Characteristic and adsorption properties of zirconia aerogel and xerogel nanostructure application to fluoride removal from drinking water of Tunisian south region

The present investigation reports the effect of the solvent evacuation mode in the preparation step of zirconia adsorbent, in removal adsorption fluoride from tap water in southern Tunisia. Aerogels and xerogels zirconia were prepared in one-step by the sol-gel method. Aerogels are obtained by drying under supercritical conditions of solvent while xerogel are obtained by ordinary drying in an oven. The characteristic properties of those solids were investigated using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Rietveld refinement of XRD patterns, N-2 physisorption (BET), scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. Experimental parameters such as adsorbent dose, contact time, initial fluoride concentration and pH value were investigated. Crystallite size showed by Rietveld refinement indicated that all crystalline xerogel and aerogel zirconia samples were of nano-crystalline nature with crystallite size in the range of 16-18 nm. Textural analysis, carried out by BET, reveals that all adsorbents are characterized by a developed mesoporous texture, high surface area and large porosity. FTIR spectra spectroscopy shows the important role of superficial hydroxyl groups in the defluorination process. The different obtained results confirmed that the efficiency of xerogel zirconia for the fluoride elimination is better than that of aerogel zirconia. The selected xerogel zirconia presents a high fluoride removal rate of about 100% in the wide pH range (2-7) with a low adsorbent dose (30 mg) and a lower equilibrium time of 25 min. Xerogel zirconia successfully reduce fluoride from natural water with a concentration of 3.83 mg L-1, to a value lower than the standard Tunisian set at 0.8 mg L-1, even in complex matrix.