• Ramasamy Ramaraj

      Articles written in Journal of Chemical Sciences

    • Photoelectrocatalytic reactions of metal complexes at chemically modified electrodes

      Ramasamy Ramaraj

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      One of the outstanding properties of the ion-exchange membranes is their multiphase structure with microheterogeneous environment. Recently we have shown that ion-exchange membranes such as Nafion and clay can be effectively used in preparing chemically modified electrodes with adsorbed photoactive and electroactive molecules. A new photogalvanic cell was constructed by coating one electrode with Nafion-[Ru(bpy)3]2+ and the other with clay-[Ru(bpy)3]2+. This new photogalvanic cell showed an additive photogalvanic response on visible light irradiation. The quenching rate constants,kq, for the reaction of excited state [Ru(bpy)3]2+ adsorbed into the membrane with Fe3+ ion and cobalt(III) complexes were determined by photoelectrochemical methods. The photoelectrocatalytic reduction of oxygen to hydrogen peroxide at chemically modified electrodes was carried out by using [Ru(bpy)3]2+ as sensitizer and macrocyclic cobalt(III) complexes as electron relay.

    • Nanostructured metal particlemodified electrodes for electrocatalytic and sensor applications

      Ramasamy Ramaraj

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      Nanotechnology has become one of the most exciting frontier fields in analytical chemistry. The huge interest in nanomaterials, for example in chemical sensors and catalysis, is driven by their many desirable properties. Although metal is a poor catalyst in bulk form, nanometre-sized particles can exhibit excellent catalytic activity due to their relative high surface area-to-volume ratio and their interface-dominated properties, which significantly differ from those of the bulk material. The integration of metal nanoparticles into thin film of permselective membrane is particularly important for various applications, for example in biological sensing and in electrocatalysis. We have already established different techniques to design permselective membrane-coated chemically modified electrodes with incorporated redox molecules for electrocatalytic, electrochromic and sensor applications. Recently, we have prepared nanostructured platinum and copper (represented Mnano, M = Pt and Cu) modified GC/Nafion electrodes (GC/Nf/Mnano) and characterized by using AFM, XPS, XRD and electrochemical techniques. The nanostructured Mnano modified electrodes were utilized for efficient electrocatalytic selective oxidation of neurotransmitter molecules in the presence of interfering species such as ascorbic acid (AA) and uric acid (UA). It has been also shown that the modified electrodes could be used as sensors for the detection of submicromolar concentrations of biomolecules with practical applications to real samples such as blood plasma and dopamine hydrochloride injection solution. The GC/Cunano electrode has been used for catalytic reduction of oxygen.

    • Core-shell Au/Ag nanoparticles embedded in silicate sol-gel network for sensor application towards hydrogen peroxide

      Shanmugam Manivannan Ramasamy Ramaraj

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      The electrocatalytic activity of core-shell Au$_{100-x}$Ag$_x$ ($x = 15$, 27, 46, and 60) bimetallic nanoparticles embedded in methyl functionalized silicate MTMOS network towards the reduction of hydrogen peroxide was investigated by using cyclic voltammetry and chronoamperometric techniques. Core-shell Au/Ag bimetallic nanoparticles were characterized by absorption spectra and HRTEM. The MTMOS silicate sol-gel embedded Au73Ag27 core-shell nanoparticles modified electrode showed better synergistic electrocatalytic effect towards the reduction of hydrogen peroxide when compared to monometal MTMOS-Aunps and MTMOS-Agnps modified electrodes. These modified electrodes were studied without immobilizing any enzyme in the MTMOS sol-gel matrix. The present study highlights the influence of molar composition of Ag nanoparticles in the Au/Ag bimetallic composition towards the electrocatalytic reduction and sensing of hydrogen peroxide in comparison to monometal Au and Ag nanoparticles.

    • Gold nanodots self-assembled polyelectrolyte film as reusable catalyst for reduction of nitroaromatics


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      Separation of homogeneous catalyst from the reaction mixture is a crucial and difficult process in any catalytic process. To address this issue, a new class of multifunctional catalyst in the form of film was developed using a facile approach to enjoy the advantages of homogeneous catalyst with the versatility of heterogeneous catalyst. To achieve the same, methionine-capped gold nanodots (AuNDs) were self-assembled on a cationic polyelectrolyte modified glass plate for the catalytic reduction of nitro functional groups in the presence ofolefinic double bond at mild conditions. Separation of this reusable catalytic film from the reactionmixture is very simple and advantageous when compared to the currently available and conventional catalytic systems. Kinetics of nitro reduction was monitored using absorption spectroscopy and the product formation was confirmed by 1H and 13CNMR analyses. Prepared AuNDs catalyst was characterized using UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution transmission electron microscopy(HRTEM), cyclic voltammetry and atomic force microscopy (AFM) techniques.

    • Gold nanoparticles decorated silicate sol-gel matrix embedded reduced graphene oxide and manganese ferrite nanocompositematerials- modified electrode for glucose sensor application


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      Gold nanoparticles decorated on silicate sol-gel matrix embedded manganese ferrite (MnFe2O4)-reduced graphene oxide (rGO) nanocomposites were synthesized through a facile chemical method. The prepared sampleswere characterized by using powder X-ray diffraction (XRD),UV–vis absorption spectroscopy (UV-VIS), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) analyses. The Au nanostructures on rGO-MnFe2O4improved the electrocatalytic activity of the rGO-MnFe2O4@Au composite-materials-modified electrodes towards glucose oxidation. Cyclic voltammetry and amperometric methods were used to evaluate the electrocatalytic activity of the rGO-MnFe2O4@Au modified electrodes towards glucose oxidation in 0.1 MNaOH at a less-positive potential (0.2 V) in the absence of any enzyme or redox mediator. The nanocompositemodified electrode (GCE/EDAS/rGO-MnFe2O4@Au) was successfully used for the amperometric sensing ofglucose and the experimental detection limit of 10 μM glucose was observed. The common interfering agents did not interfere with the detection of glucose. The present sensor showed good stability, reproducibility, and selectivity. The nanocomposite-modified electrode was successfully used for the determination of glucose in the urine sample.

    • Electrochemically co-deposited silicate sol–gel/PdAu alloy nanostructures and their application in electrocatalytic methanol oxidation


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      Bimetallic PdAu alloy nanostructures incorporated ethylene diamine functionalized silicate sol gel (ES) nanocomposite materials on indium-tin-oxide (I) electrodes (I/ES-PdAu) were prepared by facileelectrochemical method. X-ray diffraction patterns confirmed the formation of single-phase bimetal PdAualloy nanostructures at the electrode. X-ray photoelectron spectroscopy analysis confirmed the existence of azero oxidation state of Pd and Au metals at the I/ES-PdAu electrode. Morphology analysis revealed theformation of anisotropic nanostructures of Au, Pd and PdAu alloy nanostructures with different sizes andshapes at the modified electrodes. Electrocatalytic methanol oxidation reaction (MOR) was studied andenhanced methanol oxidation activity was observed at the bimetallic I/ES-Pd75Au25 and I/ES-Pd50Au50 modified electrodes when compared to pristine I/ES-Pd100, I/Pd100 and I/ES-Au100 modified electrodes. TheI/ES-Pd75Au25 modified electrode was found to be the best electrocatalyst which showed lower overpotentialwith higher mass activity (0.144 A/mgPd) for MOR. Interestingly, when Pd was combined with Au in thepresence of ES silicate sol-gel the bimetallic PdAu alloy nanomaterials showed enhanced MOR activity. TheMOR current observed at the I/ES-Pd75Au25 electrode was nearly 1.8 times higher than that of the I/Pd75Au25 electrode without ES silicate sol-gel. The stability of the I/ES-Pd75Au25 electrode was tested by scanning 200continuous cycles and the catalytic current was found to decrease only < 5%.

      Electrochemically co-deposited PdAu bimetallic materials embedded in N-[3-(trimethoxysilyl) propyl]ethylenediamine silicate (ES) sol-gel modified electrode (I/ES-Pd75Au25) displayed 8.7 and 3.2 times higher methanol oxidation current and mass activity when compared to the pristine I/ES-Pd100 modified electrode due to ES silicate sol-gel supported mass interaction between PdAu alloy nanostructure with the analyte.

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