Multi-hydroxyl containing organo-vermiculites for enhanced adsorption of coexisting methyl blue and Pb(II) and their adsorption mechanisms

To address the competitive adsorption of complex wastewater components on organo-vermiculites (organo-Vts), multi-hydroxy containing gemini surfactants varying in alkyl chain length (G(12), G(14) and G(16)) are designed and applied for modifying Na-vermiculite (Na-Vt) targeted to the removal of co-existing MB and Pb(II). Organo-Vts exhibit enhanced hydrophobicity and enlarged interlayer spacing compared with Na-Vt, with the saturated modifier dosage reaching as low as 0.4 CEC of Na-Vt. Shorter alkyl chain induces suitable packing density and interlayer environment, endowing G(12)-Vt the highest adsorption capacity towards MB/Pb(II) compared with G(14)-Vt and G(16)-Vt (178.3/63.0 mg/g compared with 143.7/38.1 and 88.6/36.6 mg/g, respectively). Freundlich isotherm and PSO kinetic model are agreeable (the values of R-2 are higher than 0.98) with the endothermic adsorption processes. Notably, a simultaneous effect in binary-component system is obtained, and the maximum adsorption capacities of G(12)-Vt towards MB/Pb(II) reaching 349.9 and 124.5 mg/g, which are 1.96 and 1.95 times higher than single-component system, respectively. Combination of theoretical fitting and molecular simulation co-reveals the adsorption mechanism: the simultaneous effect is due to the providing of additional active sites by the adsorbed MB, which is stronger than that between Pb(II) and the modifier. Existence of pi-ion interaction enhances the retention of Pb(II) for a further step. This work broadens a new research perspective for complex wastewater treatment and provides a deep understanding of the stimulative adsorption mechanism between dyes and metal ions.