Capillary microreactors wall-coated with mesoporous titania thin film catalyst supports

A new method for catalyst deposition on the inner walls of capillary microreactors is proposed which allows exact control of the coating thickness, pore size of the support, metal particle size, and metal loading. The wall-coated microreactors have been tested in a selective hydrogenation reaction. Activity and selectivity reach values close to those obtained with a homogeneous Pd catalyst. The catalyst activity was stable for a period of 1000 h time-on-stream.

Control of the thickness of mesoporous titania films for application in multiphase catalytic microreactors

A new method of sol-gel polymer template synthesis of mesoporous catalytic thin films has been proposed which allows controlling the chemical nature of the film, the porosity, thickness and loading with an active species. The mesoporous films with a long-order structure can be obtained in a narrow range of surfactant-to-metal precursor molar ratios from 0.006 to 0.009. The catalytic film thickness was varied from 300 to 1000 nm while providing a uniform catalyst distribution with a desired catalyst loading (1 wt. % Au nanoparticles) throughout the film. The films were characterized by TEM, SEM, ethanol adsorption and contact angle measurements. The calcination of the as-synthesized films at 573 K reduced Ti4+ sites to Ti3+. A 300 nm thick Au-containing film showed an initial TOF of 1.4 s(-1) and a selectivity towards unsaturated alcohols as high as 90% in the hydrogenation of citral. Thicker films demonstrated a high selectivity towards the saturated aldehyde (above 55%) and a lower intrinsic catalytic activity (initial TOF of 0.7-0.9 s(-1)) in the absence of internal diffusion limitations.

High-Performance Biosensing Using Arrays of Plasmonic Nanotubes

We show that aligned gold nanotube arrays capable of supporting plasmonic resonances can be used as high performance refractive index sensors in biomolecular binding reactions. A methodology to examine the sensing ability of the inside and outside walls of the nanotube structures is presented. The sensitivity of the plasmonic nanotubes is found to increase as the nanotube walls are exposed, and the sensing characteristic of the inside and outside walls is shown to be different. Finite element simulations showed good qualitative agreement with the observed behavior. Free standing gold nanotubes displayed bulk sensitivities in the region of 250 nm per refractive index unit and a signal-to-noise ratio better than 1000 upon protein binding which is highly competitive with state-of-the-art label-free sensors.

Combined antenna and localized plasmon resonance in Raman scattering from Random arrays of silver-coated, vertically aligned multiwalled carbon nanotubes

The electric field enhancement associated with detailed structure within novel optical antenna nanostructures is modeled using the surface integral equation technique in the context of surface-enhanced Raman scattering (SERS). The antennae comprise random arrays of vertically aligned, multi-walled carbon nanotubes dressed with highly granular Ag. Different types of "hot-spot" underpinning the SERS are identified, but contrasting characteristics are revealed. Those at the outer edges of the Ag grains are antenna driven with field enhancement amplified in antenna antinodes while intergrain hotspots are largely independent of antenna activity. Hot-spots between the tops of antennae leaning towards each other also appear to benefit from antenna amplification.

Adsorption and photocatalysed destruction of cationic and anionic dyes on mesoporous titania films: Reactions at the air-solid interface

Cationic dyes, such as methylene blue (MB), Thionine (TH) and Basic Fuschin (BF), but not anionic dyes, such as Acid Orange 7 (AO7), Acid Blue 9 (AB9) and Acid Fuschin (AF), are readily adsorbed onto mesoporous titania films at high pH (pH 11), i.e. well above the pzc of titania (pH 6.5), due to electrostatic forces of attraction and repulsion, respectively. The same anionic dyes, but not the cationic dyes, are readily adsorbed on the same titania films at low pH (pH 3), i.e. well below titania's pzc. MB appears to adsorb on mesoporous titania films at pH 11 as the trimer (lambda(max) = 570 nm) but, upon drying, although the trimer still dominates, there is an absorption peak at 665 nm, especially notable at low [MB], which may be due to the monomer, but more likely MB J-aggregates. In contrast, the absorption spectrum of AO7 adsorbed onto the mesoporous titania film at low pH is very similar to the dye monomer. For both MB and AO7 the kinetics of adsorption are first order and yield high rate constants (3.71 and 1.481 g(-1) min(-1)), indicative of a strong adsorption process. Indeed, both MB and AO7 stained films retained much of their colour when left overnight in dye-free pH 11 and 3 solutions, respectively, indicating the strong nature of the adsorption. The kinetics of the photocatalytic bleaching of the MB-titania films at high pH are complex and not well-described by the Julson-Ollis kinetic model [A.J. Julson, D.F. Ollis, Appl. Catal. B. 65 (2006) 315]. Instead, there appears to be an initial fast but not simple demethylation step, followed by a zero-order bleaching and further demethylation steps. In contrast, the kinetics of photocatalytic bleaching of the AO7-titania film give a good fit to the Julson-Ollis kinetic model, yielding values for the various fitting parameters not too dissimilar to those reported for AO7 adsorbed on P25 titania powder. (C) 2008 Elsevier B.V. All rights reserved.

Fatigue and biocompatibility properties of a poly(methyl methacrylate) bone cement with multi-walled carbon nanotubes

Composites of multi-walled carbon nanotubes (MWCNT) of varied functionality (unfunctionalised and carboxyl and amine functionalised) with polymethyl methacrylate (PMMA) were prepared for use as a bone cement. The MWCNT loadings ranged from 0.1 to 1.0 wt.%. The fatigue properties of these MWCNT–PMMA bone cements were characterised at MWCNT loading levels of 0.1 and 0.25 wt.% with the type and wt.% loading of MWCNT used having a strong influence on the number of cycles to failure. The morphology and degree of dispersion of the MWCNT in the PMMA matrix at different length scales were examined using field emission scanning electron microscopy. Improvements in the fatigue properties were attributed to the MWCNT arresting/retarding crack propagation through the cement through a bridging effect and hindering crack propagation. MWCNT agglomerates were evident within the cement microstructure and the degree of agglomeration was dependent on the level of loading and functionality of the MWCNT. The biocompatibility of the MWCNT–PMMA cements at MWCNT loading levels upto 1.0 wt.% was determined by means of established biological cell culture assays using MG-63 cells. Cell attachment after 4 h was determined using the crystal violet staining assay. Cell viability was determined over 7 days in vitro using the standard colorimetric MTT assay. Confocal scanning laser microscopy and SEM analysis was also used to assess cell morphology on the various substrates.

Limiting withdrawal rate and maximum film thickness during dip-coating of titania sols onto a Si substrate

The article highlights new insights into production of thin titania films widely used as catalyst support in many modern reactors including capillary microreactors, microstructured fixed-bed reactors and falling film microreactors. Dip-coating of a Mania sol onto a Si substrate has been studied in the range of the sol viscosities of 1.5-2.5 mPa s and the sol withdrawal rates of 0.2-18 mm/s. Different viscosities of sols were created by addition of desired amounts of nitric acid to the synthesis mixture of titanium isopropoxide and Plutonic F127 in ethanol which allowed to control the rate of the condensation reactions. Uniform inesoporous titania coatings were obtained at the solvent withdrawal rates below 10 mm/s at sol viscosities in the range from 1.6 mPa s to 2.5 mPa s. There exists a limiting withdrawal rate corresponding to a capillary number of ca. 0.01 beyond which uniform titania films cannot be obtained. Below the limiting withdrawal rate, the coating thickness is a power function of the sol viscosity and withdrawal rate, both with an exponent of 2/3. The limiting withdrawal rate increases as the solvent evaporation rate increases and it decreases as the sol viscosity increases. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Adsorption and photocatalytic bleaching of acid orange 7 on P25 titania

The observed adsorption of acid orange 7, AO7(-), on P25 titania over a range of pH values (pH 2-8) gives a good fit to data generated using a charge distribution, multisite complexation, i.e. CD-MUSIC, model, modified for aggregated dye adsorption. For this system the model predicts that both the apparent dark Langmuir adsorption constant. K-L, and the number of adsorption sites, n(o), increase with decreasing pH, and are negligible above pH 6. At pH 2 the CD-MUSIC model predicts the fraction of singly co-ordinated sites occupied by the dye,f(AO7), is ca. 32% under the in situ monitoring experimental conditions used in this work to study the photocatalytic bleaching of AO7(-) under UV light illumination ([TiO2] = 20 mgdm(-3); [AO7(-)](total) = 4.86 x 10(-5) M). Although AO7(-) adsorption on P25 titania is insignificant above pH 6 and increases almost linearly and markedly below this pH, the measured initial rate of bleaching of AO7(-), photocatalysed by titania using UV appears to only increase modestly (