Experimental and computational investigation of divalent, trivalent, and tetravalent metal ion complexes of polyvinyl alcohol as adsorbents for fluoride remediation

Abstract

Divalent, trivalent and tetravalent metal ion complexed polyvinyl alcohol (PVA) films are synthesised via solvent casting and used for fluoride removal from groundwater. Scanning electron microscopy depicts a variation in the morphology on the incorporation of these metal ions, while energy dispersive spectroscopy confirms the presence of the metal ions in the films. XRD analysis shows a decreased degree of crystallinity while TGA affirms the thermal stability of the metal ion complexed PVA films. The possible metal ion-binding interactions to PVA chains are elucidated by Density Functional Theory calculations. The quantum reactivity descriptors and natural bond orbital analysis assert that the complexation of two PVA chains with Zr4+ [(PVA)2Zr2(OH)4] is highly stable. The fluoride uptake by (PVA)2Zr2(OH)4 is thermodynamically favourable and occurs mainly by ligand to metal charge transfer interactions. Experimental fluoride adsorption studies confirm that PVA-Zr films remove ∼90% fluoride from 5 mg L−1 fluoride solution at pH 3–7. Moreover, the PVA-Zr films lower the fluoride content from 2.84 mg L−1 to 0.9 mg L−1 in the groundwater sample, which is below the permissible limit. Thus, it is proven experimentally and computationally that PVA-Zr films have potential commercial applicability in fluoride remediation.