Browsing by Author "D.K. Dwivedi"

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Chitosan-based fluorescein isothiocyanate film as a highly efficient metal-free photocatalyst for solar-light-mediated direct C-H arylation
(John Wiley and Sons Ltd, 2021) Pooja Singh; Rajesh K. Yadav; Tae Wu Kim; Abhishek Kumar; D.K. Dwivedi
Development of ecofriendly and low-cost highly efficient photocatalysis is of importance in the field of chemical synthesis. Currently, various metals-based organic materials, metal oxide nanoparticles, and metal nanomaterials have been urbanized as light harvesting photocatalysts for direct carbon (C)-hydrogen (H) arylation of aryl diazonium salts and heteroarenes. These light harvesting photocatalysts, however, still suffer from poor stability, reusability problem, high cost, or less selectivity. Herein, we report the fabrication of a novel chitosan-based fluorescein isothiocyanate (CBFITC) film photocatalyst and demonstrate its tremendous photocatalytic activity, high yields (97 ± 0.015%), selectivity (99%), and reusability to catalyze the metal free solar-light-mediated direct CH arylation of aryl diazonium salts and heteroarenes at ambient temperature. Moreover, CBFITC film photocatalyst can be recycled more than five times without loss of activity, verifying this photocatalyst excellent light harvesting ability and stability. The present approach to fabricate a metal-free film photocatalyst with the suitable band gap will be a new platform for efficient photocatalytic reaction and provide a new insight into the solar chemical synthesis. © 2020 John Wiley & Sons Ltd
Crystallization kinetics and Avrami index of Sb-doped Se–Te–Sn chalcogenide glasses
(Taylor and Francis Ltd., 2018) D.K. Dwivedi; Vandita Rao; N. Mehta; N. Chandel
Bulk amorphous samples of Sb-substituted Se78 − xTe20Sn2Sbx (0 < x < 6) have been prepared using melt quench technique. The structure of Se78− xTe20Sn2Sbx (x = 0, 2, 4, 6) glassy alloys has been investigated using X-ray diffraction technique. Calorimetric studies of the prepared samples have been performed under non-isothermal conditions using differential scanning calorimetry (DSC) and glass transition temperature as well as crystallization temperature has been evaluated using DSC scans. The activation energy of crystallization kinetics (Ec) has been determined using model-free approaches such as Kissinger, Ozawa, Tang and Starink methods. The Avrami index (n) and frequency factor (Ko) have been calculated by Matusita and Augis–Benett method. © 2018 Informa UK Limited, trading as Taylor & Francis Group.
Dielectric relaxation in glassy Se90Cd6In4
(Institution of Engineering and Technology, 2016) N. Shukla; N. Mehta; D.K. Dwivedi
In the present Letter frequency (5 × 102 Hz-1 × 105 Hz) and temperature (308-333 K) dependence of dielectric parameter of Se90Cd6In4 glassy alloy has been examined. Conventional melt quench technique has been applied to prepare Se90Cd6In4 glassy alloy. It is observed that dielectric constant (ϵ') and dielectric loss factor (ϵ") change with frequency and temperature. The dielectric loss data has been utilised to determine the barrier height Wm, which is in accordance with the Elliott's theory of hoping of charge carriers over potential barrier between charge defect states in case of chalcogenide glasses. © The Institution of Engineering and Technology 2016.
Effect of antimony on glass transition and thermal stability of Se78−xTe18Sn2Sbx (x = 0, 2, 4 and 6 at.%) multicomponent glassy alloys
(Springer Netherlands, 2018) Vandita Rao; N. Chandel; N. Mehta; D.K. Dwivedi
Multicomponent glassy alloys Se78−xTe18Sn2Sbx (x = 0, 2, 4 and 6) have been synthesized using melt quench technique. The prepared samples have been characterized by X-ray diffraction technique and differential scanning calorimetry (DSC). Glass transition kinetics of Se78−xTe18Sn2Sbx (x = 0, 2, 4 and 6 at.%) glassy alloys has been examined using DSC. DSC runs have been recorded at different heating rates (5, 10, 15 and 20 K min−1) for each sample under investigation. Heating rate dependence of glass transition temperature (Tg) has been studied using Lasocka empirical relation. The activation energy of glass transition has been evaluated using Kissinger and Moynihan’s relation. The effect of antimony concentration on glass transition temperature and activation energy has been investigated in the prepared samples. Glass-forming ability and thermal stability of Se78−xTe18Sn2Sbx (x = 0, 2, 4 and 6) glassy alloys have been monitored through the evaluation of thermal stability using Dietzal relation, Hurby parameter, and Saad and Poulin parameter. The above-mentioned parameters are found to be compositionally dependent, which indicates that among the studied glass samples the stability is maximum for Sb at 2% content. © 2018, Akadémiai Kiadó, Budapest, Hungary.
Effect of Sb incorporation on thermo-mechanical properties of amorphous Se-Te-Sn alloys
(Institute of Physics Publishing, 2018) Vandita Rao; N. Mehta; Amit Kumar; D.K. Dwivedi
In present paper, bulk Se78-xTe20Sn2Sbx (x = 0, 2, 4 & 6) amorphous alloys were developed by melt quench technique. The synthesized samples were characterized by means of XRD and DSC techniques for structural and phase transformation analysis respectively. Hardness behavior was investigated by calculating Vickers hardness number and other thermo-mechanical parameters to examine the effect of Sb in Se-Te-Sn parent alloy. © 2018 IOP Publishing Ltd.
Experimental studies of dielectric relaxation and thermally activated a.c. conduction in Se90Cd10−xSbx (2 ≤ x ≤ 8) chalcogenide glassy alloys using correlated barrier hopping model
(Springer New York LLC, 2016) Nitesh Shukla; N. Mehta; D.K. Dwivedi
Se90Cd10−xSbx (x = 2, 4, 6, 8) chalcogenide semiconducting alloys were prepared by melt quench technique. The prepared glassy alloys have been characterized by technique such as SEM and energy dispersive X-ray. Dielectric properties and a.c. conductivity of prepared glassy alloys have been measured in the frequency range 5 × 102–1 × 105 Hz and in temperature range 303–328 K. The analysis of experimental results indicate that dielectric constant (ε′), dielectric loss factor (ε″) and a.c. conductivity σac(ω) are temperature, frequency and concentration dependent. The frequency dependence of σac(ω) is found to be linear and obey the power law ωs where s ≤ 1. A strong dependence of σac(ω) and exponent s on temperature can be explained on the basis of correlated barrier hopping model. The maximum barrier height Wm has been calculated and results are found to be in good agreement with theory of hopping of charge carrier over potential barrier as per the theory proposed by Elliot for chalcogenide semiconductors. © 2016, Springer Science+Business Media New York.
Fabrication of Graphitic Carbon Nitride-Based Film: An Emerged Highly Efficient Catalyst for Direct C—H Arylation under Solar Light
(Shanghai Institute of Organic Chemistry, 2021) Surabhi Chaubey; Rajesh K. Yadav; Tae Wu Kim; Tara Chand Yadav; Abhishek Kumar; D.K. Dwivedi; B.K. Pandey; Atul P. Singh
Photoredox C—H bond formation can proceed in aerobic environment under solar light and has therefore become attractive. Nowadays, different types of expensive novel metal complexes and nanomaterials have been urbanized as photocatalysts for direct C—H bond formation in between derivatives of heteroarenes (HAs) and aryl diazonium salts. These photocatalysts, however, still suffer from poor stability, high cost, and decay. Herein, a graphitic carbon nitride-based fluorescein isothiocyanate (g-C3N4–FITC) film photocatalyst has been reported, which shows excellent light harvesting ability, and band gap suitability to catalyze the metal free direct C—H arylation of HAs under solar light at ambient temperature. Moreover, the g-C3N4–FITC film photocatalyst can be reused four times without significant loss of activity, confirming the excellent photocatalytic stability. The current strategy to construct a g-C3N4–FITC film photocatalyst for direct C—H arylation opens a new path towards replacing metal-based catalysts in fine chemical synthesis. © 2021 SIOC, CAS, Shanghai and Wiley-VCH GmbH
Investigation of Some Physico-Chemical Properties in Multi-Component Se–Te–Sn–Sb (0 ≤ x ≤ 6) Quaternary Chalcogenide Glassy System
(Pleiades Publishing, 2018) Vandita Rao; Pooja Lohia; N. Mehta; D.K. Dwivedi
Abstract: In the present work we report physico-chemical properties in novel Se78 – xTe20Sn2Sbx (x = 0, 2, 4 and 6) glassy system prepared by melt quench technique. Various physico-chemical properties such as co-ordination number, lone pair of electrons, number of constraints, density, molar volume, compactness, mean bond energy, cohesive energy, glass transition temperature and covalence character has been estimated. The compositional dependence of aforesaid physico-chemical properties has been investigated. It has been observed that average number of constraints, mean bond energy, glass transition temperature are found to increase where as number of lone pair of electrons and electro negativity decreases with increases of Sb content in the Se78 – xTe20Sn2Sbx (x = 0, 2, 4 and 6) glassy alloys. © 2018, Pleiades Publishing, Ltd.
Investigations of crystallization kinetics of Se 82-x Te 18 Sb x (x =0, 4, 8, 12) glassy alloys by iso-conversional approach
(Taylor and Francis Ltd., 2019) Vandita Rao; N. Mehta; D.K. Dwivedi
At different heating rates, the crystallization temperature (T c ) are obtained from the non-isothermal differential scanning calorimetry (DSC) measurements of bulk Se 82–x Te 18 Sb x (x = 0, 4, 8 and 12) chalcogenide glasses prepared by melt quench technique. It was observed that the crystallization temperatures increase with increasing heating rates and also by increasing Sb concentration in Se–Te system. The activation energy of crystallization (E c ), the Avrami exponent (n) and rate of crystallization (K p ) have been determined from the different models. Glassy nature of as prepared samples has been confirmed using DSC techniques. © 2017, © 2017 Informa UK Limited, trading as Taylor & Francis Group.
Revolutionizing regeneration of NADH and deoxygenation of sulfide: Harnessing visible light with SDG@TPP composites for powerful synthetic applications
(Elsevier Ltd, 2023) Lovely Kumari; Satyam Singh; Rajesh K. Yadav; Rehana Shahin; Tae Wu Kim; Suresh K. Pandey; Dhanesh Tiwari; Alok Kumar Singh; Satyanath; D.K. Dwivedi; Navneet Kumar Gupta
Aqueous ascorbic acid splitting through photocatalysis is a potential method for turning solar energy into value-added compounds. As a result, converting solar light into green solar fine chemicals in an ecologically responsible and cost-effective manner remains a difficult issue. The solvothermal approach was used to effectively construct an SDG@TPP composite photocatalyst.To that end, we present here the synthesis and development of a sulfur-doped graphene (SDG)-based visible light active composite photocatalyst (SDG@TPP), in which SDG interacts with TPP (tetraphenyl porphyrin) through - stacking. Due to its high molar extinction coefficient and delayed recombination features, the newly manufactured SDG@TPP photocatalyst acts in a highly effective way, resulting in higher NADH regeneration (66.1 %) and sulfoxide deoxygenation than SDG photocatalyst. More importantly, a little quantity of TPP on the surface of SDG can efficiently stimulate photoelectron injection and improved photocatalytic activity. This research should shed light on how to create metal-free SDG@TPP composites with good solar energy conversion. © 2023
Solar light-driven photocatalyst-enzyme attached artificial photosynthetic system for regeneration and production of 1,4-NADH and L-glutamate
(Blackwell Publishing Ltd, 2021) Chandani Singh; Abhishek Kumar; Rajesh K. Yadav; Vitthal L. Gole; D.K. Dwivedi
In artificial photosynthesis process the photocatalyst-enzyme attached system is a best strategy to utilize solar energy for solar chemical/fuels production. Herein, we prepared a solar light active graphene-based photocatalyst received by the covalent attachment of 9-aminoanthracene (AA) chromophore with chemically converted graphene (CCG) for highly efficient 1,4-NADH regeneration (79.9 %) and conversion of α-ketoglutarate (α-KG) in to L-glutamate (L-GM) (88.3 %) in 2 hrs. The present result is a benchmark example of highly selective solar light active enzyme based artificial photosynthetic system for selective formation of L-GM from α-KG. © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim