Kandalam V. Ramanujachary

Nanocrystalline Ni5P4: a hydrogen evolution electrocatalyst of exceptional efficiency in both alkaline and acidic media

Producing hydrogen (H2) by splitting water with fossil-free electricity is considered a grand challenge for developing sustainable energy systems and a carbon dioxide free source of renewable H2. Renewable H2 may be produced from water by electrolysis with either low efficiency alkaline electrolyzers that suffer 50–65% losses, or by more efficient acidic electrolyzers with rare platinum group metal catalysts (Pt). Consequently, research has focused on developing alternative, cheap, and robust catalysts made from earth-abundant elements. Here, we show that crystalline Ni5P4 evolves H2 with geometric electrical to chemical conversion efficiency on par with Pt in strong acid (33 mV dec−1 Tafel slope and −62 mV overpotential at −100 mA cm−2 in 1 M H2SO4). The conductivity of Ni5P4 microparticles is sufficient to allow fabrication of electrodes without conducting binders by pressing pellets. Significantly, no catalyst degradation is seen in short term studies at current densities of −10 mA cm−2, equivalent to ∼10% solar photoelectrical conversion efficiency. The realization of a noble metal-free catalyst performing on par with Pt in both strong acid and base offers a key step towards industrially relevant electrolyzers competing with conventional H2 sources.

Nanorods of manganese oxalate: a single source precursor to different manganese oxide nanoparticles (MnO, Mn2O3, Mn3O4)

Nanorods of anhydrous manganese oxalate were prepared by the reverse-micellar method using CTAB as the surfactant. Manganese oxalate precursor was used to synthesize single phase nanoparticles of various manganese oxides such as MnO, Mn2O3 and Mn3O4 under specific reaction conditions. Both MnO (28 nm) and α-Mn2O3 (50 nm) are stabilized as cubic phase. α-Mn2O3 shows a weak antiferromagnetic transition (TN = 80 K), while the spinel Mn3O4 (100 nm) particles show a ferrimagnetic transition at 43 K.

Amino Acid Based MOFs: Synthesis, Structure, Single Crystal to Single Crystal Transformation, Magnetic and Related Studies in a Family of Cobalt and Nickel Aminoisophthales

Four new 5-aminoisophthalates of cobalt and nickel have been prepared employing hydro/solvothermal methods: [Co(2)(C(8)H(5)NO(4))(2)(C(4)H(4)N(2))(H(2)O)(2)].3H(2)O (I), [Ni(2)(C(8)H(5)NO(4))(2)(C(4)H(4)N(2))(H(2)O)(2)].3H(2)O (II), [Co(2)(H(2)O)(mu(3)-OH)(2)(C(8)H(5)NO(4))] (III), and [Ni(2)(H(2)O)(mu(3)-OH)(2)(C(8)H(5)NO(4))] (IV). Compounds I and II are isostructural, having anion-deficient CdCl(2) related layers bridged by a pyrazine ligand, giving rise to a bilayer arrangement. Compounds III and IV have one-dimensional M-O(H)-M chains connected by the 5-aminoisophthalate units forming a three-dimensional structure. The coordinated as well as the lattice water molecules of I and II could be removed and inserted by simple heating-cooling cycles under the atmospheric conditions. The removal of the coordinated water molecule is accompanied by changes in the coordination environment around the M(2+) (M = Co, Ni) and color of the samples (purple to blue, Co; green to dark yellow, Ni). This change has been examined by a variety of techniques that include in situ single crystal to single crystal transformation studies and in situ IR and UV-vis spectroscopic studies. Magnetic studies indicate antiferromagnetic behavior in I and II, a field-induced magnetism in III, and a canted antiferromagnetic behavior in IV.

Development of a microemulsion-based process for synthesis of cobalt (Co) and cobalt oxide (Co3O4) nanoparticles from submicrometer rods of cobalt oxalate.

Rod-shaped nanostructures of cobalt oxalate dihydrate were synthesized at room temperature by the microemulsion (reverse micellar) route. These rods are highly uniform in length and can be modified with temperature (from approximately 6.5 microm at 50 degrees C to approximately 2.5 microm at 150 degrees C) while keeping the diameter nearly constant (200-250 nm). Thermal decomposition of these rods in a controlled atmosphere (air and H(2)) leads to nanoparticles of Co(3)O(4) and Co, respectively, while in a helium atmosphere a mixture of Co and CoO nanoparticles is obtained. Co(3)O(4) nanoparticles (approximately 35 nm) were slightly agglomerated, while Co nanoparticles were monodispersed and highly uniform (approximately 25 nm). The oxalate rods and Co(3)O(4) nanoparticles show an antiferromagnetic ordering at 54 and 35 K, respectively.

Microemulsion-mediated synthesis of cobalt (pure fcc and hexagonal phases) and cobalt-nickel alloy nanoparticles

By choosing appropriate microemulsion systems, hexagonal cobalt (Co) and cobalt-nickel (1:1) alloy nanoparticles have been obtained with cetyltrimethylammonium bromide as a cationic surfactant at 500 degrees C. This method thus stabilizes the hcp cobalt even at sizes (<10 nm) at which normally fcc cobalt is predicted to be stable. On annealing the hcp cobalt nanoparticles in H(2) at 700 degrees C we could transform them to fcc cobalt nanoparticles. Microscopy studies show the formation of spherical nanoparticles of hexagonal and cubic forms of cobalt and Co-Ni (1:1) alloy nanoparticles with the average size of 4, 8 and 20 nm, respectively. Electrochemical studies show that the catalytic property towards oxygen evolution is dependent on the applied voltage. At low voltage (less than 0.65 V) the Co (hexagonal) nanoparticles are superior to the alloy (Co-Ni) nanoparticles while above this voltage the alloy nanoparticles are more efficient catalysts. The nanoparticles of cobalt (hcp and fcc) and alloy (Co-Ni) nanoparticles show ferromagnetism. The saturation magnetization of Co-Ni nanoparticles is reduced compared to the bulk possibly due to surface oxidation.

(N,F)-Co-doped TiO2: synthesis, anatase–rutile conversion and Li-cycling properties

Nitrogen and fluorine co-doped Ti-oxide, TiO1.9N0.05F0.15 (TiO2(N,F)), with the anatase structure is prepared by the pyro-ammonolysis of TiF3. For the first time it is shown that TiO2(N,F) and anatase-TiO2 are converted to nanosize-rutile structure by high energy ball milling (HEB). The polymorphs are characterised by X-ray diffraction, Rietveld refinement, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and Raman spectra. The Li storage and cycling properties are examined by galvanostatic cycling and cyclic voltammetry in the voltage range 1–2.8 V vs.Li at 30 mA g−1. The performance of TiO2(N,F) is much better than pure anatase-TiO2 and showed a reversible capacity of 95 (±3) mA h g−1 stable up to 25 cycles with a coulombic efficiency of ∼98%. Nano-phase rutile TiO2(N,F) showed an initial reversible capacity of 210 mA h g−1 which slowly degraded to 165 (±3) mA h g−1 after 50 cycles and stabilised between the 50th and 60th cycle whereas the nano-phase rutile-TiO2 (prepared by HEB of anatase-TiO2) exhibited a reversible capacity of 130 (±3) mA h g−1 which is stable in the range, 10–60 cycles. The crystal structure of anatase TiO2(N,F) is not destroyed upon Li-cycling and is confirmed by ex situXRD and HR-TEM.

Lead Precipitation by Vibrio harveyi: Evidence for Novel Quorum-Sensing Interactions

ABSTRACT Three pleiotropic, quorum sensing-defective Vibrio harveyi mutants were observed to precipitate soluble Pb2+ as an insoluble compound. The compound was purified and subjected to X-ray diffraction and elemental analyses. These assays identified the precipitated compound as Pb9(PO4)6, an unusual and complex lead phosphate salt that is produced synthetically at temperatures of ca. 200°C. Regulation of the precipitation phenotype was also examined. Introduction of a luxO::kan allele into one of the mutants abolished lead precipitation, indicating that the well-characterized autoinducer 1 (AI1)-AI2 quorum-sensing system can block lead precipitation in dense cell populations. Interestingly, the V. harveyi D1 mutant, a strain defective for secretion of both AI1 and AI2, was shown to be an effective trans inhibitor of lead precipitation. This suggests that a previously undescribed V. harveyi autoinducer, referred to as AI3, can also negatively regulate lead precipitation. Experiments with heterologous bacterial populations demonstrated that many different species are capable of trans regulating the V. harveyi lead precipitation phenotype. Moreover, one of the V. harveyi mutants in this study exhibited little or no response to intercellular signals from other V. harveyi inocula but was quite responsive to some of the heterologous bacteria. Based on these observations, we propose that V. harveyi carries at least one quorum sensor that is specifically dedicated to receiving cross-species communication.

Reverse micellar based synthesis of ultrafine MgO nanoparticles (8–10 nm): Characterization and catalytic properties

Anisotropic nanostructures of magnesium oxalate dihydrate were synthesized using cationic surfactant based microemulsion method. The cationic surfactant plays an important role in forming the anisotropic structures. The oxalate nanostructures acts as an excellent precursor for the synthesis of fine magnesium oxide nanoparticles (~10 nm). Both the precursor and the oxide were characterized by using PXRD, IR, surface area and HRTEM. The surface area of these surfactant free oxide nanoparticles was found to be 108 m(2)/g. The catalytic activity of this basic oxide was examined for the Claisen-Schmidt condensation reaction and was found to be comparable to the best reported for the conventionally prepared MgO. Chalcone formation was found to increase with time as observed using gas chromatography-mass spectrometry (GC-MS). The reusability of the catalyst was checked by using the same catalyst twice which showed a reduced percentage (50% compared to first cycle) conversion.

Synthesis and characterization of different shaped Sm2O3 nanocrystals

Here, we demonstrate the synthesis of Sm2O3 nanoparticles, nanorods and nanoplates by solution-based techniques. The mechanism related to morphology control is proposed and discussed. The crystal phase of the Sm2O3 nanocrystal is tuned by varying the surfactant in the reaction. It is found that compressive strain is observed for lower temperature (600 °C) heated sample but reversal of strain appears at elevated temperature (900 °C). A chromatic change in photoluminescence (PL) emission with tuning the excitation wavelength has been observed. The PL emission is due to f–f electronic transition from excited states of 4G5/2 of the Sm3+ ion. The PL emission bands at 610 and 656 nm are observed under excitation 370 nm, but bands centred at 545, 610 and 656 nm are observed when the excitation wavelength is tuned to 400 nm. It is seen that the ratio between electric dipole and partially magnetic dipole contributions is maximum for nanorods followed by nanoplates and nanoparticles. Magnetic susceptibility study of the nanocrystals shows that the Sm3+ ion follows the well-known Van Vleck behaviour.

Reverse micellar synthesis and properties of nanocrystalline GMR materials (LaMnO3, La0.67Sr0.33MnO3 and La0.67Ca0.33MnO3) : Ramifications of size considerations

Nanoparticles of complex manganites (viz. LaMnO3, La0.67Sr0.33MnO3 and La0.67Ca{0.33}MnO3) have been synthesized using the reverse micellar route. These manganites are prepared at 800‡C and the monophasic nature of all the oxides has been established by powder X-ray diffraction studies. TEM studies show an average grain size of 68, 80 and 50 nm for LaMnO3, La0.67Sr0.33MnO3 and La0.67Ca{0.33}MnO3respectively. Ferromagnetic ordering is observed at around 250 K for LaMnO3, 350 K for La0.67Sr0.33MnO3 and 200 K for La0.67Ca{0.33}MnO3. These Curie temperatures correspond well with those reported for bulk materials with similar composition.