Effective Electron Donor Research Articles

Diferulate: A highly effective electron donor

The screening of new molecules with high electron-donor properties is important for the design of new bioactive and technologically applicable substances. Here we propose diferulate (1), (Z)-2-(5-((E)-2-carboxyvinyl)-2-hydroxy-3-methoxyphenyl)-3-(4-hydroxy-3-methoxyphenyl)acrylic acid, to be an efficient electron donor which undergoes anodic conversion in aqueous media (pH 7) at around +0.15 V, vs. Ag|AgCl|3 M KCl. The low potential of oxidation of 1 indicates its high electron-donor capacity, which was documented by DPPH and ABTS radical scavenging and anti-lipoperoxidation activity analyses and also supported by in silico approaches. The results showed that compound 1, unlike ferulic acid 2 and the P1 benzofuranone synthetic precursor of 1, exhibits unique antiradical and antioxidant properties compared to trolox 3, which served as the positive control. No cytotoxic effects were observed for 1 in the 1–50 μM range. We conclude that the proposed structure 1 can be used for the further design of molecules whose biological (chemoprotective) activity is associated with high electron-donor properties.

Hydrogen generation by irradiation of commercial CuO + TiO2 mixtures at solar pilot plant scale and in presence of organic electron donors

A CuO + TiO2 mixture, based on two commercial and well characterized CuO and TiO2 photocatalyst, has been used to produce hydrogen by solar light irradiation and in presence of different organic compounds (methanol, glycerol, formic acid, and the components of a wastewater coming from the biodiesel industry) acting as sacrificial electron donors. The experiments have been conducted at Plataforma Solar de Almería (PSA, south of Spain) with a pilot plant scale reactor using a CPC (compound parabolic collector) configuration. The tested system has shown similar hydrogen generation capacity and energy efficiency than more expensive ones based on the use of noble metal/photocatalyst composites. Formic acid has shown to be the most effective electron donor, although very close amounts of hydrogen are also produced with glycerol, and this is found as a waste compound released in large quantities at the biodiesel industry wastewaters. As seen in previous similar studies, the increase of solution conductivity hampers the hydrogen generation, and a slightly basic solution pH (pH≈9) gives the best reaction conditions. Finally, the composite can be recovered and successfully reused giving the ensuing and sustained generation of H2 while removing more than 50% of TOC.

Accelerated microbial reductive dechlorination of 2,4,6-trichlorophenol by weak electrical stimulation

Microbial reductive dechlorination of chlorinated aromatics frequently suffers from the long dechlorination period and the generation of toxic metabolites. Biocathode bioelectrochemical systems were verified to be effective in the degradation of various refractory pollutants. However, the electrochemical and microbial related working mechanisms for bio-dechlorination by electro-stimulation remain poorly understood. In this study, we reported the significantly improved 2,4,6-trichlorophenol dechlorination activity through the weak electro-stimulation (cathode potential of −0.36 V vs. SHE), as evidenced by the 3.1 times higher dechlorination rate and the complete dechlorination ability with phenol as the end dechlorination product. The high reductive dechlorination rate (20.8 μM/d) could be maintained by utilizing electrode as an effective electron donor (coulombic efficiency of 82.3 ± 4.8%). Cyclic voltammetry analysis of the cathodic biofilm gave the direct evidences of the cathodic respiration with the improved and positive-shifted reduction peaks of 2,4,6-TCP, 2,4-DCP and 4-CP. The optimal 2,4,6-TCP reductive dechlorination rate (24.2 μM/d) was obtained when a small amount of lactate (2 mM) was added, and the generation of H2 and CH4 were accompanied due to the biological fermentation and methanogenesis. The electrical stimulation significantly altered the cathodic biofilm structure and composition with some potential dechlorinators (like Acetobacterium) predominated. The microbial interactions in the ecological network of cathodic biofilm were more simplified than the planktonic community. However, some potential dechlorinators (Acetobacterium, Desulfovibrio, etc.) shared more positive interactions. The co-existence and possible cooperative relationships between potential dechlorinators and fermenters (Sedimentibacter, etc.) were revealed. Meanwhile, the competitive interrelations between potential dechlorinators and methanogens (Methanomassiliicoccus) were found. In the network of plankton, the fermenters and methanogens possessed the more positive interrelations. Electro-stimulation at the cathodic potential of −0.36 V selectively enhanced the dechlorination function, while it showed little influence on either fermentation or methanogenesis process. The study gave suggestions for the enhanced bioremediation of chlorinated aromatics, in views of the electro-stimulation capacity, efficiency and microbial interrelations related microbial mechanism.

Metal-free organic dyes with di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole as a donor for efficient dye-sensitized solar cells: Effect of mono- and bi-anchors on photovoltaic performance

Four novel metal-free organic dyes WL1a-b and WL2a-b containing di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole (DBTP) as electron donor were synthesized and applied for dye-sensitized solar cells (DSSCs), where DBTP was firstly employed as a donor in the organic dyes. It has been demonstrated that the dyes WL with DBTP as a donor show better photovoltaic performance than the reference dye PTZ with phenothiazine as a donor. In comparison with WL1a-b with one cyanoacrylic acid as mono-anchor, WL2a-b with two cyanoacrylic acids as bi-anchors show a broader light absorption on the TiO2 film and higher molar extinction coefficients in solution, resulting in higher power conversion efficiency. Under standard global AM 1.5G solar light condition, WL2a sensitized solar cell obtained a high power conversion efficiency of 8%. The results indicate that the DBTP unit can be applied as an effective electron donor and DBTP-based organic dye is a promising candidate for efficient DSSCs.

The bis-dimethylfluoreneaniline organic dye sensitizers for solar cells: A theoretical study and design

Development of novel dye sensitizers with suitable optoelectronic properties is effective to improve the power conversion efficiency of dye-sensitized solar cells (DSSCs). Considering the effectiveness of conjugate bridges in modification of optoelectronic properties, based on the dye sensitizers C201, C203, C204 and C205, five kinds of organic dye sensitizers are designed with different thiophene-based moieties and the functionalized graphene flakes (GFs) as conjugate bridges. The performances of these dye sensitizers are analyzed in terms of the calculated geometries, electronic structures and excitation properties. The transition configurations and molecular orbitals of dye sensitizers suggest that bis-dimethylfluoreneaniline is effective electron donor, and the transitions of optical absorption in visible region are charge transfer excitations. The conjugate lengths, energy level alignments, light harvesting capabilities, excitation character, and transition properties, as well as the free energy variations for electron injection and dye regeneration support that the designed dye sensitizers are effective to be applied in DSSCs. Particularly, introducing the functionalized GF into conjugate bridges significantly elongate conjugate length, reduce orbital energy gap, lead to denser distribution of orbital energy, generate red-shift of absorption spectra, enhance light harvesting capability, increase absorption bands and coefficients. Therefore, introducing the functionalized GF into conjugate bridges is effective, and the designed panchromatic dye sensitizer C20x-GF-BTD must be better than other designed dye sensitizers for DSSCs.

Degradation of diclofenac using palladized anaerobic granular sludge: Effects of electron donor, reaction medium and deactivation factors.

Biogenic nanopalladium (Bio-Pd) was formed by Anaerobic Granular Sludge (AGS). The Bio-Pd hosted in AGS (Pd-AGS) was used to degrade a pharmaceutical compound diclofenac (DCF) under the conditions of various electron donors, Pd loadings and reaction media. Results showed that hydrogen was the most effective electron donor for the Pd-AGS, followed by formate, glucose and acetate. The Pd-AGS was able to produce effective hydrogen/electron donors from organic compounds via microbial metabolism to initiate Pd activity. Over 96% of DCF (initial concentration of 20 mg L-1) was removed using the Pd-AGS within 90 min, and a maximum specific activity Kobs of 1.53 L g-1 min-1 was obtained at 3.0 wt% Pd loading, in the presence of hydrogen. The Pd-AGS exhibited a relatively high activity in the medium of PBS or Na2SO4 (25 mM) at pH = 7-7.5, but lost activity in the medium of Na2CO3 (40 mM) or NaOH (40 mM). The Pd-AGS was more resistant to deactivation by chloride or sulphide comparing to free Pd nanoparticles. The Pd-AGS could reduce DCF and nitrate simultaneously with high nitrogen selectivity. The Pd-AGS, as a novel form of Pd catalyst with AGS, shows promise for applications in reducing chlorinated organic compounds in contaminated water.

2D Electron Gas at the Interface of Atomic‐Layer‐Deposited Al2O3/TiO2 on SrTiO3 Single Crystal Substrate

AbstractThe presence of 2D electron gas (2DEG) at the interface between an amorphous Al2O3 (a‐AO) thin film and an anatase TiO2 (TO) thin film is demonstrated. The a‐AO and TO thin films are prepared via atomic layer deposition on a SrTiO3 (STO) single crystal substrate. The reduction of the TO surface during the a‐AO deposition produces oxygen vacancies, which are effective electron donors. The systematic analysis of the physical properties of the TO layer reveals that the crystallinity of the TO layer affects the conductivity, carrier concentration and the mobility of the 2DEG, and also the critical a‐AO thickness, which is the minimum thickness for exhibiting the apparent conductivity. The 2DEG between the a‐AO and the sufficiently thick TO layer exhibits an almost two‐orders‐of‐magnitude‐higher carrier concentration (≈1014 cm‐2) than the previously reported 2DEG at a‐AO/STO, while the mobility (≈10° cm2 V‐1 s‐1) is relatively low. Also, angle‐resolved X‐ray photoelectron spectroscopy elucidates the spatial distribution and atomic ratio of the reduced Ti ions. Due to the increasing fraction of the anatase phase in the TO layer, the oxygen vacancies are prone to ionize, and the carriers are better confined to the interface, making them more 2DEG‐like.

PH and a mixed carbon-substrate spectrum influence FocA- and FocB-dependent, formate-driven H2 production in Escherichia coli.

Escherichia coli encodes two formate channels, FocA and FocB, that either export formate or import it for further disproportionation by the formate hydrogenlyase (FHL) complex to H2 and CO2. We show that FocA/B appear to change their substrate-translocation direction depending on pH and electron donor. When cells were grown on glucose and glycerol at pH 7.5, formate accumulated in focB or focA-focB mutants when glucose or formate was used as electron donor because H2 production increased ∼2- and ∼1.5-fold, respectively. Moreover, addition of external formate to the growth medium increased H2 production in a focA-focB mutant. This indicates that in the wild type, formate is preferentially exported at pH 7.5 and that another FocA/B-independent uptake system exists. At pH 6.5 and 5.5, the formate channel mutants showed reduced H2 production, suggesting that formate is usually imported by them to produce H2 at acidic pH. Addition of formate to the growth medium increased H2 production at these pHs. Notably, glycerol failed to act as an effective electron donor for formate production. Taken together, our results suggest that regulation of formate translocation direction by FocA/FocB channels is important for maintaining internal pH and proton motive force by modulating H2 production.

Electrogenic reactions in Mn-depleted photosystem II core particles in the presence of synthetic binuclear Mn complexes

An electrometrical technique was used to investigate electron transfer between synthetic binuclear manganese (Mn) complexes, designated M − 2 and M − 3, and the redox-active neutral tyrosine radical (YZ•) in proteoliposomes containing Mn-depleted photosystem II (PS II) core particles in response to single laser flashes. In the absence of Mn-containing compounds, the observed flash-induced membrane potential (ΔΨ) decay was mainly due to charge recombination between the reduced primary quinone acceptor QA− and the oxidized YZ•. More significant slowing down of the ΔΨ decay in the presence of lower concentrations of M − 2 and M − 3 associated with electron donation from Mn in the Mn-binding site to YZ• indicates that these synthetic compounds are more effective electron donors than MnCl2. The exponential fitting of the kinetics of additional electrogenic components of ΔΨ rise in the presence of Mn-containing compounds revealed the following relative amplitudes (A) and lifetimes (τ): for MnCl2 - A∼ 3.5, τ∼150 μs, for M − 2 - A∼5%, τ∼1.4 ms, and for M − 3 - A∼5.5%, τ∼150 μs. This suggests that the efficiency of the manganese complexes in electron donation depends on the chemical nature of ligands. The experiments with EDTA-treated samples indicated that the ligands for M − 2 and M − 3 are required for their tight binding with the PS II reaction center. The obtained results demonstrate the importance of understanding the molecular mechanism(s) of flash-induced electrogenic reduction of the tyrosine radical YZ• by synthetic Mn complexes capable of splitting water into oxygen and reducing equivalents.

Influence of Sb5+ as a Double Donor on Hematite (Fe3+) Photoanodes for Surface-Enhanced Photoelectrochemical Water Oxidation.

To exploit the full potential of hematite (α-Fe2O3) as an efficient photoanode for water oxidation, the redox processes occurring at the Fe2O3/electrolyte interface need to be studied in greater detail. Ex situ doping is an excellent technique to introduce dopants onto the photoanode surface and to modify the photoanode/electrolyte interface. In this context, we selected antimony (Sb5+) as the ex situ dopant because it is an effective electron donor and reduces recombination effects and concurrently utilize the possibility to tuning the surface charge and wettability. In the presence of Sb5+ states in Sb-doped Fe2O3 photoanodes, as confirmed by X-ray photoelectron spectroscopy, we observed a 10-fold increase in carrier concentration (1.1 × 1020 vs 1.3 × 1019 cm-3) and decreased photoanode/electrolyte charge transfer resistance (∼990 vs ∼3700 Ω). Furthermore, a broad range of surface characterization techniques such as Fourier-transform infrared spectroscopy, ζ-potential, and contact angle measurements reveal that changes in the surface hydroxyl groups following the ex situ doping also have an effect on the water splitting capability. Theoretical calculations suggest that Sb5+ can activate multiple Fe3+ ions simultaneously, in addition to increasing the surface charge and enhancing the electron/hole transport properties. To a greater extent, the Sb5+- surface-doped determines the interfacial properties of electrochemical charge transfer, leading to an efficient water oxidation mechanism.

Photocatalytic activity of nanostructured composites based on layered niobates and C3N4 in the hydrogen evolution reaction from electron donor solutions under visible light

Nanostructured composites based on layered niobates KNb3O8, K3Н3Nb10.8O30 and HNb3O8 as well as C3N4 were obtained. It was established that the rate of hydrogen evolution from electron donors water solutions under visible light using composites niobate/C3N4 as photocatalysts significantly exceeds the rate value for an individual C3N4. This phenomenon was explained by an effective separation of photogenerated charges between the components of the composite and thus a decrease of the electron-hole recombination. Transition from an individual C3N4 to the composites niobate/C3N4 allows significantly extend the list of an effective electron donor compounds for the photocatalytic hydrogen evolution process.

Optical and electronic structure description of metal-doped phthalocyanines.

Phthalocyanines represent a crucial class of organic compounds with high technological appeal. By doping the center of these systems with metals, one obtains the so-called metal-phthalocyanines, whose property of being an effective electron donor allows for potentially interesting uses in organic electronics. In this sense, investigating optical and electronic structure changes in the phthalocyanine profiles in the presence of different metals is of fundamental importance for evaluating the appropriateness of the resulting system as far as these uses are concerned. In the present work, we carry out this kind of effort for phthalocyanines doped with different metals, namely, copper, nickel, and magnesium. Density functional theory was applied to obtain the absorption spectra, and electronic and structural properties of the complexes. Our results suggest that depending on the dopant, a different level of change is achieved. Moreover, electrostatic potential energy mapping shows how the charge distribution can be affected by solar radiation. Our contribution is crucial in describing the best possible candidates for use in different organic photovoltaic applications. Graphical Abstract Representation of meta-phthalocyanine systems. All calculations of this work are based on varying metal position along z axis, considering the z-axis has its zero point matching with the center of phthalocyanine cavityconsidering.

Efficient photocatalytic carbon monoxide production from ammonia and carbon dioxide by the aid of artificial photosynthesis.

Ammonium bicarbonate (NH4HCO3) was generated by the absorption of carbon dioxide (CO2) into an aqueous solution of ammonia (NH3). NH4HCO3 was successfully used to achieve highly efficient photocatalytic conversion of CO2 to carbon monoxide (CO). NH3 and/or ammonium ions (NH4+) derived from NH4HCO3 in aqueous solution were decomposed into nitrogen (N2) and hydrogen (H2). Stoichiometric amounts of the N2 oxidation product and the CO and H2 reduction products were generated when the photocatalytic reaction was carried out in aqueous NH4HCO3 solution. NH3 and/or NH4+ functioned as electron donors in the photocatalytic conversion of CO2 to CO. A CO formation rate of 0.5 mmol h-1 was obtained using 500 mg of catalyst (approximately 7500 ppm) in ambient conditions (303 K, 101.3 kPa). Our results demonstrated that NH4HCO3 is a novel inorganic sacrificial reagent, which can be used to increase the efficiency of photocatalytic CO production to achieve one step CO2 capture, storage and conversion.

Black Phosphorus N-Type Field-Effect Transistor with Ultrahigh Electron Mobility via Aluminum Adatoms Doping.

High-performance black phosphorus n-type field-effect transistors are realized using Al adatoms as effective electron donors, which achieved a record high mobility of >1495 cm2 V-1 s-1 at 260 K. The electron mobility is corroborated to charged-impurity scattering at low temperature, whilst metallic-like conduction is observed at high gate bias with increased carrier density due to enhanced electron-phonon interactions at high temperature.

Growth characteristics and lipid content of indigenous freshwater algae grown in dairy cattle waste-water effluent

Effects of henna plant biomass (stem) packed in an up-flow anaerobic bio-filter (UAF) on an azo dye (AO7) removal were investigated. AO7 removal, sulfanilic acid (SA) formation, and pseudo first-order kinetic constants for these reactions (kAO7 and kSA) were higher in the henna-added UAF (R2) than in the control UAF without henna (R1). The maximum kAO7 in R1 and R2 were 0.0345 and 0.2024 cm−1, respectively, on day 18; the corresponding molar ratios of SA formation to AO7 removal were 0.582 and 0.990. Adsorption and endogenous bio-reduction were the main AO7 removal pathways in R1, while in R2 bio-reduction was the dominant. Organics in henna could be released and fermented to volatile fatty acids, acting as effective electron donors for AO7 reduction, which was accelerated by soluble and/or fixed lawsone. Afterwards, the removal process weakened over time, indicating the demand of electron donation and lawsone-releasing during the long-term operation of UAF.

Photobiological transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) using Rhodobacter sphaeroides

Pump-and-treat strategies for groundwater containing explosives may be necessary when the contaminated water approaches sensitive receptors. This project investigated bacterial photosynthesis as a strategy for ex situ treatment, using light as the primary energy source to facilitate RDX transformation. The objective was to characterize the ability of photosynthetic Rhodobacter sphaeroides (strain ATCC® 17023 ™) to transform the high-energy explosive RDX. R. sphaeroides transformed 30 μM RDX within 40 h under light conditions; RDX was not fully transformed in the dark (non-photosynthetic conditions), suggesting that photosynthetic electron transfer was the primary mechanism. Experiments with RDX demonstrated that succinate and malate were the most effective electron donors for photosynthesis, but glycerol was also utilized as a photosynthetic electron donor. RDX was transformed irrespective of the presence of carbon dioxide. The electron shuttling compound anthraquinone-2,6-disulfonate (AQDS) increased transformation kinetics in the absence of CO2, when the cells had excess NADPH that needed to be re-oxidized because there was limited CO2 for carbon fixation. When CO2 was added, the cells generated more biomass, and AQDS had no stimulatory effect. End products indicated that RDX carbon became CO2, biomass, and a soluble, uncharacterized aqueous metabolite, determined using 14C-labeled RDX. These data are the first to suggest that photobiological explosives transformation is possible and will provide a framework for which phototrophy can be used in environmental restoration of explosives contaminated water.

A competitive photoelectrochemical aptasensor for thrombin detection based on the use of TiO2 electrode and glucose oxidase label

Abstract A novel competitive photoelectrochemical aptasensor for thrombin (TB) detection is proposed using TiO2 electrode coupled with TB-Au nanoparticles (AuNPs)–glucose oxidase (GOx) labels. To construct the aptasensor, chitosan was coated on the TiO2 surface for the further immobilization of TB aptamer that was bridged by the use of glutaraldehyde. TB detection was then performed based upon the competitive interaction of TB and TB-AuNPs-GOx bioconjugate with TB aptamer on the electrode. GOx could catalyze the glucose to produce H2O2, which acts as an effective electron donor to deplete the photogenerated holes located at the valence band of excited TiO2, resulting in the enhanced photocurrent response. Under the optimal conditions, the as-prepared PEC aptasensor exhibits excellent analytical property for detection of TB in the range from 1.0 × 10− 12 mol L− 1 to 1.0 × 10− 8 mol L− 1 with a detection limit of 1.9 × 10− 13 mol L− 1. Moreover, the aptasensor was also successfully applied for the determination of TB in human plasma. The present strategy provides a promising method for the future development of PEC aptasensor for advanced biochemical analysis.

A combined FTIR and infrared emission spectroscopy investigation of layered double hydroxide as an effective electron donor

A novel method has been presented to characterize electron transfer in layered double hydroxides (LDHs) utilizing an investigation combing FTIR and infrared emission spectroscopy. At room temperature, electron could transfer to interlayer Fe3+ through monodentate ligand cyanide, and resulted in a reduction of 40% Fe3+ to Fe2+. When the environmental temperature increased from 25 to 300°C, reduction of Fe3+ and Ni2+ increased to 94% and 42%. Furthermore, electron also transferred to interlayer cation through multidentate ligand EDTA. As a result, LDHs has been proven to be an effective electron donor, and FTIR was a feasible tool in characterizing this property by monitoring the valence state of cations. It was also concluded that octahedral units with OH− groups in LDH layer functioned as electron donor centers. Driving force for electron transfer is attributed to the charge density difference between cation layer and probe anion. These results could help to explain the mechanism of various applications of LDHs in catalysis and photocatalysis.

Enhanced bio-reduction of hexavalent chromium by an anaerobic consortium using henna plant biomass as electron donor and redox mediator

The effects of henna (Lawsonia inermis) flower biomass on the enhanced bio-reduction of Cr(VI) were investigated in this study. The average Cr(VI) removal rate in the anaerobic system with the addition of henna flower powder achieved 2.04 mg L−1 h−1, which was much higher than the rates in the activated sludge control, autoclaved sludge control, and adsorption control. Under anaerobic conditions, the organic compounds in henna flower powder could be leached out from the solid phase to the mixed solution, and then fermented to volatile fatty acids and H2, acting as effective electron donors for the rapid bio-reduction of Cr(VI). The released and/or fixed lawsone not only shuttles electrons from the donor to the final acceptor of Cr(VI), but might also inversely improves the fermentation process of henna flower biomass.

Assessing microbial competition in a hydrogen-based membrane biofilm reactor (MBfR) using multidimensional modeling.

The membrane biofilm reactor (MBfR) is a novel technology that safely delivers hydrogen to the base of a denitrifying biofilm via gas-supplying membranes. While hydrogen is an effective electron donor for denitrifying bacteria (DNB), it also supports sulfate-reducing bacteria (SRB) and methanogens (MET), which consume hydrogen and create undesirable by-products. SRB and MET are only competitive for hydrogen when local nitrate concentrations are low, therefore SRB and MET primarily grow near the base of the biofilm. In an MBfR, hydrogen concentrations are greatest at the base of the biofilm, making SRB and MET more likely to proliferate in an MBfR system than a conventional biofilm reactor. Modeling results showed that because of this, control of the hydrogen concentration via the intramembrane pressure was a key tool for limiting SRB and MET development. Another means is biofilm management, which supported both sloughing and erosive detachment. For the conditions simulated, maintaining thinner biofilms promoted higher denitrification fluxes and limited the presence of SRB and MET. The 2-d modeling showed that periodic biofilm sloughing helped control slow-growing SRB and MET. Moreover, the rough (non-flat) membrane assembly in the 2-d model provided a special niche for SRB and MET that was not represented in the 1-d model. This study compared 1-d and 2-d biofilm model applicability for simulating competition in counter-diffusional biofilms. Although more computationally expensive, the 2-d model captured important mechanisms unseen in the 1-d model.