Remarkable adsorption for hazardous organic and inorganic contaminants by multifunctional amorphous core–shell structures of metal–organic framework-alginate composites

Novel metal–organic framework-alginate composite beads (CA-MIL-53-AC) were synthesized using sodium alginate (gelling agent) and calcium chloride (complexing agent) via a one-pot and dropping method to selectively remove the dichlorodiphenyltrichloroethane (DDT), arsenate (As(V)), and fluoride in an aqueous solution. To evaluate the characteristics of the synthesized composite beads, scanning electron microscopy, X-ray diffraction, Fourier-transform infrared, X-ray photoelectron spectroscopy, thermal gravimetric analysis, zeta potential, and porosimetry techniques were used in this study. The adsorption kinetics showed that DDT, As(V), and fluoride removal could be described by the pseudo-first-order model. Also, the adsorption isotherms indicated that DDT and As(V)/fluoride removal followed the Langmuir and Freundlich models, respectively. Compared with granular AC and pristine CA, CA-AC, and CA-MIL-53, the CA-MIL-53-AC showed superior adsorption performance for all target contaminants (5.29, 4.89, and 3.18 mg/g for DDT, As(V), and fluoride, respectively). The adsorptive behavior for DDT was spontaneous, exothermic, and highly favorable based on thermodynamics calculations. Furthermore, the regenerated composite beads showed high removal capacity for DDT after the third recycle. The continuous DDT adsorption in the fixed-bed column at different flow rates were well fitted using Thomas, Adams–Bohart, and Yoon–Nelson models. The plausible mechanisms for the DDT, As(V), and fluoride removal by CA-MIL-53-AC were identified as hydrophobic and π–π interactions, ion exchange, surface complexation, and hydrogen bonding. These findings provide significant insight to remove DDT, As(V), and fluoride from water for practical applications.