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diffusion-reflection
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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...
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...
Tuning composition of electrospun ZnO/CuO nanofibers: toward controllable and efficient solar photocatalytic degradation of organic pollutants
, Article Journal of Physical Chemistry C ; Volume 121, Issue 6 , 2017 , Pages 3327-3338 ; 19327447 (ISSN) ; Samadi, M ; Mahmoodi, N. M ; Pourjavadi, A ; Mehdipour, H ; Moshfegh, A. Z ; Sharif University of Technology
American Chemical Society
2017
Abstract
ZnO/CuO nanofibers, with different CuO concentrations, were fabricated by one-step electrospinning of the polymer precursor and annealing in air. Scanning electron microscopy (SEM) showed smooth and beadless morphology for the synthesized nanofibers, while X-ray diffraction (XRD) analysis revealed formation of hexagonal and monoclinic crystalline structure phases for ZnO and CuO nanofibers, respectively. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of CuO on the surface of ZnO nanofibers. For further confirming the formation of chemical bonds, Fourier transform infrared (FT-IR) spectroscopy was employed. The effect of Cu contents in the overall electronic band...
Transition metal ions effect on the properties and photocatalytic activity of nanocrystalline TiO2 prepared in an ionic liquid
, Article Journal of Hazardous Materials ; Volume 172, Issue 2-3 , 2009 , Pages 1573-1578 ; 03043894 (ISSN) ; Rahimnejad, S ; Setayesh, S. R ; Rohani, S ; Gholami, M. R ; Sharif University of Technology
Abstract
TiO2 and transition metal (Cr, Mn, Fe, Co, Ni, Cu, and Zn) doped TiO2 nanoparticles were synthesized by the sol-gel method using 2-hydroxylethylammonium formate as an ionic liquid. All the prepared samples were calcined at 500 °C and characterized by X-ray diffraction (XRD), BET surface area determination, energy dispersive X-ray (EDX) analysis, diffuse reflectance spectroscopy (DRS), and Fourier transformed infrared (FT-IR) techniques. The studies revealed that transition metal (TM) doped nanoparticles have smaller crystalline size and higher surface area than pure TiO2. Dopant ions in the TiO2 structure caused significant absorption shift into the visible region. The results of...
Titania nanotubes decorated with Zn-doped titania nanoparticles as the photoanode electrode of dye-sensitized solar cells
, Article Energy Technology ; Volume 5, Issue 9 , 2017 , Pages 1571-1578 ; 21944288 (ISSN) ; Afshar, A ; Mohammadi, M. R ; Chau Nan Hong, F ; Jeng, Y. R ; Sharif University of Technology
Abstract
We decorated Zn-doped TiO2-nanoparticle-based photoanodes with carbon nanotube (CNT)-derived TiO2 nanotubes (TNs) to enhance the power conversion efficiency of dye-sensitized solar cells (DSCs). X-ray photoelectron spectroscopy analysis verified that Zn ions, in the range of 0 to 1 at %, were successfully doped into the TiO2 lattice. Field-emission SEM and TEM images of the TNs, as derived from the sol–gel template-assisted route, revealed that a uniform TiO2 coating with a thickness of 60 to 120 nm was deposited on the surface of the CNT template through a noncovalent route. We observed that the cell efficiency improved from 6.80 for pure TiO2 to 7.52 for 0.75 at % Zn-doped TiO2...
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...
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...
Synthesis of the visible-light-driven Ag3VO4/Ag3PO4/Ag photocatalysts with enhanced photocatalytic activity
, Article RSC Advances ; Volume 6, Issue 18 , 2016 , Pages 14909-14915 ; 20462069 (ISSN) ; Rahman Setayesh, S ; Gholami, M. R ; Sharif University of Technology
Royal Society of Chemistry
2016
Abstract
A novel visible-light-driven Ag3VO4/Ag3PO4/Ag photocatalyst was successfully synthesized via an anion-exchange reaction and characterized by X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse-reflectance spectroscopy and Fourier transform infrared spectroscopy. The photocatalytic activities of prepared catalysts were evaluated by degradation of acid blue 92 (AB92) aqueous solutions under visible light irradiation. The photocatalytic results indicated that the synthesized Ag3VO4/Ag3PO4/Ag hybrid displays a significantly enhanced activity in degradation of acid blue 92 under visible light compared with pure Ag3VO4. The improved...
Synthesis of mesoporous TiO2 structures through P123 copolymer as the structural directing agent and assessment of their performance in dye-sensitized solar cells
, Article Solar Energy ; Volume 133 , 2016 , Pages 24-34 ; 0038092X (ISSN) ; Mozaffari, N ; Sharif University of Technology
Elsevier Ltd
Abstract
A novel and efficacious strategy was implemented for creation of mesoporous TiO2 films and powder through an integration of sol-gel and evaporation-induced self-assembly (EISA) processes aided by triblock Pluronic P123. A mesoporous crack-free thin film with virtual thickness of 300 nm was attained under 10% relative humidity aging, for 72 h at the low temperature of 5 °C. Further, the TiO2 film with porous structure has been formed from conventional paste, exploiting as-prepared mesoporous titania powder. The X-ray Diffraction (XRD) of synthesized mesoporous powder disclosed formation of anatase phase as well as rutile phase, in such a manner that the latter constituted a very small...
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...
Synthesis and characterization of anatase-coated multiwall carbon nanotube for improvement of photocatalytic activity
, Article International Journal of Engineering, Transactions A: Basics ; Volume 30, Issue 4 , 2017 , Pages 543-550 ; 17281431 (ISSN) ; Sadrnezhaad, S. K ; Sharif University of Technology
Materials and Energy Research Center
2017
Abstract
Sol-gel technique was used to coat multiwall carbon nanotubes (MWCNTs) with anatase titania to increasing the surface area and improve the photocatalytic activity of TiO2. Room temperature ballistic conduct of MWCNT combined with semiconducting behavior of anatase brought about a photocatalytic improvement of ∼37 % with respect to the highest methyl orange decolorization flair. For characterization and photocatalytic efficiency determination, X-ray diffraction (XRD), field emission (FE) scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS) and ultraviolet visible (UV-vis) spectroscopy were rehearsed. Attachment of anatase...
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...
Solid state preparation and photocatalytic activity of bismuth oxybromide nanoplates
, Article Research on Chemical Intermediates ; Volume 42, Issue 3 , 2016 , Pages 2429-2447 ; 09226168 (ISSN) ; Tadjarodi, A ; Akhavan, O ; Moghaddasi Khiavi, M ; Sharif University of Technology
Springer Netherlands
2016
Abstract
A mechanochemical method was applied to prepare bismuth oxybromide (BiOBr) nanoplates using bismuth nitrate pentahydrate and potassium bromide for 15 (A15), 30 (A30) and 60 (A60) minutes. Scanning electron microscopy studies showed that all the products were comprised of nanoplates. Aggregated nanoplates along with microblocks were observed for A15 and A30 and the entire morphology was not homogenous. The morphology of A60 was uniform and consisted of thin and isolated nanoplates. Evaluation of the X-ray diffraction patterns showed that the purity and crystallinity of the products improved by increasing the milling time. The energy dispersive X-ray analysis confirmed the high purity of 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...
Silver nano-islands on glass fibers using heat segregation method
, Article Materials Chemistry and Physics ; Volume 113, Issue 1 , 2009 , Pages 63-66 ; 02540584 (ISSN) ; Taghavinia, N ; Sharif University of Technology
2009
Abstract
A new method for fabrication of silver nano-islands on glass fibers using a top-down process is introduced. A thin layer of silver chemically coated on the surface of the glass fibers evolves into silver islands by heat treatment. The effect of the concentration of the initial solution and the temperature were investigated. Segregation was more clearly observed for lower solution concentrations and higher temperatures. The temperature of 500 °C was found optimum where separated islands form. At higher temperatures, the coagulation and burial of silver islands occur. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and diffused reflectance spectroscopy (DRS) were...
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...
Pt nanoparticles decorated Bi-doped TiO2 as an efficient photocatalyst for CO2 photo-reduction into CH4
, Article Solar Energy ; Volume 211 , 15 November , 2020 , Pages 100-110 ; Khorasheh, F ; Larimi, A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Pt@Bi-TiO2 photocatalysts with different Bi (0–5 wt%) and Pt (0–2 wt%) contents were prepared by a two-step sol-gel and photo-deposition technique and were used in photo-reduction of CO2. The synthesized catalysts were characterized by X-ray powder diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (DRS), scanning and transmission electron microscopy (SEM and TEM), nitrogen sorption measurement (BET), Raman spectroscopy, Electron paramagnetic resonance (EPR) spectroscopy and photoluminescence spectroscopy (PL). CO2 photo-reduction results revealed that the introduction of Bi into TiO2 structure and subsequent loading of Pt on its surface significantly increased the methane yield....
Preparation of novel and highly active magnetic ternary structures (metal-organic framework/cobalt ferrite/graphene oxide) for effective visible-light-driven photocatalytic and photo-fenton-like degradation of organic contaminants
, Article Journal of Colloid and Interface Science ; Volume 602 , 2021 , Pages 73-94 ; 00219797 (ISSN) ; Kazemeini, M ; Mahmoodi, N. M ; Sharif University of Technology
Academic Press Inc
2021
Abstract
Herein, MIL-101(Fe), CoFe2O4, novel binary (MIL-101(Fe)/CoFe2O4, MIL-101(Fe)/GO and CoFe2O4/GO), and ternary (MIL-101(Fe)/CoFe2O4/(3%)GO and MIL-101(Fe)/CoFe2O4/(7%)GO) magnetic composites based upon the MIL-101(Fe) were synthesized. The XRD, FESEM, TEM, EDX, BET-BJH, FTIR, VSM, DRS, PL, EIS and other electrochemical analyses were applied to characterize samples. The MIL/CoFe2O4/(3%)GO demonstrated the best performance compared to other samples for visible light photocatalytic and photo-Fenton-like degradation of Direct Red 23 (DtR-23), Reactive Red 198 (ReR-198) dyes as well as Tetracycline Hydrochloride (TC-H) antibiotic. Degradation of dyes using the ternary composite after 70 min of...
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...