Facile synthesis of chitosan-modified ZnO/ZnFe2O4 nanocomposites for effective remediation of groundwater fluoride

This study explores the possibility of developing an eco-friendly adsorbent for effective remediation of groundwater fluoride, a well-known health hazard affecting more than 25 nations on the various continents. A facile and milder approach has been adopted to synthesize chitosan-modified ZnO/ZnFe₂O₄ nanocomposites. The synthesized materials have been characterized by different spectroscopic, microscopic, and diffractometric techniques. X-ray photoelectron spectroscopy and X-ray diffraction studies have confirmed the formation of pure and highly crystalline ZnO/ZnFe₂O₄ nanocomposites. The presence of surface-adsorbed chitosan in the modified ZnO/ZnFe₂O₄ has been confirmed by FT-IR and thermogravimetric analysis. The results from microscopic and BET surface area analysis of ZnO/ZnFe₂O₄ nanocomposites indicated that chitosan plays a crucial role in modulating the surface morphology and surface properties of the nanocomposites. The nanocomposites exhibit excellent adsorption performance in the remediation of groundwater fluoride. Experimental conditions have been systematically designed to evaluate the optimum adsorption condition for fluoride, and the results have been analyzed with various non-linear models to describe the kinetics and isotherms of adsorption. The adsorption primarily follows Lagergren pseudo-first-order kinetics, and the Langmuir adsorption capacity is varied from 10.54 to 13.03 mg g⁻¹ over the temperature range 293–323 K. The thermodynamics study reveals that the adsorption process is endothermic and spontaneous. The mechanism of adsorption has been proposed based on the spectroscopic analysis of the fluoride-loaded adsorbent. The adsorption is non-specific in nature as co-existing anion can reduce its fluoride removal capacity. The effect of the co-existing anions on adsorption of fluoride follows the trend PO₄³⁻ > CO₃²⁻ > SO₄²⁻ > Cl⁻. The adsorbent can be reused successfully for the 5th consecutive cycles of adsorption-desorption study. This study offers a very promising material for remediation of groundwater fluoride of affected areas.