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.

Automated summary

Designed gemini surfactants were used to modify vermiculite for enhanced adsorption of complex wastewater components. Shorter alkyl chain length resulted in the highest adsorption capacity. The adsorption mechanism was revealed through theoretical fitting and molecular simulation.