Studies in liquid-phase sorption at inorganic and organic surfaces

Subramanian, R. V.R (1956) Studies in liquid-phase sorption at inorganic and organic surfaces. PhD thesis, University of Glasgow.

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The present work comprises a study of the sorption of organic compounds by the anodic film on aluminium and also by chitin. Sorption by the anodic film The sorption of organic compounds by the anodic film on aluminium from solution in water and a variety of organic solvents has been investigated. Films prepared by anodisation in chromic acid were principally employed. These consist of almost pure amorphous Al2O3 in a porous form. The sorptions were carried out under a variety of conditions and thermodynamic data have been determined in some cases. One or more of the following mechanisms are found to account for the sorption of all the compounds studied: (a) hydrogen bonding between oxygen of the film and a phenolic hydroxyl or an amino-group in the solute; (b) salt formation between aluminium in the film and a sulphonic acid group in the solute; (c) chelation between aluminium in the film and pairs of o-hydroxy etc. groups in the solute; (d) an ion-exchange reaction at the film surface which takes place with certain sulphato-esters; (e) a "bridge-bonding" reaction, whereby a donor group e.g. the azo-group, may be fixed to the oxygen of the film through a "bridge" of a di-hydroxy compound e.g. quinol. The hydrogen-bonds formed by phenolic hydroxy compounds appear to be unaffected by the nature of the solvent but those formed by amino-groups have lower affinity and their formation may be prevented and the solute remain unsorbed when benzene or water is the solvent but not when carbon tetrachloride or dioxan is used. Both hydrogen atoms of the amino-group may be capable of simultaneous bonding with the film except in o-aminoazo-compounds, where chelation prevents one from reacting. The sorption of sulphonic acids from water may also be prevented if the aromatic nucleus is so small that the compound has very high solubility; this occurs with benzene sulphonic acid. The film acquires a positive charge in water and consequently no cationic compounds e.g. basic dyes, are sorbed even when they contain groups capable of forming a hydrogen bond with the film; they may sometimes be sorbed from a non-ionising solvent e.g. dioxan, but even so, they can immediately be washed out by water. Since the surface has a positive charge, most anionic compounds are readily sorbed. Many sulphonates, particularly acid dyes, are readily sorbed, and appear to take part in salt formation with the metal of the film, there being a measurable heat of sorption. Sulphato-esters, which are also readily sorbed, however, show no measurable heat of sorption. This is believed to be due to a process of ion-exchange at the film surface. Compounds capable of chelating with aluminium e.g. mordant dyes are readily sorbed by a non-reversible reaction, colouring the film with the characteristic shade of the aluminium lake, as was found by Mehta(34). No evidence has been obtained that van der Waals attraction plays any significant part in determining sorption on the substrate from solution. Sorption of simple acids, acid dyes, and hydroxy compounds by chitin. The sorption of simple mineral acids, acid azo dyes and hydroxy compounds by chitin, obtained from the shells of Nephrops Norvegicus has been investigated. The composition of the chitin sample employed in the present work has not been completely established, but it is well known that chitin is built up of acetylaminoglucose units, through 1:4-glucosidic linkages as in cellulose. The sample employed for the study was of a standard particle size, greater than 200 mesh and in all experiments a constant solid:liquid ratio of 1:2000 was employed throughout. In the sorption of simple mineral acids, no hydrolysis is observed at 60

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: C H Giles
Keywords: Physical chemistry
Date of Award: 1956
Depositing User: Enlighten Team
Unique ID: glathesis:1956-72514
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06

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