Citric acid modified β-cyclodextrin for the synthesis of water-stable and recoverable CD-MOF with enhanced adsorption sites: Efficient removal of Congo red and copper ions from wastewater

Due to the complexity of wastewater pollutants and their adverse effects on human health and the environment, there is an urgent need for the development of a recyclable adsorbent capable of removing both dyes and heavy metals. In this study, citric acid modification β-cyclodextrin metal-organic framework (CA-β-CD-MOF) was synthesized by chemical grafting followed by vapor diffusion methods. The concentration, dosage, and pH of citric acid had a certain impact on the adsorption effect of the adsorbent. The adsorption capacities for the anionic dye Congo red (CR) and copper ions (Cu2+) were as high as 900.9 and 287.4 mg·g−1, respectively. The adsorption process could be well described by the Langmuir isothermal model. The adsorption kinetics of CR and Cu2+ conformed to the pseudo-second-order kinetic model. The adsorption process was a heat absorption and spontaneous process. The combination of density functional theory (DFT) calculations and experimental results proves that electrostatic interaction is the adsorption mechanism of CR. The adsorption of Cu2+ was attributed to the complexation between the carboxyl group on citric acid (CA) and Cu2+. The CA-β-CD-MOF we prepared has good adsorption performance and recyclability and has great potential in removing Congo red and copper ions from wastewater.