Ramasamy Ramaraj

Graphene and its nanocomposite material based electrochemical sensor platform for dopamine

Dopamine (DA) is an important catecholamine neurotransmitter in the mammalian central nervous system that influences several physiological functions. The impact of DA levels within the human body significantly affects the body functions. Maintaining DA level is essential and the electrochemical detection methods are often used to detect the DA level to regulate the body function. In this review, graphene (functionalized graphene and N-doped graphene) and its composites (metal, metal oxide, polymer, carbonaceous materials, clay, zeolite, and metal–organic framework based graphene composites) modified electrodes with their improved sensing performance towards DA along with several interfering species are described. Further, recent developments on the fabrication of various graphene based composite modified electrodes are also presented. Some important strategies to improve the selectivity and sensitivity towards DA with graphene based composite modified electrodes are also described.

Gold nanoparticle based optical and electrochemical sensing of dopamine

AbstractThis review (with 110 refs.) gives an overview on the progress that has been made in the past few years on the use of gold nanoparticles (AuNPs) for use in sensors and analytical tools for the determination of dopamine (DA). Both AuNPs and their composites with other organic and inorganic materials including noble metals are treated. Following an overview on the clinical significance of DA, we discuss the various analytical methods that are (a) electrochemiluminescence (ECL); (b) surface enhanced Raman scattering (SERS); (c) colorimetric probing and visual detection; and (d) the large class of electrochemical sensors. Subsections cover sensors based on plain AuNPs, bimetallic NPs, AuNP-metal@metal oxide nanocomposites, AuNP nanocomposites with organic polymers, AuNP nanocomposites with carbon nanotubes or with graphene, and finally sensors based on ternary materials containing AuNPs. The review ends with a conclusion on current challenges of sensors for DA and an outlook on future trends. Graphical AbstractWe review the recent progress in sensing dopamine based on AuNPs and its nanocomposites including bimetallic nanoparticles, AuNPs-/metal oxide, AuNPs-polymer, AuNPs-carbon nanotubes, AuNPs-graphene and ternary materials using different types of sensing techniques such as electrochemiluminescence (ECL), colorimetric, surface enhanced Raman scattering (SERS) and electrochemical techniques.

Potential Sensing Platform of Silver Nanoparticles Embedded in Functionalized Silicate Shell for Nitroaromatic Compounds

A simple and new method to grow a pentagonally twinned structure of silver-silicate core-shell nanoparticles in aqueous environment at room temperature and its application in nitrobenzene (NB) sensing is described here. Silver-silicate core-shell nanoparticles were obtained by one-step synthesis using N-[3-(trimethoxysilyl)propyl]-ethylene diamine (EDAS) as a reducing/stabilizing agent and cetyltrimethylammonium bromide (CTAB) as the growing agent for the growth of silver nanoparticles (Ag(nps)). The silver-silicate core-shell nanoparticles were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), scanning electron microscope (SEM), UV-visible absorption, emission, excitation, and electrochemical measurements. The electrochemical studies of silver-silicate core-shell nanoparticles modified electrode showed the silver nanoparticles oxidation potential and their corresponding reduction potential at 0.24 and -0.16 V, respectively. The optical and electrochemical applications silicate-shell stabilized silver nanoparticles were established toward nitrobenzene. The optical sensing of nitrobenzene by silver-silicate core-shell nanoparticles studied using absorption and emission spectral methods showed experimentally determined lowest detection limits (LOD) of 1 and 10 microM, respectively. Silver-silicate core-shell nanoparticles showed excellent electrocatalytic activity toward the reduction of nitrobenzene. The electrochemical sensor showed the lowest detection limit (LOD) of 2.5 nM toward nitrobenzene sensing.

Boosting Photovoltaic Performance of Dye-Sensitized Solar Cells Using Silver Nanoparticle-Decorated N,S-Co-Doped-TiO2 Photoanode

A silver nanoparticle-decorated N,S-co-doped TiO2 nanocomposite was successfully prepared and used as an efficient photoanode in high-performance dye-sensitized solar cells (DSSCs) with N719 dye. The DSSCs assembled with the N,S-TiO2@Ag-modified photoanode demonstrated an enhanced solar-to-electrical energy conversion efficiency of 8.22%, which was better than that of a DSSC photoanode composed of unmodified TiO2 (2.57%) under full sunlight illumination (100 mWcm−2, AM 1.5 G). This enhanced efficiency was mainly attributed to the reduced band gap energy, improved interfacial charge transfer, and retarded charge recombination process. The influence of the Ag content on the overall efficiency was also investigated, and the optimum Ag content with N,S-TiO2 was found to be 20 wt%. Because of the enhanced solar energy conversion efficiency of the N,S-TiO2@Ag nanocomposite, it should be considered as a potential photoanode for high-performance DSSCs.

Functionalized Silicate Sol−Gel-Supported TiO2−Au Core−Shell Nanomaterials and Their Photoelectrocatalytic Activity

The N-[3-(trimethoxysilyl)propyl]ethylenediamine (EDAS) derived silicate matrix supported core-shell TiO(2)-Au nanoparticles (EDAS/(TiO(2)-Au)(nps)) were prepared by NaBH(4) reduction of HAuCl(4) precursor on preformed TiO(2) nanoparticles in the presence of EDAS monomer. The core-shell (TiO(2)-Au)(nps) nanoparticles were stabilized by the amine functional group of the EDAS silicate sol-gel network. The potential application of this EDAS/(TiO(2)-Au)(nps) modified electrode toward the photoelectrochemical oxidation of methanol was explored. The EDAS/(TiO(2)-Au)(nps) modified electrode showed a 12-fold enhancement in the catalytic activity toward photoelectrooxidation of methanol when compared to TiO(2) dispersed in EDAS silicate sol-gel matrix. This improved photoelectrochemical performance is explained on the basis of beneficial promotion of interfacial charge transfer processes of the EDAS/(TiO(2)-Au)(nps) nanocomposite. A methanol oxidation peak current density of 12.3 mA cm(-2) was achieved at an optimum loading of Au(nps) on TiO(2) particles. This novel amine functionalized EDAS silicate sol-gel stabilized core-shell (TiO(2)-Au)(nps) nanomaterial could be an excellent candidate for the photocatalytic and photoelectrochemical applications.

Titanium dioxide–gold nanocomposite materials embedded in silicate sol–gel film catalyst for simultaneous photodegradation of hexavalent chromium and methylene blue

Aminosilicate sol-gel supported titanium dioxide-gold (EDAS/(TiO(2)-Au)(nps)) nanocomposite materials were synthesized by simple deposition-precipitation method and characterized. The photocatalytic oxidation and reduction activity of the EDAS/(TiO(2)-Au)(nps) film was evaluated using hexavalent chromium (Cr(VI)) and methylene blue (MB) dye under irradiation. The photocatalytic reduction of Cr(VI) to Cr(III) was studied in the presence of hole scavengers such as oxalic acid (OA) and methylene blue (MB). The photocatalytic degradation of MB was investigated in the presence and absence of Cr(VI). Presence of Au(nps) on the (TiO(2))(nps) surface and its dispersion in the silicate sol-gel film (EDAS/(TiO(2)-Au)(nps)) improved the photocatalytic reduction of Cr(VI) and oxidation of MB due to the effective interfacial electron transfer from the conduction band of the TiO(2) to Au(nps) by minimizing the charge recombination process when compared to the TiO(2) and (TiO(2)-Au)(nps) in the absence of EDAS. The EDAS/(TiO(2)-Au)(nps) nanocomposite materials provided beneficial role in the environmental remediation and purification process through synergistic photocatalytic activity by an advanced oxidation-reduction processes.

Multielectrochromic properties of methylene blue and phenosafranine dyes incorporated into Nafion ® film

Abstract The electrochemical and spectroelectrochemical properties of phenosafranine (a phenazine dye) (PS + ) and methylene blue (a phenothiazine dye) (MB + ) immobilized into Nafion® (Nf) film were studied in 0.5 M H 2 SO 4 . The PS + dye was readily incorporated into Nf film containing MB + or vice versa, presumably by electrostatic interaction with the free sulfonate (SO 3 − ) groups and hydrophobic interaction with the fluorocarbon moieties of the Nf film. The interaction of these dyes with the hydrophobic fluorocarbon moieties could be understood from their observed higher concentration than the available sulfonate groups in the Nf film and also from their stable redox behavior. On the other hand, thionine (TH + ), another member of the phenothiazine family, was partially leached from the Nf film when the incorporation of PS + was followed because of its weak interaction with the hydrophobic fluorocarbon moieties of the Nf film. The PS incorporated Nf film containing MB + (Nf/PS + /MB + ) showed two well-separated reversible redox waves at 0.22 and −0.05 V (SCE) due to the redox process of MB + and PS + , respectively. The amount of dye molecules in the Nf film could be varied by changing the concentration of dye molecules in the immersion solution. The Nf/PS + /MB + film showed highly stable reversible color changes upon repeated cycles of applied potentials when compared to the Nf film with incorporated TH + and PS + dyes (Nf/TH + / PS + ). The changes in the absorbance of Nf/PS + /MB + film were accompanied with visible reversible changes of film color, ranging from blue-red at 0.7 V to red at 0.0 V and colorless at −0.5 V(SCE) due to the reversible redox process of the MB + and PS + dyes in the Nf film.

Aminosilicate sol–gel stabilized N-doped TiO2–Au nanocomposite materials and their potential environmental remediation applications

A facile chemical reduction method to synthesize amine functionalized silicate sol–gel-supported gold-deposited nitrogen-doped Degussa-TiO2 nanocomposite materials (APS/(N-P25-Au)NCM) is reported and the materials are characterized by DRS, PL, XRD, TEM, Raman, XPS and BET surface area analysis. The application of the synthesized APS/(N-P25-Au)NCM towards environmental remediation processes are investigated by studying the catalytic oxidation of carbon monoxide (CO) and photocatalytic reduction of toxic mercuric (Hg(II)) ions. The catalytic and photocatalytic activity of the prepared catalysts are found to be in the order of APS/(N-P25-Au)NCM ≫ APS/(P25-Au)NCM > N-P25 > P25. The enhanced catalytic and photocatalytic activities of the APS/(N-P25-Au)NCM can be attributed to the synergistic effect of Aunps and N-doped P25. The catalytic activities of the APS/(N-P25-Au)NCM are very promising in the field of green technology for the environmental cleaning applications.

TiO2–Au nanocomposite materials embedded in polymer matrices and their application in the photocatalytic reduction of nitrite to ammonia

Titanium dioxide–gold nanocomposite materials ((TiO2–Au)nps) were prepared and embedded in methyl functionalized silicate sol–gel (MTMOS) and Nafion (Nf) matrices. The nanocomposite materials were characterized by UV-vis absorption spectra, scanning electron micrographs (SEM) and high resolution transmission electron micrographs (HRTEM). When gold nanoparticles were deposited on TiO2 ((TiO2–Au)nps) and immobilized in MTMOS silicate sol–gel and Nafion matrices, the band-gap (Ebg) of the TiO2 shifted to lower energy. During the photocatalytic experiment, the (TiO2–Au)nps incorporated polymer matrices improved the photocatalytic reduction of nitrite ions to ammonia, owing to the effective interfacial charge transfer process in the presence of a hole scavenger, oxalic acid. Further increase in the photocatalytic reduction of nitrite to ammonia was observed by incorporating a [Ni(teta)]2+ complex into the MTMOS/(TiO2–Au)nps or Nf/(TiO2–Au)nps film. The immobilization of (TiO2–Au)nps in a functionalized silicate sol–gel or Nafion matrix is advantageous for the preparation of solid-phase photocatalyst film and to design a solid–solution system leading to the physical separation of the catalyst from the solution and the products in contrast compared to the colloidal photocatalyst system. The Aunps deposited on TiO2 act as an e− sink which promotes efficient interfacial electron transfer from TiO2 to the substrate upon irradiation. The ultimate contact between (TiO2–Au)nps and Ni(II) complex in the film efficiently promotes the electron transfer from Aunps to Ni(II) complex leading to the formation of an intermediate Ni(I) complex, which facilitates the efficient catalytic reduction of nitrite to ammonia.

Photocatalytic reduction of carbon dioxide to formic acid at porphyrin and phthalocyanine adsorbed Nafion membranes

Abstract The metal porphyrin (MP) and phthalocyanine (MPC) adsorbed Nafion membranes are prepared (Nf/MP and Nf/MPC) and used as photocatalysts for the photoreduction of carbon dioxide (CO2). The formation of formic acid (HCOOH) is observed when the Nf/MP and Nf/MPC membranes are dipped in CO2 saturated solution and irradiated in the presence of a sacrificial electron donor such as triethanolamine (TEA). The turnover number of the photocatalysts are very high in the presence of a sacrificial electron donor. The Nf/MP and Nf/MPC membranes behave as a p-type semiconductor. The irradiation of these membranes leads to the formation of holes (MP-« or MPC-«) and HCOOH by electron transfer. The TEA acts as sacrificial electron donor and scavenges the holes.