G. Ravi

Studies on organic indole-3-aldehyde single crystals

Abstract Indole-3-aldehyde (IA) is a new organic nonlinear material for which its solubility in methanol and acetone was found out using the apparatus fabricated by the authors. In order to get the good-quality crystals, methods of evaporation of solvent at room temperature and slow cooling of saturated solution at boiling temperature were adopted. Simulated lattice parameter values were found out using experimentally known “ d ” values. The etching and mechanical strength studies on different planes of the crystal were carried out. Decomposition temperature, weight loss and different functional bond frequencies associated with the crystal were also found out from differential thermal analysis (DTA), thermo-gravimetric analysis (TGA) and Fourier transform infra-red (FTIR) spectroscopic analysis, respectively.

Impact of alkaline metal ions Mg2+, Ca2+, Sr2+ and Ba2+ on the structural, optical, thermal and antibacterial properties of ZnO nanoparticles prepared by the co-precipitation method

Pure ZnO and alkaline metal ion (Mg2+, Ca2+, Sr2+ and Ba2+)-doped ZnO nanoparticles (NPs) were synthesized by the co-precipitation method. The synthesized nanoparticles retained the wurtzite hexagonal structure, which was confirmed by X-ray diffraction studies. The micro-strain properties were analyzed through Williamson-Hall analysis. The oxidation states of the elements (C (1s), O (1s), Zn (2p), Mg (1s), Ca (2p), Sr (3d) and Ba (3d)) were confirmed by XPS studies. HRSEM studies showed a reduction in the thickness of the ZnO nanoflakes from 63 to 47 nm after doping. EDAX studies determined the amount of dopant (alkaline metals) incorporated into the doped samples. The FT-IR spectra confirmed the Zn-O stretching bands at 432, 416, 414, 426 and 422 cm-1 for the respective ZnO NPs. The photoluminescence measurements revealed that the broad emission was composed of six different bands due to zinc and oxygen vacancies. Thermal analysis revealed that the irreversible structural transition occurred from the cubic phase to the wurtzite phase in the samples. The antibacterial studies performed against a set of bacterial strains showed that the Mg-doped ZnO NPs possessed a greater antibacterial effect than the other alkaline metal ion-doped ZnO NPs.

An ultrasensitive electrochemical sensor for simultaneous determination of xanthine, hypoxanthine and uric acid based on Co doped CeO2 nanoparticles

A novel electrochemical sensor has been fabricated using Co doped CeO2 nanoparticles for selective and simultaneous determination of xanthine (XA), hypoxanthine (HXA) and uric acid (UA) in a phosphate buffer solution (PBS, pH5.0) for the first time. The Co-CeO2 NPs have been prepared by microwave irradiation method and characterized by Powder XRD, Raman spectroscopy, HRTEM and VSM measurements. The electrochemical behaviours of XA, HXA and UA at the Co-CeO2 NPs modified glassy carbon electrode (GCE) were studied by cyclic voltammetry and square wave voltammetry methods. The modified electrode exhibited remarkably well-separated anodic peaks corresponding to the oxidation of XA, HXA and UA over the concentration range of 0.1-1000, 1-600 and 1-2200μM with detection limits of 0.096, 0.36, and 0.12μM (S/N=3), respectively. For simultaneous detection by synchronous change of the concentrations of XA, HXA and UA, the linear responses were in the range of 1-400μM each with the detection limits of 0.47, 0.26, and 0.43μM (S/N=3), respectively. The fabricated sensor was further applied to the detection of XA, HXA and UA in human urine samples with good selectivity and high reproducibility.

Synthesis, growth and characterization of nonlinear optical material: l-arginine fluoride

Abstract l -arginine fluoride (LAF) is one of the potential semi-organic materials for nonlinear optical applications. In the present study, synthesis, material purification and crystal growth of LAF have been carried out. Since the material has high solubility in water, the growth parameters have been optimized for the growth of good-quality crystals. X-ray powder diffraction studies have been carried out in order to calculate the lattice parameter values using its monoclinic crystallographic equation. From Fourier transform infrared spectroscopic analysis, different modes of vibration due to various functional groups present in LAF have been observed. In order to find the range and percentage of optical transmission, the UV–VIS spectrum was recorded for the crystal. The thermal behaviour of the LAF sample has been investigated from differential thermal and thermogravimetric analyses.

Annealing studies of electrodeposited zinc telluride thin films

Zinc telluride (ZnTe) thin films were prepared potentiostatically from an aqueous solution bath containing ZnSO4 and TeO2. Structural studies were carried out for films deposited at various potentials and lattice parameters were evaluated using the Nelson–Riley plot. The effects of annealing on the structural, optical and morphological behavior were studied. Current–voltage studies revealed a space charge limited conduction mechanism and the trap density of films was estimated. The microscopic composition was analyzed by EDAX, XPS and the results are discussed.

Inhibition of microbial growth, study of solution stability, growth and characterization of potassium fluoride mixed l-arginine phosphate single crystals

Abstract In order to alleviate the major problem of microbial growth and colouration in l -arginine phosphate (LAP), the use of potassium fluoride (KF), a new additive having higher dipole moment, has been proposed. The stabilities of the pure and KF mixed LAP solution at different temperatures have been determined. Pure and KF mixed LAP crystals were grown by the temperature lowering technique. The presence of potassium in the crystal was identified by inductively coupled plasma analysis (ICP). The lattice parameters for the grown crystals were determined from X-ray powder diffraction. The molecular vibration and thermal behaviour of KF mixed LAP were found from Fourier transform infrared (FTIR) spectroscopy and thermal analysis (DTA &TGA) respectively.

Ethylenediaminium di(4-nitrophenolate): A third order NLO material for optical limiting applications

Single crystals of ethylenediaminium di(4-nitrophenolate) [EDA4NP] were grown by slow evaporation solution growth technique using ethanol as solvent at constant temperature. It crystallizes in monoclinic centrosymmetric space group C2/c with cell dimension a=11.326Ǻ, b=7.264Ǻ, c=20.036Ǻ; β=93.55°. Fourier Transform Infra Red (FT-IR) spectrum was recorded to identify various functional groups present in EDA4NP. Nuclear Magnetic Resonance (NMR) spectral studies were performed to confirm the functional groups. Thermogravimetric analysis and differential thermal analysis showed that the compound melts at 142.9°C. The material possesses a wide optical transparency window in the visible and near IR region (500-1200nm). The nonlinear refractive index, nonlinear absorption coefficient and third-order nonlinear susceptibility of EDA4NP were estimated to be n2=5.46×10(-8)cm(2)W(-1), β=0.65×10(-3)cmW(-1) and χ((3))=2.96×10(-6)esu respectively. The limiting behavior observed with the sample is attributed mainly to nonlinear refraction.

Au–Pd bimetallic nanoparticles anchored on α-Fe2O3 nonenzymatic hybrid nanoelectrocatalyst for simultaneous electrochemical detection of dopamine and uric acid in the presence of ascorbic acid

We have found that magnetic α-Fe2O3 nanocubes exhibit an intrinsic catalytic activity toward the electrochemical sensing of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid. Au-Pd bimetallic nanoparticles, which act as efficient signal amplifiers, can be attached to the surface of α-Fe2O3 particles to further enhance the catalytic electrochemical signals. The one-step synthesized α-Fe2O3@Au-Pd hybrid nanostructure shows significantly well-separated oxidation peaks with enhanced peak currents of DA and UA. We then demonstrated the use of this nonenzymatic nanoelectrocatalyst for individual detection, and the linear responses of DA and UA were in the concentration ranges of 100 nM-1 mM and 1 μM-1 mM with detection limits of 1.34 × 10-10 M and 1.8 × 10-6 M (S/N = 3σ/b), respectively. For simultaneous detection, the same detection ranges were retained with significantly lower detection limits of 1.38 × 10-11 M and 597 nM, respectively. The fabricated sensor was finally applied in selectivity tests for the detection of DA and UA with satisfactory results. The practical analytical utility was illustrated by selective measurements of human urine, serum and pharmaceutical drugs without any preliminary treatment.

Synthesis, structural, spectroscopic and optical studies of charge transfer complex salts

New charge transfer molecular complex adducts of picric acid (C6H3N3O7) with triethylamine (C6H15N) and dimethylformamide (HCON(CH3)2) were synthesized successfully for the first time. Chemical composition and stoichiometry of the synthesized complex salts were verified by CHN elemental analysis. Solubility of the complex salts have been determined by gravimetric method and single crystals of two new salts were grown by low temperature solution growth technique. Crystal system, crystalline nature and cell parameters of the grown crystals were determined by single crystal X-ray diffraction (SXRD) and powder X-ray diffraction (PXRD) analyses. The formations of the charge-transfer complex, functional groups and the modes of vibrations have been confirmed by Fourier transform infrared (FTIR) spectroscopy. In order to know the linear and nonlinear optical suitability for device fabrication, UV-Vis (UV) spectral analysis and relative second harmonic generation (SHG) efficiency test were performed for the grown crystals.

Nucleation kinetics, growth and characterization of dLAP, dLAP:KF and dLAP:NaN3 crystals

Abstract The nucleation parameters, such as interfacial tension, radius of the critical nucleus and critical free energy change have been estimated for deuterated l -arginine phosphate (dLAP), potassium fluoride mixed dLAP and sodium azide mixed dLAP single crystals. Pure and additive mixed dLAP single crystals are grown by slow cooling technique. The effect of microbial contamination and colouration on the growth solutions has been studied. The crystalline powder of the grown crystals has been examined by X-ray diffraction and thermal analyses in order to estimate the lattice parameters and study thermal properties respectively.