Kinetic, equilibrium, and thermodynamic aspects of phenol adsorption onto acrylonitrile-divinylbenzene copolymer

Adsorption of phenol onto acrylonitrile-divinylbenzene copolymer (AN-DVB) was comprehensively investigated with the aspect of kinetic, equilibrium, and thermodynamic. The effect of adsorbent dosage, initial concentration, temperature, and pH were studied in batch adsorption process. Maximum phenol adsorption capacity was obtained at neutral pH of phenol solution (6.8), at room temperature (25 °C) and at higher initial concentrations (500 mg/L) as 117 mg/g. After examining two-parameter- and three-parameter-adsorption-isotherm models, experimental data were represented well by using Freundlich adsorption isotherm model at neutral pH. Due to the all possible interactions like hydrogen bonding, π-π stacking and hydrophobic ineractions have different strengths and energetic values, phenol adsorption at neutral pH (6.8) exhibited a heterogeneous multilayer process. On the other hand, Langmuir and BET models well represented the experimental data obtained beyond neutral pH due to the weakening of different interactions, hence, multilayer but more uniform adsorption occurred. Phenol adsorption followed pseudo-second-order kinetic model that shows the surface interactions play significant role on the adsorption rate. Analysis of Boyd's intraparticle and external diffusion kinetic models indicated that in addition to surface interactions, diffusion also controlled the adsorption rate at room temperature. Activation energy was calculated as 92.99 kJ/mol, which shows the strong interaction between phenol and AN-DVB. Adsorption enthalpy change and entropy change was calculated as -25.731 kJ/mol and -0.041 kJ/molK, respectively. Thermodynamic parameters indicated that adsorption process was exothermic and spontaneous in nature.