Preparative enrichment and separation of astragalosides from Radix Astragali extracts using macroporous resins

The enrichment and separation of astragalosides I–IV (AGs I–IV) were studied on eight macroporous resins in the present study. SA‐3 resin offered the best adsorption and desorption capacities for AGs I–IV than other resins. The models of adsorption kinetics were investigated in order to elucidate the mechanism of adsorption. The pseudo‐second‐order model was the better choice than the pseudo‐first‐order model to describe the adsorption behavior of AGs I–IV onto SA‐3 resin. The equilibrium experimental data were well fitted to Langmuir and Freundlich isotherms. SA‐3 resin adsorption chromatography tests were carried out to optimize the separation process of AGs I–IV from Radix Astragali extracts. With the optimum parameters for adsorption and desorption, the contents of AGs I–IV were 8.78‐, 11.60‐, 10.52‐ and 11.28‐fold increased with the recovery yields being 65.88, 90.92, 84.25 and 94.17%, respectively. The preparative enrichment and separation of AGs I–IV from Radix Astragali extracts can be easily and effectively achieved by SA‐3 resin adsorption chromatography. The developed methodology can also be referenced for the separation of other active constituents from herbal materials and manufacture of Radix Astragali products.     

The growth of Si/SiGe/Si structures for heterojunction bipolar transistor by gas source molecular beam epitaxy

Three n–p–n Si/SiGe/Si heterostructures with different layer thickness and doping concentration have been grown by a home-made gas source molecular-beam epitaxy (GSMBE) system using phosphine (PH₃) and diborane (B₂H₆) as n-and p-type in situ doping sources, respectively. Heterojunction bipolar transistors (HBTs) have been fabricated using these structures and a current gain of 40 at 300 K and 62 at 77 K have been obtained. The influence of thickness and doping concentration of the deposited layers on the current gain of the HBTs is discussed.     

Using mixed integer programming models to synchronously determine production levels and market prices in an integrated market for roundwood and forest biomass

Annals of Operations Research - We study a problem of integrating the supply chain of roundwood with the supply chain of forest biomass. The developed optimization model is a multiperiod,...     

Weak acid leaching of uranium ore from a high carbonate uranium deposit

Journal of Radioanalytical and Nuclear Chemistry - Mineralogical study showed that the Yuejin uranium ore is from a low grade, high carbonate and high pyrite sandstone type uranium deposit. Uranium...     

基于混合溶剂有机电解液的超低温孔洞石墨烯超级电容

适用于极低温环境的石墨烯超级电容具有广阔的应用前景。然而,由于片层间严重的堆叠团聚,目前石墨烯超级电容的低温储能性能并不理想。本文使用H₂O₂氧化刻蚀法制备了孔洞石墨烯(rHGO),将传统有机溶剂碳酸丙烯酯(PC)和低凝固点溶剂甲酸甲酯(MF)混合制备了混合溶剂有机电解液,组装获得了能够在-60 ℃极低温环境下稳定工作的超级电容。结果表明,该超级电容在-60 ℃下的比电容为106.2 F·g^-1,相对于常温电容(150.5 F·g^-1)的性能保持率高达70.6%,显著优于未做处理的石墨烯(52.3%)以及文献中的其他石墨烯材料。得益于孔洞化形貌中丰富的介孔和大孔所形成的离子传输通道和缩短的离子传输路径,孔洞石墨烯内的离子扩散阻抗远小于普通石墨烯,且受温度降低的影响更小。在-60 ℃的极低温条件下,该超级电容表现出26.9 Wh·kg^-1的最大能量密度和18.7 kW·kg^-1的最大功率密度,优于传统碳材料的低温超级电容性能。-60 ℃时在5 A·g^-1电流密度下循环充放电10000次后电容保持率达89.1%,具有良好的低温循环稳定性。     

三维MXene多孔结构的构建与应用研究进展

MXene作为一种新型二维（2D）纳米材料以其独特的高导电性、高电化学表面活性等特性在多个领域引起了广泛关注。然而,MXene纳米片在自组装过程中出现的紧密堆叠现象导致比表面积急剧下降,降低了活性表面积,从而严重阻碍了它们在能源储存、电磁屏蔽、吸附等领域的潜在应用。构建三维多孔结构是解决MXene组装过程中自堆叠问题的一种有效途径,而且通过不同的组装方法可以实现对多孔宏观结构组成成分、孔径分布以及孔径大小的调控,使得MXene多孔材料在机械性能、电学性能以及光热转换性能等方面得到更好的调整,从而满足不同应用领域的需求。本综述以Ti₃C₂T_x MXene为主要研究材料总结了各种多孔MXene宏观结构的制备方法,讨论了其在电池/超级电容器、电磁屏蔽与吸收、海水淡化、光催化以及传感和环境修复等方面的应用,阐述了MXene多孔结构在各种应用中的贡献与意义,并针对MXene多孔结构的制备、结构调控和应用等方面的机遇和挑战作了论述。     

Construction of lamellar morphology by side-chain crystalline comb-like polymers for gas barrier

A comb-like polymer containing crystallized alkyl side chains and the intermolecular hydrogen bonds between the linking groups was fabricated by grafting long-chain fatty amine onto poly(styrene-co-acrylic acid)_n (P(S-AA)_n, wherein “n” denoted AA feed ratio). The chemical structures and crystallization behaviors of the comb-like polymer P(S-AA)_n-g(p) (wherein “p” denoted the number of side-chain carbon atoms) were analyzed by Fourier transform infrared, gel permeation chromatography, X-ray photoelectron spectroscopy, and X-ray diffractometer, differential scanning calorimetry, atomic force microscopy, respectively. It was found that the lamellar morphology could be generated by controlling the grafting density and side chain length of P(S-AA)_n-g(p). Moreover, it was identified that the hydrogen bonds between amide groups could enhance the crystallinity and then adjust the interlamellar spacing of lamellar phase. As a result, P(S-AA)₇₀-g(18) with the highest degree of crystallinity and closely packed lamellar morphology showed a good gas-barrier performance, and the nitrogen permeability reached 1.78 × 10^?14 cm³·cm/cm²·s·Pa. Furthermore, the permeation switch of the obtained comb-like polymer could reach 500 times traversing the melting point.     

Sierpinski 地毯上S4模型的临界特性

通过键移动重整化群的方法, 分析了Sierpinski 地毯上S⁴模型的临界行为, 得到了系统的临界点. 由得到的结果可知, 本系统不仅有一个高斯不动点, 而且还存在着一个Wilson Fisher不动点, 把它与Sierpinski 地毯上的高斯模型相互对比, 发现本系统的临界点变化很大. 这说明这两个系统隶属于两个不同的普适类.