Rohan Weerasooriya

Charge distribution multi-site complexation (CD-MUSIC) modeling of Pb(II) adsorption on gibbsite

Abstract Lead adsorption on gibbsite was examined in batch experiments as a function of pH, adsorption density (ΓPb 0.01–3.0 μmolm−2), initial Pb(II) concentration (0.77–78 μM), electrolyte type and its concentration. The pHzpc of gibbsite in NaCl was 8.35. The Pb(II) and H+ adsorption data on gibbsite were interpreted in terms of surface complexation using charge-distribution multi-site complexation (CD-MUSIC) model. Intrinsic equilibrium constants were determined by numerical optimization using ECOSAT-FIT utility resulting in the following data: > AlOH 2 s 1/2 + Cl s − => AlOH 2 +1/2 Cl − log K − = −0.59 2(> AlOH −1 /2 )+ Pb 2+ =[(> AlOH ) . 2 0.2 Pb 0.8 ] + CD - MUSIC — three - plane model ( TPM ): log K NaCl =9.38 or log K NaNO 3 =10.07 CD - MUSIC — basic Stern - layer model ( BSM ): log K NaCl =9.70 or log K NaNO 3 =10.07. The binding constant of the [(>AlOH)x2Pby]2+surface complex (x+y=2) was determined independently using Pb(II) adsorption data in NaNO3, and NaCl differed only by 0.0.23 log units when the CD-MUSIC/BSM model combination was used.

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 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.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.

Chemical reduction of nitrate by zerovalent iron nanoparticles adsorbed radiation-grafted copolymer matrix

Abstract This research specifically focused on the development of a novel methodology to reduce excess nitrate in drinking water utilizing zerovalent iron nanoparticles (nZVI)-stabilized radiation-grafted copolymer matrix. nZVI was synthesized by borohydrate reduction of FeCl3 and stabilized on acrylic acid (AAc)-grafted non-woven polyethylene/polypropylene (NWPE/PP-g-AAc) copolymer matrix, which was grafted using gamma radiation. The use of nZVI for environmental applications is challenging because of the formation of an oxide layer rapidly in the presence of oxygen. Therefore, radiation-grafted NWPE/PP synthetic fabric was used as the functional carrier to anchor nZVI and enhance its spreading and stability. The chemical reduction of nitrate by nZVI-adsorbed NWPE/PP-g-AAc (nZVI-Ads-NWP) fabric was examined in batch experiments at different pH values. At low pH values, the protective layers on nZVI particles can be readily dissolved, exposing the pure iron particles for efficient chemical reduction of nitrate. After about 24 h, at pH 3, almost 96% of nitrate was degraded, suggesting that this reduction process is an acid-driven, surface-mediated process. The nZVI-water interface has been characterized by the 1-pK Basic Stern Model (BSM). An Eley-Rideal like mechanism well described the nitrate reduction kinetics. In accordance with green technology, the newly synthesized nZVI-Ads-NWP has great potential for improving nitrate reduction processes required for the drinking water industry.

A novel radiation-induced grafting methodology to synthesize stable zerovalent iron nanoparticles at ambient atmospheric conditions

A novel method was developed to synthesize air-stable zerovalent iron nanoparticles (hereafter nZVI) utilizing a radiation grafting technique. The nZVI were synthesized by borohydrate reduction of FeCl3 and stabilized on a radiation grafted copolymer matrix. Polyacrylic acid (PAA) grafted non-woven polyethylene/polypropylene (NWPE/PP-g-PAA) was used as the copolymer matrix and Co-60 γ-radiation was applied. The nZVI adsorbed NWPE/PP-g-PAA (hereafter nZVI-Ads-NWP) polymer composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrational spectroscopy, scanning electron microscopy (SEM), Mössbauer spectroscopy, proton titrations, and zeta potential techniques. The SEM images showed that PAA was properly grafted onto the NWPE/PP fabric during irradiation and that the nZVI were well dispersed and stabilized on the fabric surface. Vibrational spectroscopy showed supplementary evidence for the proper grafting of PAA onto the base polymer and suggested a monodentate configuration as the primary interaction between the carboxylate groups of PAA and the nZVI surface. XRD, XPS, and Mössbauer analyses revealed core zerovalent iron with a shell mainly consisting of iron oxides. The pHZPC and pHIEP values of nZVI–NaCl suspensions were 7.3. Zeta potential and surface charge data were modeled using the 1-pK Stern layer model with two dissimilar sites for electrolyte and proton binding to account for the observed charge asymmetry.