Joint adsorption of benzene and water on carbon nanotubes

The joint adsorption of water and benzene on nanosized carbon tubes (NCTs) (with a specific surface area of 413 m²/g) synthesized by carbonizing methylene chloride in cylindrical pores of an Al₂O₃ matrix was studied. ¹H NMR spectroscopy with layer-by-layer freezing of the liquid phase was used to characterize the water bound in pores at various contents of benzene and water. Due to its higher energy of interaction with carbon surfaces, benzene was demonstrated to decrease the energy of interaction of water with the surface of the NCT sample from 43 to 15 J/g. It was suggested that, in the presence of benzene, H-bonded water clusters only weakly bound to the surface are formed in the cylindrical cavities of the NCTs.     

The influence of thermal treatment on the properties of sorbents prepared from water conditioning precipitates

Sorbent samples based on the thermally activated precipitate formed in iron removal from under-ground water (water conditioning wastes) were studied by low-temperature nitrogen adsorption and thermal and X-ray analysis. The precipitate was found to be a material with a developed porous structure (the specific surface area of the initial sample was 229.9 m²/g). Calcining at 300°C decreased the specific surface area of the samples by 1.6–1.7 times and increased the volume of sorbing pores by 1.6 times. The precipitate material largely contained iron phases. An increase in the temperature of calcining contributed to deeper crystallization of the main phase, α-Fe₂O₃.     

Large Scale Synthesis of Three-dimensional Hierarchical Porous Framework with High Conductivity and its Application in Lithium Sulfur Battery

Quick capacity loss due to the polysulfide shuttle effects and poor rate performance caused by low conductivity of sulfur have always been obstacles to the commercial application of lithium sulfur batteries. Herein, an in-situ doped hierarchical porous biochar materials with high electron-ion conductivity and adjustable three-dimensional (3D) macro-meso-micropore is prepared successfully. Due to its unique physical structure, the resulting material has a specific surface area of 2124.9 m² g⁻¹ and a cumulative pore volume of 1.19 cm³ g⁻¹. The presence of micropores can effectively physically adsorb polysulfides and mesopores ensure the accessibility of lithium ions and active sites and give the porous carbon material a high specific surface area. The large pores provide channels for the storage of electrolyte and the transmission of ions on the surface of the substrate. The combined effect of these three kinds of pores and the N doping formed in-situ can effectively promote the cycle and rate performance of the battery. Therefore, prepared cathode can still reach a reversible discharge capacity of 616 mAh g⁻¹ at a rate of 5 C. After 400 charge–discharge cycles at 1 C, the reversible capacity is maintained at 510.0 mAh g⁻¹. This new strategy has provided a new approach to the research and industrial-scale production of adjustable hierarchical porous biochar materials.     

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.     

新型大孔有机膦酸锆的合成及其表征

论文以草甘膦锆(ZrGP)为原料、乙二醇和乙醇混合物为共撑物,介绍了一种新型孔材料的合成方法。利用乙醇将草甘膦锆层板撑开后,乙二醇两端的羟基与草甘膦锆内不同层板上的羧基发生脱水成酯反应,进而生成窗口型孔材料。扫描电镜和XRD分析表明,合成得到的材料内部孔径大约为55 nm左右,是典型的大孔。由于所形成的孔壁由无机骨架和有机链共同组成,该孔材料具有较大的比表面积,达到260 m2.g-1。此外,该孔材料孔内存在大量的可配位基团,因而该材料在吸附、催化等领域会有广阔的应用前景。     

Sorbents based on asbestos with a layer of an hydroxyethylcyclam derivative of PVC containing aquacomplexes of sulfuric acid or sodium hydroxide with aza-crown groups

Aquacomplexes of sulfuric acid and sodium hydroxide with aza-crown groups are synthesized in cavities of a sorbent from the porous layer of a PVC cyclam-derivative grafted onto fibers of asbestos fabric. The structure of sorbents with complexes is studied and their adsorption characteristics are determined. It is shown that the affinity of the developed surface toward ethanol, benzene, and hexane depends on the nature of complexes in the pore walls, and the volume of cavities formed as a result of the pores on the developed asbestos surface being coated with networks of aza-crown groups is larger than that of cavities with walls of aza-crown groups in the layers of a PVC cyclam derivative. Indicators of H⁺- and OH^–-conductivity of sorbents with complexes as electrochemical bridges are determined. It is shown that the major part of H⁺- and OH^–-ions moves through complexes with aza-crown groups in the region of cavities formed of pores on the surface of asbestos.     

Composite Water Sorbents of the Salt in Silica Gel Pores Type: The Effect of the Interaction between the Salt and the Silica Gel Surface on the Chemical and Phase Compositions and Sorption Properties

The influence of the inorganic salt-silica gel surface interaction on the chemical and phase compositions and sorption properties of composites of the salt in silica gel pores type is studied. Two possible interaction mechanisms are considered: (1) the ion-exchange adsorption of metal cations on the silica gel surface from a solution of a salt (CaCl₂, CuSO₄, MgSO₄, Na₂SO₄, and LiBr) and (2) the solid-phase spreading of a salt (CaCl₂) over the silica gel surface. The adsorption of metal cations on the silica gel surface in the impregnation step affords ≡Si-OM ⁿ⁺¹ surface complexes in the composites. As a result, two salt phases are formed in silica gel pores at the composite drying stage, namely, an amorphous phase on the surface and a crystalline phase in the bulk. The sorption equilibrium between the CaCl₂/SiO₂ system and water vapor depends on the ratio of the crystalline phase to the amorphous phase in the composite.     

The influence of the Si(OC2H5)4/(CH3O)3Si(CH2)3SH ratio on the structure-adsorption characteristics of xerogels formed and accessibility of functional groups in their surface layers

It was shown for the example of the Si(OC₂H₅)₄/(CH₃O)₃Si(CH₂)₃SH system that successively increasing the fraction of tetraethoxysilane in it (from 1: 1 to 5: 1 (mol)) successively decreased the content of 3-mercaptopropyl groups in xerogels synthesized by the sol-gel method (in the presence of methanol as a solvent and fluorine ions as a catalyst) from 5.0 to 1.9 mmol/g, whereas the specific surface area of such xerogels simultaneously increased from 13 to 631 m²/g. The sorption volume of pores also increased, their mean diameter varying insignificantly. The mean diameter of pores (2.2–2.5 nm) was close to the boundary between meso-and micropores, which was in agreement with the form of nitrogen adsorption isotherms (type I according to the IUPAC classification). It was shown by scanning electron microscopy that virtually nonporous xerogels formed at a 1: 1 ratio between alkoxysilanes consisted of spherical partially united particles 2.5–3 μm in diameter. All the 3-mercaptopropyl groups of this and other samples were, however, accessible to silver(I) ions. It follows that these groups are situated in the surface layer of xerogels. The number of thiol groups per 1 nm² of the surface of nonporous xerogels was 1.7–7.0 groups/nm² and depended on the ratio between reacting alkoxysilanes and s _sp.     

Mechanochemistry of hexagonal boron nitride: 1. Destruction and amorphization during mechanical treatment

The regularities of the mechanical activation of hexagonal boron nitride are analyzed using the X-ray diffraction, IR spectroscopy, transmission electron microscopy, dynamic light scattering, and adsorption methods. At the initial state of mechanical activation, the main process is material destruction. At this stage, the specific surface area increases to 400 m²/g and crystallographically oriented nanosized needles are formed. At the same time, boron nitride crystal structure is disordered with an increase in interplanar distance d(002). The disordering is assumed to be due to a shift along planes (001). At a specific dose of supplied mechanical energy above 6–8 kJ/g, the disordering processes dominate and the material is amorphized. At this stage, the specific surface area of samples decreases.     

Adsorption Properties of Mesoporous Silica Gel with β-Cyclodextrin as a Pore-Forming Agent Relative to Moxifloxacin

A method for the synthesis of mesoporous silica gel using β-cyclodextrin as a pore-forming agent is developed. The physical properties and structure of the obtained adsorbent are studied by Fourier-transform IR spectroscopy and the low-temperature adsorption–desorption of nitrogen (BET) method. The material has an average specific surface area of 435 ± 5 m²/g and an average pore size of 5 ± 0.5 nm. This value of the pore size indicates the formation of complex structures from columnar associates of β-cyclodextrin in the synthesis of the material. The adsorption capacity of the obtained material is 0.2 ± 0.05 mg of 2-hydroxypropyl-β-cyclodextrin per milligram of the adsorbent. The dissociation constant of the complexes of moxifloxacin with β-cyclodextrin inside the pores of silica gel is of the order of 5 × 10^–3 M. The resulting system of SiO₂-β-CD is promising for application in the biomedical chemistry as a carrier of biologically active molecules, particularly as an antibacterial preparation of moxifloxacin.     

Visualization and characterization of SPG membrane emulsification

Shirasu-porous-glass (SPG) membrane emulsification is highly attractive for various fields of foods, cosmetics, and pharmaceuticals because this technique produces monodispersed emulsions. However, there are few reports on the observation of membrane emulsification at the membrane surface. In the present work, we aimed to visualize the membrane emulsification using a microscope high-speed camera system. The direct observation made it possible to measure the mean rate of droplet formation and the percentage of active pores. The mean rate of droplet formation ranged 0.3–12 s⁻¹ and the percentage of active pores ranged 0.3–0.5% under the dispersed-phase flux of 0.58×10⁻⁶–5.8×10⁻⁶ m³/(m² s). We also observed that the droplets were formed without continuous-phase flow and the droplets were also formed by shear force at the continuous-phase flow under different experimental conditions. The balance among the dispersed-phase flux and the continuous-phase flow velocity influenced droplet formation.     

Complex formation involving Hg<Superscript>2+</Superscript> ions on the surface of the polysiloxane xerogels functionalized by 3-mercaptopropyl groups

The influence of parameters of the porous structure and the surface layer composition of the xerogels containing 3-marcaptopropyl and alkyl groups on their sorption properties toward the Hg²⁺ ions and the stability constants of the formed complexes, which are calculated using the model of chemical reactions, is studied. An increase in the overall surface concentration of the functional groups is shown to induce a change in the composition of the formed complexes. At the concentration of the functional groups lower than 0.01 mmol/m² the [HgS(CH₂)₃Si≡]⁺ complexes are formed, and above 0.01 mmol/m² the composition of the complexes depends on the mercury(II) content in the starting solution: at low contents the [Hg{S(CH₂)₃Si≡}₂] complexes are formed, whereas at higher concentrations the composition of the complexes becomes simpler. Only the [Hg{S(CH₂)₃Si≡}₂] complexes are formed on the nearly nonporous xerogel with the polymeric structure of the surface layer (the functional group concentration is 0.38 mmol/m²). This, in turn, leads to the situation that the maximum static sorption capacity (590–620 (mg of Hg²⁺)/(g of sorbent)) is observed for the xerogels with a rather low content of the 3-mercaptopropyl groups (3.0–3.8 mmol/g). The stability of the formed complexes also depends on the surface concentration of the functional groups: the stability constant of the 1: 1 Hg(II) complexes decreases with an increase in the concentration of thiol groups. The introduction of alkyl groups into the surface layer also decreases the stability of the complexes formed. The [Hg{S(CH₂)₃Si≡}₂] complexes formed in the surface layer of the xerogels are characterized by similar stability constants.     

Dielectric isotherms of water sorption on pyrogenic silica and titania surfaces

Water sorption on the surfaces of pyrogenic SiO₂ (S=290 m²/g) and TiO₂ (S=50 m²/g) has been studied. The dielectric isotherm curves show that on the surface of TiO₂ (anatase) a continuous water layer is formed at =1.9 but none is formed on the silica surface. Sorption occurs only as definite clusters.     

Characterization of ZrO2- Al2O3mixed oxides support prepared by urea hydrolysis

The characteristics of Al₂O₃, ZrO₂ and three binary mixtures of ZrO₂-Al₂O₃ were studied by determining their BET surface areas, micropore surface area, total pore volume, adsorption-desorption isotherms, the X-ray diffractogram, surface acidity and catalytic functionality for cumene cracking. The XRD results show that the incorporation of alumina into the zirconia from 50% and beyond renders it amorphous. Furthermore, the mixed oxide containing 50% alumina and 50% zirconia had the highest BET surface area of 199.9 m²/g whilst pure zirconia had the lowest BET surface area of 37.19 m²/g. The pores for all the mixed oxides were found to be monomodal and zirconia pores were more open. The results of the acidity measurements and cumene cracking functionality indicates that whilst pure zirconia has low total acidity, the incorporation of alumina increases its acidity through a synergistic effect. This revised version was published online in June 2006 with corrections to the Cover Date.     

Characterization of Highly Porous Materials from Cellulose Carbamate

Highly porous cellulose was formed by gelation of cellulose carbamate solutions in caustic soda. Two methods for gel preparation were optimized for the formation of beads and bulky materials – the chemical precipitation from dilute sulfuric acid and the thermal gelation by annealing at elevated temperatures. Various methods were used for characterizing of the pores of low density materials: scanning electron microscopy, small angle X-ray scattering, mercury intrusion and nitrogen sorption. These methods were optimized and used for characterizing the complete pore system from micro to macro pores. The effects of different preparation (cellulose carbamate concentration in caustic soda) and processing (precipitation, drying and pyrolysis) on the pore structure were studied by the set of complementary methods. Aerocell samples with a minimum density of 0.06 g/cm³ were prepared from cellulose carbamate. They are characterized by a broad pore size distribution ranging from 0.5 nm to 1 mm, specific internal surfaces of up to 660 m²/g and total pore volumes of up to 18 cm³/g.     

Electrokinetic study of etching latent tracks of accelerated heavy ions in poly(ethylene terephthalate) and polyimide

The etching of latent tracks and pore formation in track membranes are studied. It is shown that the incorporation of K⁺ and Ba²⁺ ions into alkaline solutions accelerates the etching of poly(ethylene terephthalate) (PET) and latent tracks in it. The etching is accelerated due to a decrease in the negative surface charge of PET surface and the pores in track membranes. Isoelectric points are determined for PET and polyimide track membranes and it is established that they depend on pore diameter. As the pore diameter is enlarged from 30 to 70 nm, the magnitude of the negative surface charge rises seemingly due to the increase in the concentration of carboxyl groups on the pore surface. It is assumed that this effect is due to either a high mobility of carboxyl groups in a gel, which is formed on pore walls as a result of etching latent tracks, or a displacement of the slipping plane caused by a decrease in the thickness of the gel layer.     

The porous structure of pulp fibres with different yields and its influence on paper strength

The porous structure of the interior of papermaking fibres is a well-known important property of the fibres. Changes of this structure will influence tensile and burst strength of paper formed from the fibres and a change in pore size of the pores within the fibre wall is also important for the ability of molecules to diffuse in and out of the fibre wall. Relevant examples of this latter effect are the removal of lignin during cooking and the addition of performance chemicals during papermaking. In this paper, pore sizes and the pore size distribution of unbleached softwood fibres have been studied. A well-characterised fibre material consisting of laboratory cooked spruce and pine pulp of various lignin contents was used. Pore size and pore size distribution were measured by studies of the relaxation behaviour of ²H in fibres saturated with ²H₂O. Beside this the total and surface charge of the fibres were also measured together with strength properties of papers from unbeaten fibres. For both pulps, there is a maximum in pore radius at a yield around 46%. Calculations of fibre wall volume from water retention values and yield levels show that there is a discontinuity in pore radius as a function of the fibre wall volume around a yield of 51%. It is suggested that this discontinuity is caused by the breakdown of the hemicellulose/lignin matrix within the fibre wall at this yield level. The strength of the papers formed from the fibres shows a correlation with the surface charge of the fibres. Based on the change in surface charge with yield and the change in total charge with yield, this correlation is suggested to be due to an opening up of the external part of the fibre wall. This stresses the importance of the chemical composition and physical structure of the outer layer of the fibre wall.     

Dispersity of materials obtained by mechanical activation and laser sintering of Al-C systems and used for production of electrochemical capacitors

Characteristics of materials designed for electrodes of electrochemical capacitors based on mechanically activated Al-C composites applied onto aluminum foil by laser sintering are considered. The methods of X-ray diffraction, X-ray photoelectron spectroscopy, and transmission and scanning electron microscopy are used to study the structure and composition of synthesized layers. It is established that mechanical activation of aluminum in the presence of graphite followed by high-speed laser sintering of the obtained material on an aluminum foil substrate noticeably increases material dispersity with a rise in its specific surface area from an initial value of 4 m²/g to a value on the order of 1000 m²/g, as estimated from the data on the capacity of the electrical double layer.     

Ring‐Opening Metathesis Polymerization Based Pore‐Size‐Selective Functionalization of Glycidyl Methacrylate Based Monolithic Media: Access to Size‐Stable Nanoparticles for Ligand‐Free Metal Catalysis

Monolithic polymeric supports have been prepared by electron‐beam‐triggered free‐radical polymerization using a mixture of glycidyl methacrylate and trimethylolpropane triacrylate in 2‐propanol, 1‐dodecanol, and toluene. Under appropriate conditions, phase separation occurred, which resulted in the formation of a porous monolithic matrix that was characterized by large (convective) pores in the 30 μm range as well as pores of <600 nm. The epoxy groups in pores of >7 nm were hydrolyzed by using poly(styrenesulfonic acid) (M_w=69 400 g mol^?1, PDI=2.4). The remaining epoxy groups inside pores of <7 nm were subjected to aminolysis with norborn‐5‐en‐2‐ylmethylamine ( 2 ) and provided covalently bound norborn‐2‐ene (NBE) groups inside these pores. These NBE groups were then treated with the first‐generation Grubbs initiator [RuCl₂(PCy₃)₂(CHPh)]. These immobilized Ru–alkylidenes were further used for the surface modification of the small pores by a grafting approach. A series of monomers, that is, 7‐oxanorborn‐5‐ene‐2,3‐dicarboxylic anhydride ( 3 ), norborn‐5‐ene‐2,3‐dicarboxylic anhydride ( 4 ), N,N‐di‐2‐pyridyl‐7‐oxanorborn‐5‐ene‐2‐carboxylic amide ( 5 ), N,N‐di‐2‐pyridylnorborn‐5‐ene‐2‐carboxamide ( 6 ), N‐[2‐(dimethylamino)ethyl]bicyclo[2.2.1]hept‐5‐ene‐2‐carboxamide ( 7 ), and dimethyl bicyclo[2.2.1]hept‐5‐en‐2‐ylphosphonate ( 8 ), were used for this purpose. Finally, monoliths functionalized with poly‐ 5 graft polymers were used to permanently immobilize Pd²⁺ and Pt⁴⁺, respectively, inside the pores. After reduction, metal nanoparticles 2 nm in diameter were formed. The palladium‐nanoparticle‐loaded monoliths were used in both Heck‐ and Suzuki‐type coupling reactions achieving turnover numbers of up to 167 000 and 63 000, respectively.     

Effect of the synthetic method and support porosity on the structure and performance of silica‐supported CuBr/pyridylmethanimine atom transfer radical polymerization catalysts. I. Catalyst preparation and characterization

Silica‐supported CuBr/pyridylmethanimine (PMI) complexes that facilitate the atom transfer radical polymerization of methyl methacrylate have been prepared and characterized. Four different synthetic routes, including multistep‐grafting (M1), two‐step‐grafting (M2), one‐pot (M3), and preassembled‐complex (M4) methods, have been evaluated on three different silica supports (mesoporous SBA15 with 48‐ and 100‐Å pores and nonporous Cab‐O‐Sil EH5). The resulting solids have been characterized by a battery of techniques, including thermogravimetric analysis/differential scanning calorimetry, FT‐Raman spectroscopy, ¹³C and ²⁹Si magic‐angle‐spinning and cross‐polarity/magic‐angle‐spinning spectroscopy, low‐temperature nitrogen physisorption, and elemental analysis. The combination of elemental analysis and spectroscopic results has indicated that a variety of different surface species likely exist for most catalysts, including copper species that are both monocoordinated and biscoordinated by PMI ligands, and PMI‐free copper bromide species interacting with the silica surface. M4 appears to give a material that has the smallest amount of the uncomplexed ligand (by FT‐Raman spectroscopy) and is, therefore, the most homogeneous. After M4, the metallation efficiency decreases in the order M2 ≥ M3 > M1, with M1 giving a material with a highly heterogeneous surface composition. The ligand loading on all the catalysts has been determined to be approximately 1 mmol/g of SiO₂, with Cab‐O‐Sil‐supported materials giving much higher ligand densities because of its lower surface area. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1367–1383, 2004