Comparative study of organo-vermiculite, organo-montmorillonite and organo-silica nanosheets functionalized by an ether-spacer-containing Gemini surfactant: Congo red adsorption and wettability

Clay minerals (vermiculite, montmorillonite and silica nanosheets) with diminishing layer charge were modified by a novel Gemini surfactant, 2,2'-bis(dodecyldimethylammonio)-ethyl ether dichloride (BDEE) for the first time. The resultant products were certified by FT-IR, Elemental analysis (EA), TG, SEM and XRD, which indicated that the BDEE in vermiculite (Vt), montmorillonite (Mt) and silica nanosheets (SiNSs) adopted different arrangements. Adsorption capacities as a function of contact time, concentration of the Congo red (CR) and temperature were explored in detail. The results showed that the saturated sorption amount of BDEE-Vt, BDEE-Mt and BDEE-SiNSs up to 298, 154 and 64 mg g(-1) at 55 degrees C within 120 min, respectively. Interestingly, the order of adsorption capacities of these organo-clays were agreed with the sequences of the layer charge and the hydrophobicity of particles characterized by Lipophilic to Hydrophilic Ratio (LHR), which further proved the importance of hydrophobic interaction to CR adsorption onto organo-clays. The pseudo-second-order and Redlich-Peterson models were more suitable for the adsorption data of each adsorbent. Thermodynamic parameters showed that the processes of absorbed CR on BDEE-Vt and BDEE-Mt were endothermic and spontaneous, while BDEE-SiNSs was endothermic and non-spontaneous converted to spontaneous with temperature increasing. This work provides theoretical guidance for further design of highly efficient modifiers and high-performance organo-clay adsorbents.