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The improved electrochemical performance of cross-linked 3D graphene nanoribbon monolith electrodes
No full textTechnical advancement in the field of ultra-small sensors and devices demands the development of novel
micro- or nano-based architectures. Here we report the design and assembly of cross-linked three
dimensional graphene nanoribbons (3D GNRs) using solution based covalent binding of individual 2D
GNRs and demonstrate its electrochemical application as a 3D electrode. The enhanced performance of
3D GNRs over individual 2D GNRs is established using standard redox probes – [Ru(NH3)6]3+/2+,
[Fe(CN)6]3−/4− and important bio-analytes – dopamine and ascorbic acid. 3D GNRs are found to have
high double layer capacitance (2482 μF cm−2) and faster electron transfer kinetics; their exceptional
electrocatalytic activity towards the oxygen reduction reaction is indicative of their potential over a wide
range of electrochemical applications. Moreover, this study opens a new platform for the design of novel
point-of-care devices and electrodes for energy device
Chemically modified flexible strips as electrochemical biosensors
No full textA flexible and disposable strip sensor for non-enzymatic glucose detection is demonstrated in this work.
The strips are prepared by using chemical modification processes followed by a simple electroless
deposition of copper. Essentially, polyester overhead projector (OHP) transparent films are modified with
a monolayer of 3-aminopropyltrimethoxysilane (APTMS) and polyaniline (PANI) conducting polymer.
Later, nanostructured copper is deposited onto this modified film. Scanning electron microscope (SEM)
and X-ray diffraction (XRD) studies are used for the structural, morphological and crystallinity
characterization of the modified films. Electrochemical techniques, namely cyclic voltammetry (CV) and
chronoamperometry (CA), are employed for the non-enzymatic detection of glucose. These studies
clearly reveal the formation of homogeneous, close-packed spherical Cu particles converged into
uniform film that exhibits a good catalytic activity towards the oxidation of glucose. The Cu/PANI/
APTMS/OHP sensor displays a remarkable enhancement in the oxidation current density, a very high
sensitivity value of 2.8456 mA cm�2 per mM, and a linear concentration range from 100 mM to 6.5 mM
associated with glucose detection. Detection limit is estimated to be 5 mM and the response time of the
sensor is determined to be less than 5 s. For comparison, similar studies are performed without PANI,
namely Cu/APTMS/OHP films for glucose detection. In this case, a sensitivity value of 2.4457 mA cm�2
per mM and a linear concentration range of 100 mM–3 mM are estimated. The higher performance
characteristics observed in the case of Cu/PANI/APTMS/OHP are attributed to the synergistic effects of
the conducting polymer acting as an electron facilitator and the nanostructured Cu films. These
disposable, flexible and low-cost strip sensors have also been applied to the detection of glucose in
clinical blood serum samples and the results obtained agree very well with the actual glucose leve
Nanocrystallization in magnetron sputtered Zr–Cu–Al–Ag thin film metallic glasses
No full textZr-based thin film metallic glasses (TFMG) were fabricated from a polycrystalline Zr48Cu36Al8Ag8 (at.%)
target by DC magnetron sputtering. A series of characterization techniques were employed to study the
structure, composition and thermal stability of the glassy coating and also the mechanical compliance of
the TFMG over stainless steel. X-ray diffraction indicated a completely amorphous microstructure. However,
specimens prepared for plan-view TEM revealed nanocrystallites of the CuZr2 phase dispersed in an
amorphous matrix. Annealing experiments showed that the primary phase to nucleate in the films is the
CuZr2 phase as observed from XRD data. The film/substrate interface did not show any inter-diffusion, as
confirmed by high resolution scanning TEM. Calorimetric studies by DSC showed a large supercooled
liquid region of about 83 K. Surface morphological studies by both FE-SEM and AFM indicated a very
smooth surface devoid of pores or cracks, with an average roughness of about 1.25 nm. X-ray photoelectron
spectroscopy (XPS) showed oxygen on the film surface; both Zr and Al revealed non-metallic
bonding peaks concomitant with a mixed or bilayer oxide on the surface. A very high scratch resistance
was observed for the specimen coated over stainless steel substrate
Nanodiamond-Based Thermal Fluids
No full textDispersions of nanodiamond (average size ∼6 nm)
within dielectric insulator mineral oil are reported for their enhanced
thermal conductivity properties and potential applications in thermal
management. Dynamic and kinematic viscositiesvery important
parameters in thermal management by nanofluidsare investigated.
The dependence of the dynamic viscosity is well-described by the
theoretical predictions of Einstein’s model. The temperature
dependence of the dynamic viscosity obeys an Arrhenius-like
behavior, where the activation energy and the pre-exponential factor
have an exponential dependence on the filler fraction of nanodiamonds.
An enhancement in thermal conductivity up to 70% is
reported for nanodiamond based thermal fluids. Additional electron microscopy, Raman spectroscopy and X-ray diffraction
analysis support the experimental data and their interpretation
Improved heterogeneous electron transfer kinetics of fluorinated graphene derivatives
No full textThough graphitic carbons are commercially available for various electrochemical processes, their
performance is limited in terms of various electrochemical activities. Recent experiments on layered
carbon materials, such as graphene, demonstrated an augmented performance of these systems in all
electrochemical activities due to their unique electronic properties, enhanced surface area, structure and
chemical stabilities. Moreover, flexibility in controlling electronic, as well as electrochemical activities by
heteroatom doping brings further leverage in their practical use. Here, we study the electron transfer
kinetics of fluorinated graphene derivatives, known as fluorinated graphene oxide (FGO) and its reduced
form, RFGO. Enhanced electron transfer kinetics (heterogeneous electron transfer (HET)) is observed
from these fluorinated systems in comparison to their undoped systems such as graphene oxide (GO)
and reduced GO. A detailed study has been conducted using standard redox probes and biomolecules
revealing the enhanced electro-catalytic activities of FGO and RFGO, and electron transfer rates are
simulated theoretically. This study reveals that fluorine not only induces defects in graphitic lattice
leading to an enhanced HET process but also can modify the electronic structure of graphene surfac
Composite Polymer Electrolytes Encompassing Metal Organic Frame Works: A New Strategy for All-Solid-State Lithium Batteries
No full textMagnesium-benzene tricarboxylate metal organic framework
(Mg-BTC MOF)-incorporated composite polymer electrolytes
(CPE) composed of poly(ethylene oxide) (PEO) and lithium
bistrifluoromethane sulfonylimide (LiTFSI) were prepared by a simple
hot-press technique. The incorporation of Mg-BTC MOF in the
polymeric matrix has significantly enhanced the ionic conductivity of
CPE up to two orders magnitudes even at 0 °C. It also improved the
thermal stability, compatibility, and elongation-at-break of the polymeric
membrane. The all-solid-state lithium polymer cell composed of Li/
CPE/LiFePO4 has delivered a stable discharge capacity of 110 mAh g−1
at 70 °C with a current rate of 1-C, which is higher than that of those
reported earlier. The appealing properties such as high ionic
conductivity, better compatibility, and stable cycling qualify this
membrane as electrolyte for all-solid-state lithium batteries for elevated
temperature application
Counter-ion Dependent, Longitudinal Unzipping of Multi-Walled Carbon Nanotubes to Highly Conductive and Transparent Graphene Nanoribbons
No full textHere we report for the first time, a simple hydrothermal approach for the bulk production of highly
conductive and transparent graphene nanoribbons (GNRs) using several counter ions from K2SO4, KNO3,
KOH and H2SO4 in aqueous media, where, selective intercalation followed by exfoliation gives highly
conducting GNRs with over 80% yield. In these experiments, sulfate and nitrate ions act as a co-intercalant
along with potassium ions resulting into exfoliation of multi-walled carbon nanotubes (MWCNTs) in an
effective manner. The striking similarity of experimental results in KOH and H2SO4 that demonstrates
partially damaged MWCNTs, implies that no individual K1, SO422 ion plays a key role in unwrapping of
MWCNTs, rather this process is largely effective in the presence of both cations and anions working in a
cooperative manner. The GNRs can be used for preparing conductive 16 kVsq21, transparent (82%) and
flexible thin films using low cost fabrication metho
Discerning Site Selectivity on Graphene Nanoflakes Using Conceptual Density Functional Theory Based Reactivity Descriptors
No full textGraphene nanoflakes (GNFs) have more configurational degrees
of freedom as compared to Graphene nanoribbons (GNRs) and are viable
candidates for future nanodevices. GNFs can be devised with disparate
geometries, and their electronic properties can be fine-tuned by genuine
chemical functionalization. Hence, it is vital to know specific sites on GNFs
where reaction is most feasible for chemical functionalization with donor−
acceptor functional groups (nucleophiles/electrophiles). Here, we present spinpolarized
and dispersion-corrected density functional theory based relative
reactivity descriptor calculations to shed light on the reactivity pattern in smallsized
GNFs. To have a clear understanding on the structure−property
relationship, we consider GNFs with 24, 42, and 54 carbon atoms having
various edges, namely, fully armchair, armchair/zigzag (arm-zig), and fully
zigzag. All the edge atoms are saturated by hydrogen atoms. On the basis of the
symmetry of the GNFs, susceptibility of assorted reactive sites pertinent to nucleophilic and electrophilic attacks is anticipated
using relative reactivity descriptors. Further, we validate these relative reactivity descriptors for nucleophilic attack on armchair-
C24H14 and zigzag-C24H12 by explicit adsorption of OH−, NH2
−, and H2O molecules. Our study reveals that the reactivity pattern
varies in small-sized GNFs as a function of shape. Importantly, few specific structural isomers have alternate Lewis acid−base
pairs. It also manifests how the reactivity of peripheral and interior carbon atoms differ with shape and size of GNFs. With a
discernment on site selectivity, GNFs can be functionalized by proper donor−acceptor groups at specific sites and hence can be
used as potential candidates for molecular- and nanoelectronic
Novel mixed hydroxy-carbonate precursor assisted synthetic technique for LiNi1/3Mn1/3Co1/3O2 cathode materials
No full textNovel mixed hydroxy-carbonate (MHC) precursors were used to synthesis technique of LiNi1/3Mn1/3Co1/
3O2 cathode material. The powder X-ray diffraction (XRD) pattern of the synthesized LiNi1/3Mn1/3Co1/3O2
cathode materials exhibited a hexagonal cell with a = 2.8535 A˚ and c = 14.2040 A˚ . Fourier transform
infrared spectroscopy (FT-IR) spectrum of MHC and LiNi1/3Mn1/3Co1/3O2 consistent with vibration
modes of functional group. Presence of sub-micrometer particle size (200 nm) and highly crystalline
morphology confirmed using scanning electron microscopy (SEM). X-ray photoelectron spectroscopy
(XPS) suggested that oxidation state of the transition metals; Ni in +2, Mn in +4 and Co in +3 states,
respectively in LiNi1/3Mn1/3Co1/3O2 cathode materials. Cyclic voltammograms (CV) revealed only one
major redox couple at 4 V and suggested the absence of structural transitions from hexagonal to
monoclinic structure. The Li vs. LiNi1/3Mn1/3Co1/3O2 cell delivered an initial discharge capacity of
175 mAh g�1 in the voltage range 2.5–4.6 V @ 0.1 C
Electrochemistry of calcium precipitating bacteria in orthodontic wire
No full textCalculus composed of inorganic and organic components with bacteria formed on teeth getsdeposited on orthodontic wires. The reason for calculus formation and impact of calcium precipitatingbacteria (CPB) on orthodontic wire were studied. A pilot study on electrochemical characterization ofCPB on orthodontic wires was done.Methods: CPB were isolated from orthodontic patients and identified by molecular techniques. The elec-trochemical behavior of two isolates (CPB-1 and CPB-3) on orthodontic wires was studied by employingpolarization and impedance techniques. The CPB morphology by scanning electron microscopy and chem-ical characterization of CPB and tooth pulp stone were studied by Fourier transform infrared (FTIR) andX-ray diffraction (XRD).Results: The two isolates Bacillus megaterium (CPB-1) and Paenibacillus sp. (CPB-3) identified with 16SrRNA sequencing method increased pH of B4 medium from 5.32 to 8.3. The carboxylic acid and phosphategroups identified in FTIR analysis acted as nucleation sites for calcium deposition. The biogenic crystalphases identified in teeth pulp stone by XRD were similar to bacterial isolates cultured in the laboratory.The electrochemical studies with two CPB species revealed that biogenic calcium phosphate species actas cathodic inhibitors on orthodontic wire.Conclusion: The present study concluded that teeth pulp stone formation is due to CPB and high pHdetermines the mineralization process. Diffusion process and dispersive capacitive behavior indicate thatthe chloride ions may penetrate through calcium deposits and initiate pitting corrosion on orthodonticwire which may enhance the leaching of toxic elements in saliva