疏水性聚丙烯酸/聚乙烯醇/葡萄糖淀粉酶复合纳米纤维膜的制备及酶学性质

利用混合静电纺丝将葡萄糖淀粉酶(GA)固定于聚丙烯酸(PAA)/聚乙烯醇(PVA)纳米纤维膜上,并通过鉴定固定化GA的酶学特征检验PAA/PVA可否成为一种优良的酶固定化载体。 对其理化性质和酶学特征进行鉴定,经红外光谱(FT-IR)和扫描电子显微镜(SEM)表征发现,GA可成功包埋于PAA/PVA纳米纤维膜内部;对包裹固定的GA进行酶学性质鉴定,发现固定化GA的最适反应温度为68 ℃,比游离GA提高了9 ℃;固定化GA的适用pH值范围明显变宽;热稳定性和存贮稳定性显著增强且可以重复使用。PAA/PVA纳米纤维膜是一种优良的酶固定化载体,可以通过混合静电纺丝包埋法简便地将蛋白质分子固定于其内部,具有一定的应用前景。     

Well‐dispersed N‐heterocyclic carbene–palladium complex anchored onto poly(acrylic acid)/poly(vinyl alcohol) nanofibers: Novel,superior and ecofriendly nanocatalyst for the Suzuki–Miyaura cross‐coupling reaction

Polymeric nanocomposite@Pd is one of the crown jewels for the catalysis of cross‐coupling reactions. This Pd nanocomposite on various polymeric supports has been well established to catalyze cross‐coupling reactions, but its preparation supported on the surface of nanofibers has been largely overlooked. Herein, we report the preparation of a poly(acrylic acid) (PAA)/poly(vinyl alcohol) (PVA) nanofiber‐supported N‐heterocyclic carbene–Pd complex. The first step involves the preparation of PAA/PVA nanofibers using the electrospinning process. The second step comprises the reaction of water‐soluble poly(ethylene glycol)‐imidazole with modified PAA/PVA nanofibers followed by introduction of PdCl₂ to achieve successfully the desired nanocomposite. The catalytic activity of this nanocomposite was examined in the expeditious synthesis of biaryl compounds using the Suzuki–Miyaura cross‐coupling reaction under mild reaction conditions. The composite offers multiple features such as good hydrophilic properties, high surface area, admirable potential in repeatability tests and being recyclable for several runs without significant loss in its activity under the optimum reaction conditions. Our results showed the superior applicability of this novel nanocatalyst in terms of conversion reaction, yields and turnover frequencies. The structure of the catalyst was characterized using a variety of techniques.     

Electrospinning fabrication and characterization of poly(vinyl alcohol)/montmorillonite/silver hybrid nanofibers for antibacterial applications

Poly(vinyl alcohol) (PVA)/montmorillonite clay (MMT)/silver (Ag) nanoparticles have been electrospun for fabricating PVA/MMT/Ag nanofiber in aqueous solutions. Since PVA is a water-soluble and biocompatible polymer, it is one of the best materials for preparation of antibacterial nanofiber. MMT has been used as an inorganic filler to enhance properties of homopolymeric nanofiber. The PVA/MMT/Ag nanofiber diameter increases with increasing contents of MMT clay and Ag nanoparticles. In preservation test, the PVA/MMT/Ag nanofiber confirms an excellent antibacterial performance, elucidating for practical uses as a new preservative. Moreover, the PVA/MMT/Ag nanofiber shows improved thermal properties.     

金纳米棒负载的静电纺丝纤维的制备及其表面增强拉曼光谱性能

为简单有效地制备高活性表面增强拉曼光谱(Surface-enhanced Raman Spectroscopy,SERS)基底。本文采用静电纺丝聚乙烯醇(PVA)/聚丙烯酸(PAA)纳米纤维为支撑材料,通过直接浸泡的方法,利用金纳米棒与电纺纤维之间的静电力,使纳米棒在纤维表面自组装,得到了性能优异的SERS基底。通过透射电子显微镜、扫描电子显微镜对金纳米棒以及不同状态下的电纺纤维的形貌进行表征,结果表明,金纳米棒均匀且密集地负载在纤维表面。通过设置不同的浸泡时间确定了金纳米棒组装平衡的时间为12 h,并通过调控纺丝时间和金纳米棒的浓度发现随着纺丝时间和金纳米棒浓度的增加,复合纤维膜SERS增强效果随之提升。该复合纤维膜具有优异的SERS均匀性,并且能够检测到浓度低至10~(-10)mol/L的4-氨基苯硫酚的存在。     

Highly catalytic spherical carbon nanocomposites allowing tunable activity via controllable Au-Pd doping

We report the synthesis of highly catalytic spherical carbon composite particles with Au-Pd bimetallic nanoparticle doping using a microwave-assisted technique that allows control over the location of the nanoparticles (NPs), putting them into stable interior, but still near-surface locations (within a 100 nm thick shell). First, composite particles with Pd NPs inside of nanoporous carbon spheres (CSs) were synthesized. Subsequent immersion of the composite particles in HAuCl(4) solutions containing PVP led to an addition of Au near the Pd. Au-Pd/CS composites with Au:Pd atomic ratios varying from 0.4 to 4.6 were prepared. The growth of Au and its location relative to the carbon's surface and the Pd are discussed. The catalytic activity towards the reduction of 4-nitrophenol is tunable via the Au:Pd atomic ratio. Optimizing the composition increases the activity a hundredfold over that of the corresponding monometallic Pd/CS. The catalytic activity arises from the synergy between different contributing mechanisms, here especially the interaction between the carbon matrix and metals, metal-metal interfaces, and the hydrogen absorption capabilities of Pd.     

PVA微晶交联和SA/PAA双网络协效增强增韧SA纤维

为了提高海藻酸钠(SA)纤维的断裂强度和断裂伸长率, 以丙烯酸(AA)为化学交联组分, SA为离子交联组分, 聚乙烯醇(PVA)为微晶交联组分, 采用湿法纺丝和冻融循环方法制备含有PVA微晶交联点和海藻酸钠/聚丙烯酸(SA/PAA)双网络结构的海藻酸钠/聚丙烯酸/聚乙烯醇(SA/PAA/PVA)复合纤维. 通过流变性能、 力学性能、 红外光谱、 X射线衍射仪(XRD)和扫描电子显微镜(SEM)测试研究了交联剂N,N-亚甲基双丙烯酰胺(MBA)含量和PVA微晶交联对SA/PAA/PVA纺丝原液和复合纤维的结构与性能的影响. 结果表明, 当MBA质量分数为0.5%时, 纺丝原液的损耗模量(G″)最小, 可纺性最好, 复合纤维的断裂强度达到2.83 cN/dtex, 断裂伸长率达到9.38%, 比再生SA纤维分别提高了15.98%和38.96%; PVA冷冻之后形成微晶交联点并且PAA和PVA已经复合到体系中; PAA和PVA的加入提高了复合纤维的结晶度; 复合纤维的表面形貌趋于光滑和规整, 纤维断面更加致密.     

Novel fabrication of magnetic thermoplastic nanofibers via melt extrusion of immiscible blends

A novel technique of fabricating magnetic thermoplastic nanofibers by the control of the phase separation of immiscible polymer blends during melt extrusion was presented. The magnetic poly(vinyl alcohol‐co‐ethylene) (PVA‐co‐PE)/Fe₃O₄ composite nanofibers were prepared via the melt extrusion of cellulose acetate butyrate matrix and PVA‐co‐PE preloaded with different amounts of Fe₃O₄ nanoparticles. The morphologies of magnetic composite nanofibers were characterized by scanning electron microscopy. The uniform dispersion of Fe₃O₄ nanoparticles in nanofiber matrixes and crystal structures were confirmed using transmission electron microscopy and wide angle X‐ray diffraction. Thermogravimetric analysis was employed to quantify the exact loading amount of Fe₃O₄ nanoparticles in the composite nanofibers. The magnetic measurements showed that composite nanofibers displayed superparamagnetic behavior at room temperature. With increasing content of Fe₃O₄ nanoparticles, the saturation magnetization of the magnetic composite nanofiber significantly improved. The prepared magnetic composite nanofibers might have found potential applications in the sensors and bio‐molecular separation fields. Copyright © 2012 John Wiley & Sons, Ltd.     

Pd/PAMAM(聚酰胺-胺)/SBA-15催化剂的制备及催化性能

利用聚酰胺-胺型(PAMAM)树形分子为模板制备出粒径可控的Pd纳米颗粒(Pd DEN),然后通过超声波法制备了SBA-15分子筛负载的Pd/PAMAM复合材料(Pd SDEN)。XRD和TEM测试表明,负载后Pd纳米颗粒的粒径没有变化,且均匀分布在分子筛的孔道中,SBA-15分子筛的结构也没有变化。以对硝基苯酚还原为例,测试了Pd SDEN的催化性能,与Pd DEN相比,其具有更高的催化效率,重复使用5次后仍具有较好的催化活性,反应速率仅下降4%,且Pd/PAMAM复合材料仍能稳定存在于分子筛的孔道中。     

魔芋葡甘聚糖/聚乙烯醇纳米纤维膜及其释药行为研究

为了研制药物缓释效果优良的薄膜材料,利用静电纺丝设备研制不同比重的魔芋葡甘露聚糖/聚乙烯醇纳米纤维膜,并通过扫描电镜、傅里叶变换红外光谱和示差扫描量热法表征纳米纤维膜的结构和性能,结合体外实验和数学模型研究其缓释行为.结果显示当魔芋葡甘露聚糖含量占纳米纤维膜总质量约76%时,纳米纤维膜中微纤丝粗细最均匀且结点较少,纳米纤维膜中魔芋葡甘聚糖和聚乙烯醇之间存在明显的相互作用,含有5-氨基水杨酸的纳米纤维膜在pH=7.4 PBS磷酸盐缓冲液中25 h的累积释放量大约为45%,显示出良好的药物缓释效果,其缓释行为与Higuchi模型具有较高的拟合度.研究表明利用静电纺丝设备研制的魔芋葡甘聚糖/聚乙烯醇纳米纤维膜可以为药物缓释载体的开发提供理论依据.     

负载钯纳米粒子聚电解质空心微球的制备及其还原对硝基苯酚的催化活性

用表面引发原子转移自由基聚合法(SI-ATRP)在二氧化硅纳米粒子表面接枝聚碘化甲基丙烯酸三甲基胺基乙酯(PMETAI),原位还原静电吸附的PdCl62-后刻蚀除去二氧化硅模板,成功制备了Pd纳米粒子复合聚电解质空心微球(air@PMETAI@Pd)。 用透射电子显微镜(TEM)、红外光谱仪(FTIR)、能谱仪(EDX)、热重分析仪(TGA)等技术手段对所制备的空心微球进行表征。 结果表明,Pd纳米粒子均匀负载在聚电解质微球上,其直径约为(1.5±0.2) nm。 将负载Pd纳米粒子的微球作为催化剂应用于硼氢化钠还原4-硝基苯酚反应,显示出很好的催化效果且具有较好的回收利用性。     

磷钼酸/聚苯乙烯/聚乙烯醇电纺纤维膜的制备及性能

采用静电纺丝法制备了磷钼酸/聚苯乙烯(PS)/聚乙烯醇(PVA)复合纤维,并将其模压成膜.利用红外光谱(IR)、扫描电子显微镜(SEM)及X射线能谱(EDX)等对复合纤维及其膜的结构与形貌进行表征,并对复合纤维膜的光催化性能、力学性能及在水中稳定性进行测试.结果表明,在复合纤维中磷钼酸的Keggin结构得到保持.PS与PVA质量比为1∶1时,复合纤维形貌最佳,表面光滑,直径较小且分布均匀,复合纤维的直径随着磷钼酸含量的增加而减小.将磷钼酸固载于复合纤维膜上比直接使用具有更高的光催化活性,光照25 min后接近98%的甲基橙降解;复合纤维膜易于回收再利用,5次重复使用后,复合纤维膜没有破损,磷钼酸损失较少,光催化性能无明显下降.复合纤维膜的强度随磷钼酸含量的增加先增大后减小,韧性随PVA含量的增加而增大,随磷钼酸含量的增加而减小.     

二氧化钛纳米颗粒/还原氧化石墨烯修饰玻碳电极在对硝基苯酚检测中的应用

本文报道了用二氧化钛纳米颗粒（TiO₂NPs）/还原氧化石墨烯（RGO）的复合物修饰玻碳电极检测微量对硝基苯酚（4-NP）的电化学方法. 本研究用扫描电子显微镜（SEM）对该复合材料形貌进行表征,用循环伏安法和交流阻抗谱对该复合物电极的电化学性能进行检测,表现出良好的电化学特性,采用差分脉冲伏安法对4-NP进行微量检测,结果令人满意,这主要得益于TiO2NPs/RGO复合物对4-NP有较高的催化活性,其电流峰值与浓度呈较高的线性关系,DPV的检测范围为10μmol·L^-1 ~ 350μmol·L^-1,检测限为0.13 μmol·L^-1. 与其他报道的一些电化学传感器相比,该传感器检测范围大,检测限低,且工作稳定,成本低,分析简单快速,具有很好的应用前景.     

Palladium nanoflowers supported on amino-fullerene as novel catalyst for reduction of 4-nitrophenol

In this study,we report the synthesis of novel palladium nanoflowers(Pd NFs)on amino-functionalized fullerene(C60-NH2)by hydrothermal self-assembly growth using ethylenediamine(EA)as a functional reagent.The successful formation of Pd nanoflowers supported amino-functionalized fullerene(C60-NH2/Pd NFs)is evidenced by UV-vis and powder X-ray diffraction(XRD).The morphology of Pd NFs over the C60-NH2 surface has been investigated by high-resolution transmission electron microscopy(TEM)and Fourier-transform infrared(FT-IR)techniques.The supported Pd nanoflowers(Pd NFs/C60-NH2)exhibit remarkably superior catalytic activity toward the reduction of 4-nitrophenol(4-NP).It exhibits remarkable UV-vis spectra response from 4-nitrophenol to 4-aminophenol(4-AP)(99%in 2.0 min)with a turnover frequency of 12.35 min^-1.Its excellent catalytic stability and durability offer the promising application in catalysis.     

Ag Nanoparticle/Nanofibrillated Cellulose Composite as an Effective and Green Catalyst for Reduction of 4-Nitrophenol

In this work, silver nanoparticles (Ag NPs) prepared through in situ green and facile synthesis by using nanofibrillated cellulose (NFC) hydrogel as support, stabilizer and reducing agent by two different methods. Their catalytic abilities were examined for conversion of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The structure of as-synthesized composites with different AgNO₃ concentrations were characterized by ultraviolet–visible spectroscopy, field emission scanning electron microscopy, transmission electron microscopy; energy dispersive spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Results show that all nanocomposites demonstrated excellent catalytic activity. Among them, Ag@NFC-2 sample, with spherical and well-dispersed Ag NPs along the nanofiber, produced by the second method having 0.25 M AgNO₃ concentration presented outstanding catalytic efficiency.     

结构型载体负载纳米银合成及催化性能

通过两步聚合法合成具有温度敏感性能的核-壳型聚(苯乙烯-N-异丙基丙烯酰胺)/N-异丙基丙烯酰胺共聚3-(甲基丙烯酰氧)丙基三甲氧基硅烷(P(St-NIPAM)/P(NIPAM-co-MPTMS))复合微凝胶材料.以经3-巯丙基-三甲氧基硅烷(MPS)表面修饰的复合微凝胶为载体,乙醇为还原剂,在温和条件下控制性还原制备纳米银微粒.通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅里叶变换红外(FT-IR)光谱仪、X-射线光电子能谱(XPS)、X射线衍射(XRD)仪、热分析(TGA)和紫外-可见(UV-Vis)分光光度计等手段对P(St-NIPAM)/P(NIPAM-co-MPTMS)-(SH)Ag复合微凝胶的结构、组成和性质进行表征.同时,以硼氢化钠还原对硝基苯酚为模型反应,对该复合材料催化还原性能进行了评价.结果表明,载体含有巯基的有机-无机杂化网络结构的限域作用使原位合成的纳米银微粒的分散性较好.载体微凝胶壳层链节中无机组分MPTMS的引入在一定程度上降低了复合凝胶温敏性,但复合凝胶仍表现出催化还原反应的温敏性调控和良好的催化活性.以上实验结果与温敏性PNIPAM链节被无机网络分隔而有利于反应传质及壳层巯基对原位纳米银形成尺寸和空间分布的有效控制有关.本研究对功能性金属纳米催化复合材料的研究具有积极借鉴意义.     

Preparation of α-Fe2O3 Nanofiber via Electrospinning Process

A thin PVA/FeCl3 composite fiber was prepared by using sol-gel processing and electrospinning tech niques. A nanofiber of α-Fe2O3 with the diameter of 50-150 nm was obtained via high temperature calcina tion of the PVA/FeCl3 composite fiber. The material was characterized by infra-red(IR) spectroscopy, X-ray diffraction(XRD), and scanning electron microscopy(SEM). The results show that the fiber after the calci nation at 700 ℃ was a pure α-Fe2O3 nanofiber.     

Pd@GO/Fe3O4/PAA/DCA: a novel magnetic heterogeneous catalyst for promoting the Sonogashira cross-coupling reaction

Abstract

A hybrid system involving graphene oxide (GO), magnetic oxide (Fe₃O₄), acrylamide and dicyandiamide was prepared via amine functionalization of GO/Fe₃O₄ by means of covalent bonding with acrylamide and subsequent reaction with dicyandiamide to provide a multinitrogen containing polymer on the surface of GO. This hybrid system was utilized as a heterogeneous catalyst support for immobilizing Pd nanoparticles to provide the hybrid, Pd@GO/Fe₃O₄/PAA/DCA. This nano-Pd composite was characterized using Fourier transform infrared, transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometer, thermogravimetric analysis, X-ray diffraction, and ICP techniques and used for promoting Sonogashira cross-coupling under mild reaction conditions. This heterogeneous and magnetic catalyst was easily separated by external magnet and was reused in a model reaction, efficiently up to six times with slight loss of catalytic activity and Pd leaching, showing the suitability of GO/Fe₃O₄/PAA/DCA for embedding Pd nanoparticles. To check the effect of the number of surface nitrogens of the polymeric chain on the catalytic performance, the activity of the catalyst was compared with Pd@GO/Fe₃O₄/PAA; increased number of the surface nitrogens on the chain polymer leads to higher loading of Pd and lower the Pd leaching.     

渗透汽化型酯化膜反应器研究 聚合物/无机固体酸管式复合膜的膜反应性能

设计了渗透汽化型管式膜反应器,以乙酸丁酯合成反应为探针,考察了Ｚｒ（ＩＶ）／ＰＶＡ,Ｚｒ（ＩＶ）－ＰＶＡ／ＰＶＡ两类聚合物担载无机固体酸管式复合膜的膜催化反应性能。探讨了功能膜的组成,结构,反应条件等对膜反应和分离性能的影响以及同步膜分离过程对反应转化的促进作用。实验结果表明,膜催化酯化反应过程主要是依赖与料液接触侧膜表面层的催化活性,膜的催化活性是影响反应速率,特别是初期反应转化速率的主要因素,后期的超平衡转化则依赖于膜分离过程     

负载金纳米粒子的聚苯乙烯/聚丙烯酸微球的合成及pH响应性能

以两步聚合法合成的聚苯乙烯(PS)/聚丙烯酸(PAA)核-壳结构复合微凝胶为载体, 硼氢化钠为还原剂, 柠檬酸钠为稳定剂, 通过原位控制性还原获得pH敏感性微凝胶负载纳米金粒子的PS/PAA-Au复合材料. 研究发现, 不同酸碱条件时, 复合微凝胶壳层高分子链的溶胀/收缩变化, 不仅可以调节纳米金粒子的表面等离子吸收, 还可以调节反应底物的扩散传质, 即借助载体微环境的变化来调控纳米金光学性能和催化性能, 从而实现复合纳米金材料的pH调控性.     

PVA‐encapsulated Palladium Nanoparticles: Eco‐friendly and Highly Selective Catalyst for Hydrogenation of Nitrobenzene in Aqueous Medium

In aqueous medium without any other additives, palladium (Pd) nanoparticles with water‐soluble polyvinyl alcohol (PVA) as stabilizer were synthesized for the catalytic hydrogenation of nitrobenzene. Under the optimum experimental conditions, the nitrobenzene conversion and the selectivity for aniline were 99.3 % and 100 %, respectively. Comprehensive characterization methods, including TEM, UV/Vis, confocal laser scanning microscopy (CLSM), XRD and XPS allowed a better understanding of the role of PVA aggregates and the properties of Pd nanoparticles. The nitrobenzene conversion exceeded 80 % even after 6 cycles without any treatment of the catalyst. A mechanism about the hydrogenation of nitrobenzene catalyzed by Pd/PVA system was proposed. The Pd/PVA catalyst also exhibited excellent activity and selectivity, particularly to ortho‐fluoronitrobenzene and ortho‐nitrotoluene. This research can provide a reference for the environmentally friendly catalysis for hydrogenation of nitrobenzene and other substituted nitrobenzene compounds.