Synthesis and characterization of packed mesoporous tungsteno-silicates: application to the catalytic dehydrogenation of 2-propanol

The synthesis of highly ordered mesoporous tungsteno-silicas in which a high percentage of tungsten is introduced into a silica framework is reported hereafter. Powder XRD and TEM have been used to characterize the materials synthesized at room temperature. The materials are shown to be homogeneous as there is no evidence for any crystalline species other than the silica framework. The pore diameter and the surface area of the materials, evaluated from the nitrogen adsorption isotherms and unit cell parameter indicate a pore diameter of about 2 nm and a surface area of 1400 m(2) g(-1) for a content of 10% tungsten. Catalyzed dehydration of 2-propanol has been investigated and the activity of the materials synthesized is significant, even for low tungsten content W-MCM-41 materials. (C) 2003 Elsevier B.V. All rights reserved.

2D hexagonal mesoporous platinum films exhibiting biaxial, in-plane pore alignment

The synthesis of 2D hexagonal mesoporous platinum films with biaxial, in-plane pore alignment is demonstrated by electrodeposition through an aligned lyotropic liquid crystal templating phase. Shear force is used to align a hexagonal lyotropic liquid crystalline templating phase of an inexpensive and a commercially available surfactant, C16EO10, at the surface of an electrode. Electrodeposition and subsequent characterisation of the films produced shows that the orientation and alignment of the phase is transferred to the deposited material. Transmission electron microscopy confirms the expected nanostructure of the films, whilst transmission and grazing incidence small angle X-ray scattering analysis confirms biaxial, in plane alignment of the pore structure. In addition further electrochemical studies in dilute sulfuric acid and methanol show that the pores are accessible to electrolyte solution as indicated by a large current flow; the modified electrode therefore has a high surface area, that catalyses methanol oxidation, and the pores have a very large aspect ratio (of theoretical maximum 2 × 105). Films with such aligned mesoporosity will advance the field of nanotechnology where the control of pore structure is paramount. The method reported is sufficiently generic to be used to control the structure and order of many materials, thus increasing the potential for the development of a wide range of novel electronic and optical devices.

Synthesis and structure of cage-like mesoporous silica using different precursors

In this work the synthesis of cubic, FDU-1 type, ordered mesoporous silica (OMS) was developed from two types of silicon source, tetraethyl orthosilicate (TEOS) and a less expensive compound, sodium silicate (Na(2)Si(3)O(7)), in the presence of a new triblock copolymer template Vorasurf 504 (EO(38)BO(46)EO(38)). For both silicon precursors the synthesis temperature was evaluated. For TEOS the effect of polymer dissolution in methanol and the acid solution (HCl and HBr) on the material structure was analyzed. For Na(2)Si(3)O(7) the influence of the polymer mass and the hydrothermal treatment time were the explored experimental parameters. The samples were examined by Small Angle X-ray Scattering (SAXS) and Nitrogen Sorption. For both precursors the decrease on the synthesis temperature from ambient, -25 degrees C, to -15 degrees C improved the ordered porous structure. For TEOS, the SAXS results showed that there is an optimum amount of hydrophobic methanol that contributed to dissolve the polymer but did not provoke structural disorder. The less electronegative Br-ions, when compared to Cl-, induced a more ordered porous structure, higher surface areas and larger lattice parameters. For Na(2)Si(3)O(7) the increase on the hydrothermal treatment time as well as the use of an optimized amount of polymer promoted a better ordered porous structure. (C) 2011 Elsevier B.V. All rights reserved.

Structure effects of self-assembled Prussian blue confined in highly organized mesoporous TiO(2) on the electrocatalytic properties towards H(2)O(2) detection

Here we report the derivatization of mesoporous TiO(2) thin films for the preparation of H(2)O(2) amperometric sensors. The coordination of the bifunctional ligand 1,10 phenantroline, 5,6 dione on the surface Ti(IV) ions provides open coordination sites for Fe(II) cations which are the starting point for the growth of a layer of Prussian blue polymer. The porous structure of the mesoporous TiO(2) allows the growth, ion by ion of the coordination polymer. Up to four layer of Prussian blue can be deposit without losing the porous structure of the film, which results in an enhanced response of these materials as H(2)O(2) sensors. These porous confined PB modified electrodes are robust sensors that exhibit good reproducibility, environmental stability and high sensitivity towards H(2)O(2) detection. (C) 2010 Elsevier B.V. All rights reserved.

N3-Dye-Induced Visible Laser Anatase-to-Rutile Phase Transition on Mesoporous TiO(2) Films

Titanium dioxide has been extensively used in photocatalysis and dye-sensitized solar cells, where control of the anatase-to-rutile phase transformation may allow the realization of more efficient devices exploiting the synergic effects at anatase/rutile interfaces. Thus, a systematic study showing the proof of concept of a dye-induced morphological transition and an anatase-to-rutile transition based on visible laser (532 nm) and nano/micro patterning of mesoporous anatase (Degussa P25 TiO(2)) films is described for the first time using a confocal Raman microscope. At low laser intensities, only the bleaching of the adsorbed N3 dye was observed. However, high enough temperatures to promote melting/densification processes and create a deep hole at the focus and an extensive phase transformation in the surrounding material were achieved using Is laser pulses of 25-41 mW/cm(2), in resonance with the MLCT band. The dye was shown to play a key role, being responsible for the absorption and efficient conversion of the laser light into heat. As a matter of fact, the dye is photothermally decomposed to amorphous carbon or to gaseous species (CO(x), NO(x), and H(2)O) under a N(2) or O(2) atmosphere, respectively.

Unravelling the Chemical Morphology of a Mesoporous Titanium Dioxide Interface by Confocal Raman Microscopy: New Clues for Improving the Efficiency of Dye Solar Cells and Photocatalysts

The presence of anatase and rutile domains on nanocrystalline films of P25 TiO(2), as well as the distinct coordination modes of carboxylates on those phases, were revealed by confocal Raman microscopy, a technique that showed to be suitable for imaging the chemical morphology down to submicrometric size.

New effective catalysts based on mesoporous nanofibrous carbon for selective oxidation of hydrogen sulfide

The systems based on granular mesoporous nanofibrous carbonaceous (NFC) materials synthesized by decomposition of hydrocarbons over nickel- containing catalysts are promising catalysts for selective oxidation of hydrogen sulfide. Sample series of nanofibrous carbon with three main types of their fiber structures and different contents of metal catalysts inherited from the catalysts for their synthesis were studied in this reaction. The correlation between NFC structure and its activity and selectivity in hydrogen sulfide oxidation was determined. The metal inherited from the initial catalysts for the synthesis of NFC influences the activity and selectivity of the resulting carbon catalysts. A particular influence is observed in the case of the catalyst withdrawn from the synthesis reactor at the stage of stationary operation of the metal catalyst (low specific carbon yields per unit weight of the catalyst). The presence of the metal phase results in an increase in the carbon catalyst activity and in a decrease in the selectivity to sulfur. NFC samples with the highest activity and selectivity are nanotubes and those with graphite planes perpendicular to the axis of the fibers. Carbon nanotubes have high selectivity, while samples obtained on copper–nickel catalysts also possess high activity. The promising NFC catalysts provide high conversion and selectivity (almost independent of the molar oxygen/hydrogen sulfide ratio) when a large excess of oxygen is contained in the reaction mixture.

Functionalized mesoporous silica nanoparticles with redox-responsive short-chain gatekeepers for agrochemical delivery.

The controlled release of salicylic acid (SA), a key phytohormone, was mediated by using a novel decanethiol gatekeeper system grafted onto mesoporous silica nanoparticles (MSNs). The decanethiol was conjugated only to the external surfaces of the MSNs through glutathione (GSH)-cleavable disulfide linkages and the introduction of a process to assemble gatekeepers only on the outer surface so that the mesopore area can be maintained for high cargo loading. Raman and nitrogen sorption isotherm analyses confirmed the successful linkage of decanethiol to the surface of MSNs. The in vitro release of SA from decanethiol gated MSNs indicated that the release rate of SA in an environment with a certain amount of GSH was significantly higher than that without GSH. More importantly, in planta experiments showed the release of SA from decanethiol gated MSNs by GSH induced sustained expression of the plant defense gene PR-1 up to 7 days after introduction, while free SA caused an early peak in PR-1 expression which steadily decreased after 3 days. This study demonstrates the redox-responsive release of a phytohormone in vitro and also indicates the potential use of MSNs in planta as a controlled agrochemical delivery system.

Functionalized mesoporous silica nanoparticles for smart agrochemical delivery system

The agrochemical delivery system has been built up based on mesoporous silica nanoparticles as carriers in a controllable fashion. Several peer reviewed papers have been published with this research work. This delivery system will benefit for the future agricultural application.

The control of epidermal growth factor grafted on mesoporous silica nanoparticles for targeted delivery

The performance of biomaterials in a biological environment is largely influenced by the surface properties of the biomaterials. In particular, grafted targeting ligands significantly impact the subsequent cellular interactions. The utilisation of a grafted epidermal growth factor (EGF) is effective for targeted delivery of drugs to tumours, but the amount of these biological attachments cannot be easily quantified as most characterization methods could not detect the extremely low amount of EGF ligands grafted on the surface of nanoparticles. In this study, hollow mesoporous silica nanoparticles (HMSNs) were functionalized with amine groups to conjugate with EGFs via carbodiimide chemistry. Time of flight secondary ion mass spectrometry (ToF-SIMS), a very surface specific technique (penetration depth <1.5 nm), was employed to study the binding efficiency of the EGF to the nanoparticles. Principal component analysis (PCA) was implemented to track the relative surface concentrations of EGFs on HMSNs. It was found that ToF-SIMS combined with the PCA technique is an effective method to evaluate the immobilization efficiency of EGFs. Based on this useful technique, the quantity and density of the EGF attachments that grafted on nanoparticles can be effectively controlled by varying the EGF concentration at grafting stages. Cell experiments demonstrated that the targeting performance of EGFR positive cells was affected by the number of EGFs attached on HMSNs.

A facile synthesis of mesoporous silica nanoparticle and its morphology manipulation by varying pH value

 Mesoporous silica nanoparticles (MSNs) with particle size of20 nm have been synthesised through the template directed method at low temperature. The pH value of the reaction solution was found to have a great impact on the morphology of the final products. The morphology of resultant MSNs were investigated through transmission electron microscope. The mesoporous structure was examined by Brunauer-Emmett-Teller and Barrett-Joyner-Halenda methods. The results suggested that the high pH value had a great effect on the morphology of the final MSNs. Higher pH value intensified the interaction between particles. The pH value less than 10 is good for the formation of nanoparticles, while at pH 12, a silica framework with heterogeneous mesopore structure can be obtained.

Advanced N-doped mesoporous molybdenum disulfide nanosheets and the enhanced lithium-ion storage performance

With the increasing interest in two-dimensional van der Waals materials, molybdenum disulfide (MoS2) has emerged as a promising material for electronic and energy storage devices. It suffers from poor cycling stability and low rate capability when used as an anode in lithium ion batteries. Here, N-doped MoS2 nanosheets with 2-8 atomic layers, increased interlayer distance, mesoporous structure and high surface area synthesised by a simple sol-gel method show an enhanced lithium storage performance, delivering a high reversible capacity (998.0 mA h g-1, 50 mA g-1), high rate performance (610 mA h g-1, 2 A g-1), and excellent cycling stability. The excellent lithium storage performance of the MoS2 nanosheets might be due to the better electrical and ionic conductivity and improved lithium ion diffusion which are related to their structural characteristics and high concentration N doping. The possible mechanism of the improved performance is proposed and discussed.

Characterization of silica-carbon mesoporous matrix with embedded nickel nanoparticles synthesized by the polymeric precursor method

Nickel nanoparticles into silica-carbon matrix composites were prepared by using the polymeric precursor method. The effects of the polyester type and the time of pyrolysis on the mesoporosity and nickel particle dispersion into non-aqueous amorphous silica-carbon matrix were investigated by thermogravimetric analysis, adsorption/desorption isotherms and TEM. A well-dispersed metallic phase could be only obtained by using ethylene glycol. Weightier polyesters affected the pyrolysis process due to a combination of more amounts of carbonaceous residues and delaying of pyrolysis process. The post-pyrolyzed composites were successfully cleaned at 200 degrees C for I h in oxygen atmosphere leading to an increase in the surface area and without the occurrence of carbon combustion or nickel nanoparticles oxidation. The matrix composites presented predominantly mesoporous with pore size well defined in 38 angstrom, mainly when tetraethylene glycol was used as polymerizing agent. (C) 2007 Elsevier B.V. All rights reserved.