U. S. Rai

Selective Detection of Mercury (II) Ion Using Nonlinear Optical Properties of Gold Nanoparticles

Contamination of the environment with heavy metal ions has been an important concern throughout the world for decades. Driven by the need to detect trace amounts of mercury in environmental samples, this article demonstrates for the first time that nonlinear optical (NLO) properties of MPA-HCys-PDCA-modified gold nanoparticles can be used for rapid, easy and reliable screening of Hg(II) ions in aqueous solution, with high sensitivity (5 ppb) and selectivity over competing analytes. The hyper Rayleigh scattering (HRS) intensity increases 10 times after the addition of 20 ppm Hg(2+) ions to modified gold nanoparticle solution. The mechanism for HRS intensity change has been discussed in detail using particle size-dependent NLO properties as well as a two-state model. Our results show that the HRS assay for monitoring Hg(II) ions using MPA-HCys-PDCA-modified gold nanoparticles has excellent selectivity over alkali, alkaline earth (Li(+), Na(+), K(+), Mg(2+), Ca(2+)), and transition heavy metal ions (Pb(2+), Pb(+), Mn(2+), Fe(2+), Cu(2+), Ni(2+), Zn(2+), Cd(2+)).

Gold-Nanorod-Based Sensing of Sequence Specific HIV-1 Virus DNA by Using Hyper-Rayleigh Scattering Spectroscopy

Infectious diseases caused by the human immunodeficiency virus (HIV) remain the leading killers of human beings worldwide, and function to destabilize societies in Africa, Asia, and the Middle East. Driven by the need to detect the presence of HIV viral sequence, here we demonstrate that the second-order nonlinear optical (NLO) properties of gold nanorods can be used for screening HIV-1 viral DNA sequence without any modification, with good sensitivity (100 pico-molar) and selectivity (single base-pair mismatch). The hyper-Rayleigh scattering (HRS) intensity increases 45 times when a label-free 145-mer, ss-gag gene DNA, was hybridized with 100 pM target DNA. The mechanism of HRS intensity change has been discussed with experimental evidence for higher multipolar contribution to the NLO response of gold nanorods.

Chemistry of eutectic and monotectic; phenanthrene-succinonitrile system

Abstract The solidification behavior of the phenanthrene-usccinonitrile system was studied by measuring the growth rates of the moving front and the microstructures of the parent components and different mixtures. The phase diagram was experimentally determined by the thaw-melt method. A eutectic (0.975 mole fraction of SCN) and a monotectic (0.225 mole fraction of SCN) were observed with a liquid miscibility gap in the system. The experimental value of the diffusion coefficient determined by the diaphragm cell technique is 0.95 × 10 -5 cm 2 / s . The experimental data were analysed using the current theories of solidification behavior of eutectics and monotectics. λ 2 v was found to be much higher for the monotectic than for the eutectic, where λ is the spacing and v the growth velocity. The enthalpy of mixing was determined experimentally to throw light on the position and structure of the liquid eutectic. The very high value of the enthalpy of mixing confirms the immiscibility in the liquid and the position of the eutectic far away from the equicomposition. Phase separation was studied in the region of immiscibility by analysing the composition of the solidified column. Ph clearly separates leaving SCN on the upper portion of the column.

Physical chemistry of the organic analog of metal-metal eutectic and monotectic alloys

The phase diagram of an organic analog of a metal–metal system involving succinonitrile (SCN) and carbontetrabromide (CTB) shows the formation of a eutectic (0.996 mole fraction of SCN) and a monotectic (0.040 mole fraction of SCN) with a wide range of miscibility gap in the system. The consolute temperature is 111.5°C above the monotectic horizontal. The growth data, determined by measuring the rate of movement of solid–liquid interface in a capillary, at different undercooling (ΔT) suggest that they obey the parabolic law, v=u(ΔT)n, where v is the linear velocity of crystallization and u and n are constants depending on the nature of materials involved. Using enthalpy of fusion of the pure components, the eutectic and the monotectic, entropy of fusion, Jacksons roughness parameter, interfacial energy, size of the critical nucleus and excess thermodynamic functions were calculated. While microstructural investigations of pure components give dendritic microstructures, those of eutectic and monotectic give characteristic lamellar structures.

Physical Chemistry of Organic Eutectics

Phase diagrams of urea-α-naphthol and urea-benzoic acid systems, determined by the thaw-melt method, show the formation of simple eutectic in each case. The growth velocity data, determined at different undercooling (ΔT) by observing the rate of movement of interface in a capillary, obey the Hillig-Turnbull equation, v=u(ΔT)n, where u and n are constants depending on the nature of the materials. Using enthalpy of fusion, undercooling (ΔT) and melting point data, entropy of fusion, interfacial energy, enthalpy of mixing, critical radius size and excess thermodynamic functions were calculated. The microstructural investigations give characteristic features of the eutectics.

Dielectric studies of a nano-crystalline CaCu2.90Zn0.10Ti4O12 electro-ceramic by one pot glycine assisted synthesis from inexpensive TiO2 for energy storage capacitors

A facile way for the synthesis of nano-crystalline CaCu2.90Zn0.10Ti4O12 (CCZTO) using a solution combustion technique based on the glycine–nitrate process with inexpensive solid TiO2 powder as the raw material is introduced in this manuscript, for the first time. The precursor powder was calcined between 200 °C and 850 °C for 3 h in air. Phase formation, crystalline nature, morphology and chemical purity of the fabricated CCZTO were investigated with TG/DTA, FT-IR, FT-Raman, XRD, SAED patterns, SEM, TEM, EDX and XPS analyses, respectively. The XRD results indicated that all sintered samples had a major CaCu3Ti4O12 structure with some amount of CaTiO3 and CuO. The bright-field TEM micrographs revealed that the particle size was in the range of 15–50 nm, which was in good agreement with the average crystallite size obtained from XRD. SEM micrographs of the sintered CCZTO ceramics showed the average grain sizes were in the range of 800 nm–7 μm. EDX and XPS studies confirmed the stoichiometry and purity of the ceramics. The nature of the relaxation behavior of the ceramics was rationalized using impedance and modulus spectroscopy. The activation energies calculated from the grain-boundary relaxation time constant were found to be in the range of 0.79–0.52 eV, which confirmed the Maxwell–Wagner type of relaxation present in the ceramic. Our inexpensive novel solution chemistry based method for CCZTO_16h gives a high dielectric constant (799) and low dielectric loss (0.091) at 100 Hz at room temperature, which has potential significance for cost-effective technological applications in microelectronic devices.

Solid-liquid equilibrium and thermochemical properties of organic eutectic in a monotectic system

The phase-diagram of an organic analogue of a metal-non-metal system, involving p-dichlorobenzene-succinonitrile (DCB-SCN), shows the formation of a eutectic and a monotectic with large miscibility gap in the system. The monotectic and the eutectic contain 0.0272 and 0.9429 mole fractions of SCN, respectively, and the critical temperature is 126 degreesC above the monotectic horizontal. The heat of mixing. entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions wen calculated based on enthalpy of fusion data determined via differential scanning calorimeter method. The interfacial energy shows the applicability of wetting condition, while the microstructures of the pure components, namely, DCB and SCN show faceted and non-faceted morphology, those of the eutectic and the monotectic show peculiar characteristic features.

Synthesis and mechanical characterization of polymer-matrix composites containing calcium carbonate/white cement filler

With a view to develop polymer-matrix composites of high mechanical strength, composites containing 0.5% to 5.0% of each of calcium carbonate or white cement were prepared by uniformly mixing polystyrene and inorganic materials followed by casting in an aluminum mold. The values of fracture toughness, flexural strength and elastic modulus were found to increase with increasing amount of the inorganic component in the polymer. In addition, for a given percentage of inorganic components, the values of mechanical strength of white cement containing composites were found to be more than those of calcium carbonate containing composites. The optical microphotographs of the composites show that there is uniform distribution of filler in the polymers.

Thermochemical studies on organic eutectics and molecular complexes

The phase diagrams of the binary systems of picric acid with naphthalene, anthracene and phenanthrene, and of α-naphthol withp-toluidine, determined by the thaw-melt method, show the formation of a molecular complex and two eutectics in each system. The heats of the pure components, eutectics and molecular complexes were determined by differential scanning calorimetry. Comparison of the experimental heats of fusion with the theoretical values calculated via the mixture law suggests cluster formation in the melts. The entropy of fusion, enthalpy of mixing and excess thermodynamic functions were also calculated from the heat of fusion data.ZusammenfassungDie Phasendiagramme der binären Systeme von Pikrinsäure mit Naphthalin, Anthrazen und Phenanthren sowie von α-Naphthol mit p-Aminotoluol wurden bestimmt. In jedem System zeigt sich die Bildung eines Molekülkomplexes sowie je zwei Eutektika. Mittels DSC wurden die Schmelzwärmen der reinen Komponenten, der eutektischen Mischungen und der Molekülkomplexe ermitteis. Der Vergleich der experimentell ermittelten Schmelzwärmen mit den mittels der Mischungsregel errechneten Werten läßt auf eine Clusterbildung in der Schmelze schließen. Weiterhin wurden aus den Schmelzwärmen auch Werte für Schmelzentropie und Mischungsenthalpie errechnet.РезюмеНайденные методом ра сстаивание — расплав фазовые диаграммы дв ойных систем пикриновой кислоты с нафталином, антрацен ом и фенантреном, а такжеα-нафтола с птолуиди ном показали образовани е в каждой системе мол екулярного комплекса и двуз эвте ктик. Методом ДСК определе ны теплоты плавления чистых компонент, эвтектик и молекулярных комплексов. Сопостав ление экспериментал ьно полученных теплот пл авления с теоретичес ки вычисленными на осно ве закона смеси, предп олагает образование кластер ов в расплавах. Исходя из данных тепл от плавления были так же вычислены энтропия п лавления, энтальпия смешения и избыточны е термодинамические функции.

Studies on physicochemical properties of the eutectic and monotectic in the urea—p. chloronitrobenzene system

Abstract The phase diagram of an organic analog of a nonmetal—nonmetal-type system involving urea and p. chloronitrobenzene shows the formation of a eutectic (0.982 mole fraction of p. chloronitrobenzene) and a monotectic (0.020 mole fraction of p. chloronitrobenzene) with a liquid miscibility gap in the system. The linear velocity of crystallization ( v ) data determined at different undercoolings ( ΔT ) by measuring the rate of advance of an interface in a capillary obey the Hillig—Turnbull equation, v = u ( ΔT ) n , where u and n are constants depending on the solidification behaviour of the materials involved. From the enthalpy of fusion of the pure components, the eutectic and the monotectic, enthalpy of mixing, excess thermodynamic functions, entropy of fusion and interfacial energy were calculated. Optical microphotographs of the eutectic and monotectic give their characteristic features.