造纸法烟草薄片天然多糖助留剂研究进展

造纸法烟草薄片原料中含有大量的细小纤维、碎片和矿物填料,其易在加工过程中流失,使得原材料消耗和水处理负荷增加,影响烟草薄片品质。天然多糖化学性质稳定、无毒、可生物降解,可以用作烟草薄片的助留剂。本文综述了天然多糖助留剂在烟草薄片中的应用情况,包括单元、双元及多元助留体系,并从微观结构出发,总结了天然多糖助留剂发挥作用的机理和效果。     

Boosting the Catalytic Performance by Confining Rich Carbon Atoms over Graphite Carbon Nitride Structure

In this study, the porous ultrathin graphitic carbon nitride (CN) nanosheets with rich C and nitrogen defects were prepared by one-step calcining the mixture of melamine and glucose (Glu) in air atmosphere (Glu-CN). Introducing simultaneously rich C atoms and nitrogen defects into CN structures continuously modulates the bandgaps from 2.67 to 1.81 eV of CN photocatalysts. Due to large surface area, more active sites, remarkably longer lifetime of charge carriers and adjustable band gap structure, the prepared ultrathin porous CN nanosheets show the enhanced photocatalytic performance for the degradation of methyl orange (MO) under visible light. The degradation efficiency of optimal CN nanosheet photocatalyst for MO is 5.75 times that of bulk CN. This work provides a facile and universal relevance approach to engineer the band structures of CN by introduction of rich C and porous morphology for high-performance photocatalytic, which can provide informative principles for the design of efficient photocatalysis systems for solar energy conversion.

Graphic Abstract

     

黄河中下游沿黄城市水资源承载力贴近度空间结构及作用机理

采用贴近度测度黄河中下游31个沿黄城市水资源承载力,分析承载力贴近度的空间特征和空间作用机理。结果表明：黄河中下游流域城市水资源承载力整体偏低,尤其是下游流域沿黄城市的水资源供需矛盾尖锐;从空间结构特征全局看,31个沿黄城市水资源承载力整体呈现空间自相关特征,从局部看,大部分城市无分异特征,但中游流域出现热点区域,下游流域尤其是河南省出现低洼区域;通过沿黄城市水资源承载力贴近度空间作用机理分析,中游流域沿黄城市水资源承载力受到驱动力（D）、压力（P）、状态（S）、影响（I）、管理（M）5个因素的影响,且城市之间存在空间虹吸效应,水资源表现出空间竞争,而不是空间协同发展。下游流域沿黄城市水资源承载力只受到驱动力（D）、状态（S）、影响（I）3个因素的作用。研究成果可为沿黄城市加强水资源的管理、优化城市发展模式提供参考。     

Characteristics of flow fields in the gas–liquid mini-bubble columns with particle image velocimetry measurements

As a new type of gas–liquid microreactors, the gas–liquid mini-bubble column has potential applications. However, few studies on the flow fields in the mini-bubble column can be found at present. In this work, particle image velocimetry (PIV) was used to visually study the velocity fields, vorticity fields and bubble dynamics in the gas–liquid mini-bubble columns with column inner diameters of 1–3 mm and mini-bubble diameters ranged from 0.7 to 1.3 mm. It is found that with the increase of superficial liquid velocity, bubbles rose from almost straight line to Z-shaped or S-shaped trajectory, and the bubble trajectory changed from one-dimension to three-dimension; when the bubble velocity changed, the bubble size and gas holdup decreased; bubble terminal velocity was controlled by bubble buoyancy and flow resistance, and increased slightly with bubble coalescence. These findings may provide basic reference for the design and scale-up of such a mini-bubble column reactor.     

莱茵衣藻响应缺硫的环状RNA的预测与鉴定

环状核糖核酸(circular ribonucleic acid,circular RNA或circRNA)是一类无5'帽子结构及3'poly A尾,以共价键连接形成闭合环形结构的非编码RNA分子,通过转录后调控的方式参与动植物细胞的众多代谢途径.莱茵衣藻(Chlamydomonas reinhardtii,C.rei...     

Fracture behaviour of ceramic–metallic glass gradient transition coating

A new composite coating material of ceramic (Al₂O₃-40?wt% TiO₂)–metallic glass (Fe₅₆Cr₂₃Mo₁₃B₈) gradient transition coating was successfully prepared by atmospheric plasma spraying technology, and a new theory of laminar–columnar structure gradient transition synergistic enhancement effect was proposed. The microstructure and element distribution of the composite coating were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron probe microanalysis (EPMA). The fracture toughness and fracture behaviour of the composite coating were analysed via micro-hardness and three-point bending (3PB) tests. The results showed that the stress release of the ceramic–metallic glass gradient transition coating was stable compared with that of the conventional gradient coating in the stage of acute deformation, and the coating exhibited better fracture toughness. Different areas of the ceramic–metallic glass gradient transition coating exhibited different fracture behaviours. Additionally, the ceramic layer was made of columnar crystals, and the metal–glass layer was lamellar. The laminar–columnar structure gradient transition synergistic enhancement effect improved the anti-crack growth and fracture toughness. This study provides a new and viable option for the improvement of thermal spraying ceramic composite coatings.     

PdAg bimetallic electrocatalyst for highly selective reduction of CO2 with low COOH* formation energy and facile CO desorption

Nano Research - For electrocatalytic reduction of CO2 to CO, the stabilization of intermediate COOH* and the desorption of CO* are two key steps. Pd can easily stabilize COOH*, whereas the strong...