Kinetic, isotherm, and thermodynamic studies of the removal of methyl orange by synthetic clays prepared using urea or coprecipitation

In this study, Mg/Al layered double hydroxides (LDHs) with a molar ratio (Mg2+/Al3+) of 3 that were intercalated with carbonate ions were synthesized using either urea or coprecipitation. These hydroxides were used as adsorbents to remove methyl orange (MO) from aqueous solution. The adsorbents were characterized by two analytical techniques: scanning electron microscopy (SEM) and infrared spectroscopy (FTIR). The conditions applied in the adsorption experiments including pH, initial MO concentration, contact time, adsorbent dosage, ionic strength, and temperature—were varied. A pseudo-second-order model was found to most accurately reflect the adsorption kinetics of MO on the surfaces of LDH-Urea (layered double hydroxide prepared using urea) and LDH-Cop (layered double hydroxide prepared using coprecipitation). The maximum adsorption capacities of LDH-Urea and LDH-Cop, as calculated using the Langmuir isotherm, were 625 and 526.31 mg g−1, respectively, and the adsorption process was exothermic. The results of this study indicate that LDH-Urea and LDH-Cop are effective adsorbents for removing anionic dyes from industrial wastewater.