Role Of Electron Donor Research Articles

Fermi level engineering of topological insulator films by tuning the substrates

The Fermi level of the topological insulators (TIs) Bi2Se3 and Bi2Te3 is usually well above the Dirac points, which is ascribed to the intrinsic donor defects, such as antisites and anion vacancies. We show here by first-principles calculations that the substrates can modulate the Fermi level of TIs considerably. It is found that in Bi2Se3/graphene and Bi2Te3/Si(1 1 1), the substrates play the role of electron donor due to their lower workfunctions and push up the Fermi level of the TIs. Thicker TI films are found to have larger density of states and hence the charge transferred to TI leads to a smaller Fermi level shift, in good agreement with experiments. We propose to use high workfunction substrates to counterbalance the upward shift of the Fermi level due to the donor defects. Our calculations found that the fluorinated substrates F-graphene and F-Si(1 1 1) have very high workfunction and become electron acceptors, leading to a downward shift of the Fermi level of TIs.

The role of electron donors generated from UV photolysis for accelerating pyridine biodegradation.

Employing an internal circulation baffled biofilm reactor (ICBBR), we evaluated the mechanisms by which photolysis accelerated the biodegradation and mineralization of pyridine (C5 H5 N), a nitrogen-containing heterocyclic compound. We tested the hypothesis that pyridine oxidation is accelerated because a key photolysis intermediate, succinate, is as electron donor that promotes the initial mono-oxygenation of pyridine. Experimentally, longer photolysis time generated more electron-donor products (succinate), which stimulated faster pyridine biodegradation. This pattern was confirmed by directly adding succinate, and the stimulation effect occurred similarly with addition of the same equivalents of acetate and formate. Succinate, whether generated by UV photolysis or added directly, also accelerated mono-oxygenation of the first biodegradation intermediate, 2-hydroxyl pyridine (2HP). 2HP and pyridine were mutually inhibitory in that their mono-oxygenations competed for internal electron donor; thus, the addition of any readily biodegradable donor accelerated both mono-oxygenation steps, as well as mineralization.

Luminescence properties and a substitution defect model for self-reduction of europium ions in silicate Ba(Eu)MgSiO4 phosphors

The variations of luminescence properties of silicate Ba(1−x)MgSiO4:xEu phosphors are investigated in view of the structure of the host matrix and different synthetic atmosphere. X-ray powder diffraction patterns, luminescent spectra and electron spin resonance are used to confirm the compound structure and detected the simultaneous existence of both divalent and trivalent europium ions. The results indicate that both Eu2+ and Eu3+ are co-existing in the silicate when synthesized under air atmosphere due to the substitution of Eu3+cations for alkaline earth (Ba2+) triggers the formation of VBa// vacancies that play the role of electron donor towards EuBa defects. The higher the concentration of VBa//, the easier the reduction of Eu3+ into Eu2+. The co-doping with higher state chemical elements (i.e., La3+, Zr4+) helps a lot in increasing the concentration of Eu2+cations at the expense of Eu3+ ions in the Ba(1−x)MgSiO4:xEu phosphors. The energy transfer between Eu2+ cations in different sites within the BaMgSiO4 host matrix is also observed and its mechanism is charged by multipolar interaction.

Photocatalytic reduction of Cr(VI) over titania suspensions

The photocatalytic reduction of hexavalent chromium over titania suspensions was investigated using a 9W UV-A lamp as the irradiation source. Experiments were carried out at acidic conditions, with varying chromium and photocatalyst concentration. Commercially available titania powders were tested, predominantly Evonik P-25 (70:30 anatase:rutile), as well as Kronos vlp7000 and Millenium PC-100 (100% pure anatase). Four different organic substrates (phthalate, methanol, ethanol, propanol) were employed as sacrificial electron donor at varying initial concentrations.Reduction is strongly favoured at acidic conditions with complete conversion of 10mgL−1 Cr(VI) being achieved after 60min at pH=2.5 in the presence of 2gL−1 TiO2 P-25 and 50mgL−1 methanol. The role of electron donors is equally important as the respective extent of reduction is only 30% in the absence of a hole scavenger. At lower Cr(VI) concentrations, the reduction appears to obey first order kinetics (as evidenced measuring initial rates and computing kinetic constants), but it shifts to lower reaction orders at higher concentrations. All four organics can promote Cr(VI) reduction with phthalate being slightly more effective than the alcohols. Kronos vlp7000, whose surface area is about 3–5 times greater than the other two, results in the higher reduction rates.

Thermoelectric Performance Optimization in p-Type Ce y Fe3CoSb12 Skutterudites

In this study, we investigated the impact of the Ce filling fraction on the thermoelectric properties of p-type filled skutterudites CeyFe3CoSb12 (y = 0.6 to 1.0). The electrical conductivity decreases gradually with increasing y, while the Seebeck coefficient displays an opposite variation tendency, consistent with the expected electron donor role of the Ce filler in this compound. The overall power factors are invariable among all the samples. Alteration of the Ce filling fraction exerts little influence on the phonon transport, but the total thermal conductivity markedly declined with increasing y due to the reduced contribution to heat transfer from carriers. As a consequence, the maximum thermoelectric figure of merit ZT reaches ∼0.8 for the sample with y = 0.9, comparable to that of pure Fe-based skutterudite CeFe4Sb12; more importantly, the former possesses a much larger average ZT between 300 K and 800 K than the latter, showing superior potential for use in intermediate-temperature thermoelectric power generation applications. Further enhancement of ZT in p-type Fe3CoSb12-based skutterudites could be realized via nanostructuring or a multiple-filling approach.

Laser Flash Photolysis on Electron Transfer Reactions between 1,8-Dihydroxyanthraquinone with Adenine and Cytosine

Electron transfer (ET) reactions between 1,8-dihydroxyanthraquinone (DHAQ) and two DNA bases, adenine (A) and cytosine (C), have been investigated in CH3CN/H2O solution with nanosecond time-resolved laser flash photolysis. After irradiation at 355 nm, the triplet DHAQ is produced via intersystem crossing and reacts with two nucleobases. ET processes for both reactions have been definitely identified, in which two bases play a significant role of electron donor. Based on the measured decay dynamics of various intermediates and the corresponding quenching rates, an initial ET process followed by a secondary proton-transfer reaction is suggested for both the overall reactions. By plotting the observed quenching rate against the concentration of two DNA bases, the bimolecular quenching rate constants are determined as 9.0×108 L/(mol?s) for the 3DHAQ*+C reaction and 3.3×108 L/(mol?s) for the 3DHAQ*+A reaction, respectively.

Computational Study on Redox-Switchable Second-Order Nonlinear Optical Properties of Totally Inorganic Keggin-Type Polyoxometalate Complexes

The electronic structure and second-order nonlinear optical (NLO) property of a series of monoruthenium-substituted Keggin-type polyoxometalates (POMs) have been studied by using density functional theory (DFT) and time-dependent (TD)DFT calculations. The DFT calculation supports that these POM complexes possess donor-π-conjugated bridge-acceptor (D-π-A) structure, which the ruthenium atom acts as the role of electron donor and the three vanadium atoms in cap region of Keggin-type POM act as the role of electron acceptor. It is well-known that D-π-A structure, as a simple molecular scheme, has been successfully used in the development of organic NLO materials. However, the totally inorganic molecule having D-π-A structure is very rare. Thereby the second-order NLO properties of these POM complexes have been analyzed in this work. According to the calculations, introduction of the electron acceptor leads to a substantial enhancement on the second-order NLO response. The calculated βHRS(−2ω; ω, ω) value of ...

Photocatalytic reduction of vanadium(V) in TiO2 suspension: Chemometric optimization and application to wastewaters

The photocatalytic reduction of V(V) to V(IV) over TiO2 in aqueous solution is presented. Experiments were undertaken on air-equilibrated water spiked with V(V) (0.6–20mgL−1), under UV-A or solar light. A chemometric study was performed to optimize the reduction yield, by considering the most important variables recognized to affect the photocatalytic process. Among pH, irradiation time and catalyst concentration, the two latter proved to be determinant. The good yields achieved (up to 98%), along with the possibility of working in aerated solution, make this procedure simple, rapid and efficient. Although a deep insight on the photochemical mechanisms was beyond our scope, the role of electron donors was investigated, proving the efficiency of 2-propanol, citric acid and formic acid in the acceleration and improvement of V(V) conversion. After irradiation, total vanadium and aqueous V(V) and V(IV) after solid-phase separation on Chelex-100 resin, were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). The procedure was applied to contaminated wastewaters, combining remediation and possible vanadium recovery as V(IV).

Starburst triarylamine based dyes bearing a 3,4-ethylenedioxythiophene linker for efficient dye-sensitized solar cells

Starburst triarylamine-based organic dyes (D1, D2, and D3) have been synthesized. For the three designed dyes, the starburst triarylamine group, thiophene (or 3,4-ethylenedioxythiophene), and cyanoacetic acid take the role of electron donor, π-conjugation bridge, and electron acceptor, respectively. These compounds are characterized by photophysical, electrochemical, and theoretical computational methods. Nanocrystalline TiO2-based dye-sensitized solar cells were fabricated using these molecules as light-harvesting sensitizers. The overall efficiencies of the sensitized cells range from 5.48 to 6.15%. It was found that the introduction of the EDOT group in D3 bathochromically extended the absorption spectra, resulting in a leap in the photovoltaic performance in comparison to D2. Incorporation of a hydrophobic carbazole-containing segment at D2 relative with D1 retarded the electron transfer from TiO2 to the oxidized dye or electrolyte, leading to an increase of electron lifetime.

Fluorine–thiophene-substituted organic dyes for dye sensitized solar cells

Novel triphenylamine (TPA)-based organic dyes were synthesized and assessed for their performance in dye-sensitized solar cells (DSSCs). In the dyes considered the TPA group and the cyanoacetic acid have the role of electron-donor and -acceptor, respectively, whereas a thienyl–fluoro-phenyl-substituted was introduced as π-linker to improve the dye performance in DSSCs. Experimental characterizations empasize that the presence of electron withdrawing substituents in the linker close to the electron-acceptor moiety leads to a more efficient intramolecular photoinduced charge transfer. In fact, photovoltaic experiments reveal that the DSSCs based on the thienyl–o-fluoro-phenyl substituted dyes yield a better solar-energy-to-electricity conversion efficiency.

Inside the alkalinity engine: the role of electron donors in the organomineralization potential of sulfate‐reducing bacteria

Mineral precipitation in microbial mats may have been the key to their preservation as fossil stromatolites, potentially documenting evidence of the earliest life on Earth. Two factors that contribute to carbonate mineral precipitation are the saturation index (SI) and the presence of nucleation sites. Both of these can be influenced by micro-organisms, which can either alter SI through their metabolisms, or produce and consume organic substances such as extracellular polymeric substances (EPS) that can affect nucleation. It is the balance of individual metabolisms within the mat community that determines the pH and the dissolved inorganic carbon concentration, thereby potentially increasing the alkalinity and consequently the SI. Sulfate-reducing bacteria (SRB) are an important component of this 'alkalinity engine.' The activity of SRB often peaks in layers where CaCO(3) precipitates, and mineral precipitation has been demonstrated in SRB cultures; however, the effect of their metabolism on the alkalinity engine and actual contribution to mineral precipitation is the subject of controversy. Here, we show through culture experiments, theoretical calculations, and geochemical modeling studies that the pH, alkalinity, and organomineralization potential will vary depending on the type of electron donor. Specifically, hydrogen and formate can increase the pH, but electron donors like lactate and ethanol, and to a lesser extent glycolate, decrease the pH. The implication of this for the lithification of mats is that the combination of processes supplying electron donors and the utilization of these compounds by SRB may be critical to promoting mineral precipitation.

Nanoparticles induced by ultraviolet rays support electrons for enzymatic reaction

BACKGROUND: The NAD(P)H cofactor, which is the reduced form of nicotinamide adenine dinucleotide phosphate, plays the important role of electron donor in enzymatic metabolism. The primary drawback of metabolism reactions involving enzymes is the dependence on this highly expensive cofactor. RESULTS: Electron formation was effectively triggered by inducing Qdots with (UV) irradiation at 365 nm. The analytical potential of the Qdots-based electron-transfer system was demonstrated by examining two different types of cofactors, i.e. chemical (NADPH) and nanoparticle (Qdots). The Qdots-based method gave promising results in comparison with the NADPH-dependent system. A Qdots-based electron supply to a CYP2B4 and 7-pentoxyresorufin incubation mixture produced a resorufin metabolite. The kinetic rates of the cytochrome P450 reactions induced by photoactivated Qdots were determined CONCLUSIONS: The influence of electron formation from ultraviolet (UV)-induced quantum dots (Qdots) on the cytochrome P450 (CYP2B4) reaction was elucidated. The process comprised UV-induced electron formation by photoactivated Qdots and subsequent enzyme reactions mediated by the resultant electron supply. Copyright © 2012 Society of Chemical Industry

Organic Dyes Incorporating Bis-hexapropyltruxeneamino Moiety for Efficient Dye-Sensitized Solar Cells

We report here on the synthesis and photophysical/electrochemical properties of three functional triarylamine organic dyes (MXD5−7) as well as their application in dye-sensitized nanocrystalline TiO2 solar cells (DSSCs). For the designed dyes, the nonplanar structures of bis-hexapropyltruxeneamino take the role of electron donor. The introduction of bis-hexapropyltruxeneamino units brought about superior performance over the simple triphenylamine dye, in terms of light-capturing abilities and suppressing dye aggregation. Among three dyes, the DSSCs based on the dye MXD7 showed the best photovoltaic performance: a short-circuit photocurrent density (JSC) of 11.8 mA cm−2, an open-circuit photovoltage (VOC) of 772 mV, and a fill factor (ff) of 0.68, corresponding to an overall conversion efficiency of 6.18% under 100 mW cm−2 irradiation. These dyes exhibited high VOC values, possible origin for which was investigated regarding the TiO2 surface blocking, conduction band movement, and electrolyte-dye interaction.

Microstructure control of magnesium dichloride crystallites by electron donors: The effect of methanol

The ability to control the microstructure of magnesium dichloride (MgCl2) crystallites by electron donors was demonstrated by quantum chemical calculations, using methanol as a model donor. Investigation of sets of differently shaped MgCl2 crystallites showed the dominance of the five-fold coordinated (100) crystal surface over the four-fold coordinated (110) surface to emerge as a factor increasing crystallite stability. To study the role of electron donors in controlling MgCl2 crystallite shape, crystallites were saturated with methanol. The stability order of the crystallites was significantly affected by donor adsorption. Reverse to the case of pure MgCl2, crystallites with the highest (110) to (100) surface site ratio became the most stable after donor adsorption. This indicates control of the shape of MgCl2 crystallites to be attainable by appropriate choice of electron donor, a result utilizable in heterogeneous Ziegler–Natta olefin polymerization catalysis.

Nonflowering plants possess a unique folate-dependent phenylalanine hydroxylase that is localized in chloroplasts.

Tetrahydropterin-dependent aromatic amino acid hydroxylases (AAHs) are known from animals and microbes but not plants. A survey of genomes and ESTs revealed AAH-like sequences in gymnosperms, mosses, and algae. Analysis of full-length AAH cDNAs from Pinus taeda, Physcomitrella patens, and Chlamydomonas reinhardtii indicated that the encoded proteins form a distinct clade within the AAH family. These proteins were shown to have Phe hydroxylase activity by functional complementation of an Escherichia coli Tyr auxotroph and by enzyme assays. The P. taeda and P. patens AAHs were specific for Phe, required iron, showed Michaelian kinetics, and were active as monomers. Uniquely, they preferred 10-formyltetrahydrofolate to any physiological tetrahydropterin as cofactor and, consistent with preferring a folate cofactor, retained activity in complementation tests with tetrahydropterin-depleted E. coli host strains. Targeting assays in Arabidopsis thaliana mesophyll protoplasts using green fluorescent protein fusions, and import assays with purified Pisum sativum chloroplasts, indicated chloroplastic localization. Targeting assays further indicated that pterin-4a-carbinolamine dehydratase, which regenerates the AAH cofactor, is also chloroplastic. Ablating the single AAH gene in P. patens caused accumulation of Phe and caffeic acid esters. These data show that nonflowering plants have functional plastidial AAHs, establish an unprecedented electron donor role for a folate, and uncover a novel link between folate and aromatic metabolism.

The role of electron donors on lateral surfaces of MgCl 2-supported Ziegler–Natta catalysts: Observation by AFM and SEM

An active model for a Ziegler–Natta propylene polymerization catalyst has been prepared by spin-coating of a MgCl 2/diether donor solution in ethanol on a flat silicon wafer, followed by crystal growth by Ostwald ripening to give well-defined MgCl 2⋅donor⋅ nEtOH crystallites. The growth of the crystallites on the flat wafer indicates the formation of only 120° edge angles in the presence of the diether donor, suggesting the preference for the formation of one particular crystallite face for the MgCl 2. In contrast, the presence of diisobutyl phthalate or ethyl benzoate leads to the formation of both 120° and 90° edge angles, indicating the formation of more than one face for the MgCl 2. Subsequent treatment with TiCl 4 generates the catalyst and in propylene polymerization polymer forms on the lateral face of each crystallite. This work represents the first visualization of the effect of an internal donor in controlling the crystallite faces of magnesium chloride formed during a Ziegler–Natta catalyst preparation.

Starburst Triarylamine Based Dyes for Efficient Dye-Sensitized Solar Cells

We report here on the synthesis and photophysical/electrochemical properties of a series of novel starburst triarylamine-based organic dyes (S1, S2, S3, and S4) as well as their application in dye-sensitized nanocrystalline TiO2 solar cells (DSSCs). For the four designed dyes, the starburst triarylamine group and the cyanoacetic acid take the role of electron donor and electron acceptor, respectively. It was found that the introduction of starburst triarylamine group to form the D-D-pi-A configuration brought about superior performance over the simple D-pi-A configuration, in terms of bathochromically extended absorption spectra, enhanced molar extinction coefficients and better thermo-stability. Moreover, the HOMO and LUMO energy levels tuning can be conveniently accomplished by alternating the donor moiety, which was confirmed by electrochemical measurements and theoretical calculations. The DSSCs based on the dye S4 showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 85%, a short-circuit photocurrent density (J(sc)) of 13.8 mA cm(-2), an open-circuit photovoltage (V(oc)) of 0.63 V, and a fill factor (ff) of 0.69, corresponding to an overall conversion efficiency of 6.02% under 100 mW cm(-2) irradiation. This work suggests that the dyes based on starburst triphenylamine donor are promising candidates for improvement of the performance of the DSSCs.

Role of Electron Donor in Polymer Catalyst Synthesis: An XPS Study

X-ray photoelectron spectroscopy (XPS) has been applied to the study pertaining to preparation and characterization of catalysts used in propylene polymerization. The analysis has indicated support/donor interaction in active support (adduct) and active support/TiCl4 interaction during catalyst preparation process. A systematic study has been made to identify suitable adduct from a set of three adducts for catalyst synthesis. Precise binding energy of Titanium species on catalyst surface has been measured and its dispersion on support has been evaluated to correlate catalyst performance with the surface spectroscopic parameters.

AeMg5In3 (Ae = Ba, Sr): New Intermetallic Compounds with Well-Differentiated Roles for the Normal Cation Types

The isostructural phases BaMg4.787(3)In3.213 and SrMg4.837(2)In3.163 were synthesized via high-temperature reactions of the elements in welded Ta tubes. The orthorhombic crystal structure established for these by single-crystal X-ray diffraction means (space group Pnma, Z = 4) features a 3D Mg-In network formed from condensed 21-vertex polyhedra that are centered by Ba (Sr), viz., Ae@Mg5M7In9 (M = Mg/In). Three of eight independent network sites are co-occupied by >90% Mg and <10% In(M). The network structure is the inverse of that found in the isopointal Ca(CaIn4)Au3, as clearly delineated by site charge estimates for the equivalent In3 versus Au3 positions. Tight-binding LMTO and extended Hückel calculations on the ordered AeMg5In3 support the differentiation of Mg and Ae in the structure, with substantial participation of Mg in dominant Mg-In bonding, but mainly an electron donor role for Ae. The Fermi energies lie close to pseudo gaps but with substantial DOS remaining, consistent with their measured metallic properties. An unmixed ideal AeMg5In3 would be isostructural with YCo5P3, with comparable polyhedra, but the small P in the latter lacks an effective interbridging role.

Effect of electron-acceptor strength of zeolite on the luminescence decay rate of Ru(bpy)32+ incorporated within zeolites

We carried out time-resolved luminescence and transient absorption studies of tris(2,2'-bipyridine)ruthenium(ii) complex, Ru(bpy)3(2+) assembled in the supercages of zeolites X and Y exchanged with various alkali metal cations. The average lifetime of the luminescence decay, a measure of the photoinduced electron transfer (PET) rate, of Ru(bpy)3(2+)* was found to decrease with increasing the electron-acceptor strength of the host which is represented by the Sanderson's electronegativity scale. This result strongly suggests that the zeolite host plays the role of electron acceptor for Ru(bpy)3(2+)*. However, we could not detect Ru(bpy)3(3+) in the transient absorption spectra, most likely due to very low absorption coefficient of Ru(bpy)3(3+) and to the low efficiency of net PET. For the above observation to be made, it is essential to employ the dehydrated zeolite hosts to allow direct interaction between the guest Ru(ii) complex and the host framework. The present study demonstrates the active role of the zeolite hosts during the PET of incorporated Ru(bpy)3(2+) under the carefully controlled experimental conditions. This report demonstrates the fact that the zeolite hosts can serve as electron acceptors although in the past zeolites were shown to play the role of electron donors.