Efficient Fluoride Removal from Aqueous Solution Using Zirconium-Based Composite Nanofiber Membranes

Abstract

Herein, composite nanofiber membranes (CNMs) derived from UiO-66 and UiO-66-NH2 Zr-metal-organic frameworks (MOFs) were successfully prepared, and they exhibited high performance in adsorptive fluoride removal from aqueous media. The resultant CNMs were confirmed using different techniques, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Brunauer–Emmett–Teller (BET) in addition to Fourier-transform infrared spectroscopy (FTIR). The parameters that govern the fluoride adsorption were evaluated, including adsorbent dose, contact time, and pH value, in addition to initial concentration. The crystalline structures of CNMs exhibited high hydrothermal stability and remained intact after fluoride adsorption. It could also be observed that the adsorbent dose has a significant effect on fluoride removal at high alkaline values. The results show that UiO-66-NH2 CNM exhibited high fluoride removal due to electrostatic interactions that strongly existed between F− and metal sites in MOF in addition to hydrogen bonds formed with MOF amino groups. The fluoride removal efficiency reached 95% under optimal conditions of 20 mg L−1, pH of 8, and 40% adsorbent dose at 60 min. The results revealed that UiO-66-NH2 CNM possesses a high maximum adsorption capacity (95 mg L−1) over UiO-66 CNM (75 mg L−1), which exhibited better fitting with the pseudo-second-order model. Moreover, when the initial fluoride concentration increased from 20 to 100 mg/L, fluoride adsorption decreased by 57% (UiO-66 CNM) and 30% (UiO-66-NH2 CNM) after 60 min. After three cycles, CNM revealed the regeneration ability, demonstrating that UiO-66-NH2 CNMs are auspicious adsorbents for fluoride from an aqueous medium.

A Mini Review of Recent Findings in Cellulose-, Polymer- and Graphene-Based Membranes for Fluoride Removal from Drinking Water

“…The use of zirconium for the modification of membranes was studied very recently by Mohamed et al [16], according to whose research, composite nanofiber membranes (CNMs) were modified by using zirconium based on UiO-66 and its amino version (UiO-66-NH 2 ) powders, resulting in UiO-66-NH 2 CNM membranes. According to the results of this study, high fluoride removal occurred owing to both electrostatic interactions between the fluoride ions and the metal sites in MOF and the hydrogen bonds formed with MOF amino groups, with an adsorption capacity of 95 mg g −1 at pH 8.…”

“…Another method, The aforementioned information demonstrates that the problem of the occurrence of fluoride ions in natural waters is of major importance. It is for this reason that various technologies have been developed to decrease fluoride concentration from waters, such as adsorption [13], coagulation [1], precipitation [14] and membrane separations [15,16], in order to render the treated water potable. Table 1 summarizes the commonly applied defluoridation techniques and their main advantages and disadvantages.…”

Fluoride Removal from Water Sources by Adsorption on MOFs

“…Several treatment methods, such as precipitation [7][8][9], reverse osmosis [10], membrane separation [11][12][13], coagulation [14], etc., are commonly used to remove fluoride anions from water. However, the disadvantages of these technologies are that they have high costs and require expensive operational and labor costs and advanced technologies.…”