Sustainable β-cyclodextrin functionalized porous adsorbent for the selective elimination of cationic dyes from wastewater

The development of sustainable and efficient adsorbents for wastewater treatment is of great importance in addressing environmental pollution caused by synthetic dyes. In this study, a porous organic polymer (BMQ) was synthesized via crosslinking of β-cyclodextrin (β-CD) with the natural polyphenol, quercetin. The BMQ polymer was characterized by solid state NMR, PXRD, FT-IR, BET, SEM and TGA, which confirmed the formation of a porous, multifunctional framework with abundant active sites. Batch adsorption experiments revealed that BMQ exhibits remarkable selectivity toward cationic dyes, achieving > 95 % adsorption of crystal violet (CV) and rhodamine B (RhB), while depicting < 5 % adsorption for Alizarin Red S (ARS) and < 23.6 % for Fast Sulphon Black F (FSB) under optimized conditions. Adsorption equilibrium data were best described by the Langmuir isotherm, yielding maximum adsorption capacities (Q max ) of 234.08 mg/g and 255.02 mg/g at 323 K for CV and RhB, respectively. Kinetic studies indicated that the pseudo-second-order (PSO) model provided the best fit. Thermodynamic analyses confirmed that the adsorption process is endothermic and spontaneous. Furthermore, BMQ demonstrated excellent recyclability, retaining high adsorption efficiency (>81.5 %) over five successive cycles. These findings highlight the potential of BMQ as a robust, high-capacity, and reusable adsorbent for the efficient removal of toxic cationic dyes from contaminated water, contributing to sustainable water purification strategies.