Self-assembled cylindrical Zr (IV), Fe (III) and Cu (II) impregnated polyvinyl alcohol-based hydrogel beads for real-time application in fluoride removal

Novel nanoporous hydrogel beads were obtained by one-pot synthesis, by cross-linking polyvinyl alcohol with glutaraldehyde and metal ions like zirconium, iron, and copper. These cylindrical beads had a porous morphology with the metal ion content of 11-14%. The beads exhibited a pH-independent, highly selective fluoride removal efficiency of similar to 98% in simulated 10 mg L-1 fluoride solution, with negligible interference from HCO3-, PO43- and SO42-. Electrostatic interaction, hydrogen bonding and pore diffusion governed the mechanism of adsorption as ascertained by X-ray diffraction, differential scanning calorimetry, Raman and Fourier transform-infrared spectroscopy. The adsorption data fitted well in the Langmuir adsorption isotherm and predominantly obeyed pseudo-second-order kinetics accompanied by intra-particle diffusion. The maximum Langmuir adsorption capacity of hydrogel beads was 136.37 mg g(-1), 130.21 mg g(-1) and 74.96 mg g(-1) for PVA-zirconium, PVA-copper-zirconium, and PVA-iron-zirconium respectively. The adsorption process was exothermic and spontaneous with Delta G degrees ranging from similar to 37.0 kJ mol(-1) to similar to 52.0 kJ mol(-1). The hydrogel beads had an excellent regenerability with similar to 97% fluoride removal efficiency even after 10th adsorption-desorption cycle. The hydrogel beads reduced the fluoride concentration below 0.2 mg L-1 in the groundwater samples, making them promising adsorbents for real-time application in fluoride endemic regions.

Automated summary

Novel nanoporous hydrogel beads were synthesized by one-pot method, showing highly selective fluoride removal efficiency and regenerability in groundwater. The beads had a porous morphology with metal ion content and exhibited excellent adsorption capacity, fitting well in Langmuir adsorption isotherm and pseudo-second-order kinetics. The adsorption process was exothermic and spontaneous, making the hydrogel beads promising adsorbents for real-time application in fluoride endemic regions.