Synthesis of Li–Al Layered Double Hydroxides (LDHs) for Efficient Fluoride Removal

Abstract

A novel adsorbent of Li−Al layered double hydroxides (LDHs) was prepared through the precipitation of metal nitrates and further applied to remove excessive fluoride ions from water. The physical and chemical properties of synthesized materials were examined by powder transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, N 2 adsorption/ desorption analysis, and thermogravimetric analysis (TGA). The TEM results indicated that the materials synthesized via coprecipitation present a preferential orientation of the nanoscale LDH platelets. The XRD analysis confirmed that the synthesized products have a highly crystalline nature and a well-ordered layer structure. The high specific surface areas (37.24− 51.27 m 2 /g) of calcined products were demonstrated to be beneficial for the adsorption of fluoride. For the adsorption experiment, the effects of the adsorption conditions including pH, coanions and adsorbent dose were investigated at initial fluoride concentration of 20 mg/L. The kinetics and isotherms of fluoride adsorption by calcined Li−Al LDHs were studied. The results indicated that the Li−Al LDHs can be effectively used to remove fluoride from water, where the maximum percentage removal (97.36%) could be reached and the adsorption equilibrium could be attained within 1 h. The kinetic data were well-fitted to the pseudo-second-order model, while the Freundlich isotherm model provided the better correlation of the equilibrium data. Based on FT-IR and kinetic analysis, the "memory effect" may play an important role in the early adsorption stage, while the ionexchange process may control the adsorption rate at the second adsorption stage. Since the Li−Al LDHs show excellent fluoride removal efficiency, they are expected to separate fluoride from water in pollution control.

Effect of Non-Thermal Plasma Modified NiAl Layered Double Hydroxides on the Removal of Fluoride from Aqueous Solution

“…The divalent and trivalent anions have more effect than monovalent anions on adsorption capacity, similar results were observed in the literature for fluoride adsorption by Li/Al-LDHs [31]. This may be due to a high negative charge density of ions which were easily absorbed by the PO − ion appears to display a maximum interference for F − ion.…”

Novel paper‐templated fabrication of hierarchically porous Ni–Al layered double hydroxides/Al2O3 for efficient BSA separation

“…The percentage desorption of BSA increased with increasing desorption time. Compared with the adsorption process, the BSA desorption process was relatively fast and desorption equilibrium was attained after 2 h. The equilibrium times of desorption were approaching the equilibrium times of fluoride adsorption onto LDH materials, as previously reported . It is indicated that the BSA desorption rates were determined by interactions between anions and the surface of composites.…”

“…Layered double hydroxides (LDHs) are a family of lamellar compounds containing exchangeable anions in the interlayer space, and have the strong intralayer bonds and weak interlayer interactions . As a natural clay mineral, they are widely used in the fields of bioseparation, catalysis, pollution control, and biomedicine . Due to the metal hydroxide layer having positive surplus charges, a large number of guest anions can be inserted into the interlayer space of LDHs through electrostatic interactions.…”

Excellent fluoride decontamination and antibacterial efficacy of Fe–Ca–Zr hybrid metal oxide nanomaterial

“…The increase in pH above 7 declined the percentage fluoride removal. This can be attributed to the change of the adsorbent surface charge as can be illustrated by the help of point of zero charge (pHpzc) [41]. The point of zero charge is the most significant factor utilized to illustrate variable charge surfaces in phenomenon of adsorption.…”