title: Zirconium-carbon hybrid sorbent for removal of fluoride from water: oxalic acid mediated Zr(IV) assembly and adsorption mechanism.
abstract: When activated carbon (AC) is modified with zirconium(IV) by impregnation or precipitation, the fluoride adsorption capacity is typically improved. There is significant potential to improve these hybrid sorbents by controlling the impregnation conditions, which determine the assembly and dispersion of the Zr phases on carbon surfaces. Here, commercial activated carbon was modified with Zr(IV) together with oxalic acid (OA) used to maximize the zirconium dispersion and enhance fluoride adsorption. Adsorption experiments were carried out at pH 7 and 25 °C with a fluoride concentration of 40 mg L(-1). The OA/Zr ratio was varied to determine the optimal conditions for subsequent fluoride adsorption. The data was analyzed using the Langmuir and Freundlich isotherm models. FTIR, XPS, and the surface charge distribution were performed to elucidate the adsorption mechanism. Potentiometric titrations showed that the modified activated carbon (ZrOx-AC) possesses positive charge at pH lower than 7, and FTIR analysis demonstrated that zirconium ions interact mainly with carboxylic groups on the activated carbon surfaces. Moreover, XPS analysis demonstrated that Zr(IV) interacts with oxalate ions, and the fluoride adsorption mechanism is likely to involve -OH(-) exchange from zirconyl oxalate complexes.
authors.affiliation: Division of Environmental Sciences, Instituto Potosino de Investigación Científica y Tecnológica, A.C. , Camino a la Presa San José 2055, Col. Lomas 4a sección, C.P. 78216, San Luis Potosí, S.L.P., México.
authors.forename: Litza Halla
authors.initials: LH
authors.lastname: Velazquez-Jimenez
authors.forename: Robert H
authors.initials: RH
authors.lastname: Hurt
authors.forename: Juan
authors.initials: J
authors.lastname: Matos
authors.forename: Jose Rene
authors.initials: JR
authors.lastname: Rangel-Mendez
mesh_terms: D000327:Adsorption; D002244:Carbon / Q000737:chemistry*; D002606:Charcoal / Q000737:chemistry; D005459:Fluorides / Q000737:chemistry / Q000302:isolation & purification*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007477:Ions; D007700:Kinetics; D019815:Oxalic Acid / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D058105:Polymerization; D012996:Solutions; D013696:Temperature; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification; D014961:X-Ray Diffraction; D015040:Zirconium / Q000737:chemistry*
chemical_list: D007477:Ions; D012996:Solutions; D014874:Water Pollutants, Chemical; D014867:Water; D002606:Charcoal; D002244:Carbon; D019815:Oxalic Acid; D015040:Zirconium; D005459:Fluorides