Reflectance of surfactant-templated mesoporous silica thin films: Simulations versus experiments

In this study, cubic and hexagonal mesoporous amorphous silica thin films were synthesized using evaporation-induced self-assembly process followed by calcination leaving highly ordered spherical or cylindrical pores in a silica matrix. The films featured pores with diameter between 4 and 11 nm, lattice parameter from 7.8 to 24 nm, and porosity between 22% and 45%. All films were dehydrated prior to reflectance measurements except for one film which was fully hydrated. The present study compares the spectral reflectance measured experimentally between 400 and 900 nm with that computed numerically by solving three-dimensional Maxwell's equations in mesoporous silica thin films with the same morphology as those synthesized. The matrix was assumed to have the same optical properties as bulk fused silica. The pore optical properties were either those of air or liquid water whether the film was dehydrated or hydrated, respectively. Excellent agreement was found between experimental and numerical reflectance for both cubic and hexagonal mesoporous silica films. This study experimentally validates our simulation tool and offers the prospect of ab-initio design of nanocomposite materials with arbitrary optical properties without using effective medium approximation or mixing rules.     

Third-order optical nonlinearity of cadmium sulfide nanoparticles loaded in mesostructured silica materials

Cadmium sulfide nanoparticles have been successfully incorporated in three forms of CTAB-templated mesoporous silica materials: one is the mesoporous silica spheres suspended in ethanol solution, the other is the mesoporous silica spheres spin-coated on glass slide, and the third is the dip-coated mesoporous silica thin film. The mesostructures were characterized by XRD and TEM, respectively. Linear optical properties were investigated using UV-visible spectra, and the diameter of the incorporated CdS nanoparticles was measured to be around 3.1 nm. Z-scan technique manifested that these three composites exhibited distinct third-order optical nonlinearities due to the different preparation techniques. Reverse saturation absorption could be detected in the CdS-loaded mesoporous silica spheres suspended in solution, while those dispersed on glass slide presented saturation absorption. The difference in nonlinear absorption of the two mesoporous silica sphere samples could be attributed to defect-related transitions. On the contrary, the CdS-loaded mesoporous silica thin film showed self-defocusing behavior with no nonlinear absorption signals. Compared to that of the CdS nanoparticles with larger size previously reported, the intrinsic microscopic third-order nonlinear optical susceptibility of those incorporated in CTAB-templated mesoporous thin film was increased as predicted by the quantum theory, and the third-order optical nonlinearity was further determined to arise from intraband transitions induced by quantum confinement.     

The Role of Defects in the Formation of Mesoporous Silica Fibers,Films, and Curved Shapes

The main goal of this research news article is to describe how different kinds of topological defects that exist in a silicate liquid crystal seed can initiate and direct the growth of particular forms of mesoporous silica. This avenue of investigation emerged from the results of scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and polarized optical microscopy (POM) studies of hexagonal mesoporous silica fibers, films, and curved shapes, which delineated the essential relations between synthesis conditions, morphology, bulk and surface mesostructure, and optical birefringence textures.^[1–3] While SEMs of faceted mesoporous silica first appeared in 1992,^[4] the recognition, understanding, and significance of morphogenesis of mesoporous silica with curved shapes emerged in a series of papers from our laboratory.     

纳米镍/介孔二氧化硅复合材料的组装及结构和性质 Ⅱ :纳米镍/介孔二氧化硅复合材料的光吸收性质

研究了SiO₂介孔组装复合材料的光学性质。对于Ni介孔组装体系,随着组装成分和还原温度的提高,纳米颗粒尺寸增大;由于纳米颗粒的表面效应,光吸收边发生明显的红移。光吸收行为与纳米颗粒和基体之间的相互作用,以及相互之间电子转移有关;纳米金属颗粒介孔组装体系光吸收符合间接带隙半导体光吸收模式。在组装体系中加入稀土元素Ce,还原气氛处理后体系的光吸收增强,随着稀土元素添加量的提高,组装体系的吸收边发生较大红移。     

退火CdS/SiO2介孔组装体系光吸收的行为

用溶胶-凝胶法获得多孔SiO2载体，浸泡合成法得到不同复合量的CdS/SiO2块材料介孔组装体系。研究了复合量、气氛条件及退火温度对其光吸收特征的影响，发现吸收边随复合量增加往长波方向移动；在氮气和空气中退火时，随退火温度升高前者表现为红移而后者表现为蓝移，这归属于量子尺寸效应。     

Langmuir-Blodgett films of gold/silica core/shell nanorods

We report the preparation of Langmuir- and Langmuir-Blodgett films of mesoporous silica coated gold nanorods. The silica coating on the gold nanorods was found to prevent the aggregation of the plasmonic particles trapped at the air/water interface. Due to the small aspect ratio of the gold core and the presence of the silica shell, the orientational alignment of the nanorods in the Langmuir-Blodgett film is hindered. After particle deposition, no plasmon coupling was observed, which enables the design of the resulting film's optical property at the particle level. By using mesoporous silica as the shell material, the accessibility of the metal core's surface is preserved. Organic dye (Rhodamine 6G) was found to be able to penetrate into the mesoporous shell of the gold nanorods, resulting in a red shift of the longitudinal plasmon mode.     

退火CdS/SiO2介孔组装体系光吸收的行为

用溶胶-凝胶法获得多孔SiO₂载体,浸泡合成法得到不同复合量的CdS/SiO₂块材介孔组装体系.研究了复合量、气氛条件及退火温度对其光吸收特性的影响,发现吸收边随复合量增加往长波方向移动;在氮气和空气中退火时,随退火温度升高前者表现为红移而后者表现为蓝移,这归属于量子尺寸效应.     

Mesoporous silica directly modified by incorporation or impregnation of some heteropolyacids: Synthesis and structural characterization

The synthesis of heteropolyacids-mesoporous silica composites was carried out in acidic media by impregnation and/or by direct incorporation of active phase. The effect of incorporation of heteropolyacids (HPAs) species into organized mesoporous silica was studied by using non-ionic and cationic surfactants. A comparison between direct incorporation of HPAs into mesoporous silica and impregnation of HPAs on mesoporous silica was done. The structure and texture of H₃PMo₁₂O₄₀ and H₄PVMo₁₁O₄₀ included on mesoporous silica were studied by XRD, SEM-EDS, FT-IR and Raman spectroscopies and BET and pore size distribution. Thermal stability was determined by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). FT-IR and Raman studies showed that HPAs anions preserved their Keggin structure after incorporation or impregnation on mesoporous silica support.     

Encapsulation of CdSe/ZnS nanocrystals within mesoporous silica spheres

Quantum dots (QDs) have attracted much attention on account of their unique optical and electronic properties. Applications of QDs in biological systems face challenges owing to their toxicity and hydrophobicity. Incorporation of QDs in mesoporous silica spheres affords not only hydrophilic shell for QDs in order to enhance their dispersion in aqueous medium, but also offers chemically inert shielding to reduce QD cytotoxicity. In the current work, two types of mesoporous silica encapsulated QDs were synthesized by rationally adjusting the reaction conditions. Mesoporous silica coated single CdSe/ZnS nanoparticles (sCdSe/ZnS@mSiO₂) were prepared through the one-pot reaction. Further modification of this reaction offered hollow mesoporous silica spheres (CdSe/ZnS@HMSS) encapsulating multiple CdSe/ZnS QDs assembled on the internal surface of the spheres. Both of sCdSe/ZnS@mSiO₂ and CdSe/ZnS@HMSS show significant photophysical properties. Possible formation mechanism of the two types of nanostructures was investigated and discussed.     

Direct synthesis of polyoxometalates-functionalized mesoporous hybrid silicas

Novel polyoxometalates (POMs)-functionalized mesoporous hybrid silicas (SiW11/MHS) were synthesized for the first time by the co-condensation of tetraethoxysilane (TEOS) with Keggin-type monovacant SiW11 in the presence of block copolymer EO20PO70EO20 (P123). The as-obtained SiW11/MHS samples were characterized by FT-IR, UV/DRS, XRD, ICP-AES, and N2 adsorption-desorption measurements. It is shown that not only a hexagonal packing of channels with homogeneous pore diameter is obtained, but also Keggin units remain perfectly in the hybrid materials, and Si species insert into the vacancies of lacunary SiW11 during the synthesis to form SiW11Si2 structure, which condenses with the framework of mesoporous silica thus grafting POM molecules onto the pore wall of mesoporous silica by covalent linkage. This linkage results in a firmer immobilization of POMs on the mesoporous material. The water-leaching percent of POMs in the hybrid material is much less than those in the impregnated samples. Therefore, the synthesis strategy for the hybrid material is significant for acquiring supported POM catalysts of high efficiency and practicability.     

Mesoporous‐Silica‐Coated Up‐Conversion Fluorescent Nanoparticles for Photodynamic Therapy

Near‐infrared (NIR)‐to‐visible up‐conversion fluorescent nanoparticles have potential to be used for photodynamic therapy (PDT) in deep tissue because NIR light can penetrate thick tissue due to weak absorption in the optical window. Here a uniform layer of mesoporous silica is coated onto NaYF₄ up‐converting nanocrystals, with a large surface area of ≈770 m² g^?1 and an average pore size of 2 nm. A photosensitizer, zinc phthalocyanine, is incorporated into the mesoporous silica. Upon excitation by a NIR laser, the nanocrystals convert NIR light to visible light, which further activates the photosensitizer to release reactive singlet oxygen to kill cancer cells. The photosensitizer encapsulated in mesoporous silica is protected from degradation in the harsh biological environment. It is demonstrated that the photosensitizers loaded into the porous silica shell of the nanoparticles are not released out of the silica while they continuously produce singlet oxygen upon excitation by a NIR laser. The nanoparticles are reusable as the photosensitizers encapsulated in the silica are removed by soaking in ethanol.     

High-performance, single-layer antireflective optical coatings comprising mesoporous silica nanoparticles

Mesoporous silica nanoparticles are used to fabricate antireflectance coatings on glass substrates. The combination of mesoporous silica nanoparticles in conjunction with a suitable binder material allows mechanically robust single layer coatings with a reflectance <0.1% to be produced by simple wet processing techniques. Further advantages of these films is that their structure results in broadband antireflective properties with a reflection minimum that can tuned between 400 nm and 1900 nm. The ratio of binder material to mesoporous nanoparticles allows control of the refractive index. In this report, we discuss how control of the structural properties of the coatings allows optimization of the optical properties.     

The size-controllable synthesis of nanometer-sized mesoporous silica in extremely dilute surfactant solution

10–60 nm-sized mesoporous silica particles with ordered or worm-like pore structures were controllably synthesized in extremely dilute surfactant solution, and the lowest concentrations of TEOS and CTAB were 12.45 mM, 1.52 mM, respectively. The synthesis of nanometer-sized Al-incorporated mesoporous silica particles (Al-MS) was also performed under the similar conditions. Compared to the mesoporous silica without doping of aluminum, those Al-incorporated silica particles have a certain textural mesoporosity. The results indicate that the size and pore structure of mesoporous silica can be adjusted by changing the concentration of reactants. The mesoporous silica nanoparticles, including Al-MS, were characterized by transmission electron microscopy (TEM), small-angle X-ray diffraction (SAXRD), as well as nitrogen adsorption/desorption techniques. It was suggested that the formation of the mesoporous silica nanoparticles could be attributed to the deposition of self-assembled silicate micelles.     

Pd Nanosheet‐Covered Hollow Mesoporous Silica Nanoparticles as a Platform for the Chemo‐Photothermal Treatment of Cancer Cells

A versatile system combining chemotherapy with photothermal therapy for cancer cells using Pd nanosheet‐covered hollow mesoporous silica nanoparticles is reported. While the hollow mesoporous silica core can be used to load anticancer drugs (i.e., doxorubicin) for chemotherapy, the Pd nanosheets on the surface of particles can convert NIR light into heat for photothermal therapy. More importantly, the loading of Pd nanosheets on hollow mesoporous silica nanospheres can dramatically increase the amount of cellular internalization of the Pd nanosheets: almost 11 times higher than the unloaded Pd nanosheets. The as‐prepared nanocomposites efficiently deliver both drugs and heat to cancer cells to improve the therapeutic efficiency with minimal side effects. Compared with chemotherapy or photothermal therapy alone, the combination of chemotherapy and phototherapy can significantly improve the therapeutic efficacy, exhibiting a synergistic effect.     

Palladium supported on functionalized mesoporous silica as an efficient catalyst for Heck reaction

Pd nanoparticles supported in functionalized mesoporous silica were prepared. Mesoporous silica support was modified with [3-(2-aminoethyl aminopropyl)] trimethoxysilane. Palladium ions were grafted onto the functionalized mesoporous silica and reduced with hydrazine hydrate to obtain the Pd nanoparticles supported on functionalized mesoporous silica. The Pd loading in the nanocomposite of Pd supported on the functionalized mesoporous silica is 4.30 wt%. CO chemisorption analysis on the nanocomposite shows a Pd dispersion as high as 35% and a Pd surface area of 156 m²/g. The surface area, pore size, and pore volume decrease slightly with the incorporation of the Pd nanoparticles into the functionalized mesoporous silica. Pd supported on the functionalized mesoporous silica with controlled molar ratio of amino groups to palladium exhibits an excellent catalytic activity and low Pd leaching for the Heck carbon-carbon coupling reaction. The catalyst can be reused for at least six recycles in air with only a minor loss of activity.     

Preparation and Optical Properties of Nanocomposites Containing Palladium Within Mesoporous Silica via Sol-Gel Chemistry

The preparation and optical characterization of nanocomposites comprised of palladium into mesoporous silica are presented in this paper. Introduction of palladium was conducted through two different routes involving the sol-gel technique. In the first route, monolithic porous silica produced by hydrolysis of alkoxides in advance was then impregnated into the concentrated solution containing palladium precursor, and the nanocomposite was manufactured after a sequent thermal treatment. In the another route, a mixture made with the alkoxides and palladium precursor added in water was stoichiometrically prepared with the hydrolysis and condensation reactions, resulting in a formation of the composite silica gel. The introduced palladium particle was subjected to the matrix, varied with the composition and found to be 5–10 nm in scale. The optical absorption measurements show that the edges were red-shifted to a certain extent with an increase in the composition and heated temperature. The changes can be responsible for the interactions between the matrix and the introduced phase. IR characterization for the monolithic silica and the nanocomposites was also performed for the further explanation.     

Observation of quantum confinement effect on ZnO embedded mesoporous silica

Nonionic surfactant as liquid organic template and tetraethoxysilane as silica precursor were used for the synthesis of mesoporous silica with ordered arrangement of nanopores (diameters are about 1-6 nm). The synthesized mesoporous silica was used as the template for the synthesis of ZnO nanoparticles using zinc acetylacetonate as ZnO precursor. The as synthesized ZnO incorporated in the mesoporous silica nanocomposite were analyzed using X-ray diffraction, TEM and Photoluminescent spectrum. ZnO introduction has no extensive influence on the mesoporous structure of silica. Quantum confinement effects are observed in the case of ZnO nanoparticles embedded in mesoporous silica. The particle size of ZnO is about 3.2 nm. The band gap is broadening to 3.47 eV.     

Beyond Silica: Nonoxidic Mesostructured Materials

Recent advances in the design and synthesis of mesostructured and mesoporous materials with nonoxide frameworks are reviewed. Chalcogenides comprise the most important class, and all possible pore arrangements known for silica can be achieved in these materials. The special molecular chemistry that leads to organized nonoxidic mesostructures that have a variety of compositions, pore sizes, and semiconductor bandgaps is presented. Also reviewed are recent developments in mesoporous elements, such as metals and germanium. The goal in research on mesoporous semiconductors is to create materials scaffolds with new physical phenomena that derive from the combined characteristics of long‐range porosity and electronic and optical properties.     

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.     

Self-assembly,microstructure and photoluminescence properties of nanocomposite mesoporous silica loaded with In2O3 and In2O3–SnO2

Abstract

The mesoporous nanocomposite fabricated by self-assembly has many unique properties compared with the original materials. In₂O₃ (IO) and In₂O₃–SnO₂ (ITO) in mesoporous silica were studied in the present paper. They were self-assembled in a nanoscale mesoporous silica by an adsorption–annealing process. The composite of IO and ITO in mesoporous silica was characterised by transmission electron microscopy, atomic force microscopy and nitrogen sorption isotherms. Photoluminescence spectra of the samples were measured by a fluorescence spectrophotometer. The results show that the composite was synthesised from IO and ITO in a nano-scale mesoporous silica with assembly structure, and bulk mesoporous silica is easier to be loaded by the particles than the sheet one, but the specific surface area decreases with increasing atomic weight of the substances loaded in silica mesoporous. The results also show that the mesoporous composite doped with some substance may enhance the effect of photoluminescence. For instance, the mesoprous composite of IO/SiO₂ has an enhancement in the effect of photoluminescence, and that of the mesoprous nanocomposite of ITO/SiO₂ is greater. Mesoporous nanocomposite is a promising photoluminescence material in the application to industry.