Alga-mediated facile green synthesis of silver nanoparticles: Photophysical,catalytic and antibacterial activity

A facile, convenient and green method has been employed for the synthesis of silver nanoparticles (AgNPs) using dried biomass of a green alga, Chlorella ellipsoidea. The phytochemicals from the alga, as a mild and non-toxic source, are believed to serve as both reducing and stabilizing agents. The formation of silver nanoparticles was confirmed from the appearance of a surface plasmon resonance band at 436 nm and energy dispersive X-ray spectroscopy. The transmission electron microscopy images showed the nanoparticles to be nearly spherical in shape with different sizes. A dynamic light scattering study revealed the average particle size to be 220.8 ± 31.3 nm. Fourier transform infrared spectroscopy revealed the occurrence of alga-derived phytochemicals attached to the outer surface of biogenically accessed silver nanoparticles. The powder X-ray diffraction study revealed the face-centred cubic crystalline structure of the nanoparticles. The as-synthesized biomatrix-loaded AgNPs exhibited a high photocatalytic activity for the degradation of the hazardous pollutant dyes methylene blue and methyl orange. The catalytic efficiency was sustained even after three reduction cycles. A kinetic study indicated the degradation rates to be pseudo-first order with the degradation rate being 4.72 × 10⁻² min⁻¹ for methylene blue and 3.24 × 10⁻² min⁻¹ for methyl orange. The AgNPs also exhibited significant antibacterial activity against four selected pathogenic bacterial strains.     

Synthesis, structure and application of chiral copper(II) coordination polymers for asymmetric acylation

Chiral copper(II) coordination polymers 1a-c have been prepared by one-pot synthesis in high yield. Their single-crystal X-ray analysis showed that repeating units are connected to each other by carboxylate linker and copper(II) atoms are pentacoordinated with distorted square-pyramidal geometry for 1a-b and square-planar geometry for 1c. These polymers have catalyzed the kinetic resolution of secondary alcohols by acylation with up to 90% ee ( s = 50).     

Structure and optical properties of [Ba1–xY2x/3](Zr0.25Ti0.75)O3 powders

[Ba_1–xY_2x/3](Zr_0.25Ti_0.75)O₃ powders with different yttrium concentrations (x = 0, 0.025 and 0.05) were prepared by solid state reaction. These powders were analyzed by X-ray diffraction (XRD), Fourier transform Raman scattering (FT-RS), Fourier transform infrared (FT-IR) and X-ray absorption near-edge (XANES) spectroscopies. The optical properties were investigated by means of ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) measurements. Even with the addition of yttrium, the XRD patterns revealed that all powders crystallize in a perovskite-type cubic structure. FT-RS and FT-IR spectra indicated that the presence of [YO₆] clusters is able to change the interaction forces between the O–Ti–O and O–Zr–O bonds. XANES spectra were used to obtain information on the off-center Ti displacements or distortion effects on the [TiO₆] clusters. The different optical band gap values estimated from UV–vis spectra suggested the existence of intermediary energy levels (shallow or deep holes) within the band gap. The PL measurements carried out with a 350 nm wavelength at room temperature showed that all powders present typical broad band emissions in the blue region.     

Molecular structure of thiocyanatotris (2,2′-iminodiethanoldithiocarbamato) tellurium(IV) monohydrate

The synthesis, properties, and structural characterization of the title compound, C₁₆H₃₀N₄O₄S₇Te(IV)·H₂O, are reported. The crystals are monoclinic, space groupP2₁/n, withZ=4 in a unit cell of dimensionsa=13.291(5),b=21.306(6),c=10.450(1) Å, 0=104.25(2)° and,V _c=2868 ų. The structure was solved by the heavy atom method and refined by full-matrix least squares toR=0.025 andR _w =0.027 for 2894 reflections. The dithiocarbamate groups are linked in an unequal bidentate manner with Te-S average distance 2.695(1) Å. The thiocyanate group is bonded through the sulfur atom with much larger Te-S length [2.964(2) Å].     

Total synthesis of (-)-sacidumlignans B and D

The first total synthesis of naturally occurring sacidumlignans A (1), B (2), and D (4) was executed and the absolute configuration of 2 and 4 was determined. A diastereoselective α- methylation of a lactone was used as the key step for the control of the chiral centers of the central lignan core. An acid mediated dehydrative cyclization of an aldehyde to construct the dihydronaphthalene unit of 2 and the aromatization of the intermediate dihydronaphthalene derivative to synthesize 1 are the key reactions employed in this regard.     

Sensors for the nitrogen oxides, NO2, NO and N2O, based on In2O3 and WO3 nanowires

Sensing characteristics of ZnO, In₂O₃ and WO₃ nanowires have been investigated for the three nitrogen oxides, NO₂, NO and N₂O. In₂O₃ nanowires of ∼20 nm diameter prepared by using porous alumina membranes are found to have a sensitivity (defined as the ratio of the sensor resistance in the gas concerned to that in air) of about 60 for 10 ppm of all the three gases at a relatively low temperature of 150 °C. The response and recovery times are around 20 s. The sensitivity of these In₂O₃ nanowires is around 40 for 0.1 ppm of NO₂ and N₂O at 150 °C. WO₃ nanowires of 5–15 nm diameter, prepared by the solvothermal process show a sensitivity of 20–25 for 10 ppm of the three nitrogen oxides at 250 °C. The response and recovery times are 10 s and 60 s, respectively. The sensitivity is around 10 for 0.1 ppm of NO₂ at 250 °C. The sensitivity of In₂O₃ and WO₃ nanowires is not affected by humidity even up to 90% relative humidity. The study also reveals that the sensing mechanism for the three nitrogen oxides have a commonality in that the desorption of oxygen is a crucial step in all the cases. PACS 07.07.Df; 85.35.-p; 82.35.Np     

Investigations on the Physicochemical and Radiolytic Degradation Properties of Tri-<Emphasis Type="Italic">n</Emphasis>-butylphosphate–Ionic Liquid in the Presence of Nitric Acid

Tri-n-butylphosphate (TBP) in an ionic liquid (IL) has been proposed as a suitable alternative for the solvent extraction of actinides from nitric acid solutions. This paper reports the detailed investigations on the physicochemical and hydrodynamic properties of the solvent system containing TBP in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C₄mim][NTf₂]) IL. The properties such as density, viscosity, phase separation time (PST), etc., were measured for irradiated and unirradiated solvent phases composed of TBP, [C₄mim][NTf₂] and 1.1 mol·L^–1 TBP in [C₄mim][NTf₂]. The results are compared with the values obtained in acid-equilibrated IL phases. ATR–FTIR spectroscopy and dynamic light scattering measurement of the IL phase were employed to characterize the interactions among the IL, TBP and nitric acid medium, and the aggregate size of the adduct formed in the IL phase.     

Surface modification of coir fibers I: studies on graft copolymerization of methyl methacrylate on to chemically modified coir fibers

Graft copolymerization of methyl methacrylate (MMA) onto chemically modified coir fiber was studied using a CuSO₄–KIO₄ combination as initiator in an aqueous medium in the temperature range of 50–70 °C. Concentrations or [IO₄−] = 0.005 mol/l and [Cu2+] = 0.002 mol/l produce optimum grafting. The effects of time, temperature, amount of coir fiber, some inorganic salts and organic solvents on graft yield have also been investigated. On the basis of experimental findings, a reaction mechanism has been proposed. Evidence of grafting was studied from fourier transform infrared spectroscopy and scanning electron microscopy of chemically modified coir and MMA‐grafted coir. Tensile properties such as maximum stress at break, extension at break and Young's modulus of untreated, defatted, chemically treated and grafted coir fibers were evaluated and compared. Grafted coir fiber showed an increase in tensile properties such as maximum stress at break, extension at break and Young's modulus. Copyright © 1999 John Wiley & Sons, Ltd.