Papers by Author: Zhi Hong Zhang

Abstract: Wastewater from the munitions decomposing process typically contains the widely used explosive-trinitrotoluene (TNT), which is also toxic and mutagenic. Commonly used technologies for degradation of TNT,such as activated carbon adsorption and chemical oxidation, are proved to be feasible but not cost-effective. In this study, the effectiveness of biodegradation of TNT by co-metabolism was evaluated in a hybrid hydrolysis acidification and aerobic membrane bioreactor. After six weeks acclimatization, over 90% TNT was removed with influent TNT concentration ranging between 70-85mg/L. Simultaneously remarkable MLSS concentration increase from 1.4 g/l to 6.9 g/l was observed, which indicated that the acclimatization and incubation of biomass was successful. The membrane effectively prevented loss of sludge and kept large biomass in the reactor, which made the system maintained in a high volume loading rate and low sludge loading rate. The experiment results showed that addition of carbon source was an essential factor in biodegradation of TNT wastewater.

Abstract: The defect structure for Ni3+ in ZnO crystal is theoretically investigated using the perturbation formulas of the spin Hamiltonian parameters for a 3d7 ion in trigonally distorted tetrahedra. In view of the significant covalency of the system due to the high valence state of Ni3+, the ligand orbital and spin-orbit coupling contributions are taken into account in a uniform way based on the cluster approach. The impurity Ni3+ is found not to occupy the ideal Zn2+ site in ZnO but to undergo the small axial displacement of about 0.044 Ǻ away from the oxygen triangle along the C3 axis. The theoretical spin Hamiltonian parameters based on the above impurity displacement show good agreement with the experimental data. The defect structure of this impurity center is compared with that for the similar Fe3+ in ZnO.

Abstract: The electron paramagnetic resonance (EPR) parameters g factor and the hyperfine structure constant A factor for the substitutional Rh+ in NaCl are theoretically studied from the perturbation formulas of these parameters for a 4d8 ion in cubic octahedra. In these formulas, the ligand orbital and spin-orbit coupling contributions which were normally omitted in the previous studies are taken into account using the cluster approach. The calculated g and A factors are in good agreement with the experimental data. The ligand contributions to the EPR parameters are somewhat important and should be considered in the analysis of the EPR spectra for a 4d8 ion in chlorides. The local structure of this center is also discussed.

Abstract: The spin Hamiltonian parameters (zero-field splitting D and the g factors) for NiX2 and CdX2:Ni2+ (X=Cl, Br) are quantitatively investigated from the perturbation formulas of these parameters for a 3d8 ion in trigonally distorted octahedra based on the cluster approach. In the calculations, the trigonal field parameters  and ′ are determined from the superposition model and the local structures of Ni2+ in the halides. The theoretical g factors show reasonable agreement with the observed values, and the experimental D for CdX2:Ni2+ are also interpreted by considering suitable lattice distortions (angular decreases) in the impurity-ligand bond angles related to the C3 axis due to the size mismatching substitution. The contributions from the ligand orbital and spin-orbit coupling interactions are important and should be taken into account.

Abstract: The defect structures and the electron paramagnetic resonance (EPR) parameters zero-field splitting and the g factors for the tetragonal and cubic Ni2+ centers in AgX (X=Cl, Br) are theoretically studied from the perturbation formulas of these parameters for a 3d8 ion in tetragonal and cubic octahedra. In these formulas, the ligand s-orbital contributions, which were usually neglected in the previous studies, are taken into account based on the cluster approach. The ligand X− intervening in the Ni2+ and the next nearest neighbour Ag+ vacancy VAg is suggested to suffer a small inward displacement (≈ 0.11 or 0.15Å for AgCl or AgBr, respectively) towards Ni2+ along the [100] (or C4) axis. The calculated EPR parameters based on the above defect structures show reasonable agreement with the experimental data.