Kinetics and adsorption behavior of carboxymethyl starch on α-alumina in aqueous medium

The adsorption of carboxymethyl starch (CMS) at the α-alumina/aqueous solution interface has been investigated through adsorption studies, electrokinetics mobility measurements, and FTIR spectroscopy. Zeta potential measurements show that the addition of CMS results in a more dramatic increase in the absolute zeta potential in the alkaline region, as well as a shift of the isoelectric point to lower values, indicating the adsorption of CMS from the aqueous solution onto the alumina surface. The positive hydrophilic surface sites of alumina are responsible for the adsorption of CMS molecules. The adsorption of CMS is possible after charge reversal by the addition of excess CMS. Nearly 30 min of contact time are found to be sufficient for the adsorption of CMS to reach equilibrium. CMS adsorption follows a Langmuir isotherm with adsorption capacities of 91.74 mg CMS per gram of α-alumina. For the adsorption of CMS, pseudo-second-order chemical reaction kinetics provides the best correlation with the experimental data. FTIR analysis indicated that CMS forms outer complexes with alumina surfaces depending on the shifting of the asymmetric and symmetric bands.

Graphical abstractThe adsorption mechanism of carboxymethyl starch at acidic pH values was investigated on α  -alumina through electrokinetic and the Fourier transform infrared (FTIR) spectroscopy. The experimental results of the specific energy of interaction (ΔG0ΔG0), the pseudo-second-order model, and FTIR studies indicated that CMS is chemisorbed onto the alumina surfaces by forming a chelate complex.Figure optionsDownload full-size imageDownload as PowerPoint slide