Porous self-protonating spiropyran-based NIPAAm gels with improved reswelling kinetics

The final publication is available at Springer via http://dx.doi.org/[10.1007/s10853-015-9458-2]

In situ characterization of porous VPO catalysts with fibrous structure: Identifying the redox behavior and the stability of active sites

Two VPO materials with fibrillar morphology have been prepared by the aid of electrospinning technique. One is a VPO carbon-supported material (VCF200) with fibrous morphology and very high surface area that is stable under oxidizing conditions up to 350C. The other material is a bulk mixed VPO oxide (VPO500) with fibrous structure obtained after optimizing the calcination of the carbon support in VCF200. Despite it is a bulk oxide material, this material exhibits a high surface area (> 60 m2/g). The redox behavior of both samples was monitored by in situ Raman spectroscopy under oxidation/reduction cycles. For the dehydrated supported sample (VCF200), the pyrophosphate phase (VO)2P2O7 (Raman ~930 cm-1) is detected, which has been described as the active phase (see Figure (a) below). This phase is quite stable since it does not disappear upon subsequent oxidation/reduction cycles. Under reduction conditions at 125C, in consecutive cycles, additional Raman bands appear at ~1090 cm-1 that are characteristic of the αII-VOPO4 phase. On the other hand, the bulk phases show a reversible behavior under redox cycles (Figure (b)). Under reducing conditions, a Raman band appears at ~980 cm-1 (β-VPO phase), whereas under oxidation conditions some segregation to VOx oxides occurs. Nevertheless, this segregation is reversible and the β-VPO phase forms again under reducing conditions. Thus, these results demonstrate that the active VPO phases of these fibrous catalysts are quite stable, and that their structure is reversible under several redox cycles, which make them suitable as oxidation catalysts.

Synthesis of porous graphene/TiO2 by use of recycled graphite

Graphene-based nanomaterials are a kind of new technological materials with high interest for physicists, chemists and materials scientists. Graphene is a two-dimensional (2-D) sheet of carbon atoms in a hexagonal configuration with atoms bonded by sp2 bonds. These bonds and this electron configuration provides the extraordinary properties of graphene, such as very large surface area, a tunable band gap, high mechanical strength and high elasticity and thermal conductivity [1]. Graphene has also been investigated for preparation of composites with various semiconductors like TiO2, ZnO, CdS aiming at enhanced photocatalytic activity for their use for photochemical reaction as water splitting or CO2 to methanol conversion [2-3]. In this communication, the synthesis of porous graphene@TiO2 obtained from a powder graphite recycled, supplied by ECOPIBA, is presented. This graphite was exfoliated, using a nonionic surfactant (Triton X-100) and sonication. Titanium(IV) isopropoxide was used as TiO2 source. After removing the surfactant with a solution HCl/n-propanol, a porous solid is obtained with a specific area of 358 m2g-1. The solid was characterized by XRD, FTIR, XPS, EDX and TEM. Figure 1 shows the graphene 2D layer bonded with nanoparticles of TiO2. When a water suspension of this material is exposed with UV-vis radiation, water splitting reaction is carried out and H2/O2 bubbles are observed (Figure 2)

Meshfree Method for Prediction of Thermal Properties of Porous Ceramic Materials

In the presented thesis work, meshfree method with distance fields is applied to create a novel computational approach which enables inclusion of the realistic geometric models of the microstructure and liberates Finite Element Analysis(FEA) from thedependance on and limitations of meshing of fine microstructural feature such as splats and porosity.Manufacturing processes of ceramics produce materials with complex porosity microstructure.Geometry of pores, their size and location substantially affect macro scale physical properties of the material. Complex structure and geometry of the pores severely limit application of modern Finite Element Analysis methods because they require construction of spatial grids (meshes) that conform to the geometric shape of the structure. As a result, there are virtually no effective tools available for predicting overall mechanical and thermal properties of porous materials based on their microstructure. This thesis is a separate handling and controls of geometric and physical computational models that are seamlessly combined at solution run time. Using the proposedapproach we will determine the effective thermal conductivity tensor of real porous ceramic materials featuring both isotropic and anisotropic thermal properties. This work involved development and implementation of numerical algorithms, data structure, and software.

Micropolar flow in a porous channel with high mass transfer

Two dimensional flow of a micropolar fluid in a porous channel is investigated. The flow is driven by suction or injection at the channel walls, and the micropolar model due to Eringen is used to describe the working fluid. An extension of Berman's similarity transform is used to reduce the governing equations to a set of non-linear coupled ordinary differential equations. The latter are solved for large mass transfer via a perturbation analysis where the inverse of the cross-flow Reynolds number is used as the perturbing parameter. Complementary numerical solutions for strong injection are also obtained using a quasilinearisation scheme, and good agreement is observed between the solutions obtained from the perturbation analysis and the computations.

Effect of surface conditions on flow of a micropolar fluid driven by a porous stretching sheet

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