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Haldorai, Yuvaraj,Huh, Yun Suk,Han, Young-Kyu American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.7
<P>We successfully fabricated zinc oxide/reduced graphene oxide (ZnO/rGO) nanocomposite via a simple and environmentally-friendly route using supercritical carbon dioxide (scCO(2)), where reduction of graphene oxide and growth of ZnO nanoparticles occurred in one-step. Transmission electron microscopic analysis revealed that the ZnO nanoparticles of size 10-20 nm were decorated onto the rGO surface. The ZnO nanoparticles on the rGO surface were spherical and well dispersed. Antibacterial activity of the composite was tested against Escherichia coli, Bacillus cereus, and Staphylococcus aureus as model strains. Minimum inhibitory concentrations (MICs) ranging 0.08-1.3 mu g/mL were observed for all the pathogens. The MIC of the composite against the test strains showed that it has a less significant effect on the growth of S. aureus than B. cereus and E. coli. The efficient antibacterial activity was attributed to the synergistic effect of rGO and ZnO nanoparticles.</P>
Haldorai, Yuvaraj,Kim, Jun Yeong,Vilian, A.T. Ezhil,Heo, Nam Su,Huh, Yun Suk,Han, Young-Kyu Elsevier 2016 Sensors and actuators. B, Chemical Vol.227 No.-
<P><B>Abstract</B></P> <P>Cobalt oxide (Co<SUB>3</SUB>O<SUB>4</SUB>) nanospindles-decorated reduced graphene oxide (RGO) composite is prepared via thermal decomposition of a three-dimensional coordination complex precursor, cobalt benzoate dihydrazinate, at 200°C. Transmission electron microscopy reveals that Co<SUB>3</SUB>O<SUB>4</SUB> nanospindles with an average particle size of <25nm are decorated on the RGO surface. The low decomposition temperature and lack of residual impurities are significant aspects of this simple and facile method. The electrochemical performance of the proposed sensor is investigated using cyclic voltammetry and chronoamperometry. Under optimum conditions, anodic peak currents are linearly proportional to their concentrations, in the range of 1–380μM for nitrite with a regression equation of <I>I</I> (μA)=2.0660C+6.7869 (<I>R</I> <SUP>2</SUP> =0.9992). The sensor exhibits a high sensitivity of 29.5μAμM<SUP>−1</SUP> cm<SUP>−2</SUP>, a rapid response time of 5s, and a low detection of limit of 0.14μM. The proposed electrode shows good reproducibility and long-term stability. The sensor is used to determine the nitrite level in tap water with acceptable recovery, implying its feasibility for practical application.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Facile synthesis of Co<SUB>3</SUB>O<SUB>4</SUB> nanospindles/RGO composite. </LI> <LI> The low detection limit for nitrite sensing was identified as 0.14μM. </LI> <LI> Detection of wide range (1–380μM) of nitrite concentrations. </LI> <LI> High stability and reproducibility of the composite electrode. </LI> <LI> Excellent anti-interference capacity towards various common ions. </LI> </UL> </P>
Haldorai, Yuvaraj,Huh, Yun Suk,Han, Young-Kyu The Royal Society of Chemistry 2015 New journal of chemistry Vol.39 No.11
<P>We report a simple, one-pot hydrothermal method for synthesizing tin oxide (SnO<SUB>2</SUB>) nanoparticle-decorated reduced graphene oxide (RGO) nanocomposites. Transmission electron microscopy images show that flower-like SnO<SUB>2</SUB> architectures are homogeneously dispersed onto the RGO surface. The composite exhibits a maximum specific capacitance of 396 F g<SUP>−1</SUP> (at a current density of 4.5 A g<SUP>−1</SUP>), with a capacitance retention of 92.6% even after 10 000 continuous charge/discharge cycles, which is sevenfold higher than that of pure RGO (55 F g<SUP>−1</SUP>). The high capacitance is attributed to the synergetic effect of SnO<SUB>2</SUB> and RGO. In addition, the composite shows efficient photodegradation of methylene blue under visible light. The enhanced degradation is ascribed to good adsorption and improved separation efficiency of photo-induced electron–hole pairs.</P> <P>Graphic Abstract</P><P>SnO<SUB>2</SUB>/graphene nanocomposites showed excellent capacitance with a capacitance retention of 92.6% even after 10 000 continuous charge/discharge cycles. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5nj01442e'> </P>
Haldorai, Yuvaraj,Vilian, A.T. Ezhil,Rethinasabapathy, Muruganantham,Huh, Yun Suk,Han, Young-Kyu Elsevier 2017 Sensors and actuators. B, Chemical Vol.247 No.-
<P><B>Abstract</B></P> <P>A composite comprising reduced graphene oxide (RGO) and titanium nitride (TiN) was fabricated via a combined two-step process of sol-gel and ammonia annealing. Transmission electron microscopy showed that TiN nanoparticles with a mean diameter of <10nm were densely decorated onto the RGO surface. Cyclic voltammetry indicated that a glassy carbon electrode (GCE) modified with the RGO–TiN nanocomposite exhibited an excellent electrocatalytic activity toward the oxidation of dopamine in 0.1M phosphate buffer solution (pH=7). The combined use of RGO and TiN resulted in a higher current response and a lower oxidation potential (0.23V) than those of bare GCE, RGO/GCE, and TiN/GCE. In addition, the developed electrochemical sensor showed a linear relationship with the dopamine concentration from 0.1 to 80μM with a limit of detection of 0.012μM (S/N=3). The sensor demonstrated excellent selectivity, good stability, and reproducibility. The sensor was applied to the determination of dopamine in urine samples by the standard addition method and gave recoveries of 97.0–101.5%.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Facile synthesis of RGO-TiN composite. </LI> <LI> Excellent electrocatalytic activity towards the oxidation of DA. </LI> <LI> The low detection limit for DA sensing was identified as 0.012μM. </LI> <LI> The sensor showed a high sensitivity of 35.8μA μM<SUP>−1</SUP> cm<SUP>−2</SUP>. </LI> <LI> Excellent selectivity with good stability and reproducibility of the electrode. </LI> </UL> </P>
Haldorai, Yuvaraj,Yeon, Sun-Hwa,Huh, Yun Suk,Han, Young-Kyu Elsevier 2017 Sensors and actuators. B Chemical Vol.239 No.-
<P><B>Abstract</B></P> <P>A nanocomposite consisting of reduced graphene oxide (rGO) decorated with tin oxide (SnO<SUB>2</SUB>) nanoparticles was fabricated using a hydrothermal route. Cyclic voltammetry showed that a glassy carbon electrode (GCE) modified with the rGO/SnO<SUB>2</SUB> composite exhibited an excellent electrocatalytic activity towards the oxidation of amino acid tryptophan (Trp) in 0.1M phosphate buffer solution (pH=7). The combined use of rGO and SnO<SUB>2</SUB> results in higher current response and lower oxidation potential (0.76V) compared to those of a bare GCE, SnO<SUB>2</SUB>/GCE, and rGO/GCE. Differential pulse voltammetry study showed a linear relationship to the Trp concentration of 1–100μM. The low detection limit of Trp was identified at 0.04μM (S/N=3) with sensitivity of 37.3μAμM<SUP>−1</SUP> cm<SUP>−2</SUP>. The sensor demonstrated an excellent selectivity, good stability, and reproducibility. The sensor was applied to the determination of Trp in spiked milk and amino acid injection samples by the standard addition method and gave recoveries of 98.0–101.3% and 98.1–102.5%, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hydrothermal synthesis of rGO/SnO<SUB>2</SUB> flower-like nanocomposite. </LI> <LI> Excellent electrocatalytic activity towards the oxidation of tryptophan. </LI> <LI> The low detection limit for tryptophan sensing was identified as 0.04μM (S/N=3). </LI> <LI> The sensor showed a high sensitivity of 37.3μAμM<SUP>−1</SUP> cm<SUP>−2</SUP>. </LI> <LI> Excellent selectivity with good stability and reproducibility of the electrode. </LI> </UL> </P>
Chemo-responsive bilayer actuator film: fabrication, characterization and actuator response
Haldorai, Yuvaraj,Shim, Jae-Jin The Royal Society of Chemistry 2014 NEW JOURNAL OF CHEMISTRY Vol.38 No.6
<P>A chemo-responsive bilayer actuator was fabricated by cross-linking a polysaccharide based highly hydrophilic material with the polyamide-6 (PA-6) substrate. The hydrogel material was prepared by grafting the polyacrylamide (PAAm) and poly(acrylic acid) (PAA) copolymer onto carboxymethyl cellulose (CMC) [poly(AA-<I>co</I>-AAm)-<I>g</I>-CMC]. The successful grafting of the copolymer onto CMC was confirmed by Fourier transform infrared spectroscopy and thermogravimetric analysis. The swelling behavior of the poly(AA-<I>co</I>-AAm)-<I>g</I>-CMC hydrogel was examined at a range of pH values and ionic strengths. Fabrication of the bilayer actuator was performed by drop casting a poly(AAm-<I>co</I>-AA)-<I>g</I>-CMC solution onto a PA-6 substrate followed by subsequent cross-linking under ultraviolet radiation. Cross-linking was performed to make the material readily swellable in water but prevent complete dissolution. The actuator response was measured in both water and ethanol.</P> <P>Graphic Abstract</P><P>A bilayer actuator showing fast and stable curling/uncurling motion was prepared by photo-cross-linking poly(AAm-<I>co</I>-AA)-<I>g</I>-CMC onto PA-6. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4nj00014e'> </P>
Yuvaraj, Haldorai,Shim, Jae-Jin,Lim, Kwon Taek John WileySons, Ltd. 2010 Polymers for advanced technologies Vol.21 No.6
<P>Organic-inorganic hybrid nanocomposites composed of conductive polypyrrole (PPy) and surface modified silica (SiO2) were successfully prepared through an in situ chemical oxidative polymerization in supercritical carbon dioxide (scCO(2)). SiO2 nanoparticles were surface modified using 3-methacryloxypropyltrimethoxysilane (MPTMS) in order to disperse well in the medium. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that the SiO2 nanoparticles were encapsulated into the polymer. UV-visible spectra of the diluted colloidal dispersions of PPy/SiO2 hybrid nanocomposites were similar to those of PPy system. Fourier transform infrared spectroscopy (FT-IR) suggested the strong interaction between PPy and SiO2. Surface characterizations of nanocomposites were described by X-ray photoelectron spectroscopy (XPS). The nanocomposites synthesized in scCO2 have been shown to possess higher electrical conductivity and thermal stability. Copyright (C) 2009 John Wiley & Sons, Ltd.</P>