Kinetics and thermodynamics studies of pentachlorophenol adsorption on covalently functionalized Fe3O4@SiO2-MWCNTs core-shell magnetic microspheres

A novel core-shell covalently functionalized Fe3O4 coated SiO2 decorated multi-walled carbon nanotubes (Fe3O4@SiO2-MWCNTs) adsorbent was synthesized and characterized by scanning electron microscopy, transmission electron microscopy, Fourier Transform Infrared Spectrum (FTIR), Thermogravimetry, X-ray diffraction and magnetic measurements. The pentachlorophenol (PCP) adsorption effect factors of initial concentration, contact time, solution pH and temperature were investigated in detail. It was found the absorption capacity was strongly depended on pH, and the maximum adsorption value for PCP (96.4 mg/g) was obtained at pH 2.5. The equilibrium was attained within 30 min, and the adsorption kinetics was better described by pseudo-second-order kinetic model. The data pointed out excellent fit to Freundlich isotherm model. Thermodynamic parameters such as standard enthalpy (Delta H-theta), standard entropy (Delta S-theta) and standard free energy (Delta G(theta)) showed that the adsorption of PCP onto Fe3O4@SiO2-MWCNTs was spontaneous, endothermic and random within the temperature range of 288-318 K. The results indicate that the Fe3O4@SiO2-MWCNTs adsorbent is a potential low-cost effective material for PCP removal from contaminated wastewater. (C) 2014 Elsevier B.V. All rights reserved.