Electrospinning of silica sub-microtubes mats with platinum nanoparticles for NO catalytic reduction

Silica sub-microtubes loaded with platinum nanoparticles have been prepared in flexible non-woven mats using co-axial electrospinning technique. A partially gelated sol made from tetraethyl orthosilicate was used as the silica precursor, and oil was used as the sacrificial template for the hollow channel generation. Platinum has been supported on the wall of the tubes just adding the metallic precursor to the sol–gel, thus obtaining the supported catalyst by one-pot method. The silica tubes have a high aspect ratio with external/internal diameters of 400/200 nm and well-dispersed platinum nanoparticles of around 2 nm. This catalyst showed a high NO conversion with very high selectivity to N2 at mild conditions in the presence of excess oxygen when using C3H6 as reducing agent. This relevant result reveals the potential of this technique to produce nanostructured catalysts onto easy to handle conformations.

Capillary microreactors based on hierarchical SiO2 monoliths incorporating noble metal nanoparticles for the Preferential Oxidation of CO

Novel hierarchical SiO2 monolithic microreactors loaded with either Pd or Pt nanoparticles have been prepared in fused silica capillaries and tested in the Preferential Oxidation of CO (PrOx) reaction. Pd and Pt nanoparticles were prepared by the reduction by solvent method and the support used was a mesoporous SiO2 monolith prepared by a well-established sol–gel methodology. Comparison of the activity with an equivalent powder catalyst indicated that the microreactors show an enhanced catalytic behavior (both in terms of CO conversion and selectivity) due to the superior mass and heat transfer processes that take place inside the microchannel. TOF values at low CO conversions have been found to be ∼2.5 times higher in the microreactors than in the powder catalyst and the residence time seems to have a noticeable influence over the selectivity of the catalysts designed for this reaction. The Pd and Pt flexible microreactors developed in this work have proven to be effective for the CO oxidation reaction both in the presence and absence of H2, standing out as a very interesting and suitable option for the development of CO purification systems of small dimensions for portable and on-board applications.

Silica Microparticles Supported Gold and Copper Ferrite Nanoparticles: A Magnetically Recyclable Bimetallic Catalyst for Sonogashira Reaction

Novel silica supported gold and copper ferrite nanoparticles (NPs) have been synthesized, characterized and used as a separable dual catalyst in Sonogashira type reaction. These Au.CuFe2O4@Silica NPs show a high efficiency as catalyst in the alkynylation not only of aryl iodides but also aryl bromides. By using only 0.5 mol% loading and t-BuOK as base in N,N-dimethylacetamide as solvent, aryl iodides react at 115 ºC in 1 d, whereas for aryl bromides the cross-coupling takes place at 130 ºC in 2 d. The catalyst can be successfully recycled using an external magnet for four consecutive runs.

Mesoporous silicas as versatile supports to tune the palladium-catalyzed selective aerobic oxidation of allylic alcohols

Surfactant templating offers a simple route to synthesize high-surface area silicas with ordered, tunable mesopore architectures. The use of these materials as versatile catalyst supports for palladium nanoparticles has been explored in the aerobic selective oxidation (selox) of allylic alcohols under mild conditions. Families of Pd/mesoporous silicas, synthesized through incipient wetness impregnation of SBA-15, SBA-16, and KIT-6, have been characterized by using nitrogen porosimetry, CO chemisorption, diffuse reflection infrared Fourier transform spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and high-resolution TEM and benchmarked in liquid phase allylic alcohol selox against a Pd/amorphous SiO2 standard. The transition from amorphous to two-dimensional parallel and three-dimensional interpenetrating porous silica networks conferred significant selox rate enhancements associated with higher surface densities of active palladium oxide sites. Dissolved oxygen was essential for insitu stabilization of palladium oxide, and thus maintenance of high activity on-stream, whereas selectivity to the desired aldehyde selox product over competing hydrogenolysis pathways was directed by using palladium metal. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Support-enhanced selective aerobic alcohol oxidation over Pd/mesoporous silicas

The influence of silica mesostructure upon the Pd-catalyzed selective oxidation of allylic alcohols has been investigated for amorphous and surfactant-templated SBA-15, SBA-16, and KIT-6 silicas. Significant rate enhancements can be achieved via mesopore introduction, most notably through the use of interconnected porous silica frameworks, reflecting both improved mass transport and increased palladium dispersion; catalytic activity decreases in the order Pd/KIT-6 ≈ Pd/SBA-16 > Pd/SBA-15 > Pd/SiO2. Evidence is presented that highly dispersed palladium oxide nanoparticles, not zerovalent palladium, are the catalytically active species. © 2011 American Chemical Society.

Surface plasmon resonance-induced photocatalysis by Au nanoparticles decorated mesoporous g-C3N4 nanosheets under direct sunlight irradiation

In recent years, surface plasmon-induced photocatalytic materials with tunable mesoporous framework have attracted considerable attention in energy conversion and environmental remediation. Herein we report a novel Au nanoparticles decorated mesoporous graphitic carbon nitride (Au/mp-g-C3N4) nanosheets via a template-free and green in situ photo-reduction method. The synthesized Au/mp-g-C3N4 nanosheets exhibit a strong absorption edge in visible and near-IR region owing to the surface plasmon resonance effect of Au nanoparticles. More attractively, Au/mp-g-C3N4 exhibited much higher photocatalytic activity than that of pure mesoporous and bulk g-C3N4 for the degradation of rhodamine B under sunlight irradiation. Furthermore, the photocurrent and photoluminescence studies demonstrated that the deposition of Au nanoparticles on the surface of mesoporous g-C3N4 could effectively inhibit the recombination of photogenerated charge carriers leading to the enhanced photocatalytic activity. More importantly, the synthesized Au/mp-g-C3N4 nanosheets possess high reusability. Hence, Au/mp-g-C3N4 could be promising photoactive material for energy and environmental applications.

Silica promoted self-assembled mesoporous aluminas. Impact of the silica precursor on the structural, textural and acidic properties

This paper investigates the effect of silica addition on the structural, textural and acidic properties of an evaporation induced self-assembled (EISA) mesoporous alumina. Two silica addition protocols were applied while maintaining the EISA synthesis route. The first route is based on the addition of a Na-free colloidal silica suspension (Ludox®), and the second method consists of the co-hydrolysis of tetraethyl orthosilicate (TEOS) with aluminium tri-sec-butoxide, to favour a more intimate mixing of the Al- and Si-hydrolysed species. The properties of the so derived materials were compared to the SiO2-free counterpart. The SiO2 addition was always beneficial from a structural and textural standpoint. TEOS appears to have a truly promoting effect; the ordering, surface area and pore volume are all improved. For Ludox®, the enhancement comes from the formation of smaller pores by a densification of the structure. The crystallization of γ-alumina depends on the interaction between the Al- and Si-species in the mesophase. Ludox®-based materials achieved crystallization at 750 °C but the intimate mixing in the TEOS-based mesophases shows a suppression of the phase transformation by 50-100 °C, with respect to the SiO2-free counterpart. This reduces the textural features substantially. For all SiO2-modified materials, the enhancement in the surface area is not accompanied by a concomitant improvement of total acidity, and the formation of weak Lewis acid sites was promoted. These effects were ascribed to SiO2 migration to the surface that blocks part of the acidity.

Biologically Inspired Design of Protein-Silica Hybrid Nanoparticles for Drug Delivery Applications

The design and application of effective drug carriers is a fundamental concern in the delivery of therapeutics for the treatment of cancer and other vexing health problems. Traditionally utilized chemotherapeutics are limited in efficacy due to poor bioavailability as a result of their size and solubility as well as significant deleterious effects to healthy tissue through their inability to preferentially target pathological cells and tissues, especially in treatment of cancer. Thus, a major effort in the development of nanoscopic drug delivery vehicles for cancer treatment has focused on exploiting the inherent differences in tumor physiology and limiting the exposure of drugs to non-tumorous tissue, which is commonly achieved by encapsulation of chemotherapeutics within macromolecular or supramolecular carriers that incorporate targeting ligands and that enable controlled release. The overall aim of this work is to engineer a hybrid nanomaterial system comprised of protein and silica and to characterize its potential as an encapsulating drug carrier. The synthesis of silica, an attractive nanomaterial component because it is both biocompatible as well as structurally and chemically stable, within this system is catalyzed by self-assembled elastin-like polypeptide (ELP) micelles that incorporate of a class of biologically-inspired, silica-promoting peptides, silaffins. Furthermore, this methodology produces near-monodisperse, hybrid inorganic/micellar materials under mild reaction conditions such as temperature, pH and solvent. This work studies this material system along three avenues: 1) proof-of-concept silicification (i.e. the formation and deposition of silica upon organic materials) of ELP micellar templates, 2) encapsulation and pH-triggered release of small, hydrophobic chemotherapeutics, and 3) selective silicification of templates to potentiate retention of peptide targeting ability.

Fenton-like degradation of Bisphenol A catalyzed by mesoporous Cu/TUD-1

A family of copper oxide catalysts with loadings spanning 1–5 wt% were dispersed on a three dimensional, mesoporous TUD-1 silica through a hydrothermal, surfactant-free route employing tetraethylene glycol as a structure-directing agent. Their bulk and surface properties were characterized by N2 physisorption, XRD, DRUVS, EPR, TEM and Raman spectroscopy, confirming the expected mesoporous wormhole/foam support morphology and presence of well-dispersed CuO nanoparticles (∼5–20 nm). The catalytic performance of Cu/TUD-1 was evaluated as heterogeneous Fenton-like catalysts for Bisphenol A (BPA) oxidative degradation in the presence of H2O2 as a function of [H2O2], and CuO loading. Up to 90.4% of 100 ppm BPA removal was achieved over 2.5 wt% Cu/TUD-1 within 180 min, with negligible Cu leaching into the treated water.

Predicting the localized surface plasmon resonances of spherical nanoparticles on substrate : electrostatic eigenmode method

We present experimental results that demonstrate that the wavelength of the fundamental localised surface plasmon resonance for spherical gold nanoparticles on glass can be predicted using a simple, one line analytical formula derived from the electrostatic eigenmode method. This allows the role of the substrate in lifting mode degeneracies to be determined, and the role of local environment refractive indices on the plasmon resonance to be investigated. The effect of adding silica to the casting solution in minimizing nanopaticle agglomeration is also discussed.

SWCNT networks on nanoporous silica catalyst support : morphological and connectivity control for nanoelectronic, gas-sensing, and biosensing devices

Effective control of morphology and electrical connectivity of networks of single-walled carbon nanotubes (SWCNTs) by using rough, nanoporous silica supports of Fe catalyst nanoparticles in catalytic chemical vapor deposition is demonstrated experimentally. The very high quality of the nanotubes is evidenced by the G-to-D Raman peak ratios (>50) within the range of the highest known ratios. Transitions from separated nanotubes on smooth SiO2 surface to densely interconnected networks on the nanoporous SiO2 are accompanied by an almost two-order of magnitude increase of the nanotube density. These transitions herald the hardly detectable onset of the nanoscale connectivity and are confirmed by the microanalysis and electrical measurements. The achieved effective nanotube interconnection leads to the dramatic, almost three-orders of magnitude decrease of the SWCNT network resistivity compared to networks of similar density produced by wet chemistry-based assembly of preformed nanotubes. The growth model, supported by multiscale, multiphase modeling of SWCNT nucleation reveals multiple constructive roles of the porous catalyst support in facilitating the catalyst saturation and SWCNT nucleation, consistent with the observed higher density of longer nanotubes. The associated mechanisms are related to the unique surface conditions (roughness, wettability, and reduced catalyst coalescence) on the porous SiO2 and the increased carbon supply through the supporting porous structure. This approach is promising for the direct integration of SWCNT networks into Si-based nanodevice platforms and multiple applications ranging from nanoelectronics and energy conversion to bio- and environmental sensing.

Size dependent photodegradation of CdS particles deposited onto TiO2 mesoporous films by SILAR method

The properties of CdS nanoparticles incorporated onto mesoporous TiO2 films by a successive ionic layer adsorption and reaction (SILAR) method were investigated by Raman spectroscopy, UV-visible spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). High resolution TEM indicated that the synthesized CdS particles were hexagonal phase and the particle sizes were less than 5 nm when SILAR cycles were fewer than 9. Quantum size effect was found with the CdS sensitized TiO2 films prepared with up to 9 SILAR cycles. The band gap of CdS nanoparticles decreased from 2.65 eV to 2.37 eV with the increase of the SILAR cycles from 1 to 11. The investigation of the stability of the CdS/TiO2 films in air under illumination (440.6 µW/cm2) showed that the photodegradation rate was up to 85% per day for the sample prepared with 3 SILAR cycles. XPS analysis indicated that the photodegradation was due to the oxidation of CdS, leading to the transformation from sulphide to sulphate (CdSO4). Furthermore, the degradation rate was strongly dependent upon the particle size of CdS. Smaller particles showed faster degradation rate. The size-dependent photo-induced oxidization was rationalized with the variation of size-dependent distribution of surface atoms of CdS particles. Molecular Dynamics (MD) simulation has indicated that the surface sulphide anion of a large CdS particle such as CdS made with 11 cycles (CdS11, particle size = 5.6 nm) accounts for 9.6% of the material whereas this value is increased to 19.2% for (CdS3) based smaller particles (particle size: 2.7 nm). Nevertheless, CdS nanoparticles coated with ZnS material showed a significantly enhanced stability under illumination in air. A nearly 100% protection of CdS from photon induced oxidation with a ZnS coating layer prepared using four SILAR cycles, suggesting the formation of a nearly complete coating layer on the CdS nanoparticles.

Regenerative silver nanoparticles for SERRS investigation of metmyoglobin with conserved heme pocket

Shell isolated silver nanoparticles with an ultrathin silica layer (Ag@SiO2NPs) are used as a surface-enhanced resonance Raman scattering (SERRS) substrate for probing metmyoglobin (metMb) in aqueous solution. The ultrathin silica layer protects metMb from reaching the bare silver surface and conserves the heme pocket during SERRS analysis with a Raman enhancement factor (EFSERS) of 4.78 × 104. In spite of the good SERRS enhancement, the interaction between the protein and Ag@SiO2NPs is weak enough to separate them by centrifugation in such a way that both are regenerated in their original form and can be reused. Using Ag@SiO2NPs as the SERRS substrate, the lowest detection limit of 2 nM was achieved for metMb whilst conserving the native structure of the heme centre.

High lithium storage in micrometre sized mesoporous spherical self-assembly of anatase titania nanospheres and carbon

Composite of anatase titania (TiO2) nanospheres and carbon grown and self-assembled into micron-sized mesoporous spheres via a solvothermal synthesis route are discussed here in the context of rechargeable lithium-ion battery. The morphology and carbon content and hence the electrochemical performance are observed to be significantly influenced by the synthesis parameters. Synthesis conditions resulting in a mesoporous arrangement of an optimized amount carbon and TiO2 exhibited the best lithium battery performance. The first discharge cycle capacity of carbon-titania mesoporous spheres (solvothermal reaction at 150 degrees C at 6 h, calcination at 500 degrees C under air, BET surface area 80 m(2)g(-1)) was 334 mAhg(-1) (approximately 1 Li) at current rate of 0.066 Ag-1. High storage capacity and good cyclability is attributed to the nanostructuring of TiO2 (mesoporosity) as well as due to formation of a percolation network of carbon around the TiO2 nanoparticles. The micron-sized mesoporous spheres of carbon-titania composite nanoparticles also show good rate cyclability in the range (0.066-6.67) Ag-1.

Structurally stabilized mesoporous TiO2 nanofibres for efficient dye-sensitized solar cells

One-dimensional (1D) TiO2 nanostructures are very desirable for providing fascinating properties and features, such as high electron mobility, quantum confinement effects, and high specific surface area. Herein, 1D mesoporous TiO2 nanofibres were prepared using the electrospinning method to verify their potential for use as the photoelectrode of dye-sensitized solar cells (DSSCs). The 1D mesoporous nanofibres, 300 nm in diameter and 10-20 μm in length, were aggregated from anatase nanoparticles 20-30 nm in size. The employment of these novel 1D mesoporous nanofibres significantly improved dye loading and light scattering of the DSSC photoanode, and resulted in conversion cell efficiency of 8.14%, corresponding to an ∼35% enhancement over the Degussa P25 reference photoanode.