Adsorption of malachite green on the modified montmorillonite/xanthan gum-sodium alginate hybrid nanocomposite

In this study, montmorillonite (MMT)/xanthan gum (XG)-sodium alginate (Alg) hybrid hydrogel nanocomposite has been synthesized for adsorption of malachite green (MG) from aqueous solution. The MMT nanoparticles were modified by cetyltrimethylammonium bromide (CTAB), with specific fraction of the critical micelle concentration (CMC) of CTAB, and applied to synthesize MMT(0.5CMC)/XG-Alg, MMT(1CMC)/XG-Alg and MMT(2CMC)/XG-Alg, and unmodified MMT nanoparticles were applied to synthesis MMT/XG-Alg as control adsorbent. BET, FTIR and SEM analyses were conducted, in order to identify the structure and morphologies of hybrid nanocomposites. The results of FTIR, showed that the functional groups of carboxylates and hydroxyl in the structure of the nanocomposite play an important role in the adsorption process. According to SEM analysis, the unevenness on the adsorbents surface has disappeared, due to the adsorption of the MG dye. Also, by the surface modification of MMT nanoparticles using CTAB, the MMT(0.5CMC)/XG-Alg specific surface area increased from 6.38 to 72.48 m 2 /g, compared to MMT/XG-Alg. Maximum adsorption capacity was occurred in pH = 6, temperature 318 K, contact time 240 min and 0.02 g/50 mL of the hybrid nanocomposites. According to the results, adsorption process was fitted on the Langmuir isotherm model, with maximum adsorption capacity of 769.23 mg/g for the MMT(0.5CMC)/XG-Alg as the best adsorbent, and 476.19, 666.66 and 588.23 mg/g for the MMT/XG-Alg, MMT(1CMC)/XG-Alg and MMT(2CMC)/XG-Alg, respectively. Adsorption kinetics is well described by the pseudo-second order. The thermodynamic parameters, the enthalpy (∆ H °) and Gibbs-free-energy (∆ G °), indicated that sorption process was endothermic and spontaneous, respectively.