Adsorption behavior and mechanism of β-cyclodextrin–styrene-based polymer for cationic dyes

Cyclodextrin polymers are efficient adsorbents for dye adsorption. Herein, a β-cyclodextrin polymer (β-CDSP) with carboxyl groups and benzene rings was prepared via free radical polymerization of β-cyclodextrin-maleate and styrene. The adsorption performance of β-CDSP was studied by adsorbing neutral red (NR), basic fuchsin (BF) and safranine T (ST) dyes under different adsorption conditions (e.g., adsorption time, temperature and pH of the solution). The results showed that the adsorption of BF and ST was faster and better than that of NR. The adsorption kinetic behavior fitted well with both the pseudo-first-order and the pseudo-second-order models for NR and BF, but it fitted better with the latter for ST. The adsorption equilibrium data followed the Langmuir isotherm model. The adsorption process was endothermic and spontaneous, and a higher temperature was favorable for dye adsorption. Higher q(t) values were obtained in a basic medium, which resulted from the electrostatic interactions between β-CDSP and cationic dyes. Furthermore, inclusion complexion and π–π interactions also contributed to the dye adsorption. The stability and reusability of β-CDSP were estimated by four regeneration cycles.