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Harraz F.A.,Najran University | Harraz F.A.,Central Metallurgical Research and Development Institute
Sensors and Actuators, B: Chemical

The use of porous silicon (PSi) as a sensor for detection of various analytes is reviewed. The optical or electrical properties of PSi are key sensing parameters that have been used in many chemical and biological sensing applications. PSi is a promising candidate due to ease of fabrication, large surface area, various accessible pore sizes and morphologies, controllable surface modification and its compatibility with conventional silicon processing technology. The adsorption of chemical or biological molecules into the pores modifies the electrical and/or optical properties, allowing convenient and sensitive measurement approach. In this review, we provide a critical assessment of the development of PSi as a promising material for chemical and biosensing applications. Formation procedures of PSi with various pore sizes and morphologies are firstly given. Surface properties and structural characteristics of the material are briefly described. The recent progress on utilization of such porous structures in chemical and biosensing applications is then addressed in the context of surface chemistry effects and nanostructures, measuring approaches, operating concepts and device sensitivity and stability. Finally, concluding remarks with existing challenges that hinder the material for commercial use are highlighted. © 2014 Elsevier B.V. Source

Ismail A.A.,Central Metallurgical Research and Development Institute | Bahnemann D.W.,Leibniz University of Hanover
Journal of Materials Chemistry

Titanium dioxide is a very important semiconductor with a high potential for applications in photocatalysis, solar cells, photochromism, sensoring, and various other areas of nanotechnology. Increasing attention has recently been focused on the simultaneous achievement of high bulk crystallinity and the formation of ordered mesoporous TiO2 frameworks with high thermal stability. Mesoporous TiO2 has continued to be highly active in photocatalytic applications because it is beneficial for promoting the diffusion of reactants and products, as well as for enhancing the photocatalytic activity by facilitating access to the reactive sites on the surface of photocatalyst. This steady progress has demonstrated that mesoporous TiO2 nanoparticles are playing and will continue to play an important role in the protection of the environment and in the search for renewable and clean energy technologies. This review focuses on the preparation and characterisation of mesoporous titania, noble metals nanoparticles, transition metal ions, non-metal/doped mesoporous titania networks. The photocatalytic activity of mesoporous titania materials upon visible and UV illumination will be reviewed, summarized and discussed, in particular, concerning the influence of preparation and solid-state properties of the materials. Reaction mechanisms that are being discussed to explain these effects will be presented and critically evaluated. © The Royal Society of Chemistry 2011. Source

Ismail A.A.,Central Metallurgical Research and Development Institute | Bahnemann D.W.,Leibniz University of Hanover
Journal of Physical Chemistry C

Mesoporous Pt/TiO 2 nanocomposites have been synthesized by using two pathways: (1) the in-situ preparation of Pt/TiO 2 nanocomposites was carried out using a one-step synthesis by dissolving the Pt and TiO 2 precursors in the presence of a triblock copolymer as the structure-directing agent followed by drying, calcinations, and reduction under H 2 gas. (2) Platinum particles have been photochemically deposited onto mesoporous TiO 2. The TEM images of the mesoporous Pt/TiO 2 nanocomposites calcined at 450 °C demonstrate that the TiO 2 nanoparticles with an average diameter of about 10 nm are not agglomerated and are quite uniform in size and shape. Following the photodeposition process, the Pt nanoparticles are well-dispersed and highly uniform, exhibiting diameters of ∼3 nm; however, following the in situ preparation, the Pt particles are reaching diameters of approximately 15 nm, most likely as a result of the calcination and reduction at high temperatures. The photocatalytic activity of the newly synthesized mesoporous photocatalysts was measured and compared with that of nonporous commercial Aeroxide TiO 2 P 25 and Pt/TiO 2 P 25 by measuring the rate of H + ion release during the photodegradation of dichloroacetic acid (DCA) and confirmed by measuring the concomitant total organic carbon removal. For both preparation routes the photonic efficiency of the mesoporous TiO 2 photocatalysts is found to be increased by the addition of the Pt islands and to correlate with the size of the Pt particles. The mesoporous Pt/TiO 2 nanocomposites showed 2 times higher activity for the photocatalytic DCA photodegradation than Aeroxide TiO 2 P 25. The larger photoactivity of the mesoporous Pt/TiO 2 nanocomposites prepared by the photodeposition process is attributed to the higher dispersity and the small size of the Pt particles (3 nm). To the best of our knowledge, the measured photonic efficiency of ξ= 7.95% for the photodeposited Pt/TiO 2 nanocomposites is among the highest ξ value reported up to now. © 2011 American Chemical Society. Source

Ismail A.A.,Central Metallurgical Research and Development Institute | Bahnemann D.W.,Leibniz University of Hanover
Green Chemistry

Mesostructured Pt/TiO 2 nanocomposites have been synthesized at different Pt (0-2 wt%) and anatase/rutile ratios through simple one-step sol-gel reactions. The as-made mesostructured hybrids were subjected to H 2 gas for 2 h at 450°C to obtain ordered hexagonal mesoporous Pt/TiO 2 nanocomposites with highly crystalline TiO 2. Subsequently, the samples were calcined at 350°C in air for 4 h to remove the surfactant. XRD data clearly show that biphasial anatase and rutile mixtures are formed by the addition of the Pt islands. The TEM results indicated that TiO 2 and Pt, are partly in close contact; the lattice fringes exhibit the typical distances, i.e., Pt (111) (2.2 Å) and TiO 2 (101) (3.54 Å). TiO 2 nanoparticles with an average diameter of about 10 nm particles are not agglomerated and quite uniform in size and shape. Also, Pt nanoparticles are well dispersed and exhibit diameters of about 5-12 nm based on the Pt content. Our photocatalysts have been compared with colloidal 0.5 wt% Pt loaded onto commercial photocatalysts either UV-100 Hombikat or Aeroxide TiO 2 P25 by the determination of the initial rate of HCHO formation generated by the photooxidation of CH 3OH in aqueous suspensions to calculate the corresponding photonic efficiencies. The overall photocatalytic activities of 0.5 wt% Pt/TiO 2 nanocomposites are significantly 3-times higher than that of colloidal 0.5 wt% Pt loaded onto commercial photocatalysts either UV-100 Hombikat or Aeroxide TiO 2 P25. To the best of our knowledge, the measured photonic efficiency ξ = 15.5% of hexagonal mesostructured Pt/TiO 2 nanocomposites is found to be among the highest ξ values reported up to now. The superiority of Pt/TiO 2 is attributed to the bicrystalline (anatase/rutile) framework, large surface area, high crystallinity and mesoporous structure of Pt/TiO 2 nanocomposites. © 2011 The Royal Society of Chemistry. Source

El-Kady O.,Central Metallurgical Research and Development Institute | Fathy A.,Zagazig University
Materials and Design

In this work, the effect of SiC particle size and its amount on both physical and mechanical properties of Al matrix composite were investigated. SiC of particle size 70. nm, 10. μm and 40. μm, and Al powder of particle size 60. μm were used. Composites of Al with 5 and 10. wt.% SiC were fabricated by powder metallurgy technique followed by hot extrusion. Phase composition and microstructure were characterized. Relative density, thermal conductivity, hardness and compression strength were studied. The results showed that the X-ray diffraction (XRD) analysis indicated that the dominant components were Al and SiC. Densification and thermal conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Scanning electron microscope (SEM) studies showed that the distribution of the reinforced particle was uniform. Increasing the amount of SiC leads to higher hardness and consequently improves the compressive strength of Al-SiC composite. Moreover, as the SiC particle size decreases, hardness and compressive strength increase. The use of fine SiC particles has a similar effect on both hardness and compressive strength. © 2013 Elsevier Ltd. Source

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