Development of a New Inorganic-Organic Hybrid Ion-Exchanger of Zirconium(IV)-Propanolamine for Efficient Removal of Fluoride from Drinking Water

This investigation reports the synthesis of a new adsorbent material (ZrPA), from Zr(IV) and propanolamine (PA), synthesized by sol-gel technique at room temperature following the green chemistry principle. The suitability of ZrPA as a potential adsorbent is assessed for the removal of fluoride following the batch mode of operation. The isotherm, kinetics, and thermodynamics of fluoride adsorption on ZrPA have been studied at various experimental conditions (initial fluoride concentration, adsorption time, adsorbent dose, and temperature). The characteristic of the adsorbent, before and after fluoride adsorption, was examined using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), coupled with energy dispersive spectrum (EDS) techniques. Further measurement of surface area, pore volume, and pore diameter using N-2 intrusion automated gas sorption system shows the microporous nature of the prepared material. Adsorption of fluoride was found to be strongly affected by pH. Mathematically, pseudosecond-order kinetic model was found to best describe the reaction rate, which was consistent with the actual measurement. Applications of Freundlich, Langmuir, Temkin, and Dubinin-Radushkevich (D-R) isotherm models for the adsorption process were evaluated, and the data were also compared for six different error functions, that is, the sum of the squares of errors (SSE), sum of the absolute errors (SAE), the average relative error (ARE), the hybrid fractional error function (HYBRID), the Marquardt's percent standard deviation (MPSD), and regression coefficient (R-2), to test the adequacy and accuracy of the model equations. Thermodynamic parameters such as enthalpy, entropy, and free energy were calculated using van't Hoff equations, which shows that fluoride adsorption on ZrPA indicates the spontaneous and endothermic nature of adsorption. The reusability of the ZrPA adsorbent material was tested up to 10 consecutive cycles for a sustainable commercial application purpose. Quantitative desorption of fluoride from ZrPA was found to be more than 95% at pH 12. To test the efficacy, the performance of the adsorbent material was studied with water samples collected from a fluorosis endemic region.