Browsing by Author "Mamta Yadav"

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A Co and Fe bimetallic MOF with enhanced electrocatalytic oxygen evolution performance: exploring the electronic environment modifications upon Fe incorporation
(Royal Society of Chemistry, 2024) Varsha Singh; Devesh Kumar Singh; Mamta Yadav; Smita Singh; Vikram Rathour; Ananya Tiwari; Vellaichamy Ganesan
The incorporation of iron into the cobalt-based metal-organic framework (Co-MOF) modifies the electronic environment and the resulting bimetallic MOF exhibits enhanced oxygen evolution reaction (OER) performance. The Co-MOF, Fe-MOF, and different ratios of bimetallic Co-Fe-MOFs are prepared using 2,2′-bipyridine 4,4′-dicarboxylic acid (H2bpdc) by a single-step hydrothermal process. The MOFs are evaluated by necessary spectroscopy and microscopy techniques like Fourier transform infrared spectroscopy, inductively coupled plasma emission spectroscopy, powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray analysis, and X-ray photoelectron spectroscopy. The incorporation of Fe3+ into the Co-MOF significantly increases the electrocatalytic activity of the resulting bimetallic Co-Fe-MOF towards the OER. An optimized bimetallic MOF having a Co : Fe ratio of 2 : 1 shows the lowest overpotential (310 mV) to realize the 10 mA cm−2 current density and the lowest Tafel slope of 53 mV dec−1 with excellent durability in comparison to the Co-MOF, the Fe-MOF, and the state-of-the-art catalyst, RuO2. Furthermore, this manuscript addresses the inherent electrocatalytic properties of MOF-based electrocatalysts and demonstrates their possible exploitation in water electrolysis. © 2024 RSC.
Amperometric assay of hydrazine utilizing electro-deposited cobalt hexacyanoferrate nanocrystals on graphene oxide sheets
(Springer, 2020) Mamta Yadav; Vellaichamy Ganesan; Rupali Gupta; Dharmendra Kumar Yadav; Piyush Kumar Sonkar
Abstract: In-situ electrochemical deposition of cobalt hexacyanoferrate (CoHCF) on graphene oxide (GO) and its application for the electrocatalytic hydrazine determination in real samples are described in this research study. Co2+ is immobilized on GO and the resulting material, GO-Co2+ is coated on the surface of glassy carbon (GC) electrode. The fabricated electrode (GC/GO-Co2+) is subjected to a continuous potential cycling in the range of 0.0–1.0 V which results in the formation of a thin CoHCF film on the surface of GO coated on the GC electrode (abbreviated as GC/GO-CoHCF). The synthesized GO-CoHCF composite material is characterized by Fourier transform infrared and scanning electron microscopy. GC/GO-CoHCF electrode electrocatalytically oxidizes hydrazine at low overpotential (0.63 V) and this phenomenon is subsequently utilized for the sensitive determination of hydrazine in aqueous solutions. It exhibits a wide linear calibration range (0.1–400 µM), high sensitivity (0.93 µA µM−1 cm−2) and low limit of detection (17.5 nM) for the determination of hydrazine. Further, this electrode is employed for hydrazine determination in real samples. Graphic abstract: [Figure not available: see fulltext.] © 2020, Indian Academy of Sciences.
Co(II) Porphyrin-MWCNT Nanoconjugate as an Efficient and Durable Electrocatalyst for Oxygen Reduction Reaction
(American Chemical Society, 2023) Mohammad Tasleem; Mamta Yadav; Vellaichamy Ganesan; Muniappan Sankar
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.
Co(II)-porphyrin-decorated carbon nanotubes as catalysts for oxygen reduction reactions: An approach for fuel cell improvement
(Royal Society of Chemistry, 2017) Piyush Kumar Sonkar; Kamal Prakash; Mamta Yadav; Vellaichamy Ganesan; Muniappan Sankar; Rupali Gupta; Dharmendra Kumar Yadav
The development of high-performance and cost-effective catalysts for the oxygen reduction reaction (ORR) is essential for the advancement of fuel cells. In this work, three different functionalized cobalt porphyrins, meso-tetraphenylporphyrinatocobalt(ii) (CoTPP), meso-tetrakis(4′-hydroxyphenyl)porphyrinatocobalt(ii) (CoTHPP) and meso-tetrakis(4′-carboxy-phenyl)porphyrinatocobalt(ii) (CoTCPP), are prepared. These porphyrins are immobilized non-covalently on multiwalled carbon nanotubes (MWCNTs) and used for the ORR in 0.1 M HClO4, 0.1 M phosphate buffer solution (pH 7.0) and 0.1 M KOH media. The composite materials are characterized by using spectroscopic and electrochemical techniques and their oxygen reduction efficiencies are compared in different media. Kinetic interpretations and hydrodynamic voltammetry (in three media) studies demonstrated that the MWCNT-CoTPP, MWCNT-CoTHPP and MWCNT-CoTCPP composite materials exhibit significant efficiency with decreased overpotential, considerable methanol tolerance and long term operational stability (up to 3000 cycles) for the ORR similar to commercially available platinum carbon (Pt-C) catalysts. These results reveal that the new MWCNT-cobalt porphyrin composite materials can be a potential alternative to the expensive Pt-C catalysts or other commercial cathode materials in fuel cells. © 2017 The Royal Society of Chemistry.
Coarse-grained Hamiltonian and effective one component theory of colloidal suspensions
(Elsevier B.V., 2022) Mamta Yadav; Yashwant Singh
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 ηb and ηs 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 ηb; when ηb is increased from zero, initially the potential becomes more attractive but beyond a certain value of ηb 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 σb and n is an integer, become stronger on increasing ηb. These results show that many-body contribution to the effective potential depends in a subtle way on packing fractions ηb,ηs, 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) Dharmendra Kumar Yadav; Fatin Saiha Omar; Mamta Yadav; Xian Liang Ho; Malcolm E. Tessensohn; K. Ramesh; S. Ramesh; Richard D. Webster; Vellaichamy Ganesan
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
Cobalt oxide nanocrystals anchored on graphene sheets for electrochemical determination of chloramphenicol
(Elsevier Inc., 2019) Mamta Yadav; Vellaichamy Ganesan; Rupali Gupta; Dharmendra Kumar Yadav; Piyush Kumar Sonkar
This study demonstrates the hydrothermal synthesis of cobalt oxide (Co 3 O 4 ) nanocrystals on reduced graphene oxide (rGO) which is further utilized to construct an electrochemical sensing scaffold for precise determination of chloramphenicol (CP). CP is an antibiotic used for the treatment of typhoid fever and infections including salmonellosis. Due to its antibacterial property, low cost and availability it was extensively used in the fields of agriculture, but its presence in animal derived food products create detrimental effects on consumers. Therefore it is important to monitor the level of CP in different food products. The formation of Co 3 O 4 on rGO (Co 3 O 4 @rGO) is characterized with FT-IR, XRD, TEM and SEM techniques. The working electrode is fabricated by drop coating the catalyst (0.1% Co 3 O 4 @rGO in DMF) on glassy carbon (GC) electrode (symbolized as GC/Co 3 O 4 @rGO) and further used for electrochemical sensing of CP with cyclic voltammetry (CV), amperometry and differential pulse voltammetry (DPV) techniques. The calibration curve for the determination of CP through CV shows a linear range from 1 to 2000 μM with two different slopes. Sensitivity of the CP determination and limit of detection (LOD) are calculated to be 1.32 μA μM cm −2 and 0.55 μM, respectively. Further the sensing scaffold, GC/Co 3 O 4 @rGO is successfully applied for the CP determination present in real samples like milk products. © 2019 Elsevier B.V.
Copper oxide immobilized clay nano architectures as an efficient electrochemical sensing platform for hydrogen peroxide
(Springer, 2020) Dharmendra Kumar Yadav; Vellaichamy Ganesan; Rupali Gupta; Mamta Yadav; Piyush Kumar Sonkar; Pankaj Kumar Rastogi
Abstract: An electrochemical sensor for hydrogen peroxide (H2O2) present in face bleach cream is fabricated using a composite based on bentonite (Bt) clay and copper oxide(CuO) nanoparticles (CuO-Bt). The CuO nanoparticles’ immobilization into Bt was carried out by a two-step process in which Cu2+ is ion-exchanged into Bt layers (Cu2+-Bt) in the first step followed by the chemical reaction of NaOH with Cu2+-Bt in the second step to get the target material, CuO nanoparticles immobilized Bt (CuO-Bt). The successful immobilization of CuO nanoparticles into Bt is investigated by a variety of techniques like scanning electron microscopy, transmission electron microscopy, FT-IR spectroscopy, UV-Vis spectroscopy, and electrochemical methods. The CuO-Bt composite is coated on a glassy carbon electrode and used as a selective electrochemical sensing platform for the determination of H2O2 based on the significant electrocatalytic property of CuO-Bt towards the H2O2 oxidation. This amperometric electrochemical sensor shows two linear detection ranges (5–50 μM and 50–10000 μM) with a limit of detection of 4.9 μM. The sensitivity is calculated to be 0.06 µA µM−1 cm−2. This electrochemical sensor exhibits high selectivity, stability, and practical applicability for the H2O2 determination in real samples. Graphic Abstract: [Figure not available: see fulltext.]. © 2020, Indian Academy of Sciences.
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) Devesh Kumar Singh; Mamta Yadav; Vellaichamy Ganesan; Preeti A. Bhobe
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.
Depletion potential, correlation functions and demixing transition in model colloid-polymer mixtures
(Academic Press Inc., 2024) Mamta Yadav; Yashwant Singh
We describe a theoretical framework to calculate depletion potential between colloid particles induced by non-adsorbing ideal polymer chains (s-species) and correlation functions in a coarse-grained one-component system of colloids (c-species). A Padé approximant is used to express the depletion potential as a pair potential with many-body contributions subsumed in it. The depletion potential and correlation functions of c-species are calculated using a self-consistent procedure. Results for several values of size ratio [Formula presented] (σs and σc are, respectively diameters of the polymer chain and a colloid particle) and packing fractions of s- and c-species are reported. The spinodal curve and critical point of demixing transition are determined for several values of q. Calculated values are compared with values found from other theories and simulations. © 2024 Elsevier Inc.
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) Rashmi Gupta; Mamta Yadav; Smita Singh; Vellaichamy Ganesan; Bachcha Singh
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 µA µM−1 cm−2 and 0.09 µM, 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.
Electrochemical sensing of rifampicin in pharmaceutical samples using meso-tetrakis(4-hydroxyphenyl)porphyrinato cobalt(II) anchored carbon nanotubes
(Springer Netherlands, 2018) Piyush Kumar Sonkar; Mamta Yadav; Kamal Prakash; Vellaichamy Ganesan; Muniappan Sankar; Dharmendra Kumar Yadav; Rupali Gupta
Abstract: In this work, an electrochemical sensing platform is prepared for rifampicin determination based on multiwalled carbon nanotubes (MWCNTs) modified with meso-tetrakis(4-hydroxyphenyl)porphyrinato cobalt(II) (CoTHPP) nanocomposite (abbreviated as MWCNTs-CoTHPP). The material is characterized by different techniques such as UV–Vis, Fourier transform-infrared, Raman, transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray analysis. For the electrochemical sensing platform, the nanocomposite, MWCNTs-CoTHPP is immobilized on glassy carbon (GC) electrode (represented as GC/MWCNTs-CoTHPP) and applied for electrochemical recognition of rifampicin. It is found that the GC/MWCNTs-CoTHPP electrode facilitates the electrochemical oxidation of rifampicin with decreased overpotential in 0.1 M acetate buffer (pH 4.7). Further, GC/MWCNTs-CoTHPP exhibits broad calibration range (0.01 µM–5.0 mM), high sensitivity (217 µA mM−1 cm−2), high reproducibility (relative standard deviation = 4.83%, n = 6), and low detection limit (0.008 µM) for rifampicin determination. In addition, this method is successfully applied for real sample (rifampicin capsule) analysis with consistent results. The results suggest that MWCNTs-CoTHPP is a potential candidate for an effective, rapid, and simple electrochemical sensor to detect rifampicin in pharmaceutical formulations. © 2018, Springer Nature B.V.
Enhanced Four-Electron Selective Oxygen Reduction Reaction at Carbon-Nanotube-Supported Sulfonic-Acid-Functionalized Copper Phthalocyanine
(John Wiley and Sons Inc, 2023) Mamta Yadav; Devesh Kumar Singh; Dharmendra Kumar Yadav; Piyush Kumar Sonkar; Rupali Gupta; Vellaichamy Ganesan
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.
Facile Synthesis of Sulfur-Doped Mesoporous Carbon Nitride Supported Defect-Rich Cobalt Sulfide for Electrocatalytic Water Oxidation
(American Chemical Society, 2020) Devesh Kumar Singh; Vellaichamy Ganesan; Dharmendra Kumar Yadav; Mamta Yadav
The synthesis of defect-rich materials is of significant interest for electrochemical energy conversion, including water splitting. Herein, we report a novel strategy for the synthesis of sulfur-doped mesoporous conducting carbon nitride supported defect-rich cobalt sulfide (O-Co3S4@S-MCN). Mesoporous silica material (MCM-41) is used as a template for the synthesis, and it performs dual functions: introducing porosity and providing in situ oxygen to fill the defects. O-Co3S4@S-MCN is highly crystalline and shows characteristic diffractions indicating the formation of defect-rich Co3S4. X-ray photoelectron spectroscopy proves the presence of Co-S (777.9 eV) and Co-O (782.4 eV) bonds in O-Co3S4@S-MCN. Further, Fourier-transform infrared spectroscopy clearly indicates the presence of C=N (1620 cm-1) and C=S (1090 cm-1) bonds. This composite material, O-Co3S4@S-MCN, shows a low onset potential (1.6 V for 10 mA cm-2), high mass activity (71 A/g at 1.7 V), high rate (Tafel slope, 52 mV/dec), and excellent stability (only 5% decrease in current density after 2 h continuous electrolysis) for the electrocatalytic oxygen evolution reaction in 1.0 M KOH. © 2020 American Chemical Society.
Functionalization of carbon-based materials for the electrochemical sensing applications
(Nova Science Publishers, Inc., 2021) Mamta Yadav; Devesh Kumar Singh; Vellaichamy Ganesan; Ramasamy Ramaraj
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.
Gold Nanoparticles Incorporated in a Zinc-Based Metal-Organic Framework as Multifunctional Catalyst for the Oxygen Reduction and Hydrogen Evolution Reactions
(Wiley-VCH Verlag, 2018) Dharmendra K. Yadav; Rupali Gupta; Vellaichamy Ganesan; Piyush K. Sonkar; Mamta Yadav
Successful synthesis of gold nanoparticles incorporated in a zinc-based metal-organic framework (Au@Zn-MOF) is reported in this paper. The synthesis of Au@Zn-MOF is confirmed by UV-Vis, FT-IR and X-ray photoelectron spectroscopy (XPS) studies. The Au@Zn-MOF catalyst demonstrates electrocatalytic activity towards the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER). The relative catalytic performance of Au@Zn-MOF towards ORR and HER has been studied under acidic condition. ORR proceeds via a two electron and two proton mechanism with hydrogen peroxide as the end product, while HER follows the Volmer mechanism i. e., adsorption of H+ on the catalyst's active sites. Au@Zn-MOF exhibits an ORR onset potential of 0.45 V (vs. RHE) with two different Tafel slopes, −93 and −103.6 mV in acidic solution. Further, an excellent catalytic activity is observed for HER with an onset potential of 0.02 V (vs. RHE) and a Tafel slope of 87 mV in N2 saturated 0.1 M HClO4 solution. However, in O2 saturated 0.1 M HClO4 solution, a HER onset potential of 0.04 V (vs. RHE) is observed with two different Tafel slopes, 610 and 220 mV. The value of Tafel slopes in the presence of O2 advocates the diminution of the ORR activity because of the HER. Thus, Tafel slope values of HER and ORR suggest that protons and O2 compete to reach the electrode surface for getting reduced. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Highly dispersed multiwalled carbon nanotubes coupled manganese salen nanostructure for simultaneous electrochemical sensing of vitamin B2 and B6
(Elsevier B.V., 2017) Piyush Kumar Sonkar; Vellaichamy Ganesan; Susanta K. Sen Gupta; Dharmendra Kumar Yadav; Rupali Gupta; Mamta Yadav
A nanocomposite of Mn(salen)Cl (where salen is N,N′-bis(salicylidene)ethylenediamine) and multiwalled carbon nanotubes (MWCNTs) is prepared. The advantageous properties of MWCNTs and catalytic properties of Mn(salen)Cl (represented as MnIIIsalen) are combined in this new nanocomposite (represented as MWCNTs-MnIIIsalen). Several techniques including electrochemical ones are used for the characterization of the MWCNTs-MnIIIsalen nanostructure. After complete characterization it is utilized for simultaneous determination of vitamin B2 (riboflavin) and B6 (pyridoxine) using differential pulse voltammetry (DPV). MWCNTs-MnIIIsalen coated on glassy carbon electrode (GC), represented as GC/MWCNTs-MnIIIsalen exhibits high sensitivity and low detection limit. This electrode demonstrates high reproducibility (R.S.D. = 3.7% and 3.4% for vitamin B2 and B6, respectively) and long storage stability (more than 10 days under normal room temperature condition). Methodologies for the analysis of vitamins B2 and B6 using GC/MWCNTs-MnIIIsalen in pharmaceutical formulations using simple electrochemical techniques are elucidated. © 2017
Improving Functional Behavior of MCM-41 by Encapsulating MnO2 Nanorods towards Simultaneous Determination of Purine Bases in DNA Samples
(Wiley-VCH Verlag, 2018) Rupali Gupta; Dharmendra Kumar Yadav; Vellaichamy Ganesan; Piyush Kumar Sonkar; Mamta Yadav
MnO2 nanorods incorporated MCM-41 nanocomposite (MnO2@MCM-41) is synthesized and employed as an electrode modifier for individual as well as simultaneous detection of purine bases, guanine (GU) and adenine (AD). For this purpose MnO2 nanorods are encapsulated within MCM-41 by simple one pot synthetic approach. FT-IR, UV-vis absorption spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical methods are employed to characterize the nanocomposite and other materials. The electrochemical attributes of glassy carbon electrode (GCE) modified with the MnO2@MCM-41 (represented as GCE/MnO2@MCM-41) towards the determination of GU and AD is studied in detail. Upon incorporation of MnO2 nanorods on MCM-41, noticeable upsurge in anodic peak current with a decline in peak potential is observed for both GU and AD oxidations in cyclic voltammetry studies. Individual as well as simultaneous determination of GU and AD are performed using differential pulse voltammetry (DPV) technique which offered a linear range of 100 nM to 100 μM for GU and AD with respective limit of detections, 44 and 66 nM. The practical applicability of the GCE/MnO2@MCM-41 for real world samples analysis is satisfactorily demonstrated with certain DNA samples by DPV. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
In situ Electrochemical Synthesis of a Composite Film Containing Nickel Hexacyanoferrate and Bentonite Clay for the Sensitive Determination of Acetaminophen and Dopamine
(Wiley-VCH Verlag, 2020) Mamta Yadav; Preeti Singh; Vellaichamy Ganesan; Rupali Gupta; Piyush Kumar Sonkar; Dharmendra Kumar Yadav
A composite film of nickel hexacyanoferrate (NiHCF) and bentonite (Bt) clay (abbreviated as NiHCF−Bt) is synthesized by an in situ electrochemical method. For this synthesis, nickel ions are immobilized on Bt clay by an ion-exchange process, equilibrating Bt clay with nickel nitrate. On a glassy carbon electrode (GCE), the nickel ion-exchanged Bt clay (Ni2+−Bt) is coated to get the modified electrode which is represented as GCE/Ni2+−Bt. The NiHCF−Bt composite film is prepared on the GCE surface using the GCE/Ni2+−Bt and scanning the electrode potentials between −0.10 to 1.00 V continuously in an aqueous solution containing potassium hexacyanoferrate and potassium chloride. This NiHCF−Bt modified GCE (GCE/NiHCF−Bt) exhibits redox peaks due to the oxidation and reduction of the central metal ion, Fe2+. The electro-generated Fe3+ present in the GCE/NiHCF−Bt, electrocatalytically oxidizes a range of drugs like acetaminophen (AC), dopamine (DA), and tyrosine (TY) at decreased overpotentials with high current. This property is advantageously used for the precise quantification of AC, DA, and TY. Sensitivity, limit of detection, and linear calibration range for the determination of AC are found to be 0.20 μA μM−1 cm−2, 1.5 μM, and 25.0–1000.0 μM, respectively. Further, the amount of AC present in pharmaceutical products is satisfactorily quantified which demonstrated the use of the NiHCF−Bt composite film in electroanalysis. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Insight into efficient bifunctional catalysis: Oxygen reduction and oxygen evolution reactions using MWCNTs based composites with 5,10,15,20-tetrakis(3′,5′-dimethoxyphenyl)porphyrinato cobalt(II) and 5,10,15,20-tetrakis(3′,5′-dihydroxyphenyl)porphyrinato cobalt(II)
(Elsevier Ltd, 2020) Mamta Yadav; Piyush Kumar Sonkar; Kamal Prakash; Vellaichamy Ganesan; Muniappan Sankar; Dharmendra Kumar Yadav; Rupali Gupta
Development of cost-effective, durable, and efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still required for efficient fuel cells, metal-air-batteries, and water electrolysis. For that purpose we have prepared tetrakis(3′,5′-dimethoxyphenyl)porphyrinato cobalt(II) (CoDMTPP) and 5,10,15,20-tetrakis(3′,5′-dihydroxyphenyl)porphyrinato cobalt(II) (CoDHTPP). Further, multi-walled carbon nanotubes (MWCNTs) based composites of CoDMTPP (MWCNTs-CoDMTPP) and CoDHTPP (MWCNTs-CoDHTPP) are also prepared and characterized through spectroscopy (UV–vis, FTIR, and XPS), microscopy (SEM, TEM with EDAX), X-ray diffraction, thermogravimetry, and electrochemical techniques. The materials, MWCNTs-CoDMTPP and MWCNTs-CoDHTPP are immobilized on glassy carbon (GC) electrodes, represented as GC/MWCNTs-CoDMTPP and GC/MWCNTs-CoDHTPP. They show efficient ORR activity in acidic, basic, and neutral (pH 7.0 buffer) mediums. Further, both of these electrodes exhibit significant OER activity in 0.1 M KOH, indicating the bifunctional activity in basic medium. Based on the kinetic studies, the presence of –OH in the CoDHTPP is found to enhance the ORR activity. The electrodes, GC/MWCNTs-CoDMTPP and GC/MWCNTs-CoDHTPP exhibit high methanol tolerance capacity. A very small change in onset potential of 12 mV at GC/MWCNTs-CoDMTPP and 3 mV at GC/MWCNTs-CoDHTPP electrodes are observed for the ORR after 3000 continuous potential cycles indicating the high operational stability of the modified electrodes. © 2020 Hydrogen Energy Publications LLC