Dense Silica Layer Research Articles

Facile Strategy for Fabricating an Organosilica-Modified Fe3O4 (OS/Fe3O4) Hetero-nanocore and OS/Fe3O4@SiO2 Core-Shell Structure for Wastewater Treatment with Promising Recyclable Efficiency.

The development of a sustainable process for heavy metal ion remediation has become a point of interest in various fields of research, including wastewater treatment, industrial development, and health and environmental safety. In the present study, a promising sustainable adsorbent was fabricated through continuous controlled adsorption/desorption processes for heavy metal uptake. The fabrication strategy is based on a simple modification of Fe3O4 magnetic nanoparticles with organosilica in a one-pot solvothermal process, carried out in order to insert the organosilica moieties into the Fe3O4 nanocore during their formation. The developed organosilica-modified Fe3O4 hetero-nanocores had hydrophilic citrate moieties, together with hydrophobic organosilica ones, on their surfaces, which facilitated the further surface coating procedures. To prevent the formed nanoparticles from leaching into the acidic medium, a dense silica layer was coated on the fabricated organosilica/Fe3O4 (OS/Fe3O4). In addition, the prepared OS/Fe3O4@SiO2 was utilized for the adsorption of cobalt(II), lead(II), and manganese(II) from the solutions. The data for the adsorption processes of cobalt(II), lead(II), and manganese(II) on OS/(Fe3O4)@SiO2 were found to follow the pseudo-second-order kinetic model, indicating the fast uptake of heavy metals. The Freundlich isotherm was found to be more suitable for describing the uptake of heavy metals by OS/Fe3O4@SiO2 nanoparticles. The negative values of the ΔG° showed a spontaneous adsorption process of a physical nature. The super-regeneration and recycling capacities of the OS/Fe3O4@SiO2 were achieved, comparing the results to those of previous adsorbents, with a recyclable efficiency of 91% up to the seventh cycle, which is promising for environmental sustainability.

Suppressing the Photocatalytic Activity of Titania by Precisely Controlled Silica Coating.

A homogeneous thin silica layer with the thickness of a few nanometers was successfully deposited on an anatase particle by the hydrolysis and condensation of tetraethyl orthosilicate. The heat treatment of the titania/silica hybrid at 1000 °C led to the densification of the silica layer on the anatase particles. The anatase particle after the silica coating did not transform to rutile, and no change in the crystallite size was seen by the heat treatment at 1000 °C. The coating and subsequent heating were repeated to vary the thickness of the silica layer to obtain each coating with similar thickness by each coating procedure (ca. 3 and 2 nm, before and after the heat treatment). The samples were evaluated for the photocatalytic decomposition of methylene blue by the UV irradiation to find that the decomposition became slower after the coating and subsequent heat treatment, and the repeated procedures led to further suppression of the photocatalytic decomposition of methylene blue. The quite small decomposition rate constant (0.01 h-1) was successfully achieved by the coating and subsequent heating for three times (the thickness of the dense silica layer was ca. 7 nm).

Highly biocompatible Co@Silica@meso-Silica magnetic nanocarriers

Core-shell structured Co@Silica@meso-Silica nanoparticles have been synthesized via a layer-by-layer approach. The magnetic cobalt core makes the nanoparticles easy to separate with an external magnetic field. The inner dense silica layer prevents the Co from oxidation and leaching. The outer mesoporous silica presents high surface area and pore volume, endowing the material with superior adsorption properties of organic molecules. The core-shell structure prevents the direct contact of cobalt with living cells, thus enhancing the biocompatibility remarkably. This dual encapsulation provides a golden opportunity to the nanocarrier design with easy magnetic separation, high drug loading, and high biocompatibility.

Quantitative Measure of the Size Dispersity in Ultrasmall Fluorescent Organic-Inorganic Hybrid Core-Shell Silica Nanoparticles by Small-angle X-ray Scattering.

Small-angle X-ray scattering (SAXS) was performed on dispersions of ultrasmall (d < 10 nm) fluorescent organic-inorganic hybrid core-shell silica nanoparticles synthesized in aqueous solutions (C' dots) by using an oscillating flow cell to overcome beam induced particle degradation. Form factor analysis and fitting was used to determine the size and size dispersity of the internal silica core containing covalently encapsulated fluorophores. The structure of the organic poly(ethylene glycol) (PEG) shell was modelled as a monodisperse corona containing concentrated and semi-dilute regimes of decaying density and as a simple polydisperse shell to determine the bounds of dispersity in the overall hybrid particle. C' dots containing single growth step silica cores have dispersities of 0.19-0.21; growth of additional silica shells onto the core produces a thin, dense silica layer, and increases the dispersity to 0.22-0.23. Comparison to FCS and DLS measures of size shows good agreement with SAXS measured and modelled sizes and size dispersities. Finally, comparison of a set of same sized and purified particles demonstrates that SAXS is sensitive to the skewness of the gel permeation chromatography elugrams of the original as-made materials. These and other insights provided by quantitative SAXS assessments may become useful for generation of robust nanoparticle design criteria necessary for their successful and safe use, for example in nanomedicine and oncology applications.

Research on design, fabrication, and properties of Fe2O3@SiO2/CDs/PEG@nSiO2 nanocomposites

Multimodal imaging, which can combine information from different imaging modalities, offers huge advantages. Among various multifunctional images, magnetic resonance imaging (MRI) combination with fluorescence imaging has attracted considerable attention for their potential biomedical applications. In this study, we present a facile method for fabrication of core-shell-structured nanocomposite particles. First, Fe2O3 nanoparticles were synthesized as the magnetic core. Then, the Fe2O3 nanoparticles were covered with a silica shell. Carbon dots and PEG could be absorbed into the mesoporous silica layer and then sealed by a dense silica layer (denoted as Fe2O3@SiO2/CDs/PEG@nSiO2). The results show that the as-prepared nanocomposite has a uniform size, strong magnetization and good fluorescence properties, which has application as a bioimaging probe.

(Invited) Driving Metal Oxide Water Oxidation Catalyst By Visible Light Absorber Separated By an Ultrathin Proton Conducting Silica Membrane with Embedded Molecular Wires

We are developing nanoscale photosynthetic assemblies for coupling the catalysis for CO2 reduction with the H2O oxidation half reaction, taking an inorganic molecular approach that utilizes heterobinuclear units such as ZrOCoII as light absorber coupled to metal oxide catalyst. Artificial nanoscale photosystems are inspired by natural photosynthesis, the only existing technology for producing energy-dense chemicals on the terawatt scale, which has as key design feature the closing of the cycle of water oxidation and formation of primary reduction intermediates on the shortest possible length scale, the nanometer scale, while separating the incompatible redox environments by an ultrathin membrane. To accomplish the photocatalytic cycle of CO2 reduction by H2O under membrane separation, we are exploring a Co oxide – silica core-shell nanotube geometry.1-3 The inside surface of the Co oxide nanotube core provides the catalytic sites for H2O oxidation, which are separated from light absorber and sites of CO2 reduction on the outside by an ultrathin (2 nm) dense phase silica layer. The latter functions as proton conducting, O2 impermeable membrane.4 Tight, molecular-level control of charge transfer between light absorber and Co oxide nanotube catalyst is accomplished by oligo-para(phenylene vinylene) molecules with 3 aryl units embedded in the silica shell.5 This approach addresses the requirements of robustness and tunability of the electronic properties of the photosystem components with the objective of converting the maximum fraction of the solar photon energy into chemical energy of the fuel.6 The core-shell nanotube geometry offers the opportunity of assembling macroscale arrays of enormous numbers of nanotubes, each operating as independent photosynthetic unit while at the same time providing separation of evolving O2 and reduced CO2 products on all length scales from nano to centimeters.3 Detailed characterization of charge transfer between light absorber and Co oxide catalyst across the silica membrane was investigated by transient optical absorption spectroscopy and photoelectro-chemical methods using nanotube, spherical, or planar morphology depending on the type of experiment. Ultrafast optical monitoring allowed us to detect transient positive charge (hole) on the silica embedded molecular wire and revealed very efficient, 255 ps transfer to the Co oxide catalyst.7 Short circuit current measurements upon visible light sensitized hole injection using sensitizers with different redox potentials showed that charge transfer is controlled by the HOMO and LUMO energetics of the silica embedded wire molecules.4,5 Synthetic methods were developed for the accurate selection of embedded molecular wire loading and tuning of the concentration. Electron transfer processes of visible light excited ZrOCo or TiOCo light absorbers coupled to silica embedded wires and Co oxide catalyst are being explored by transient optical spectroscopy and photoelectrochemical methods, and will be the main topic of the presentation.8 Time permitting, recent application of ultrathin silica membrane with embedded molecular wires for separating incompatible catalytic environments of electronically coupled inorganic and microbial components will also be discussed.9 [1] Kim, W.; Edri, E.; Frei, H. Acc. Chem. Res. 49, 1634 (2016) [2] Kim, W.; McClure, B. A.; Edri, E.; Frei, H. Chem. Soc. Rev. 45, 3221 (2016) [3] Edri, E.; Aloni, S.; Frei, H., ACS Nano, submitted [4] Yuan, G.; Agiral, A.; Pellet, N.; Kim, W.; Frei, H. Faraday Discuss. 176, 233 (2014) [5] Edri, E.; Frei, H. J. Phys. Chem. C 119, 28326 (2015) [6] Frei, H. Curr. Opin. Electrochem. 2, 128 (2017) [7] Edri, E.; Cooper, J. K.; Sharp, I. D.; Guldi, D. M.; Frei, H. J. Am. Chem. Soc. 139, 5458 (2017) [8] Katsoukis, G.; Frei, H., to be submitted [9] Cornejo, J. A.; Sheng, H.; Edri, E.; Ajo-Franklin, C.; Frei, H., submitted

Silica-coated gold nanorod@CdSeTe ternary quantum dots core/shell structure for fluorescence detection and dual-modal imaging

Abstract The applications based on ternary quantum dots (QDs) in biosensor have attracted wide interest due to their unique optical properties. It makes sense to construct a comprehensive optical biologic probe with fluorophores and plasmonic functional groups in precise co-localized bio-imaging probe development. Herein, we fabricated a novel hierarchical Au nanorod (NR)@CdSeTe quantum dots core/shell structure using silicon isolation layer for biological application. AuNRs were mediated by an initial mesoporous silica layer and coated with a dense layer of silica, and then CdSeTe QDs were directly assembled on the surface. The dense silica layer can reduce the potential fluorescence resonance energy transfer (FRET) between QDs and AuNRs. The molecular beacon (MB)-conjugated AuNR@CdSeTe fluorescent biosensors were prepared by nucleic acid hybridization technology in order to overcome the limitations of conventional probes for Norovirus (NV). The MB-conjugated AuNR@CdSeTe bioprobes have a good performance in the linearity, and the linear range of this assay is from 2 to 18 copies/mL with a limit of detection (LOD) of 1.2 copies/mL. In addition, PEGylated AuNR@CdSeTe-SiO2 nanoparticles have implemented in a dual-modal imaging with high contrasting fluorescence and dark field signals in cell imaging, which has a great potential in cancer diagnosis.

Enhanced high temperature oxidization resistance of silica coated γ-Ce2S3 red pigments

Silica layer coated γ-Ce2S3 red pigments were successfully prepared based on a Stober method followed by a hydrogen-argon atmosphere heat treatment at 700°C. The effect of water/ethanol volume ratio and tetraethoxysilane concentration on the microstructure of the coating layer and its high temperature oxidizing protection to pigments was investigated. A transparent silica coating layer with dense microstructure and about 60nm thickness can provide a favorable protection for the red hue of the γ-Ce2S3 pigments. The oxidization resistant temperature was enhanced to 550°C for the dense silica layer coated γ-Ce2S3 pigments as compared to ≤350°C for the uncoated ones. A red color (L*=29.59, a*=27.53 and b*=27.66) was still remained for such silica coated γ-Ce2S3 pigments after heated treated at 550°C in air, indicating its potential for high temperature industrial applications.

Synthesis of Hollow Mesoporous Silica Nanorods with Controllable Aspect Ratios for Intracellular Triggered Drug Release in Cancer Cells.

Here, we have reported a straightforward and effective synthetic strategy for synthesis of aspect-ratios-controllable mesoporous silica nanorods with hollow structure (hMSR) and its application for transcription factor (TF)-responsive drug delivery intracellular. Templating by an acid-degradable nickel hydrazine nanorods (NHNT), we have first synthesized the hollow dense silica nanorods and then coated on a mesoporous silica layer. Subsequently, the dense silica layer was removed by the surface-protected etching method and the hollow structure of hMSR was finally formed. The aspect ratios of the hMSR can be conveniently controlled by regulating the aspect ratios of NHNT. Four different hMSR with aspect ratios of ca. 2.5, ca. 5.3, ca. 8.1, and ca. 9.0 has been obtained. It was demonstrated that the as-prepared hMSRs have good stability, high drug loading capacity, and fast cell uptake capability, which makes them to a potential nanocarrier for drug delivery. As the paradigm, hMSR with an aspect ratio of ca. 8.1 was then applied for TF-responsive intracellular anticancer drug controlled release by using a Ag(+)-stabilized molecular switch of triplex DNA (TDNA) as capping agents and probes for TFs recognition. In the presence of TF, the pores of hMSR can be unlocked by the TFs induced disassembly of TDNA, leading to the leakage of DOX. The research in vitro displayed that this system has a TFs-triggered DOX release, and the cytotoxicity in L02 normal cells was lower than that of HeLa cells. We hope that this developed hMSR-based system will promote the development of cancer therapy in related fields.

Silica Encapsulation of SrAl&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;:Eu&lt;sup&gt;2+&lt;/sup&gt;, Dy&lt;sup&gt;3+&lt;/sup&gt; Phosphors by Sol-Gel Method

SrAl2O4:Eu2+,Dy3+ phosphors were synthesized under different temperature by high temperature solid phase method. Encapsulation modification of SrAl2O4:Eu2+,Dy3+ by using SiO2glycol were made over chemically unstable against water. Photoluminescence measurement result shows that when the sintering temperature is 1300 °C, the initial afterglow brightness of SrAl2O4:Eu2+,Dy3+ is up to the highest, 12101 mcd/m2. FTIR results showed that new IR peaks at 1085 cm−1 due to the vibration of Si-O-Si and at 931cm−1 due to the vibration of Si-O-Al appeared after silica encapsulation. This verified that the silica encapsulation is not only a physical absorption process but also involving chemical bonding process. Both phosphors before and after encapsulation have same emission peak at 510 nm. A dense layer of silica formed on phosphor surface has the highest water-resistance after being encapsulated for 2h under the condition of pH 4 and encapsulation amount 10:1. The pH value of aqueous solution contained phosphor was steadily 8, and the initial afterglow brightness decreased only by 9%, that is, from 12101 to 11011 mcd/m2.

Synthesis of Absorption-Dominant Small Gold Nanorods and Their Plasmonic Properties.

Absorption-dominant small Au nanorods with diameters of less than 10 nm are prepared using a facile seed-mediated growth method. The diameters of the small gold nanorods range from 6 to 9 nm, and their lengths vary from 16 to 45 nm. Their aspect ratios can be tailored from 2.7 to 4.7. As a result, the longitudinal plasmon resonance wavelengths are readily tunable from ∼720 nm to ∼830 nm by changing the seed-to-Au(III) molar ratio in the growth solution. The fractions of the scattering in the total extinction of the small Au nanorods are found to be in the range of 0.005 to 0.025 with finite-difference time-domain simulations, confirming that the extinction values of these small Au nanorods are dominantly contributed to by the light absorption. Moreover, the small Au nanorod sample is coated with a dense silica layer for photothermal therapy with three cell lines. It shows improved photothermal therapy performance compared to a large Au nanorod sample for the same cellular Au contents. Our study suggests that small Au nanorods are promising light absorbers and photothermal therapy agents.

Magnetically Recoverable, Thermostable, Hydrophobic DNA/Silica Encapsulates and Their Application as Invisible Oil Tags

A method to encapsulate DNA in heat-resistant and inert magnetic particles was developed. An inexpensive synthesis technique based on co-precipitation was utilized to produce Fe2O3 nanoparticles, which were further functionalized with ammonium groups. DNA was adsorbed on this magnetic support, and the DNA/magnet nanocluster was surface coated with a dense silica layer by sol-gel chemistry. The materials were further surface modified with hexyltrimethoxysilane to achieve particle dispersibility in hydrophobic liquids. The hydrodynamic particle sizes were evaluated by analytical disc centrifugation, and the magnetic properties were investigated by vibrating sample magnetometry. The obtained nanoengineered encapsulates showed good dispersion abilities in various nonaqueous fluids and did not affect the optical properties of the hydrophobic dispersant when present at concentrations lower than 10(3) μg/L. Upon magnetic separation and particle dissolution, the DNA could be recovered unharmed and was analyzed by quantitative real-time PCR and Sanger sequencing. DNA encapsulated within the magnetic particles was stable for 2 years in decalin at room temperature, and the stability was further tested at elevated temperatures. The new magnetic DNA/silica encapsulates were utilized to developed a low-cost platform for the tracing/tagging of oils and oil-derived products, requiring 1 μg/L=1 ppb levels of the taggant and allowing quantification of taggant concentration on a logarithmic scale. The procedure was tested for the barcoding of a fuel (gasoline), a cosmetic oil (bergamot oil), and a food grade oil (extra virgin olive oil), being able to verify the authenticity of the products.

Cyclodextrin glucanotransferase immobilization onto functionalized magnetic double mesoporous core–shell silica nanospheres

article i nfo Background: Cyclodextrin glucanotransferase (CGTase) from Amphibacillus sp. NPST-10 was covalently immobilized onto amino-functionalized magnetic double mesoporous core-shell silica nanospheres (mag@d-SiO2@m-SiO2-NH2), and the properties of the immobilized enzyme were investigated. The synthesis process of the nanospheres included preparing core magnetic magnetite (Fe3O4) nanoparticles, coating the Fe3O4 with a dense silica layer, followed by further coating with functionalized or non-functionalized mesoporous silica shell. The structure of the synthesized nanospheres was characterized using TEM, XRD, and FT-IR analyses. CGTase was immobilized onto the functionalized and non-functionalized nanospheres by covalent attachment and physical adsorption. Results:The results indicated that the enzyme immobilization by covalent attachment onto the activated mag@d-SiO2@m-SiO2-NH2, prepared using anionic surfactant, showed highest immobilization yield (98.1%), loading efficiency (96.2%), and loading capacity 58 µg protein (CGTase)/mg (nanoparticles)) which were among the highest yields reported so far for CGTase. Compared with the free enzyme, the immobilized CGTase demonstrated a shift in the optimal temperature from 50°C to 50-55°C, and showed a significant enhancement in the enzyme thermal stability. The optimum pH values for the activity of the free and immobilized CGTase were pH 8 and pH 8.5, respectively, and there was a significant improvement in pH stability of the immobilized enzyme. Moreover, the immobilized CGTase exhibited good operational stability, retaining 56% of the initial activity after reutilizations of ten successive cycles. Conclusion: The enhancement of CGTase properties upon immobilization suggested that the applied nano-structured carriers and immobilization protocol are promising approach for industrial bioprocess for production of cyclodextrins using immobilized CGTase.

Preparation and characterization of magnetic α-Fe2O3 nanofibers coated with uniform layers of silica

Magnetic composite fibers with α-Fe2O3/SiO2 core–shell structure were prepared by the electrospinning and sol–gel method. The α-Fe2O3 ceramic nanofibers were prepared by electrospinning of solution of poly (vinyl alcohol) (PVA) and Fe(NO3)3·9H2O composite nanofibers followed by calcinations. Controlled hydrolysis and condensation of tetraethyl orthosilicate (TEOS) caused a dense silica layer deposit on the surface of α-Fe2O3 nanofibers with a desired thickness using the sol–gel method (denoted as α-Fe2O3@SiO2). The products were characterized with scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscope (EDX), vibrating sample magnetometer (VSM), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR). The α-Fe2O3@SiO2 core/shell fibers showed a high value of specific saturation magnetization.

Immobilization of cyclodextrin glucanotransferase on aminopropyl-functionalized silica-coated superparamagnetic nanoparticles

Background: Cyclodextrin glycosyltransferase (CGTase) from Amphibacillus sp. NPST-10 was successfully covalently immobilized on aminopropyl-functionalized silica coated superparamagnetic nanoparticles; and the properties of immobilized enzyme were investigated. The synthesis process included preparing of core magnetic magnetite (Fe3O4) nanoparticles using solvothermal synthesis; followed by coating of Fe3O4 nanoparticles with dense amino-functionalized silica (NH2-SiO2) layer using in situ functionalization method. The structure of synthesized Fe3O4@NH2-SiO2 nanoparticles was characterized using TEM, XRD, and FT-IR analysis. Fe3O4@NH2-SiO2 nanoparticles were further activated by gluteraaldehyde as bifunctional cross linker, and the activated nanoparticles were used for CGTase immobilization by covalent attachment. Results: Magnetite nanoparticles was successfully synthesized and coated with and amino functionalized silica layer (Fe3O4/NH2-SiO2), with particle size of 50-70 nm. The silica coated magnetite nanoparticles showed with saturation magnetization of 65 emug -1 , and can be quickly recovered from the bulk solution using an external magnet within 10 sec. The activated support was effective for CGTase immobilization, which was confirmed by comparison of FT-IR spectra of free and immobilized enzyme. The applied approach for support preparation, activation, and optimization of immobilization conditions, led to high yields of CGTase immobilization (92.3%), activity recovery (73%), and loading efficiency (95.2%); which is one of the highest so far reported for CGTase. Immobilized enzyme showed shift in the optimal temperature from 50 to 55oC, and significant enhancement in the thermal stability compared with free enzyme. The optimum pH for enzyme activity was pH 8 and pH 7.5 for free and immobilized CGTase, respectively, with slight improvement of pH stability of immobilized enzyme. Furthermore, kinetic studies revealed that immobilized CGTase had higher affinity toward substrate; with km values of 1.18 ± 0.05 mg/ml and 1.75 ± 0.07 mg/ml for immobilized and free CGTase, respectively. Immobilized CGTase retained 87% and 67 of its initial activity after 5 and 10 repeated batches reaction, indicating that immobilized CGTase on Fe3O4/NH2-SiO2 had good durability and magnetic recovery. Conclusion: The improvement in kinetic and stability parameters of immobilized CGTase makes the proposed method a suitable candidate for industrial applications of CGTase. To best of our knowledge, this is the first report about CGTase immobilization on silica coated magnetite nanoparticles.

Detoxification of hexavalent chromate by Amphibacillus sp. KSUCr3 cells immobilised in silica-coated magnetic alginate beads

Recently isolated Cr(VI)-reducing Amphibacillus KSUCr3 whole cells were immobilised in magnetic gels. Magnetic magnetite (Fe3O4) nanoparticles were synthesised with an average particle size of 47 nm and 80 electromagnetic unit (emu)/g saturation magnetisation. Whole cells were immobilised by entrapment in agar, agarose, alginate, or gelatin in the presence or absence of Fe3O4 nanoparticles for the preparation of both magnetic and nonmagnetic immobilised cells. Of the gels tested, alginate was selected as the best immobilisation matrix, and following optimisation of the entrapment process, the immobilisation yield reached 92.5%. In addition to the ease of separation and reuse of the magnetic cell-containing alginate beads using an external magnet, the magnetically immobilised cells showed approximately 16% higher Cr(VI) reduction activity compared with nonmagnetic immobilised cells. To improve their physical and mechanical properties, the magnetic alginate beads were successfully coated with a dense silica layer using sol-gel chemistry and Ca(OH)2, an alkaline catalyst for tetraethyl orthosilicate, to avoid leaching of Ca2+ ions. Amphibacillus KSUCr3 cells immobilised in silica-coated magnetic alginate beads showed approximately 1.4- to 3.9-fold enhancement of thermal stability compared with free cells. Furthermore, after seven batch cycles, the Cr(VI) reduction activity of free cells decreased to 48%, whereas immobilised cells still retained 81.1% of their original activity. In addition, the Cr(VI)-reduction rate of immobilised cells was higher relative to free cells, especially at higher Cr(VI) concentrations. These results supported the development of a novel, efficient biocatalysts for Cr(VI) detoxification using a combination of whole cell immobilisation, sol-gel chemistry, and nanotechnology.

Preparation of saline-stable, silica-coated triangular silver nanoplates of use for optical sensing

Triangular silver nanoplates (TSNPs) may find application in next generation optical bio-sensors owing to the high sensitivity of the spectral position of their main plasmon band to changes in local refractive index. Unfortunately, etching of the anisotropic nanoplates to spherical particles occurs upon exposure to chloride ions from salt, with a concomitant decrease in optical sensitivity. Herein are detailed two general methods for the silica coating of TSNPs, with the aim of forming a protective barrier against chloride etching. It has been necessary to modify literature approaches for the coating of spherical Ag nanoparticles, since these are either ineffective for anisotropic nanoplates or lead to their degradation. The first method is a modified Stöber approach using tetraethylorthosilicate (TEOS) as the alkoxide precursor and dimethylamine in low concentration as the basic catalyst, with prior priming of the nanoplate surfaces by diaminopropane. The thickness of the silica layer can be tuned between 7 and 20nm by varying the primer and alkoxide concentrations. The second method involves deposition of a thin dense layer of silica from sodium silicate solution onto mercaptopropyltriethoxysilane (MPTES) or mercaptopropyltrimethoxysilane (MPTMS) primed TSNPs. This latter method offers protection against anion etching – experiments suggest that the adsorbed MPTES provides much of the barrier to chloride ions, while the silica shell serves to prevent particle aggregation. It was found that the silica coated particles substantially retained the sensitivity to refractive index of the as-grown TSNPs while being able to withstand salt concentrations typical of bio-testing conditions.

Optimization of Synthesis Parameters for Mesoporous Shell Formation on Magnetic Nanocores and Their Application as Nanocarriers for Docetaxel Cancer Drug

In this work, Fe3O4@SiO2 nanoparticles were coated with mesoporous silica shell by S−N+I− pathway by using anionic surfactant (S−) and co-structure directing agent (N+). The role of co-structure directing agent (CSDA) is to assist the electrostatic interaction between negatively charged silica layers and the negatively charged surfactant molecules. Prior to the mesoporous shell formation step, magnetic cores were coated with a dense silica layer to prevent iron oxide cores from leaching into the mother system under any acidic circumstances. However, it was found that both dense and mesoporous coating parameters affect the textural properties of the produced mesoporous silica shell (i.e., surface area, pore volume and shell thickness). The synthesized Fe3O4@SiO2@m-SiO2 (MCMSS) nanoparticles have been characterized by low-angle X-ray diffraction, transmission electron microscopy (TEM), and N2 adsorption-desorption analysis, and magnetic properties. The synthesized particles had dense and mesoporous silica shells of 8–37 nm and 26–50 nm, respectively. Furthermore, MCMSS possessed surface area of ca. 259–621 m2·g−1, and pore volume of ca. 0.216–0.443 cc·g−1. MCMSS showed docetaxcel cancer drug storage capacity of 25–33 w/w% and possessed control release from their mesochannels which suggest them as proper nanocarriers for docetaxcel molecules.

Visible Light Induced Hole Transport from Sensitizer to Co3O4 Water Oxidation Catalyst across Nanoscale Silica Barrier with Embedded Molecular Wires

In an artificial photosynthetic system, separation of the catalytic sites for water oxidation from those of carbon dioxide reduction by a gas impermeable physical barrier is an important requirement for avoiding cross and back reactions. Here, an approach is explored that uses crystalline Co3O4 as an oxygen evolving catalyst and a nanometer-thin dense phase silica layer as the separation barrier. For controlled charge transport across the barrier, hole conducting molecular wires are embedded in the silica. Spherical Co3O4(4 nm)–SiO2(2 nm) core–shell nanoparticles with p-oligo(phenylenevinylene) wire molecules (three aryl units, PV3) cast into the silica were developed to establish proof of concept for charge transport across the embedded wire molecules. FT-Raman, FT-infrared, and UV–visible spectroscopy confirmed the integrity of the organic wires upon casting in silica. Transient optical absorption spectroscopy of a visible light sensitizer (ester derivatized [Ru(bpy)3]2+ complex) indicates efficient charge injection into Co3O4–SiO2 particles with embedded wire molecules in aqueous solution. An upper limit of a few microseconds is inferred for the residence time of the hole on the embedded PV3 molecule before transfer to Co3O4 takes place. The result was corroborated by light on/off experiments using rapid-scan FT-IR monitoring. These observations indicate that hole conducting organic wire molecules cast into a dense phase, nanometer thin silica layer offer fast, controlled charge transfer through a product-separating oxide barrier.

Preparation of Thin Li4SiO4 Membranes by Using a CVD Method

CVD (chemical vapor deposition) procedures were investigated by using a counter diffusion CVD method. The effects of silica precursors on the hydrogen permeation properties of the silica membranes were discussed. 5 types of silica alkoxides (tetramethylorthosilicate (TMOS), methyltrimethoxysilane (MTMOS), propyltrimethoxysilane (PTMOS), dimethyldimethoxysilane (DMDMOS), and trimethylmethoxysilane (TMMOS)) were employed as the silica precursors; they have different numbers of methyl groups. Hydrogen permeance through the DMDMOS membrane prepared at 500°C was 9.0 × 10–7mol m–2 s–1 Pa–1, and H2/N2 selectivity was 920. Activation energy of H2 permeation through the silica membrane prepared from TMOS was 10.5kJ mol-1 that was the maximum among the 5 types of the silica precursor. This indicates dense silica layer can be obtained from TMOS. Thus, TMOS was employed for the further Li4SiO4 preparation.High temperature CO2 permselective membranes were successfully prepared by using Li4SiO4 as a CO2 selective layer. Pinholes of the Li4SiO4 layer was filled by the CVD post treatment at 600°C. CO2/N2 permselectivity was 1.2 at the 600°C permeation test. The CO2 permeance ratio is higher than the Knudsen diffusion difference. Thus, this selectivity was explained by the CO2 selective adsorption on the Li4SiO4 layer.