title: Removal of 2,4-dichlorophenoxyacetic acid by calcined Zn-Al-Zr layered double hydroxide.
abstract: The adsorption equilibrium, kinetics, and thermodynamics of removal of 2,4-dichlorophenoxy-acetic acid (2,4-D) from aqueous solutions by a calcined Zn-Al layered double hydroxide incorporated with Zr(4+) were studied with respect to time, temperature, pH, and initial 2,4-D concentration. Zr(4+) incorporation into the LDH was used to enhance 2,4-D uptake by creating higher positive charges and surface/layer modification of the adsorbent. The LDH was capable of removing up to 98% of 2,4-D from 5 to 400 ppm aqueous at adsorbent dosages of 500 and 5000 mg L(-1). The adsorption was described by a Langmuir-type isotherm. The percentage 2,4-D removed was directly proportional to the adsorbent dosage and was optimized with 8% Zr(4+) ion content, relative to the total metals (Zr(4+)+Al(3+)+Zn(2+)). Selected mass transfer and kinetic models were applied to the experimental data to examine uptake mechanism. The boundary layer and intra-particle diffusion played important roles in the adsorption mechanisms of 2,4-D, and the kinetics followed a pseudo-second order kinetic model with an enthalpy, ΔH(ads) of -27.7±0.9 kJ mol(-1). Regeneration studies showed a 6% reduction in 2,4-D uptake capacity over six adsorption-desorption cycles when exposed to an analyte concentration of 100 ppm.
authors.affiliation: Department of Chemistry, Marquette University, PO Box 1881, Milwaukee, WI 53201-1881, USA.
authors.forename: Allen
authors.initials: A
authors.lastname: Chaparadza
authors.forename: Jeanne M
authors.initials: JM
authors.lastname: Hossenlopp
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000302:isolation & purification*; D000327:Adsorption; D000535:Aluminum / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000138:chemical synthesis / Q000737:chemistry*; D007700:Kinetics; D008567:Membranes, Artificial; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D006878:Hydroxides; D008567:Membranes, Artificial; D015084:2,4-Dichlorophenoxyacetic Acid; D015040:Zirconium; D000535:Aluminum; D015032:Zinc