Simultaneous adsorption of anionic alkyl sulfate surfactants onto alpha alumina particles: Experimental consideration and modeling

Simultaneous adsorption of four anionic alkyl sulfate (AS) surfactants, including sodium octyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate and sodium tetradecyl sulfate named as C8, C10, C12 and C14, onto alpha alumina (alpha-Al2O3) particles were systematically investigated. Concentrations of all mixtures of anionic AS surfactants in aqueous solution were quantified by capillary electrophoresis coupled with contactless conductivity detection (CE-(CD)-D-4). Adsorption isotherms of the four anionic AS surfactant homologs increased with either the decrease of pH from 6.0 to 4.0 due to enhancement of electrostatic attractions between the positively charged alpha-Al2O3 surface and the anionic AS surfactants or the increase of carbon chain length due to enhanced hydrophobic interactions. At different salt concentrations, a common intersection point (CIP) obtained for adsorption isotherms demonstrated that the contributions of electrostatic and hydrophobic interactions were reversed. The ionic strength effect on anionic AS surfactant adsorption isotherms onto alpha-Al2O3 particles was thoroughly studied. Simultaneous adsorption of the four AS surfactants onto the alpha-Al2O3 was controlled by both electrostatic and hydrophobic interactions that were in accordance with Langmuir and two-step models. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The simultaneous adsorption of four anionic alkyl sulfate surfactants onto alpha alumina particles was systematically investigated. Adsorption isotherms increased with decreasing pH or increasing carbon chain length, and a common intersection point was observed at different salt concentrations, indicating a reversal in the contributions of electrostatic and hydrophobic interactions. The study demonstrated that adsorption onto alpha alumina particles was controlled by both electrostatic and hydrophobic interactions in accordance with Langmuir and two-step models.