Enhanced adsorption of perchlorate by gemini surfactant-modified montmorillonite: Synthesis, characterization and their adsorption mechanism

Organo-montmorillonites (OMt) adsorb perchlorate (ClO4-) through anion exchange mechanism. Each gemini surfactant (GC(n)) provides two anion exchangeable sites due to its unique molecular structure. Due to the presence of more anion exchangeable sites, the preparation of OMt with GC(n) enables the possibility for higher amount of ClO4- uptake than their single-chain counterparts. In this work, gemini surfactant modified montmorillonites (GC(n)-Mt) were synthesized using three different alkyl chain length containing gemini surfactants (CnH2n+1(Me)(2)-C6H12-CnH2n+1(Me)(2)center dot 2Cl), where n varied to 12, 14 and 16 and were examined in detail for the adsorption of ClO4- from aqueous solution. The structure of the GC(n)-Mt before and after adsorption of ClO4- was characterized by an array of techniques such as powder XRD, FT-IR, XPS, TGA and CHN analysis. The adsorption of ClO4- onto the GC(n)-Mt was best described by the Langmuir adsorption isotherm and pseudo second-order kinetic model. The GC(16)-Mt showed the highest removal capacity of 1.08 mmol/g and at a rapid rate, achieving 95% within 1 min, with an equilibrium time of 15 mins. The GC(16)-Mt retained its high removal capacity and selectivity in presence of a variety of coexisting anions such as HCO3-, NO3-, CO32-, SO42- SiO32-, and H2PO4-, and at a wide pH range (2-12). Combining the high removal capacity and selectivity with fast kinetics, the GC(n)-Mt has great potential for ClO4- removal from aqueous solutions.