Linker impact on the adsorption capacity of polyaspartate/montmorillonite composites towards methyl blue removal

•Preparation of Na+-Mt with poly(aspartate-co-succinimde) composite with two different linkers.•The adsorption of methyl blue dye from aqueous solution onto the two composites was investigated.•The equilibrium amount of adsorbed dye depends largely on the chemical composition of the linkers.•The adsorption process is physical, endothermic, and spontaneous.

In this work, the effect of linkers such as alkyl quaternary ammonium and alkyl quaternary phosphonium salts intercalated with Na+-montmorillonite (Na+-Mt) via cation exchange followed by the reaction with poly(aspartate-co-succinimide) as biodegradable and superabsorbent polymer has been investigated. The prepared composites were spectroscopically characterized by elemental analysis, X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TAG), and Brunauer-Emmett-Teller (BET) surface analyzer. Polyaspartate-montmorillonite composite with quaternary phosphonium salt (Mt/IPS2) exhibited higher surface area and pore volume compared with polyaspartate-montmorillonite composite with quaternary ammonium (Mt/IPS1), due to its bulky structure. Mt/IPS2 composite displays a maximum adsorption capacity of 9.95 mmol/g for methyl blue (MB) dye which is larger than Mt/IPS1 composite with 8.55 mmol/g. The kinetic data of adsorption were evaluated with pseudo first-order, pseudo second-order and intra-particle diffusion models. The equilibrium time of 20 min toward MB adsorption and the pseudo-second-order was the best fit model for adsorption process. The adsorption isotherm of MB on the IPS1 and IPS2 has been investigated at 25, 30, and 35 °C and the data were in good agreement with the Langmuir isotherm model. Furthermore, the thermodynamic parameters namely; Gibbs free energy change (ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) were calculated and the negative ΔG° values indicate the spontaneity of the process. The adsorption mechanism was studied by FT-IR and the electrostatic interaction between cationic active sites of adsorbent surface and anionic MB dye was proposed.

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