Rattle-type silica colloidal particles prepared by a surface-protected etching process

This paper explores the capability of the “surface-protected etching” process for the creation of rattle-type SiO₂@void@SiO₂ colloidal structures featuring a mesoporous silica shell and a mesoporous movable silica core. The surface-protected etching process involves stabilization of the particle surface using a polymer ligand, and then selective etching of the interior to form hollow structures. In this paper, this strategy has been extended to the formation of rattle-like structures by etching SiO₂@SiO₂ core shell particles which are synthesized by a two-step sol gel process. The key is to introduce a protecting polymer of polyvinylpyrrolidone (PVP) to the surface of both core and shell in order to tailor their relative stability against chemical etching. Upon reacting with NaOH, the outer layer silica becomes a hollow shell as only the surface layer is protected by PVP and the interior is removed, while the core remains its original size thanks to the protection of PVP on its surface. This process can be carried out at room temperature without the need of additional templates or complicated heterogeneous coating procedures. The etching process also results in the rattle-type colloids having mesoscale pores with two distinct average sizes. In our demonstration of a model drug delivery process, such mesoporous structures show an interesting two-step elution profile which is believed to be related to the unique porous rattle structures. This article is published with open access at Springerlink.com     

Ordered porous diamond films fabricated by colloidal crystal templating

We have developed a colloidal crystal templating method for preparation of diamond films with 2D and 3D ordered porous structures. The technological process involved breaks down into (a) impregnation into the pores of silica colloidal crystal (opal) films of detonation nanodiamond (DND) particles from their hydrosol; (b) microwave plasma-enhanced chemical vapor deposition (MWPECVD) regrowth with diamond of pores with high DND filling; (c) Ar(+) ion dry etching of fragments of shells of coalesced diamond crystallites which form in the course of MWPECVD on the surface of the SiO(2) beads making up the outer surface of a film and (d) wet etching of the SiO(2) template in aqueous HF solution. The final samples are either connected to the substrate or free-standing films of various thicknesses having 2D or 3D ordered porous structures. The morphology of the diamond films fabricated by this method replicates the pore network of the opal template. Raman measurements confirm the diamond structure of the synthesized ordered porous material.     

Hexagonal geometric patterns formed by radial pore growth of InP based on Voronoi tessellation

To fabricate ordered geometric patterns consisting of InP nanoporous structures, a photoresist mask with periodic opening arrays was prepared by sphere photolithography. The diameter and interval of the openings of the photoresist mask could be controlled independently by adjusting the diameter of silica spheres used as a lens and the exposure time. Through this resist mask with a two-dimensional (2D) hexagonal array of openings, the pore growth of InP during anodic etching was investigated. The isolated openings could act as initiation sites for the radial growth of pores, resulting in the formation of hexagonal geometric patterns based on Voronoi tessellation in 2D space. With further anodic etching, inside the substrate, the growth direction of the pores changed from radial to perpendicular relative to the substrate. Moreover, by removing domains consisting of nanopores by anisotropic chemical etching, the fabrication of InP microhole arrays with circular and triangular cross sections was also achieved.     

Fabrication of hollow silver spheres by MPTMS-functionalized hollow silica spheres as templates

In this study, we provide a strategy to prepare the hollow silver spheres by accumulating the silver nanoparticles on the surface of 3-mercaptopropyltrimethoxysilane (MPTMS)-functionalized silica as templates, which was accomplished by the chemisorption between silver nanoparticles and thiol groups. Then, the resulting hollow silver spheres were obtained through the chemical wet etching process with 10 M HF solution. In conventional method, the fabrication of hollow silver spheres from core-shell spheres was not easy due to the difficulties in retaining the shell structures during core removal. The method in this paper could overcome this limitation. The major focus of study is on understanding the mechanism of formation of the hollow silver spheres through the self-assembly behavior by chemisorption between silver nanoparticles and thiol groups. The silver-coated silica and hollow silver spheres were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), and X-ray photoelectron spectroscopy (XPS).     

Mechanistic insight into gold nanorod transformation in nanoscale confinement of ZIF-8

Core-shell hybrid nanomaterials have shown new properties and functions that are not attainable by their single counterparts.Nanoscale confinement effect by porous inorganic shells in the hybrid nanostructures plays an important role for chemical transformation of the core nanoparticles.However,metal-organic frameworks(MOFs)have been rarely applied for understanding mechanical insight into such nanoscale phenomena in confinement,although MOFs would provide a variety of properties for the confining environment than other inorganic shells such as silica and zeolite.Here,we examine chemical transformation of a gold nanorod core enclosed by a zeolitic imidazolate framework(ZIF)through chemical etching and regrowth,followed by quantitative analysis in the core dimension and curvature.We find the nanorod core shows template-effective behavior in its morphological transformation.In the etching event,the nanorod core is spherically carved from its tips.The regrowth on the spherically etched core inside the ZIF gives rise toformation of a raspberry-like branched nanostructure in contrast to the growth of an octahedral shape in bulk condition.We attribute the shell-directed regrowth to void space generated at the interfaces between the etched core and the ZIF shell,intercrystalline gaps in mult-domain ZIF shells,and local structural deformation from the acidic reaction conditions.     

A novel approach to a fine particle coating using porous spherical silica as core particles

The applicability of porous spherical silica (PSS) was evaluated as core particles for pharmaceutical products by comparing it with commercial core particles such as mannitol (NP-108), sucrose and microcrystalline cellulose spheres. We investigated the physical properties of core particles, such as particle size distribution, flow properties, crushing strength, plastic limit, drying rate, hygroscopic property and aggregation degree. It was found that PSS was a core particle of small particle size, low friability, high water adsorption capacity, rapid drying rate and lower occurrence of particle aggregation, although wettability is a factor to be carefully considered. The aggregation and taste-masking ability using PSS and NP-108 as core particles were evaluated at a fluidized-bed coating process. The functional coating under the excess spray rate shows different aggregation trends and dissolution profiles between PSS and NP-108; thereby, exhibiting the formation of uniform coating under the excess spray rate in the case of PSS. This expands the range of the acceptable spray feed rates to coat fine particles, and indicates the possibility of decreasing the coating time. The results obtained in this study suggested that the core particle, which has a property like that of PSS, was useful in overcoming such disadvantages as large particle size, which feels gritty in oral cavity; particle aggregation; and the long coating time of the particle coating process. These results will enable the practical fine particle coating method by increasing the range of optimum coating conditions and decreasing the coating time in fluidized bed technology.     

Photodegradation of SiO2-coated CdS nanoparticles within silica gels

A comparative study of the photodegradation of CdS nanoparticles coated with silica shells dispersed in water and embedded in two silica gels with different pore size is presented. Although encapsulation of the quantum dots in a silica shell previously was proven to provide a basically permanent protection against light-induced surface oxidation (photodegradation), this protection is not always maintained when the coated particles are incorporated within different silica gels. Degradation of the CdS occurs when the coated particles are incorporated within silica gels with an open structure, which suggests that the shells somehow crack due to tension in the gel structure. This behavior is analyzed by absorption and luminescence spectroscopies, electron microscopy, and nitrogen sorption.     

Formation of CdSe/CdS/ZnS-Au/SiO2 dual-yolk/shell nanostructures through a Trojan-type inside-out etching strategy

In this work we report the development of a rapid and selective etching strategy to synthesize a dual-yolk/shell nanostructure consisting of semiconductor-metal hybrid nanocrystals and hollow SiO₂ for the first time. By utilizing CdSe/CdS/ZnS quantum dot (CSSQD)/SiO₂ core/shell nanoparticles as the template and aurate hydroxyl complexes [Au(OH) ₄ ^? ] as the Trojan-type inside-out etching agent, rapid formation of CSSQD-Au hybrid nanocrystal dual-yolk and SiO₂ hollow shell occur during the reduction of Au(OH) ₄ ^? on CSSQD cores accompanied by localized hydroxyl-liberation from Au(OH) ₄ ^? at the interface between silica and CSSQD. Unlike surface-protected etching strategies, a selective as well as directional etching takes place from the silica internal surface and the thickness of the silica shell can be controlled by varying the etching time. Moreover, the size of attached Au nanoclusters can be tuned by subsequent light exposure. Consequently, the resulting platform offers a number of attractive features: (1) a new, directional, and rapid etching approach toward the formation of hollow silica nanostructures in solution; (2) semiconductor/metal hybrid nanocrystals as yolks within hollow silica nanospheres have been reported for the first time; and (3) the ability, through light exposure, to tune the size of the attached metal nanoclusters on the encapsulated CSSQD within the hollow silica nanospheres. Most importantly, the synthetic method has the capability of introducing additional guest species (e.g. metals) into a primary yolk (e.g. semiconductor) of hollow silica nanoparticles, potentially leading to many promising applications in fuel cells, photocatalysis, bioimaging, and cancer therapy.      

凹凸结构纳米多孔氧化硅的制备

采用金属辅助化学反应刻蚀法制备了具有凹凸结构的纳米多孔氧化硅，利用光学显微镜、原子力显微镜、扫描电子显微镜和透射电子显微镜等，研究了刻蚀时间对纳米多孔氧化硅形貌结构的影响。结果表明：刻蚀初期在强氧化性酸的作用下，硅表面形成一层氧化硅薄膜，进一步刻蚀，氧化硅薄膜出现规则的周期性凹凸结构裂纹。最后展望了这种凹凸结构纳米多孔氧化硅的应用前景。     

Preparation and properties of porous polyimide films with TiO2/polymer double shell hollow spheres

Without the template removal process, double shell hollow spheres were prepared by encapsulating the polymeric hollow spheres with TiO₂ shells. TiO₂ encapsulated hollow spheres were incorporated with the polyamic acid solutions and imidized to prepare the porous polyimide films. The final porous texture of the film depends on the as-doped arrangement and the properties of the hollow spheres. The TiO₂ shell exhibits good thermal stability and chemical resistance to prevent the collapse of hollow spheres during the polyamic acid solution/hollow particle mixing and the imidization procedures. The effects of preparation conditions on the morphology of the encapsulated hollow spheres were investigated. The dielectric constant of the porous polyimide films (pore diameter around 0.6 µm) decreased to 2.8. The influences of hollow particles on the porous textures, the dielectric and dynamic mechanical properties of the porous films were studied.     

Fused-core silica column high-performance liquid chromatography/tandem mass spectrometric determination of rimonabant in mouse plasma

A high-performance liquid chromatography (HPLC) method using a fused-core silica particle packing was evaluated to allow fast and efficient separation for the analysis of pharmaceutical compounds. Fused-core particles are produced by "fusing" a porous silica layer onto a solid silica particle. The efficiencies of columns packed with 2.7 microm "fused-core" particles (a 0.5 microm porous shell fused to a solid 1.7 microm silica core particle) and 1.7 microm porous particles were compared in reversed-phase HPLC using rimonabant as an analyte. The fused-core silica materials providing the shorter diffusional mass transfer path for solutes are less affected in resolving power by increases in mobile-phase velocity than the sub-2 microm porous silica packings resulting in faster separations and higher sample throughput. This fast HPLC technology is comparable with ultrahigh-pressure liquid chromatography (UHPLC) in terms of chromatographic performance but demands neither expensive ultra-high-pressure instrumentation nor new laboratory protocols. The column effluent was directly connected to the atmospheric pressure chemical ionization (APCI) source prior to tandem mass spectrometric detection. In this work, the described fast HPLC-MS/MS and UHPLC-MS/MS approaches requiring approximately 1.5 min per sample were applied and compared for the determination of the rimonabant in mouse plasma samples at the low nanograms per milliliter region in support of a pharmacodynamic study.     

Controlled nanoporous structures of a marine diatom

We demonstrated chemical etching of a marine diatom shell with 1 N NaOH for controlling the pore size of nanoporous structures of the shell under various conditions. Scanning electron microscopy (SEM) images clearly revealed that the pore size of the diatom shells was regulated in the case of etching at 25 degrees C. In contrast, fluctuations in the etched structures was relatively high even during short periods degradation at 40, 60, and 90 degrees C; therefore, controlled nanoporous structures could not be fabricated. This is the first example of artificial modification of natural diatom shells at the nanoscale although diatom shells have been widely used in industry. In addition, a backbone-like structure was observed during the etching process. The structure was similar to the intermediate structure observed during the primitive stage of the diatom cell growth. Probably, this information is valuable for studying the mechanism of nanoporous structures of diatoms.     

Fabrication of Submicron-Diameter and Taper Fibers Using Chemical Etching

The thin, long length and high smoothness silica photonic nanowires and taper optical fiber were fabricated using a simple and low cost chemical etching method. A two-steps wet etch process were used consisting of etching with 30% HF acid to remove cladding and 24% HF acid to decrease fiber core diameter. An approach for on-line monitoring of etching using 1300 nm light power transmitted in the optical fiber was used to determine the diameter of the remaining core and showed a transition between two different operation regimes of nanofiber from the embedded regime, where the mode was isolated from the environment, to the evanescent regime. The data indicated that the diameter of the silica fiber decreased linearly for both 30% and 24% HF acid with 1.2 and 0.1 μm/min grad diameter, respectively at room temperature, and more than 70% of the mode intensity could propagate outside fiber when the core diameter was less than 1 μm. The results of fiber taper showed that the fiber was tapered by a factor of 20 while retaining a thin core structure and leaving about more than 85% of core structure.     

Synthesis and Photoluminescence Properties of Eu3+‐Doped Silica@Coordination Polymer Core–Shell Structures and Their Calcinated Silica@Gd2O3:Eu and Hollow Gd2O3:Eu Microsphere Products

The conjugation of Eu³⁺‐doped coordination polymers constructed from Gd³⁺ and isophthalic acid (H₂IPA) with silica particles is investigated for the production of luminescent microspheres. A series of doping ratio‐controlled silica@coordination polymer core–shell spheres is easily synthesized by altering the amounts of metal nodes used in the reactions, where the ratios of Gd³⁺ and Eu³⁺ are 10:0 ( 1a ), 9:1 ( 1b ), 8:2 ( 1c ), 7:3 ( 1d ), 5:5 ( 1e ), and 0:10 ( 1f ). The formation of monodisperse uniform core–shell structures is achieved throughout the entirety of a series. Investigations of the photoluminescence property of the resulting series of silica@coordination polymer core–shell spheres reveal that 20% Eu³⁺‐doped product ( 1c ) has the strongest emission intensity. The subsequent calcination process on the silica@coordination polymer core–shell structures ( 1a ‐ f ) results in the formation of a series of doping ratio‐controlled silica@Gd₂O₃:Eu core–shell microspheres ( 2a ‐ f ) with uniform shell thickness. During the calcination step, the coordination polymers within silica@coordination polymer core–shells are transformed into metal oxides, resulting in silica@Gd₂O₃:Eu core–shell structures. The final etching process on the silica@Gd₂O₃:Eu core–shell microspheres ( 2a ‐ f ) produces a series of hollow Gd₂O₃:Eu microspheres ( 3a ‐ f ) as a result of the elimination of silica cores. The luminescence intensities of silica@Gd₂O₃:Eu core–shell ( 2a ‐ f ) and hollow Gd₂O₃:Eu microspheres ( 3a ‐ f ) also vary depending upon the doping ratio of Eu³⁺ ions.     

Synthesis of submicrometer-sized hollow titania spheres with controllable shells

Submicrometer-sized hollow titania spheres with controllable shells have been prepared using polystyrene particles as a template in conjunction with the sol–gel method. The hollow spherical structures could be confirmed by transmission electron microscope (TEM) and scanning electron microscope (SEM). The void sizes of the hollow spheres were 15–20% smaller than the diameters of the polystyrene template. The shell thickness and surface roughness of the hollow titania spheres increased with increasing the concentrations of titanium tetrabutoxide ethanol solutions. Furthermore, when the volume ratio of titanium tetrabutoxide to ethanol was 1:5, a porous titania structure was yielded, rather than dispersive hollow titania spheres. As expected, the shell thickness of the hollow titania spheres could be readily controlled by altering the number of the titanium tetrabutoxide layers coated on the polystyrene template.     

超浓乳液界面引发制备核-壳粒子

利用超浓乳液界面引发制备疏水性核／亲水性壳的两性粒子,首先,通过超浓乳液聚合得到聚苯乙烯胶体粒子,作为疏水性的核,然后,通过界面引发使丙烯酰胺在核的表面聚合,形成亲水性的聚丙烯酰胺的壳层,界面引发体系由过氧化羟基导丙苯和硫酸亚铁组成,控制条件,可得到网孔（半包覆）,褶皱（全包覆）两种结构的壳层,核－壳间无化学键键连,无共聚物过渡层,另外,壳层孔的存在使得核层聚合物能与外界接触。     

Enhanced accumulation and visible light-assisted degradation of azo dyes in poly(allylamine hydrochloride)-modified mesoporous silica spheres

A new route for the economic and efficient treatment of azo dye pollutants is reported, in which surface-modified organic-inorganic hybrid mesoporous silica (MS) spheres were chosen as microreactors for the accumulation and subsequent photodegradation of pollutants in defined regions. The surface-modified silica materials were prepared by anchoring the polycationic species such as poly(allylamine hydrochloride) on MS spheres via a simple wet impregnation method. The as-synthesized spheres with well-defined porous structures exhibited 15 times of accumulating capacity for orange II and Congo red compared to that of the pure MS spheres. Diffuse reflectance UV-vis spectroscopy and confocal laser scanning microscopy demonstrated that the accumulated orange II and CR in defined MS spheres were rapidly degraded in the presence of Fenton reagent under visible radiation. Kinetics analysis in recycling degradation showed that the as-synthesized materials might be utilized as environment-friendly preconcentrators/microreactors for the remediation of dye wastewater.     

炭化聚甲基丙烯酸甲酯／聚丙烯腈核壳聚合物制备炭纳米空心球

采用炭化聚甲基丙烯酸甲酯(PMMA)/聚丙烯腈(PAN)核壳聚合物的方法制备了炭纳米空心球.以两步无皂乳液聚合法制备了PMMA/PAN核壳粒子:首先以间歇无皂乳聚合法制备出直径约200 nm的PMMA粒子乳液,再以其作为种子乳液,以饥饿滴定法在PMMA外表而聚合一层厚度约30 nm的PAN外壳.将制备的PMMA/PAN乳液冷冻干燥后,分别经过250℃预氧化及1000℃炭化工艺,制备了炭纳米空心球.透射电镜结果显示所有核壳粒子均炭化成空心球并呈现交联状态.     

Interfacial assembly of partially hydrophobic silica nanoparticles induced by ultrasonic treatment

A sonochemical approach has effectively been applied to prepare aqueous dispersions of air-filled nanostructured quartz silica shells from surface-engineered amorphous silica nanoparticles. The non-equilibrium nature of the cavitation process and high temperature and pressure in the cavitation microbubble can lead to partial crystallization of the amorphous silica nanoparticles producing the quartz phase and a high degree of interconnection between the silica nanoparticles in the microsphere shells. The very high stability of the silica shells against collapse and aggregation is determined by the hydrophobic nature of the silica nanoparticles. Because of the shell thickness and its high density caused by sintering of the silica nanoparticles, the gas (liquid) permeability through the shell is limited thus prolonging the life time of the air-filled nanostructured silica shells.     

Gas sensors with porous three-dimensional framework using TiO2/polymer double-shell hollow microsphere

The correlations between the structures and gas-sensing properties of porous thin-film gas sensors made of packed hollow spheres are investigated. For this purpose, hollow polymeric spheres were used as templates. Double-shell hollow spheres were prepared by encapsulating the polymeric hollow spheres with TiO₂ shells. Solid polymeric spheres were used as templates for comparison. Porous thin-film gas sensor with interconnected three-dimensional pores was prepared by using the TiO₂ encapsulated hollow spheres. The double-shell hollow spheres and porous titania films were characterized by XRD, BET, TEM and SEM. The gas-sensing properties of the sensors toward NO₂ depend on the type of template and the three-dimensional porous structure of the films. Using the hollow sphere template and adding precursors during the film formation procedure help to prevent the collapse of hollow sphere and form the mesopores in films after removing the template. These films show enhanced gas sensitivity when compared to TiO₂ polycrystalline films. Such improvement in sensitivity results from the porous architecture of the hollow microsphere films which not only increase the active surface area but also promotes the gas diffusion.