Synthesis of graphene nano-sheets using eco-friendly chemicals and microwave radiation

Sridhar, V.,Jeon, Jin-Han,Oh, Il-Kwon Elsevier 2010 Carbon Vol.48 No.10

<P><B>Abstract</B></P><P>A novel approach to synthesize graphene nano-sheets by combining chemical treatment and microwave radiation is demonstrated using eco-friendly chemicals. Microwave radiation was used to produce strong expansion of the graphite worm in the thickness direction. The graphene nano-sheets obtained in this study were characterized by morphology images, nanoprofilometry, Raman and X-ray photoelectron spectroscopy. Besides being eco-friendly, the proposed method has also the attractive advantage of being rapidly able to produce a lot of graphene nano-sheets.</P>

Concomitant endoscopic biliary, duodenal and colonic stent placement for advanced carcinoma of gall bladder

Sridhar Sundaram,Sidharth Harindranath,Praveen Kumar Rao,Nitin Ramani,Aditya Kale,Shraddha Patkar 소화기인터벤션의학회 2021 International journal of gastrointestinal interven Vol.10 No.4

Combined biliary and duodenal stent placement has been reported previously in multiple series. Rarely, colonic obstruction may present simultaneously with duodenal and biliary obstruction in advanced pancreaticobiliary cancers. Biliary, duodenal and colonic obstruction managed simultaneously using endoscopic modalities have been reported in only one case report previously. Here we report outcomes of a case of carcinoma of the gall bladder with biliary, gastric outlet and colonic obstruction managed by endoscopic placement of biliary, gastroduodenal and colonic self-expanding metal stents.

Synthesis of Cyclic Type Semi-Fluorinated Disodium Alkanesulfonate

Sridhar Chirumarry,고요한,장기완,신동수 대한화학회 2016 대한화학회지 Vol.60 No.4

A new perfluorobutyl substituted cyclic type disodium alkanesulfonate is designed, synthesized and characterized as alternative substance to perfluorooctane sulfonic acid (PFOS, 1), a well-known surfactant. Cylic type sulfonate was accomplished from commercially available 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol in four steps. Bio-degradable perfluorobutyl moiety was introduced from fluorous diol, which is symmetrically substituted amphiphile via installation of an intermediate trifluoromethanesulfonyl ester and easily manipulated by double displacement of triflate using potassium malonate and further reduction followed by nucleophilic ring opening are key reactions to get target disodium alkanesulfonate. The efficiency and simplicity in the synthesis of this material offer a new strategy to design PFOS alternatives.

Electrochemical, Photocatalytic and Photoluminescence properties of BaWO4 and rGO-BaWO4 nano-composites: A Comparative study

Sridhar Ch,Neha,Seo Young-Soo,Rabani Iqra,Turpu G.R.,Tigga Salinta,Padmaja G. 한국물리학회 2024 Current Applied Physics Vol.58 No.-

The rGO-BaWO4 (rGO-BWO) nanocomposites were synthesized by employing the ultrasonic-assisted co-precipitation method. Nanocomposites formed with BWO nanoparticles anchored to layers of reduced graphene oxide through in situ reduction and a homogeneous distribution of BWO nanoparticles were confirmed by SEM images. The rGO-BWO nanocomposite showed improved photocatalytic activity for the visible light degradation of Methylene Blue (MB) dye with a rate constant of 27 × 10 3 min 1 compared to pristine BWO. The band gaps for BWO nanoparticles estimated using UV–Vis DRS are of the order of 3.25 eV–4.25 eV, while they were 2.78 eV–3 eV for rGO BWO nanocomposites. The delocalized surface charges induced by the interactions between the rGO and BWO nanoparticles in the composite material might be responsible for the observed reduction in the band gap. Photoluminescent investigations demonstrate that rGO-BWO nanocomposites have a lower peak intensity compared to pure BWO particles, indicating a reduced recombination rate and better photocatalytic activity. In particular, when used as supercapacitor electrodes, the produced nanocomposites outperform BWO. Because of its larger surface area, the rGO-BWO nanocomposites display two-fold higher outcomes including 586, 571, 406, 375 and 307 F/g compared to BWO 391, 352, 291, 214 and 174 F/g at each current density 1, 2, 3, 5 and 10 A/g and faster charge transfer owing to improved porosity in the surface of rGO-BWO.

From rheometry to rheology

Sridhar, T. The Korean Society of Rheology 2000 Korea-Australia rheology journal Vol.12 No.1

Using a variety of examples from the recent literature on extensional flow of polymer solutions, this paper shows that simple constitutive equations are unable to capture the diversity of chain conformations in such flows. Such diversity is a feature of extensional flows and arises because deformation leads to significant chain extension. Substantial local extension appears even at low strains and the behaviour of these stretched out portions influences the dynamics of the chain and makes a dominant contribution to the stress. Both the distribution function and the chain conformation appear to follow different paths during stretching and relaxation. As a result the second moment of the distribution function does not contain enough information to correctly predict the dynamics. Resolution of this deficiency in simple constitutive models is one of the challenges for rheology.

Sediment geochemistry with population of recent benthic ostracoda in Palk Bay, southeast coast of India

Sridhar G.D. Sithu,Baskar Kuppusamy,Maniyarasan Subramaniyan,Hussain M. Sheik 한국지질과학협의회 2016 Geosciences Journal Vol.20 No.2

Seasonal observation on trace elements of shallow inner shelf sediments and their correlation with the population of recent benthic ostracoda off Rameswaram, Ramanathapuram District, Tamil Nadu, Southeast coast of India is the aim of this study. The sediments were analysed for trace elements Al, Fe, Mn, Zn, Cu, Pb, Cd, Ni, Co and Cr and being correlated with the population of benthic ostracoda for four different seasons. Cu has a positive correlation, and Fe, Mn, Zn, Pb, Cd, Ni, Co and Cr have negative correlation with the total population of ostracoda. Al has no considerable correlation with the total population of ostracoda. In the middle segment plenty of corals were found in the study area and their effect being discussed.

Dielectric and dynamic mechanical relaxation behavior of exfoliated nano graphite reinforced flouroelastomer composites

Sridhar, V.,Xu, Deng,Pham, Thanh Tu,Mahapatra, S.P.,Kim, Jin Kuk Wiley Subscription Services, Inc., A Wiley Company 2009 Polymer composites Vol.30 No.3

<P>Dynamic mechanical analysis and dielectric relaxation spectra of exfoliated nano graphite reinforced flouroelastomer composites were used to study their relaxation behavior as a function of temperature (−80°C to +40°C) and frequency (0.01 to 10<SUP>5</SUP> Hz). The effect of filler loadings on glass transition temperature was marginal for all the composites and T<SUB>g</SUB> value was in the narrow range of 7.8–8.4°C, which has been explained on the basis of relaxation dynamics of polymer chains in the vicinity of fillers. Strain-dependent dynamical parameters were evaluated at dynamic strain amplitudes of 0.01–10%. The nonlinearity in storage modulus has been explained on the concept of filler-polymer interaction and filler aggregation of the nano graphite platelets. The variation in real and complex part of impedance with frequency has been studied as a function of filler. The percolation of the nano graphite as studied by conductivity measurements is also reported. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.</P>

Tunnel Recognition for Vision Based Driver Assistance System

Sridhar S,Jitesh K. Singh,Roh Seung Hyun 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11

Detecting changes in the environment while driving is critical in any vision based driving assistance system. These environmental changes have to be handled separately to enhance ADAS (advanced driver assistance system) performance. In particular, this paper focuses on detecting tunnel using a simple and computationally efficient approach. Conventional tunnel detection approaches use tunnel entry and exit information for its recognition. These approaches fail for different tunnel cases and during night condition. In this paper, we propose tunnel recognition algorithm using the pattern of lights available inside the tunnel. The first order line fitting algorithm is used to track the tunnel lights, which almost follow straight lines. The magnitude of error in line fitting decides whether the image has a tunnel or not. It has been observed that the intensity inside the tunnel is less compared to outside environment during day condition. Using this criterion, brightness parameter is calculated to avoid unnecessary processing of normal day image. The proposed algorithm has been tested on both day and night images captured from grayscale monocular camera mounted on the ego vehicle.

Novel clays: Solid-state synthesis, characterization and cation exchange selectivity

Sridhar Komarneni,Ramesh Ravella 한국물리학회 2008 Current Applied Physics Vol.8 No.1

Several novel swelling mica-type clays have been synthesized by solid-state processes. Synthetic clays of ideal compositions such asNa2Si6Al2Mg 6O20F4 ÆxH2O (Na-2-mica), Na3Si5Al3Mg 6O20F4 ÆxH2O (Na-3-mica) and Na4Si4Al4Mg 6O20F4 ÆxH2O (Na-4-mica) havebeen prepared and characterized by powder X-ray diraction (XRD), scanning electron microscopy (SEM) and27Al and29Si solid-statemagic angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. Powder XRD showed that all syntheses yielded water swol-len micas withc-axis spacing of. 1.2 nm except in the case of Na-2-mica which also showed a small peak of anhydrous mica phase with ac-axis spacing of 0.96 nm. Solid-state27Al MASNMR spectroscopy revealed that almost all the Al is present in the tetrahedral environ-29Si MASNMR spectroscopy revealed dierent Si (Al) nearest neighbor environments dependingupon the composition of the various micas. Selective cation exchange studies were performed on the various micas using 0.5 N NaClsolution containing 12.9 ppm Sr2+ or 8.12 ppm of La3+. The results showed, for the rst time, that Na-3-mica has a high selectivityfor the trivalent cation tested. The previously reported high selectivity of these synthetic micas for the divalent cations has been con-rmed. These selective cation exchange studies are of relevance in cation separations from drinking and waste waters.

Defect-Engineered Three-Dimensional Graphene–Nanotube–Palladium Nanostructures with Ultrahigh Capacitance

Sridhar, Vadahanambi,Kim, Hyun-Jun,Jung, Jung-Hwan,Lee, Changgu,Park, Sungjin,Oh, Il-Kwon American Chemical Society 2012 ACS NANO Vol.6 No.12

<P>The development of three-dimensional carbon-based nanostructures is the next step forward for boosting industrial applications of carbon nanomaterials such as graphenes and carbon nanotubes. Some defects, which have been considered as detrimental factors for maintaining exceptional materials properties of two-dimensional graphene, can be actively used to synthesize three-dimensional graphene-based carbon nanostructures. Here we describe a fast and heretofore unreported defect-engineered method to synthesize three-dimensional carbon nanohybrid structures with strong bonding between graphene nanoplatelets and carbon nanotubes using simple microwave irradiation and an ionic liquid. Our one-pot method utilizes defect-engineered sequential processes: microwave-based defect generation on graphene nanoplatelets, anchoring of palladium nanoparticles on these defects, and subsequent growth of carbon nanotubes by use of an ionic liquid. The unique three-dimensional nanostructures showed an ultrahigh redox capacitance due to high porosity, a high surface-to-volume ratio from the spacer role of vertically standing one-dimensional carbon nanotubes on graphene sheets, and capacitance-like redox response of the palladium nanoparticles. The proposed defect-engineered method could lead to novel routes to synthesizing three-dimensional graphene-based nanostructures with exceptionally high performance in energy storage systems.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-12/nn3046133/production/images/medium/nn-2012-046133_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn3046133'>ACS Electronic Supporting Info</A></P>