Carbonaceous materials adsorbents

Interestingly, the presence of residual chlorine in the hypercrosslinked polymer enhances the yield of the final carbonizate (plot 1 in Fig. 7.48). It was found that the presence of carboxyl or sulfonic substituents in the aromatic rings of the polymer also enhances the yield of final carbons [207]. In fact it has been known [208] that sulfbnated styrene—DVB copolymers can be used for the preparation of carbonaceous adsorbing materials. However, because of the ehmination of heavy sulfonic substituents (over 40% of the material weight), the final yield of carbons is by no means hi er than in the... 

In general, pyrolysis of certain hypercrosslinked polystyrene materials at a temperature of about 600°C may result in interesting carbonaceous adsorbing materials with a yield of up to 55-60% within 50-60 min. The products maintain the spherical form of the initial materials and their overall texture, and acquire an exceptional mechanical strength of up to 8 kg per bead. They are basically nanoporous and show size-dependent adsorbing properties [207, 210]. In particular, they efficiently separate mineral ions in accordance with the new frontal ion size exclusion process... 

Adsorption. Adsorption involves the transfer of a component onto a solid surface. An example is the adsorption of organic vapors by activated carbon. Activated carbon is a highly porous form of carbon manufactured from a variety of carbonaceous raw materials such as coal or wood. The adsorbent may need to be... 

Effect of Carrier Material on the Character of Adsorbed CO on Nickel. It is clear from the data in Table I that the carbonaceous carrier material is essential for catalysis. The results of H2 adsorption and CO adsorption are given in Table IV. The amount of chemisorbed H2 was far less than that of CO for every sample, and thus the ratio of chemisorbed CO to H2 very much higher than... 

Activated carbons [171-182] are amorphous materials showing highly developed adsorbent properties. These materials can be produced from approximately all carbon-rich materials, including wood, fruit stones, peat, lignite, anthracite, shells, and other raw materials. The properties of the produced adsorbent materials will depend not merely on the preparation technique but as well on the carbonaceous raw material used for their production. Actually, lignocellulosic materials account for 47% of the total raw materials used for active carbon production [178],... 

Most of these discussions regarding fluorine contamination of aluminum surfaces have focused on the conversion of aluminum oxide to fluoride or oxyfluoride. Evidence for similar conversions was included, and in extreme cases conversion to aluminum bonding quite similar to that in AIF3 was found. However, the poor adhesion of the samples skipping the O2 plasma treatment is related not to the fluorine contamination as such, but rather to the carbonaceous nature of the adsorbed materials, which is subjected to the plasma polymerization of TMS. Oxygen plasma cleaning removes this carbonaceous component, while the surface fluorine concentration is enhanced. 

For description of textural properties of carbonaceous adsorbents, adsorption/desorption isotherms of vapours and gases in static conditions as well as mercury porosimetry are used. The latter method often leads to destruction of porous structure of investigated materials while the usage of the former one is affected by the specific properties of molecular sieves described above. Taking into account these limitations, in this work the authors have made an attempt of determination of porous structure of carbon molecular sieves with the used of the pycnometric technique. 

According to the data presented in the Table 1, the fi action of pores inaccessible and accessible for benzene molecules was essentially affected not only by fraction of introduced carbonaceous deposit to the adsorbent material, but also by its quality and circumstances of carbonization process. 

The constitution of ordered layers of water at interfaces with carbonaceous adsorbents in aqueous suspensions is governed by three major factors, namely, hydrophilic properties of the surface, porosity of the material, and the feasibility of polarization of the surface at the expense of the formation of regions carrying electric charges of opposite signs. In the general case, the thickness of an adsorbed water layer on the surface is detennined by the action radius of surface forces in whose field the orientation of electric dipoles of water molecules occurs and the formation of its surface clusters takes place. 

Highly porous carbons can be produced from a variety of natural and synthetic precursors [11, 12]. Relatively inexpensive activated carbons are useful adsorbents, but generally their surface and pore structures are exceedingly complex [11, 13]. However, it is now possible to prepare a number of more uniform carbonaceous adsorbents. For example, molecular sieve carbons (MSCs) are available with narrow distributions of ultramicropores, which exhibit well-defined molecular selectivity [11], and carbon nanotubes, aerogels, and membranes are also amongst the most interesting advanced materials for research and development [12, 14]. 

This chapter is concerned with the energetics of gas adsorption on carbons, or more specifically the thermodynamic quantities involved when carbon materials are employed as the adsorbents. Out of these solids, activated carbons, due to their exceptional surface area development and consequent technological implications, are the carbonaceous adsorbents that have attracted the attention of most publications. A more comprehensive account of the energetic aspects of adsorption on carbons has been published elsewhere [1]. 

The enhancement in the oxidation of SO2 due to the presence of active inorganic matter was also found by Bashkova et al. [89] on carbonaceous adsorbents derived firom sewage sludge. In those materials, a high content of CaO was identified as a favorable fiictor. The effect of calcium was also studied when fly ash mixtures with calcium hydroxide were tested as SO2 adsorbents [89]. It was found that Ca(OH)2 enhances the dispersion of calcium reagent and thus improves the efficiency of the adsorbent. 

Most common ions (sodium, calcium, nitrate, phosphate, chlonne, bromide, and iodine) found in natural or wastewater are not really adsorbed onto activated carbons. An exception is fluoride that can be removed by activated carbon as well as by activated alumina. Table 24.6 gives some indications of the adsorption potential of some inorganic cations and anions onto carbonaceous porous material. 

Blumbach J, Nethe LP. 1996. Organic components reduction (PCDD/PCDF/PCB) in flue-gases and residual materials from waste incinerators by use of carbonaceous adsorbents. Chemosphere 32(1) 119-131. 

Other adsorbent materials investigated in Hterature include carbonaceous resins such as Ambersorb 563, 572, 575, synthetic resins (Amberhte XAD4, XAD7), porous graphitic resins (Hypercarb), and zeolites (mordenite, ZSM-5, Beta, Y) with different Si02/Al203 ratios or pore sizes. Results are shown in Tables 4 to 6. 

Activated carbons were the first adsorbents to be developed. As stated in previous sections, activated carbons are produced from a solid carbonaceous based material, which is non-graphitic and non-graphitizable, and has an initial isotropic structure. The precursor is transformed or activated by means of medium to high temperature treatments, which remove solid mass, and at the same time, create pores where the removed mass was previously located. The common properties of activated carbons and other kinds of carbon adsorbents is their well developed pore network, and the similar ways in which they are... 

Despite a significantly lower adsorption capacity of activated carbons for the removal of SOj and NO from flue gases in comparison with the VOC removal capacity, there are many processes in which they (or activated cokes) are applied for purification of industrial fumes [171-174] from coal fired power plants and waste incinerators. Activated coke is a carbonaceous adsorbent manufactured from lignites or hard coals. Typically, the specific surface areas of commercially available activated cokes are relatively low (up to 400 m g" ) and the pore volumes are only up to ca. 0.25 cm g Depending on the material origin and the manufacturing process, either adsorptive or catalytic characteristics may play a dominant role in the removal of contaminants on this adsorbent. The majority of activated cokes is used for the removal of SO and dioxins fiom waste and flue gases. 

Both reflectance FT-IR spectra and the dependence of the reduction peak current on the scan rate revealed that cat adsorbed onto the SWNTs surfaces. The redox wave corresponds to the Fe(lll)/Fe(ll) redox center of the heme group of the cat adsorbate. Compared to other types of carbonaceous electrode materials (e.g. graphite and carbon soot), the electron-transfer rate of cat redox reaction was greatly enhanced at the SWNTs-modified electrode. The catalytic activity of cat adsorbate at the SWNTs appeared to be retained, as the addition of H2O2 produced a characteristic catalytic redox wave. The facile electron-transfer reaction of cat could be attributed to the unique properties of SWNTs (e.g. the excellent electrical conductivity of SWNTs, the enhanced surface area arising from the high aspect ratio of the nanotubes, and the amenability of SWNTs for the attachment of biomolecules). 

Indeed, in experiments on dogs who received with their food a dose of ethylene dichloride (2000 mg/kg) and then, after 1 h of exposure to the poison, a hemoperfusion therapy using lOOmL cartridges with different adsorbing materials, only hypercrosslinked polymers showed an intensive removal of ethylene dichloride from the blood with no changes in blood formulation (platelets, white and red blood cells, monocytes, lymphocytes). Carbonaceous materials coated with a hemocompatible layer produced hemolysis and severe drops in platelet and WBC counts, with a slow kinetics of detoxification. 

In short, pyrolysis of hypercrosslinked polystyrene beads leads to chemically and mechanically robust carbonaceous materials in a beaded form and with a high carbon yield. This could present a convenient way of converting used-up or contaminated (i.e., in blood perfusion procedures) hypercrosslinked adsorbing materials into a product of high value and many application possibilities. 

Adsorption is an easy way to attach nucleic acids to solid surfaces, since no reagents or modified-DNA are required, as shown in Fig. 3.3. These features have promoted extensive use of adsorption as immobilization methodology in genetic analysis. The mainly claimed disadvantages of adsorption with respect to covalent immobilization are (i) nucleic acids may be readily desorbed from the substrate and (ii) base moieties may be unavailable for hybridization if they are bonded to the substrate in multiple sites [76]. However, the electrochemical detection strategy based on the intrinsic oxidation of DNA requires the DNA to be adsorbed in close contact with the electrochemical substrate by multisite attachment, as schematically shown in Fig. 3.4. This multisite attachment of DNA can be thus detrimental for its hybridization but is crucial for the detection based on its oxidation signals. The common method for the multisite physical adsorption of DNA on carbonaceous-based materials can be classified into dry or wet adsorptions. 

Activated carbon " is the trade name for a carbonaceous adsorbent which is defined as follows Activated carbons are non-hazardous, processed, carbonaceous products, having a porous structure and a large internal surface area. These materials can adsorb a wide variety of substances, i.e., they are able to attract molecules to their internal surface, and are therefore called adsorbents. The volume of pores of the activated carbons is generally greater than 0.2 mlg" . The internal surface area is generally greater than 400 mV - The width of the pores ranges from 0.3 to several thousand run. 

The book Porous Materials for Carbon Dioxide Capture is aimed at providing researchers with the most pertinent and up-to-date advances related to the fields of porous materials design and fabrication and subsequent evaluation in innovative cyclic CO2 adsorption processes, with special emphasis on uncovering the relationships between structural characteristics and CO2 capture performance. The book is divided into seven chapters that provide a resume of the current state of knowledge of porous CO2 capture materials, which include ionic liquid-derived carbonaceous adsorbents, porous carbons, metal-organic frameworks, porous aromatic frameworks, microporous organic polymers, sorption techniques such as cyclic calcination and carbonation reactions, and membrane separations. 

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