Effect of modification on electrochemical and sorption properties of woven carbon materials

Relationship between electrochemical, structural, and sorption properties of woven carbon materials modified with chitosan was studied.     

Synthesis of porous carbon materials from wood waste pre-treated with water

The possibility of producing porous carbon materials from birch sawdust exposed to natural decomposition in water was demonstrated. It was established that the carbon material carbonized at 800°C was of a specific surface area nearly by one order of magnitude higher than that of a product produced using ordinary sawdust under the same conditions. It was suggested that developing porous structure of the carbon product was due to structural changes in wood mainly by reducing an amount of α-cellulose and its interaction with water.     

Adsorption properties and porous structure of new carbon materials

The adsorption properties of the new carbon materials, sibunites, which are mesoporous samples with a developed surface of pores, were studied. The isotherms of the adsorption of benzene vapor were determined to estimate the porous structure of these materials. The principal methods for calculating the parameters of the porous structure of sibunites were analyzed. The application of the BET equation even in the presence of a small number of micropores can distort the results, therefore the most suitable method for estimating the surface of mesopores is one that is based on the Dubinin—Zaverina equation. The estimation of the surface of sibunites using water vapor adsorption is demonstrated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1377–1380, August, 1993.     

Surface properties of porous carbon obtained from polystyrene sulfonic acid-based organic salts

Pyrolysis ofpolysterene sulfonic acid-co-maleic acid salts at 800 degrees C resulted in formation of new materials consisting of porous carbon and metal species dispersed on the surface. After hydrochloric acid treatment, the metal oxides/salts were removed. Obtained materials were characterized using adsorption of nitrogen, thermogravimetric analysis, Raman spectroscopy, and scanning electron microscopy with energy dispersive analysis of X-rays. The results showed highly developed porous structures in the range of micro- and mesopores. The porous features of new materials resemble those characteristics for carbon foams. The differences in the porous structure are linked to the type of transition metal used for the modification of the initial polymer and the chelation process. Macro- and mesopores are spherical/cylindrical in shape, and they are likely formed when release of pyrolysis gases, such as CO2, NO2, SO2, H2S, and CxHy, occurs. Moreover, reduction of metal, its migration to the surface, and agglomeration contribute to development of porosity. Depending on the reactivity of the metal used for cation exchange (Fe, Co, or Ni) either sulfides (nickel and cobalt) or oxides (cobalt and iron) are formed on the carbon surface.     

Efficient thermal conversion of polyyne-type conjugated polymers to nano-structured porous carbon materials

Summary Some aromatic based conjugated polymers having carbon-carbon triple bonds moiety were synthesized and carbonized. The polymers were efficiently carbonized by heating up to 900°C under an argon atmosphere, affording porous carbons in high yields. The polymer characteristics were appropriate to form nano-structured carbons in the pyrolytic carbonization process. The carbon materials were consisted of 2-4 nm sized graphitic crystallites and had slit-shaped micropores with ca. 0.7 nm pore width. Structural defects in the pre-carbon materials caused generation of mesopores with ca. 4 nm pore width after carbonization.     

Effect of alkaline materials on interfacial rheological properties of oil-water systems

Interfacial rheological properties of a model crude oil-water system were studied in the presence of sodium hydroxide. The interfacial viscosity, the non-Newtonian flow behavior and the activation energy of viscous flow were determined as a function of shear rate, alkali concentration and aging time. The fundamental conclusion of the experimental results is that the interfacial viscosity drastically decreases in the presence of alkaline materials and the change under favorable conditions may exceed 3 or 4 orders of magnitude. Simultaneously, the sodium hydroxide effectively suppresses the non-Newtonian flow behavior of the interfacial layer. The experimental observations are explained by simultaneous chemical processes taking place in the boundary layer. The present data may help to elucidate the formation, stability and breaking of alkali-containing oil-water emulsions and they provide additional information for better understanding of the displacement mechanism and for the formulation of alkaline flooding as a potential chemically enhanced oil-recovery method. Received: 6 April 1998 Accepted: 18 August 1998     

Evolution of rheological properties of starch solutions obtained by mechanothermal and thermal methods

Regularities of the time variation of viscosity of colloidal starch solutions obtained by combined mechanical and thermal actions on biopolymer dispersions were studied.     

Novel carbon materials for thermal energy harvesting

To decrease the consumption of fossil fuels, research has been done on utilizing low grade heat, sourced from industrial waste streams. One promising thermoenergy conversion system is a thermogalvanic cell; it consists of two identical electrodes held at different temperatures that are placed in contact with a redox-based electrolyte [1, 2]. The temperature dependence of the direction of redox reactions allows power to be extracted from the cell [3, 4]. This study aims to increase the power conversion efficiency and reduce the cost of thermogalvanic cells by optimizing the electrolyte and utilizing a carbon based electromaterial, reduced graphene oxide, as electrodes. Thermal conductivity measurements of the K₃Fe(CN)₆/K₄Fe(CN)₆ solutions used, indicate that the thermal conductivity decreases from 0.591 to 0.547?W/m?K as the concentration is increased from 0.1 to 0.4?M. The lower thermal conductivity allowed a larger temperature gradient to be maintained in the cell. Increasing the electrolyte concentration also resulted in higher power densities, brought about by a decrease in the ohmic overpotential of the cell, which allowed higher values of short circuit current to be generated. The concentration of 0.4?M K₃Fe(CN)₆/K₄Fe(CN)₆ is optimal for thermal harvesting applications using R-GO electrodes due to the synergistic effect of the reduction in thermal flux across the cell and the enhancement of power output, on the overall power conversion efficiency. The maximum mass power density obtained using R-GO electrodes was 25.51?W/kg (three orders of magnitude higher than platinum) at a temperature difference of 60?°C and a K₃Fe(CN)₆/K₄Fe(CN)₆ concentration of 0.4?M.     

Synthesis of porous carbon materials from birch sawdust modified with ZnCl<Subscript>2</Subscript>

Carbonization of birch sawdust modified with zinc chloride and selected properties of the resulting porous carbon materials were studied.     

Mesoporous carbon materials: synthesis and modification

Porous carbon materials are of interest in many applications because of their high surface area and physicochemical properties. Conventional syntheses can only produce randomly porous materials, with little control over the pore-size distributions, let alone mesostructures. Recent breakthroughs in the preparation of other porous materials have resulted in the development of methods for the preparation of mesoporous carbon materials with extremely high surface areas and ordered mesostructures, with potential applications as catalysts, separation media, and advanced electronic materials in many scientific disciplines. Current syntheses can be categorized as either hard-template or soft-template methods. Both are examined in this Review along with procedures for surface functionalization of the carbon materials obtained.     

Effect of crystallite size on the thermal phase change and porous properties of boehmite

The effect of crystallite size on the thermal phase change and porous properties of boehmite was investigated using boehmites with crystallite sizes of 2.9 to 24.4 nm and boehmite gels prepared by precipitation and hydrothermal methods. The dehydroxylation temperature of boehmite increases, its phase transition temperature from gamma- to theta-Al(2)O(3) decreases and the theta- to alpha-Al(2)O(3) transition temperature increases as the crystallite size of the boehmite increases. Boehmite with a crystallite size of approximately 5 nm shows the highest specific surface area and greatest thermal stability. This boehmite contains pores of about 2-3 nm radius, suggested to be responsible for the superior porous properties and thermal stability.     

Study by thermal methods on the materials obtained by dye removal from waste waters with beech flour

The study is devoted to the characterization by both TG-DTG analysis and FTIR spectroscopy of beech flour, dyes and the sorbent-dyes products obtained through retention of the dyes from aqueous solution on the beech flour, to the aim of obtaining information on the nature of dyes’ retention, thermal behavior of the sorbent-dye materials as well as on their possible upgrading as fuel. Thermal analysis led to the conclusion that the mechanism of thermo-oxidative degradation is specific and the retention of dyes occurs on cellulose from beech flour. The nature of the bonds involved in dyes’ retention is also investigated by FTIR analysis, which evidences that dyes retention on cellulose is realized through hydrogen bonding between the NH and, respectively, OH groups from dye molecule and the oxygen atoms from cellulose. Involvement of the non-participating electrons of the nitrogen and, respectively, oxygen atoms of these groups in the extended electronic conjugation with aromatic nuclei strongly influences the capacity of the amino and, respectively, hydroxyl groups of forming hydrogen bonds, thus achieving dyes fixation on the sorbent. DTA analysis led to the conclusion that an improvement in the quality of the sorbent-dye materials as fuels is possible, as compared to untreated beach flour, as a result of the modification of the cellulosic fibers in the process of dyes retention.     

壳聚糖基多孔碳材料的制备及其超级电容性能

以胶态SiO₂纳米粒子为模板,壳聚糖为碳源,ZnCl₂为活化剂,制备了具有不同比表面积和孔体积的氮掺杂介孔碳。采用多种表征手段对碳材料的微观形貌、比表面积和孔道结构进行了表征,探究了壳聚糖与SiO₂纳米粒子的比例以及ZnCl₂活化剂对碳材料孔体积和比表面积的影响。结果表明,在未使用活化剂时碳材料(CSi-1.75)的孔体积高达4.53 cm³·g^-1,但其比表面积最小(729 m²·g^-1);使用ZnCl₂作为活化剂制备的碳材料(CSi-1.75-Zn)比表面积为1 032 m²·g^-1,但其孔体积下降到1.99 cm³·g^-1,且具有最多的吡啶氮和吡咯氮。在以6.0 mol·L^-1KOH为电解液的三电极体系中,当电流密度为0.5 A·g^-1时,CSi-1.75...     

壳聚糖基多孔碳材料的制备及其超级电容性能

以胶态SiO₂纳米粒子为模板,壳聚糖为碳源,ZnCl2为活化剂,制备了具有不同比表面积和孔体积的氮掺杂介孔碳。采用多种表征手段对碳材料的微观形貌、比表面积和孔道结构进行了表征,探究了壳聚糖与SiO₂纳米粒子的比例以及ZnCl2活化剂对碳材料孔体积和比表面积的影响。结果表明,在未使用活化剂时碳材料(CSi-1.75)的孔体积高达4.53 cm³·g^-1,但其比表面积最小(729 m²·g^-1);使用ZnCl₂作为活化剂制备的碳材料(CSi-1.75-Zn)比表面积为1032 m²·g^-1,但其孔体积下降到1.99 cm³·g^-1,且具有最多的吡啶氮和吡咯氮。在以6.0 mol·L^-1 KOH为电解液的三电极体系中,当电流密度为0.5 A·g^-1时,CSi-1.75-Zn的比电容为344 F·g^-1,而CSi-1.75的比电容仅为255 F·g^-1。这表明碳材料的比表面积对超级电容性能影响最大,而孔体积影响较小。电容贡献分析结果表明,相对于CSi-1.75,CSi-1.75-Zn的双电层电容和赝电容都得到了提高,这表明更大的比表面积和更多的吡啶氮和吡咯氮有利于提高碳材料的超级电容性能。     

Effect of some ammonium salts on thermal decomposition of impregnated wood and properties of activated carbons

Methods of chemical, thermal, IR spectral, and X-ray phase analysis were used to study the effect of ammonium additives NH₄Cl + NH₄NO₃ introduced into a phosphorus-nitrogen formulation on the thermal decomposition of impregnated wood in the temperature range 20–700°C and on adsorption characteristics of the resulting activated carbon.     

Modern microscopy methods for the structural study of porous materials

This article describes a number of important recent microscopy tools and their application in particular to the study of porous inorganic materials. The authors believe that these new techniques are on the threshold of delivering enormous new power in the chemist's arsenal for understanding new and complex behaviour in multi-component, hierarchical or composite materials. In particular we consider the contribution of electron crystallography, three-dimensional electron tomography, ultra-high resolution scanning electron microscopy as well as the combined application of high-resolution electron microscopy and atomic force microscopy to the study of surfaces and crystal growth. Much of this work has taken on a particular significance owing to the ground breaking work of scientists at Mobil and in Japan 10 years ago in the successful synthesis of materials with porosity on many length scales achieved through the cooperative self-assembly between inorganic and organic phases. This resulted in a series of materials known as M41S of which MCM-41 and MCM-48 were two of the first and most important structures to be synthesised. This has led to a wealth of new porous structures with order over many length scales and has presented new problems in characterisation. Microscopy methods properly executed are particularly important in the study of this new class of material.     

Using a quasi-heat-pulse method to determine heat and moisture transfer properties for porous orthotropic wood products or cellular solid materials

Understanding heat and moisture transfer in a wood specimen as used in the K-tester has led to an unconventional numerical solution and intriguing protocol to deriving the transfer properties. Laplace transform solutions of Luikov's differential equations are derived for one-dimensional heat and moisture transfer in porous hygroscopic orthotropic materials and for a gradual finite heat pulse applied to both surfaces of a flat slab. The K-tester 637 (Lasercomp) supplies a quasi-heat-pulse to both sides of a 2-ft-square specimen and records precise signals as function of time from surface thermocouples and heat flux thermopiles. We obtained transfer properties for moist and oven-dried redwood lumber flooring.     

Development and evaluation of porous materials for carbon dioxide separation and capture

The development of new microporous materials for adsorption separation processes is a rapidly growing field because of potential applications such as carbon capture and sequestration (CCS) and purification of clean-burning natural gas. In particular, new metal-organic frameworks (MOFs) and other porous coordination polymers are being generated at a rapid and growing pace. Herein, we address the question of how this large number of materials can be quickly evaluated for their practical application in carbon dioxide separation processes. Five adsorbent evaluation criteria from the chemical engineering literature are described and used to assess over 40 MOFs for their potential in CO(2) separation processes for natural gas purification, landfill gas separation, and capture of CO(2) from power-plant flue gas. Comparisons with other materials such as zeolites are made, and the relationships between MOF properties and CO(2) separation potential are investigated from the large data set. In addition, strategies for tailoring and designing MOFs to enhance CO(2) adsorption are briefly reviewed.     

Effect of the modification of silica on thermal properties and flammability of cross-linked butadiene-acrylonitrile rubbers

The paper presents the results of testing the thermal stability and flammability of butadiene-acrylonitrile rubber vulcanizates with different contents of combined acrylonitrile: Perbunan NT 1845 and Perbunan NT 3945 from Bayer, containing unmodified and bromine- or iodine-modified silica. The test results were obtained with the use of a derivatograph, measurements of flammability by the method of oxygen index, in air and also with the use of a cone calorimeter. The effect of the modification on the zeta potential was also examined. A considerable reduction in the flammability of nitrile rubber vulcanizates filled with silica can be obtained by the modification of filler with bromine or iodine. All the vulcanizates containing modified silica are self-extinguishing. An appropriate filling of NBR 39 vulcanizates with bromine-modified silica makes it possible to obtain non-flammable polymeric materials. They neither ignite nor glow under the action of a flame source for 30 s. The findings can be a rational basis for the synthesis of modified silica that can act as active filler and effective flame-retardant agent at the same time.