Isolation of rhizosheath and analysis of microbial community structure around roots of Stipa grandis.

Root zone microbial structure is particularly complex in plants with rhizosheaths, and greater understanding of the rhizosheath may play an important role in the future development of sustainable agricultural practices. However, one important reason to focus study on rhizosheath microbial structure is that there is no definite method for rhizosheath separation. The aim of this study was to explore rhizosheath isolation methods and the diversity characteristics of microorganisms around the rhizosphere. In this study, we isolated the rhizosheath of Stipa grandis, a dominant species in desert steppe, and the microorganisms in the roots, root epidermis, rhizosheath and rhizosphere soil were extracted and sequenced by 16S rRNA and ITS. The alpha diversity index of bacteria in Stipa grandis rhizosphere soil was the greatest, followed by rhizosheath, and the alpha diversity index of endophytic bacteria in root system was the smallest. The alpha diversity index of fungi in the rhizosheath and rhizosphere soil were significantly higher than that in the root epidermis and root system. There were significant differences in bacterial community structure between the root epidermis, endophytic bacteria, rhizosheath and rhizosphere soil. Unlike bacterial community structure, the community structure of fungi in the root epidermis was similar that of endophytic fungi, but significantly different from those in rhizosheath and rhizosphere soil. This study demonstrated a feasible method for separating plant rhizosheath and root epidermis. We suggest that the root epidermis can act as the interface between the host plant root and the external soil environment. We will have to re-examine the biological and ecological significance of rhizosheath and microorganisms in rhizosheath, as well as the mechanism explaining the close relationship of the rhizosheath and the plant root epidermis. This study provides theoretical and technical guidance for the isolation of the plant rhizosheath and the study of microorganisms in plant rhizosheath.

TiO2-supported Au-Ag plasmonic nanocatalysts achieved by plasma restructuring and activation.

Plasmonic Au-Ag/TiO2 bimetallic nanocatalyst is regarded as a promising visible-light (VL) photocatalyst due to its wide light absorption and potentially enhanced activity. For its preparation, Au precursors usually contain Cl and co-impregnation/co-deposition suffers from AgCl precipitation, and consequently Au and Ag have to be sequentially supported. However, Au and Ag species of the sequential preparation are individually isolated and difficult to be homogeneously mixed. Here we report an Au-Ag plasmonic nanocatalyst achieved by plasma restructuring and activation from the sequential preparation. The isolated cationic Au and Ag species on the sequentially-prepared Au-Ag/TiO2 sample are restructured to be homogeneously mixed and highly activated by O2 plasma, which can be partially auto-reduced to Au-Ag bimetallic nanoparticles within the induction period of a few minutes in VL photocatalytic oxidation of CO. The Au-Ag plasmonic nanocatalyst exhibits a strongly enhanced activity in the VL photocatalytic reaction. The contribution of O2 plasma treatment and the enhancement mechanism for the Au-Ag plasmonic nanocatalyst are disclosed.

Steam reforming of tar derived from lignin over pompom-like potassium-promoted iron-based catalysts formed on calcined scallop shell.

In order to understand the improvement effect of potassium (K) on the catalytic activity of iron-loaded calcined scallop shell (CS) for the steam reforming tar derived from biomass, various K precursors were applied for the catalyst preparation. It is found that pompom-like iron-based particles with a mesoporous structure were easily formed on the surface of calcined scallop shell (CS) when K2CO3 was used as K precursor while no such kind of microsphere was formed when other kinds of K precursors such as KOH and KNO3 were applied. The optimum K-loading amount for the preparation of this catalyst was investigated. Based on the experimental results obtained, a mechanism for the formation of these microspheres was proposed. This pompom-like potassium-promoted iron-based catalyst showed a better catalytic activity and reusability for the steam reforming of tar derived from lignin.

Enhanced effect of water vapor on complete oxidation of formaldehyde in air with ozone over MnOx catalysts at room temperature.

At room temperature, the enhanced effect of water vapor on ozone catalytic oxidation (OZCO) of formaldehyde to CO2 over MnOx catalysts and the reaction stability was reported. In a dry air stream, only below 20% of formaldehyde could be oxidized into CO2 by O3. In humid air streams (RH≥55%), ∼100% of formaldehyde were oxidized into CO2 by O3 and the reaction stability was significantly enhanced. Meanwhile, in situ Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectra of OZCO of HCHO demonstrate that the amount of both monodentate and bidentate carbonate species on MnOx, in the dry stream, increased gradually with time on stream (TOS). However, in the humid stream, almost no accumulation of carbonate species on the catalysts was observed. To clarify the enhanced mechanism, formaldehyde surface reactions and CO2 adsorption/desorption on the fresh, O3 and O3+H2O treated MnOx catalysts were examined comparatively.

[Spectroscopic measurements of atomic hydrogen concentrations in dielectric barrier discharge hydrogen plasmas].

Atomic hydrogen plays important roles in chemical vapor deposition of functional materials, plasma etching, and surface cleaning. The present work introduces the fundamental principle to determine atomic hydrogen density via optical emission spectroscopy using Ar as an actinometer, and also reports the experimental results of atomic hydrogen density in the DBD discharge hydrogen plasmas. The variations of atomic hydrogen density and the hydrogen dissociation fraction as a function of pressure were calculated based on some of the available electron-impact excitation cross section and quenching cross sections in the literatures. In this work, as the pressure increases from 0.32 to 5.1 kPa, the hydrogen dissociation fraction decreases from 5.2% to 0.089%, and the atomic hydrogen density decreases from 4.9 x 10(15) cm(-3) to 1.3 x 10(15) cm(-3). The variations of H atom Balmer lines and Ar (750.4 nm) emission intensity as functions of gas pressure, discharge voltage, and frequency were also investigated.

Determination of atomic hydrogen in non-thermal hydrogen plasmas by means of molecular beam threshold ionization mass spectrometry.

Atomic hydrogen plays important roles in chemical vapor deposition of functional materials, plasma etching and new approaches to chemical synthesis of hydrogen-containing compounds. The present work reports experimental determinations of atomic hydrogen near the grounded electrode in medium-pressure dielectric barrier discharge hydrogen plasmas by means of molecular beam threshold ionization mass spectrometry (MB-TIMS). At certain discharge conditions (a.c. frequency of 24 kHz, 28 kV of peak-to-peak voltage), the measured hydrogen dissociation fraction is decreased from approximately 0.83% to approximately 0.14% as the hydrogen pressure increases from 2.0 to 14.0 Torr. A simulation method for extraction of the approximate electron beam energy distribution function in the mass spectrometer ionizer and a semi-quantitative approach to calibrate the mass discrimination effect caused by the supersonic beam formation and the mass spectrometer measurement are reported.