Using of chelating resin to study the kinetic desorption of Eu(III) from humic acid-Al2O3 colloid surfaces

The association of organic-inorganic colloid-borne trace elements was investigated. Radionuclide ^152+154Eu(III) was chosen as a representative and chemical homologue for trivalent lanthanide and actinide ions present in radioactive nuclear waste. Effect of pH and contact time of organic-inorganic/Eu(III) on the kinetic dissociation of Eu(III) from HA-Al₂O₃ colloids was studied. The kinetic desorption behavior of sorbed ^152+154Eu(III) from humic acid-γ-Al₂O₃ colloids was studied at pH values of 4.5 ± 0.2, 5.3 ± 0.2 and 6.5 ± 0.2, respectively, by the addition of the chelating resin. The experimental results suggest that the fractions of irreversible sorption of radionuclide ^152+154Eu(III) to HA-Al₂O₃ colloids increase with increasing pH values, and are independent of aging time. At least two different species, “weak” and “strong” dissociation fractions, are required to simulate the kinetic desorption of ^152+154Eu(III) from HA-Al₂O₃ colloids. The species of Eu(III) sorbed on HA-Al₂O₃ colloids move from “weak” sites to “strong” sites with increasing aging time, whereas the fractions of irreversible sorption are independent of aging time. The results are important for the evaluation of radionuclides’ behavior in the environment.     

Theoretical study of ZnO adsorption and bonding on Al<Subscript>2</Subscript>O<Subscript>3</Subscript> (0001) surface

ZnO adsorption on sapphire (0001) surface is theoretically calculated by using a plane wave ultrasoft pseudo-potential method based onab initio molecular dynamics. The results reveal that the surface relaxation in the first layer Al-O is reduced, even eliminated after the surface adsorption of ZnO, and the chemical bonding energy is 434.3(±38.6) kJ · mol⁻¹. The chemical bond of ZnO (0.185 ± 0.01 nm) has a 30° angle away from the adjacent, Al-O bond, and the stable chemical adsorption position of the Zn is deflected from the surface O-hexagonal symmetry with an angle of about 30°. The analysis of the atomic populations, density of state and bonding electronic density before and after the adsorption indicates that the chemical bond formed by the O²⁻ of the ZnO and the surface Al³⁺ has a strong ionic bonding characteristic, while the chemical bond formed by the Zn²⁺ and the surface O²⁻ has an obvious covalent characteristic, which comes mainly from the hybridization of the Zn 4s and the O 2p and partially from that of the Zn 3d and the O 2p.     

Au adsorption and Au-mediated charge transfer on the SrO-termination of SrTiO3 (0 0 1) surface

Atomic Au adsorption on the SrO-termination of SrTiO₃ (0 0 1) surface has been studied by means of the first-principles calculations based on the density functional theory (DFT). It indicates that charge polarization dominantly contributes to the bonding between Au and SrO-termination. Interfacial charge transfer induces dipole moment and changes work function. The mediating role Au played in charge transfer from electron-doped SrTiO₃:Nb to NO has been simulated. Charge transfer from SrTiO₃:Nb to Au is ascertained indicating that Au plays as an electron trapping center. SrO-termination has weak activity to NO while the molecule can be strongly adsorbed on negatively charged Au atom. It has been represented that Au mediates the charge transfer from SrTiO₃:Nb to NO. Antibonding orbital (π_2p*) of NO accommodates the charge and thus molecular bond is weakened (activated). Fukui functions demonstrate the role Au played in transiting the charge transfer from electronically excited SrTiO₃ to target species. Evidence that metal deposited on photocatalyst surface effectively separates the electron-hole pairs and improves the photocatalytic activity is presented in the current work.