Adsorption property

Among the studied adsorption processes which have focused on CNFs, hydrogen adsorption is the most studied one, theoretical calculations, experimental measurements and molecular simulations being reported in the literature [93]. However, only a limited number of works have focused on adsorption of organic molecules on CNFs, in spite of the potential application (adsorption filters, key step for catalytic applications, etc.). In this way, the adsorption of several organic molecules over CNFs was compared to carbon nanotubes and high surface area graphites, all of them 

The main reason for the recent popularity of nanotechnology is that the reduction of the dimensions of a material to nanosize leads to new specific properties [82]. Carbon nanofibers have very high tensile strength and Yormg s modulus (can reach values of about 12,000 MPa and 600 GPa respectively) which are approximately 10 times that of steel. Besides mechanical strength, CNFs are attractive in electrical applications as well due to their high electrical conductivity. These CNF properties provide a huge number of opportunities for future applications in all spheres of life [95]. 

The superb mechanical properties of CNFs make them a good reinforcement agent for different synthetic materials. In comparison with macroscopic fibers, a lower quantity of nanofibers is required to attain the same reinforcement result and reduce brittleness their large specific surface area promotes relaxation processes in the matrix as well, which improves the impact strength of the reinforced matrix. More than that, the small diameters of CNFs provide very limited refraction of fight, which makes them transparent in matrices [82]. 

The large surface area and chemical inertness of CNFs can be applied in catalysis. For example, nanofibers loaded with metallic nanoparticles (Rh, Pt, Pd) are appropriate catalyst carriers for hydrogenation reactions. The elimination and recycling of the catalyst after the reaction is not a problem, nanofibers are very effective in the terms of time and conversion, and they can serve several times without loss of activity [82], 

Carbon nanofibers have also found their way into the medical field. The reason is that the dimensions of proteins, viruses, and bacteria belong to 

Due to their large specific surface areas, carbon blacks have a remarkable adsorption capacity for water, solvents, binders, and polymers, depending on their surface chemistry. Adsorption capacity increases with increasing specific surface area and porosity. Chemical and physical adsorption not only determine wettability and dis-persibihty to a great extent, but are also most important factors in the use of carbon blacks as fillers in rubber as well as in their use as pigments. Carbon blacks with high specific surface areas can adsorb up to 20 wt.% of water when exposed to humid air. In some cases, the adsorption of stabilizers or accelerators can pose a problem in polymer systems. 

Density measurements using the helium displacement method yield values between 1.8 and 2.1 g cm for different types of carbon black. A mean density value of 1.86 g cm is commonly used for the calculation of electron microscopic surface areas. Graphitization raises the density to 2.18 g cm . The lower density with respect to graphite (2.266 g cm ) is due to sHghtly greater layer distances. 

The interaction of carbon nanotnbes with their environment, and in particular with gases or liquids adsorbed either on their internal or external surfaces, is attracting increasing attention dne to the possible infinence of such adsorption on the CNT electronic properties (application to chemical sensors) and to the possibility of nsing these materials for efficient gas storage or for gas separation [11]. 

In summary, it appears that carbon nanotubes present peculiar adsorption properties if compared to graphite or to activated carbon, due mainly to their peculiar 

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Note Some of Grahame s values for and included in this table. For a common cation, the sequence of anions in order of increasing adsorption is similar to that of the Hofmeister series in coagulation studies, and it is evident that specific adsorption properties are involved. 

Tarazona A, Kreisig S, Koglin E and Schwuger M J 1997 Adsorption properties of two cationic surfactant classes on silver surfaces studied by means of SERS spectroscopy and ab initio calculations Prog. Colloid Polym. Sol. 103 181-92... 

An interesting example of a large specific surface which is wholly external in nature is provided by a dispersed aerosol composed of fine particles free of cracks and fissures. As soon as the aerosol settles out, of course, its particles come into contact with one another and form aggregates but if the particles are spherical, more particularly if the material is hard, the particle-to-particle contacts will be very small in area the interparticulate junctions will then be so weak that many of them will become broken apart during mechanical handling, or be prized open by the film of adsorbate during an adsorption experiment. In favourable cases the flocculated specimen may have so open a structure that it behaves, as far as its adsorptive properties are concerned, as a completely non-porous material. Solids of this kind are of importance because of their relevance to standard adsorption isotherms (cf. Section 2.12) which play a fundamental role in procedures for the evaluation of specific surface area and pore size distribution by adsorption methods. 

Activated carbons contain chemisorbed oxygen in varying amounts unless special cate is taken to eliminate it. Desired adsorption properties often depend upon the amount and type of chemisorbed oxygen species on the surface. Therefore, the adsorption properties of an activated carbon adsorbent depend on its prior temperature and oxygen-exposure history. In contrast, molecular sieve 2eohtes and other oxide adsorbents are not affected by oxidi2ing or reducing conditions. 

CHEMICAL ANALYTICAL AND ADSORPTION PROPERTIES OE HYDRATED ALUMINA... 

As a possible method of concentrating trace amounts of bioactive organic compounds occurring in the hydrosphere, adsorption properties of various compounds have been explored by employing hydrous metal oxides as the adsorbents. To date, a family of organophosphoms compounds and carbonic acids were adsorbed onto hydrous iron oxide, along with the adsoi ption of monosaccharides onto hydrous zirconium oxide. 

The term activation refers to the development of the adsorption properties of carbon. Raw materials such as coal and charcoal do have some adsorption capacity, but this is greatly enhanced by the activation process. There are three main forms of activated carbon. 

Adsorptive Properties. Substances such as silica gel and activated charcoal can be used to collect (adsorb) certain solids from solution. The adsorber bed may be discarded when depleted or recycled by washing and heating. 

Some authors have suggested the use of fluorene polymers for this kind of chromatography. Fluorinated polymers have attracted attention due to their unique adsorption properties. Polytetrafluoroethylene (PTFE) is antiadhesive, thus adsorption of hydrophobic as well as hydrophilic molecules is low. Such adsorbents possess extremely low adsorption activity and nonspecific sorption towards many compounds [109 111]. Fluorene polymers as sorbents were first suggested by Hjerten [112] in 1978 and were tested by desalting and concentration of tRN A [113]. Recently Williams et al. [114] presented a new fluorocarbon sorbent (Poly F Column, Du Pont, USA) for reversed-phase HPLC of peptides and proteins. The sorbent has 20 pm in diameter particles (pore size 30 nm, specific surface area 5 m2/g) and withstands pressure of eluent up to 135 bar. There is no limitation of pH range, however, low specific area and capacity (1.1 mg tRNA/g) and relatively low limits of working pressure do not allow the use of this sorbent for preparative chromatography. 

Though as yet in its infancy, the application of laser Raman spectroscopy to the study of the nature of adsorbed species appears certain to provide unusually detailed information on the structure of oxide surfaces, the adsorptive properties of natural and synthetic zeolites, the nature of adsorbate-adsorbent interaction, and the mechanism of surface reactions. 

Dynamic Methods for Characterization of Adsorptive Properties of Solid Catalysts L. POLINSKI AND L. NaPHTALI Enhanced Reactivity at Dislocations in Solids... 

The dried polyoxazoline-modified silica gel was immersed into distilled water. The adsorption property of the resulting gel was estimated by the water content. The water uptake was calculated from an expression of (W -W)jW, where Wis the weight of dried gel and W is the weight of water-absorbed gel. The modified gel showed a higher water-adsorption property than that of untreated silica gel, which absorbed 10.8 multiples of water. The water uptake of modified gel was up to 13.7 multiples of the weight of dried gel. Thus, silica gel has been made more hydrophilic by a polyoxazoline segment. 

Table 6. Preparation and water adsorption property of POZO modified silica gel...

These poly(2-alkyl-2-oxazoline) silane coupling agents were copolycondensed with tetraethoxysilane by acid-catalyst to produce poly(2-alkyl-2-oxazoline)-modified silica gel. The composite gel from 2-ethyl-2-oxazoline was also homogeneous and transparent glass. Poly(2-alkyl-2-oxazoline)-modified silica gels, especially gels based on poly(2-ethyl-2-oxazoline) absorbed water and also organic solvents such as DMF or alcohols as shown in Table 7. This result means that the obtained composite gel shows the amphiphilic adsorption property. 

Hydrated metal sulphates have long been used to study water removal processes, and characteristic kinetic behaviour is conveniently illustrated by reference to these substances. Frost and co-workers [602,603] have investigated the structures, stabilities and adsorption properties of various intermediate amorphous phases, the immediate reaction products which can later undergo reorganization to yield crystalline phase. 

Results for other metals of the Pt-group are due to Frumkin and co-workers8,10,11,14 (Table 22). However, an electrode with the surface renewed in closed circuit has been used by Lazarova767 to study depend linearly on pH with a slope ofca. 55 mV. This has been explained by the adsorption properties of Rh toward H and O, which shift <7-0 to more negative values. Anions have been observed to specifically adsorb on Rh more strongly than on Pt in the sequence... 

The key features of soot are its chemical inertness, its physical and chemical adsorption properties, and its light absorption. The large surface area coupled with the presence of various organic functional groups allow the adsorption of many different materials onto the surfaces of the particles. This type of sorption occurs both in the aerosol phase and in the aqueous phase once particles are captured by cloud droplets. As a result, complex chemical processes occur on the surface of soot particles, and otherwise volatile species may be scavenged by the soot particles. 

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