Adsorption of phenolic compounds onto calix[4]arene-bonded silica gels from aqueous solutions

This article describes the preparation of calix[4]arene-bonded silica gels (C[4]BS and DMC[4]BS), and their application to the removal of some selected phenolic compounds such as phenol (PHE), p-chlorophenol (PCP), m-nitrophenol (MNP) and p-nitrophenol (PNP) from aqueous solutions by adsorption method. In initial adsorption experiments appeared that C[4]BS was much more effective in adsorption of PNP rather than PHE, PCP and MNP, whereas DMC[4]BS exhibited too little adsorption ability towards all phenols. Herein, it was concluded that the hydrogen bonding capacities of both phenols and calix[4]arene based adsorbents played a predominant role in the interactions between adsorbate and adsorbent within the adsorption mechanism. Thus, in subsequent studies, the C[4]BS was employed as an adsorbent in the adsorption of PNP, and adsorption conditions were optimized. Furthermore, isotherm and kinetic studies were performed to clarify the phenomena of PNP adsorption onto C[4]BS.