Series of bis-morpholinium-based organo-Vts for the removal of anionic dyes

Organo-vermiculites (organo-Vts) functionalized by emerging bis-morpholinium gemini surfactants (CnMor(+)-4-Mor(+)Cn 2Br(-), n = 8, 12, 16, corresponding to BMOB, BMDB and BMHB, respectively) are prepared and used for disposing the dyeing wastewater for the first time. Several characterization methods are employed for exploring the structure and wettability of the organo-Vts. The results show that the modifiers have been loaded onto the vermiculite (Vt) successfully with the paraffin type arrangements, enhancing the hydrophobicity of organo-Vts. The adsorption of methyl orange/acid green 25 (MO/AG25) on BMOB-Vt, BMDB-Vt and BMHB-Vt reaches experimental maximum adsorption capacity of 108.68/67.38, 159.11/135.40 and 206.65/161.13 mg/g within 120 min at 25 degrees C, respectively. The adsorption of MO and AG25 is better fitted by pseudo-second-order kinetic, Freundlich and Langmuir models. As the results of thermodynamics, the adsorption processes of MO/AG25 on organo-Vts are exothermic and spontaneous, except for that of AG25 on BMOB-Vt showing an endothermic process. It is noteworthy that the more the hydrophobicity of adsorbent, the smaller the structure of dyes, the greater the adsorption capacities of organo-Vts. Combining with the results of adsorption and characterizations, it can be confirmed that: (i) the hydrophobic interaction works as the mainly driven force in adsorption of MO/AG25; (ii) the pi-pi stacking takes part into the adsorption of MO due to its smaller molecular structure; (iii) the electrostatic interaction takes a synergistic effect. In binary-dyes system, MO and AG25 show a competitive adsorption on organo-Vts, and MO is less affected than AG25. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the use of organo-vermiculites functionalized by bis-morpholinium gemini surfactants for the treatment of dyeing wastewater. The results show successful loading of modifiers onto the vermiculite surface, enhancing its hydrophobicity. The organo-vermiculites exhibit higher adsorption capacities for methyl orange/acid green 25, and the adsorption processes are well described by pseudo-second-order kinetic, Freundlich, and Langmuir models. Hydrophobic interaction is identified as the main driving force for adsorption, with pi-pi stacking and electrostatic interaction playing supporting roles.