Synthesis and characterization of a β-cyclodextrin-MOF-based porous hydrogel for efficient adsorption of Au3+, Ag+, and Pb2+ ions

Abstract

Wastewater containing heavy metal ions produced by electroplating, smelting and other industries poses a threat to human safety. Recently, metal–organic frameworks (MOFs) have emerged as porous crystalline adsorbents for the removal of heavy metal ions. Starch-derived cyclodextrins (CDs), a series of cyclic oligosaccharides, have been explored for fabrication of cost-efficient MOF materials. However, the coordination bonds in CD-based MOFs can be destroyed by water, which limits their application as absorbent materials for the removal of heavy metal ions from wastewater. In this work, a β-CD-MOF-based porous hydrogel was developed by incorporating a crosslinked hydrogel network based on acrylic acid (AA) and N,N’-methylenebis(acrylamide) (MBA) monomers into a β-CD-based MOF structure. The synthesized porous hydrogel, denoted A/M−CDMOF−gel, not only showed enhanced structural stability but also exhibited excellent properties for simultaneous adsorption of Au3+, Ag+, and Pb2+ ions. A kinetic study revealed that the A/M−CDMOF−gel had a satisfactory binding rate within 60 min of contact, and the higher fit coefficient from the pseudo-second-order model indicated its chemical adsorption property. Moreover, according to the Langmuir isotherm model fitting results, the maximum capacity of the A/M−CDMOF−gel reached 316.4, 60.9, and 414.2 mg/g for Au3+, Ag+, and Pb2+, respectively. Therefore, the regenerable A/M−CDMOF−gel adsorbent is expected to provide ideas for the development of renewable absorbent materials in the field of wastewater treatment and remediation.