Immobilization of Chlorosulfonyl-Calix[4]arene onto the surface of silica gel through the directly estrification

For the first time Chlorosulfonyl-Calix[4]arene has been chemically bonded to silica gel through the directly estrification without silane coupling agent to prepare Chlorosulfonyl-Calix[4]arene-bonded silica gel. Sample characterization was performed by various techniques such as elemental analysis, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), powder X-ray diffraction (XRD), N2 adsorption–desorption, thermal gravimetric analysis (TGA), 29Si CP/MAS spectroscopy and acid–base titration. All data approve the successful incorporation of organic group via covalent bond. From the comparison between sulfur content determined by elemental analysis and the number of H+ determined by acid–base titration, it was shown that two ester units took place onto the new synthesized sample and two acidic sites exist on the surface.