Enhanced fluoride remediation from aqueous solution by La-modified ZIF-8 hybrids

Abstract

To ensure water safety, fluoride elimination from aqueous environment is an urgent affair. In this study, a series of La-modified ZIF-8 (denoted as La-ZIF-8) hybrids with different contents of La were fabricated via a solvothermal reaction and used for fluoride recovery from wastewater. The structure and morphology of the fabricated La-ZIF-8 hybrid were confirmed by various techniques (SEM, XRD, BET, FTIR, and XPS). The specific surface area along with the pore volume of La-ZIF-8 hybrid was 121 m2 g−1 and 0.816 cm3 g−1, respectively. The defluoridation performance of La-ZIF-8 under different conditions was assessed by static batch trials. The optimized La-ZIF-8 with a La/Zn molar ratio of 4:1 achieved the supreme defluoridation performance. The fluoride uptake was greatly enhanced from 1.85 mg g−1 for pure ZIF-8–49.5 mg g−1 for La-ZIF-8 at C0 = 10 mg L−1. The results revealed that La-ZIF-8 had a maximal fluoride uptake of 224.72–230.95 mg g−1 at 30–50 °C, pH 4, and C0 = 80 mg L−1. Adsorption of fluoride on La-ZIF-8 obeyed to the Langmuir isotherm (R2 > 0.99) and pseudo-second order model (R2 > 0.999), reflecting a single-layer chemical adsorption process. ΔH0 (36.38 kJ mol−1) > 0, ΔS0 (155.36 J mol−1 K−1) > 0, and ΔG0 < 0 stated that the defluoridation by La-ZIF-8 is an endothermic nature, random state, highly feasible and spontaneous process. The co-existing of cations and anions effect inferred that Mg2+, Ca2+, SO42–, Cl–, and NO3– only had a trivial impact on fluoride removal performance, illustrating the high selectivity for F–. The La-ZIF-8 can be deemed to be a candidate adsorbent for tackling F− pollution.