Abstract
The influence of surfactants (anionic sodium dodecyl sulfate, and nonionic tert-octylphenol ethoxylate with 9.5EO) and their mixtures on the adsorption of carboxymethylcellulose (CMC) in the presence of 0.001 M NaCl on the manganese dioxide surface (MnO2) was studied. The increase in CMC adsorption was observed in all measured systems in the presence of surfactants. The reason for this is the formation of complexes between polymer macromolecules and surfactants. Moreover, the dependence between the amount of surfactants adsorption and the CMC initial concentration was also studied. It proves that surfactant adsorption does not depend on the initial concentration of CMC. Another observation is that the increase in pH caused the decrease in CMC adsorption. The explanation of this phenomenon is connected with the influence of pH on the dissociation degree of the polyelectrolyte, kind and concentration of the surface active groups of the adsorbent. To characterize the compact and diffuse adsorption layer the surface charge density and the zeta potential of MnO2 in the presence of CMC and surfactants were measured. The surface charge density of MnO2 decreases in the presence of CMC or CMC/surfactant complexes. This is due to the presence of negatively charged groups in the compact part of the electric double layer. The zeta potential of MnO2 is also lower in the presence of CMC and the CMC/surfactants complexes. The main reason for that is the shift of the slipping plane towards the bulk solution.
Highlights
The adsorption of polysaccharides on the solid is a very sophisticated process determined by many factors
It is clearly visible that the presence of Carboxymethyl cellulose (CMC) and surfactants causes a decrease in the zeta potential and a shift of the isoelectric point of MnO2 towards a lower pH
The results obtained prove that the adsorption of CMC and complexes between CMC and surfactants strongly influences the structure of the electric double layer MnO2/ electrolyte
Summary
The adsorption of polysaccharides on the solid is a very sophisticated process determined by many factors. These factors can be divided into three categories. The first one, connected with the polysaccharide, includes such parameters as molecular weight of the polymer used, its polydispersity, purity and chemical character. The second, related with the adsorbent, includes its chemical character, surface charge, specific surface area, homogeneity and purity. Because of so many parameters which have an influence on the adsorption of polysaccharides, the mechanism of this process has not been fully explained. The adsorption of polysaccharides on the surface of solids has been widely studied with hydrogen bonding and hydrophobic interaction as the primary adsorption mechanisms [1, 2]. According to other scientists [3,4,5], the adsorption of polysaccharides results from an acid–base reaction between the polysaccharide active groups and the metal hydroxyl groups from the solid
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