M-Al-SO4 layered double hydroxides (M=Zn, Mg or Ni): synthesis, characterization and textile dyes removal efficiency

Abstract

Mg–Al, Zn–Al, and Ni–Al layered double hydroxides (LDH) materials with molar ratio (M2+/Al3+) of 3 were synthesized via co-precipitation method. 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 sulfate anions in the structure of LDHs with the presence of carbonate impurity in the interlayer. TGA/DTA analysis indicates a better thermal stability of Zn–Al-SO4 vs. Ni–Al-SO4 and Mg–Al-SO4. The capability of the materials for textile dye removal was investigated using methyl orange (MO) as a model dye and an industrial textile effluent. Experimental results showed that pH is the most affecting factor in dye removal. The effective pH range for dye removal was between 3.5 and 5. The adsorption process can be well described by the pseudo-second-order kinetic model. The Langmuir model fit equilibrium data with exceptional maximum adsorption capacities for MO of 2,758, 1,622, and 800 mg/g, respectively, in the case of Zn–Al-SO4, Mg–Al-SO4, and Ni–Al-SO4. Color and chemical oxygen demand (COD) reduction from industrial textile effluent increased with the increase in the amount of LDHs. The optimum color and COD reduction were obtained by Zn–Al-SO4.