Aqueous Boron Removal by Using Electrospun Poly(vinyl alcohol) (PVA) Mats: A Combined Study of IR/Raman Spectroscopy and Computational Chemistry.

We report the use of a novel and efficient method to remove aqueous boron by using electrospun, water-resistant poly(vinyl alcohol) (PVA) mats stabilized in methanol. The removal of the primary aqueous boron species as (B(OH)3), was accomplished by chemical adsorption in reactions with -OH (hydroxyl) groups on the PVA mat surface. The chemical adsorption of B(OH)3 was qualitatively confirmed by the analysis of IR and Raman spectra. The bands, corresponding to the molecular vibration modes of chemically bonded boron in PVA, were identified by using the frequency calculation from the computational chemistry for the first time. The adsorption capacities of PVA mats for aqueous boron were then quantitated at a low boron concentration (range: 0.0010 to 0.0025 g of aqueous boron per g of PVA mats) by the Carmine method. The PVA mats were prepared by a well-established electrospinning technique, which make these substrates promising potential candidates for use as boron-selective sorbent media in applications such as reverse osmosis desalination processes.

Preparation of anatase/rutile mixed-phase titania nanoparticles for dye-sensitized solar cells.

Acid-labile high surface mesoporous ZnO/Zn(OH)2 composite material is used as a novel hard template for the preparation of mesoporous amorphous TiO2. The template-free amorphous TiO2 material is then thermally crystallized at suitable temperature to control the relative ratio of anatase and rutile phases in a particle. Four different anatase/rutile (AR) mixed-phase TiO2 nanoparticles (AR-3, AR-15, AR-20, and AR-23 denoted for the samples of 3%, 15%, 20%, and 23% rutile phase, respectively) are prepared and characterized by powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM). The coexistence of anatase and rutile phases in a TiO2 nanoparticle is visually confirmed by HRTEM analysis. These mixed-phase TiO2 nanoparticles are examined as candidates for photoelectrodes of dye-sensitized solar cells (DSSCs). The J-V curves and IPCE spectra for the DSSCs prepared from the mixed-phase TiO2 nanoparticles are obtained, and their photovoltaic properties are investigated. The photo-conversion efficiency (eta) indicates the highest value of 5.07% for AR-20. The synergistic effect of coexisting anatase and rutile phases with an optimal ratio in a TiO2 nanoparticle of AR-20 for an efficient interfacial transfer of photo-generated electrons is likely to lead to the highest efficiency among the AR-n samples.

Intracellular protein delivery by hollow mesoporous silica capsules with a large surface hole.

We prepared cell membrane-permeable hollow mesoporous silica capsules (HMSCs) by a simple new method. CTAB micellar assembly in cholesterol emulsion gave rise to a novel capsular morphology of the HMSC particles. The HMSCs consisted of mesostructured silica walls with a large surface hole (25-50 nm) and the average particle dimension was 100-300 nm. They exhibited high surface areas of up to 719.3 m(2) g(-1) and a mesoporous range of pores of 2.4-2.7 nm. The surface-functionalized HMSCs could also be prepared by a similar co-condensation method using tetraethoxysilane with various organoalkoxysilane precursors in the presence of cholesterol. These organically modified HMSCs could be further modified on demand. For example, a carboxy-functionalized HMSC could be surface-functionalized by a green fluorescent 5-aminofluorescein (AFL) through an amidation reaction to afford a fluorescent AFL-HMSC. The hollow capsular morphology of the HMSCs with a large surface hole enabled us to develop very efficient intracellular delivery systems for membrane-impermeable ions, molecules, and various functional proteins. Non-covalent sequestration and delivery of proteins as well as covalent linkage of fluorescent molecules on the silica surface are effective for this system. The highly negatively charged green fluorescent probe mag-fluo-4 could be intracellularly delivered into HeLa cells by HMSC without any difficulty. The HMSCs could also effectively transport large functional proteins such as antibodies into HeLa cells. The efficiency of protein delivery by HMSC seems to be 3-22-fold higher than that of mesoporous silica nanospheres (MSNs) based on confocal laser scanning microscopy (CLSM) analysis.

Investigation of 1H NMR chemical shifts of organic dye with hydrogen bonds and ring currents.

The (1)H NMR chemical shifts were theoretically computed for the organic dyes 2-(2,6-dimethyl-4H-pyran-4-ylidene)-malononitrile (1), cyano-(2,6-dimethyl-4H-pyran-4-ylidene)-acetic acid methyl ester (2), 2-(2,6-bis(4-(dimethylamino)styryl)-4H-pyran-4-ylidene)-malononitrile (3), and methyl 2-(2,6-bis(4-(dimethylamino)styryl)-4H-pyran-4-ylidene)-2-cyanoacetate (4) at the GIAO/B3LYP/6-311++G(d,p)//B3LYP/6-311++G(d,p) level of theory. Moreover, the intramolecular rotational barriers of the molecules were calculated to evaluate the internal flexibility with respect to the torsional degrees of freedom, and the nuclear-independent chemical shifts (NICS) were employed to analyze the ring currents. The difference was explained in terms of intramolecular hydrogen bonds and ring currents of the molecules. The (1)H NMR spectra were reproduced by experiments for the comparison with computationally constructed data. Our results suggest a good guideline in interpreting (1)H NMR chemical shifts using computational methods and furthermore a reliable perspective for designing molecular structures.

Preparation of macroporous carbon nanofibers with macroscopic openings in the surfaces and their applications.

Macroporous carbon nanofibers with mesoscale surface openings were produced by electrospinning. During the electrospinning of polyacrylonitrile (PAN) solution including crosslinked polymer colloids, the polymer colloids were concentrated in the center of PAN fibers. Carbonization left interconnected spherical pores inside the carbon fibers and mesoscale openings in the fiber surfaces. The existence of surface openings facilitated inward diffusion of various solvent molecules, nanoparticles, and large molecules such as proteins. The porous fibers could be dispersed in both hydrophilic and hydrophobic solvents and materials, which enabled production of polymer composites in which the fibers and polymers were interpenetrating through the pores. Silica coating on the macroporous carbon fibers enriched the surface chemistry to effectively immobilize proteins helped by easy diffusion through surface openings.

Homogeneous decomposition mechanisms of diethylzinc by Raman spectroscopy and quantum chemical calculations.

The gas-phase decomposition pathways of diethylzinc (DEZn), a common precursor for deposition of Zn-VI compounds, were investigated in detail. The homogeneous thermal decomposition of DEZn in N2 carrier was followed in an impinging-jet, up-flow reactor by Raman scattering. Density Functional Theory calculations were performed to describe the bond dissociation behavior using the model chemistry B3LYP/6-311G(d) to estimate optimal geometries and Raman active vibrational frequencies of DEZn, as well as anticipated intermediates and products. Comparison of the measured DEZn decomposition profile to that predicted by a 2-D hydrodynamic simulation revealed that simple bond dissociation between zinc and carbon atoms is the dominant homogeneous thermal decomposition pathway. The calculations suggest several reactions involving intermediates and Raman scattering experiments confirming the formation of the dimer (ZnC2H5)2. In a different set of experiments, photolysis of DEZn gave evidence for decomposition by beta-hydride elimination. The results suggest that beta-hydride elimination is a minor pathway for the gas-phase homogeneous pyrolysis of diethylzinc. A reasonable transition state during beta-hydride elimination was identified, and the calculated energies and thermodynamic properties support the likelihood of these reaction steps.

Study on the Aging Mechanism of Boron Potassium Nitrate (BKNO3) for Sustainable Efficiency in Pyrotechnic Mechanical Devices.

The aging of propellants in PMDs is considered to be one of the primary factors affecting the performance of PMDs. Thus, studies on the aging mechanism of propellants, which have not yet been addressed extensively, pose a solution to securing the sustainable operation of PMDs. We characterized one of the most commonly used commercial propellants (boron potassium nitrate (BKNO3)) and investigated its aging mechanism rigorously. Based on thermal analyses, we demonstrate that the decomposition of laminac, a polymer binder, is the fastest spontaneous reaction. However, it will not self-initiate at a storage temperature as high as 120 °C. The effect of the humidity level was examined by characterizing BKNO3 samples prepared. The heat of reaction and the reaction rate decreased by 18% and 67% over 16 weeks of aging, respectively. This is attributed to the oxide shells on the surface of boron particles. The formation of oxide shells could be confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy-energy dispersive spectroscopy. In conclusion, surface oxide formation with the aging of BKNO3 will decrease its propulsive efficiency; oxidation reduces the potential energy of the system and the resulting oxide decreases the reaction rate.

Simple preparation of lotus-root shaped meso-/macroporous TiO2 and their DSSC performances.

In pursuit of superior TiO2 photoanode materials for dye-sensitized solar cells (DSSCs), we prepared lotus-root shaped meso-/macroporous TiO2. The lotus-root shaped meso-/macroporous TiO2 was easily prepared by using a cetyltrimethylammonium hydroxide (CTAOH) template in aqueous solution. The crystallization of the as-prepared amorphous lotus-root shaped TiO2 was performed at 700 °C in air. Crystalline anatase phase with a very small portion of rutile phase was generated after the heat treatment at 700 °C and the BET surface area of crystalline lotus-root shaped meso-/macroporous TiO2 material (LR-700) was 30.0 m(2) g(-1). The wall of LR-700 displayed well-developed mesoporosity with a pore dimension of 28.3 nm. Periodically arranged microscale one-dimensional (1D) macropores were also observed in the particles. The photon-to-current conversion efficiencies (η) of LR-700 photoanodes in Grätzel type DSSCs were examined. The conversion efficiency of DSSC prepared by mixing nanoparticulate Evonik P25 and LR-700 (ratio=85:150 by mass) was 28% greater compared to the reference electrode using P25. Incident photon-to-current efficiencies (IPCE) of the DSSCs were dramatically improved by employing the photoanodes composed of a mixture of P25 and LR-700 but impedance analysis indicated that P25/LR-700 mixed cells have resistances similar to the standard P25 reference cell. Thus, photovoltaic performances could be improved mainly due to the increases of dye uptake and external quantum efficiency by using a mixed photoanode composed of LR-700 and nanocrystalline P25 particles.

Exploring the Catalytic Potential of ZIF-90: Solventless and Co-Catalyst-Free Synthesis of Propylene Carbonate from Propylene Oxide and CO2.

Reported is the application of ZIF-90, which is a highly porous zeolitic imidazolate framework, as a novel catalyst for the cycloaddition of propylene oxide (PO) with CO2 in the absence of co-catalysts and solvents under moderate reaction conditions. The effects of various reaction parameters were investigated. The activity of ZIF-90 was compared with that of various metal-organic-framework (MOF)-based catalysts for the cycloaddition of PO with CO2 . Density functional theory calculations elucidated the role of ZIF-90 in creating a favorable environment for the PO-CO2 cycloaddition reaction. A reaction mechanism for the ZIF-90-catalyzed PO-CO2 cycloaddition on the basis of DFT calculations is proposed and the regeneration of ZIF-90 is discussed.

Amino acid/KI as multi-functional synergistic catalysts for cyclic carbonate synthesis from CO2 under mild reaction conditions: a DFT corroborated study.

Naturally occurring amino acids were identified as efficient co-catalysts for the alkali metal halide-mediated synthesis of cyclic carbonates from carbon dioxide and epoxides under mild, solvent free reaction conditions. The binary system of histidine/potassium iodide gave an appreciable turnover number of 535 for propylene oxide in 3 h. Detailed studies evaluating a variety of amino acids revealed that the basic amino acids afforded better conversion rates. The formation of a seven membered ring involving the zwitterionic ends of the amino acid, the metal halide, and the epoxide was considered to accelerate the catalysis rate. Density functional theory calculations were performed for the first time on amino acid co-catalyzed cycloaddition to provide further evidence for this hypothesis. The iodide ions of the alkali metal halide displayed excellent synergism with the hydrogen bonding groups of the amino acids in the production of cyclic carbonates, whereas bromide and chloride anions functioned less efficiently. The utilization of amino acids to enhance the catalytic activity of the cheap and eco-friendly alkali metal halides for cyclic carbonate synthesis represents a cost-effective, greener route towards the chemical fixation of carbon dioxide.

Effect of nitrogen doping on the performance of dye-sensitized solar cells composed of mesoporous TiO2 photoelectrodes.

Nitrogen-doped mesoporous TiO2 (NMP TiO2) nanoparticles are synthesized using a soft triblock copolymer template by TiCl4 hydrolysis with ammonia water and applied to the photoelectrodes of dye-sensitized solar cells (DSSCs). The large surface area of a TiO2 mesoporous structure is favorable for dye uptake, and nitrogen doping of TiO2 is expected to increase the charge transport in the photoelectrode as well as the scattering of visible light. Structural characterizations for NMP TiO2 nanoparticles by XRD, XPS, BET, and BJH analyses revealed successful synthesis. However, the photovoltaic performances of the DSSCs prepared from NMP TiO2 were not improved, as had been expected: the photo-conversion efficiency (η) of DSSCs from undoped mesoporous TiO2 (MP TiO2) was 4.69%, an improvement over the 4.15% with the application of P25 TiO2, but the efficiency of DSSCs from NMP TiO2 decreased to 3.2-3.6%. The measured amounts of adsorbed dye showed that nitrogen doping did not significantly affect dye adsorption. Therefore, it can be concluded that nitrogen doping increases isotropic charge transport in a TiO2 nanoparticle to promote charge recombination into an electrolyte, despite its advantages. The full benefits of nitrogen doping may be obtained through measures such as the deposition of a thin barrier layer of oxide onto the TiO2 surface to prevent charge recombination during charge transport in the TiO2 network.

Effect of the rutile content on the photovoltaic performance of the dye-sensitized solar cells composed of mixed-phase TiO2 photoelectrodes.

The effect of the rutile content on the photovoltaic performance of dye-sensitized solar cells (DSSCs) composed of mixed-phase TiO(2) photoelectrode has been investigated. The mixed-phase TiO(2) particles with varied amounts of rutile, relative to anatase phase, are synthesized by an in situ method where the concentration of sulfate ion is used as a phase-controlling parameter in the formation of TiO(2) using TiCl(4) hydrolysis. The surface area (S(BET)) varies from 33 (pure rutile) to 165 (pure anatase) m(2) g(-1). Generally, both the current density (J(sc)) and photo-conversion efficiency (η) decrease as the rutile content increases. The incorporation of rod-shaped rutile particles causes low uptake of dye due to the reduced surface area, as well as slow electron transport in less efficiently-stacked structure. However, maximum J(sc) (14.63 mA cm(-2)) and η (8.69%) appear when relatively low rutile content (16%) is employed. The reported synergistic effect by the efficient interparticle electron transport from rutile to anatase seems to overbalance the decrease of surface area when small amount of rutile particles is incorporated.

Facile preparation of SERS-active nanogap-rich Au nanoleaves.

To simply reduce HAuCl(4) using 2-thiophenemethanol in an aqueous solution at room temperature, a novel metallic Au nanostructure with a high SERS activity was obtained. Flat sheet-like Au nanoleaves possessing many nanogap hotspots bound with a large percentage of high-index facets were obtained.

Homogeneous decomposition of aryl- and alkylimido precursors for the chemical vapor deposition of tungsten nitride: a combined density functional theory and experimental study.

MOCVD growth of tungsten nitride (WN(x)()) and tungsten carbonitride (WN(x)()C(y)()) thin films has been reported from the complexes Cl(4)(CH(3)CN)W(NR) (1: R = Ph; 2: R = (i)Pr; 3: R = C(3)H(5)). To evaluate the role of the imido substituent in film growth, gas-phase homogeneous decomposition of precursor molecules was investigated using density functional theory (DFT) calculations. Computational results and NMR kinetics of acetonitrile exchange by 2 in solution verified that dissociation of the acetonitrile ligand should be facile for 1-3 in the temperature range used for film growth (>450 degrees C). A computational search for transition states for cleavage of W-Cl bonds in the presence of H(2) carrier gas was consistent with a sigma-bond metathesis pathway. Natural bonding orbital (NBO) analysis and bond energy calculations indicated that 1 has a stronger N-C(imido) bond and a slightly weaker W-N bond than 2 and 3, suggesting a greater role for W-N bond cleavage in depositions from 1. These results are consistent with mass spectrometric fragmentation patterns from 1-3 and low nitrogen content in films deposited from 1 as compared to those from 2 and 3.