The enhanced adsorption of layered double hydroxides modification from single to ternary metal for fluoride by TEA-assisted hydrothermal method

Layered double hydroxides (LDHs) have attracted increasing attention as promising candidates by anion exchanges and selective adsorption in the fluoride treatment field. In this study, three new ternary Zn-Co-Cr-LDHs were synthesized by primarily a one-step TEA-assisted hydrothermal process at various times. They were characterized by X-ray powder diffraction, thermogravimetric analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, N2 gas adsorption and desorption curves and zeta potential. The effects of dosage amount, reaction duration, initial solution pH, temperature, and co-existing ions were evaluated systematically for the Zn-Co-Cr-LDHs in fluoride removal process. Compared to Zn-LDHs and Zn-Co-LDHs, three Zn-Co-Cr-LDHs showed excellent adsorption performance for F- with maximum adsorption amounts of 108.87 mg/g, 97.27 mg/ g, and 97.62 mg/g, respectively. The coexisting anions have less effect on the adsorption of F-. The introduction Cr3+ ion modulation in the Zn-Co-LDHs greatly improved the adsorption of fluoride ions. The kinetic process of fluoride ion adsorption is in accordance with the quasi-secondary kinetic model and the Elovich model, and the adsorption isotherm is in accordance with the Langmuir model. The quasi-secondary kinetic and Elovich models suggest that the process is chemisorption-controlled ion exchange adsorption. Zn-Co-Cr-LDHs are expected to have potential applications in fluoride removal process.