Removal of 4-Chlorophenol from Contaminated Water Using Activated Carbon from Dried Date Pits: Equilibrium, Kinetics, and Thermodynamics Analyses

Five different activated carbons (ACs) have been prepared from dried date pits using air and phosphoric acid as activating agents. The used phosphoric acid:date pit ratio dictated the characteristics of the prepared ACs; the equivalent BET-nitrogen surface area varied from 794 m(2)/g for a ratio of 5:1, to 1707 m(2)/g for a ratio of 2:1, whereas the micropore volume changed in value from 0.24 cm(3)/g for the 5:1 ratio to 0.59 cm(3)/g for the 2:1 ratio. The prepared ACs were tested to remove 4-chlorophenol (4-CP) from aqueous solutions by means of batch adsorption process. The prepared 2:1 AC exhibited the highest uptake with a maximum of 525 mg/g. Equilibrium pH studies showed that 4-CP removal was pH dependent; the maximum uptake occurred at an equilibrium pH value of 5.5. Dynamic studies showed that 4-CP uptake on 2:1 AC is rapid, with 80% of the maximum uptake achieved during the first 40 min. Both surface adsorption and intraparticle diffusion were identified to be effective adsorption mechanisms. Kinetic studies indicated a pseudo second-order reaction. Results of equilibrium adsorption experiments showed that the adsorption of the 4-CP on 2:1 AC is best described by the Langmuir model. The thermodynamics parameters of the adsorption (ΔG(0), ΔH(0), and ΔS(0)) were determined by studying the adsorption equilibrium at different temperatures. The values of these parameters indicated the spontaneous and endothermic nature of the adsorption phenomenon of 4-CP on the prepared ACs.