Prestructured MXene fillers with uniform channels to enhance CO2 selective permeation in mixed matrix membranes

The packing pattern of two-dimensional (2D) sheet-like fillers in membranes is relatively random, leading to the unfavorable permeability from tortuous diffusion pathway. A new strategy that using prestructured materials with uniform channels as fillers was proposed. In this work, Ti₃AlC₂ is etched to prepare multilayered MXene (m-MXene), the channels aggregate as a whole unit, ensure the impossibility of ineffective packing compared with traditional individual sheets, largely facilitating the selective permeation. Then, the m-MXene/Poly (amide-6-b-ethylene oxide) (Pebax) MMMs are synthesized. SEM images demonstrate the accordion shaped structure of filler, which is the multi-channels laminates. Furthermore, the results of gas permeation test exhibit enhanced performance of m-MXene/Pebax MMMs. MMM with 0.5 wt.% m-MXene behaved best, CO₂ permeability of 86.22 Barrer as well as CO₂/N₂ selectivity of 104.85, transcending the Robeson upper bound (2008). Having distinct enhancement for CO₂ separation, the m-MXene/Pebax MMMs in this work offer prospective practical applications.     

Thin-film composite forward osmosis membrane prepared from polyvinyl chloride/cellulose carbamate substrate and its potential application in brackish water desalination

Synthesized by the reaction between α-cellulose and m-tolyl isocyanate (MTI), cellulose carbamate (CC) was blended with polyvinyl chloride (PVC) to fabricate substrates for thin-film composite (TFC) forward osmosis (FO) membranes. The introduction of CC into substrates improved both membrane structure and performance. The substrates exhibited higher porosity and hydrophilicity, and better connective pore structure; while rejection layer exhibited better morphology but limited cross-linked degree decrease after the introduction of CC. According to the results, the CC blend ratio of 10% was the optimal ratio. With this blend ratio, the TFC-10 membrane presented favorable water permeability (1.86 LMH/bar) and structure parameter (337 μm), which resulted in excellent FO performance (water flux with a value of 40.40 LMH and specific salt flux with a value of 0.099 g/L under rejection layer faces draw solution [DS] mode when 1 M NaCl and deionized water were utilized as DS and feed solution). In addition, the TFC-10 membrane showed good water flux and low-sulfate ion leakage in the potential application of brackish water desalination.     

An improved strategy to synthesize graphite oxide with controllable interlayer spacing as coatings for anticorrosion application

A facile method to synthesize nanoscale graphene oxide (GO) with controllable interlayer spacing was carried out using two-step oxidation process and much less acid to improve the efficiency of the oxidation. The X-ray diffraction results demonstrated that GO had been successfully prepared from graphite because of disappearance of characteristic peaks of pristine graphite at about 2θ = 26.5° along with appearance of a sharp major peak of GO at about 2θ = 9.4°. The increased basal spacing d₀₀₁ of as-prepared GO could reach as high as 9.39 Å, suggesting higher degree of oxidation than that prepared by the classical Hummers' synthesis, and characterization results from Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy further confirmed this conclusion. The influence of GO on anti-corrosion performance of nanocomposite coatings composited with the 2,5-dimethoxyaniline (DMA) conductive polymer was examined via potentiodynamic polarization curve tests in 3.5 wt% NaCl aqueous solution. The results demonstrated that the incorporation of GO significantly decreased the corrosion current density (i_corr = 2.62 μA/cm²) in the case of GO-PDMA coating, reflecting excellent physical isolation of GO and its synergistic effect with PDMA against the infiltration of water and corrosive electrolyte.     

Sodium citrate-assisted synthesis of nano-manganese oxide on carbon fiber for enhancing the mechanical and frictional performances of carbon fiber-reinforced resin matrix composites

Aiming to enhance the carbon fiber (CF)/resin interfacial adhesion, this report describes the novel application of sodium citrate (SC) as an auxiliary reducing agent and surface regulator to control the morphology of nano-manganese dioxide (MnO₂) on the CF surface. The composites were fabricated by means of controlling the molar concentration ratio of SC to Mn source (0:1, 1:3, 1:2, and 1:1) in hydrothermal synthesis. The results reveal that MnO₂ nanosheets on the CF surface become denser as the concentration of SC is 1/3 of Mn source, which makes advance to the surface roughness and surface energy of CF. Simultaneously, the tensile strength of as-prepared composite is increased by 52.8%. The homologous friction coefficient tends to be high and stable and the wear volume is significantly reduced by 63.8 and 26.5% under the applied loads of 3 and 5 N in contrast with the original composites prepared without SC. As a result, it can be inferred that SC plays a crucial role in enhancing the interfacial bonding strength between the CF and matrix, providing insights into the interface control of CF-reinforced resin matrix composites.     

Fabrication of Pebax/SAPO mixed matrix membranes for CO2/N2 separation

Mixed matrix membranes (MMMs) were prepared by solvent evaporation method using Pebax-1074 polymer as matrix and inorganic zeolite SAPO-23 as dopant. The morphology, surface functional groups, microstructure, thermal stability, and separation performance of MMMs were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and gas permeation, respectively. The effects of dopant loading amount, permeation temperature, and permeation pressure on the structure and properties of MMMs were investigated. The results showed that the introduction of SAPO zeolite reduced the crystallinity of the MMMs and improved the CO₂/N₂ selectivity. Under the conditions of 30°C and 0.15 MPa, the MMMs prepared by incorporating with 5% SAPO zeolite in content exhibited the highest CO₂/N₂ selectivity of 72.0 together with the CO₂ permeability of 98.2 Barrer.     

Supercritical carbon dioxide assisted fabrication of biomimetic sodium alginate/silk fibroin nanofibrous scaffolds

In this study, biomimetic sodium alginate (SA)/silk fibroin (SF) scaffolds were successfully fabricated by supercritical CO₂ technology. The SA/SF scaffolds exhibited an interconnected porous and extracellular matrix (ECM)-like nanofibrous structures. Moreover, the SA microparticles were embedded in the SF scaffolds. Increasing the content of SA microparticles could improve tensile strength and compressive strength of the SF scaffolds and reduce the porosity of the SF scaffolds. The addition of the SA microparticles could also regulate the degradation rate of the SA/SF scaffolds. Furthermore, the results of in vitro biocompatibility evaluation, indicated that the SA/SF scaffolds exhibited no obvious cytotoxicity and higher cell adhesion ability and were more favorable for L929 fibroblasts proliferation than pure SF scaffolds. Therefore, the SA/SF scaffolds with ECM-like nanofibrous and interconnected porous structure have potential application in skin tissue engineering.     

Study on polyurethane-acrylate/cerium dioxide modified by 3-(Methylacryloxyl)propyltrimethoxy silane and its UV absorption property

Firstly, cerium dioxide(CeO₂) was modified by 3-(Methylacryloxyl)propyltrimethoxy silane (KH-570), and modified CeO₂ (mCeO₂) was prepared. Then poly (urethane-acrylate) was modified by mCeO₂, and poly (urethane-acrylate)/modified CeO₂ (PUA/mCeO₂) composites with ultraviolet absorption property were prepared. The morphology, thermal hydrophobicity, mechanical properties, optical properties, and UV-absorption properties of PUA/mCeO₂ composites were studied. XRD and SEM analysis showed that the modified CeO₂ had better dispersion in the matrix than that of pure CeO₂. Ultraviolet–visible spectrum and thermogravimetric analysis were used to characterize the optical properties and thermal stability of PUA/mCeO₂ composites. The results showed that with the increasing of the mCeO₂ content, the UV-absorption property of PUA/mCeO₂ composites was improved gradually. When the content of mCeO₂ is 3%, the absorption of ultraviolet of PUA/mCeO2 composites is about 5 times of pure PUA film, and the absorption band is mainly in the UVA section. The thermal stability of PUA/mCeO₂ composites was improved with the adding of mCeO₂. With the increasing of mCeO₂ content, the contact angle of PUA/mCeO₂ composites increased significantly. And the UV-absorption mechanism of PUA/mCeO₂ Composites was studied. UV-curable PUA/mCeO₂ composites have good UV absorption property and water resistance. They will be used in the sun screen and protect people's skin.     

永磁同步直线电机无模型电流控制

为改善永磁同步直线电机的动态响应性能,提高电机控制系统的鲁棒性,针对传统永磁同步直线电机PID控制方法中参数不确定性导致的控制不稳定问题,提出一种无模型电流控制方法.该文基于超局部模型设计永磁同步直线电机控制系统的无模型电流控制器,分别搭建PID控制和无模型电流控制系统,在此基础上进行稳态运行、负载突加减和电机参数摄动的仿真及实验对比.结果表明,所提方法改善了永磁同步直线电机控制系统的动态响应性能,对电机参数不确定性具有较强的鲁棒性.     

基于电压和电流特征的双馈风电变流器功率器件开路故障综合诊断

变流器功率器件开路故障监测与识别对提高双馈风电系统智能运维至关重要.针对现有基于变流器电压或电流单一特征以及固定阈值的方法难以同时实现功率器件故障诊断监测与识别问题,该文提出一种基于变流器直流母线电压的故障监测与基于转子电流故障识别的综合诊断方法.首先,理论分析变流器功率器件开路故障对直流母线电压的影响,基于累积和(CUSUM)算法,提出基于直流母线电压特征的故障监测方法;其次,针对转子输出电流非平稳特性和阈值固定问题,提出基于归一化输出电流平均值和绝对平均值为故障特征量及自适应阈值的故障识别方法;最后,仿真模拟不同功率器件先后开路,验证所提方法的有效性,以风速随机及电网电压跌落为场景验证所提方法的鲁棒性.同时,以功率器件典型开路故障实验数据验证仿真分析的准确性.仿真与实验结果表明,所提方法能准确实现变流器功率器件开路故障诊断.     

一种适用于配电网的新分布式潮流控制器拓扑

常规分布式潮流控制器(DPFC)需通过3次谐波电流以实现串联侧与系统的有功功率交换,串联侧所在支路首末端分别需△/YN、YN/△联结型变压器,因此在配电网中的安装地点受到一定限制.为此该文提出一种适用于配电网的新DPFC(NDPFC)拓扑;分析NDPFC工作原理,应用配电网典型系统验证其潮流调节范围与调控特性;此外,研究NDPFC串并联侧电磁暂态数学模型,为提高鲁棒性与控制精度,提出一种采用三环控制的串联侧Ⅰ、Ⅱ控制策略;最后,在不同配电网场景下,通过仿真验证了NDPFC可实现配电网综合潮流调控、补偿三相不平衡、促进新能源消纳,有效地提高了配电网电能质量.