title: Sorption characteristics and mechanisms of oxyanions and oxyhalides having different molecular properties on Mg/Al layered double hydroxide nanoparticles.
abstract: The sorption ability of fast-coprecipitated and hydrothermally-treated Mg/Al layered double hydroxide nanoparticles (FCHT-LDH) for various oxyhalides and oxyanions was evaluated. Interactions of oxyhalide such as monovalent bromate or oxyanions such as divalent chromate and divalent vanadate with FCHT-LDH were investigated using a combination of macroscopic (batch sorption/desorption studies and electrophoretic mobility (EM) measurements) and microscopic techniques (CHNS/O, XRD, FTIR, XPS, and EXAFS analyses). The sorption studies on various oxyanions and oxyhalides suggested that their sorption characteristics on FCHT-LDH were largely governed by their ionic potentials and molecular structures. Oxyanions which have ionic potentials higher than 7 nm(-1) were found to be more readily sorbed by FCHT-LDH than oxyhalides with ionic potentials lower than 5 nm(-1). The results obtained also demonstrated that trigonal pyramid oxyhalides showed a lower degree of specificity for FCHT-LDH than the tetrahedral coordinated oxyanions. From the macroscopic and microscopic studies, monovalent oxyhalide sorption on FCHT-LDH was postulated to occur mainly via anion exchange mechanism with subsequent formation of outer-sphere surface complexes. For polyvalent oxyanion sorption on FCHT-LDH, the mechanisms were possibly associated with both anion exchange and ligand exchange reactions, resulting in the coexistence of outer-sphere and inner-sphere surface complexes.
authors.affiliation: School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Republic of Singapore. gohk0020@ntu.edu.sg
authors.forename: Kok-Hui
authors.initials: KH
authors.lastname: Goh
authors.forename: Teik-Thye
authors.initials: TT
authors.lastname: Lim
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Banas
authors.forename: Zhiling
authors.initials: Z
authors.lastname: Dong
mesh_terms: D000327:Adsorption; D000465:Algorithms; D000536:Aluminum Hydroxide / Q000737:chemistry*; D002840:Chromates / Q000032:analysis; D004586:Electrophoresis; D006219:Halogens / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008276:Magnesium Hydroxide / Q000737:chemistry*; D008670:Metals / Q000032:analysis*; D053758:Nanoparticles; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013816:Thermodynamics; D014638:Vanadates / Q000032:analysis; D014961:X-Ray Diffraction
chemical_list: D002840:Chromates; D006219:Halogens; D008670:Metals; D014638:Vanadates; D000536:Aluminum Hydroxide; D008276:Magnesium Hydroxide