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diffusion-reflection
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Permeability correlation with porosity and Knudsen number for rarefied gas flow in Sierpinski carpets
, Article Journal of Natural Gas Science and Engineering ; Volume 56 , 2018 , Pages 549-567 ; 18755100 (ISSN) ; Salimi, M. R ; Taeibi Rahni, M ; Sharif University of Technology
Elsevier B.V
2018
Abstract
In recent years, application of porous media is highlighted among researchers due to their wide range of usability in micro-scale problems, such as gas reservoirs, micro-filtering, heat exchangers, etc. With this respect, the accurate description of flow behavior using governing equations based on the continuum assumption is not valid since the mean free path is comparable to the characteristics length of the problem. For this purpose, a simple methodology for diffusion reflection boundary condition is developed and validated for two valuable benchmarks, namely micro-channel flow and fractal porous media, where the results were in good agreement with literature. Then, pore-scale simulation...
Expanding Visibility Polygons by Mirrors
, M.Sc. Thesis Sharif University of Technology ; Ghodsi, Mohammad (Supervisor)
Abstract
We consider extending the visibility polygon of a given point q inside a simple polygon by converting one or some of the edges to mirrors. It is known that the visibility polygon of a point inside a polygon in the presence of a mirror can be computed in linear time. We propose a linear time algorithm that checks whether a given segment inside a simple polygon is visible by a given point q via a mirror-edge, and finds all such edges. And we prove that finding edges to add exactly k unit squares to the visibility polygon of a query point q in most cases is NP-complete and its minimization is NP-hard. These cases contain single and muliple, either with secular or difuse reflections. Moreover,...
Visibility Via Reflection
, Ph.D. Dissertation Sharif University of Technology ; Ghodsi, Mohammad (Supervisor)
Abstract
This document deals with the following results in details:Given a simple polygon P with $n$ vertices, the visibility polygon (VP) of a point q, or a segment pq inside P can be computed in linear time. It is known that the visibility polygon of a point inside a polygon in the presence of a mirror can be computed in linear time. We propose a linear time algorithm to extend the VP of a viewer (point or segment) by converting some edges of P into mirrors (reflecting-edges with specular type of reflection), such that a given non-visible segment uw can also be seen from the viewer.Various definitions for the visibility of a segment, such as weak, strong, or complete visibility, are considered. Our...
Optimal Ag2S nanoparticle incorporated TiO2 nanotube array for visible water splitting
, Article RSC Advances ; Volume 4, Issue 15 , 2014 , Pages 7838-7844 ; ISSN: 20462069 ; Qorbani, M ; Moradlou, O ; Naseri, N ; Moshfegh, A. Z ; Sharif University of Technology
Abstract
Free-standing TiO2 nanotube array (TNA) films were fabricated via two-step anodization of a titanium sheet. The X-ray diffraction pattern indicated amorphous TNAs were transformed into anatase after annealing the films at 500 °C in air. The surface of TNA was modified by a sequential-chemical bath deposition (S-CBD) method to fabricate Ag2S nanoparticles and forming TNA/Ag2S-n nanostructure, by varying the number of cycles (n). Based on SEM observations, the produced films consisted of vertically ordered tubular structure arrays, each with 125 nm in diameter and 4.1 μm in length containing silver sulphide nanoparticles of ∼12 nm diameter. X-Ray photoelectron spectroscopy (XPS) confirmed the...
Simply synthesized TiO2 nanorods as an effective scattering layer for quantum dot sensitized solar cells
, Article Chinese Physics B ; Vol. 23, issue. 4 , 2014 ; Zad, A. I ; Molaei, M ; Sharif University of Technology
Abstract
TiO2 nanorod layers are synthesized by simple chemical oxidation of Ti substrates. Diffuse reflectance spectroscopy measurements show effective light scattering properties originating from nanorods with length scales on the order of one micron. The films are sensitized with CdSe quantum dots (QDs) by successive ionic layer adsorption and reaction (SILAR) and integrated as a photoanode in quantum dot sensitized solar cells (QDSCs). Incorporating nanorods in photoanode structures provided 4- to 8-fold enhancement in light scattering, which leads to a high power conversion efficiency, 3.03% (Voc = 497 mV, Jsc = 11.32 mA/cm2, FF = 0.54), in optimized structures. High efficiency can be obtained...
TiO2 surface nanostructuring for improved dye loading and light scattering in double-layered screen-printed dye-sensitized solar cells
,
Article
Journal of Applied Electrochemistry
;
Volume 45, Issue 8
,
2015
,
Pages 831-838
;
0021891X (ISSN)
; Moakhar, R. S
; Kushwaha, A
; Goh, G. K. L
; Sadrnezhaad, S. K
; Riahi Noori, N
;
Sharif University of Technology
Kluwer Academic Publishers
2015
Abstract
Abstract: Surface-nanostructured TiO2 nanorods were synthesized hydrothermally at 180 °C. Such nanorods have ‘crack-like’ surfaces that resemble burnt charcoal. Compared to nanorods with relatively smoother surfaces, the charcoal-like nanorods have higher-specific surface areas. By using the nanorods as a light-scattering layer in double-layered dye-sensitized solar cells, the cells based on the charcoal-like nanorods have 20 % higher dye loading and also higher diffuse reflectance compared with cells utilizing ‘smooth’ nanorods. The efficiency of a screen-printed double-layer dye-sensitized solar cell based on the charcoal-like nanorods is higher at 7.29 %. Electrochemical...
Impact of chromium doping on physical, optical, electronic and photovoltaic properties of nanoparticle TiO2 photoanodes in dye-sensitized solar cells
, Article New Journal of Chemistry ; Volume 41, Issue 23 , 2017 , Pages 14516-14527 ; 11440546 (ISSN) ; Mohammadi, M. R ; Sharif University of Technology
Royal Society of Chemistry
2017
Abstract
Herein, we report the impact of chromium doping on the physical properties, electronic band structure and photovoltaic characteristics of their corresponding devices based on dye-sensitized solar cells (DSCs). Different DSCs with various compositions of the photoanode electrodes are fabricated to study their optical, structural, conduction band edge, donor density, depth of trap states and photoelectrochemical properties using X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), field-emission scanning electron microscopy (FE-SEM), Mott-Schottky capacitance analysis, chemical capacitance and electrochemical impedance spectroscopy (EIS) measurements. For such studies, the Cr-doped...
Pore-scale modeling of rarefied gas flow in fractal micro-porous media, using lattice Boltzmann method (LBM)
, Article Journal of Thermal Analysis and Calorimetry ; Volume 135, Issue 3 , 2019 , Pages 1931-1942 ; 13886150 (ISSN) ; Salimi, M. R ; Taeibi Rahni, M ; Sharif University of Technology
Springer Netherlands
2019
Abstract
Due to the widespread use of rarefied gas flow in micro-porous media in industrial and engineering problems, a pore-scale modeling of rarefied gas flow through two micro-porous media with fractal geometries is presented, using lattice Boltzmann method. For this purpose, square- and circular-based Sierpinski carpets with fractal geometries are selected due to their inherent behavior for real porous media. Diffusive reflection slip model is used and developed for these porous media through this study. With this respect, the planar Poiseuille flow is selected as a benchmark and validated with the literature. The effect of Knudsen number (Kn) on the permeability is investigated and compared in...
Preparation of Ag-Al₂O₃ nano structures by combustion method and investigation of photocatalytic activity
, Article International Journal of Applied Ceramic Technology ; Volume 18, Issue 6 , 2021 , Pages 2064-2074 ; 1546542X (ISSN) ; Khodadadipoor, Z ; Fazli, M ; Einafshar, N ; Mohebbi Zinab, J ; Asaei, S ; Sharif University of Technology
John Wiley and Sons Inc
2021
Abstract
In this research, Ag-Al2O3 nanostructures have been prepared via combustion synthesis and ammonium acetate and urea have been applied as fuels. The prepared Ag-Al2O3 nanostructures were characterized by DTA, XRD, SEM, TEM, and BET spectroscopy. The effect of different ratios of silver to alumina and fuel percentage on morphology and particle size of prepared products were investigated. The results showed that using ammonium acetate fuel led to the production of Ag-γ-Al2O3 nanocompounds, while using urea produced Ag-α-Al2O3. Also, the photocatalytic activity of Ag-Al2O3 nanostructures for Congo red degradation was evaluated by UV-Vis diffuse reflectance spectroscopy. The photocatalytic...
Enhanced electron collection efficiency in dye-sensitized solar cells based on nanostructured TiO2 hollow fibers
, Article Nano Letters ; Volume 10, Issue 5 , April , 2010 , Pages 1632-1638 ; 15306984 (ISSN) ; Taghavinia, N ; Zakeeruddin, S. M ; Grätzel, M ; Moser, J. E ; Sharif University of Technology
2010
Abstract
Nanostructured TiO2 hollow fibers have been prepared using natural cellulose fibers as a template. This cheap and easily processed material was used to produce highly porous photoanodes incorporated in dye-sensitized solar cells and exhibited remarkably enhanced electron transport properties compared to mesoscopic films made of spherical nanoparticles. Photoinjected electron lifetime, in particular, was multiplied by 3-4 in the fiber morphology, while the electron transport rate within the fibrous photoanaode was doubled. A nearly quantitative absorbed photon-to-electrical current conversion yield exceeding 95% was achieved upon excitation at 550 nm and a photovoltaic power conversion...
Enhancement of efficient Ag-S/TiO2 nanophotocatalyst for photocatalytic degradation under visible light
, Article Industrial and Engineering Chemistry Research ; Vol. 53, issue. 23 , 2014 , Pages 9578-9586 ; ISSN: 08885885 ; Vossoughi, M ; Zakeri, S. M. E ; Rahimi, M ; Sharif University of Technology
Abstract
A new photocatalyst (Ag-S/PEG/TiO2) was synthesized by adding polyethylene glycol (PEG) to an efficient Ag-S/TiO2 photocatalyst, to obtain a photocatalyst that is highly active under visible light. In addition to Ag-S/PEG/TiO2, Ag-S/TiO2 and pure TiO2 were prepared to compare their properties and activities. Specifically, the morphologies and microstructures of the nanophotocatalysts were characterized by means of powder X-ray diffraction (XRD), N2 adsorption-desorption measurements, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) microanalysis, transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy,...
Role of CdO addition on the growth and photocatalytic activity of electrospun ZnO nanofibers: UV vs. visible light
, Article Applied Surface Science ; Vol. 298, issue , April , 2014 , pp. 147-154 ; ISSN: 01694332 ; Pourjavadi, A ; Moshfegh, A. Z ; Sharif University of Technology
Abstract
(ZnO)1-x(CdO)x nanofibers were fabricated via electrospinning of polymer precursor by subsequent annealing in air. Field emission scanning electron microscopy (FESEM) showed the smooth and beadless nanofibers and X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed the ZnO hexagonal and the CdO cubic structure. Diffuse reflectance spectroscopy (DRS) showed the band gap energy reduction by increasing the amount of CdO in (ZnO)1-x(CdO)x nanofibers that resulted in the photocatalytic activity under the visible light for dye degradation. Under the UV light CdO acted as both electron and hole sink in the (ZnO) 1-x(CdO)x nanofibers and a possible photocatalytic activity...
Application of the statistical Taguchi method to optimize TiO2 nanoparticles synthesis by the hydrothermal assisted sol-gel technique
, Article Ceramics International ; Vol. 40, Issue 3 , 2014 , pp. 4193-4201 ; ISSN: 02728842 ; Faghihi Sani, M. A ; Madaah Hosseini, H. R ; Sharif University of Technology
Abstract
TiO2 nanoparticles were synthesized by hydrothermal assisted sol-gel technique. The preparation parameters including pH value, the amount of water, titanium tetra isopropoxide content, temperature and time of hydrothermal process were investigated by Taguchi statistical experiments to determine the influence of synthesizing variables on the optimal conditions and to realize the highest degree of crystallinity or smallest crystallite size. X-ray diffraction (XRD) analysis and direct band gap energy (Eg) values, measured via diffuse reflectance spectra (DRS), proved that all the samples consist of anatase as a unique phase. Transmission electron microscopy (TEM) and specific surface area...
Synthesis and characterization of co-doped TiO2 thin films on glass-ceramic
, Article Materials Science in Semiconductor Processing ; Vol. 26, Issue 1 , October , 2014 , pp. 41-48 ; ISSN: 13698001 ; Nemati, A ; Solati-Hashjin, M ; Sharif University of Technology
Abstract
In this research, an attempt was made to improve TiO2 photo-catalyst properties, thus pure, N-Ce co-doped TiO2 thin films were prepared on glass-ceramic substrate using a sol-gel dip-coating technique. The samples were calcinated in air at 475 °C, 550°C, and 650°C for 2 h. The result of simultaneous thermal analysis (STA) and X-ray diffraction (XRD) showed that the presence of Ce in TiO2 could inhibit the phase transformation from anatase to rutile and enhance the thermal stability, and anatase was the dominant phase in N-Ce co-doped TiO2 samples. Also based on the results, the doping results in decreasing the size of TiO 2 crystallite. The results of ultra violet-visible light diffuse...
Vanadium pentoxide catalyst over carbon-based nanomaterials for the oxidative dehydrogenation of propane
, Article Industrial and Engineering Chemistry Research ; Volume 52, Issue 46 , 2013 , Pages 16128-16141 ; 08885885 (ISSN) ; Kazemeini, M ; Khorasheh, F ; Rashidi, A. M ; Sharif University of Technology
2013
Abstract
A series of V2O5 catalysts supported on multiwall carbon nanotube (MWCNT), single wall carbon nanotube (SWCNT), and graphene were synthesized by hydrothermal and reflux methods for oxidative dehydrogenation of propane (ODHP) to propylene. The catalysts were characterized by techniques including the BET surface area measurements, XRD, FTIR, H2-TPR, NH3-TPD, FESEM, and UV-vis diffuse reflectance spectroscopy. The performance of the catalysts and the supports were subsequently examined in a fixed bed reactor. The main products were propylene, ethylene and CO x. The vanadium catalyst supported on graphene with C/V molar ratio of 1:1 synthesized through the hydrothermal method had the best...
Synergism of oxygen vacancy and carbonaceous species on enhanced photocatalytic activity of electrospun ZnO-carbon nanofibers: Charge carrier scavengers mechanism
, Article Applied Catalysis A: General ; Volume 466 , September , 2013 , Pages 153-160 ; 0926860X (ISSN) ; Shivaee, H. A ; Pourjavadi, A ; Moshfegh, A. Z ; Sharif University of Technology
2013
Abstract
Novel ZnO-carbon and ZnO nanofibers were fabricated by electrospinning of polymer precursor followed by subsequent annealing in nitrogen and air, respectively. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) indicated the smooth and beadless nanofibers with wurtzite crystal structure. X-ray photoelectron spectroscopy (XPS) showed the presence of oxygen vacancies (VO) and chemisorbed O2 on the surface of the samples. Band gap narrowing of the ZnO-carbon nanofibers in comparison to ZnO were measured by diffuse reflectance spectroscopy (DRS). Photo-degradation of azo dye under the UV and visible light was evaluated and ZnO-carbon showed an enhancement in...
Improved efficiency of dye-sensitized solar cells by design of a proper double layer photoanode electrodes composed of Cr-doped TiO2 transparent and light scattering layers
, Article Journal of Sol-Gel Science and Technology ; Volume 67, Issue 1 , 2013 , Pages 77-87 ; 09280707 (ISSN) ; Bakhshayesh, A. M ; Sadri, F ; Masroor, M ; Sharif University of Technology
2013
Abstract
A new strategy for enhancing the efficiency of TiO2 dye-sensitized solar cells (DSSCs) by design of a new double layer film doped with Cr ions, with various morphologies, is reported. X-ray diffraction and field emission scanning electron microscope (FE-SEM) analyses revealed that the synthesized nanoparticles had uniform and nanometer grains with different phase compositions and average crystallite size in the range of 10-12 nm depending upon Cr atomic percentage. UV-vis absorption showed that Cr introduction enhanced the visible light absorption of TiO2 nanoparticles by shifting the absorption onset to visible light region. Furthermore, the band gap energy of nanoparticles decreased with...
Adsorption and solar light activity of transition-metal doped TiO 2 nanoparticles as semiconductor photocatalyst
, Article Journal of Materials Science: Materials in Electronics ; Volume 23, Issue 3 , 2012 , Pages 659-667 ; 09574522 (ISSN) ; Simchi, A ; Jafari, T ; Sharif University of Technology
Abstract
There is an eminent interest to improve the photoactivity of TiO 2 nanostructures via doping with midband gap donors or acceptors to achieve a high solar absorption. In the present work, Cr- and V-doped TiO 2 nanoparticles were prepared via a facile chemical vapor synthesis method. The effect of the transition metals (TM) on the solar light activity of the semiconductor nanoparticles as photocatalyst was examined by degradation of methylene blue and acid red 27. Induced coupled plasma and X-ray photoelectron spectroscopy analyses indicated high efficiency of the doping process in the hot wall reactor without surface covering of the TiO 2 nanoparticles by the dopants. Diffuse reflectance...
Photocatalytic activity of TiO 2-capped ZnO nanoparticles
, Article Journal of Materials Science: Materials in Electronics ; Volume 23, Issue 2 , 2012 , Pages 361-369 ; 09574522 (ISSN) ; Simchi, A ; Nemati, Z. A ; Sharif University of Technology
Abstract
Using a combined hydrothermal and sol-gel route, TiO 2 -capped ZnO nanoparticles with an average size of 60 nm were prepared. The titania shell was amorphous with a thickness of ∼10 nm. Formation of Zn 2TiO 4 phase at higher calcination temperature was noticed. Effects of Ti/Zn molar ratio and coating time on the thickness of TiO 2 shell and the photoactivity of the particles for decolorization of Methylene Blue (MB) under UV lamp irradiation (3 mW/cm 2) were investigated. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, fourier-transform infrared spectrometry (FTIR), diffuse reflectance spectroscopy (DLS), and atomic absorption spectroscopy....
The effect of multiwalled carbon nanotubes and activated carbon on the morphology and photocatalytic activity of TiO2/C hybrid materials
, Article Catalysis Science and Technology ; Volume 1, Issue 2 , 2011 , Pages 279-284 ; 20444753 (ISSN) ; Ghasemi, S ; Gholami, M. R ; Sharif University of Technology
2011
Abstract
TiO2 nanoparticles supported on activated carbon (AC) and multiwalled carbon nanotubes (MWCNTs) were prepared by the sol-gel method using ultrasonic irradiation. All the prepared samples were calcined at different temperatures and characterized by X-ray diffraction, nitrogen adsorption/desorption isotherms, scanning electron microscopy, transmission electron microscopy and diffuse reflectance spectroscopy. The effects of size and type of carbon on the morphology and photocatalytic activity of the resulting hybrid materials were investigated. The results showed that a decrease in the size of the carbon led to a decrease in size of TiO2 nanoparticles. Both AC and MWCNTs retarded the...