Nanohybrid materials from interlayer functionalization of kaolinite. Application to the electrochemical preconcentration of cyanide

A novel nanohybrid material was prepared by functionalization of the interlayer space of kaolinite, using kaolinite intercalated with dimethylsulfoxide as starting material. The method consisted, in a first step, to graft covalently triethanolamine on the interlayer aluminol surfaces of kaolinite by the formation of Al–O–C bonds. The grafted material was then further reacted by alkylation of the tertiary amino group with an alkyl halide, namely iodomethane (CH3I), to form a positively charged organo-inorganic layered material, in which the charge is balanced by the halide located in the interlayer space. This functionalized nanohybrid material was fully characterized by several physicochemical techniques including X-ray diffraction (XRD), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR) and solid-state nuclear magnetic resonance (13C and 29Si CP/MAS). Since this new material should have ion-exchange properties, it was evaluated for its efficiency as electrode modifier for the accumulation of cyanide anions. To that effect, the surface of a glassy carbon electrode was modified by spin-coating of a thin film of the quaternary ammonium functionalized kaolinite. The steady state voltammogram displayed a current with intensity 2.5 times higher than that obtained for the same solution at the bare glassy carbon electrode. The glassy carbon electrode was also modified by the triethanolamine grafted kaolinite bearing no charge, and was tested for a similar experiment. In this case, the observed redox process was comparable to the signal recorded for the blank electrolyte at the bare glassy carbon electrode, confirming the active participation of the cationic charge of the functionalized clay to the accumulation of the cyanide anions.