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1.
Phys Chem Chem Phys ; 21(45): 25196-25205, 2019 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-31696882

RESUMO

Vertical graphene nanosheets (VGN) are envisioned as supercapacitor (SC) electrode materials due to their distinct geometry and remarkable properties. Of late, the hybrid structures of graphene-transition metal (TM) or oxides were found to exhibit enhanced charge storage capacity. Herein, we report the charge storage performance of VGN-transition metal nanoparticle (Au, Ag, Cu, and Ni) hybrid electrodes. Amongst them, Ni-decorated VGN exhibited the highest enhancement, up to 3.04 mF cm-2 (121.6 F g-1) compared to 0.16 mF cm-2 (6.4 F g-1) for as-grown VGN. Further, this was corroborated by the improved electrical as well as ionic conductivity of the metal-decorated VGN structures. Additionally, the presence of metal-oxygen-carbon bonding ensured a contribution of pseudocapacitance. Ab initio calculations elucidated the extent as well as the nature of charge (e-) transfer in TM nanoparticle-VGN hybrid structures. These findings are well corroborated with the charge storage performance. A combined effect from charge transfer and pseudocapacitance on the charge storage performance of TM nanoparticle-VGN hybrid electrodes is demonstrated. A symmetric coin-cell supercapacitor device using Ni/VGN electrodes was fabricated and the sustained performance tested over 10 000 charge-discharge cycles.

2.
Nanotechnology ; 28(41): 415702, 2017 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-28745613

RESUMO

Vertical graphene nanosheets (VGN) are the material of choice for application in next-generation electronic devices. The growing demand for VGN-based flexible devices for the electronics industry brings in restriction on VGN growth temperature. The difficulty associated with the direct growth of VGN on flexible substrates can be overcome by adopting an effective strategy of transferring the well-grown VGN onto arbitrary flexible substrates through a soft chemistry route. In the present study, we report an inexpensive and scalable technique for the polymer-free transfer of VGN onto arbitrary substrates without disrupting its morphology, structure, and properties. After transfer, the morphology, chemical structure, and electrical properties are analyzed by scanning electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and four-probe resistive methods, respectively. The wetting properties are studied from the water contact angle measurements. The observed results indicate the retention of morphology, surface chemistry, structure, and electronic properties. Furthermore, the storage capacity of the transferred VGN-based binder-free and current collector-free flexible symmetric supercapacitor device is studied. A very low sheet resistance of 670 Ω/□ and excellent supercapacitance of 158 µF cm-2 with 86% retention after 10 000 cycles show the prospect of the damage-free VGN transfer approach for the fabrication of flexible nanoelectronic devices.

3.
Mater Sci Eng C Mater Biol Appl ; 76: 203-210, 2017 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-28482518

RESUMO

Graphene oxide (GO) based nanocomposites have gained considerable attention in the field of material science due to their excellent physicochemical and biological properties. Incorporation of nanomaterials into GO sheets prevents the formation of π-π stacking bond thereby giving rise to composites that show the improved properties compared to their individual counterparts. In this work, reduced graphene oxide (rGO) - hydroxyapatite (HAP) nanocomposites were synthesized by ultrasonic method. Increasing the c/a ratio of HAP in the diffraction pattern of rGO/HAP nanocomposites indicates the c-axis oriented grown HAP nanorods interacting with rGO layers. Shift in wavenumber (15cm-1) and increase of full width at half maximum (45cm-1) of G band in Raman spectra of the rGO/HAP nanocomposites are observed and attributed to the tensile strain induced due to the intercalated HAP nanorods between the rGO layers. Atomic force microscopy (AFM) and phase imaging studies revealed the intercalation of HAP nanorod with diameter 30nm and length 110-120nm in rGO sheets was clearly perceived along with improved elasticity compared to pristine HAP. 13C-NMR results proved the synergistic interaction between both components in rGO/HAP nanocomposite. The novel properties observed and the microscopic mechanism responsible for this are a result of the structural modification in rGO layers brought about by the intercalation of HAP nanorods.


Assuntos
Nanocompostos , Fenômenos Químicos , Durapatita , Grafite , Óxidos
4.
Phys Chem Chem Phys ; 18(32): 22160-7, 2016 Aug 10.
Artigo em Inglês | MEDLINE | ID: mdl-27445041

RESUMO

Defects in planar and vertically oriented nanographitic structures (NGSs) synthesized by plasma enhanced chemical vapor deposition (PECVD) have been investigated using Raman and X-ray photoelectron spectroscopy. While Raman spectra reveal the dominance of vacancy and boundary type defects respectively in vertical and planar NGSs, XPS provides additional information on vacancy related defect peaks in the C 1s spectrum, which originate from non-conjugated carbon atoms in the hexagonal lattice. Although an excellent correlation prevails between these two techniques, our results show that estimation of surface defects by XPS is more accurate than Raman analysis. Nuances of these techniques are discussed in the context of assessing defects in nanographitic structures.

5.
J Nanosci Nanotechnol ; 9(9): 5268-72, 2009 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-19928211

RESUMO

Ceria is an important rare-earth oxide with ever increasing applications. In nanocrystalline form, ceria exhibits novel and improved properties compared to its microcrystalline counterpart. The variation in the properties was observed to be a function of lowering particle size. This was also attributable to the presence and extent of Ce in 3+ state in ceria. Thermal decomposition of a thermally less stable cerium metal salt is an useful and simple method for the synthesis of nanocrystalline ceria. As atmosphere under which the decomposition occurs is expected to alter the Ce3+ content and thus the property, the present study is to investigate the effect of reactive atmosphere of decomposition vis-à-vis the particle size on the property of nanocrystalline ceria. Nanocrystalline ceria was synthesized by controlled thermal decomposition of cerium nitrate under four different atmospheres and the products were analyzed by X-Ray Diffraction, X-ray photoelectron spectroscopy and Laser Raman Spectroscopy. The observed property variation was found to be more dependent on the Ce3+ content thus the synthesis atmosphere rather than the particle size.

6.
J Nanosci Nanotechnol ; 9(9): 5480-3, 2009 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-19928248

RESUMO

Biofouling is one of the major impediment in the use of titanium, which is otherwise excellent material with respect to corrosion resistance and mechanical properties, for seawater-cooled condensers of power plants. The routine chlorination treatment and sponge ball cleaning may not be successful to keep the titanium condenser tube clean over a period extending to years. This brings into focus the relevance of surface modification of titanium to improve the antimicrobial properties, which can effectively supplement the present treatment programmes. In this study antimicrobial thin film of copper (Cu) is developed on titanium surfaces, as copper is known to be very toxic to microorganisms and effectively kills most of the microbes by blocking the respiratory enzyme system. The preparation of nanocrystalline thin films of copper on titanium surfaces was done by pulsed DC magnetron-sputtering technique. Then this thin film was characterized using Glancing Incidence X-ray Diffraction (GIXRD) and Atomic Force Microscopy (AFM). Antimicrobial properties of these specimens were evaluated by exposure studies in seawater. Results showed two order decrease in the bacterial density on copper coated surface and epifluorescence micrographs depicted very few fluorescing cells and no biofilm formation clearly demonstrating the superior antibacterial capability of this nanocrystalline copper thin film.


Assuntos
Cobre , Titânio , Incrustação Biológica , Cobre/química , Microscopia de Força Atômica , Propriedades de Superfície , Titânio/química , Difração de Raios X
7.
Biofouling ; 25(8): 705-10, 2009 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-20183129

RESUMO

Biofouling, especially microfouling, is a major concern with the use of titanium (Ti) in the marine environment as a condenser material in cooling water systems. Earlier, copper-nickel (Cu/Ni) alloys were extensively used in marine environments due to their high corrosion and biofouling resistance. However, the choice of condenser material for the new fast breeder reactor in Kalpakkam is Ti to avoid steam side corrosion problems, which may pose a threat to steam generator parts having sodium as the secondary coolant. This study evaluates the surface modification of Ti using nano films of copper (Cu) and nickel (Ni) to utilize the antibacterial property of copper ions in reducing microfouling. The surface modification of Ti was carried out by the deposition of a Cu/Ni bilayer and (Cu/Ni)(10) multilayer films using a pulsed laser deposition technique. Various surface characterization studies revealed that the deposited Cu/Ni films were thin and nanocrystalline in nature. The antibacterial properties were evaluated using total viable count and epifluorescence microscopic techniques. The results showed an apparent decrease in bacterial attachment on multilayered and bilayered Cu/Ni thin films on Ti surfaces. Comparative studies between the two types of films showed a bigger reduction in numbers of microorganisms on the multilayers.


Assuntos
Antibacterianos/farmacologia , Bactérias , Biofilmes , Cobre/farmacologia , Nanoestruturas/química , Níquel/farmacologia , Titânio/farmacologia , Antibacterianos/química , Bactérias/efeitos dos fármacos , Bactérias/crescimento & desenvolvimento , Biofilmes/efeitos dos fármacos , Biofilmes/crescimento & desenvolvimento , Cobre/química , Lasers , Biologia Marinha/métodos , Teste de Materiais , Microscopia de Fluorescência , Nanopartículas , Níquel/química , Propriedades de Superfície , Titânio/química
8.
J Nanosci Nanotechnol ; 7(6): 2005-9, 2007 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-17654981

RESUMO

A novel methodology based on a hybrid approach has been evolved for synthesizing nearly monodisperse nanocrystalline oxides. The approach basically involves precipitation of gelatinous hydroxide in liquid phase hydrolysis and subsequent temperature programmed calcination to obtain nanocrystalline oxide. Cr2O3 and ZrO2 have been synthesized through this route. This paper describes synthesis procedures giving details of temperature windows required for this synthesis. In addition, solid state analytical technique like X-Ray Diffraction (XRD) and Photoluminescence (PL) have been used to characterize these materials. Especially PL was used to derive information on confinement effect. Transmission Electron Microscope (TEM), Scanning Probe Microscope (SPM), and Scanning Near Field Optical Microscope (SNOM) were used to derive morphology.


Assuntos
Cerâmica/química , Compostos de Cromo/química , Cristalização/métodos , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Nanotecnologia/métodos , Zircônio/química , Impedância Elétrica , Substâncias Macromoleculares/química , Magnetismo , Teste de Materiais , Conformação Molecular , Tamanho da Partícula , Propriedades de Superfície
9.
J Nanosci Nanotechnol ; 7(6): 2176-81, 2007 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-17655013

RESUMO

Nanocrystalline CrN coatings, widely required for surface engineering application covering wear and corrosion resistance, need to be investigated for atomic scale morphology, surface roughness, local stiffness, phase uniformity, and homogeneity. Evolution of these properties as a function of thickness need to be studied. In this paper, we have attempted to address these issues through use of a multimode scanning probe microscope (SPM) equipped to carry out Atomic Force Microscopy (AFM) and Atomic Force Acoustic microscopy (AFAM) of Chromium nitride films (100-500 nm thick) on Si prepared under high vacuum by pulsed Laser Ablation using Nd-YAG Q-switched laser. Prior to SPM analysis, the coatings were annealed in N2 atmosphere at 700 degrees C for 30 minutes for improving crystallanity and coating substrate adhesion. The GIXRD patterns of these annealed specimens showed formation of nanocrystalline CrN. Also signature of amorphous phases was seen. The grain size was estimated to be less than 30 nm. Contact mode AFM imaging revealed a roughness value less than 50 nm. Local stiffness values were calculated from AFM force-distance curves. Imaging of frictional force and surface flaws are being investigated by Frictional Force Microscopy (FFM), resonance spectroscopy, and AFAM, respectively. The contrast in AFAM images is seen due to variation in surface elasticity in reference and CrN samples. Stiffness constant and elastic modulus were calculated for both the samples and compared.

10.
J Nanosci Nanotechnol ; 7(3): 970-6, 2007 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-17450861

RESUMO

Nanocrystalline chromiuim nitride has been synthesised by direct gas phase nitridation of nanocrystalline chromia at 1100 degrees C in ammonia-atmosphere. XRD of this material showed formation of single phase CrN with particle size around 20 nm. AFM studies showed particle distribution along with some soft agglomerated nanostructures. Nanocrystalline Cr2O3 and partially-as well as fully--converted nanocrystalline CrN were also investigated using various spectroscopic techniques like XPS, FT-IR, and Raman for gaining insight into the conversion pathways. Spectroscopic investigations of these materials clearly indicate that complete conversion of CrN occurs by nitriding at 1100 degrees C for 4 hrs. The salient spectroscopic features of these nanocrystalline materials with respect to their microcrystalline counterparts are discussed.


Assuntos
Compostos de Cromo/química , Nanopartículas Metálicas/química , Nanopartículas Metálicas/ultraestrutura , Microscopia de Força Atômica , Nanotecnologia , Tamanho da Partícula , Difração de Pó , Espectrofotometria Infravermelho , Análise Espectral , Análise Espectral Raman , Raios X
11.
J Phys Condens Matter ; 18(17): 4427-42, 2006 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-21690793

RESUMO

In this paper, we examine the possible influence of extrinsic factors on the electrical and magnetotransport of La(0.67)Ca(0.33)Mn(1-x)Ru(x)O(3) (x≤0.10). Ru substitution results in double metal-insulator transitions (MITs) at T(MI1) and T(MI2), both exhibiting magnetoresistance (MR). No additional magnetic signal corresponding to a second low-temperature maximum (LTM) at T(MI2) could be observed, either in ac susceptibility (χ(')) or in specific heat (C(p)). Typical grain sizes of ∼18 000-20 000 nm, as estimated from the scanning electron microscope (SEM) micrographs, are not so small as to warrant an LTM. The absence of additional peaks in the high statistics powder x-ray diffraction (XRD), a linear systematic increase of the unit cell parameters, close matching of the transition temperatures in resistivity, χ(') and C(p) and their linear systematic decrease with x, and an homogeneous distribution of Mn, Ru and O at arbitrarily selected regions within and across the grains exclude chemical inhomogeneity in the samples. The insensitivity of grain boundary MR at 5 K to Ru composition indicates that the grain boundary is not altered to result in an LTM. Oxygen stoichiometry of all the compounds is close to the nominal value of 3. These results not only exclude the extrinsic factors, but also establish that double MITs, both exhibiting MR, are intrinsic to Ru substituted La(0.67)Ca(0.33)MnO(3).

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