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

Abstract

• Novel bis -morpholinium-based organo-Vts are prepared for removing MO and AG25. • The sequence of removal of MO/AG25 is BMHB-Vt > BMDB-Vt > BMOB-Vt. • Selective adsorption of MO and AG25 on bis -morpholinium-based organo-Vts is clarified. • The preferable adsorption of MO is revealed by the structure-adsorptive capacity relationship. Organo-vermiculites (organo-Vts) functionalized by emerging bis -morpholinium gemini surfactants (C n Mor + -4-Mor + C n 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 °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 π-π 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.