Adsorption of phenol from water on activated carbon prepared from shaddock peel by ZnCl2 and H3PO4 : equilibrium, kinetics and thermodynamics

The study consists of the preparation of the activated carbon (AC) from shaddock peel by ZnCl2 and H3PO4 and the effect of adsorption conditions such as contact time, adsorbent dosage, phenol initial concentration, pH and temperature on the removal behaviors of phenol from aqueous solutions onto the AC. The prepared ACs were characterized by N-2 adsorption, elemental analysis, scanning electron micrograph and Boehm titration. To understand the equilibrium isotherms, the adsorption data were analyzed by Langmuir, Freundlich, Dubinin-Radushkevich and Temkin model. The pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models were used to investigate the kinetic parameters and the mechanism of adsorption. To predict the nature of adsorption, the thermodynamic parameters (Delta G degrees, Delta H degrees and Delta S degrees) were calculated. The results showed that the micropore structures of two ACs prepared by ZnCl2 and H3PO4 activation are similar, but surface chemical properties of different ACs are significantly different. Adsorption removal percentages of ACs for phenol from water increase with increasing the contact time and AC dosage, respectively, whereas phenol removal decreases with an increase in temperature. The changes in the removal of phenol by AC-Z and AC-H with the initial pH were different. The Langmuir and Temkin model can better describe phenol adsorption process for AC-Z; whereas, the Langmuir model can well describe the phenol adsorption process of AC-H. The pseudo-second order and Elovich model better described the adsorption behaviors on AC-H and AC-Z, respectively. The thermodynamic studies indicate phenol adsorption on ACs is spontaneous and exothermic. The experimental results indicate that ACs from shaddock peel by chemical activation methods are technologically feasible. The ACs can be used to effectively remove phenol from wastewater.