Photonic crystals with tunable optical stop band through monodispersed silica–polypyrrole core-shell spheres

We prepared monodispersed silica–polypyrrole core-shell spheres (SiO₂–Ppy) using adsorbed surfactant bilayers on silica as templates and demonstrated the construction of photonic crystal with tunable stop band from SiO₂–Ppy core-shell spheres. Since the photonic stop band is very dependent on the refractive index, it can be tuned by simply changing the refractive index of Ppy shell via changing doping level. In fact, the stop band was shifted about 15 nm when the photonic crystal was exposed to fuming sulfuric acid due to the change of the doping level of Ppy shell.     

Fabrication of hollow silica spheres and their application in polyacrylate film forming agent

Polystyrene (PS)/silica core/shell spheres were fabricated using mono-dispersed PS as templates by hydrolysis and condensation of two different silica precursors. The PS cores of PS/silica core/shell spheres were dissolved subsequently in the tetrahydrofuran medium to form mono-dispersed hollow silica spheres. The structures and morphologies of hollow silica spheres were characterized by scanning electron microscopy and transmission electron microscopy. Then, polyacrylate/hollow silica composite film forming agents were prepared via physical blending of polyacrylate and two different hollow silica spheres, and the water vapor permeability of their films were compared. The results showed that the structure of hollow silica spheres were very typical and obvious. The silica shell was continuous and uniform using tetraethylorthosilicate as precursor, which was accumulated by many silica seeds with size of 10–20 nm, and the thickness of silica shell was about 16.7 nm. However, the hollow silica spheres using tetraethylorthosilicate and vinyl triethoxysilane as precursors had mesoporous structure in the shell. The introduction of hollow silica spheres could significantly improve the water vapor permeability of polyacrylate film. At last, a possible mechanism for the formation of hollow silica spheres was proposed and the process of water vapor through polyacrylate/hollow silica composite films was modeled.     

Novel hollow sub-microspheres with movable Au nanoparticles and excessive Pt nanoparticles in core and silica as shell

A simple route has been designed for the syntheses of a kind of electrocatalyst, i.e., hollow spheres with Au and excessive Pt nanoparticles in core and silica as shell. The Au@carbon spheres synthesized by hydrothermal process can act as the transitional templates, and the carbonaceous matrix can in situ reduce H₂PtCl₆·H₂O solution and load with Pt nanoparticles, and then a slightly modified Stöber process was applied to encapsulate the structures with silica shell. Further calcination at high temperatures removed the carbon matrix to form the hollow spheres with Au and excessive Pt nanoparticles in core and silica as shell. This new kind of structures shows excellent electrocatalytic properties compared with that of similar hollow spheres but only with pure Pt nanoparticles inside, and it might provide an efficient way to improve the electrocatalytic property of a bulk Pt/GC electrode.     

Morphology and dispersivity modulation of hollow microporous spheres synthesized by a hard template route

Uniform hollow microporous silica spheres (HMS) have been synthesized in an easy route using polystyrene spheres (PS) and cetyltrimethylammonium bromide (CTAB) as co-templates at room temperature in concentrated aqueous ammonia. The hexagonally ordered pore channels are formed on the shell of the HMS. Effects of various processing parameters such as the tetraethyl orthosilicate (TEOS) adding rate, the amount of aqueous ammonia and ultrasonic treatment, on the dispersivity and morphology, were investigated. The slow syringing addition of TEOS favors the formation of highly dispersed hollow spheres with a certain and uniform shell thickness. More aqueous ammonia and proper time of ultrasonic are helpful to the synthesis of uniform hollow silica spheres with good dispersivity. The morphology, dispersivity and micropore structure of as-synthesized HMS were characterized using X-ray diffraction, N₂ sorption isotherms, scanning electron microscope and transmission electron microscope.     

Large‐Scale Fabrication of Core–Shell Structured C/SnO2 Hollow Spheres as Anode Materials with Improved Lithium Storage Performance

Due to the high theoretical capacity as high as 1494 mAh g^?1, SnO₂ is considered as a potential anode material for high‐capacity lithium–ion batteries (LIBs). Therefore, the simple but effective method focused on fabrication of SnO₂ is imperative. To meet this, a facile and efficient strategy to fabricate core–shell structured C/SnO₂ hollow spheres by a solvothermal method is reported. Herein, the solid and hollow structure as well as the carbon content can be controlled. Very importantly, high‐yield C/SnO₂ spheres can be produced by this method, which suggest potential business applications in LIBs field. Owing to the dual buffer effect of the carbon layer and hollow structures, the core–shell structured C/SnO₂ hollow spheres deliver a high reversible discharge capacity of 1007 mAh g^?1 at a current density of 100 mA g^?1 after 300 cycles and a superior discharge capacity of 915 mAh g^?1 at 500 mA g^?1 after 500 cycles. Even at a high current density of 1 and 2 A g^?1, the core–shell structured C/SnO₂ hollow spheres electrode still exhibits excellent discharge capacity in the long life cycles. Consideration of the superior performance and high yield, the core–shell structured C/SnO₂ hollow spheres are of great interest for the next‐generation LIBs.     

Optical properties of graphene based annular photonic crystals

The optical properties of a graphene based annular photonic crystal (APC) are theoretically investigated. The proposed structure is a hollow core cylindrical shell consists of the alternate dielectric layer and graphene monolayer immersed in free space. In order to study the photonic band structures of the APC, we obtained the optical spectra of the graphene based APC by employing the transfer matrix method in the cylindrical waves for both TE and TM polarizations. In this work we study the effect of different geometrical and optical parameters of the structure on the low loss high reflectance graphene induced band gap. It is found that the graphene induced band gap which appeared in the frequency below 10 THz is polarization independent and remains almost invariant with the change in the period number, the radius of the inner core region and the refractive indices of the inner core region and the surrounding medium. However, its width increases by increasing the azimuthal mode number and the chemical potential of the graphene monolayers and decreases by increasing the refractive index and the thickness of the dielectric layers.     

Sol-gel synthesis, microstructure and adsorption properties of hollow silica spheres

Spherical colloidal particles with a hollow interior and a mesoporous shell are particularly useful for drug delivery and release because such spheres combine the unique properties of hollow interior (for storing the drug) with mesoporous shell (for controlled release). Hollow silica spheres (HSS) with a mesoporous shell were prepared via a sol-gel process in the presence of dual templates polystyrene spheres and cetyltrimethylammonium bromide for creating the hollow core and mesopore shell. The effect of the ratio of silica precursor over polystyrene spheres on particle morphology and pore structure of the HSS was investigated. The adsorption kinetics of methyl blue on the HSS was evaluated and correlated with the mesoporous shell structure.     

A dual template method for synthesizing hollow silica spheres with mesoporous shells

PS/silica core/shell composites were synthesized by the modified Stöber method using polystyrene spheres and cetyltrimethylammonium bromide as dual templates under room temperature. The silicate species and the templates were self-assembled to form mesoporous silica shell on the surface of the PS spheres. Hollow silica spheres with mesoporous shell were obtained by removing the polymer core and the templates through calcination. The hollow silica spheres showed high specific surface area of 1099.5 m²/g and narrow pore size distribution centered at 2.31 nm.     

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.     

Tunable photonic nanojet achieved using a core–shell microcylinder with nematic liquid crystal

A tunable photonic nanojet achieved using a core–shell microcylinder with nematic liquid crystal is reported. The core–shell microcylinder can be obtained by the infiltration of liquid crystal into the air core of a microcylinder. The refractive indices of the liquid crystals can be changed by rotating the directors of the liquid crystals. Therefore, we were able to control the flow direction of the photonic nanojet in two-dimensional core–shell microcylinder structures. Using high resolution finite-difference time-domain simulation, we demonstrate that the photonic nanojet can be continuously tuned in the core–shell microcylinder. The horizontal and vertical shifts of photonic nanojet depend strongly on the director of the liquid crystals. Such a mechanism of nanojet adjustment should open up a new application for using visible light to detect nanoparticles, optical gratings, and single molecules with subwavelength spatial resolution.     

单分散SiO_2/TiO_2/SiO_2多层复合微球的制备

采用一种以醇盐水解法为基础的生长硅溶胶的方法,制备了粒径为２００ｎｍ的单分散二氧化硅球形颗粒,并将其作为核心,利用常温连续进料的钛酸丁酯水解的多步法,在二氧化硅核心外经多次包覆形成厚层二氧化钛;在正硅酸乙酯的水解和陈化环境下,将上述ＴｉＯ２／ＳｉＯ２复合颗粒外再包覆一薄层二氧化硅,形成一种高折射率,可用于组装光子晶体的ＳｉＯ２／ＴｉＯ２／ＳｉＯ２多层复合微球．对该复合微球用重力沉降法、透射电镜法（ＴＥＭ）、Ｘ射线能谱分析法（ＥＤＳ）进行了表征．其中,重力沉降法是一种将Ｓｔｏｋｅｓ公式为基础推导的复合颗粒的粒径与沉降速度关系式所得的一系列数据进行拟合外延,来测定复合颗粒的粒径及包覆厚度的方法．     

Design of Multifunctional Fluorescent Hybrid Materials Based on SiO2 Materials and Core–Shell Fe3O4@SiO2 Nanoparticles for Metal Ion Sensing

Hybrid fluorescent materials constructed from organic chelating fluorescent probes and inorganic solid supports by covalent interactions are a special type of hybrid sensing platform that has gained much interest in the context of metal ion sensing applications owing to their excellent advantages, recyclability, and solubility/dispersibility in particular, as compared with single organic fluorescent molecules. In recent decades, SiO₂ materials and core–shell Fe₃O₄@SiO₂ nanoparticles have become important inorganic solid materials and have been used as inorganic solid supports to hybridize with organic fluorescent receptors, resulting in multifunctional fluorescent hybrid systems for potential applications in sensing and related research fields. Therefore, recent progress in various fluorescent‐group‐functionalized SiO₂ materials is reviewed, with a focus on mesoporous silica nanoparticles and core–shell Fe₃O₄@SiO₂ nanoparticles, as interesting fluorescent organic–inorganic hybrid materials for sensing applications toward essential and toxic metal ions. Selective examples of other types of silica/silicon materials, such as periodic mesoporous organosilicas, solid SiO₂ nanoparticles, fibrous silica spheres, silica nanowires, silica nanotubes, and silica hollow microspheres, are also mentioned. Finally, relevant perspectives of metal‐ion‐sensing‐oriented silica‐fluorescent probe hybrid materials are provided.     

Transmittance analysis of three-dimensional photonic crystals by the effective medium theory

A simple method for calculating the transmittance of three-dimensional photonic crystals is proposed. The crystals are divided into multilayer thin films, and each film is divided into rectangles with a minute width to calculate the effective permittivity of the film by the effective medium theory. Transmittance of the multilayer thin films is calculated with the matrix method. As the number of atomic layers increases, remarkable stop bands appear. When the refractive index of photonic atoms increases, the stop band shifts to a lower frequency, the band widens, and the number of bands increases. Polarization and incident angle dependences are also analyzed. The limit of application for this calculation method is also discussed.     

Facile synthesis and microwave absorbability of C@Ni–NiO core–shell hybrid solid sphere and multi-shelled NiO hollow sphere

We reported the preparation of C@Ni–NiO core–shell hybrid solid spheres or multi-shelled NiO hollow spheres by combining a facile hydrothermal route with a calcination process in H₂ or air atmosphere, respectively. The synthesized C@Ni–NiO core–shell solid spheres with diameters of approximately 2–6 μm were in fact built from dense NiO nanoparticles coated by random two-dimensional metal Ni nanosheets without any visible pores. The multi-shelled NiO hollow spheres were built from particle-like ligaments and there are a lot of pores with size of several nanometers on the surface. Combined Raman spectra with X-ray photoelectron spectra (XPS), it suggested that the defects in the samples play a limited role in the dielectric loss. Compared with the other samples, the permeability of the samples calcined in H₂ and air was increased slightly and the natural resonance frequency shifted to higher frequency (7, 11 and 14 GHz, respectively), leading to an enhancement of microwave absorption property. For the sample calcined in H₂, an optimal reflection loss less than − 10 was obtained at 7 GHz with a matching thickness of 5.0 mm. Our study demonstrated the potential application of C@Ni–NiO core–shell hybrid solid sphere or multi-shelled NiO hollow sphere as a more efficient electromagnetic (EM) wave absorber.     

A novel synthesis of micrometer silica hollow sphere

Silica microcapsules (hollow spheres) were synthesized successfully by a novel CTAB-stabilized water/oil emulsion system mediated hydrothermal method. The addition of urea to a solution of aqueous phase was an essential step of the simple synthetic procedure of silica hollow spheres, which leads to the formation of silica hollow spheres with smooth shell during hydrothermal process. The intact hollow spheres were obtained by washing the as-synthesized solid products with distilled water to remove the organic components. A large amount of silanol groups were retained in the hollow spheres by this facile route without calcination. The morphologies and optical properties of the product were characterized by transmission electron microscopy, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy. Furthermore, on the basis of a series of SEM observations, phenomenological elucidation of a mechanism for the growth of the silica hollow spheres has been presented.     

A high sensitivity refractive index sensor based on photonic crystal fibre Mach–Zehnder interferometer

A compact and high sensitivity refractive index sensor based on a photonic crystal fibre Mach–Zehnder mode–mode interferometer is proposed. The sensing part is formed by in fibre SMF-PCF-SMF structure (SMF: single-mode fibre; PCF: photonic crystal fibre) using fusion splicing method. The fully collapse air holes of photonic crystal fibre make coupling of fibre core and cladding mode in the splicing collapse region which establish a Mach–Zehnder interferometer. The Mach–Zehnder interferometers with different photonic crystal fibre length are fabricated to investigate refractive index sensing characteristics. The refractive index measuring sensitivity can reach 224.2 nm/RIU (RIU: Refractive Index Unit) with a length of PCF L = 4 cm, experimentally. The proposed refractive index sensor is attractive due to its simple production process, compact size and high sensitivity.     

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).     

3D photonic crystals with a hierarchical pore structure

Perfect 3D film photonic crystals are synthesized from submicron spherical silica particles consisting of a nonporous core and a mesoporous shell. The obtained photonic crystals with a hierarchical pore arrangement—transport macropores between particles and mesopores inside the shell—are promising for application in optical gas sensors.     

核-壳式聚苯乙烯/二氧化硅复合微球及空腔硅球的制备

利用层层自组装的方法制备了粒径和组成可裁剪、具有核-壳式结构的单分散聚苯乙烯(PS)/二氧化硅(SiO₂)复合微球.对复合微球进行热处理除去有机物中心,制备出壁厚可剪裁的空腔硅球.透射电镜(TEM)照片显示二氧化硅纳米颗粒在中心外生成均匀壳层,而煅烧后则可得到轮廓分明的球形空腔;热重分析(TG)说明复合球体的硅含量随着所组装的纳米二氧化硅的粒径的增加而增加;比较PS、SiO₂、复合球体及热处理后的粉体的红外光谱,可分别验证二氧化硅的成功组装和热处理过程中作为中心的PS的完全去除.在吸附相同层的前提下,随着所选用的二氧化硅纳米粒子(10um,20um,40um)的粒径的增大,复合微球的粒径增大,空腔球体的壁厚增加.     

Responsive Block Copolymer Photonic Microspheres

Responsive photonic crystals (PCs) have attracted much attention due to their broad applications in the field of chemical and physical sensing through varying optical properties when exposed to external stimuli. In particular, assembly of block copolymers (BCPs) has proven to be a robust platform for constructing PCs in the form of films or bulk. Here, the generation of BCPs photonic microspheres is presented with 3D periodical concentric lamellar structures through confined self‐assembly. The structural color of the spherical PCs can be tuned by selective swelling of one block, yielding large change of optical property through varying both layer thickness and refraction index of the domains. The as‐formed spherical PCs demonstrate large reflection wavelength shift (≈400–700 nm) under organic solvent permeation and pH adjustment. Spherical shape and structural symmetry endow the formed spherical PCs with rotation independence and monochrome, which is potentially useful in the fields of displays, sensing, and diagnostics.