包钯纳米颗粒的中空介孔硅铝酸盐纳米球的合成及其在多步催化反应和尺寸选择催化氢化中的应用

最近, 具有中空核壳结构的纳米材料在催化领域中有着深入的研究和广泛的应用. 在本文中, 我们使用一种简单易行的方法合成了一种包裹钯纳米颗粒的中空介孔硅铝酸盐纳米球(简写为Pd@HMAN). 首先, 通过一种先原位合成钯纳米粒子再对其进行二氧化硅包裹的方法, 在Brij56-环己烷-水的反相胶束中合成了具有核壳结构的包裹钯纳米颗粒的二氧化硅纳米球(简写为Pd@SiO₂). 然后, 使用CTAB, Na₂CO₃和NaAlO₂试剂, 通过简单的碱性条件下刻蚀Pd@SiO₂的过程, 我们成功得到了具有多孔性能的中空核壳型Pd@HMAN纳米催化剂. 由于硅铝酸盐外壳具有酸催化作用, 并且内核钯纳米颗粒又是一种高活性的催化媒介, 因此, 这种复合的多功能纳米催化剂能够很好的应用于多步催化反应中. 此外, 通过一个简单的热处理的方法, 能够缩小硅铝酸盐外壳上的孔道, 我们发现这种孔道调节后的Pd@HMAN纳米催化剂在尺寸选择性氢化反应中有很好的应用前景.     

助表面活性剂对介孔二氧化硅孔径的影响

在十六烷基三甲基溴化铵(CTAB)与硝酸形成的胶束体系中,分别加入正戊醇与正辛胺作助表面活性剂,合成出介孔二氧化硅.经小角XRD和N₂气体吸附与脱附实验证实,随着CTAB与正戊醇摩尔比的增加,介孔二氧化硅的孔径增加;而随CTAB与正辛胺摩尔比的增加,介孔二氧化硅的孔径减小.主要原因是正戊醇增大了CTAB胶束体积,从而导致介孔二氧化硅的孔径增加.而在CTAB与正辛胺的混合胶束中,正辛胺同硅酸盐作用力比CTAB强,导致介孔二氧化硅的孔径减小.     

树枝状介孔二氧化硅的研究进展

介绍了树枝状介孔二氧化硅的三种合成方法,分别是微乳液合成、两相界面合成及球形胶束自组装合成法,为精确调节树枝状介孔二氧化硅的结构,探讨了不同方法可能的形成机理.由于球形胶束自组装合成法的绿色经济,重点讨论了球形胶束自组装合成法的发展及形成机理.介绍了树枝状介孔二氧化硅纳米材料在催化和生物医学方面的应用效果,并对树枝状介...     

介孔SiO_2包覆Ag/ZIF-8核壳型催化材料的合成

通过液相自组装制备了Ag/ZIF-8;进一步以十六烷基三甲基溴化铵(CTAB)为结构导向剂,在疏水Ag/ZIF-8颗粒表面包覆一层介孔二氧化硅(MS)壳,合成了具有核壳结构的Ag/ZIF-8@MS催化剂,并对其进行了结构和性能表征.结果表明,Ag/ZIF-8@MS具有均一的颗粒尺寸(Ag/ZIF-8@MS粒径约为100 nm,Ag粒径约为15 nm)、较高的比表面积(539 m~2/g)及较大的孔体积(0.64 m~3/g);透射电子显微镜表征结果表明,介孔二氧化硅表层厚度约为20 nm.于550℃煅烧后,催化剂结构转变成Ag/Zn O@MS核壳结构.以催化对硝基苯酚生成对氨基苯酚为模型反应,对2种结构的Ag催化剂的催化性能进行了测试.催化反应结果表明,核壳型结构Ag/ZIF-8@MS材料催化对硝基苯酚反应的转化率超过95%,证明了这种以ZIF-8为载体的核壳型材料的优势.     

以阴离子表面活性剂/阳离子聚铵复合胶束为模板合成有序介孔二氧化硅

基于静电作用, 阴离子表面活性剂可与阳离子聚铵组装形成复合胶束. 借助阳离子聚铵,复合胶束可以作为模板与硅源协同组装, 形成高度有序的介孔二氧化硅. 本文通过调变不同种类阴离子表面活性剂、合成体系pH值、合成温度及阳离子聚铵和硅源用量等因素, 合成了具有不同介观结构和形貌的介孔二氧化硅. 实验证实阴离子表面活性剂/阳离子聚铵复合胶束模板法是合成介孔二氧化硅的一种通用方法.     

基于中空介孔二氧化硅小球的pH响应性控制释放系统

空心结构的介孔二氧化硅纳米材料具有较大的比表面积和孔容积,相对于传统介孔氧化硅材料可以负载更多的药物分子,在药物缓释领域具有广阔的应用前景.本文利用改进的模板法制备了粒径与壳厚度可控的中空介孔二氧化硅纳米小球.采用透射电镜(TEM)、小角X射线散射分析(SAXS)和氮气吸附-脱附等方法对合成的中空纳米二氧化硅小球进行了表征分析,得出最佳制备工艺条件.选择优化的制备条件得到的中空介孔二氧化硅与普通介孔二氧化硅对比,将两者分别负载一定量的染料分子罗丹明B(RhB),接着在两者表面修饰溶菌酶分子作为开关分子,构筑了两个pH响应的药物控制释放系统,并对两者的装载量进行了评估,通过观察在575 nm(RhB)处荧光发射峰强度的变化来评估两者的控制释放效果在相同的时间内,空心结构的介孔二氧化硅小球释放染料分子的量要明显多于普通介孔二氧化硅小球释放染料分子的量.     

具有可控分散性的不同粒径氨基酸双功能化介孔二氧化硅纳米颗粒

通过表面活性剂,共结构导向剂（CSDAs）和硅源的自组装合成了具有分散性的不同粒径氨基酸双功能化介孔二氧化硅纳米颗粒. 通过表面活性剂头部与带相反电荷的CSDAs之间的静电相互作用使氨基和羧基基团均匀排列在介孔孔道表面. 通过调节助溶剂或分散剂的加入量来控制颗粒粒径,调节合成溶液pH改变纳米颗粒表面羧基和氨基基团的电荷切换性及其量来控制颗粒的分散性.     

Au@SiO2核壳纳米粒子的制备及其表面增强拉曼光谱

采用柠檬酸钠还原氯金酸法制备金溶胶, 以正硅酸乙酯(TEOS)为硅源, 氨水作催化剂, 制备以金为核, 二氧化硅为壳的核壳纳米粒子. 金纳米粒子的粒径可以通过柠檬酸钠和氯金酸的比例控制, 通过调节TEOS的量和反应的时间可以控制二氧化硅壳层的厚度. 以苯硫酚为探针分子研究了核壳结构纳米粒子的表面增强拉曼散射(SERS)效应与二氧化硅壳层厚度之间的关系. 研究结果表明, 金内核电磁场增强效应随着二氧化硅壳层厚度的增加逐渐减弱, 且其衰减速度比具有相同尺度的双金属核壳结构纳米粒子的慢. 此外, 探针分子主要以物理作用吸附在二氧化硅的表面, 可通过洗涤方法将探针分子除去, 从而可使该复合结构基底用于循环SERS分析.     

ZSM-5@Mesoporous Silica核壳复合结构分子筛的制备及其甲苯甲醇烷基化择形催化性能的研究

采用阳离子表面活性剂模板法在ZSM-5晶体颗粒表面外延生长介孔氧化硅壳层来调变其外表面酸性, 制备了具有高择形催化性能的介孔氧化硅包裹ZSM-5分子筛的微孔-介孔核壳结构复合材料ZSM-5@mesosilica. 扫描电镜和高分辨透射电镜表征显示, 具有无序孔道结构的介孔壳层均匀包覆于ZSM-5晶粒的外表面, 而且壳层的厚度在一定范围内可调变; 另外, 壳层介孔的孔道走向垂直于分子筛核, N₂吸附曲线表明复合材料的微孔和介孔具有互通性. 吡啶吸附和氨吸脱附实验结果证明这些分子可以自由扩散进入分子筛的微孔道, 并且介孔壳层包覆以后ZSM-5分子筛内的酸性位和强度基本没有变化. 用固定床评价了该复合分子筛对甲苯甲醇烷基化反应的催化性能, 结果表明, 与常规ZSM-5相比, ZSM-5@mesosilica核壳材料表现出了较高的对位选择性. 核壳材料独特的择形催化性能归因于介孔氧化硅壳层将ZSM-5非择形性的外表面酸性位部分覆盖, 从而抑制了对二甲苯在外表面的二级异构化反应.     

钯纳米颗粒形貌控制合成及其SPR／SERS性质

在水溶液中分别以十六烷基三甲基溴化铵（CTAB）和CTAB／柠檬酸钠混合剂为包覆剂合成钯纳米颗粒,并研究其形貌演变．钯纳米颗粒在成核阶段会形成具有不同孪晶结构的晶核,在生长阶段又会选择性的放大某一组晶面,这两个因素导致了钯纳米颗粒形貌的多样性．在合成中CTAB既会影响钯纳米颗粒的成核,也会影响颗粒晶面的选择性生长．通过改变CTAB和还原剂的量可以调控钯纳米颗粒的形貌．溶液中CTAB和还原剂浓度的改变,非常明显地影响合成产物中不同形貌钯纳米颗粒的产率．通过向溶液中引入柠檬酸离子调控纳米颗粒的成核与生长过程,首次合成出了星状钯二十面体和截面为五角星形的钯纳米棒．这些不同形貌的钯纳米颗粒有着不同的表面等离子体共振和表面增强拉曼散射性质．     

Facile fabrication of hollow mesoporous silica nanospheres for superhydrophilic and visible/near-IR antireflection coatings

A series of hierarchically mesostructured silica nanoparticles (MSNs) less than 100 nm in size were fabricated by means of a one-step synthesis using dodecanethiol (C(12)-SH) and cetyltrimethylammonium bromide (CTAB) as the dual template, and trimethylbenzene (TMB) as the swelling agent. Silica nanoparticles with varied morphologies and structures, including mesoporous silica nanoparticles with tunable pore size, mesoporous silica nanoparticles with a thin solid shell, hollow mesoporous silica nanoparticles with tunable cavity size, and hollow mesoporous silica nanoparticles with a thin solid shell, were obtained by regulating the TMB/CTAB molar ratio and the stirring rate with the assistance of C(12)-SH. Silica particulate coatings were successfully fabricated by using MSNs with varied morphologies and structures as building block through layer-by-layer dip-coating on glass substrates. The thickness and roughness of the silica particulate coatings could be tailored by regulating the deposition cycles of nanoparticles. The silica particulate coatings composed of hollow mesoporous silica nanoparticles with a thin shell (S2) increased the maximum transmittance of slide glass from 90 to 96%, whereas they reduced its minimum reflection from 8 to 2% at the optimized wavelength region that could be adjusted from visible to near-IR with a growing number of deposition cycles. The coatings also exhibited excellent superhydrophilic and antifogging properties. These mesostructured silica nanoparticles are also expected to serve as ideal scaffolds for biological, medical, and catalytic applications.     

Dual Soft‐Template System Based on Colloidal Chemistry for the Synthesis of Hollow Mesoporous Silica Nanoparticles

A new dual soft‐template system comprising the asymmetric triblock copolymer poly(styrene‐b‐2‐vinyl pyridine‐b‐ethylene oxide) (PS‐b‐P2VP‐b‐PEO) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) is used to synthesize hollow mesoporous silica (HMS) nanoparticles with a center void of around 17 nm. The stable PS‐b‐P2VP‐b‐PEO polymeric micelle serves as a template to form the hollow interior, while the CTAB surfactant serves as a template to form mesopores in the shells. The P2VP blocks on the polymeric micelles can interact with positively charged CTA⁺ ions via negatively charged hydrolyzed silica species. Thus, dual soft‐templates clearly have different roles for the preparation of the HMS nanoparticles. Interestingly, the thicknesses of the mesoporous shell are tunable by varying the amounts of TEOS and CTAB. This study provides new insight on the preparation of mesoporous materials based on colloidal chemistry.     

A facile and controllable one-pot synthesis approach to amino-functionalized hollow silica nanoparticles with accessible ordered mesoporous shells

The development of a practical synthetic method to functionalize hollow mesoporous silica with organic groups is of current intere st for selective adsorption and ene rgy storage applications.Herein,a facile and controllable one-pot approach for the synthesis of monodisperse amino-functionalized hollow mesoporous silica nanoparticles is presented.A novel solid-to-hollow structural transformation procedure of the silica nanoparticles is presented.The structural transformation is easily designed,as obse rved through transmission electro n microscopy,by tailo ring the HCl and N-lauroylsarcosine sodium molar ratio and the water content in the sol-gel.Ordered and radially oriented in situ aminofunctionalized mesochannels were successfully introduced into the shells of the hollow silica nanoparticles.A formation mechanism for the hollow mesoporous silica materials is discussed.     

Dual latex/surfactant templating of hollow spherical silica particles with ordered mesoporous shells

Hollow spherical silica particles with hexagonally ordered mesoporous shells are synthesized with the dual use of cetyltrimethylammonium bromide (CTAB) and unmodified polystyrene latex microspheres as templates in concentrated aqueous ammonia. In most of the hollow mesoporous particles, cylindrical pores run parallel to the hollow core due to interactions of CTAB/silica aggregates with the latices. Effects on the product structure of the CTAB:latex ratio, the amount of aqueous ammonia, and the latex size are studied. Hollow particles with hexagonally patterned mesoporous shells are obtained at moderate CTAB:latex ratios. Too little CTAB causes silica shell growth without surfactant templating, and too much induces nucleation of new mesoporous silica particles without latex cores. The concentration of ammonia must be large to induce co-assembly of CTAB, silica, and latex into dispersed particles. The results are consistent with the formation of particles by addition of CTAB/silica aggregates to the surface of latex microspheres. When the size and number density of the latex microspheres are changed, the size of the hollow core and the shell thickness can be controlled. However, if the microspheres are too small (50 nm in this case), agglomerated particles with many hollow voids are obtained, most likely due to colloidal instability.     

Facile synthesis of monodisperse microspheres and gigantic hollow shells of mesoporous silica in mixed water-ethanol solvents

Mesoporous silica materials with a variety of morphologies, such as monodisperse microspheres, gigantic hollow structures comprising a thin shell with a hole, and gigantic hollow structures consisting of an outer thin shell and an inner layer composed of many small spheres, have been readily synthesized in mixed water-ethanol solvents at room temperature using cetyltrimethylammonium bromide (CTAB) as the template. The obtained mesoporous silica generally shows a disordered mesostructure with typical average pore sizes ranging from 3.1 to 3.8 nm. The effects of the water-to-ethanol volume ratio (r), the volume content of tetraethyl orthosilicate TEOS (x), and the CTAB concentration in the solution on the final morphology of the mesoporous silica products have been investigated. The growth process of gigantic hollow shells of mesoporous silica through templating emulsion droplets of TEOS in mixed water-ethanol solution has been monitored directly with optical microscopy. Generally, the morphology of mesoporous silica can be regulated from microspheres through gigantic hollow structures composed of small spheres to gigantic hollow structures with a thin shell by increasing the water-to-ethanol volume ratio, increasing the TEOS volume content, or decreasing the CTAB concentration. A plausible mechanism for the morphological regulation of mesoporous silica by adjusting various experimental parameters has been put forward by considering the existing state of the unhydrolyzed and partially hydrolyzed TEOS in the synthesis system.     

A General Route to Hollow Mesoporous Rare‐Earth Silicate Nanospheres as a Catalyst Support

Hollow mesoporous structures have recently aroused intense research interest owing to their unique structural features. Herein, an effective and precisely controlled synthesis of hollow rare‐earth silicate spheres with mesoporous shells is reported for the first time, produced by a simple hydrothermal method, using silica spheres as the silica precursors. The as‐prepared hollow rare‐earth silicate spheres have large specific surface area, high pore volume, and controllable structure parameters. The results demonstrate that the selection of the chelating reagent plays critical roles in forming the hollow mesoporous structures. In addition, a simple and low‐energy‐consuming approach to synthesize highly stable and dispersive gold nanoparticle–yttrium silicate (AuNPs/YSiO) hollow nanocomposites has also been developed. The reduction of 4‐nitrophenol with AuNPs/YSiO hollow nanocomposites as the catalyst has clearly demonstrated that the hollow rare‐earth silicate spheres are good carriers for Au nanoparticles. This strategy can be extended as a general approach to prepare multifunctional yolk–shell structures with diverse compositions and morphologies simply by replacing silica spheres with silica‐coated nanocomposites.     

Polyelectrolyte-surfactant complex as a template for the synthesis of zeolites with intracrystalline mesopores

Mesoporous zeolite silicalite-1 and Al-ZSM-5 with intracrystalline mesopores were synthesized with polyelectrolyte-surfactant complex as the template. Complex colloids were first formed by self-assembly of the anionic polymer poly(acrylic acid) (PAA) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) in basic solution. During the synthesis procedure, upon the addition of the silica source, microporous template (tetrapropylammonium hydroxide), and NaCl, these PAA/CTA complex colloids underwent dissociation and gave rise to the formation of hollow silica spheres with mesoporous shells templated by CTAB micelles and PAA domains as the core. Under hydrothermal treatment, the hollow silica spheres gradually merged together to form larger particles with the PAA domains embedded as the space occupant, which acted as a template for intracrystalline mesopores during the crystallization of the zeolite framework. Amphiphilic organosilane was used to enhance the connection between the PAA domain and the silica phase during the synthesis. After calcination, single crystal-like zeolite particles with intracrystalline mesopores of about 5-20 nm were obtained, as characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N(2) adsorption measurements. With the addition of an aluminum source in the synthesis, mesoporous zeolite Al-ZSM-5 with intracrystalline mesopores was also synthesized, and enhanced catalytic property was observed with mesoporous Al-ZSM-5 in acetalization of cyclohexanone with methanol.     

Ag/mSiO2空心微球的制备及SERS标记性能

以聚苯乙烯微球为模板, 经过原位还原和种子生长过程在聚苯乙烯微球表面包覆银(Ag)纳米粒子; 以正硅酸乙酯为硅源, 在十六烷基三甲基溴化铵的导向下实现介孔二氧化硅(mSiO₂)可控包覆, 去除模板得到Ag/mSiO₂空心微球. 透射电子显微镜(TEM)和氮气吸附-脱附分析结果表明, SiO₂壳层厚度约为20 nm, 介孔孔径为2.1 nm, 孔道分布均匀. 进一步利用虹吸作用使对巯基苯胺(4-ATP)分子进入微球内与Ag粒子结合, 构建表面增强拉曼散射(SERS)标记材料. SERS测试结果表明, 该标记材料检测限达到10^-7 mol/L, SERS增强因子达到3.7×10⁵.     

Influence of surfactant concentration on the surface morphology of hollow silica microspheres and its explanation

The surface morphology of hollow silica microspheres has influence on their applications. After a thorough investigation of the deposition of silica nanoparticles on polystyrene (PS) beads and the surface morphology and texture of the resultant hollow silica shells with scanning electron microscopy, transmission electron microscopy, and N2-sorption measurements, the influence of surfactant [cetyltrimethylammonium bromide (CTAB)] concentration on the surface morphology of hollow silica microspheres templated by PS beads is explained. Previously, CTAB was believed to turn the surface charge of PS beads from negative into positive so that negatively charged silica could be deposited on the PS template. Here, we show CTA+ cations preferentially assemble with silica species to form silica-CTA+ composite nanoparticles. Since the zeta potential of silica-CTA+ composite nanoparticles is smaller than that of pure silica nanoparticles, these composite nanoparticles encounter less repulsion when they are deposited on the surface of PS beads and close to each other. As more CTAB is added, the silica-CTA+ nanoparticles are less negatively charged, and more compact and smooth hollow silica microspheres are obtained.     

Robust Amino-Functionalized Mesoporous Silica Hollow Spheres Templated by CO2 Bubbles

Hollow-structured mesoporous silica has wide applications in catalysis and drug delivery due to its high surface area, large hollow space, and short diffusion mesochannels. However, the synthesis of hollow structures usually requires sacrificial templates, leading to increased production costs and environmental problems. Here, for the first time, amino-functionalized mesoporous silica hollow spheres were synthesized by using CO₂ gaseous bubbles as templates. The assembly of anionic surfactants, co-structure directing agents, and inorganic silica precursors around CO₂ bubbles formed the mesoporous silica shells. The hollow silica spheres, 200–400 nm in size with 20–30 nm spherical shell thickness, had abundant amine groups on the surface of the mesopores, indicating excellent applications for CO₂ capture, Knoevenagel condensation reaction, and the controlled release of Drugs.