Xiao Li

Multilayered microwave absorbers which can provide massive interfaces are highly needed for electromagnetic-wave absorption property enhancement. Meanwhile, how to effectively avoid agglomeration and further widen the absorption band is still a challenge. Herein, accordion-like magnetized MXene/Ni composites were fabricated by the electrostatic self-assembly interaction between multilayer MXene and Ni(OH)2 nanoplates and subsequent in situ reduction in the H2/Ar atmosphere. Ni nanoparticles were uniformly distributed without magnetic agglomeration between the multilayered gaps of the adjacent 2D (2 dimension) MXene (Ti3C2Tx) of MXene/Ni nanocomposites (magnetized MXene), which hold the distinct absorption performance that the reflection loss maximum measures up to −50.5 dB at 5.5 GHz. Moreover, dynamic magnetic response of the magnetized MXene absorber was first researched by the electron holography analysis. The related key mechanism includes the enhanced magnetic loss, less dual-agglomeration (multilayer MXene itself and magnetic agglomeration), and more interfaces and intrinsic defects for related polarization. A broadened absorption bandwidth can further be obtained by changing the mass ratio of MXene to Ni that possesses the widest absorption bandwidth of 5.28 GHz. This work provides a new route for the balance among strong absorption intensity, tunable electromagnetic properties, and wide absorption bandwidth of the MXene-based nanocomposites.

Rapid urbanization would lead to deterioration of the eco-environment and damage the functioning of ecosystem services. Ecological security pattern (ESP) is one of important national strategies in China for coordinating the ecosystem protection and economic development. Previous studies have mainly focused on how to identify ecological sources and extract ecological corridors, but optimization of the identified ecological sources and resistance surfaces are seldom explored. In this study, a new strategy to optimize ecological sources and resistance surfaces was proposed. The optimal diffusion distance of each existing ecological source with poor landscape connectivity was analyzed to meet future needs. The radial effect of resistance in areas with high resistance values were considered in combination with the characteristics of species migration. Hunan is an important province in the Yangtze River Economic Belt (YREB) and the Rise of Central China strategies. Taking a rapidly urbanizing region in Hunan Province as an example, the results showed that the total area of the optimized ecological sources was 9.60% higher than that of the existing area, which expanded the radial range of ecosystem services and enhanced ecosystem internal connectivity. According to the spatial distribution of important ecological landscape elements, the ecological framework of “two axes, four cores, and four belts” was proposed. This study offers a new insight for ESP construction, which can provide a new reference for ecological protection and development planning of rapidly urbanizing regions in central-south China.

Abstract. Organosulfates (OSs) with ambiguous formation mechanisms are a potential source of missing secondary organic aerosol (SOA) in current atmospheric models. In this study, we chemically characterized OSs and nitrooxy-OSs (NOSs) formed under the influence of biogenic emissions and anthropogenic pollutants (e.g., NOx, SO42−) in summer in Beijing. An ultrahigh-resolution mass spectrometer equipped with an electrospray ionization source was applied to examine the overall molecular composition of S-containing organics. The number and intensities of S-containing organics, the majority of which could be assigned as OSs and NOSs, increased significantly during pollution episodes, which indicated their importance for SOA accumulation. To further investigate the distribution and formation of OSs and NOSs, high-performance liquid chromatography coupled with mass spectrometry was employed to quantify 10 OSs and 3 NOS species. The total concentrations of quantified OSs and NOSs were 41.4 and 13.8 ng m−3, respectively. Glycolic acid sulfate was the most abundant species among all the quantified species, followed by monoterpene NOSs (C10H16NO7S−). The total concentration of three isoprene OSs was 14.8 ng m−3 and the isoprene OSs formed via the HO2 channel were higher than those formed via the NO ∕ NO2 channel. The OS concentration coincided with the increase in acidic sulfate aerosols, aerosol acidity, and liquid water content (LWC), indicating the acid-catalyzed aqueous-phase formation of OSs in the presence of acidic sulfate aerosols. When sulfate dominated the accumulation of secondary inorganic aerosols (SIAs; sulfate, nitrate, and ammonium; SO42− ∕ SIA > 0.5), OS formation would obviously be promoted as the increasing of acidic sulfate aerosols, aerosol LWC, and acidity (pH < 2.8). Otherwise, acid-catalyzed OS formation would be limited by lower aerosol acidity when nitrate dominated the SIA accumulation. The nighttime enhancement of monoterpene NOSs suggested their formation via the nighttime NO3-initiated oxidation of monoterpene under high-NOx conditions. However, isoprene NOSs are presumed to form via acid-catalyzed chemistry or reactive uptake of oxidation products of isoprene. This study provides direct observational evidence and highlights the secondary formation of OSs and NOSs via the interaction between biogenic precursors and anthropogenic pollutants (NOx, SO2, and SO42−). The results imply that future reduction in anthropogenic emissions can help to reduce the biogenic SOA burden in Beijing or other areas impacted by both biogenic emissions and anthropogenic pollutants.