Hongdi Xiao

Structural properties and photoluminescence of zinc nitride nanowires

Zinc nitride nanowires can be synthesized by nitridation reaction of zinc powder with ammonia gas in 500ml∕min at the nitridation temperature of 600 °C for 120 min. Studies by using x-ray diffraction indicate that zinc nitride nanowires are cubic in structure with the lattice constant a=0.9788nm. Observations by using scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy show that zinc nitride is of nanowire structure. Typical room temperature photoluminescence spectrum of zinc nitride nanowires exhibits an ultraviolet emission peak at 385 nm (3.22 eV) and a blue emission band centered at 450 nm (2.76 eV).

Electrical and optical characterizations of β-Ga2O3:Sn films deposited on MgO (110) substrate by MOCVD

Tin-doped β-Ga2O3 (β-Ga2O3:Sn) films doped with different tin concentrations were deposited on MgO (110) substrates by metal organic chemical vapor deposition (MOCVD) at 700 °C. The effect of doping on the structural, electrical and optical properties of the films was investigated. The 10% Sn-doped film exhibited the best electrical conductivity properties with the lowest resistivity about 5.21 × 10−2 Ω cm, which is over ten orders of magnitude lower than the un-doped film. Micro-structural analysis revealed that the film with 10% Sn content had a clear in-plane relationship of β-Ga2O3 (100) ‖ MgO (110) with β-Ga2O3 (01) ‖ MgO (111). The average transmittance of the samples in the visible range exceeded 87% and the optical band gap of the films varied from 4.12 to 4.80 eV.

Behaviors of Microcystis aeruginosa cells during floc storage in drinking water treatment process.

This is the first study to systematically investigate the different behaviors of Microcystis aeruginosa in the sludges formed by AlCl3, FeCl3, and polymeric aluminium ferric chloride (PAFC) coagulants during storage. Results show that the viability of Microcystis aeruginosa in PAFC sludge was stronger than that of cells in either AlCl3 or FeCl3 sludge after the same storage time, while the cells’ viability in the latter two systems stayed at almost the same level. In AlCl3 and FeCl3 sludges high concentrations of Al and Fe were toxic to Microcystis aeruginosa, whereas in PAFC sludge low levels of Al showed little toxic effect on Microcystis aeruginosa growth and moderate amounts of Fe were beneficial to growth. The lysis of Microcystis aeruginosa in AlCl3 sludge was more serious than that in PAFC sludge, for the same storage time. Although the cell viability in FeCl3 sludge was low (similar to AlCl3 sludge), the Microcystis aeruginosa cells remained basically intact after 10 d storage (similar to PAFC sludge). The maintenance of cellular integrity in FeCl3 sludge might be due to the large floc size and high density, which had a protective effect for Microcystis aeruginosa.

Degradation mechanism of hydrogen-terminated porous silicon in the presence and in the absence of light

Si is well-known semiconductor that has a fundamental bandgap energy of 1.12 eV. Its photogenerated electrons in the conduction band can react with the ubiquitous oxygen molecules to yield ⋅O2− radicals, but the photogenerated holes in the valance band can’t interact with OH− to produce ⋅OH radicals. In this paper, we study the degradation of methyl orange (MO) by hydrogen-terminated porous Si (H-PSi) in the presence and in the absence of light. The absorption spectra of the degraded MO solutions indicated that the H-PSi had superior degradation ability. In the dark, the reduction of dye occurs simply by hydrogen transfer. Under room light, however, some of the dye molecules can be reduced by hydrogen transfer first and then decomposed in the conduction and valance bands. This result should be ascribed to its wide band gap energies centered at 1.79-1.94 eV.

Structure and growth mechanism of quasi-aligned GaN layer-built nanotowers

Quasi-aligned GaN layer-built nanotowers on silicon (111) substrates by employing ultrathin Ni catalyst films have been grown at 800 °C in a metal-organic chemical vapor deposition system. The nanotower size and the degree of alignment were found to be highly sensitive to changes in the Ni catalyst film thickness. The several growth stages of nanotowers were examined by microscopic technique, which indicates the variation in surface morphology from Ni islands to hexagonal prismatic GaN particles, and finally to GaN layer-built nanotowers. For the third stage, the growth may be attributed to an asymmetric and step by step copying process.

16S rRNA Gene Amplicon Sequencing Reveals Significant Changes in Microbial Compositions during Cyanobacteria-Laden Drinking Water Sludge Storage

This is the first study to systematically investigate the microbial community structure in cyanobacteria-laden drinking water sludge generated by different types of coagulants (including AlCl3, FeCl3, and polymeric aluminum ferric chloride (PAFC)) using Illumina 16S rRNA gene MiSeq sequencing. Results show that Cyanobacteria, Proteobacteria, Firmicutes, Bacteroidetes, Verrucomicrobia, and Planctomycetes were the most dominant phyla in sludge, and because of the toxicity of high Al and Fe level in AlCl3 and FeCl3 sludges, respectively, the PAFC sludge exhibited greater microbial richness than that in AlCl3 and FeCl3 sludges. Due to lack of light and oxygen in sludge, relative abundance of the dominant genera Microcystis, Rhodobacter, Phenylobacterium, and Hydrogenophaga clearly decreased, especially after 4 days storage, and the amounts of extracellular microcystin and organic matter rose. As a result, the relative abundance of microcystin and organic degradation bacteria increased significantly, including pathogens such as Bacillus cereus, in particular after 4 days storage. Hence, sludge should be disposed of within 4 days to prevent massive growth of pathogens. In addition, because the increase of extracellular microcystins, organic matter, and pathogens in AlCl3 sludge was higher than that in FeCl3 and PAFC sludges, FeCl3 and PAFC may be ideal coagulants in drinking water treatment plants.

Inactivation of Microcystis aeruginosa by hydrogen-terminated porous Si wafer: Performance and mechanisms

We proposed a method to inactivate Microcystis aeruginosa by using hydrogen-terminated porous Si (H-PSi) wafer. The influences of oxidation time on the removal of M. aeruginosa were investigated. Samples oxidized by H-PSi wafer were subsequently grown under illuminated culture conditions. The results demonstrated that the optimal oxidation time was about 1h, which could control the growth of M. aeruginosa about 65%, after 3days culture. Simultaneously, extracellular microcystins was decreased from 14.65 to 7.06μgL(-1) and remain relative integrity of M. aeruginosa cells which could avoid secretion of large amounts of organic material. Multiple analysis techniques including fluorescence excitation-emission matrix (EEM) and fluorescence microscope were used to reveal the inhibition mechanisms of M. aeruginosa. Meanwhile, analyses of reactive oxygen level, malondialdehyde content, and superoxide dismutase activity indicated that the damage and inactivate of M. aeruginosa cells are mainly due to accumulation of lipid peroxidation and inhibition of normal physiological metabolism by free radicals produced by H-PSi wafer under visible light irradiation. In conclusion, these results suggest that H-PSi wafer may be useful in controlling growth and survival of M. aeruginosa in many large lakes and reservoirs, thus mitigating many of the economic, esthetic ecological impacts of the invasive alga.

Nano-Structures and Properties of Zinc Nitride Prepared by Nitridation Technique

This paper reports that Zn3N2 powders of high quality have been synthesized by nitridation reaction of Zn powders with NH3 gas in 500 ml/min at a nitridation temperature of 600 oC for 120 min. X-ray diffraction (XRD) indicates that Zn3N2 powder has a cubic structure with lattice constants a=9.788 Å. Observations through scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) show that Zn3N2 powder is of nanowire structure. X-ray photoelectron spectroscopy (XPS) tells the differences of chemical bonding states between Zn3N2, and ZnO, and confirms the formation of N–Zn bonds.

Synthesis and Properties of GaN Nanostructures

One-dimensional GaN nanostructure films were successfully synthesized by the recently developed sputtering post-nitridation technique. The morphology and structure of GaN nanowires are investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results indicate that the crystalline GaN nanostructures have a hexagonal wurtzite structure, and there is not any other phase such as Ga2O3 or Ga in the specimen. It also confirms that high quality crystal was obtained in the resulting sample due to the lattice defects decreased and the crystallinity improved in the process of nitridation at high temperature. The growth mechanism of the GaN nanostructures is briefly discussed.