title: Sulfate-doped Fe3O4/Al2O3 nanoparticles as a novel adsorbent for fluoride removal from drinking water.
abstract: A novel adsorbent of sulfate-doped Fe3O4/Al2O3 nanoparticles with magnetic separability was developed for fluoride removal from drinking water. The nanosized adsorbent was characterized and its performance in fluoride removal was evaluated. Kinetic data reveal that the fluoride adsorption was rapid in the beginning followed by a slower adsorption process, nearly 90% adsorption can be achieved within 20 min and only 10-15% additional removal occurred in the following 8 h. The fluoride adsorption isotherm was well described by Elovich model. The calculated adsorption capacity of this nanoadsorbent for fluoride by two-site Langmuir model was 70.4 mg/g at pH 7.0. Moreover, this nanoadsorbent performed well over a considerable wide pH range of 4-10, and the fluoride removal efficiencies reached up to 90% and 70% throughout the pH range of 4-10 with initial fluoride concentrations of 10 mg/L and 50 mg/L, respectively. The observed sulfate-fluoride displacement and decreased sulfur content on the adsorbent surface reveal that anion exchange process was an important mechanism for fluoride adsorption by the sulfate-doped Fe3O4/Al2O3 nanoparticles. Moreover, a shift of the pH of zero point charge (pHPZC) of the nanoparticles and surface analysis based on X-ray photoelectron spectroscopy (XPS) suggest the formation of inner-sphere fluoride complex at the aluminum center as another adsorption mechanism. With the exception of PO4(3-), other co-existing anions (NO3(-), Cl(-) and SO4(2-)) did not evidently inhibit fluoride removal by the nanoparticles. Findings of this study demonstrate the potential utility of the nanoparticles as an effective adsorbent for fluoride removal from drinking water.
authors.affiliation: School of Metallurgical Science and Engineering, National Engineering Research Center for Pollution Control of Heavy Metal, Central South University, Lushan South Road 932, Changsha Hunan 410083, China.
authors.forename: Liyuan
authors.initials: L
authors.lastname: Chai
authors.forename: Yunyan
authors.initials: Y
authors.lastname: Wang
authors.forename: Na
authors.initials: N
authors.lastname: Zhao
authors.forename: Weichun
authors.initials: W
authors.lastname: Yang
authors.forename: Xiangyu
authors.initials: X
authors.lastname: You
mesh_terms: D000327:Adsorption; D000537:Aluminum Oxide / Q000737:chemistry*; D000838:Anions; D060766:Drinking Water / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D005459:Fluorides / Q000302:isolation & purification*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D056951:Photoelectron Spectroscopy; D055672:Static Electricity; D013431:Sulfates / Q000737:chemistry*; D013997:Time Factors
chemical_list: D000838:Anions; D060766:Drinking Water; D005290:Ferric Compounds; D013431:Sulfates; C000499:ferric oxide; D000537:Aluminum Oxide; D005459:Fluorides