金丝桃素的研究进展

对金丝桃素的最新研究成果进行了综述。包括测定,药理作用,着重介绍了金丝桃素的制备,为金丝桃素的进一步研究开发提供了文献依据。     

Boosting the antimicrobial and Azo dye mineralization activities of ZnO ceramics by enhancing the light-harvesting and charge transport properties

Herein, we report the wet-chemical synthesis of a ferromagnetic nickel-doped ZnO (Zn_1-xNi_xO) nanocatalyst as a novel and visible-light-driven photocatalyst. Through X-ray diffraction, UV/Vis absorption, electronic studies, and current-voltage experiments, the effect of the ferromagnetic nickel dopant on the structural, optical, morphological, and electrical properties of the synthesized Zn_1-xNi_xO nanocatalyst was studied. The Ni-doping introduced the structural variation in the Zn_1-xNi_xO nanocatalyst, exhibiting a visible light-triggered optical band gap of 2.96 eV and an excellent current conductivity of 6.3 × 10⁻⁴ Sm⁻¹. Moreover, the synthesis of the Zn_1-xNi_xO catalyst at the nanoscale enhanced its surface energy, showing a robust affinity to stick with the dye and pathogenic microbes. The synergistic effects of all the mentioned features enable our Zn_1-xNi_xO nanocatalyst to efficiently generate and transport reactive oxygen species (ROS) under visible light illumination. Regarding antibacterial action, the as-synthesized Zn_1-xNi_xO nanocatalyst showed 1.7% higher activity against E. coli than that of the drug Ciprofloxacin. In addition, doped nanocatalysts mineralize almost 97% of the Allura red dye in just 80 min with a constant rate value of 0.036 min⁻¹. The impedance study and post-application XRD proposed that our Zn_1-xNi_xO nanocatalyst has good conductivity and structural stability. Applications studies show the unusual photocatalytic activity of as-synthesized Zn_1-xNi_xO nanocatalysts, which makes it a suitable candidate for industrial discharge treatment applications at the expense of solar light.     

Effects of YH2 addition on pressureless sintered AlN ceramics

A new type of non-oxide sintering additive of YH₂ was introduced for the fabrication of AlN ceramics with high thermal conductivity and flexural strength. The effects of YH₂ addition (0–5 wt%) on the phase composition, densification, microstructure, thermal conductivity and flexural strength of pressureless sintered AlN ceramics were investigated and compared with those Y₂O₃-added samples (1–5 wt%). The addition of 1 wt% YH₂ led to an in-situ reduction reaction with oxygen impurities, the formation of Y₂O₃ and finally the formation of yttrium aluminate, which in turn improved densification and microstructure. A high flexural strength (408.69 ± 28.23 MPa) was achieved. The addition of 3 wt% YH₂ increased the average grain size and purified the lattice. All these effects are believed to help achieve a high thermal conductivity of 184.82 ± 1.75 W·m^?1·K^?1. Although the thermal conductivity was close to the value of 3 wt% Y₂O₃-added sample, its strength was much increased to 381.53 ± 43.41 MPa. Meanwhile, it demonstrated a good combination of the thermal conductivity and flexural strength than the values reported in some literature. However, further increasing the YH₂ addition to 5 wt% resulted in a high N/O ratio that inhibited the densification behavior of AlN ceramics. The current study showed that AlN ceramics with excellent thermal and mechanical properties could be obtained by the introduction of a suitable YH₂ additive.     

Prediction model for methanation reaction conditions based on a state transition simulated annealing algorithm optimized extreme learning machine

Methanation is the core process of synthetic natural gas, the performance of the entire reaction system depends on precise values of the reaction condition parameters. Accurate predictions of the CO conversion rate of the methanation reaction can eliminate time-consuming and complex steps in experiments and speed up the discovery of the best reaction conditions. However, the methanation reaction is an uncertain, highly complex, and highly nonlinear process. Thus, this paper proposes a machine learning prediction model for the methanation reaction to facilitate the subsequent search for optimal reaction conditions. The reaction temperature, pressure, hydrogen–carbon ratio, water vapor content, CO₂ content, and space velocity were selected as the condition variables. The CO conversion rate was the optimization objective. An extreme learning machine (ELM) was selected as a prediction model. Because the input weights and bias matrices of the ELM are randomly generated, an ELM based on a state transition simulated annealing (STASA-ELM) algorithm is proposed. The STASA algorithm was used to optimize the ELM to improve the accuracy and stability of the model. Five additional sets of experimental data were designed for the experiment, and the error between the experimental and predicted values was small. Thus, the STASA-ELM algorithm can accurately predict the conversion of CO for different values of reaction conditions.     

Type-II van der Waals heterostructures of GeC,ZnO and Al2SO monolayers for promising optoelectronic and photocatalytic applications

Two-dimensional materials stacked via van der Waals (vdW) forces provide a revolutionary route toward high-performance optoelectronic and renewable energy devices. Here, we report vdW heterostructures (vdWHs) consisting of GeC, ZnO and Al₂SO monolayers on first-principles computations. GeC (ZnO)–Al₂SO vdWHs are both stable type-II semiconductors with indirect (direct) band gaps. This significantly suppresses the recombination of photogenerated charge carriers across the interface, making them promising for light detection and harvesting applications. Charge transfer from GeC (Al₂SO) layer to Al₂SO (ZnO) layer leads to p-doping in GeC (Al₂SO) and n-doping in Al₂SO (ZnO) of GeC (ZnO)–Al₂SO vdWHs. In contrast to pristine monolayers, higher carrier mobility promotes charge transfer to the surface and reduces carrier recombination in GeC (ZnO)–Al₂SO vdWHs. Further, the absorption spectra indicate redshift (blueshift) and reveal more solar light is absorbed by GeC (ZnO)–AlS₂O vdWHs in the visible (ultraviolet) region. The band edge positions suggest that GeC–Al₂SO vdWHs can reduce water into H₂ but fails to perform an oxidation reaction at pH = 0. More interestingly, ZnO–Al₂SO vdWHs can perform redox reactions, making them prominent for overall water-splitting reactions. Our computational findings provide a path for the design of vdWHs for future optoelectronic and photovoltaic devices.     

Analysis of PFPE lubricating film in NEMS application via molecular dynamics simulation

Interfacial lubrication plays an important role in the functional performance of nanoelectrome-chanical (NEMS) systems. Here, we used molecular dynamics simulation to analyze the lubricating effect of a perfluoropolyether (PFPE) film to reveal the mechanism behind our experimental observations and understand the performance of the film. There was good agreement in the trends of the coefficients of friction between our simulation results and experimental characterizations. By studying the atomic motion, interfacial mechanics and polymer chain deformation, we found that PFPE films provide good lubrication because their linear flowability promotes surface reconstruction. Our simulations suggest that a high performance lubricant film needs to have low resistance to shear deformation, possess high linear flowability, promote surface reconstruction and adhere effectively to the substrates.     

Effects of pyrolysis temperature on the chemical composition of refined softwood and hardwood lignins

The current study uses nuclear magnetic resonance, Fourier-transform infrared spectroscopy and Raman spectroscopy to investigate the evolution of refined softwood and hardwood lignins under various pyrolytic exposures. Little chemical change occurred at pyrolysis temperatures of 250 and 300 °C, whereas significant mass loss and chemical change was observed at 400 and 500 °C. These losses were mainly attributed to evolution of methoxyl, hydroxyl, and propyl groups. Mass loss plateaued following pyrolysis at 500 °C, but rearrangements continued to occur at higher temperatures, resulting in char that became increasingly polyaromatic in nature. Following brief pyrolytic exposures at 500 and 600 °C, the refined hardwood and softwood lignins yielded coal-like products. Lignin pyrolyzed at higher temperatures yielded chars with greater order, similar in composition to coke. These coal and coke-like products are called “lignin-based carbon” (LBC). The polyaromatic nature of the LBC after high temperature pyrolysis was perceived as the result of radical formation and recombination, leading to fused aromatic structures, which occurs more readily at higher temperatures.     

Highly thermally conductive POSS-g-SiCp/UHMWPE composites with excellent dielectric properties and thermal stabilities

Polyhedral oligomeric silsesquioxane grafting thermally conductive silicon carbide particle (POSS-g-SiCp) fillers, are performed to fabricate highly thermally conductive ultra high molecular weight polyethylene (UHMWPE) composites combining with optimal dielectric properties and excellent thermal stabilities, via mechanical ball milling followed by hot-pressing method. The POSS-g-SiCp/UHMWPE composite with 40 wt% POSS-g-SiCp exhibits relative higher thermal conductivity, lower dielectric constant and more excellent thermal stability, the corresponding thermally conductive coefficient of 1.135 W/mK, the dielectric constant of 3.22, and the 5 wt% thermal weight loss temperature of 423 °C, which holds potential for packaging and thermal management in microelectronic devices. Agari’s semi-empirical model fitting reveals POSS-g-SiCp fillers have strong ability to form continuous thermally conductive networks.     

US electric industry response to carbon constraint: a life-cycle assessment of supply side alternatives

This study explores the boundaries of electric industry fuel switching in response to US carbon constraints. A ternary model quantifies how supply side compliance alternatives would change under increasingly stringent climate policies and continued growth in electricity use. Under the White House Climate Change Initiative, greenhouse gas emissions may increase and little or no change in fuel-mix is necessary. As expected, the more significant carbon reductions proposed under the Kyoto Protocol (1990—7% levels) and Climate Stewardship Act (CSA) (1990 levels) require an increase of some combination of renewable, nuclear, or natural gas generated electricity. The current trend of natural gas power plant construction warrants the investigation of this technology as a sustainable carbon-mitigating measure. A detailed life-cycle assessment shows that significant greenhouse gas emissions occur upstream of the natural gas power plant, primarily during fuel-cycle operations. Accounting for the entire life-cycle increases the base emission rate for combined-cycle natural gas power by 22%. Two carbon-mitigating strategies are tested using life-cycle emission rates developed for US electricity generation. Relying solely on new natural gas plants for CSA compliance would require a 600% increase in natural gas generated electricity and almost complete displacement of coal from the fuel mix. In contrast, a 240% increase in nuclear or renewable resources meets the same target with minimal coal displacement. This study further demonstrates how neglecting life-cycle emissions, in particular those occurring upstream of the natural gas power plant, may cause erroneous assessment of supply side compliance alternatives.     

Poly(ethylene glycol)-oligodeoxyribonucleotide block copolymers for affinity capillary electrophoretic separation of single-stranded DNAs with a single-base difference

An affinity capillary electrophoretic method was developed to detect a single-base difference of single-stranded DNA (ssDNA). Poly(ethylene glycol)-oligodeoxyribonucleotide block copolymers (PEG-b-ODN) were prepared for use as a novel affinity ligand. We introduced a running buffer solution of PEG-b-ODN into a capillary tube, and electrophoretically separated a mixture of chemically synthesized 20 mer ssDNA (normal ssDNA) and a single-base-substituted 20 mer ssDNA (mutant ssDNA). When the base sequence of PEG-b-ODN was designed to be complementary to part of the normal ssDNA, the migration rate of the normal ssDNA was significantly decreased by reversible hybridization with PEG-b-ODN, depending on the base number of PEG-b-ODN, the salt concentration of the running buffer, and the capillary temperature. In contrast, the mobility of mutant ssDNA did not change because the interaction with PEG-b-ODN was negligible. Optimization of the analytical conditions gave two distinct peaks, one for normal and the other for mutant ssDNA, on the electropherogram, allowing for facile discrimination of the single-base difference. The results indicate that PEG-b-ODN is a promising affinity ligand for the capillary electrophoretic separation of normal and single-base mutated ssDNA.