Preparation of nanosized gold particles in a biopolymer using UV photoactivation

Gold nanoparticles have been prepared by UV photoactivation in the presence of a biopolymer, sodium alginate. The particles are characterized by UV-vis spectra and TEM studies. Both particle size and the UV-visible absorption peak are dependent on the sodium alginate concentration. The effects of various other parameters such as change of light source, cell material of the reaction chamber, heating effect, irradiation time, and HAuCl4 concentration are studied. The particles are spherical and in situ stabilized by the biopolymer. The method is very simple and reproducible.     

Crystal and electronic structures of neptunium nitrides synthesized using a fluoride route

A low-temperature fluoride route was utilized to synthesize neptunium mononitride, NpN. Through the development of this process, two new neptunium nitride species, NpN(2) and Np(2)N(3), were identified. The NpN(2) and Np(2)N(3) have crystal structures isomorphous to those of UN(2) and U(2)N(3), respectively. NpN(2) crystallizes in a face-centered cubic CaF(2)-type structure with a space group of Fm3m and a refined lattice parameter of 5.3236(1) ?. The Np(2)N(3) adopts the body-centered cubic Mn(2)O(3)-type structure with a space group of Ia3. Its refined lattice parameter is 10.6513(4) ?. The NpN synthesis at temperatures ≤900 °C using the fluoride route discussed here was also demonstrated. Previous computational studies of the neptunium nitride system have focused exclusively on the NpN phase because no evidence was reported experimentally on the presence of NpN(x) systems. Here, the crystal structures of NpN(2) and Np(2)N(3) are discussed for the first time, confirming the experimental results by density functional calculations (DFT). These DFT calculations were performed within the local-density approximation (LDA+U) and the generalized-gradient approximation (GGA+U) corrected with an effective Hubbard parameter to account for the strong on-site Coulomb repulsion between Np 5f electrons. The effects of the spin-orbit coupling in the GGA+U calculations have also been investigated for NpN(2) and NpN.     

Formation and drying of colloidal crystals using nanosized silica particles

Much interest has been generated in the fabrication of colloidal crystals from suspensions because of the promise of photonic band gap applications. However, since the case of small, nonsedimenting colloidal particles indeed remains rather rarely treated, spherical silica particles with diameters varying from 75 down to 20 nm have been used in the present work to fabricate colloidal crystals by drying the suspending liquid. Typical events that take place during the drying process of a particulate film, such as cracking, compaction and penetration of air into a porous network, have been evaluated using existing theories, and the maximum stress in the drying film could be approximated. Investigation on the dry film structure by scanning electron microscopy showed the arrangement of particles in a close-packed system. To interpret the formation of such crystals, the amplitudes of the interparticle and capillary forces have been estimated from existing models. The repulsive interparticle forces allow the particles to remain stable and thus rearrange up to fairly high particle concentration. These modeling results showed the dominance of the capillary contribution at the end of the drying process. Nitrogen adsorption/desorption measurements gave very coherent results regarding both pore volume and pore size of the dry particulate films when compared to the expected ordered packing arrangements.     

Structure and catalytic properties of nanosized alumina supported platinum and palladium particles synthesized by reaction in microemulsion

Mixtures of nanosized platinum and palladium particles have been prepared by reduction of salt-containing microemulsion droplets using hydrazine as the reducing agent. To avoid possible negative effects of the presence of sulfur compounds during the preparation the microemulsion was made using the sulfur-free nonionic polyoxyethylene 4 lauryl ether surfactant. Transmission electron microscopy showed that the as-prepared mixtures contained crystalline platinum particles of fairly homogeneous size (20 to 40 nm) with adsorbed amorphous palladium particles 2 to 5 nm in size. Catalyst samples were prepared by depositing the nanoparticles on a gamma-Al(2)O(3) support followed by heating in air at 600 degrees C. Alloyed particles of platinum and palladium with sizes ranging from 5 to 80 nm were obtained during the heating. The majority of the particles had the fcc structure and their compositional range was dependent upon the Pt:Pd molar ratio of the microemulsion. A catalyst prepared from a microemulsion with a 20:80 Pt:Pd molar ratio showed the highest catalytic activity for CO oxidation, while pure platinum and palladium catalysts showed higher sulfur resistance. These results differ from the performance of conventional wet-impregnated catalysts, where a 50:50 Pt:Pd molar ratio resulted in the highest catalytic activity as well as the highest sulfur resistance.     

Enhanced optical oxygen sensing using a newly synthesized ruthenium complex together with oxygen carriers

In this article, an emission based, simple and fast method is proposed for the determination of gaseous oxygen. A newly synthesized fluorophore, dichloro-{2,6-bis[1-(4-dimethylamino-phenylimino) ethyl]pyridine}ruthenium(II) has been used for oxygen sensing together with oxygen carrier perfluorochemicals (PFCs) in silicon matrix. It should be noted that the solubility of oxygen in fluorocarbons is about three to ten times large as that observed in the parent hydrocarbons or in water, respectively. Employed PFCs are chemically and biochemically inert, have high dissolution capacities for oxygen, and, once doped into sensing film, considerably enhance the response of sensing agent.     

Novel layered crystalline zinc poly(styrene-phenylvinyl phosphonate)-phosphate synthesized by a simple route in a THF-water medium

A novel type of organic polymer-inorganic hybrid material layered crystalline zinc poly(styrene-phenylvinyl phosphonate)-phosphate (ZnPSPPP) was prepared by the reaction of styrene-phenylvinyl phosphonic acid copolymer with zinc acetate dihydrate and sodium dihydrogen phosphate. The ZnPSPPP were characterized by FT-IR, diffusion reflection UV-Vis, AAS, N(2) volumetric adsorption, SEM, TEM and TG. Unexpectedly, the layered crystalline ZnPSPPP obtained was not synthesized with traditional methods as other zinc phosphonates, but with the ones for amorphous reactions without addition of any template. It can be deduced that the layered crystalline ZnPSPPP could have potential applications for heterogeneous catalyst supports.     

Fine tuning the production of nanosized beta-carotene particles using spinning disk processing

Nanoparticles of trans-beta-carotene are accessible using spinning disk processing (SDP), by varying the reaction conditions and the choice of surfactant, macrocyclic amphiphiles, sulfonato-calix[4,5,6,8]arenes, and alpha,beta-cyclodextrins. SDP ensures rapid mixing and fast kinetics, and nanoparticles of the carotene formed in the presence of the calixarenes are stable with respect to extraction of the carotene into an organic solvent, unlike in the presence of the cyclodextrins. Insight into the supramolecular structure of the carotene nanoparticles has also been established. The mean particle sizes (dynamic light scattering, DLS) have been optimized at 40(2) and 56(1) nm and 71.4(6) and 82(1) nm, respectively, for each sulfonato-calix[5,6 and 4,8]arene, whereas the cyclodextrins form nanoparticles with a mean diameter of 71(1) and 68.5(6) nm, respectively. Zeta-potential studies show stability of all the colloidal dispersions at pH > 4 with values below -30 mV. UV-visible spectroscopy shows a blue shift indicative of H-aggregates of the carotene within the nanoparticles. The surface area derived from BET studies is 39.12 m(2)/g corresponding to particles of 76.7(5) nm in diameter, in agreement with sizes obtained from DLS and TEM measurements.     

Synthesis of nanosized silicon particles by a rapid metathesis reaction

A solid-state rapid metathesis reaction was performed in a bed of sodium silicofluoride (Na₂SiF₆) and sodium azide (NaN₃) powders diluted with sodium fluoride (NaF), to produce silicon nanoparticles. After a local ignition of Na₂SiF₆+4NaN₃+kNaF mixture (here k is mole number of NaF), the reaction proceeded in a self-sustaining combustion mode developing high temperatures (950–1000 °C) on very short time scales (a few seconds). Silicon nanoparticles prepared by the combustion process was easily separated from the salt byproducts by simple washing with distilled water. The structural and morphological studies on the nanoparticles were carried out using X-ray diffractometer (XRD) and field emission scanning electron microscope (FESEM). The mean size of silicon particles calculated from the FESEM image was about 37.75 nm. FESEM analysis also shows that the final purified product contains a noticeable amount of silicon fibers, dendrites and blocks, along with nanoparticles. The mechanism of Si nanostructures formation is discussed and a simple model for interpretation of experimental results is proposed.     

A simple route for fabricating poly(para-phenylene vinylene) (PPV) particles by using ionic liquids and a solvent evaporation process

Particles of a poly(para-phenylenevinylene) (PPV) precursor were prepared from an aqueous solution of the polymer by simple evaporation of water from the solution, which also contained an ionic liquid as a poor solvent (self-organized precipitation (SORP) method); PPV precursor nanoparticles were successfully converted to PPV nanoparticles after annealing at 240 degrees C under reduced pressure, this simple process constituting a novel route to nanoparticles of functional polymeric materials.     

Rapid preparation and characterization of uniform, large, spherical Ag particles through a simple wet-chemical route

In this article we report the rapid preparation of uniform, large, spherical Ag particles through a simple wet-chemical route. The formation of Ag particles with about 750 nm in diameter occurs in a single process, carried out by direct mix of AgNO3 aqueous solution and ortho-phenylenediamine N-methyl-2-pyrrolidone solution at room temperature, producing a relatively low-polydispersity product. It is also found that raising the temperature results in larger particles. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectra have been used to characterize the resulting product.     

Durable Lotus-effect surfaces with hierarchical structure using micro- and nanosized hydrophobic silica particles

Surfaces with a very high apparent water contact angle (CA) and low water contact angle hysteresis (CAH) exhibit many useful characteristics, among them extreme water repellency, low drag for fluid flow, and a self-cleaning effect. The leaf of the Lotus plant (Nelumbo nucifera) achieves these properties using a hierarchical structure with roughness on both the micro- and nanoscale. It is of great interest to create durable surfaces with the so-called "Lotus effect" for many important applications. In this study, hierarchically structured surfaces with Lotus-effect properties were fabricated using micro- and nanosized hydrophobic silica particles and a simple spray method. In addition, hierarchically structured surfaces were prepared by spraying a nanoparticulate coating over a micropatterned surface. To examine the similarities between surfaces using microparticles versus a uniform micropattern as the microstructure, CA and CAH were compared across a range of pitch values for the two types of microstructures. Wear experiments were performed using an atomic force microscope (AFM), a ball-on-flat tribometer, and a water jet apparatus to verify multiscale wear resistance. These surfaces have potential uses in engineering applications requiring Lotus-effect properties and high durability.     

Improved oxygen reduction cathodes using polyoxometalate cocatalysts

We report on the influence of a series of transition-metal-substituted Wells-Dawson (P2W17MnO62(12-n)-; M = WVI, FeII, CoII, RuII) and Keggin (PW12O40(3-) and PCoW11O39(5-) anions on the oxygen reduction reaction (ORR) at Au, Pd, and Pt. Wells-Dawson POMs adsorbed on Au lead to large positive shifts of the ORR potential. The magnitude of the shift depends on the transition metal and is explained using a simple thermodynamic model. The best cathode performance was achieved using a PCoW11O39(5-) cocatalyst and a Pt cathode. The +54 mV positive shift in the ORR potential that we observed is comparable to the performance of the best-known bimetallic catalysts.     

The adsorption interaction of a rutin-biopolymer complex with nanosized silica particles

The influence of complex formation with biopolymers on the optical and acid properties of natural flavonoid rutin was studied. The adsorption interaction of biologically active flavonoids from officinal plants with the surface of nanosized silica particles was found to depend on the chemical nature of the biopolymer and adsorbate and solution properties.     

Improved oxygen reduction reaction via a partially oxidized Co-CoO catalyst on N-doped carbon synthesized by a facile sand-bath method

Partially oxidized Co-CoO on N-doped carbon was synthesized via a facile sand-bath route. Co-CoO_x/N-C (SBM) exhibited much O_latt sites and catalytic activity of oxygen reduction action.     

Activation of metal-acyl oxygen atoms by triflic anhydride: a simple synthetic route to reactive cationic vinylidene complexes

(η⁵-Cyclopentadienyl) (acyl) (carbonyl) (tertiary phosphine) iron complexes react rapidly with trifluoromethanesulfonic acid anhydride to afford cationic vinylidene complexes, via the intermediacy of cationic carbene complexes. Spectroscopic and chemical characterizations of these vinylidene complexes are reported.     

Improved oxygen delivery in a continuous-roller-bottle reactor

Variations to the original aeration system in a continuous roller bottle reactor of novel design have been tested and compared for optimal oxygen (O) delivery. Reactor operating parameters that affect O transfer are rotation rate, liquid-volume level, fresh-feed rate, and supplementary-aeration rate. Design modifications to enhance gas-liquid O transfer include the addition of wall baffles and center baffles. The number and location of each of these baffles are compared for their effect on k_La values in the reaction chamber. The liquid feed into the system has been modified to improve the axial liquid mixing and O transfer.     

InOOH hollow spheres synthesized by a simple hydrothermal reaction

Novel micrometer-sized indium oxyhydroxide (InOOH) hollow spheres were successfully synthesized via a citric acid (CA) assisted hydrothermal process. The morphology, crystal structure, and optical properties of the product were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and UV-vis diffuse reflectance spectroscopy (DRS). The optical band gap, E(g), was estimated to be 3.5 eV from the DRS spectrum, which is almost equal to that of indium oxide. Furthermore, on the basis of a series of SEM observations, phenomenological elucidation of a mechanism for the growth of the InOOH hollow spheres has been presented; key factors for the formation of the structures have been proposed.     

Colloidal and chemical aspects of nanosized hydrated zirconium dioxide synthesized via a sol-gel process

The processes of coagulation and gelation of sols in zirconium oxychloride aqueous solutions and the properties of hydrated zirconium dioxide sols (pH, particles size, dynamic viscosity) depending on the aging conditions of partially neutralized zirconium oxychloride feedstock solution-zirconyl hydroxychloride used for the synthesis and molar ratio of initial reagents (Zr/NaOH, Zr/CH(3)COO(-)) were first studied in the paper. The concentration and temperature limits of hydrated zirconium dioxide sols stability were determined. The coagulation constant, gelation activation energy, and gelation thermal effect values were found.