Thermodynamic insights into the adsorption behaviors of amphoteric cellulose on charged silica surface

This study investigates amphoteric cellulose (AC) adsorption behaviors on the charged silica surface and the associated thermodynamics, a key area with broad industrial relevance. We synthesized a range of ACs with different degrees of substitution (DS) and examined their adsorption on silica using quartz crystal microbalance with dissipation monitoring (QCM-D). By applying Langmuir and Freundlich isotherm models, the maximum adsorption capacity and the interactions between ACs and silica were assessed, and then Van't Hoff equation was employed to estimate the thermodynamic parameters to unveil the mechanisms involved. In terms of ΔG°, ΔH°, and ΔS° associated with the adsorption of AC-0.23 at 298 K were assessed to be −6.68 kJ·mol −1 , 18.98 kJ·mol −1 , and 85.61 J·mol −1 ·K −1 , respectively. Accordingly, those for AC-0.56 were − 11.21 kJ·mol −1 , −10.53 kJ·mol −1 , and 1.86 J·mol −1 ·K −1 . These findings underscore the substantial influence of DS on adsorption behavior and thermodynamics of ACs due to the molecular flexibility playing a crucial role in adsorption. The low-charge-density polymer exhibits higher flexibility and entropy-driven adsorption, while the high-charge-density polymer shows stronger electrostatic interactions and more enthalpy-driven adsorption. Our research provides crucial insights into the adsorption behavior of ACs with varying DS, which is essential for enhancing their performance in industrial applications.