Fabrication of ZIF-8 membranes on dual-layer ZnO-PES/PES organic hollow fibers by in-situ crystallization

Compared to inorganic supports, polymeric supports can offer additional benefits, e.g., easier processing and cheaper. However, the organic surface has weak adhesion to the zeolitic imidazolate frameworks(ZIFs) membrane layer, which usually requires complex surface modification or seeding. Herein, we demonstrate that a dual-layer asymmetric polymer support prepared by a simple spinning process is a good candidate for the preparation of ZIF-8 membrane. The inner layer of the support is an organic hollow fiber(PES) with finger-like pores, and the outer layer is a ZnO-PES composite layer with finger-like pores also. The ZnO-PES composite layer is expected to contain uniform ZnO crystals in the polymer matrix, i.e., the ZnO particles in the skin layer of the support are not easy to fall off. Under the induction of ZnO particles in the outer layers, continuous ZIF-8 membranes can be prepared by single in-situ crystallization, showing good adhesion to the supports. The obtained ZIF-8 membranes show a H_(2) permeance of 8.7 × 10^(-8)mol·m^(-2)·s^(-1)·Pa^(-1) with a H_(2)/N_(2) ideal separation selectivity of 18.0. The design and preparation of this dual-layer polymer support is expected to promote the large-scale application of MOF membranes on polymer supports.

Gold/Mg-Al mixed oxides catalysts for oxidative esterification of methacrolein:Effects of support size and composition on gold loading

Gold catalysts supported on Mg-Al mixed oxides for oxidative esterification of methacrolein are prepared by impregnation.Effects of the support particle size,concentration of HAuCl4 solution and Mg/Al ratio on gold loading and catalytic properties are investigated.The catalysts are characterized by CO_(2)-TPD,EDS,XPS,STEM and XRD techniques.Catalysts with smaller support particle size show more uniform gold distribution and higher gold dispersion,resulting in a higher catalytic performance,and the uniformity of gold and the activity of the catalysts with larger support particle size can be improved by decreasing the concentration of HAuCl4 solution.The Mg/Al molar ratio has significant effect on the uniformity of gold and the activity of the catalyst,and the optimum Mg/Al molar ratio is 0.1–0.2.This study underlines the importance of engineering support particle size,concentration of HAuCl4 solution and density of adsorption sites for efficient gold loading on support by impregnation.

儒家文化会影响企业的投资效率吗?

本文从文化心理学和文化地理学的角度出发,以2003~2018年我国沪深A股的上市公司为研究样本,实证检验上市公司所在地儒家文化氛围能否影响及如何影响企业的投资效率,并探究这种影响在不同市场化程度下是否存在差异。研究结果表明:上市公司所在地儒家文化氛围越浓厚,企业的非效率投资行为越少,上述关系在国有企业中更明显。进一步研究发现,市场化会削弱儒家文化与企业非效率投资的负向关系,这说明正式与非正式制度之间存在一定程度的替代关系,这一点有助于深刻理解我国新兴转轨经济的不同运行机制。机制检验发现,儒家文化提升企业投资效率的机制是改善信息环境和抑制管理者私利动机。本文不仅丰富了企业投资效率影响因素的研究,也丰富了儒家文化这种非正式制度对微观企业行为作用的研究。

Structure and Mechanical Performance of Nitrogen Doped Diamond-like Carbon Films

Nitrogen doped diamond-like carbon （DLC：N） films were prepared by electron cyclotron resonance chemical vapor deposition （ECR-CVD） on polycrystalline Si chips. Film thickness is about 50 nm. Auger electron spectroscopy （AES） was used to evaluate nitrogen content, and increasing N2 flow improved N content from 0 to 7.6%. Raman and X-ray photoelectron spectroscopy （XPS） analysis results reveal CN-sp^3C and N-sp^2C structure. With increasing the N2 flow, sp^3C decreases from 73.74% down to 42.66%, and so does N-sp^3C from 68.04% down to 20.23%. The hardness decreases from 29.18 GPa down to 19.74 GPa, and the Young＇s modulus from 193.03 GPa down to 144.52 GPa.

冰湖溃决洪水威胁高亚洲基础设施

青藏高原及其周边地区冰湖灾害频发,目前对其灾害特征及导致的破坏缺乏系统的分析.本研究旨在揭示冰湖灾害过去和未来的变化趋势及其对基础设施造成的影响,以指导区域及跨境流域冰湖灾害防控技术和策略的构建.研究梳理了1900-2022年间发生的298例冰湖灾害事件,发现其呈增长的趋势,尤其是1964年以来的部分冰湖灾害严重损坏了下游基础设施,不同类型冰湖灾害在空间分布、爆发和成灾特征等方面存在明显差异.例如,西斯帕冰川阻塞湖在2019-2022年连续爆发了5次溃决洪水,最近一次冲毁了下游中巴公路的桥梁和路基,影响中巴经贸.高山区冰川冰湖变化、交通和水电等基础设施及人口增长,致使冰湖灾害风险上升.为此,重大基础设施的规划应充分考虑相关风险,建立防控措施以保障人员和基础设施安全.

问询函会影响企业实际税率吗——来自中国上市公司的证据

近年来非行政处罚性监管越来越成为维护资本市场稳定的重要手段,据此本文以证券交易所出具的问询函为研究对象,收集2014—2019年中国A股上市公司数据,检验企业收到问询函对实际税率的影响。研究发现,收到问询函后,上市公司实际税率有所提高,当问询函涉及税务问题且涉及的税务问题数量越多时,其对实际税率的提高作用越强;这一作用主要通过降低企业的代理成本来实现。进一步的研究发现,问询函对企业实际税率的影响因产权性质、政治关联、当地税务机关执法力度的差异而有所不同;相较于国有企业、政治关联企业以及当地税务执法力度较强的企业,问询函对实际税率的提高在民营企业、无政治关联企业、执法力度更弱的企业中更显著。本文的研究结果表明,问询函对企业实际税率具有监管作用,可以作为监管上市公司、维护市场稳定的手段。本文不仅丰富了新近关于问询函的研究,也对相关机构监管手段的创新有重要启示。