title: Adsorption characteristics of 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solution on powdered activated carbon.
abstract: The removal of 2,4-dichlorophenoxyacetic acid (2,4-D), one of the most commonly used phenoxy acid herbicides, from aqueous solution was studied by using acid-washed powdered activated carbon (PAC) as an adsorbent in a batch system. Adsorption equilibrium, kinetics, and thermodynamics were investigated as a function of initial pH, temperature, and initial 2,4-D concentration. Powdered activated carbon exhibited the highest 2,4-D uptake capacity of 333.3 mg g(-1) at 25 degrees C and an initial pH value of 2.0. Freundlich, Langmuir, and Redlich-Peterson isotherm models were used to express the equilibrium data of 2,4-D depending on temperature. Equilibrium data fitted very well to the Freundlich equilibrium model in the studied concentration range of 2,4-D at all the temperatures studied. Three simplified models including pseudo-first-order, pseudo-second-order, and saturation-type kinetic models were used to test the adsorption kinetics. It was shown that the adsorption of 2,4-D on PAC at 25, 35, and 45 degrees C could be best fitted by the saturation-type kinetic model with film and intraparticle diffusions being the essential rate-controlling steps. The activation energy of adsorption (EA) was determined as--1.69 kJ mole(-1). Using the thermodynamic equilibrium coefficients obtained at different temperatures, the thermodynamic constants of adsorption (deltaG degrees, deltaH degrees, and deltaS degrees) were also evaluated.
authors.affiliation: Department of Chemical Engineering, Hacettepe University, Ankara, Turkey. zaksu@hacettepe.edu.tr
authors.forename: Z
authors.initials: Z
authors.lastname: Aksu
authors.forename: E
authors.initials: E
authors.lastname: Kabasakal
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000737:chemistry* / Q000493:pharmacokinetics; D000327:Adsorption; D002606:Charcoal / Q000737:chemistry* / Q000493:pharmacokinetics; D004305:Dose-Response Relationship, Drug; D006540:Herbicides / Q000737:chemistry* / Q000493:pharmacokinetics; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D012996:Solutions; D013696:Temperature
chemical_list: D006540:Herbicides; D012996:Solutions; D002606:Charcoal; D015084:2,4-Dichlorophenoxyacetic Acid