Material Science and Engineering

Biography

Biography: Mahjoubi Fatima Zahra

Abstract

In recent decades, a class of anionic clays known as layered double hydroxides (LDHs) or hydrotalcite-like compounds has attracted considerable attention from both industries. The general formula for an LDH is [MII(1-x) MIIIx(OH)2] [An-x/n .mH2O], where MII represents a divalent metal and MIII represents a trivalent metal. An enormous variety of interlayer anions (An-) can be incorporated in LDHs such as CO32-, SO42-, NO3- or Cl-. From a structural viewpoint, the effect of divalent/trivalent cations and interlayer anionic composition may provide insights regarding the crystal chemistry of different LDHs types, which may ultimately govern their ability to adsorb organic pollutant. In this work, Mg-Al, Ni-Al and Zn-Al layered double hydroxide (LDH) materials with molar ratio (M2+/Al3+) of 3 were synthesized via a co-precipitation route. The as-synthesized samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and Simultaneous thermogravimetric-differential thermal analysis (TGA/DTA). XRD analyses showed that Zn-Al-SO4 had the greatest lattices parameters followed by Mg-Al-SO4 and Ni-Al-SO4. FTIR confirmed clearly the presence of sulfates anions in the structure of LDHs in the interlayer. Two major stages of mass loss occurred for all the samples with better thermal stability of Zn-Al-SO4 vs. Ni-Al-SO4 and Mg-Al-SO4. The capability of LDHs for dye removal from aqueous solutions was investigated using methyl orange as a model and industrial textile effluent. The “batch” method for evaluating the adsorption of methyl orange dye into synthesized LDHs was investigated under various conditions such as solution pH, contact time and initial dye concentration. Experimental results showed that pH is the most affecting factor in the adsorbent. The effective pH range for dye removal was between 3.5 and 4.5. The adsorption process can be well described by the pseudo-second-order kinetic model. The equilibrium adsorption data were analyzed using three isotherm models: Langmuir, Freundlich and Dubinin-Radushkevich. The results showed that Langmuir model fit with exceptional maximum adsorption capacities of 2758, 1622 and 800 mg/g, respectively, for Zn-Al-SO4, Mg-Al-SO4 and Ni-Al-SO4.