Preferential adsorption of various anionic and cationic dyes from aqueous solution over ternary CuMgAl layered double hydroxide

To investigate the effect of Cu on structural and adsorption properties of CuMgAl LDH towards the efficient removal of organic dye contaminants from aqueous solution, a series of CuMgAl LDHs with different molar ratio of Cu/Mg were synthesized via co-precipitation method. The synthesized materials were characterized by using various techniques such as powder X-ray diffraction (PXRD), Fourier transformed infrared (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), N-2 adsorption-desorption, transmission electron microscopy (TEM) and diffuse-reflectance UV-vis (UV-DRS) spectroscopy. The presence of Cu greatly enhanced the adsorption capacity of the adsorbents for efficient removal of organic dye pollutant from aqueous solution. The adsorption performance of the Cu-rich LDH was examined for preferential adsorption of various anionic and cationic dyes such as methyl orange, bromothymol blue, erichrome black-T, Congo red, methylene blue and rhodamine B from aqueous solution. The anionic dyes were adsorbed in higher amount over the ternary LDH compared to that of cationic dyes. The influence of various reaction parameters like contact time, adsorbent dosage, initial dye concentration and solution pH on adsorption process was studied thoroughly. The adsorption process was analyzed by using various isotherm models and the Langmuir isotherm model showed the best fitting to the isotherm data. The kinetics study showed that the adsorption process followed second order kinetic model. The successful interaction of dye with the adsorbent surface was studied by FTIR spectroscopy. The adsorbent was stable and active upto three successive cycles.