Adsorptive removal of congo red from aqueous solution by sonochemically synthesized NiAl layered double hydroxide

Abstract

NiAl layered double hydroxides (LDHs) were synthesized using sonochemical method by keeping the molar ratio of Ni/Al=3. The synthesized materials were characterized through various analytical techniques like powder X–ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) surface area analyzer. The LDH materials were employed as adsorbents towards the adsorptive removal of congo red (CR) from aqueous solution. The adsorption experiments were carried out in batch mode and optimization of various factors such as contact time, adsorbent amount, initial dye concentration, solution pH and temperature were studied thoroughly. NiAl LDH synthesized with ultrasound irradiation for 1h, NiAl-S1 exhibited the highest dye removal efficiency with monolayer adsorption capacity, qm of 120.5mg/g at 25°C and pH 6. The Langmuir isotherm model showed best fitting to the adsorption data and the adsorption process followed pseudo-second order kinetics. The interaction of the dye molecules to the LDH surface was further confirmed by the FTIR study. The adsorption mechanism was associated with the H-bonding and electrostatic attraction between the anionic CR dye and LDH surface. The reusability test of the material showed that the regenerated material could reuse upto three successful cycles showing stability of the adsorbent.