Novel nanoporous polyvinyl alcohol (PVA) hydrogel beads impregnated with zirconium (PZH), zirconium-iron (PFZH) and zirconium-copper (PCZH) were obtained by one-pot synthesis. These beads exhibited a pH-independent and highly selective fluoride removal efficiency of ~98% from 10 mg/L fluoride solution. Moreover, there is negligible interference to fluoride removal by frequently competing ions like HCO3−, PO43− and SO42−. SEM micrographs and BET studies established the porous morphology whereas EDS confirmed the presence of fluoride post adsorption. The change in glass transition temperature, enthalpy of fusion and degree of crystallinity of the hydrogels before and after fluoride adsorption was calculated using DSC thermograms. The average crystallite size estimated from XRD diffractograms, increased after fluoride adsorption and TGA analysis asserted that metal ion content in the hydrogel is about 11-14 %. The data obtained from XRD, DSC, Raman and FT-IR aided in establishing the mechanism of fluoride adsorption by the hydrogel beads. The equilibrium adsorption data fit well in Langmuir, Freundlich, Temkin, D-R adsorption model at 25 °C, 35 °C, 45 °C and maximum Langmuir adsorption capacity for hydrogel beads is 136.37 mg/g for PZH, 130.21 mg/g for PCZH, and 74.96 mg/g for PFZH at room temperature. . Moreover, the hydrogel beads exhibited excellent regenerability and had ~97% fluoride removal efficiency even after the 10th regeneration cycle. The hydrogels reduced the fluoride concentration below 0.2 mg/L in real-time water samples and the ICP-MS analysis showed an insignificant amount of zirconium, iron and copper in treated water. Fixed bed column adsorption studies are conducted with metal complexed polyvinyl alcohol (PVA) hydrogel beads to remove fluoride from groundwater. The fixed bed column (bed height = 8 cm) of copper-zirconium-PVA (PCZH), zirconium-PVA (PZH) and iron-zirconium (PFZH) hydrogel beads have 74%, 58% and 61 % fluoride removal efficiency from a 10 mg L−1 fluoride solution maintained at a flow rate of 0.5 mL/min at pH 6.5. Additionally, the hydrogel beads are used for the removal of arsenate and chromate ions. The percentage arsenate removal is PFZH (90 %)&gt; PCZH (88 %)&gt; PZH (77 %) from 100 mg L−1 solution. About 96 %, 74 % and 90 % of chromate is removed from 100 mg L−1 of chromate solution by PZH, PFZH and PCZH respectively. Therefore, the hydrogel beads could be used as potent filters for removal of these contaminants.

Self-assembled metal ion incorporated poly vinyl alcohol hydrogel beads for fluoride removal from groundwater

ACS Spring 2022

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