Adsorption Kinetics and Thermodynamics of Methylene Blue onto p-tert-Butyl-calix[4,6,8]arene-Bonded Silica Gel

New-style adsorbents of p-tert-butyl-calix[4,6,8]arene-bonded silica gel-CnABS (C4ABS, C6ABS, C8ABS)-were prepared by bonding p-tert-butyl-calix[4,6,8]arene to the silica gel surface through the coupling reagent, 3-glycidoxypropyltrimethoxysilane. The products were characterized by FTIR, thermogravimetry, elemental analysis, and scanning electron microscopy. The adsorption of methylene blue from aqueous solution by CnABS was studied. Kinetic studies showed that the adsorption of the dye onto CnABS fit a first-order kinetic model. The equilibrium adsorption data were interpreted using the Langmuir and Freundlich models. The adsorption of methylene blue onto CnABS was better represented by the Langmuir equation. The saturation adsorption quantity monotonically increased with the number of phenolic units in the calixarene ring. The thermodynamic parameters for the adsorption reaction were calculated through a van't Hoff analysis. The whole adsorption process was endothermic, which resulted in an increase of the adsorption quantity with a temperature increase. The new-style adsorbent of CnABS was regarded as a potential adsorbent to deal with dyes or organics in wastewaters.