Browsing by Author "Muniappan Sankar"

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2D self-assembly of twisted porphyrins appended on multiwalled carbon nanotubes for the oxygen reduction reaction
(Royal Society of Chemistry, 2025) Varusha Bhardwaj; Varsha K. Singh; Vellaichamy Ganesan; Muniappan Sankar
The spontaneous formation of an ordered array of twisted cobalt(ii) porphyrins yields a 2D self-assembled structure that is then wrapped around multiwalled carbon nanotubes (MWCNTs) and characterized using different techniques. The structure of β-tetracyano-meso-tetraphenylporphyrinatocobalt(ii) (2-Co) shows axial ligation of the metal center with cyano groups when it is adsorbed on the nanotube sidewalls, and the nanotube acts as a template for the formation of the framework layer. The electrocatalytic applications of the formed conjugate are explored in terms of the activity and the selectivity in the oxygen reduction reaction (ORR) in basic media. © 2025 The Royal Society of Chemistry.
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.
Electrocatalysis Using Cobalt Porphyrin Covalently Linked with Multi-Walled Carbon Nanotubes: Hydrazine Sensing and Hydrazine-Assisted Green Hydrogen Synthesis
(John Wiley and Sons Inc, 2025) Mohd Tasleem; Varsha K. Singh; Ananya Tiwari; Vellaichamy Ganesan; Muniappan Sankar
Acid-treated multi-walled carbon nanotube (MWCNT) covalently functionalized with cobalt triphenothiazine porphyrin (CoTriPTZ-OH) A3B type porphyrin, containing three phenothiazine moieties (represented as MWCNT-CoTriPTZ) is synthesized and characterized by various spectroscopic and microscopic techniques. The nanoconjugate, MWCNT-CoTriPTZ, exhibits a pair of distinct redox peaks due to the Co2+/Co3+ redox process in 0.1 M pH 7.0 phosphate buffer. Further, it electrocatalytically oxidizes hydrazine at a low overpotential with a high current. This property is advantageously utilized for the sensitive determination of hydrazine. The developed electrochemical sensor exhibits high sensitivity (0.99 µAµM−1cm−2), a low limit of detection (4.5 ppb), and a broad linear calibration range (0.1 µM to 3.0 mM) for the determination of hydrazine. Further, MWCNT-CoTriPTZ is exploited for hydrazine-assisted green hydrogen synthesis. The high efficiency of hydrazine oxidation is confirmed by the low onset potential (0.45 V (vs RHE)) and 0.60 V (vs RHE) at the current density of 10 mA.cm−2. MWCNT-CoTriPTZ displays a high current density (77.29 mA.cm−2) at 1.45 V (vs RHE). © 2024 Wiley-VCH GmbH.
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.
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
Porphyrin-Based Covalent Organic Framework Encapsulating Multiwalled Carbon Nanotubes: A High-Performance Electrocatalyst for Oxygen Reduction Reaction
(American Chemical Society, 2025) Pradeep Singh Thakur; Varsha K. Singh; Vellaichamy Ganesan; Muniappan Sankar
The development of efficient and cost-effective oxygen reduction reaction (ORR) catalysts is crucial for advancing fuel cell technologies, given the limitations of platinum-based catalysts. Here, we present a novel nanocomposite, cobalt-based porphyrinic covalent organic framework wrapped on multiwalled carbon nanotubes (Co-pCOF@MWCNTs), synthesized via template-directed in situ polymerization. This composite combines the high porosity and tunable catalytic properties of porphyrinic COFs with the excellent electrical conductivity of MWCNTs. The Co-pCOF@MWCNT demonstrates superior ORR activity, exhibiting an onset potential (Eonset) of 0.86 V vs RHE in 0.1 M KOH, surpassing the performance of its individual components (Co-pCOF and MWCNT) and other related materials. The enhanced catalytic efficiency is attributed to the synergistic interactions between the conductive MWCNT scaffold and the active porphyrinic COF nanolayers, which facilitate efficient charge transfer and increase catalytic site exposure. Furthermore, the nanocomposite exhibits high stability and methanol tolerance, establishing its potential as a cathodic material for fuel cells. This work highlights the promise of integrating COFs with conductive carbon materials and opens new avenues for the design of advanced ORR catalysts for energy conversion applications. © 2025 American Chemical Society.
Zn(II) porphyrin-based polymer facilitated electrochemical synthesis of green hydrogen peroxide
(Elsevier B.V., 2022) Varsha Singh; Pradeep S. Thakur; Vellaichamy Ganesan; Muniappan Sankar
A polymer consisting of Zn(II) porphyrin (ZnP-polymer) is synthesized and characterized by various spectroscopic and microscopic techniques. The UV–Vis absorption spectrum proves that the ZnP-polymer possesses monomeric zinc porphyrin moieties. FT-IR spectral features and powder X-ray diffraction pattern support the successful synthesis of ZnP-polymer. Field emission scanning electron microscopy studies show the flake like structures of the synthesized ZnP-polymer. Atomic force microscopy reveals the surface roughness indicating the availability of catalytically active sites. The high-resolution transmission electron microscopy images show homogenously distributed elements and uniform morphology of ZnP-polymer. X-ray photoelectron spectroscopy further confirms the successful synthesis of ZnP-polymer with the characteristic deconvoluted bands of carbon, nitrogen, and zinc. The as-synthesized ZnP-polymer shows high selectivity towards the two-electron oxygen reduction reaction (ORR) and produces H2O2 selectively. It exhibits a high-positive onset potential (0.79 V) for the ORR in a basic medium with 72% H2O2 molar selectivity. In an acidic medium, the onset potential is 0.24 V with 50% H2O2 molar selectivity. ZnP-polymer shows high stability in both acidic and basic media with negligible change in onset potential/overpotential even after 3000 continuous cyclic voltammetry cycles and 7200 s amperometric response. The synthesized ZnP-polymer has the potential to be used as the ORR catalyst to synthesize industrial-scale green H2O2. © 2022 Elsevier B.V.
π-Extended nonplanar cobalt porphyrins immobilized on MWCNTs as efficient electrocatalysts for selective oxygen reduction reaction
(Royal Society of Chemistry, 2024) Amir Sohel Bulbul; Vikram Rathour; Vellaichamy Ganesan; Muniappan Sankar
Two π-extended cobalt porphyrins are synthesized and one of them is crystallographically characterized. The nanocomposites of nonplanar (curved) porphyrin immobilized multi-walled carbon nanotubes were thoroughly characterized spectroscopically and microscopically, showing ∼200 mV positive shift in the O2 reduction peak potential in aqueous media and ∼100 mV shift in the onset potential of the O2 reduction relative to the control meso-tetraphenylporphyrinatocobalt(ii) nanocomposite. Both the π-extended cobalt porphyrin immobilized nanocomposites efficiently catalyze selective 4e−/4H+ O2 reduction under ambient conditions with excellent methanol tolerance and high stability due to effective π-π interactions, and could be an alternative for expensive Pt-based cathode materials in fuel cells. © 2024 The Royal Society of Chemistry.