The self-assembly behaviors of two series of monodispersed oligomers consisting of perylenediimide (PDI) linked by ethynylene and butadiynylene spacers are investigated in solutions. In spite of the very similar chemical structures, the two sets of oligomers manifest completely different optical properties upon self-aggregation, implying differed aggregate structures. While the oligomers containing butadiynylene spacers form H-aggregates, those featuring ethynylene linkers display J-aggregation characteristics. Thermodynamic analysis revealed that the self-association constants of both series of oligomers increase with the number of PDI units in the backbones. Oligomers containing the same number of PDI units but different spacers display nearly identical enthalpy changes. According to the molecular exciton theory, the observed H-and J-aggregates are suggested to comprise similar packing motifs with slightly varied slipping angles, giving rise to greatly disparate optical properties.
Using readily available aryl glyoxylic acids and arylene diacetic acids as starting materials, a series of polycyclic aromatic molecules bearing two phthalimide functional groups are synthesized via Perkin condensation followed by intramolecular cyclization reactions. Two different cyclization methods, photo-oxidation and Heck cross-coupling, are employed, both of which effectively accomplish the transformations from diaryl maleic anhydride or maleimide to polycyclic aromatic phthalimide functionality. The photocyclization protocol conveniently allows direct bridging of two plain aromatic C-H sites linked by a maleic anhydride group and uniquely produces the more twisted polycyclic framework as the major product, whereas the Heck coupling approach can typically afford more extended polycyclic skeletons. Thionation reactions are then carried out for the obtained polycyclic diimide molecules using Lawesson's reagent. For all isolated stable products, partial thionation occurs. The prepared polycyclic diimide compounds possess relatively low LUMO levels, and thionation further decreases the LUMO energy of the molecules by 0.2-0.3 eV. Electron-transporting properties are characterized by using solution-processed OFET devices, and an electron mobility of 0.054 cm(2) V-1 s(-1) is demonstrated by a selected compound. Such semiconducting performance promises great potentials of this class of compounds as useful electron-accepting and transporting building blocks in developing various new semi-conductive materials.
To improve the efficiency of TiO<sub>2</sub> as a photocatalyst for contaminant degradation, a novel nanocomposite catalyst of (N, Fe) modified TiO<sub>2</sub> nanoparticles loaded on bentonite (B-N/Fe-TiO<sub>2</sub>) was successfully prepared for the first time by sol-gel method. The synthesized B-N/Fe-TiO<sub>2</sub> catalyst composites were characterized by multiple techniques, including scanning electron microscope (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), X-ray fluorescence (XRF), nitrogen adsorption/desorption, UV-Vis diffuse reflectance spectra (DRS), and electron paramagnetic resonance (EPR). The results showed that bentonite significantly enhanced the dispersion of TiO<sub>2</sub> nanoparticles and increased the specific surface area of the catalysts. Compared with nondoped TiO<sub>2</sub>, single element doped TiO<sub>2</sub>, or unloaded TiO<sub>2</sub> nanoparticles, B-N/Fe-TiO<sub>2</sub> had the highest absorption in UV-visible region. The photocatalytic activity of B-N/Fe-TiO<sub>2</sub> was also the highest, based on the degradation of methyl blue (MB) at room temperature under UV and visible light irradiation. In particular, the synthesized B-N/Fe-TiO<sub>2</sub> showed much greater photocatalytic efficiency than N/Fe-TiO<sub>2</sub> under visible light, the newly synthesized B-N/Fe-TiO<sub>2</sub> is going to significantly increase the photocatalytic efficiency of the catalyst using sun light.
Abstract Human activities are the main drivers of alterations of regional N cycles. With increasing population and economic development, human-induced N inputs are expected to continue to increase in the future, especially in many regions of developing countries. Because N sources vary substantially at different temporal and spatial scales and stages of economic development, it is of great importance for environmental managers to be able to simulate the dynamics of N inputs to a specific region of interest. Based on the concept of net anthropogenic N inputs (NANI), a quasi-mass-balance method, a system dynamics model simulating regional N inputs (NANI-SD) is developed and presented here for the first time. The NANI-SD model evaluates how much new N from anthropogenic activities is introduced to the whole basin, providing a simple but effective way to examine human influences on regional N cycles. Our application of the NANI-SD model to the Lake Dianchi basin in China shows that human-induced N inputs will continue to increase under current trends of development. Scenarios focused on lowering population growth rate and banning crop production were not effective in achieving long-term reductions in N inputs because their impacts were compensated by the increases in croplands and food imports, respectively. However, adjusting diet patterns and limiting livestock numbers within the basin were shown to be highly effective in controlling regional N inputs without compromising environmental sustainability of food imported regions. There was a significant trade-off between N self-sufficiency and N inputs to the region, posing the issue of “pollution transfer” as the regions of livestock production providing animal products to the Lake Dianchi basin could suffer from locally intensified levels of N pollution introduced while producing those animal N products. The positive relationship between NANI and the proportion of animal-based protein in food indicates that reducing meat consumption could be an effective way of controlling local N inputs without sacrificing food sovereignty. NANI to the basin could also be reduced by recycling N in human and livestock wastes, but its capacity to reduce NANI is limited and projected to diminish with time.
Anthropogenic activities usually contaminate water environments, and have led to the eutrophication of many estuaries and shifts in microbial communities. In this study, the temporal and spatial changes of the microbial community in an industrial effluent receiving area in Hangzhou Bay were investigated by 454 pyrosequencing. The bacterial community showed higher richness and biodiversity than the archaeal community in all sediments. Proteobacteria dominated in the bacterial communities of all the samples; Marine_Group_I and Methanomicrobia were the two dominant archaeal classes in the effluent receiving area. PCoA and ANOVA revealed strong seasonal but minor spatial changes in both bacterial and archaeal communities in the sediments. The seasonal changes of the bacterial community were less significant than those of the archaeal community, which mainly consisted of fluctuations inabundance of a large proportion of longstanding species rather than the appearance and disappearance ofmajor archaeal species. Temperaturewas found to positively correlatewith the dominant bacteria, Betaproteobacteria, and negatively correlate with the dominant archaea,Marine_Group_I; and might be the primary driving force for the seasonal variation of the microbial community.
In either eutrophic Dianchi Lake or mesotrophic Erhai Lake, the abundance, diversity, and structure of archaeaplankton communities in spring were different from those in summer. In summer, archaeaplankton abundance generally decreased in Dianchi Lake but increased in Erhai Lake, while archaeaplankton diversity increased in both lakes. These two lakes had distinct archaeaplankton community structure. Archaeaplankton abundance was influenced by organic content, while trophic status determined archaeaplankton diversity and structure. Moreover, in summer, lake sediment archaeal abundance considerably decreased. Sediment archaeal abundance showed a remarkable spatial change in spring but only a slight one in summer. The evident spatial change of sediment archaeal diversity occurred in both seasons. In Dianchi Lake, sediment archaeal community structure in summer was remarkably different from that in spring. Compared to Erhai Lake, Dianchi Lake had relatively high sediment archaeal abundance but low diversity. These two lakes differed remarkably in sediment archaeal community structure. Trophic status determined sediment archaeal abundance, diversity and structure. Archaeal diversity in sediment was much higher than that in water. Water and sediment habitats differed greatly in archaeal community structure. Euryarchaeota predominated in water column, but showed much lower proportion in sediment. Bathyarchaeota was an important component of sediment archaeal community.
Spoof surface plasmons (SSP) has become an active research topic in microwave and terahertz (THz) spectrum since its extraordinary optical and physical properties. The strong near field of SSP mode on the corrugated metal surfaces makes it especially attractive for developing a THz electronic source. A THz electronic source based on the efficient generation of SSP modes on the doubly corrugated metallic waveguide is proposed and studied in this paper. The analytical dispersion relations of SSP modes are obtained based on a modal expansion method and the field profiles of SSP modes are also presented by the finite integration method. Besides, the interaction between SSP and injected electron beam is modeled and implemented by particle-in-cell (PIC) simulation based on finite difference time domain algorithm. The gap size between the doubly corrugated metal surfaces can significantly influence the output power and PIC simulation results reveal that output power can be increased from 272 mW to 36.5 W when the gap size decreases from 90 to 40 μm at the frequency near 1 THz by the 19.55 kV, 1 A injected electron beam within 4.5-mm interaction length. The dependencies of the output performance on electron beam parameters are also investigated and we find that there is an optimized beam voltage for the given operation frequency. Various electron beams of pulse and direct current electron beam are studied and we find that half pulsewidth of periodical electron beam is more preferable than other emissive shape of injected electron beam for the given structure. Our studies on the efficient generation of SSP modes on the doubly corrugated metallic waveguide may provide a new way to develop THz electronic sources.
A terahertz electronic source based on the spoof surface plasmon (SSP) with 2-D subwavelength metallic grating is presented. The SSP dispersion relation of plasmonic grating is derived by a simplified modal expansion method, and the coupling and interaction between the SSP and the electron beam is studied by particle-in-cell simulation. The results reveal that the output performance highly depends on the location of electron beam from grating surface. For an injected electron beam with 19.15 kV and 0.5 A, the SSP output power can reach 22.7 W for the optimized distance of the beam from the grating surface at a frequency near 1 THz for the given structure. Besides, the influence of different electron beam parameters on output power is also investigated and we find that pulse electron beam is preferable than continuous electron beam for good performance. There is an optimized operation frequency for the given beam voltage. Furthermore, output performance can be improved by changing grating structure parameters. By decreasing the grating groove filling factor from 0.8 to 0.2, the SSP output power can be increased from 17.2 to 23.6 W. The SSP power can also be significantly enhanced from 14 to 28.6 W using shallow grating with a groove depth changing from 76 to 56 渭m for the optimized operation frequency with the same electron beam. The present work may provide a new avenue to obtain powerful THz electronic sources.