分子的空间有序参数表明大多数苯分子采取“平躺”在纳米管表面的定位, 而线性的N₂和O₂分子则多数平行于孔轴方向. 最后研究了温度和苯分子主体相浓度对分离效果的影响. 我们发现较大孔中的选择性随着温度的增加比小孔下降更加明显. 与此对比, 主体相苯浓度对小孔中的选择性起到更加重要的作用.     

Deposition and characterization of a CoHCF nanorod array in a templated ormosil film on an electrode and application to electrocatalysis

Cobalt hexacyanoferrate (CoHCF) was electrodeposited into an organically modified silica (ormosil) film with a nanoarray of parallel, cylindrical channels, which were obtained using 20-nm poly(styrene sulfonate), PSS, beads as a templating agent. The PSS was bound to the electrode surface with 3-aminopropyltriethoxysilane, APTES. Methoxytrimethylsilane was the ormosil precursor. Electrochemically assisted processing at a positive potential where the hydrogen ion catalyst was generated was used to deposit the ormosil film. Subsequently, the PSS and APTES were removed to provide the pores. The CoHCF was deposited in the 20-nm channels by cyclic voltammetry of a freshly prepared K₃Fe(CN)₆, CoCl₂ mixture with 1.0 mol dm^?3 KCl as the supporting electrolyte. Limiting the number of electrodeposition cycles to 10–20 resulted in CoHCF nanorods in the pores, whereas with 50 cycles bulk-form CoHCF spilled over the outer ormosil surface. Electrocatalytic oxidation of cysteine was successfully performed on these nanorod arrays, which showed greater catalytic activity than bulk-form CoHCF.     

NH3‐Driven Benzene C−H Activation with O2 that Opens a New Way for Selective Phenol Synthesis

Catalytic benzene C?H activation toward selective phenol synthesis with O₂ remains a stimulating challenge to be tackled. Phenol is currently produced industrially by the three‐steps cumene process in liquid phase, which is energy‐intensive and not environmentally friendly. Hence, there is a strong demand for an alternative gas‐phase single‐path reaction process. This account documents the pivotal confined single metal ion site platform with a sufficiently large coordination sphere in β zeolite pores, which promotes the unprecedented catalysis for the selective benzene hydroxylation with O₂ under coexisting NH₃ by the new inter‐ligand concerted mechanism. Among alkali and alkaline‐earth metal ions and transition and precious metal ions, single Cs⁺ and Rb⁺ sites with ion diameters >0.300 nm in the β pores exhibited good performances for the direct phenol synthesis in a gas‐phase single‐path reaction process. The single Cs⁺ and Rb⁺ sites that possess neither significant Lewis acidic?basic property nor redox property, cannot activate benzene, O₂, and NH₃, respectively, whereas when they coadsorbed together, the reaction of the inter‐coadsorbates on the single alkali‐metal ion site proceeds concertedly (the inter‐ligand concerted mechanism), bringing about the benzene C?H activation toward phenol synthesis. The NH₃‐driven benzene C?H activation with O₂ was compared to the switchover of the reaction pathways from the deep oxidation to selective oxidation of benzene by coexisting NH₃ on Pt₆ metallic cluster/β and Ni₄O₄ oxide cluster/β. The NH₃‐driven selective oxidation mechanism observed with the Cs⁺/β and Rb⁺/β differs from the traditional redox catalysis (Mars‐van Krevelen) mechanism, simple Langmuir‐Hinshelwood mechanism, and acid?base catalysis mechanism involving clearly defined interaction modes. The present catalysis concept opens a new way for catalytic selective oxidation processes involving direct phenol synthesis.     

Determination of dispersive and nondispersive components of the surface free energy of glass fibers

The dispersive component _s ^d of the surface free energy of glass fibers and its interaction energy with alkanes, benzene, 1-nitropropane, ethyleneglycol, glycerol, formamide, and water were quantitatively determined by the tensiometric method within two liquids. The values of nondispersive interaction energy I _SL ^p were found to be a linear function of the square root of the nondispersive component of the surface free energy of liquids. This suggests that the nondispersive interaction energy may be represented by the geometric mean of the nondispersive component of the surface free energy of a solid and a liquid. The slope gave the nondispersive component _s ^p of the surface free energy. The _s ^p values are 33 and 14 mJ/m² for the untreated and aminosilane-treated fibers, respectively, suggesting that organophilic character has developed on the surface after aminosilane treatment. The _s ^p value was almost similar after the treatment, probably because of the polar characteristics of amino groups.     

Discussion of thermodynamic data obtained by adsorption gas chromatography of hydrocarbons on carbograph 4

Summary A new graphitized carbon black, Carbograph 4, with a specific surface area of 240 m² g⁻¹ was studied in terms of enthalpy, entropy and free energy of adsorption, determined by gas chromatographic method on a series of alkanes (C₂−C₆) and on benzene. The changes in the isosteric heat and entropy of adsorption when a non-polar stationary phase (squalane) was added to the adsorbent were also investigated. The data obtained are discussed and compared to those present in the literature for other graphitized carbon blacks. Some examples of separations obtained with Carbograph 4 are reported.     

Studies of surface properties of pure and modified by Mn<Superscript>2+</Superscript> and Ni<Superscript>2+</Superscript> ions of aluminium oxide samples using complex methods

Complex studies of physicochemical properties of pure and modified of aluminia oxides samples are presented. The presence of Mn²⁺ and Ni²⁺ modifiers on the aluminium oxide surface causes increase in water adsorption capacity and decrease in benzene and n-octane adsorption. This is due to decrease of specific surface area, volume and radius of pores as a result of surface impregnation and microcrystal formation during modification with manganese and nickel chlorides. Microcrystal formation on the surface and porosity decrease as confirmed by AFM, EDX and powder diffraction studies using automated diffractometer by step scanning. From the Q-TG and Q-DTG data, the energies of liquid desorption from the surface of the samples and the functions of desorption, energy distribution were calculated. High degree of nonlinearity of the functions resulting from great heterogeneity of the studied surface was found. Adsorption of cations creates more homogeneous surface in aluminium oxide, and it is responsible for the change in adsorbate molecule interaction energy and changes mechanism of adsorption and desorption as well as thickness and structure of the adsorbed film. From the experimental data some parameters characterizing adsorption properties and porosity of the studied samples were determined using the complex measuring methods (thermal analysis, sorptometry, porosimetry, AFM and EDX).     

Molecular Mechanisms of the Effect of Water on CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> Mixture Adsorption in Slitlike Carbon Pores

The grand canonical ensemble Monte Carlo method has been used to study adsorption of carbon dioxide, methane, and their mixtures with different compositions in slitlike carbon pores at a temperature of 318 K and pressures below 60 atm. The data obtained have been used to show the effect of fixed amounts of pre-adsorbed water (19, 37, and 70 vol %) on the adsorption capacity and selectivity of carbon micro- and mesopores. The presence of water reduces the adsorption capacity throughout the studied pressure range upon adsorption of gaseous mixtures containing less than 50% CO₂, as well as in narrow micropores (with widths of 8?12 Å). Upon adsorption of mixtures with CO₂ contents higher than 50%, the adsorption capacity of pores with low water contents appears, in some region of the isotherm, to be higher than that in dry pores. In the case of wide pores (16 and 20 Å), this region is located at low and moderate pressures, while for mesopores it is located at high pressures. The analysis of the calculated data has shown that the molecular mechanism of the influence of preadsorbed water on the adsorption capacity is based on the competition between the volume accessible for adsorption (decreases the capacity) and the strength of the interaction between carbon dioxide molecules and water molecules (increases the capacity). Therewith, the larger the surface area of the water–gas contact, the stronger the H₂O–CO₂ interactions.     

Carbon dioxide adsorption on carbon nanomaterials

The adsorption of CO₂ on a number of activated carbons, thermal carbon black, and oxide materials at 195 K was studied using static and dynamic techniques. The landing surface areas ω(CO₂) ≈ 0.19 nm² on thermal carbon black and the absolute values of sorption for P/P ₀ < 0.4 were determined. The density of adsorbed CO₂ in the micropore volume was estimated at ρ(CO₂) = 0.91 g/cm³. It was demonstrated that the previously found effect of a weakening of the sorption interaction of nitrogen molecules with thin-walled materials (which manifested itself in an analysis of sorption isotherms by a comparative method) was pronounced to a lesser degree for the sorption of CO₂. At the same time, the presence of supermicropores in activated carbon samples resulted in overestimated values of surface areas. A dynamic method was proposed to measure the spectra of CO₂ desorption at 195–260 K using a SORBI-MS system for evaluating the binding energy of sorbate molecules with the surface.     

Effect of zeolite pore morphology on solvent-less alkylation of benzene with 1-hexene

In an attempt to convert the carcinogenic benzene which is almost restricted for its use in gasoline, alkylation reaction with olefin 1-hexene has been conducted on various zeolites. Four zeolites having different pore topology and pore size have been applied as solid acid catalysts for effective production of alkylate in a liquid phase, solvent-less low temperature reaction. The textural properties of all the four zeolites (ZSM-5, MOR, BEA, HY) have been characterized for crystal morphology by TEM, crystal structure by XRD and FTIR, BET for surface area, N₂ sorption for porosity and TPD for acidity. Among the zeolite, BEA possessed high surface area (600.61 m²/g) and enhanced meso pores volume (0.3956 cm³/g) as compared to other zeolite samples. The performance of BEA was also observed to be superior in the liquid phase alkylation of benzene with 1-hexene in a batch reactor under autogenous pressure without using any solvent. At the optimum reaction conditions, the benzene conversion was 86.6 wt% and 3-Phenylhexane, 2-Phenylhexane yield were about 47.9 wt% and 38.7 wt% respectively on this catalyst. The BEA also exhibited longer time-on-stream and reusability performance, thus offers an attractive route for converting benzene into valuable (3-Phenylhexane, 2-Phenylhexane) alkylate product useful for the manufacturing of fine chemicals, dyestuff, detergents and scents.     

Encapsulation of Arenes within a Porous Molybdenum Oxide {Mo132} Nanocapsule

The use of confined space to modulate chemical reactivity and to sequester organic compounds spans significant disciplines in chemistry and biology. Here, the inclusion and assembly of arenes into a water‐soluble porous metal oxide nanocapsule [{(Mo^VI)Mo^V₅O₂₁(H₂O)₆}₁₂{Mo^V₂O₄(CH₃COO)}₃₀]^42? (Mo₁₃₂) is reported. The uptake of benzene, halobenzenes, alkylbenzenes, phenols, and other derivatives was studied by NMR, where it was possible to follow the encapsulation process from the outside of the capsule through its pores and then into the interior. The importance of size or shape of the arenes, and various intermolecular bond interactions contributed by the benzene substituent on the encapsulation process was studied, showing the importance of π–π stacking and CH–π interactions. Furthermore, by using NOESY, ROESY, and HOESY NMR techniques it was possible to understand the interaction of the encapsulated arenes and the acetate linkers or ligands that line the interior of the Mo₁₃₂ capsule.     

Laser-induced pinpoint hydrogen evolution from benzene and water using metal free single-walled carbon nanotubes with high quantum yields

Metal-free photocatalytic hydrogen evolution occurred efficiently in benzene containing single-walled carbon nanotubes under laser irradiation at 532 nm with an extremely high turnover number of 2 000 000 and a high quantum yield of 130%. The rate of hydrogen evolution increased with increasing laser intensity to exhibit a fourth power dependence, suggesting that hydrogen was evolved via four-photon processes in which the coupling of two radical anions derived from benzene is the rate-determining step and the benzene radical anion is produced by electron transfer from benzene to the doubly excited state of single-walled carbon nanotubes, which requires two photons. Polymerisation of benzene was induced by the photogenerated C₆H₆˙^–, accompanied by hydrogen evolution, resulting in a leverage effect to increase the quantum yield of hydrogen evolution to well over the 25% expected for the four-photon process. Laser-induced hydrogen evolution also occurred in water containing single-walled carbon nanotubes. In contrast to the case of benzene, water was not oxidized but hydrogen evolution from water was accompanied by the multi-oxidation of single-walled carbon nanotubes. The yield of hydrogen based on one mole of single-walled carbon nanotubes with 1.4 nm diameter and 1–5 mm length was determined to be 2 700 000%, when oxidations of single-walled carbon nanotubes occurred to produce the polyhydroxylated product.     

Charge-Transfer Interactions of Aluminum Copper(I) Chloride with Polystyrene and Related Compounds

Interactions between polystyrene and aluminum copper(I) chloride (AlCuCl₄) were investigated by various spectroscopic measurements in order to elucidate the structure of polystyrene-AlCuCl₄ complex in solution and the mechanism of water resistance of the complex as a carbon monoxide absorbent. The chemical shift (101 ppm) and half line width (145 Hz) of AlCuCl₄ in benzene by ²⁷Al-NMR suggest a dimer structure bridged by two chlorine atoms, which is almost identical with that of aluminum chloride. The coordination of benzene or other aromatic compounds to AlCuCl₄ was confirmed by charge-transfer bands in UV and visible absorptions. The equilibrium constants (K) for complex formation of AlCuCl₄ with various aromatic compounds were determined by ¹³C-NMR spectroscopy. In the case of AlCuCl₄ and benzene in 1,2-dichloroethane, for example, K is 2.2 M ^?1 at 303 K. For the polymer complex solution and 1,3-diphenyl-propane solution, strong charge-transfer bands have been observed in the wavelength region at about 380 to 500 nm, where no band is observed in benzene derivatives. This strong charge-transfer band is considered to be due to the strong interaction of AlCuCl₄ with adjacent aromatic rings of polystyrene or 1,3-diphenylpropane of a chelate type, which, as a result, causes the water resistance of the present carbon monoxide absorbent system.     

The influence of Mn2+ and Ni2+ ions on the surface properties of the aluminium oxide samples using Q-TG and Q-DTG data

The paper presents the complex studies of adsorption and porosity of pure and modified–aluminium oxides samples. The presence of Mn²⁺ and Ni²⁺ modifiers on the aluminium oxide surface causes increase in water adsorption capacity and its decrease in the case of benzene and n-octane. This is due to decrease of specific surface area, volume and radius of pores as a result of surface impregnation and microcrystals formation during modification with manganese and nickel chlorides. Microcrystals formation on the surface and porosity decrease where confirmed by the AFM and SEM studies. From the Q-TG and Q-DTG data, the energies of liquid desorption from the surface of the samples and the functions of desorption, energy distribution were calculated. High degree of nonlinearity of the run of the functions resulting from great heterogeneity of the studied surface was found. Adsorption of cations creates more homogeneous surface of aluminium oxide, and it is responsible for the change in adsorbate molecule interaction energy and changes mechanism of adsorption and desorption as well as thickness and structure of the adsorbed film. From the experimental data some parameters characterizing adsorption properties and porosity of the studied samples were determined using the measuring methods (thermal analysis, sorptomate, porosimetry, AFM).     

Synthesis of Na-A and/or Na-X zeolite/porous carbon composites from carbonized rice husk

Na-A and/or Na-X zeolite/porous carbon composites were prepared under hydrothermal conditions by NaOH dissolution of silica first from carbonized rice husk followed by addition of NaAlO₂ and in situ crystallization of zeolites i.e., using a two-step process. When a one-step process was used, both Na-A and Na-X zeolites crystallized on the surface of carbon. Na-A or Na-X zeolite crystals were prepared on the porous carbonized rice husk at 90 °C for 2-6 h by changing the SiO₂/Al₂O₃, H₂O/Na₂O and Na₂O/SiO₂ molar ratios of precursors in the two-step process. The surface area and NH₄⁺-cation exchange capacity (CEC) of Na-A zeolite/porous carbon were found to be 171 m²/g and 506 meq/100 g, respectively, while those of Na-X zeolite/porous carbon composites were 676 m²/g and 317 meq/100 g, respectively. Na-A and Na-X zeolites are well-known microporous and hydrophilic materials while carbonized rice husk was found to be mesoporous (pores of ∼3.9 nm) and hydrophobic. These hybrid microporous-mesoporous and hydrophilic-hydrophobic composites are expected to be useful for decontamination of metal cations as well as organic contaminants simultaneously.     

Sol-Gel Preparation of Fast Proton-Conducting P2O5-SiO2 Glasses

We have investigated the proton conductivities of the sol-gel-derived P₂O₅-SiO₂ glass at –50 to 120°C. The obtained glass is porous, where the surface area, pore volume and pore diameter are 740 m²/g, 0.5 cm³/g and <5 nm, respectively. The freezing temperature of water molecules adsorbed in the pores was –20°C, which is much lower than that of free liquid water due to the quantum size effect of the water confined in the pores. The electrical conductivities followed the Arrhenius equation in the temperatures between –20 and 120°C. Below –20°C, the adsorbed-water molecules were frozen, resulting in a rapid decrease of the proton conductivity. Considering the high conductivity, chemical and thermal stability, this oxide glass membranes have potential for the fuel cell membrane.