Adsorption at inorganic surfaces. III. The mechanism of adsorption of organic solutes, including dyes, by graphite
| Autor: | J. W. Galbraith, A. S. A. Hassan, C. H. Giles, D. C. McAllister, A. G. Halliday, N. W. Macmillan, N. Macaulay |
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| Rok vydání: | 2007 |
| Předmět: | |
| Zdroj: | Journal of Applied Chemistry. 8:416-424 |
| ISSN: | 1934-998X 0021-8871 |
| Popis: | The adsorption by graphite of a variety of organic solutes, mainly acid and basic dyes, from water, has been studied. Adsorption occurs rapidly and only at the outer surface of the graphite particles. The adsorptive forces are coulombic (ion exchange) and non-polar van der Waals' attraction. Basic dyes are adsorbed by ion exchange, the process being independent of temperature, but dependent on the surface charge on the graphite. Sulphonated dyes are adsorbed by van der Waals' (dispersion) forces; their affinity increases linearly with the area of the adsorbed molecule in contact with the substrate, but it falls with increase in the number of sulphonate groups, because of increase of water attraction. From solutions of low concentration most solutes are adsorbed as monolayers. In the early stages of adsorption they are probably oriented flat on the surface, but in the completed monolayer they are oriented with ionic groups as far away as possible from the graphite surface. From solutions of high concentration, multilayers of single molecules or monolayers of micelles appear to be adsorbed. Glucose and sucrose are adsorbed to a much greater extent than is accounted for by monolayer adsorption, but the reason for this is obscure. The shapes of the isotherms are shown to be related to the affinity of the solutes for the graphite surface. The rate-controlling factor in adsorption of dyes is believed to be the proportion of bombarding ions which have a favourable orientation relative to the graphite surface at the moment of impact. |
| Databáze: | OpenAIRE |
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