S. Manivannan

Effect of functional groups on dielectric, optical gas sensing properties of graphene oxide and reduced graphene oxide at room temperature

Graphene oxide (GO) was synthesized from graphite through a chemical oxidation process and heat treated at 110 and 220 °C in a vacuum atmosphere. The partial reduction and sp3 to sp2 phase transition of GO was characterized by powder X-ray diffraction, Fourier-transform infrared, micro Raman, ultraviolet-visible-near infrared spectroscopy techniques. Dielectric properties of pristine GO and heat-treated GO were studied in the frequency range 102 to 106 Hz at 27 °C. Hydroxyl, carboxyl functional groups removed GO after 220 °C heat treatment, expressed higher electrical conductivity, dielectric constant and dielectric loss in the order of 10−2 S m−1, 103 and 105 respectively than the pristine GO (10−6 S m−1, 101 and 101). Pristine and heat-treated GO were coated on the partially cladding removed poly-methyl methacrylate optical fiber and used as fiber optic gas sensors. GO and heat treated GO coated fibers were responsive to detect ammonia, ethanol and methanol vapors from 0 to 500 ppm at 27 °C. Sensitivities of GO coated fiber optic sensor were calculated as −0.32, −0.26 and −0.20 counts per ppm for ammonia, ethanol and methanol vapors respectively. The effect of functional groups on dielectric and gas sensing properties of GO was investigated and reported.

Growth and characterization of a new organic nonlinear optical crystal: semicarbazone of p-dimethylamino benzaldehyde

Semicarbazone of p-dimethylamino benzaldehyde (SCPDB) is a new organic material with interesting quadratic nonlinear optical properties, in particular second harmonic generation (SHG). SCPDB was synthesized and single crystals were grown by low temperature solution method. Unit cell parameters were evaluated by single crystal X-ray diffraction technique. The formation of the material was confirmed qualitatively by FT-IR and FT-Raman spectral analyses and its optical transmittance studied. SHG efficiency is found to be comparable to urea.

Pure and Iso-Butyl Methyl Ketone Treated Multi-Walled Carbon Nanotubes for Ethanol and Methanol Vapor Sensing

Multi-walled carbon nanotubes (MWCNTs) coated intensity modulated fiber optic sensor for the detection of ethanol and methanol vapors at room temperature is reported. Pure, 30 and 60 min iso-butyl methyl ketone (IBMK) treated MWCNT were coated on cladding removed polymethyl methacrylate fiber by the dip coating technique. The pure and IBMK treated MWCNT coated fibers were used as sensors. Response of the sensors was studied by measuring the change in output light intensity for different methanol and ethanol vapor concentrations in the range of 0-500 ppm. The 60 min IBMK treated MWCNT coated sensor showed 2 and 3.4 fold increase in the sensitivity for methanol and ethanol vapors at 640 and 630 nm wavelengths light, respectively, compared with the pristine MWCNT coated sensor. Fourier transform infrared spectroscopy confirmed the attachment of C=O functional group in IBMK treated MWCNT. Thermogravimetry results reveal the functionalized nanotubes decomposed at 475 °C after the elimination of attached functional groups. The pristine nanotubes start to decompose at 540 °C. The randomly oriented nanotubes layer of average thickness 1.5 μm on the cladding modified fiber is observed from scanning electron microscope images.

One pot rapid synthesis of silver nanowires using NaCl assisted glycerol mediated polyol process

AbstractWe report, one pot rapid synthesis of silver nanostructures from AgNO3 through glycerol mediated polyol process with the assistance of polyvinyl pyrrolidone (PVP) and NaCl. The growth of silver nanostructures was studied by monitoring changes in the position of localized surface plasmon resonance band using the UV-vis-NIR spectroscopy. Morphology of the silver nanostructures was indentified using the scanning electron microscope which confirms the formation of nanoparticle, V-shaped and linear silver nanowires. The favorable temperature and NaCl concentration to obtain nanoparticles, V-shaped and linear silver nanowires are optimized. 5 mM NaCl at 250°C produced 55 — 65 nm width, 4 μm long silver nanowires along [100] in PVP added glycerol medium within 25 minutes.

Anticancer activity of graphene oxide-reduced graphene oxide-silver nanoparticle composites

In the present study, a chemical route was employed to synthesize graphene oxide (GO)-reduced graphene oxide (rGO)-Ag nanoparticle (AgNP) composites from graphite and AgNO3 using vitamin C as reducing agent. Powder X-ray diffraction pattern and field emission scanning electron microscope images revealed that the AgNP were uniformly distributed on the surface of GO and rGO nanosheets. For the first time, the cytotoxicity of GO, rGO, AgNP, GO-AgNP and rGO-AgNP composites were examined against human lung cancer A549 cells using MTT assay and reported quantitatively. The rGO-AgNP showed significant cytotoxicity activity with an IC50 value of 30μg/mL towards A549 cells which is higher than that of GO (180μg/mL), rGO (160μg/mL) and GO-AgNP (100μg/mL). Compared to AgNP (6μg/mL), rGO-AgNP shows partial agglomeration of AgNP on rGO sheets, which reduces the interaction between rGO-AgNP and A549 cells leading to lesser anticancer activity than AgNP. The interaction between rGO and AgNP leads to increase in the material biocompatibility, reducing the toxicity and corrosive characteristic.

Reduced graphene oxide coated optical fiber for methanol and ethanol vapor detection at room temperature

Successful isolation of single layer of graphene from graphite by mechanical exfoliation method, attracted a great attention due to its unique structural, optical, mechanical and electronic properties. This makes the graphene as a promising material in many possible applications such as energy-storage, sensing, electronic, optical devices and polymer composite materials. High quality of reduced graphene oxide (rGO) material was prepared by chemical reduction method at 100°C. The structural and optical properties of the rGO sheets were characterized by FT-IR, micro Raman, powder XRD and UV-vis-NIR techniques. FT-IR reveals the absence of oxygen functional groups on rGO due to the reduction process. Powder XRD shows the broad peak at 2θ=24.3° corresponding to interlayer spacing 3.66Å which is smaller than the graphene oxide (GO). UV-vis-NIR of rGO displays the absorption peak at 271 nm indicates the reduction of GO and the restoration of C=C bonds in the rGO sheets. The cladding removed and rGO coated poly-methyl methacrylate (PMMA) optical fiber is used for methanol and ethanol vapors detection in the concentration ranging from 0 to 500 ppm at room temperature. The spectral characteristics along with output intensity modulation of cladding removed and rGO coated fiber optic sensor reveal the potential of methanol and ethanol vapor sensing properties.

Carbon nanotubes coated fiber optic ammonia gas sensor

We report, intrinsic fiber optic carbon nanotubes coated sensor for the detection of ammonia gas at room temperature. Multimode step index polymethyl methacrylate (PMMA) optical fiber passive cladding is partly replaced by an active coating of single and multi-walled carbon nanotubes following the dip coating technique and the reaction with ammonia is studied by measuring the change in output intensity from the optical fiber under various ammonia gas concentrations in the range 0-500 ppm in step of 50 ppm. The sensitivity is calculated for different wavelengths in the range 200-1100 nm both for single and multi-walled carbon nanotubes coated fiber. Higher sensitivities are obtained as 0.26 counts/ppm and 0.31 counts/ppm for single-walled (average diameter 1.3 nm, 30 wt.% purity) and multi-walled (average diameter 10-15 nm, 95 wt.% purity) carbon nanotubes respectively. The role of diameter and purity of carbon nanotubes towards the ammonia sensing is studied and the results are discussed.

Corrosion behavior of as-cast Mg–8Li–3Al+xCe alloy in 3.5wt% NaCl solution

Mg–8Li–3Al+xCe alloys (x = 0.5wt%, 1.0wt%, and 1.5wt%) were prepared through a casting route in an electric resistance furnace under a controlled atmosphere. The cast alloys were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The corrosion behavior of the as-cast Mg–8Li–3Al+xCe alloys were studied under salt spray tests in 3.5wt% NaCl solution at 35°C, in accordance with standard ASTM B–117, in conjunction with potentiodynamic polarization (PDP) tests. The results show that the addition of Ce to Mg–8Li–3Al (LA83) alloy results in the formation of Al2Ce intermetallic phase, refines both the α-Mg phase and the Mg17Al12 intermetallic phase, and then increases the microhardness of the alloys. The results of PDP and salt spray tests reveal that an increase in Ce content to 1.5wt% decreases the corrosion rate. The best corrosion resistance is observed for the LA83 alloy sample with 1.0wt% Ce.

4-Hydroxy-1,2,6-trimethylpyridinium chloride monohydrate

In the crystal of the title hydrated molecular salt, C8H12NO+·Cl−·H2O, the water molecule makes two O—H⋯Cl hydrogen bonds, generating [010] zigzag chains of alternating water molecules and chloride ions. The cation is bonded to the chain by an O—H⋯O hydrogen bond and two weak C—H⋯Cl interactions. Weak aromatic π–π stacking [centroid–centroid separation = 3.5175 (15) Å] occurs between the chains.

4-Hy­droxy-1,2,6-tri­methyl­pyridinium bromide monohydrate

The title salt, C8H12NO+·Br−·H2O, is isomorphous with the chloride analogue [Seethalakshmi et al. (2013). Acta Cryst. E69, o835–o836]. In the solid state, the cations, anions and water molecules are interlinked by a network of O—H⋯O, O—H⋯Br and C—H⋯Br interactions. The water molecule makes two O—H⋯Br hydrogen bonds, generating [010] zigzag chains of alternating water molecules and bromide anions. The cation is involved in two intermolecular C—H⋯Cl interactions in the chloride salt, whereas three intermolecular C—H⋯Br interactions are observed in the title bromide salt. This additional intermolecular C—H⋯Br interaction links the adjacent water and bromide zigzag chains via cationic molecules. In addition, weak π–π stacking interactions are observed between pyridinium rings [centroid–centroid distance = 3.5664 (13) Å].