Alginate assisted montmorillonite clay beads for malachite green adsorption: kinetics and mechanisms

In present study, a low-cost alginate assisted nickel oxide modified montmorillonite (Alg@NiO-Mt) or montmorillonite (Alg@Na-Mt) composite beads were prepared and utilized for the removal of malachite green (MG) cationic dye in batch mode adsorption. The prepared beads were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis/differential thermogravimetric analysis (TGA/DTG). Alg@NiO-Mt and Alg@Na-Mt beads achieved a complete removal of MG after 60 min and 90 min for a concentration of 100 mg L⁻¹ at an optimal mass of beads (1 g), natural pH of solution (3.8) and ambient temperature (25 ± 1 °C). Adsorption isotherm results showed that the Freundlich model fitted well for the adsorption of MG onto Alg@NiO-Mt and Alg@Na-Mt beads. Kinetic and thermodynamic studies also indicated that the MG adsorption were found to be well fitted with a pseudo-second order kinetic model, endothermic and spontaneous in nature. In addition, the Alg@NiO-Mt and Alg@Na-Mt beads showed excellent reusability for removal of MG after seven adsorption cycles. The adsorption of MG onto the beads is facilitated by multiple mechanisms, including electrostatic interactions, Yoshida H-bonding, dipole–dipole H-bonding, n–π interactions, and π–π interactions. Overall, the obtained results suggest that Alg@NiO-Mt and Alg@Na-Mt beads could be considered as a low-cost and eco-friendly adsorbent for MG removal from aquatic media.