Polymer based on beta-cyclodextrin for the removal of bisphenol A, methylene blue and lead(II): Preparation, characterization, and investigation of adsorption capacity

Abstract

A bioadsorbent was prepared by applying a green facile synthesis route, using water as solvent and beta-cyclodextrin (βCD), citric acid (CA), and polyethylene glycol (PEG) as raw materials. The synthesis parameters were optimized, and the prepared βCD-CA-PEG polymer was thoroughly characterized. With FT-IR analysis, the formation of the new polymeric structure based on a network with ester bonds between βCD, PEG, and citric acid was detected. The increase in thermal stability revealed by the TGA analysis confirmed further the polymerization. The XRD and SEM analyses demonstrated that the original structure of βCD was changed, and a new amorphous structure was formed. The results of the SEM and BET analyses showed that the polymer has relatively low surface area and porosity. The zeta potential study revealed that the polymer has a negative surface charge at a pH range of 3–10. The swelling test showed moderate water uptake, suggesting good hydrophilicity and flexibility of the polymer’s network, thus enhancing the interaction with pollutants’ molecules. Regarding the adsorption performance of the βCD-CA-PEG polymer, bisphenol A (BPA), methylene blue (MB), and lead (Pb(II)) were rapidly and efficiently removed from aqueous solutions. The adsorption processes followed the pseudo-second-order kinetic model for all pollutants in both mono-pollutant and multi-pollutant systems. Furthermore, BPA and Pb(II) adsorption equilibrium data were well simulated by the Langmuir model, while MB adsorption fitted well to the Sips model. The presence of natural organic matter (humic acid) or the increased ionic strength (addition of NaCl) did not significantly impact the adsorption capacity. Finally, the polymer could be easily regenerated at room temperature and retained its good adsorption performance even after five adsorption–desorption cycles. The prepared βCD-CA-PEG polymer can pose an efficient alternative adsorptive in water and wastewater treatment targeting several pollutant categories, including specific organic micropollutants, cationic dyes and heavy metals.