A. Youssefi

Ferdowsi University Of Mashhad, Mashhad, Razavi Khorasan, Iran

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Publications (18)22.96 Total impact

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    ABSTRACT: هدف از اين تحقيق، اتصال کووالانسی نانوذرات TiO2روی سطح نانولوله­های کربنی و بررسی پایداری و هدایت حرارتی نانوسيال می­باشد. نانولوله­های آرایش یافته با میکروسکوپ الکترونی عبوری (TEM) جهت اطمینان از اتصال نانوذرات TiO2 و طیف سنجی رامان جهت بررسی تغییرات میزان گرافیته شدن مورد بررسی قرار گرفتند. پایداری نانوسیال به کمک پتانسیل زتا بررسی گردید. تصاویر TEM نشان دهنده اتصال نانوذرات TiO2روی سطح نانولوله­ها می­باشد. طیف­سنجی رامان نشان­دهنده افزایش میزان عیوب ایجاد شده در ساختار نانولوله با افزایش میزان نانوذرات متصل شده می­باشد. نتایج حاصل از بررسی پایداری نانوسیال نشان داد که با افزایش میزان نانوذرات متصل شده، پایداری نانوسیال کمتر می­شود. همچنین نتایج بررسی ها نشان داد که دما و غلظت تاثیر معناداری بر روی میزان هدایت حرارتی نانوسیال دارند.
    فرآیندهای نوین در مهندسی مواد. 01/2014; 8(2):1-8.
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    ABSTRACT: Synthesis of different phases of titania nanoparticles (TiO2) and decorated Multi-walled carbon nanotubes (MWCNTs) with various content of rutile titania have been performed. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The XRD results showed that the amount of precursor strongly influenced by phase transition of TiO2 nanoparticles. TEM images showed that the outer surface of MWCNTs modified with TiO2 nanoparticles. The selected-area electron diffraction (SAED) of TiO2 nanoparticles and MWCNTs-TiO2 revealed the polycrystalline structure of the samples. FTIR analysis confirmed the presence of oxygen containing groups on the surface of oxidized MWCNTs and TiO2 on the surface of decorated MWCNTs. Optical properties of samples measured using UV-Vis spectrophotometer and the achieved results demonstrated that dispersibility of oxidized and decorated MWCNTs is higher than that of pristine MWCNTs. The XPS results showed that TiO2 nanoparticles were covalently attached on the side walls of acid-treated multi-walled carbon nanotubes.
    Synthesis and Reactivity in Inorganic Metal-Organic and Nano-Metal Chemistry 11/2013; · 0.50 Impact Factor
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    ABSTRACT: In this paper, we report for the first time the statistical analysis of thermal conductivity of nanofluids containing TiO2 nanoparticles, pristine MWCNTs and decorated MWCNTs with different amount of TiO2 nanoparticles. The functionalized MWCNT and synthesized hybrid of MWCNT-TiO2 were characterized using transmission electron microscopy (TEM). TEM image confirmed that the ends of MWCNTs were opened during the oxidation of them in HNO3 and TiO2 nanoparticles successfully attach to the outer surface of oxidized MWCNTs. Thermal conductivity measurements of nanofluids were analyzed via two factor completely randomized design and comparison of data means is carried out with Duncan’s multiple range test. Statistical analysis of experimental data shows that temperature and weight fraction have a reasonable impact on the thermal conductivity of all tested nanofluids (α=0.05). The results also show that increasing temperature and weight fraction leads to the increasing of thermal conductivity.
    Bulletin of Materials Science 10/2013; · 0.58 Impact Factor
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    ABSTRACT: Synthesis of different phases of titania nanoparticles (TiO2) and decorated Multi-walled carbon nanotubes (MWCNTs) with various content of rutile titania have been performed. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The XRD results showed that the amount of precursor strongly influenced by phase transition of TiO2 nanoparticles. TEM images showed that the outer surface of MWCNTs modified with TiO2 nanoparticles. The selected-area electron diffraction (SAED) of TiO2 nanoparticles and MWCNTs-TiO2 revealed the polycrystalline structure of the samples. FTIR analysis confirmed the presence of oxygen containing groups on the surface of oxidized MWCNTs and TiO2 on the surface of decorated MWCNTs. Optical properties of samples measured using UV-Vis spectrophotometer and the achieved results demonstrated that dispersibility of oxidized and decorated MWCNTs is higher than that of pristine MWCNTs. The XPS results showed that TiO2 nanoparticles were covalently attached on the side walls of acid-treated multi-walled carbon nanotubes.
    01/2013;
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    ABSTRACT: A novel electrochemical hydride generation (ECHG) system working in flow-injection (FI) mode was developed for determination of cadmium coupled to an electrically heated quartz tube atomizer (QTA) by atomic absorption spectrometry (AAS). A Plackett-Burman experimental design for screening has been used to evaluate the influence of several variables on the analytical response. Then, the significant parameters such as the concentration of NaCl in catholyte, applied electrolytic current and flow rate of carrier gas have been simultaneously optimized using a central composite design (CCD). Under the optimized conditions, the detection limit (3σ(b), n=9) was found to be 0.51 ng mL(-1) Cd and the relative standard deviation (RSD) for nine replicate analyses of 20 ng mL(-1) Cd was 6.5%. The calibration curve was linear in the range of 2-50 ng mL(-1) of Cd. The potential interferences from various ions were also evaluated. The analysis of a reference material showed good agreement with the certified value. The proposed method was successfully applied to the determination of Cd in tap water sample.
    Talanta 08/2012; 97:229-34. · 3.50 Impact Factor
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    ABSTRACT: Electrochemical hydride generation (EcHG) as a sample introduction system for determination of zinc was developed. It was directly coupled to an electrically heated quartz tube atomizer (QTA) atomic absorption spectrometry (AAS) system. The hydride generator is a laboratory-made semi-batch electrolytic cell that consists of a lead-tin alloy cathode and a platinum anode. The effects of typical parameters on the generation efficiency of the technique, such as types of cathode material and catholyte and anolyte solutions, were studied. The influences of numerical experimental operating parameters on the analytical signal were evaluated in detail and optimum conditions were obtained. The analytical figures of merit for the developed method were determined. The calibration curve was linear up to 300 ng mL(-1) of Zn. A concentration detection limit (3σ, n = 9) of 11 ng mL(-1) Zn and a relative standard deviation of 5.0% (RSD, n = 9) for 200 ng mL(-1) Zn were accessed. In addition, the susceptibility of interference from various ions was evaluated. The accuracy of the method was verified by determination of Zn in a certified reference material and in tap water. The achieved concentrations were found to be in good agreement with both the certified value and the data obtained using flame AAS.
    Analytical Sciences 01/2012; 28(7):717-22. · 1.57 Impact Factor
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    ABSTRACT: In this paper, nanospinels NiMnxFe2−xO4 (x=0.05, 0.1, 0.3, 0.5, 0.7, and 1) were prepared by sol–gel method in the presence of nitrate–metal–ethylene glycol (EG) polymerized complex. The nanospinels were characterized using thermogravimetry analysis (TGA), X-ray powder diffraction (XRD), Fourier infrared spectroscopy (FTIR), and transmission electron microscope (TEM). The adsorption of an azo dye, reactive blue 5 (RB5), from water was determined using the prepared nanospinels. The effect of operational parameters such as the initial dye concentration, the concentration of nanospinels, temperature, and pH on the degradation of dye was investigated. The adsorption process follows second-order kinetics and Arrhenius behavior. Two common models, the Langmuir and Freundlich isotherms were used to investigate the interaction of dye and nanospinels. The isotherm evaluations revealed that the Freundlich model provides better fit to the experimental data than that of the Langmuir model. The photocatalytic degradation of RB5 at pH 1 under UV irradiation was examined. The results showed that the degradation of RB5 dye follows merely an adsorption process.
    Materials Chemistry and Physics - MATER CHEM PHYS. 01/2011; 130(3):1156-1161.
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    ABSTRACT: For the first time, nanoparticles of zinc chromite, spinel ZnCr(2)O(4) have been fabricated by the thermal decomposition of Zn-Cr gel prepared by sol-gel method in the presence of oxalic acid as a chelating agent. It was shown that the well-crystallized spinel structure is formed after calcination at 450°C. The nanospinel has been characterized by differential thermal analysis (DTA), X-ray powder diffraction (XRD), infrared spectroscopy (IR), and transmission electron microscope (TEM). The average particle size is approximately 13 nm according to the TEM image. The nanoparticles of zinc chromites showed excellent adsorption properties towards reactive dye, reactive blue 5 (RB5). The adsorption studies have been carried out for contact time, different pH values, different temperatures, and adsorbent doses. The investigation of removal kinetics of RB5 indicates that the removal process obeys the rate of second-order kinetic equation. The results indicate that the Langmuir adsorption isotherm fitted the data better than the Freundlich. Also, the photocatalytic degradation of RB5 using spinel ZnCr(2)O(4) under UV irradiation at pH=1 has been also examined. The results showed that the degradation of RB5 dye follows merely an adsorption process.
    Journal of hazardous materials 12/2010; 184(1-3):684-9. · 4.14 Impact Factor
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    ABSTRACT: Magnetite Fe3O4 nanoparticles were synthesized by a co-precipitation method at different pH values. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electronic microscopy. Their magnetic properties were evaluated on a vibrating sample magnetometer. The results show that the shape of the particles is cubic and they are superparamagnetic at room temperature. Magnetic nanofluids were prepared by dispersing the Fe3O4 nanoparticles in water as a base fluid in the presence of tetramethyl ammonium hydroxide as a dispersant. The thermal conductivity of the nanofluids was measured as a function of volume fraction and temperature. The results show that the thermal conductivity ratio of the nanofluids increases with increase in temperature and volume fraction. The highest enhancement of thermal conductivity was 11.5% in the nanofluid of 3 vol% of nanoparticles at 40 °C. The experimental results were also compared with the theoretical models.
    Journal of Magnetism and Magnetic Materials 01/2010; · 2.00 Impact Factor
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    ABSTRACT: Thermal conductivity enhancements of nanodiamond particles (NDs) suspended in pure deionized (DI) with different volume fractions in the range from 0.8% to 3% have been measured. The highest observed enhancement in the thermal conductivity is 7.2% for a volume fraction of 3% at a temperature of 30 °C. The thermal conductivity increases by about 9.8% as the temperature rises to 50 °C. The new Murshed model (Murshed et al. (2009) [31]) was used to describe the heat transfer enhancement in the ND fluid. While the predicted results overestimate the experimental data, they are in agreement within the experimental errors.
    International Journal of Heat and Mass Transfer. 01/2010;
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    ABSTRACT: ZnO nanofluids have been prepared by dispersing ZnO nanoparticles in the ethylene glycol (EG) and glycerol (G) as the base fluids. Ammonium citrate, as a dispersant, has been used to improve the dispersion of nanoparticles and suppressing formation of particle clusters to obtain stable suspensions.The thermal conductivity of ZnO nanofluids has been measured as a function of the volume fraction and temperature. The thermal conductivity of ZnO/EG and ZnO/G nanofluids increases nonlinearly up to 10.5% and 7.2%, respectively, as the volume fraction of nanoparticles increases up to 3 vol.%. The thermal conductivity of a ZnO nanofluid increases nonlinearly with increasing the temperature at a constant volume fraction of nanoparticles.For the first time, we have measured the viscosity and surface tension of ZnO nanofluids. The viscosity ratio of nanofluids increases with increasing concentration and decreasing the temperature. The surface tension ratio of suspensions containing solid particles increases with increasing the volume fraction of the solid nanoparticles.The experimental data for thermal conductivity and viscosity have been compared with some existing theoretical models.
    International Journal of Heat and Fluid Flow. 01/2010;
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    ABSTRACT: In this paper, we report structural, electrical, optical, and especially thermoelectrical characterization of iron (Fe) doped tin oxide films, which have been deposited by spray pyrolysis technique. The doping level has changed from 0 to 10 wt% in solution ([Fe]/[Sn] = 0-40 at% in solution). The thermoelectric response versus temperature difference has exhibited a nonlinear behavior, and the Seebeck coefficient has been calculated from its slope in temperature range of 300-500 K. The Hall effect and thermoelectric measurements have shown p-type conductivity in SnO(2):Fe films with [Fe]/[Sn] textgreater= 7.8 at%. In doping levels lower than 7.8 at%, SnO(2):Fe films have been n-type with a negative thermoelectric coefficient. The Seebeck coefficient for SnO(2):Fe films with 7.8 at% doping level has been obtained to be as high as + 1850 mu V/K. The analysis of as-deposited samples with thicknesses similar to 350 nm by X-ray diffraction (XRD) and scanning electron microscopy (SEM) has shown polycrystalline structure with clear characteristic peak of SnO(2) cassiterite phase in all films. The optical transparency (T%) of SnO(2):Fe films in visible spectra decreases from 90% to 75% and electrical resistivity (rho) increases from 1.2 x 10(-2) to 3 x 10(3) Omega cm for Fe-doping in the range 0-40 at%. (C) 2008 Elsevier Masson SAS. All rights reserved.
    Solid State Sciences. 01/2009; 11(1):233-239.
  • Spectrochimica Acta Part B-atomic Spectroscopy - SPECTROCHIM ACTA PT B-AT SPEC. 01/2009;
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    ABSTRACT: The band structure, the dielectric function, the reflectivity, the refractive index and the oscillator strength sum rule were calculated for pure In2O3 and alloyed In1.5T0.5O3 (where T represents Sc, Y, La and Ac) using density functional theory (DFT). The full potential linearized augmented plane wave (FP-LAPW) method was used with the local density approximation (LDA + U). Calculations of the optical spectra were performed for the energy range 0–30 eV. The calculated results indicate that the upper valance bands of In2O3 show a small dispersion and the value of the band gap increases for Sc and Y dopants and decreases for Ac and La dopants. The calculations indicate that there are two band gaps for In2O3. The first shows a strong optical absorption, as a direct band gap occurs from a 0.81 eV energy level below the top of valence band. The second shows a much weaker absorption from the top of the valence band to the bottom of the conduction band. The refractive index for In2O3 is 1.69 nm at 800 nm, near the visible region. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (b) 01/2009; 246(5):1072-1081. · 1.49 Impact Factor
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    ABSTRACT: Nano-crystalline SnO2 particles have been synthesized by sol–gel process using a simple starting hydro-alcoholic solution consisting of SnCl4, 5H2O and citric acid as complexing and ethylene glycol as polymerization agents. The structural properties of the prepared tin oxide nano-powders annealed at different temperatures (300–700 °C) have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. The XRD patterns show SnO2-cassiterite phase in the nano-powders, and size of crystals increases by increasing the annealing temperatures. The TEM images show nano-particles as clusters with size in the range of 5–25 nm. Electron diffraction pattern of nano-powders annealed at different temperatures shows a homogeneous distribution of spherical particles due to the effect of ethylene glycol as polymerizing agent in sol–gel process. The optical direct band gap values of SnO2 nano-particles were calculated to be about 4.05–4.11 eV in the temperature range 300–700 °C by optical absorption measurements. These values exibit nearly a 0.5 eV blue shift from that of bulk SnO2 (3.6 eV), which is related to size decrease of the particles and reaching to the quantum confinement limit of nano-particles.
    Physica B Condensed Matter 01/2008; 403:2431-2437. · 1.28 Impact Factor
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    ABSTRACT: The mechanistic aspects of a novel methodology for the electrochemical hydride generation (EcHG) of cadmium, entitled as the catholyte variation, have been studied. The hydrogen overvoltage of different cathode materials was determined in dilute electrolyte. The lead-tin alloy used as the cathode material for the EcHG of Cd had the highest hydrogen overpotential. In this technique, both electrolyte medium and cathode surface would change during electrolysis. The catholyte variation EcHG coupled with a flame heated quartz tube atomizer (QTA) atomic absorption spectrometer (AAS) produced peak-shaped transient signal of Cd. The analytical signal was significantly enhanced at neutralization time. The simultaneous production of lead and tin hydrides as well as the hydrogen at that time may speed up the desorption of cadmium species from the surface of the cathode. Also the high hydrogen overvoltage and the neutral medium aided the formation and separation of cadmium hydride molecules. The generated CdH2 vapour was kinetically stable.
    Analytica chimica acta 09/2006; 576(2):215-20. · 4.31 Impact Factor
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    ABSTRACT: An electrolytic hydride generation system for determination of another hydride forming element, cadmium, by catholyte variation electrochemical hydride generation (EcHG) atomic absorption spectrometry is described. A laboratory-made electrolytic cell with lead–tin alloy as cathode material is designed as electrolytic generator of molecular hydride. The influences of several parameters on the analytical signal have been evaluated using a Plackett–Burman experimental design. The significant parameters such as cathode surface area, electrolytic current, carrier gas flow rate and catholyte concentration have been optimized using univariate method. The analytical figures of merit of procedure developed were determined. The calibration curve was linear up to 20 ng ml−1of cadmium. The concentration detection limit (3σ, n = 8) of 0.2 ng ml−1 and repeatability (relative standard deviation, n = 7) of 3.1% were achieved at 10.0 ng ml−1. It was shown that interferences from major constituents at high concentrations were significant. The accuracy of method was verified using a real sample (spiked tap water) by standard addition calibration technique. Recovery of 104% was achieved for Cd in the spiked tap water sample.
    Analytica Chimica Acta. 01/2005;
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    ABSTRACT: A new flow injection method coupled to an electrochemical hydride generator with atomic absorption spectrometry was proposed for determination of cadmium. The influence of the experimental parameters such as cathode material, catholyte type, sample volume, catholyte flow rate, temperature of the atomizer, catholyte concentration, carrier gas flow rate, electrolytic current and cathode surface area on the analytical response was studied. Under the optimized conditions, the calibration curve was linear in the range of 2–50 ng mL− 1 of Cd. A concentration detection limit (3σb, n = 9) of 0.61 ng mL− 1 Cd and a relative standard deviation of 5.1% (RSD, n = 9) for 20 ng mL− 1 Cd were obtained. The potential interferences from various ions were also evaluated. The accuracy of the method was verified by the determination of cadmium in a certified reference material. The calculated concentration of Cd in CRM was found to be in good agreement with the certified value.
    Microchemical Journal 108:188–192. · 3.58 Impact Factor