Complex investigation of cluster adsorbtion of water molecules on hydrophilic centers of graphite and graphitized thermal carbon black

Abstract

A complex theoretical-experimental investigation has been carried out on the interaction of water with hydrophilic centers -phenolic and carboxyl groups -on the surface of graphite and graphitized thermal carbon black in low surface occupation range. It is shown that microclusters, formed by the absorption on such centers, have a cyclic structure of 4-5 molecules similar to those observed in liquid water and on the surface of silver iodide. The formation of such structures is shown to be energetically advantageous. It is shown that the generalized Langmuir equation, derived from molecular-statistical considerations, is considerably better over a wide range of relative pressure for the description of the experimental isotherm for the adsorption of water on graphitized thermal carbon black and allows for a better interpretation of structural and energetic characteristics of adsorbed systems obtained by a complex of methods.Graphite and graphitized thermal carbon black (GTC) are suitable models for the study of the interaction of molecules of water with hydrophilic centers in basically hydrophobic adsorbents. The hydrophilic centers found on the surfaces of these molecules are 3-12 nm [1] apart from one another which is considerably greater than the van der Waals diameter of a water molecule (0.3 nm). This permits the study of the interactions of the water molecules with such hydrophilic centers at low to medium coverage of the surface "in a pure form," without complicated appearance of surface (two-dimensional) association.The study of the adsorption of water on carbon adsorbents is associated with a large number of investigations. A detailed review of this work is given, for example, in [2]. In recent years the study of the interaction of water with the surfaces of carbon surfaces, apart from its theoretical value, has acquired an important practical aspect [3][4][5] in connection with the formation of stable sooty aerosols in the upper levels of the troposphere -products of the incomplete combustion of fuels of internal combustion engines. On interaction with water, sooty aerosols not only form cirrus clouds but also appear as condensation nuclei which affect the formation of cloudiness in the troposphere.Since the surface of soot particles is similar in all properties to GTC, then the study of the interaction of water with graphite and GTC permits, if not regulation, then in ever case to predict the negative effect of the formation of cirrus clouds on the radiation balance of atmosphere and the climate of the planet.In this work we present the results of complex gas chromatographic, molecular-statistical, and quantum-chemical investigations of cluster formation of water molecules on the active centers of graphitized thermal carbon black. 0040-5760/07/4303-0191

Estimation of the energetic nonhomogeneity of the surface of oxide and carbon materials

“…Our ab initio calculation showed that the higher-energy adsorption sites in the range of relative pressures studied are residual carboxyl groups of the lateral and basal surface of the graphite crystallites with adsorption energies equal to 43.6 and 40.2 kJ/mol, respectively [11]. The difference in these values is in very good accord with the difference in the positions of the maxima in Fig.…”

“…2d. This conclusion is supported also by the results of quantum-chemical calculations showing that the energy of the interaction of water molecules with vicinal OH groups on the silica gel surface is about 70 kJ/mol [12], while the energy of the interaction of water molecules with carboxyl groups of the carbon surface is much lower, about 40 kJ/mol [11]. In the relative pressure range studied, adsorption occurs on the first type of sites.…”

Ship particulate pollutants: Characterization in terms of environmental implication

“…41,42 The acidic carboxyl groups are strongest with respect to the hydrogen bond, near 15-20 kJ mol À1 . 43,44 The hydroxyl group in carboxyl is stronger than in phenols with respect to its protondonor ability and polarity of the O-H bond. The carbonyl group is stronger than the oxygen-containing group in esters and ethers.…”

Energetics of the interaction of water and other liquids with the surface of hydrophilic and hydrophobic sorbents according to data on the heats of wetting

“…The degree of coverage of the hydrophobic surface of graphitized thermal black (GTB) does not reach unity even at a pressure close to saturation [89], i.e., a conventional monolayer of water on the surface of this sorbent in the classical sense is not formed, although bulky water microclusters are formed on its residual active centers [86,92]. On account of intracluster interaction between the molecules the Q(a) relationship does not decrease, as for hydrophilic sorbents, but conversely increases with increase in coverage, reaching a maximum at P/P S ® 1.0 [89].…”

“…The differential heats of adsorption of water on this sample, obtained in a direct calorimetric experiment, and the first quantum-chemical calculations of the energy of interaction of water molecules with the active centers of GTB were presented in [90]. The evolution of these investigations can be found in [91,92].…”