Solid-state intercalation of cationic surfactants into Tunisian smectites

Intercalation of cationic surfactants hexadecylpyridinium (HDPy+) and hexadecyltrimethylammonium (HDTMA(+)) into the interlayer space of homoionic (Na-, Ca- and Zn-) smectites by solid-solid reactions was investigated. These reactions were complete within 15 mm. Changes in the surface and structure of the smectites modified with different surfactants were characterized using XRD, FTIR and DSC. The intercalation of surfactant is controlled by the exchangeable cation of smectite and monofunctional ammonium cation type. HDPy+ and HDTMA(+) surfactants were retained by Zn-exchanged smectite, suggesting important surface properties (CEC = 80 meq/100 g clay, S-BET = 116.5 m(2)/g) and acid-base properties (point of zero proton charge PZC, density charge HDPy cation loading was effective, suggesting that the aromatic polar group is favoured for intercalation. Comparing with original clay, modification with surfactants increased the basal spacings d(001). Based on the d(001) spacing of modified smectites, different configurations of surfactants within smectite interlayer were proposed as a function of surfactant concentration, which were examined by FTIR and DSC.