Zn-Al Layered Double Hydroxides Synthesized on Aluminum Foams for Fluoride Removal from Water

Fluoride excess in water represents an environmental issue and a risk for human healthsince it can cause several diseases, such as fluorosis, osteoporosis, and damage of the nervous system.Layered double hydroxides (LDHs) can be exploited to remove this contaminant from water bytaking advantage of their high ion-exchange capability. LDHs are generally mixed with pollutedwater in the form of powders, which then cause the problem of uneasy separation of the contaminatedLDH sludge from the purified liquid. In this work, Zn-Al LDH films were directly grown in situ onaluminum foams that acted both as the reactant and substrate. This method enabled the removal offluoride ions by simple immersion, with ensuing withdrawal of the foam from the de-contaminatedwater. Different LDH synthesis methods and aluminum foam types were investigated to improve theadsorption process. The contact time, initial fluoride concentration, adsorbent dosage, and pH werestudied as the parameters that affect the fluoride adsorption capacity and efficiency. The highestabsorption efficiency of approximately 70% was obtained by using two separate growth methodsafter four hours, and it effectively reduced the fluoride concentration from 3 mg/L to 1.1 mg/L,which is below the threshold value set by WHO for drinking water.