Comparative study of removal of reactive dye by LDHs: The effect of cation variety

Three types of layered double hydroxides (LDHs) including Mg-Fe, Mg-Al-Fe, and Mg-Zn-Al-Fe were synthesized by the coprecipitation method. Nanoparticles of the LDH adsorbents were characterized by X-ray powder diffraction (PXRD), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and specific surface area measurement. The size and morphology of nanoparticles were inspected by scanning electron microscopy (SEM). The comparative study was performed to evaluate the effect of cation variety on removal of C.I. Reactive Red 43 dye. Adsorption capacity of LDHs was obtained as: 279.23, 210.4, 150.03 mg/g for 4, 3, and 2 cationic LDH respectively. Batch adsorption experiments were carried out at room temperature (25°C) under various conditions such as contact time, solution pH, and dye concentration (20–60-100 mg/L). Results revealed that adsorption rate increases with increase in contact time as long as equilibration is established and decreases as dye concentration increases. The effect of solution pH was investigated and urban water pH without adjustment was selected as the operational pH. It was found that the adsorption capacity of LDH containing four cations (Mg-Zn-Al-Fe) is higher than that of others which can be attributed to the highest degree of crystallinity and the highest total pore volume (0.059 cm3/g) of this LDH. The kinetic and isotherm studies were performed on four cationic LDH and the results show that adsorption of dye onto LDH fits to the Freundlich equation as well, which confirms multilayer adsorption. Moreover, the regeneration study indicates that the prepared LDH could be used for several cycles. © 2016 American Institute of Chemical Engineers Environ Prog, 2016