Agglomerated nanoparticles of hydrous Ce(IV)+Zr(IV) mixed oxide: Preparation, characterization and physicochemical aspects on fluoride adsorption

Abstract

Abstract Hydrous Ce(IV)–Zr(IV) oxide (Ce/Zr ∼ 1:1, mol/mol) (HCZMO) prepared by simple chemical precipitation was nanoparticles (60–70 nm) agglomerate with irregular surface morphology. The BET surface area, pore volume and pH zpc were estimated to be 185.04 m 2 g −1 , 0.1219 cm 3 g −1 and 5.8 (±0.2), respectively. Investigation of fluoride adsorption over HCZMO from its aqueous phase at an optimized pH ∼ 6.0 showed that the adsorption kinetics and equilibrium data described, respectively, the pseudo-second order equation ( R 2 = 0.98–0.99) and the Langmuir isotherm ( R 2 > 0.99) very well. Values of the computed Arrhenius activation energy, E a (1.16 kJ mol −1 ), Langmuir monolayer capacity, θ (19.5 mg g −1 ), D–R adsorption energy, E D–R (15.05 kJ mol −1 ) and isosteric heat of reaction, Δ H r (0.518 kJ mol −1 ) suggested that the fluoride has high affinity for homogeneous HCZMO surface for adsorption. Evidences appeared from the equal distribution co-efficient values and too well Langmuir isotherm fit. The fluoride adsorption reactions at 298–313 K with HCZMO were spontaneous (Δ G 0 = negative) despite endothermic nature (Δ H 0 , kJ mol −1 = +3.53, +4.04), owing to the increase of entropy (Δ S 0 , J mol −1 K −1 = +12.4, 13.8). More than 95% fluoride was released from F − HCZMO (24.8 mg F − g −1 ) by 1.0 M NaOH, confirming the ion-exchange adsorption mechanism inclining to chemisorption. 1 g HCZMO per liter of a groundwater (F − : 4.40 mg L −1 ) can reduce fluoride level below 1.5 mg L −1 in batch treatment.