title: Fluoride adsorption on γ - Fe2O3 nanoparticles.
abstract: BACKGROUND
  Fluoride contamination of groundwater, both anthropogenic and natural, is a major problem worldwide and hence its removal attracted much attention to have clean aquatic systems. In the present work, removal of fluoride ions from drinking water tested using synthesized γ-Fe2O3 nanoparticles.
  
  
  METHODS
  Nanoparticles were synthesized in co-precipitation method. The prepared particles were first characterized by X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). Density functional theory (DFT) calculations on molecular cluster were used to model infrared (IR) vibrational frequencies and inter atomic distances.
  
  
  RESULTS
  The average size of the particles was around 5 nm initially and showed a aggregation upon exposure to the atmosphere for several hours giving average particle size of around 5-20 nm. Batch adsorption studies were performed for the adsorption of fluoride and the results revealed that γ-Fe2O3 nanoparticles posses high efficiency towards adsorption. A rapid adsorption occurred during the initial 15 min by removing about 95 ± 3 % and reached equilibrium thereafter. Fluoride adsorption was found to be dependent on the aqueous phase pH and the uptake was observed to be greater at lower pH. Fourier transform infrared spectroscopy (FT-IR) was used for the identification of functional groups responsible for the adsorption and revealed that the direct interaction between fluoride and the γ-Fe2O3 particles.
  
  
  CONCLUSIONS
  The mechanism for fluoride removal was explained using the dehydoxylation pathway of the hydroxyl groups by the incoming fluoride ion. FT-IR data and other results from the ionic strength dependence strongly indicated that formation of inner-spherically bonded complexes. Molecular clusters were found to be good agreement with experimental observations. These results show direct chemical interaction with fluoride ions.
authors.affiliation: Material Technology Section, Industrial Technology Institute, No 363, Bauddhaloka Mawatha, Colombo 07, Sri Lanka.|Chemical and Environmental System Modeling group, Institute of Fundamental Studies, Hanthana Road, Kandy, Sri Lanka.
authors.forename: Lakmal
authors.initials: L
authors.lastname: Jayarathna
authors.affiliation: Department of Chemistry, University of Peradeniya, Peradeniya, Sri Lanka.
authors.forename: Athula
authors.initials: A
authors.lastname: Bandara
authors.affiliation: Nanyang Environment and Water Research Institute, Singapore, Singapore.
authors.forename: W J
authors.initials: WJ
authors.lastname: Ng
authors.affiliation: Department of Soil Science, University of Peradeniya, Peradeniya, Sri Lanka.
authors.forename: Rohan
authors.initials: R
authors.lastname: Weerasooriya
keywords: Adsorption and removal; DFT; FTIR; Fluoride; Gaussian 09; High efficiency; Molecular modeling; γ-Fe2O3 nanoparticles