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141 results on '"Tayyebi, Ahmad"'

26. Immobilizing Low‐Cost Metal Nitrides in Electrochemically Reconstructed Platinum Group Metal (PGM)‐Free Oxy‐(Hydroxides) Surface for Exceptional OER Kinetics in Anion Exchange Membrane Water Electrolysis (Adv. Energy Mater. 6/2023)

Author

Thangavel, Pandiarajan, primary, Lee, Hojeong, additional, Kong, Tae‐Hoon, additional, Kwon, Seontaek, additional, Tayyebi, Ahmad, additional, Lee, Ji‐hoon, additional, Choi, Sung Mook, additional, and Kwon, Youngkook, additional

Published
2023
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31. Photoelectrochemical Epoxidation of Cyclohexene on an α-Fe2O3Photoanode Using Water as the Oxygen Source

Author

Tayebi, Meysam, Masoumi, Zohreh, Tayyebi, Ahmad, Kim, Jun-Hwan, Lee, Hyungwoo, Seo, Bongkuk, Lim, Choong-Sun, and Kim, Hyeon-Gook

Abstract

This study developed a safe and sustainable route for the epoxidation of cyclohexene using water as the source of oxygen at room temperature and ambient pressure. Here, we optimized the cyclohexene concentration, volume of solvent/water (CH3CN, H2O), time, and potential on the photoelectrochemical (PEC) cyclohexene oxidation reaction of the α-Fe2O3photoanode. The α-Fe2O3photoanode epoxidized cyclohexene to cyclohexene oxide with a 72.4 ± 3.6% yield and a 35.2 ± 1.6% Faradaic efficiency of 0.37 V vs Fc/Fc+(0.8 VAg/AgCl) under 100 mW cm–2. Furthermore, the irradiation of light (PEC) decreased the applied voltage of the electrochemical cell oxidation process by 0.47 V. This work supplies an energy-saving and environment-benign approach for producing value-added chemicals coupled with solar fuel generation. Epoxidation with green solvents via PEC methods has a high potential for different oxidation reactions of value-added and fine chemicals.

Published
2023
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34. Supercritical Synthesis and Characterization of Graphene-PbS Quantum Dots Composite with Enhanced Photovoltaic Properties

Author

Shafiekhani, Azizollah, Tayyebi, Ahmad, Tavakoli, Mohammad Mahdi, Outokesh, Mohammad, and Abdolreza (Arash) Simchi

Abstract

Lead sulfide quantum dots (PbS QDs) were decorated onto a graphene surface in a semi-core-shell structure using supercritical ethanol. The temperature of ethanol played significant role in controlling size and agglomeration of QDs as well as the extent of reduction of graphene. Average size of the QDs was estimated by transmission electron microscopy to be around 3.96 nm and by quantum models to be about 4.34 nm. PbS QDs prepared at 330 °C were of high purity, and the yield was 99%. Instrumental and chemical analyses demonstrated formation of a strong bond between PbS QDs and graphene, through a Pb-O-C bridge. UV and photoluminescence measurements along with theoretical considerations revealed that integration of PbS QDs with graphene results in efficient separation of the electron-hole, thus enhancing photo → electric energy conversion. This outcome was further evidenced by comparison of performance of PbS/G in a solar cell, with the performance of pristine PbS QDs.

Published
2020
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45. Synthesis of “L-cysteine–graphene oxide” hybrid by new methods and elucidation of its uptake properties for Hg(II) ion.

Author

Daneshmand, Maryam, Outokesh, Mohammad, Akbari, Ahmad, Kosari, Mohammadreza, and Tayyebi, Ahmad

Subjects
GRAPHENE, SORBENTS, CHEMICAL reactions, ACIDIFICATION, ACIDOLYSIS
Abstract

This study introduces two new, simple, and scalable methods for synthesis of “cysteine–graphene oxide” hybrid, namely nucleophilic and covalent methods. Produced adsorbents could uptake 500 and 600 mg Hg2+/g, respectively, which are larger than capacities of most of the commercial adsorbents. By means of different instrumental techniques, chemical structures of the obtained graphene products were disclosed, and two pertinent mechanisms for their formations were suggested. Time for attaining uptake equilibrium for nucleophilic/covalent samples was 30 min/150 min, and kinetics was controlled by liquid film resistance/chemical reaction mechanisms, respectively. High selectivity and good regenerability are other key features of the prepared adsorbents. [ABSTRACT FROM PUBLISHER]

Published
2018
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47. Physicochemical properties of hybrid graphene-lead sulfide quantum dots prepared by supercritical ethanol

Author

Tavakoli, Mohammadmahdi, Tayyebi, Ahmad, Simchi, Abdolreza, Aashuri, Hossein, Outokesh, Mohmmad, Fan, Zhiyong, Tavakoli, Mohammadmahdi, Tayyebi, Ahmad, Simchi, Abdolreza, Aashuri, Hossein, Outokesh, Mohmmad, and Fan, Zhiyong

Abstract

Recently, hybrid graphene–quantum dot systems have attracted increasing attention for the next-generation optoelectronic devices such as ultrafast photo-detectors and solar energy harvesting. In this paper, a novel, one-step, reproducible, and solution-processed method is introduced to prepare hybrid graphene–PbS colloids by employing supercritical ethanol. In the hybrid nanocomposite, PbS quantum dots (~3 nm) are decorated on the reduced graphene oxide (rGO) nanosheets (~1 nm thickness and less than 1 micron lengths). By employing X-ray photoelectron and Raman and infrared spectroscopy techniques, it is shown that the rGO nanosheets are bonded to PbS nanocrystals through carboxylic bonds. Passivation of {111} planes of PbS quantum dots with rGO nanosheets is demonstrated by employing density function theory. Quenching of the photoluminescence emission of PbS nanocrystals through coupling with graphene sheets is also shown. In order to illustrate that the developed preparation method does not impair the quantum efficiency of the PbS nanocrystals, the photovoltaic efficiency of solar cell device is reported and compared with oleic acid-capped PbS colloidal quantum dot solar cells. By employing the “Hall effect” measurement, it is shown that the carrier mobility is significantly increased (by two orders of magnitudes) in the presence of graphene nanosheets.

Published
2015

48. Supercritical Synthesis and Characterization of Graphene-PbS Quantum Dots Composite with Enhanced Photovoltaic Properties

Author

Tayyebi, Ahmad, Tavakoli, Mohammad Mahdi, Outokesh, Mohammad, Shafiekhani, Azizollah, Simchi, Abdolreza (Arash), Tayyebi, Ahmad, Tavakoli, Mohammad Mahdi, Outokesh, Mohammad, Shafiekhani, Azizollah, and Simchi, Abdolreza (Arash)

Abstract

Lead sulfide quantum dots (PbS QDs) were decorated onto a graphene surface in a semi-core shell Structure. using supercritical ethanol. The temperature of ethanol played significant role in controlling size and agglomeration Of QDs as well as the extent of reduction of graphene. Average size Of the QDS was estimated by transmission electron microscopy to be around 3.96 nm and by quantum models to be about 4.34 mu. PbS QDs prepared at 330 degrees C were of high purity,. and the yield was 99%. Instrumental- and chemical analyses demonstrated formation of a strong bond betv between PbS QDs and, graphene, through a Pb-O-C bridge. tIV and photoluminescence measurements along with -theoretical considerations revealed that integration of PbS QDs with grapherie'results in efficient separation of the electron hole, thus enhancing photo electric energy conversion. This Outcome was further evidenced by comparison of performance of PbS/G in a Solar cell, with the performance of pristine PbS QDs.

Published
2015

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