Facile Fabrication of Zirconium–Organic Framework–Embedded Chitosan Hybrid Spheres for Efficient Fluoride Adsorption

Abstract

In this research paper, zirconium–organic frameworks [Uio-66, named as Zr@BDC metal–organic frameworks (MOFs)] were prepared using Zr(IV) and 1,4-benzenedicarboxylic acid (BDC) for efficient fluoride removal. However, the prepared Zr@BDC MOFs possess some limitations such as column blockage and pressure drop during field tests. To overcome this difficulty, the prepared Zr@BDC MOFs structurally modified with a chitosan (CS) biopolymer offer easily separable and novel biocomposite spheres, namely, Zr@BDC-CS spheres, for effective retention of fluoride in aqueous media. The structural, surface, crystalline nature, and bonding properties of Zr@BDC-CS spheres were analyzed by refined instrumental techniques, viz., Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses. The prepared Zr@BDC MOFs and Zr@BDC-CS spheres possess the highest defluoridation capacities (DCs) of 4935 and 4982 mgF– kg–1 within 20 min, respectively. To attain the maximum DC of Zr@BDC-CS spheres, the defluoridation studies were optimized using a batch method. Defluoridation by Zr@BDC-CS spheres was typically dominated by complexation and electrostatic adsorption mechanism. The nature of fluoride adsorption and order of reaction of Zr@BDC-CS spheres were explored by isotherms and kinetic models of adsorption. Moreover, thermodynamic studies show that the fluoride removal of Zr@BDC-CS spheres was spontaneous and an endothermic nature. The suitability in the field level and reusability of Zr@BDC-CS spheres were investigated.