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

Abstract

Surface modified hydrous zirconium oxide (HZO) with β-cyclodextrin (β-CD) material (CY-HZO) was characterized as micro-structured (150nm), 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 (6300nm−2) compared to pristine HZO (26nm−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 333K). Langmuir capacity (qm, mgg−1) of CY-HZO (31.45) is significantly higher than HZO (22.45) at 303K. About 95% of the adsorbed fluoride could be released from CY-HZO surface by 3.0M NaOH solution. Thus, CY-HZO should be a more potent material than HZO for fluoride removal from aqueous media.