Removal of Naphthol Green B from Aqueous Solution by Calcined Layered Double Hydroxides: Adsorption Property and Mechanism Studies

The adsorption of naphthol green B (NGB) by Mg/Al-LDO (layered double oxides) with a Mg/Al molar ratio of 3 : 1 was investigated in a batch mode. Our study indicates that the maximum capacity of NGB adsorption at equilibrium is 193.4 mg and the percentage of absorption is 96.7%, with an adsorbent dose of 1.0 g/L under the following condition: 200 mg/L NGB concentration, temperature 298 K pH 10.0 and an equilibrium time of 80 min. Langmuir and Freundlich adsorption models were used for fitting the isotherms, and the thermodynamic parameters have been calculated, which showed that the adsorption process was spontaneous and exothermic in nature. In the light of so called memory effect, the Mg/Al-LDO was found to recover their original layered structure after adsorption, and part of NGB ions intercalated into the interlayer of LDH (layered double hydroxides), which has been supported by XRD and FTIR. In addition, the competitive anions for adsorption and the regeneration of Mg/Al-LDO have also been investigated.