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.     

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.     

单分散中空介孔结构的盐模板合成及形貌调控

中空介孔结构因具有丰富的内部空间以及多孔渗透性外壳等优势,在催化、能源储存与转化及生物医药等领域得到了广泛应用.然而,目前仍然缺少高效、简便且绿色的合成中空介孔结构的方法.本文以柠檬酸钠胶体颗粒作为模板,通过十六烷基三甲基溴化氨(Cetyltrimethylammonium bromide, CTAB)胶束与正硅酸四乙酯(Tetraethyl orthosilicate, TEOS)的水解低聚物在胶体颗粒表面进行界面共组装,直接生长介孔二氧化硅壳层;然后通过简便的醇洗和水洗分别除去CTAB胶束和柠檬酸钠胶体颗粒后,得到中空介孔结构.进一步研究表明,负电荷的柠檬酸钠胶体颗粒与CTAB胶束之间的静电相互作用是诱导氧化硅低聚物在颗粒表面进行交联组装的关键.基于此,通过控制生长时间实现了对中空介孔结构形貌和壳层厚度的精确调控.所得中空介孔二氧化硅纳米球可以显著增强物质的扩散传输,是理想的催化剂载体,负载金纳米颗粒后可以高效催化4-硝基苯酚的还原反应.研究结果为中空介孔材料的绿色简便合成提供了思路.     

Elaboration of monodisperse spherical hollow particles with ordered mesoporous silica shells via dual latex/surfactant templating: radial orientation of mesopore channels

Monodisperse spherical hollow nanoparticles of mesoporous silica featuring mesopores with a radial orientation in the silica shell were synthesized via a dual-templating method. Specifically designed polystyrene latexes with anionic or cationic surface charges acted as the core templates, while cetyltrimethylammonium bromide served as a co-template to structure the mesopore formation during tetraethoxysilane hydrolysis/condensation. The particles were well-separated and presented homogeneous mesoporous silica shells. Average particle diameters were less than 200 nm, and the particles displayed high values of specific surface area and pore volume. The shell thickness and the hollow core diameter could be tuned independently while the radial pore structure was preserved. A detailed analysis of the nitrogen adsorption-desorption isotherms proved that the central cavity was completely isolated from the external medium, that is, only accessible through the radial mesopores of the shell. Consequently, our particles gather the advantages of a well-defined structure, straight penetrating channels across the silica shell, and a high accessible porous volume of the central core. These properties make them far better candidates than simple mesoporous particles for any storage and/or controlled release applications.     

中空纳米二氧化硅微球的制备及表征

本文介绍了一种制备中空纳米二氧化硅微球的新方法。利用模板首先合成介孔纳米二氧化硅微球,再用水热反应法,成功制备了非功能化和巯基、氨基功能化中空纳米二氧化硅微球。利用透射电子显微镜,热重分析等手段对其形貌进行了表征。另外,对中空介孔纳米二氧化硅微球的形成机制进行了探讨。     

Green preparation of hollow mesoporous silica nanosphere inside-loaded gold nanoparticles and the catalytic activity

In this work, an active nano-catalyst with gold nanoparticles loaded in hollow mesoporous silica nanospheres (HMSNs/Au) was prepared by a one-pot sol-gel method, in which gold ions were loaded in hollow mesoporous silica spheres followed by sodium alginate reduction. The characterization of the HMSNs/Au were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂ adsorption–desorption isotherms (BET). The high catalytic activity of HMSNs/Au, denoted as apparent turn-over frequency (TOF), was detected by UV-Vis spectrophotometer for the catalytic reduction of 4-nitrophenol (74.5 h^?1) and 2-nitrophenol (108.7 h^?1) in the presence of sodium borohydride solution due to the small gold nanoparticles size and overall exposure of active sites. It is expected that this ecofriendly approach to prepare inorganic composited nanoparticles as high active catalysts based on hollow mesoporous materials was a promising platform for loading noble metal nanoparticles.     

Ag-deposited hollow mesoporous silica microspheres for rapid decolorizing of dye pollutants

Research on Chemical Intermediates - In this paper, we demonstrate a facile electroless plating method for fabricating silver nanoparticles deposited onto hollow mesoporous silica microspheres...     

Spontaneous formation and characterization of silica mesoporous crystal spheres with reverse multiply twinned polyhedral hollows

A crystal is an object with translational symmetry. Basic research into and production of new materials necessitates the preparation of crystals of a particular morphology and with well-defined crystal defects. In this work, we found novel silica mesoporous crystal spheres with polyhedral hollows (icosahedral, such as those observed for proteins of virus capsids, decahedral, Wulff polyhedral, etc.) formed by the reverse multiply twinned bicontinuous double diamond mesostructure. Vesicles with a low-curvature lamellar structure were first formed by the self-assembly of amphiphilic carboxylic acid molecules in the presence of a nonionic surfactant and then underwent a structural transformation process that gave a reverse multiply twinned mesoporous shell while maintaining the hollow shape. These polyhedral hollow crystals showed an enhanced contrast of backscattering signatures relative to the incident acoustic signals and thus could be used as a potential contrast agent in medical ultrasonography with drug loadings in the mesopores.     

Mesoporous silicas by self-assembly of lipid molecules: ribbon, hollow sphere, and chiral materials

Using lipids (N-acyl amino acids) and 3-aminopropyltriethoxysilane as structure- and co-structure-directing agents, mesoporous silicas with four different morphologies, that is, helical ribbon (HR), hollow sphere, circular disk, and helical hexagonal rod, were synthesized just by changing the synthesis temperature from 0 degrees C to 10, 15, or 20 degrees C. The structures were studied by electron microscopy. It was found that 1) the structures have double-layer disordered mesopores in the HR, radially oriented mesopores in the hollow sphere, and highly ordered straight and chiral 2D-hexagonal mesopores in the disklike structure and helical rod, respectively; 2) these four types of mesoporous silica were transformed from the flat bilayered lipid ribbon with a chain-interdigitated layer phase through a solid-solid transformation for HR formation and a dissolving procedure transformation for the synthesis of the hollow sphere, circular disk, and twisted morphologies; 3) the mesoporous silica helical ribbon was exclusively right-handed and the 2D-hexagonal chiral mesoporous silica was excessively left-handed when the L-form N-acyl amino acid was used as the lipid template; 4) the HR was formed only by the chiral lipid molecules, whereas the 2D-hexagonal chiral mesoporous silicas were formed by chiral, achiral, and racemic lipids. Our findings give important information for the understanding of the formation of chiral materials at the molecular level and will facilitate a more efficient and systematic approach to the generation of rationalized chiral libraries.     

DNA-based intelligent logic controlled release systems

DNA assembles that can perform "OR" and "AND" logic gate operations were fabricated. The feasibility of intelligent logic controlled release was demonstrated through the controlled organization of gold nanoparticles on the surface of mesoporous silica by stimuli-induced structural transformation of DNA ensembles.     

Fabrication of hollow multifunctional spheres containing MCM-41 nanoparticles and magnetite nanoparticles using layer-by-layer method

Macroscopic mesoporous silica spheres have been fabricated by alternatively depositing preformed MCM-41 nanoparticles and polyelectrolytes onto polystyrene lattices. High surface area hollow mesoporous spheres were obtained by removal of the core by solvent or calcination. Further, the versatility of the layer-by-layer (LBL) method was extended to fabricate magnetite-mesoporous silica composites by depositing magnetite and MCM-41 nanoparticles onto polystyrene beads. Such high surface area composites are important since the mesopores can be used for encapsulation of varied materials like enzymes and drugs while the presence of magnetite ensures application in biocatalysis and separation under magnetic field.     

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.     

Synthesis of Monodisperse Hollow Carbon Nanocapsules by Using Protective Silica Shells

Monodisperse hollow carbon nanocapsules (<200 nm) with mesoporous shells were synthesized by coating their outer shells with silica to prevent aggregation during their high‐temperature annealing. Monodispersed silica nanoparticles were used as starting materials and octadecyltrimethoxysilane (C18TMS) was used as a carbon source to create core–shell nanostructures. These core–shell nanoparticles were coated with silica on their outer shell to form a second shell layer. This outer silica shell prevented aggregation during calcination. The samples were characterized by TEM, SEM, dynamic light scattering (DLS), UV/Vis spectroscopy, and by using the Brunauer–Emmett–Teller (BET) method. The as‐synthesized hollow carbon nanoparticles exhibited a high surface area (1123 m² g^?1) and formed stable dispersions in water after the pegylation process. The drug‐loading and drug‐release properties of these hollow carbon nanocapsules were also investigated.     

Mesoporous Silica Nanoparticles Functionalized with Amino Groups for Biomedical Applications

The synthesis and characterization of amino-functionalized mesoporous silica nanoparticles are presented following two different synthetic methods: co-condensation and post-synthesis grafting of 3-aminopropyltriethoxysilane. The amino groups’ distribution on the mesoporous silica nanoparticles was evaluated considering the aggregation state of a grafted photosensitizer (Verteporfin) by using spectroscopic techniques. The homogeneous distribution of amino groups within the silica network is a key factor to avoid aggregation during further organic functionalization and to optimize the performance of functionalized silica nanoparticles in biomedical applications. In addition, the formation of a protein corona on the external surface of both bare and amino-functionalized mesoporous silica was also investigated by adsorbing Bovine Serum Albumin (BSA) as a model protein. The adsorption of BSA was found to be favorable, reducing the aggregation phenomena for both bare and amino-modified nanoparticles. Nevertheless, the dispersant effect of BSA was much more evident in the case of amino-modified nanoparticles, which reached monodispersion after adsorption of the protein, thus suggesting that amino-modified nanoparticles can benefit from protein corona formation for preventing severe aggregation in biological media.     

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.     

Synthesis of ordered mesoporous silica membrane on inorganic hollow fiber

This paper reports on a new method for the preparation of mesoporous silica membranes on alumina hollow fibers. A surfactant-silica sol is filled in the lumen of an alpha-alumina hollow fiber. The filtration technique combined with an evaporation-induced self-assembly (EISA) process results in the formation of a continuous ordered mesoporous silica layer on the outer side of alpha-alumina hollow fibers. X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen isothermal adsorption measurements reveal that these membranes possess hexagonal (P6mm) mesostructures with pore diameters of 4.48 nm and BET surfaces of 492.3 m(2) g(-1). Scanning electron microscopy (SEM) studies show that the layers are defect free and energy-dispersive spectroscopy (EDS) mapping images further confirm the formation of continuous mesoporous silica layer on the outer side of alpha-alumina hollow fibers. Nitrogen and hydrogen permeance tests show that the membranes are defect free.     

Formation of SnO2 hollow nanospheres inside mesoporous silica nanoreactors

We report an interesting approach for efficient synthesis of SnO(2) hollow spheres inside mesoporous silica "nanoreactors". The as-prepared products are shown to have a uniform size distribution and good structural stability. When evaluated for their lithium storage properties, these SnO(2) hollow spheres manifest improved capacity retention.     

Rigid nanoscopic containers for highly dispersed, stable metal and bimetal nanoparticles with both size and site control

We demonstrate a novel strategy for the preparation of mesoporous silica-supported, highly dispersed, stable metal and bimetal nanoparticles with both size and site control. The supporting mesoporous silica, functionalized by polyaminoamine (PAMAM) dendrimers, is prepared by repeated Michael addition with methyl acrylates (MA) and amidation reaction with ethylenediamine (EDA), by using aminopropyl-functionalized mesoporous silica as the starting material. The encapsulation of metal nanoparticles within the dendrimer-propagated mesoporous silica is achieved by the chemical reduction of metal-salt-impregnated dendrimer-mesoporous silica by using aqueous hydrazine. The site control of the metal or bimetal nanoparticles is accomplished by the localization of inter- or intradendrimeric nanoparticles within the mesoporous silica tunnels. The size of the encapsulated nanoparticles is controlled by their confinement to the nanocavity of the dendrimer and the mesopore. For Cu and Pd, particles locate at the lining of mesoporous tunnels, and have diameters of less than 2.0 nm. For Pd/Pt, particles locate at the middle of mesoporous tunnels and have diameters in the range of 2.0-4.2 nm. The Pd and Pd/Pt nanoparticles are very stable in air, whereas the Cu nanoparticles are stable only in an inert atmosphere.     

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.     

Gemini Surfactants Templated Mesoporous Silica Microparticles: from Solid to Hollow Mesoporous Spheres

We synthesized a series of mesoporous silica microparticles (MSs) using cationic gemini surfactants C_14–2‐n (n = 2, 6, 10, 14) as templates. The porous structures and pore size of these MSs can be tuned by varying the length of alkyl chain in gemini surfactant templates. These MSs showed effective doxorubicin (DOX) loading and a pH‐responsive drug release characteristics. These results indicate that the MSs, especially the hollow mesoporous silica nanoparticles, have great potential for biomedical applications.