β-Cyclodextrin modified hydrous zirconium oxide: Synthesis, characterization and defluoridation performance from aqueous solution

• Novel surface modified hydrous zirconium oxide with β cyclodextrin composite (CY-HZO) preparation.
• Significantly higher capacity of fluoride adsorption of CY-HZO than pristine HZO.
• Efficient, economical and eco-friendly fluoride remediation possible.
• Fluoride adsorption by CY-HZO via ion-exchange.
• About 95% reactivation of used CY-HZO is possible with 3 M NaOH.

Surface modified hydrous zirconium oxide (HZO) with β-cyclodextrin (β-CD) material (CY-HZO) was characterized as micro-structured (150 nm), predominantly amorphous with irregular and undulated surface morphology using analytical tools such as XRD, SEM, TEM, AFM,BET surface analysis etc. Too high surface site concentrations of CY-HZO (6300 nm−2) compared to pristine HZO (26 nm−2) is owing to the abundance of surface –OH groups afforded by β-CD, which plays a decisive role in enhancing fluoride adsorption power of HZO. Fluoride adsorption over CY-HZO shows a discernible rise up to a pH ∼ 5.0, and declines sharply at pH > 6.0. Kinetically pseudo second order type fluoride adsorption reactions with CY-HZO and HZO were isothermally Langmuir type but endothermic with CY-HZO and exothermic with HZO. But both were spontaneous (−ΔG0 = 1.78, 2.06 & 5.18 for CY-HZO and 3.14, 3.0 & 2.66 for HZO at T = 303, 318 and 333 K). Langmuir capacity (qm, mg g−1) of CY-HZO (31.45) is significantly higher than HZO (22.45) at 303 K. About 95% of the adsorbed fluoride could be released from CY-HZO surface by 3.0 M NaOH solution. Thus, CY-HZO should be a more potent material than HZO for fluoride removal from aqueous media.