Enhanced removal of bisphenol A from aqueous solution by aluminum-based MOF/sodium alginate-chitosan composite beads

Aluminum-based metal-organic framework/sodium alginate-chitosan (Al-MOF/SA-CS) composite beads were synthesized and employed as an adsorbent for the removal of bisphenol A (BPA). Several methods, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), nitrogen adsorption-desorption isotherms and X-ray photoelectron spectroscopy (XPS), were used to characterize the prepared adsorbents. Results demonstrated that the introduction of CS could change the porosity of the beads and the obtained Al-MOF/SA-CS composite beads possessed higher surface area and total pore volume comparing with the beads without CS. Batch experiments were carried out to explore the adsorption performance and the results displayed that the enhanced adsorption capacity was achieved by Al-MOF/SA-CS beads compared to the Al-MOF/SA ones. It is also found from the fitting results that the adsorption process fitted well with the pseudo-second-order kinetics model and followed the Freundlich isotherm model. Importantly, the composite beads could be easily recycled and regenerated by methanol and the adsorption efficiency still maintained as high as 96% even after five cycles. Furthermore, it can be inferred from the experimental results that the π-π stacking, hydrogen bonding and cation-π interaction could be the primary adsorption mechanisms. Considering the high adsorption properties, good water stability, especially easy separation, and excellent recyclability, Al-MOF/SA-CS composite beads could be a promising adsorbent for the removal of BPA from contaminated water.