BHU Institutional Repository :: Browsing by Author "Yadav, Mamta"

Browsing by Author "Yadav, Mamta"

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Co(II) Porphyrin-MWCNT Nanoconjugate as an Efficient and Durable Electrocatalyst for Oxygen Reduction Reaction
(American Chemical Society, 2023) Tasleem, Mohammad; Yadav, Mamta; Ganesan, Vellaichamy; Sankar, Muniappan
Recently, researchers are seeking alternatives to replace Pt-based oxygen reduction reaction (ORR) catalysts used in fuel cells due to their high cost and certain stability and selectivity issues. For this purpose, we have synthesized a nanoconjugate, cobalt(II) porphyrin (5,10,15-triphenyl-20-(4-aminophenyl)porphyrinatocobalt(II), CoTPP-NH2) covalently attached to the acid-functionalized multiwalled carbon nanotubes and characterized by various techniques including UV-vis spectroscopy, FTIR, TGA, FESEM, TEM, and Raman spectroscopy. The oxygen reduction performance of the nanoconjugate is checked in basic medium. The ORR onset potential of the nanoconjugate-modified electrode is nearly the same as that of the state-of-the-art platinum-carbon electrode and stable for more than 3000 CV cycles with a 20 mV difference in the onset potential before and after the 3000 CV cycles. The above extrapolations reveal that the nanoconjugate has efficient performance for the ORR in basic medium. � 2023 American Chemical Society.
Coarse-grained Hamiltonian and effective one component theory of colloidal suspensions
(Elsevier B.V., 2022) Yadav, Mamta; Singh, Yashwant
We develop a theory to trace out the solvent degrees of freedom from the grand partition function of colloid-solvent mixtures. Our approach to coarse-graining is based on density functional formalism of density profile and the grand thermodynamic potential of solvent. The solvent-induced interaction which is many-body in character is expressed in terms of two functionals; one that couples the solvent to the colloidal density distribution and the second represents the density�density correlation function of the solvent. The nature, strength, and range of the potential depend on these functionals and therefore on the thermodynamic state of the solvent. The solvent-induced contribution to free energy functional is also derived. A self-consistent procedure is developed to calculate the effective potential between colloidal particles, colloid-solvent, and colloid-colloid correlation functions. The theory is used to investigate both additive and nonadditive binary hard-sphere mixtures. Results are reported for the two systems for several values of packing fractions ?b and ?s and particles diameter ratio [Formula presented] where symbols b and s refer to colloid and solvent, respectively. Several interesting features are found: The short-range attractive part of the potential shows non-monotonic dependence on ?b; when ?b is increased from zero, initially the potential becomes more attractive but beyond a certain value of ?b that depends on q, the attraction starts weakening. The repulsive peaks formed at [Formula presented] where R is a distance between centers of colloidal particles expressed in units of ?b and n is an integer, become stronger on increasing ?b. These results show that many-body contribution to the effective potential depends in a subtle way on packing fractions ?b,?s, size ratio q, and on nature of the interaction model and makes a non-negligible contribution to the coarse-grained Hamiltonian. � 2022 Elsevier B.V.
Cobalt oxide decorated zirconium oxide immobilized multiwalled carbon nanotubes as scaffolds for supercapacitors and the CO2 reduction reaction
(Elsevier Ltd, 2021) Yadav, Dharmendra Kumar; Omar, Fatin Saiha; Yadav, Mamta; Ho, Xian Liang; Tessensohn, Malcolm E.; Ramesh, K.; Ramesh, S.; Webster, Richard D.; Ganesan, Vellaichamy
In the field of renewable energy research, the development of materials for use as highly efficient supercapacitors and designing electrocatalytic materials for the reduction of CO2 to produce useful chemicals are envisaged as two important sustainable routes. However, developing stable, selective, and efficient materials for these purposes is a highly challenging task requiring numerous design attempts. In this work, cobalt oxide decorated zirconium oxide immobilized multiwalled carbon nanotubes (MWCNTs-ZrO2-Co3O4) is reported as a catalyst and battery electrode material for the electrochemical reduction of CO2 and supercapacitor applications, respectively. The MWCNTs-ZrO2-Co3O4 electrode assembled for the supercapacitor shows a specific capacity of 258.9 C/g at a current density of 1.0 A/g. The MWCNTs-ZrO2-Co3O4 and activated carbon (AC) based asymmetric supercapacitor (MWCNTs-ZrO2-Co3O4//AC) displays specific energy in the range of 8.9 Wh/kg (at 837.2 W/kg) to 6.23 Wh/kg (at 1674.4 W/kg). The device, MWCNTs-ZrO2-Co3O4//AC displays high cycling stability with 97% capacity retention after 7000 cycles at a current density of 1.0 A/g. In the electrocatalytic reduction of CO2, the MWCNTs-ZrO2-Co3O4 scaffold produces selectively formic acid during the electrolysis at -1.1 V (vs. Ag/AgCl) in 0.1 M aqueous KCl solution. These results indicate that MWCNTs-ZrO2-Co3O4 can serve as a bifunctional material. � 2021 Elsevier Ltd
Cox(VO)yOzNanocrystal-Integrated Covalent Organic Polymers as a Highly Active and Durable Catalyst for Electrochemical Water Oxidation: An Untold Role of the VO2+/VO2+Redox Couple
(American Chemical Society, 2022) Singh, Devesh Kumar; Yadav, Mamta; Ganesan, Vellaichamy; Bhobe, Preeti A.
Water oxidation is a crucial half-cell reaction in water splitting, metal-air batteries, and CO2reduction. In this work, cobalt- and vanadium-containing mixed oxides [Cox(VO)yOz] are synthesized, and further, a unique composite of mixed oxide nanocrystals with a covalent organic polymer [Cox(VO)yOz@COP] is prepared. A high increase in activity and stability is exhibited by the Cox(VO)yOz@COP in comparison to its independent oxide counterparts. Higher activity is attributed to the presence of the VO2+/VO2+couple, which helps in the facile oxidation of CoOOH to CoO2and enhances the oxygen evolution reaction activity. The optimized composite material Cox(VO)yOz@COP(1:1) shows a low overpotential of 265 and 298 mV for the current densities of 10 and 30 mA cm-2, respectively. The composite shows a low Tafel slope (43 mV/dec), high turnover frequency (3.6 s-1at 1.58 V), and high durability (tested for 14 h continuous oxygen evolution at 1.53 and 1.60 V). The durability is further supported by (i) chronopotentiometry (10,000 s at 25 mA cm-2), (ii) negligible variation in the linear sweep voltammetry responses and electrochemically active surface area values before and after 1000 cyclic voltammetry cycles, (iii) negligible dissolution of cobalt during catalysis observed from inductively coupled plasma mass spectroscopy of the electrolyte, and (iv) insignificant change in the catalyst surface composition observed from post-catalysis X-ray photoelectron spectroscopy. To the best of our knowledge, this Cox(VO)yOz@COP(1:1) material shows a higher activity in comparison to previously reported crystalline/amorphous cobalt-vanadium oxides. In addition, the increase in activity and stability from bare oxides to composite suggests that the COP shall work as a reliable catalytic support for future applications. � 2022 American Chemical Society. All rights reserved.
Design and development of a multiwalled carbon nanotubes-based copper (II) Schiff base complex for the facile non-enzymatic electrochemical sensing of glucose
(Springer, 2023) Gupta, Rashmi; Yadav, Mamta; Singh, Smita; Ganesan, Vellaichamy; Singh, Bachcha
A new bifunctional nanomaterial, [SBCu(II)Hyd]-MWCNTs, exhibiting exotic electrical and magnetic properties has been synthesized via chemical modification of MWCNT-COOH. Double probe DC electrical conductivity, CV and EIS studies show better conductivity of the material than that of MWCNT-COOH. With higher saturation and remanent magnetization, as well as coercivity, [SBCu(II)Hyd]-MWCNTs showed better ferromagnetic characteristics. Mott�Schottky electrochemical analysis was carried out to explore capacitive and dielectric properties. The enhancement in electrical conductivity of [SBCu(II)Hyd]-MWCNTs is also confirmed by optical and electrochemical band gaps studies. Subsequently, this material has been utilized to fabricate an electrochemical sensor by coating it over glassy carbon electrode for the determination of glucose. The corresponding sensitivity and limit of detection values are calculated to be 1.1 �A �M?1�cm?2 and 0.09��M, respectively. Graphical Abstract: [Figure not available: see fulltext.] � 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Enhanced Four-Electron Selective Oxygen Reduction Reaction at Carbon-Nanotube-Supported Sulfonic-Acid-Functionalized Copper Phthalocyanine
(John Wiley and Sons Inc, 2023) Yadav, Mamta; Kumar Singh, Devesh; Kumar Yadav, Dharmendra; Kumar Sonkar, Piyush; Gupta, Rupali; Ganesan, Vellaichamy
In the present work, the oxygen reduction reaction (ORR) is explored in an acidic medium with two different catalytic supports (multi-walled carbon nanotubes (MWCNTs) and nitrogen-doped multi-walled carbon nanotubes (NMWCNTs)) and two different catalysts (copper phthalocyanine (CuPc) and sulfonic acid functionalized CuPc (CuPc-SO3?)). The composite, NMWCNTs-CuPc-SO3? exhibits high ORR activity (assessed based on the onset potential (0.57 V vs. reversible hydrogen electrode) and Tafel slope) in comparison to the other composites. Rotating ring disc electrode (RRDE) studies demonstrate a highly selective four-electron ORR (less than 2.5 % H2O2 formation) at the NMWCNTs-CuPc-SO3?. The synergistic effect of the catalyst support (NMWCNTs) and sulfonic acid functionalization of the catalyst (in CuPc-SO3?) increase the efficiency and selectivity of the ORR at the NMWCNTs-CuPc-SO3?. The catalyst activity of NMWCNTs-CuPc-SO3? has been compared with many reported materials and found to be better than several catalysts. NMWCNTs-CuPc-SO3? shows high tolerance for methanol and very small deviation in the onset potential (10 mV) between the linear sweep voltammetry responses recorded before and after 3000 cyclic voltammetry cycles, demonstrating exceptional durability. The high durability is attributed to the stabilization of CuPc-SO3? by the additional coordination with nitrogen (Cu-Nx) present on the surface of NMWCNTs. � 2023 Wiley-VCH GmbH.
Functionalization of carbon-based materials for the electrochemical sensing applications
(Nova Science Publishers, Inc., 2021) Yadav, Mamta; Singh, Devesh Kumar; Ganesan, Vellaichamy; Ramaraj, Ramasamy
Carbon-based materials are group of materials in which carbon forms covalent bonds with other carbon atoms or with other elements (metal or non-metal) that leads to the formation of variety of materials. Carbon-based materials when coated on electrode surfaces, lead to the enhancement of electroactive surface area, electron transport properties, and promote adsorption of molecules which are advantageous for the electrochemical sensors. Depending on their hybridization (sp, sp2, and sp3) and geometrical structure (0D, 1D, 2D, and 3D), carbon-based materials exist in multiforms like carbon nanodiamonds, fullerenes, graphene, carbon nanotubes, carbon nanodots, and carbon nanofibers. The functionalization of carbon-based materials is another important factor for selective sensing which leads to the change in the surface chemistry that optimizes the interaction of the carbon surface with the exterior domain. Numerous recent electrochemical sensors have been reported on the functionalization of carbon-based materials. Mesoporous carbon nitride (MCN) is another emerging class of carbon material having exchangeable N-H groups which makes it a potential material for sensing applications. The suitability of carbon materials (including MCN) in sensors is further supported by their biocompatibility, high stability, tunable electronic structure, and cost-effective synthesis. In addition to the above advantages, carbon materials are liable for easy chemical modification through heteroatom doping or adsorption of metal and/or organic species for analyte sensing. In this chapter, the role of the functionalization of carbon-based materials and their exploitation in electrochemical sensing will be clarified. � 2021 by Nova Science Publishers, Inc. All rights reserved.
Mesoporous carbon nitride supported 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine cobalt(ii) as a selective and durable electrocatalyst for the production of hydrogen peroxideviatwo-electron oxygen reduction
(Royal Society of Chemistry, 2021) Singh, Devesh Kumar; Ganesan, Vellaichamy; Yadav, Dharmendra Kumar; Yadav, Mamta; Sonkar, Piyush Kumar; Gupta, Rupali
Mesoporous carbon nitride (MCN) is synthesized using a mesoporous silica material (MCM-41) as a sacrificial template. 5,10,15,20-Tetrakis(4-methoxyphenyl)-21H,23H-porphine cobalt(ii) (cobalt tetramethoxyphenylporphyrin, CoTMPP), which consists of methoxy groups as the electron-rich center is integrated with MCN and the resulting composite material (CoTMPP@MCN) without any further heat treatment is used for the electrocatalytic reduction of oxygen. CoTMPP@MCN shows a higher onset potential (0.65 and 0.84 V, respectively, in 0.1 M HClO4and 0.1 M KOH) for the oxygen reduction reaction (ORR) than the bare MCN (0.34 and 0.60 V, respectively, in 0.1 M HClO4and 0.1 M KOH). The ORR onset potential exhibited by CoTMPP@MCN is comparable to several non-pyrolyzed mono-nuclear metal porphyrin integrated on carbon-based supports in both acidic and basic media. Kinetic measurements of CoTMPP@MCN show high selectivity for two-electron oxygen reduction to H2O2in both media. The H2O2yield in terms of faradaic efficiency is measured to be 87.6 and 89.0%, respectively, in 0.1 M HClO4and 0.1 M KOH. CoTMPP@MCN exhibits amazingly high durability (minute changes in the onset potential and current density at high reduction potentials after 3000 CV cycles) facilitated by the surface coordination of CoTMPP through the nitrogen present on the MCN surface. Being highly selective and outstandingly durable, CoTMPP@MCN fulfills all necessary requirements for an economically efficient electrocatalyst for industrial hydrogen peroxide synthesis and related commercial applications. � The Royal Society of Chemistry 2020.
Nafion-multi-walled Carbon Nanotubes Supported Tris(bipyridyl)iron(II) for Nicotine Detection
(John Wiley and Sons Inc, 2023) Tiwari, Ananya; Yadav, Mamta; Kumar Singh, Devesh; Ganesan, Vellaichamy
This work reports an electrochemical sensing framework for nicotine determination based on glassy carbon electrode (GC) immobilized with Fe(bpy)32+ (where bpy is 2,2�-bipyridyl) supported by Nafion and multi-walled carbon nanotubes (Nf-MWCNTs). Fe(bpy)32+ immobilized Nf-MWCNTs modified GC (GC/Nf-MWCNTs/Fe(bpy)32+) manifests stable redox peaks, characteristics of Fe(bpy)32+. The GC/Nf-MWCNTs/Fe(bpy)32+ exhibits effective electrochemical oxidation of nicotine, diminishing the overpotential relative to GC/Nf-MWCNTs. The limit of detection is 0.1 ?M (experimentally observed) with two different linear calibration ranges between 0.1 to 600 ?M and 600 to 3000 ?M. Electrocatalytic responses observed at GC/Nf-MWCNTs/Fe(bpy)32+ indicate superior performance for nicotine determination with acceptable selectivity, stability, and reproducibility. Additionally, the nicotine present in real samples such as beedi and tobacco are also analyzed with satisfactory recovery percentages. � 2022 Wiley-VCH GmbH.
One step synthesis of a bimetallic (Ni and Co) metal-organic framework for the efficient electrocatalytic oxidation of water and hydrazine
(Royal Society of Chemistry, 2022) Singh, Smita; Yadav, Mamta; Singh, Devesh Kumar; Yadav, Dharmendra Kumar; Sonkar, Piyush Kumar; Ganesan, Vellaichamy
A series of metal-organic frameworks (MOFs) with varying Ni : Co ratios are synthesized by an easy one-step solvothermal method using trimesic acid as an organic linker. Physicochemical characterization of the synthesized MOFs was done by high-resolution transmission electron microscopy, energy dispersive X-Ray, powder X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis, which depicts that the monometallic and bimetallic MOFs have a similar crystal structure. Among the synthesized MOFs, NiCo-MOF (1 : 1) (where the 1 : 1 ratio indicates Ni : Co ratio) exhibits efficient bifunctional electrocatalytic properties, i.e. it electrocatalytically oxidizes water and hydrazine (HZ). Electrocatalytic water oxidation leading to oxygen evolution can be exploited in the production of green hydrogen. NiCo-MOF (1 : 1) exhibits a low overpotential of 330 mV at a current density of 10 mA cm?2, a low Tafel slope of 32 mV dec?1, and high stability for water oxidation. Electrocatalytic oxidation of HZ leads to its sensitive amperometric determination in real samples. For the electrochemical detection of HZ, NiCo-MOF (1 : 1) displays a low limit of detection (1.1 ?M), broad linear range (1-2000 ?M) and high selectivity and stability. Thus, the present results demonstrate a new scheme to fabricate an economical and high-performance oxygen evolution catalyst and HZ sensor. � 2022 The Royal Society of Chemistry.
Phenosafranine encapsulated mesoporous silica as efficient electrocatalyst for Cr(VI) reduction and its subsequent sensitive determination
(Elsevier Inc., 2023) Gupta, Rupali; Ganesan, Vellaichamy; Sonkar, Piyush Kumar; Yadav, Dharmendra Kumar; Yadav, Mamta
This work presents an easy, highly specific, and sensitive route for the electrochemical reduction of Cr(VI) by phenosafranine (PSF+) integrated sulfonic acid functionalized mesoporous silica microspheres (MS-SO3?), denoted as PSF+-MS-SO3?. The synthesized material is characterized using various spectroscopic and microscopic methods. The glassy carbon electrode (GCE) is modified with this material (represented as GCE/PSF+-MS-SO3?) and employed for electroanalytical applications. The electrochemical characteristics of PSF+-MS-SO3? are established by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Further, it is exploited for the electrocatalytic reduction of, Cr(VI). Superior electron transfer kinetics and stable electrochemical response for Cr(VI) are observed at the GCE/PSF+-MS-SO3? electrode. Moreover, the quantitative estimation of Cr(VI) at the GCE/PSF+-MS-SO3? done using linear sweep voltammetry (LSV). Dual linear calibration ranges (1 to 20 �M and 20 to 100 �M) is obtained from the LSV response. A low limit of detection (0.5 �M) and superior sensitivity (1.1 �A �M?1 cm?2) are recognized at this electrode. In addition, significant selectivity in the existence of other interfering ions is also shown by fabricated sensing scaffold. The precise measurement of Cr(VI) in spiked water samples with simple matrix is also demonstrated successfully with sufficient durability and reproducibility. � 2023 Elsevier B.V.
Template-free hydrothermal synthesis of nickel sulfide nanocrystals on MWCNTs: efficient and stable bifunctional electroactive material for oxygen electrocatalysis
(Royal Society of Chemistry, 2023) Yadav, Mamta; Singh, Devesh Kumar; Ganesan, Vellaichamy
Developing efficient and low-cost bifunctional electrocatalysts for oxygen electrocatalysis is extremely desirable in energy conversion and storage systems. In this work, a facile growth of nickel sulfide on the multi-walled carbon nanotubes (MWCNTs) is achieved hydrothermally via a template-free approach. Further, the material is annealed to obtain a highly active nanostructure with much more exposed active sites. The annealed product (Ni-S@MWCNTs-500) and the control samples are characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy techniques. The prepared catalyst, Ni-S@MWCNTs-500 in 1.0 M KOH displays an improved oxygen evolution reaction (as compared to the benchmark catalyst, RuO2) exhibiting an overpotential of 320 mV at 10 mA cm?2 current density and a Tafel slope value of 84 mV dec?1. In addition, Ni-S@MWCNTs-500 demonstrates a highly selective two-electron reduction of oxygen with an onset potential of 0.92 V. It reveals a high mass activity (115.59 A g?1) and high electrochemically active surface area (17.0 cm2). The durability of the catalyst is studied by chronopotentiometry and continuous cyclic voltammetry cycles. The oxygen electrocatalysis activity is surprisingly stable without any noticeable change in the current response and overpotential/onset potential. Ni-S@MWCNTs-500 improves the electrical accessibility of the active sites and decreases the chances of nanoparticle aggregation. � 2023 The Royal Society of Chemistry.

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