Athula Bandara

Surface complexation modeling of cadmium adsorption on gibbsite

Abstract Cadmium adsorption on gibbsite was examined as a function of pH, background electrolyte concentration, and adsorbate loading. The adsorption data was quantified by charge distribution multi-site ion complexation (CD MUSIC) model using reaction stoichiometry given; 2(>AlOH−1/2)+Cd2+=(>AlOH)2xCdy; logxa0K=6.727. The charge distribution factor, f is treated as an adjustable parameter in model fitting yielding x=1.2 valence units (vu) and y=0.8 vu.

Nanogibbsite: synthesis and characterization.

Nanogibbsite was synthesized using a supersaturated Al(OH)(3) solution which was prepared by titration of AlCl(3) with NaOH at pH 4.6. Excess chloride ions in the system were stripped off by dialyzing the Al(OH)(3) suspension against distilled water. The dialysis step is critical for initiation of gibbsite crystallization or the Al(OH)(3) suspension would remain amorphous. Chloride ions seem to mask the seeding sites and so retard the overall process of gibbsite formation. When subjected to heat treatment, gibbsite→alumina conversion occurred by two mechanisms. Nanogibbsite→α-alumina phase transition occurred forming χ- and κ-alumina polymorphs.

Fluoride adsorption on γ - Fe2O3 nanoparticles.

BackgroundFluoride 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.MethodsNanoparticles 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.ResultsThe 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 95u2009±u20093 % 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.ConclusionsThe 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.

Adsorption Mechanism of Cr(VI) onto Coir Pith

ABSTRACT Reductive adsorption of Cr(VI) on coir pith (hereafter CP) was examined as a function of pH, ionic strength, and temperature. The CP contains 1.33 meq g− 1 phenolic, 0.43 meq g− 1 of lactonic, and 0.35 meq g− 1 carboxylic sites. Thus the CP surface is enriched with electron-donating oxygen functionalities. As evidenced by infrared (IR) spectroscopy, the Cr(VI) → Cr(III) conversion is facilitated by CP sites that are enriched with O─ O functional groups. The adsorption of reduced Cr(VI) was found to occur via C─ O─ functional groups first forming innersphere complexes with the CP surface, yielding keto (> C═ O) groups on the CP surface. The reductive adsorption of Cr(VI) was almost completed within 3 to 4 h, and it was dependent on pH and background ionic strength, yielding the highest monolayer coverage (9.56E-7 mol m− 2) at pH 3.7 in 0.1 M NaNO3. The ΓCr(III) followed the order with respect to the ionic strength: Γ0.1 M > Γ0.01 M > Γ0.001 M. The initial rate constant, k i , increased with temperature as k i 313 K > k i 303 K > k i 293 K > k i 283 K.