China Particuology最新文献

Core–shell silica nanoparticles are superior in modifying surface wetting behavior, enhancing nucleation and growth in crystallization, improving dispersion of naked nanoparticles, and thus upgrading the overall properties of organic polymers. The dispersion behavior and morphology of monodisperse core–shell silica particles in several polymers including polyesters are reviewed and their potential applications are discussed.

Three basic modules of gas-phase photochemical reactions involved in the formation of secondary aerosol are developed for modeling the concentration variation of precursors of aerosol, including ketone (RCO_x), aldehyde (ALD), peroxyacetylnitrate (PAN), NO₂, and SO₂, followed by numerical solution for each of the modules. Reasonable trends of concentration variation of the precursors can be obtained from the proposed modules.

Related referential studies on gas–solid two-phase flows were briefly reviewed. Bubble ascending in a two-dimensional (2D) gas–solid fluidized bed was studied both experimentally and numerically. A modified continuum model expressed in the conservation form was used in numerical simulation. Solid-phase pressure was modeled via local sound speed; gas-phase turbulence was described by the K–ɛ two-equation model. The modified implicit multiphase formulation (IMF) scheme was used to solve the model equations in 2D Cartesian/cylindrical coordinates. The bubble ascending velocity and particle motion in the 2D fluidized bed were measured using the photochromic dye activation (PDA) technique, which was based on UV light activation of particles impregnated with the dye. Effects of bed height and superficial gas velocity on bubble formation and ascent were investigated numerically. The numerically obtained bubble ascending velocities were compared with experimental measurements. Gas bubble in jetting gas–solids fluidized bed was also simulated numerically.

PM₁₀ (particulate matter with aerodynamic diameter less than 10 μm) samples were collected simultaneously at nine urban sites and one urban background site during two intensive observation campaigns in 2006. Concentrations of elemental carbon (EC) and organic carbon (OC) in PM₁₀ were analyzed using an element analyzer. The characteristics regarding spatial and seasonal distribution patterns of OC and EC concentrations and their contributions to PM₁₀ mass, as well as correlation between OC and EC, were investigated in detail. The average OC and EC concentrations for urban sites were 57.5 ± 20.8 and 8.3 ± 3.9 μg/m³, respectively, both being around three times higher than those for urban background site. As a whole, EC concentrations did not show distinct seasonal variations, though OC concentrations were generally higher in autumn than in spring. For urban sites, total carbonaceous aerosol (TCA) accounted for 33.2% in spring and 35.0% in autumn of PM₁₀ mass. The OC and EC concentrations were found significantly correlated to each other both in spring and in autumn, implying the existence of similar emission sources such as coal combustion. The OC/EC ratios generally exceeded 2.0, indicating the presence of secondary organic carbon (SOC), whose estimated concentration for urban Chongqing was 26.7 and 39.4 μg/m³, accounting for 48.9 and 61.9% of the total OC observed in the samples, in spring and in autumn, respectively.

A new dual-composition catalyst based on Ni–Mo/MgO with high efficiency of producing carbon nanotubes (CNTs) from methane was reported recently. In the present article, with this type of catalyst, the impact of such experimental parameters as reaction temperature, reaction time, concentration of H₂, flow rate ratio of CH₄ to H₂ on yield and graphitization were investigated, leading to the following optimal growth conditions: reaction time 60 min, reaction temperature 900 °C, CH₄:H₂ about 100:20 mL/min, under which high-yield multi-walled CNTs bundles were synthesized. Raman measurement indicated that the as-synthesized product was well-graphitized, and the purity was estimated over 95% by TG–DSC analysis. In terms of the above results, an explanation of high-efficiency formation of CNTs bundles and the co-catalysis mechanism of Ni–Mo/MgO were suggested.

In order to gain an insight into the aerosol properties and their climatic effect over the continental source regions of China, it is of significance to carry out long-term ground-based measurements of aerosol optical properties and radiative forcing. A couple of temporary and permanent Aerosol Robotic Network (AERONET) sites and three comprehensive radiative sites were established in China as a result of international cooperation in recent years. Heavy aerosol loading and significant temporal and spatial variation over North China are revealed by the AERONET data. Aerosol-induced reductions in surface radiation budget are examined on the basis of collocated observations by sun photometers and pyranometers.

Gold nanoparticles decorating the surface of multiwalled carbon nanotubes (MWCNTs) are prepared by photochemical reduction. The gold clusters form different interesting geometrical faceted shapes in accordance to time duration of synchrotron X-ray irradiation. The shape of nanogold could be spherical, rod-like, or triangular. Carbon nanotubes serve as optimal templates for the heterogeneous nucleation of gold nanocrystals. These nanocrystal structures are characterized by transmission electron microscope (TEM) and element analysis by energy dispersive spectroscopy (EDS).