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Wpływ surfaktantów na właściwości adsorpcyjne substancji organicznych i jonów metali ciężkich w układach koloidalnych

Chibowski Stanisław, Wiśniewska Małgorzata

Wiadomości Chemiczne

2021

[Z] 75, 9-10

1181--1202

The main purpose of this paper is description of the mechanisms governing the adsorption process of organic substances (such as polymers and dyes soluble in water) and inorganic substances (i.e. heavy metal ions) on the solid surface in the presence of synthetic surfactants of various ionic nature (anionic SDS, cationic CTAB and nonionic Triton X-100). The following polymers were applied: polyacrylamide, poly(ethylene glycol), poly(vinyl alcohol) and poly(acrylic acid). Moreover, the mono-, di- and triazo dyes with acidic, reactive and direct characters were used. Metal oxides – both simple (alumina, zirconia, titania) and mixed (double: silica-alumina, silica-titania and triple: alumina-silica-titania), as well as activated carbons obtained from biomass and peat were applied in the role of adsorbents. The effects of solution pH, ionic character of adsorbate, its molecular weight, elemental composition of the solid, its acid-base properties and textural structure, were determined. The understanding of the phenomena occuring at this type of interface is extremaly important for the effective control of colloidal suspensions stability, which is essential for practical applications. The formation of mixed adsorption layers composed of polymer-surfactant, dye-surfactant or polymer-surfactant-metal ion complexes results in many cases in a significant modification of the surface properties of solids, which is manifested not only by the changes in amount of bound adsorbate, but also by the changes in the structure of electrical double layer. The analysis of the obtained results indicated two main mechanisms of the surfactants influence on the adsorption process of organic and inorganic substances in colloidal systems containing a highly dispersed solid. The first one is the formation of polymer-surfactant, dye-surfactant or polymer-surfactant-metal complexes through both hydrophobic and electrostatic interactions, which show different affinity to the adsorbent surface. In most of the examined systems, these complexes were effectively bound at the solid-liquidinterface, which resulted in the adsorption increase of polymer, dye and heavy metal ions. The second important mechanism is the competition of surfactant molecules and other adsorbates for the active sites of the solid surface (the components of mixed adsorbates had the same ionic character). As a result of these two processes, mixed adsorption layers with a specific structure were formed, which determined the stability of the colloidal suspension.