Dual-functional ZnO nanorod aggregates as scattering layer in the photoanode for dye-sensitized solar cells

A bilayered ZnO photoanode was constructed for dye-sensitized solar cells with a high conversion efficiency of 4.0%. One layer made of ZnO nanocrystallites increases dye adsorption, and the other consisting of ZnO nanorod aggregates provides a directed electron pathway for the electron transport together with a prominent aggregation-induced light scattering.     

Solvent tuning from normal to inverted marcus region of intramolecular electron transfer in ferrocene-based organic radicals

The solvent dependence of spectroscopic data of two neutral paramagnetic donor-acceptor dyads, based on a polychlorinated triphenylmethyl radical acceptor unit linked through a vinylene pi-bridge to a ferrocene (compound 1) or a nonamethylferrocene donor (compound 2) unit, is described. Both compounds exhibit broad absorptions in the near-IR region, with band maxima appearing around 1000 and 1500 nm for 1 and 2, respectively. These bands correspond to the excitation of a neutral DA ground state to the charge-separated D+A- state, indicative of an intramolecular electron-transfer process. Compounds 1 and 2 show two reversible one-electron redox processes associated with the oxidation of the ferrocene and the reduction of the polychlorotriphenylmethyl radical subunits. The solvent dependence of the redox potentials was also investigated, allowing the determination of the redox asymmetries DeltaG degrees of both dyads. The latter values, along with the experimental Eopt spectroscopic data, allow us to estimate, using the total energy balance Eopt = lambda + DeltaG degrees , the reorganization energy values, lambda, and their solvent polarity dependence. Since DeltaG degrees and lambda are of the same order of magnitude but exhibit opposite trends in their solvent polarity dependence, a unique shift from the normal to the inverted Marcus region with the change in solvent polarity is found. The kinetics of the charge recombination step of the excited charge-separated D+A- state was studied by picosecond transient absorption spectroscopy, which allows us to observe and monitor for the first time the charge-separated D+A- state, thereby confirming unambiguously the photoinduced electron-transfer phenomena.     

Metalloporphyrin-based covalent organic frameworks composed of the electron donor-acceptor dyads for visible-light-driven selective CO2 reduction

The visible-light-driven photocatalytic CO_2 reduction with high efficiency is highly desirable but challenging. Herein, we present porphyrin-tetraphenylethene-based covalent organic frameworks(MP-TPE-COF, where M=H_2, Co and Ni;TPE=4,4′,4″,4?-(ethane-1,1,2,2-tetrayl) tetrabenzaldehyde; COF=covalent organic framework) as ideal platforms for understanding photocatalytic CO_2 reduction at molecular level. Experimental and theoretical investigations have demonstrated crucial roles of metalloporphyrin units in selective adsorption, activation and conversion of CO_2 as well as in the separation of charge carriers and electron transfer, thus allowing for flexible modulation of photocatalytic activity and selectivity. Co P-TPE-COF exhibits high CO evolution rate of 2,414 μmol g~(-1) h~(-1) with the selectivity of 61% over H_2 generation under visible-light irradiation, while Ni P-TPE-COF provides CO evolution rate of 525 μmol g~(-1) h~(-1) and 93% selectivity with superior durability.Moreover, the photocatalytic system is feasible for the simulated flue gas, which provides CO evolution rate of 386 μmol g~(-1) h~(-1) and selectivity of 77%. This work provides in-depth insight into the structure-activity relationships toward the activation and photoreduction of CO_2.     

Corrections to the impulse approximation for use in electron compton scattering experiments

The breakdown of the impulse approximation for K-shell electrons in electron Compton scattering measurements on solids is parameterized in a form which makes it possible to assess the importance of this effect and where necessary to apply a suitable correction.     

Development of heterodyne detection of dynamic light scattering enhanced by the Talbot effect for the size measurement of nanoparticles.

A new type of dynamic light scattering method for the size measurement of nanoparticles was developed using a transmission grating. A sample cell was located behind the grating, and light was incident from the grating side. The scattered light by a solution with nanopariticles was mixed with diffracted light by the grating, and the mixed signal was detected; namely, the diffracted light was used as reference light for heterodyne detection. It was confirmed that the S/N ratio of the autocorrelation curve was 26-times improved by heterodyne detection. Furthermore, the S/N ratio was improved by setting the sample cell at the sample grating distance where the electromagnetic field is maximum due to the Talbot effect. Size measurements for several kinds of nanoparticles were demonstrated by this new method.     

Evidence for through-space electron transfer in the distance dependence of normal and inverted electron transfer in oligoproline arrays

Four new helical oligoproline assemblies containing 16, 17, 18, and 19 proline residues and ordered arrays of a Ru(II)-bipyridyl chromophore and a phenothiazine electron-transfer donor have been synthesized in a modular fashion by solid-phase peptide synthesis. These arrays are illustrated and abbreviated as CH(3)CO-Pro(6)-Pra(PTZ)-Pro(n)()-Pra(Ru(II)b(2)m)(2+)-Pro(6)-NH(2), where PTZ is 3-(10H-phenothiazine-10)propanoyl and (Ru(II)b'(2)m)(2+) is bis(4,4'-diethylamide-2,2'-bipyridine)(4-methyl,4'-carboxylate,2,2'-bipyridine)ruthenium(II) dication with n = 2 (2), 3 (3), 4 (4), and 5 (5). They contain PTZ as an electron-transfer donor and (Ru(II)b'(2)m)(2+) as a metal-to-ligand charge transfer (MLCT) light absorber and are separated by proline-to-proline through-space distances ranging from 0 (n = 2) to 12.9 A (n = 5) relative to the n = 2 case. They exist in the proline-II helix form in water, as shown by circular dichroism measurements. Following laser flash Ru(II) --> b'(2)m MLCT excitation at 460 nm in water, excited-state PTZ --> Ru(2+) quenching (k(2)) occurs by reductive electron transfer, followed by Ru(+) --> PTZ(+) back electron transfer (k(3)), as shown by transient absorption and emission measurements in water at 25 degrees C. Quenching with DeltaG degrees = -0.1 eV is an activated process, while back electron transfer occurs in the inverted region, DeltaG degrees = -1.8 eV, and is activationless, as shown by temperature dependence measurements. Coincidentally, both reactions have comparable distance dependences, with k(2)( )()varying from = 1.9 x 10(9) (n = 2) to 2.2 x 10(6) s(-)(1) (n = 4) and k(3) from approximately 2.0 x 10(9) (n = 2) to 2.2 x 10(6) s(-)(1) (n = 4). For both series there is a rate constant enhancement of approximately 10 for n = 5 compared to n = 4 and a linear decrease in ln k with the through-space separation distance, pointing to a significant and probably dominant through-space component to intrahelical electron transfer.     

On the role of parallel architecture supercomputers in time-dependent approaches to quantum scattering

Summary Results of our initial study of the use of parallel architecture super-computers in solving time-dependent quantum scattering equations are reported. The specific equations solved are obtained from the time-dependent Lippmann-Schwinger integral equation by means of a quadrature approximation to the time integral. This leads to a modified Cayley transform algorithm in which the primary computational step is a matrix-vector multiplication. Implementation has been carried out both for the MasPar MP-1 and the NCUBE 6400 parallel machines. The codes are written in a modular form that greatly facilitates porting from one machine architecture to another. Both parallel machines prove to be more powerful for this application than the serial architecture VAX 8650. Specific analysis of machine performance is given.Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. 2-7405-ENG-82. This research was supported by the Division of Chemical Sciences and Applied Mathematical Sciences, Office of Basic Energy SciencesR.A. Welch Predoctoral Fellow under R.A. Welch Foundation Grant E-608Supported in part under National Science Foundation Grant CHE89-07429     

Immobilized metal complexes in porous organic hosts: development of a material for the selective and reversible binding of nitric oxide.

Delivery of NO to specific targets is important in fundamental studies and therapeutic applications. Various methods have been reported for delivery of NO in vivo and in vitro; however, there are few examples of systems that reversibly bind NO. Reported herein is the development of a new polymer (P-1[Co(II)]) that reversibly binds NO. P-1[Co(II)] has a significantly higher affinity for NO compared to O(2), CO(2), and CO. The polymer is synthesized by template copolymerization methods and consists of a porous methacrylate network, containing immobilized four-coordinate Co(II) sites. Binding of NO causes an immediate color change, indicating coordination of NO to the site-isolated Co(II) centers. The formation of P-1[Co(NO)] has been confirmed by EPR, electronic absorbance, and X-ray absorption spectroscopies. Electronic and X-ray absorbance results for P-1[Co(II)] and P-1[Co(NO)] show that the coordination geometry of the immobilized cobalt complexes are similar to those of their monomeric analogues and that NO binds directly to the cobalt centers. EPR spectra show that the binding of NO to P-1[Co(II)] is reversible in the solid state; the axial EPR signal associated with the four-coordinate Co(II) sites in P-1[Co(II)] is quenched upon NO binding. At room temperature and atmospheric pressure, 40% conversion of P-1[Co(NO)] to P-1[Co(II)] is achieved in 14 days; under vacuum at 120 degrees C this conversion is complete in approximately 1 h. The binding of NO to P-1[Co(II)] is also observed when the polymer is suspended in liquids, including water.     

A sensitive and selective assay of nucleic acids by measuring enhanced total internal reflected resonance light scattering signals deriving from the evanescent field at the water/tetrachloromethane interfacet

A total internal reflected resonance light scattering (TIR-RLS) technique, the coupling of resonance light scattering (RLS) technique with total internal reflected light at the interface of two immiscible liquids, where the steep change of the refractive indexes occurs to result in an evanescent field, is proposed with the characteristics of separation and enrichment properties of analytes and direct use of oil-soluble reagents free from surfactants. At pH 8.69 and ion strength 0.008, ternary amphiphilic species formed by the interaction of nucleic acids, including calf thymus DNA (ctDNA), fish sperm DNA (fsDNA), and yeast RNA (yRNA), with Eu(III) in the presence of oil-soluble trioctylphosphine oxide (TOPO), are adsorbed to the water/tetrachloromethane (H20/CCl4) interface, giving rise to significantly enhanced TIR-RLS signals. It has been found that the enhanced TIR-RLS intensity at 348.0 nm is proportional to the concentration of thermally denatured ctDNA, fsDNA and yRNA in the range 0.002-2.5 microg ml(-1), 0.002-2.5 microg ml(-1) and 0.003-2.0 microg ml(-1), respectively and their limits of determination (3sigma) are 0.16 ng ml(-1), 0.19 ng ml(-1) and 0.28 ng ml(-1), correspondingly. Complicated artificial samples with highly interfering backgrounds were determined satisfactorily.     

Modification to the cumulant analysis of polydispersity in quasielastic light scattering data

The electric field correlation function of light scattered from a polydispersed population of spherical particles having log-normal distribution with varying polydispersity is simulated. The correlation function with different polydispersity is compared with the method of cumulants over a wide range of correlation time. The large positive deviation of the method of cumulants at long correlation time is identified. This necessitates the truncation of the data at long correlation time or use of an appropriate weighting function to eliminate errors in the analysis. A modified cumulant analysis is used to overcome the limitation of truncating the correlation function. QELS data from polydisperse samples of micelles, liposomes and polyaniline nanoparticles are compared using the two methods. This method can be extended to the analysis of other multi-exponential decays such as stress relaxation, positron annihilation and NMR relaxation.     

A sensitive and selective resonance light scattering bioassay for homocysteine in biological fluids based on target-involved assembly of polyethyleneimine-capped Ag-nanoclusters

A specific resonance light scattering bioassay for homocysteine is developed on the basis of target-involved assembly of polyethyleneimine-capped Ag-nanoclusters. The bioassay permits discriminating homocysteine from cysteine, glutathione and other amino acids, and allows sensitive and selective detection of homocysteine with a detection limit of 42 nM.     

Dual silane surface functionalization for the selective attachment of human neuronal cells to porous silicon

Porous silicon (pSi) surfaces were chemically micropatterned through a combination of photolithography and surface silanization reactions. This patterning technique produces discretely defined regions on a pSi surface functionalized with a specific chemical functionality, and the surrounding surface displays a completely different functionality. The generated chemical patterns were characterized by a combination of IR microscopy and the conjugation of two different fluorescent organic dyes. Finally, the chemically patterned pSi surface was used to direct the attachment of neuronal cells to the surface. This patterning strategy will be useful for the development of high-throughput platforms for investigating cell behavior.     

Fe/SiO_2纳米复合物上合成气制低碳烯烃催化性能研究

分别采用一步合成法和常规共沉淀法制备了Fe/SiO2催化剂,通过N2物理吸附、X射线衍射、透射电镜、傅里叶变换红外光谱和程序升温还原等方法对催化剂进行了表征,并在固定床反应器中对其费托合成制低碳烯烃的催化性能进行了评价。结果表明,与共沉淀铁基催化剂不同,采用一步合成法制备的纳米复合物主要由Fe3O4相构成,形貌呈规则球形,平均粒径为30 nm,尺寸分布窄,更容易还原。一步合成法制得的Fe/SiO2催化剂对费托合成反应具有较高的活性和低碳烯烃选择性、较低的甲烷选择性和良好的稳定性。     

The importance of polarization for electron scattering in the intermediate energy region

The angular dependence of electron scattering from the helium atom and the hydrogen molecule for small scattering angles in the 34 – 100 eV impact energy range is explained in terms of the first Born approximation and the polarized Born approximation. The theoretical results compare favorably with the experimental data for both elastic and inelastic scattering. New experimental and theoretical results are presented.     

Thermally reversible light scattering films based on the melting/crystallization of organic crystals dispersed in an epoxy matrix

Films that can be reversibly switched from opaque to transparent states by varying temperature (TRLS films), have potential applications in thermal sensors, optical devices, recording media, etc. A dispersion of organic crystals in a thermoset may be used for these purposes provided that at temperatures higher than the melting point there is a matching of refractive indices of both phases. A model system consisting on a dispersion of diphenyl (DP) crystals in an epoxy matrix based on diglycidyl ether of bisphenol A and m-xylylenediamine, was analyzed as a possible TRLS film encapsulated between transparent covers to avoid sublimation of DP. To obtain a uniform dispersion of DP-rich domains in the epoxy matrix by polymerization-induced phase separation, it was necessary to add 5 wt% of polystyrene (PS) to the initial formulation. Phase separation induced by polymerization at 80 °C led to a dispersion of PS/DP domains in the epoxy matrix due to the low compatibility of PS with the epoxy and its high compatibility with DP. Crystallization and melting processes were confined to the interior of dispersed domains leading to an excellent reproducibility of the optical properties of TRLS films in the course of successive heating-cooling cycles.     

A novel and selective assay for the quantitative analysis of molybdenum(VI) at nanogram level by resonance light scattering quenching technique

A novel method is designed for the direct determination of trace amounts of molybdenum(VI) in tap water, human hair, and Chinese herbal medicine by means of decreasing resonance light scattering (RLS) technique. The characteristics of RLS spectra, the effective factors, and optimum conditions of the reaction were studied. In the medium of hydrochloric acid (pH 2.38), Mo(VI), dibromohydroxyphenylfluorone (DBHPF), and Triton X-100 react to form a complex, resulting in significant decreasing RLS signals of DBHPF-Triton X-100. The decreasing RLS intensity at 583.0 nm is proportional to the concentration of Mo(VI) up to 8.0 ng mL(-1). The detection limit is 0.013 ng mL(-1). The method is simple, reproducible, with reaction rapidity and stability of complexes formed. Moreover, the high selectivity and sensitivity of this method permits its direct determination of molybdenum(VI) in tap water, human hair, and Chinese herbal medicine and the results are in agreement with those obtained by the inductively coupled plasma atomic emission spectrometry (ICP-AES) method.     

Fe2O3/ZnO/ZnFe2O4 composites for the efficient photocatalytic degradation of organic dyes under visible light

In this study, novel ternary Fe₂O₃/ZnO/ZnFe₂O₄ (ZFO) composites were successfully prepared through a simple hydrothermal reaction with subsequent thermal treatment. The as-prepared products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) analysis, Barrett-Joyner-Halenda (BJH) measurement, and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). The photocatalytic degradation of rhodamine B (Rh B) under visible light irradiation indicated that the ZFO composites calcined at 500 °C has the best photocatalytic activity (the photocatalytic degradation efficiency can reach up to 95.7% within 60 min) and can maintain a stable photocatalytic degradation efficiency for at least three cycles. In addition, the photocatalytic activity of ZFO composites toward dye decomposition follows the order cationic Rh B > anionic methyl orange. Finally, using different scavengers, superoxide and hydroxyl radicals were identified as the primary active species during the degradation reaction of Rh B.     

An endogenous multiple scattering method for the calculation of the elastic scattering cross sections of electron shape resonances in polyatomic molecu

A procedure is described for obtaining the scattering potential for elastic electron—molecule scattering within the one-electron overlapping sphere multiple scattering Xα method. The method has been used to calculate the total elastic electron scattering cross sections for the nitrogen, ethylene and 1,3,5-trifluorobenzene molecules, which compare well with experimental data.