Removal of Phenol and Monochlorophenols Pollution from Aqueous Solutions with HDTMA-Modified Halloysite

Abstract

ABSTRACT Dynamic and equilibrium research on the adsorption of phenol and monochlorophenols (2-chlorophenol, 3-chlorophenol, 4-chlorophenol) on modified halloysite with the use of HDTMA (hexadecyltrimethylammonium) bromide was conducted at three temperatures: 293, 303, and 313 K. The interpretation of experimental data was based on the Temkin, the Dubinin-Radushkevich, the Freundlich, and the Langmuir equations to establish the appropriate adsorption models and to define the characteristic parameters describing the process. We determined that the Freundlich isotherm perfectly described experimental data as regards the adsorption equation concerning phenol; however, 2-chlorophenol, 3-chlorophenol, and 4-chlorophenol sorption took place in compliance with the Langmuir model. The adsorption of the studied compounds on the HDTMA-modified halloysite increased in the following order: phenol <4-chlorophenol <2-chlorophenol <3-chlorophenol. Thermodynamic parameters of the processes indicated the physical as well as exothermal adsorption character. The adsorption kinetics of phenol and monochlorophenols was discussed based on the following models: pseudo-first-order, pseudo-second-order, Elovich, intraparticle diffusion, and film-diffusion model. The rate of the sorption process was described with the pseudo-second-order model. The global electrophilicity indices of phenol and the monochlorophenols were applied to demonstrate the difference through the interaction of these adsorbates with a molecule of surfactant (HDTMA) and, as a result, the different properties of the studied compounds.