Browsing by Author "Jokar, Effat"

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Characterization of three-dimensional reduced graphene oxide/copper oxide heterostructures for hydrogen sulfide gas sensing application
(2018-04-05)
Mirmotallebi, Mona
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Zad, Azam Iraji
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Hosseini, Zahra Sadat
;
Jokar, Effat
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應用化學系
Three-dimensional reduced graphene oxide (3D-rGO) structures decorated with CuO particles (GCu) are synthesized through a simple and scalable method for detection of hydrogen sulfide (H2S) gas. For characterization and investigation of porous structure various techniques were employed. Decorated 3D structures demonstrated higher sensitivity and selectivity in comparison to pure structure. Optimized structure for sensing was obtained through introducing different amounts of CuO. The GCu heterostructures containing 35 mu mol of CuO powder demonstrated reproducible response of about 30% to the concentration of 10 ppm at room temperature, while complete recovery was obtained through heating to 150 degrees C. Sensing behaviour of the samples to H2S gas was investigated at temperatures in the range of 25-150 degrees C and in different relative humidity levels from 3 to 80%. We discussed the sensing model based on the adsorption of H2S molecules on the additives, and electron injection to the sample, resulting in the electrical resistance enhancement. (C) 2018 Elsevier B.V. All rights reserved.
Inter- and Intragrain Inhomogeneity in 2D Perovskite Thin Films Revealed by Relative Grain Orientation Imaging Using Low-Frequency Polarized Raman Microspectroscopy
(2020-05-21)
Toda, Shogo
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Yanagita, Naoya
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Jokar, Effat
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Diau, Eric Wei-Guang
;
Shigeto, Shinsuke
Two-dimensional (2D) organic-inorganic hybrid lead halide perovskites make up an emerging class of semiconductor materials for optoelectronic applications such as solar cells. The grain structure of polycrystalline 2D perovskites is one of the key factors that dictate their functionality in the devices, but currently available methods for in situ, chemically specific characterization of 2D perovskite grains are scarce. Here we show that ultra-low-frequency polarized Raman microspectroscopy is a facile yet powerful tool for visualizing relative grain orientations within 2D perovskite thin films. We demonstrate this method on the simplest 2D perovskite, (CH3(CH2)(3)NH3)(2)PbI4. Hierarchical clustering and detailed band decomposition analysis of the low-frequency polarized Raman imaging data reveal not only relative grain orientations but also intragrain inhomogeneity. We envisage that with high chemical specificity, this method will find broad applications ranging from other 2D perovskites to perovskite-based optoelectronic devices.
New Insight into the Concept of Carbonization Degree in Synthesis of Carbon Dots to Achieve Facile Smartphone Based Sensing Platform
(2017-09-08)
Bagheri, Zeinab
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Ehtesabi, Hamide
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Rahmandoust, Moones
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Ahadian, Mohammad Mahdi
;
Hallaji, Zahra
Direct pyrolysis of citric acid (CA) has been proved to be a facile bottom-up technique for making pristine carbon dots (CD) with homogenous size distribution. However, limited reports are available on systematic optimization of carbonization degree. In this investigation, pyrolysis temperatures between 160 degrees C and 220 degrees C were studied, based on CA thermal decomposition path, using various heating durations. The effect of the formation of more carbonized carbon particles (MCCPs), as the major byproduct of this method, on photoluminescence properties of CDs was also considered. The NaOH amount that neutralizes the solution and the effect of dilution on the emission intensity, were introduced as simple and accessible factors for monitoring carbonization degree, and an estimate of MCCP/ CD ratio, respectively. The results show that the CDs fabricated at 160 degrees C, 50 minutes attain almost twice higher quantum yield (QY) of 29% than highest QY reported based on pyrolysis of CA. The so-prepared CDs can be employed as excellent candidates for turn-off sensing. As a proof of concept, detection limit of 50 nM for Hg2+ was achieved using a facile and inexpensive smartphone set-up that is able to quantify and compare fluorescent intensity in several samples simultaneously.