阻燃纳米二氧化硅气凝胶的仿生制备进展

摘要l自然界中的稻秆是一种二氧化硅（SiO2）／纤维素的纳米复合材料,SiO2与纤维素在纳米尺度的复合,使稻秆质轻和刚柔并具。效仿天然植物复合材料的构筑原理,纳米纤维素模板法仿生制备轻质阻燃材料纳米二氧化硅气凝胶。综述了二氧化硅的仿生制备、二氧化硅气凝胶的制备,探讨了仿生制备的轻质阻燃材料纳米二氧化硅气凝胶的应用前景。     

疏水性中空二氧化硅提高泡沫稳定性研究

采用硬模板法合成了中空二氧化硅(SiO2)纳米颗粒,并对其进行了(3-氯丙基)三甲氧基硅烷改性,使其具有疏水性.用TEM、FT-IR和接触角测量仪进行了表征.改性后的疏水性中空SiO2纳米颗粒具有良好的泡沫稳定性能,使加入纳米颗粒的泡沫性能在油/SDS溶液中提高了40.3％.同时,由于SiO2纳米颗粒的环境友好性,使其...     

仿生合成法制备二氧化硅的研究进展

目前,纳米材料领域研究的焦点是纳米二氧化硅的研究,而传统的化学方法制备二氧化硅需要严格控制反应的条件,试剂污染比较严重,资源的损耗较大,反应的时间也比较长;然而,自然界中的一些植物,在常温常压及近中性pH下,就能形成比较精美的硅纳米材料,这些有趣的现象使人们日益关注仿生硅化的研究。文章就二氧化硅的仿生合成进行简要评述。     

表面处理方式对纳米SiO2/PS复合粒子粒径及分布的影响

纳米SiO2粒子进行表面处理时所用表面活性剂的种类及用量直接影响二氧化硅/聚苯乙烯(SiO2/PS)复合粒子的粒径及分布。纳米SiO2粒子在超声波场作用下经十六烷基三甲基溴化胺(CTAB)处理后,可在纳米SiO2粒子表面形成单体和引发剂的富集区,在适当条件下引发以纳米SiO2粒子为核心的原位分散聚合反应。当纳米SiO2粒子对CTAB的吸附与初级粒子对聚乙烯吡咯烷酮(PVP)K-30的吸附达到动态平衡时,制备出的SiO2/PS复合粒子表面光滑,分散性好,仅有少量的游离纳米SiO2粒子存在,大部分纳米SiO2粒子被PS包裹。     

模板引导纳米TiO2的研制和应用

综述了仿生合成中模板引导纳米TiO2的制备方法,阐述了模板对TiO2的晶体型态、晶体结构、比表面积和微孔结构的调节作用,并简要介绍了纳米TiO2在光催化、太阳能电池、气体传感器等领域的应用.     

烧结温度对SiO2胶体晶体模板结构的影响研究

采用St(o)ber法制备了单分散的SiO2球形颗粒,并在重力沉积条件下制得了高度有序的SiO2胶体晶体模板.采用TG、FTIR、UV-Vis和SEM等表征手段研究了烧结温度对SiO2胶体晶体模板结构的影响.结果表明,随着烧结温度的升高,二氧化硅微球间的间隙逐渐减小、排列更加规整有序.采用该二氧化硅胶体晶体(700℃下烧结)为模板制得了聚偏氟乙烯有序多孔材料.     

二氧化硅球的制备及其功能化

以正硅酸四乙酯为硅源,分别在碱性和酸性条件下制备了二氧化硅(SiO2)球状粒子;在碱性条件下制备了具有荧光功能的SiO2-FITC复合纳米球;以Sn2+作为敏化剂,在SiO2球表面沉积Ag纳米颗粒,制备了SiO2/Ag核-壳结构纳米粒子。通过透射电子显微镜(TEM)、紫外-可见近红外(UV-vis-NIR)分光光度计,荧光分光光度计对SiO2球,SiO2-FITC荧光纳米球,SiO2/Ag核-壳结构纳米粒子的形貌和光学吸收、荧光发射特性进行了表征。结果表明,碱性环境下制备的SiO2球粒径大小为纳米级,酸性环境下制备的SiO2球粒径大小为微米级,酸性环境下制备的SiO2球比碱性环境下制备的硅球致密。掺入FITC的SiO2球具有荧光发射特性,且发光强度可以控制。Ag纳米颗粒修饰的SiO2/Ag核-壳结构纳米粒子具有等表面等离子体共振吸收特性。     

纳米二氧化硅模板的制备

以微乳液法制备纳米二氧化硅（SiO2）粒子，经压制、烧结制备SiO2模板。通过红外（IR）、热分析（TGDTA）、扫描电镜（SEM）等方法对SiO2模板进行表征，结果表明所得SiO2粒度在100nm左右．烧结温度在800℃时，SiO2粒子之间将实现颈长，有利于有机／无机杂化多孔材料的制备。     

前躯体形态对燃烧合成碳化硅纳米粉微观结构的影响

碳化硅纳米粉是基于燃烧的方法合成的,燃烧合成在还原SiO2-Mg-C系统中进行,具有不同形态和平均粒径尺寸的二氧化硅粉作为初始粉末。结果说明,甚至可以用微米级的二氧化硅来合成纳米级的碳化硅粉。然而,合成的SiC颗粒的比表面积随二氧化硅前躯体粒径的减小而增大。对燃烧波中碳化硅的形成机理也进行了讨论。     

FA共聚物/SiO_2杂化薄膜的制备及表面性能的研究

以含氟丙烯酸酯(FA)共聚物乳胶粒为模板,四甲氧基硅烷(TMOS)为硅源,环境条件下仿生矿化制备得到核壳型FA共聚物/SiO2杂化纳米粒子,其中壳层由数十个纳米级的小SiO2粒子组成。进一步采用溶剂直接挥发法制备得到FA共聚物/SiO2杂化薄膜,结果证实无机SiO2粒子杂化可有效提高薄膜表层粗糙度,降低表面自由能,导致水滴静态接触角明显增加,并且一定范围内TMOS用量的增加和矿化反应时间的延长均有利于提高杂化薄膜的疏水、疏油性能。     

Silicification and Biosilicification Part 7: Poly-L-Arginine Mediated Bioinspired Synthesis of Silica

Precipitated silica is synthesized commercially by neutralizing sodium silicate solution under harsh conditions of pH and temperature. In contrast, the formation of ornate silica structures in biological systems (biosilicification) occurs at (or close to) pH 7 under ambient conditions and is thought to be mediated by proteins. Determination of the primary sequences of these proteins has led to the identification of various amino acids that have been proposed to be important in biosilicification. The corresponding synthetic polyamino acids are now being successfully used in bioinspired materials chemistry for developing new materials and processes. Here we report the formation of well-defined silica in vitro as facilitated by poly-L-arginine (PLAr) under ambient conditions and at neutral pH. Two different silica precursors were used in this investigation; tetramethoxysilane (TMOS) and water glass. Scanning Electron Microscopy (SEM) was used for studying the silica morphology and it was revealed that the silica spheres had typical diameters in the range 300–500nm. The PLAr is a cationically charged macromolecule at neutral pH and is believed to act as a catalyst/template/scaffold for the formation of silica in vitro in analogous fashion to certain biomacromolecules that are able to facilitate silicification/biosilicification. These results are discussed here in the context of the role(s) of (bio)macromolecules that facilitate (bio)mineralization.     

The Use of Poly-L-Lysine to Form Novel Silica Morphologies and the Role of Polypeptides in Biosilicification

Silicification at neutral pH and under ambient conditions in vitro is of great interest due to its relationship with silicification in vivo as well as for the benign conditions of the process. As it is important to know the exact group(s) or a particular site in the macromolecules that are responsible for the silicification under these conditions in vivo, poly-L-lysine (PLL) was chosen for this investigation in vitro. Here we report the use of tetramethoxysilane (TMOS) as a silica precursor and the utilization of poly-L-lysine (PLL) for silicification at neutral pH and under ambient conditions. We describe (1) the use of PLL to precipitate silica, (2) the effect of mixing of macromolecules PLL and poly(allylamine hydrochloride) (PAH) to control morphologies of the product, and (3) the formation of novel silica morphologies.     

Studies on the hydrogenation of alkenes and alkynes using polymer coated silica-Pd catalysts

Palladium complexes of crosslinked polyacrylamide and poly-N-vinylimidazole coated on silica gel have been prepared and used as hydrogenation catalysts for alkenes, dienes and alkynes under ambient conditions. The characterisation of the catalysts, the kinetic and mechanistic aspects of the hydrogenation of a few substrates, the effect of temperature, selectivity and the recycling efficiency of the catalysts are presented. A comparison of their activity is made with other silica supported and silica free polymer-Pd catalysts.     

二氧化硅气凝胶常压干燥工艺的研究进展

二氧化硅气凝胶因具有低密度、高比表面积、稳定的物理化学性质等特性在吸附分离、隔热保温等领域表现出巨大的应用潜力。但长耗时、高成本的制备工艺限制了它的发展,尤其是湿凝胶向气凝胶转变的干燥工艺。本文介绍了二氧化硅气凝胶在常压干燥的过程中面临的主要难点及解决方法,虽然常压干燥方法工艺简单、过程安全、对设备要求低且可连续制备,成为近年来的研究热点,但也存在制备周期长、体积收缩大、需要消耗大量有机溶剂和改性剂等不足。文中从凝胶基体增强与优化、降低毛细管力与减少不可逆收缩两种角度,介绍了二氧化硅气凝胶常压干燥的改进方法及其发展现状,分析归纳了不同改进方法的优缺点,总结了二氧化硅气凝胶常压干燥目前面临的技术挑战。并且,立足于目前二氧化硅气凝胶基体增强和表面改性技术发展的趋势,对今后二氧化硅气凝胶常压干燥过程中结构可控、成本降低以及产品多功能化的发展路线进行了展望。     

Water-assisted sintering of silica: Densification mechanisms and their possible implications in biomineralization

Taking silica as an exemplary material system, we studied water-assisted densification behaviors of different crystallinities (quartz, glass, and vitreous silica). To avoid the complexity in data interpretation, we adopted a simple procedure similar to those used for pressing salt pellets for IR: compressing silica powders in a mold with pure water under ambient conditions. It is discovered that crystalline silica is compacted through liquid lubrication, while amorphous silica's densification behaviors contradict the widely regarded dissolution-reprecipitation mechanism. Another mechanism is thus proposed: stress-driven water incorporation into the solid structures produces hydrated silica of considerable plasticity for deformation and fusion. Inspired by this water-assisted mechanism, a more effective sintering method is developed via repetitive stressing/destressing treatments at room temperature, enabling dramatically boosted densities (e.g., over 90% with transparent appearance for silica glass) and enhanced mechanical performance. This generic strategy may apply to a wide range of materials. Furthermore, the hydration-enabled deformation/sintering mechanism proposed in this work offers fresh insights into the biomineralization puzzles, particularly those on how life accomplishes some of the most challenging tasks faced by humans in modern ceramic technology, for example, to fuse, mend or reshape the rigid brittle ceramic objects in aqueous environments under ambient conditions. This purely inorganic biomineralization mechanism may be particularly important for life at its early stage of evolution on earth.     

Surface assisted laser desorption–ionization mass spectrometry on patterned nanoporous silica thin films

We describe the preparation and use of patterned nanocomposite silica thin films deposited on silicon for laser desorption-ionization mass spectrometry (LDI-MS) without the use of conventional matrices. Ordered nanocomposite silica thin films deposited on silicon substrates were prepared by evaporation induced self-assembly using Brij56 as the surfactant template. The films were then exposed to masked deep-UV light to selectively remove the template to yield isolated regions of ordered nanoporous silica in a field of nanostructured silica. The nanoporous regions act as isolated “wells” that allow for the mass spectral characterization of analytes by laser induced desorption–ionization MS using a commercial MALDI-TOF instrument. We demonstrate the utility of these patterned films for the mass spectral analysis of small organic molecules, such as amino acids, peptides and siderophores. No consistent background signal from the films was observed at laser intensities typically used to desorb/ionize analytes. We also show that the films remain active for over a year when stored at ambient laboratory conditions. Because these patterned nanocomposite films are straightforward to produce, readily modifiable and stable at ambient laboratory conditions, they provide a potentially useful alternative to currently available films and substrates for matrix-free LDI-MS analysis of small molecules.     

常压干燥合成水玻璃基SiO_2气凝胶

以水玻璃和双氧水为原料一步合成二氧化硅湿凝胶,经老化、溶剂置换及三甲基氯硅烷修饰后,并于常压干燥后获得二氧化硅气凝胶。样品经低温N_2吸附-脱附、红外光谱和扫描电镜测试表明所得二氧化硅气凝胶具有三维多孔结构,且其比表面积可达482 m~2·g~(-1)、平均孔径为24.9nm及表观密度为0.12g·cm~(-3)。     

疏水性二氧化硅气凝胶的常压制备与表征

采用溶胶-凝胶技术,以正硅酸乙酯为有机前驱体,三甲基氯硅烷为改性剂,在常压下干燥制备出疏水性二氧化硅(SiO2)气凝胶,同时采用密度测量、比表面积和孔径分布仪、扫描电镜、热重分析仪对SiO2气凝胶进行表征。文章重点研究反应物配比和表面修饰对SiO2气凝胶性能的影响。结果表明,采用正硅酸乙酯、水、乙醇体积配比为25︰6︰80和三甲基氯硅烷的正己烷溶液表面修饰合成的SiO2气凝胶性能质量较好。     

通过控制醇凝胶强度常压制备低密度疏水SiO2气凝胶

常压干燥制备低密度气凝胶是促进高性能气凝胶发展应用的重要途径。以正硅酸乙酯为硅源,采用溶胶-凝胶和常压干燥工艺制备出低密度(<100 kg·m^-3)的疏水SiO₂气凝胶,通过工艺参数的控制制备出不同压缩模量的醇凝胶,探讨了反应物配比对醇凝胶压缩模量和气凝胶密度间的影响关系,获得了通过控制醇凝胶压缩模量制备低密度疏水SiO₂气凝胶的方法;发现将醇凝胶压缩模量控制在0.25~2.5 kPa范围内,可制备出密度小于100 kg·m^-3的疏水SiO₂气凝胶,该研究可以为低密度疏水SiO₂气凝胶的低成本常压制备及其控制方法提供指导。