Fate Of Electrons Research Articles

Gamma rays from nebulae around recurrent novae

Novae were discovered to emit transient γ rays during the period of several days to a few weeks after initial explosion, indicating presence of acceleration processes of particles in their expanding shells. In the case of recurrent novae, electrons can be in principle accelerated in the nova shells for the whole recurrence period of nova producing delayed γ ray emission as considered in Bednarek (2022). Here we extend the ideas presented in this article by considering the fate of electrons which diffuse out of the shells of novae supplying fresh relativistic electrons to the recurrent nova super-remnants during the whole active period of nova (≥104 yrs). We develop a model for the acceleration of electrons and their escape from the nova shells. The electrons within the recurrent nova super-remnants produce γ rays in the comptonization process of the radiation from the red giant companion and the Cosmic Microwave Background Radiation. As an example, the case of a symbiotic nova RS Oph (with the recurrence period estimated on ∼10-50 yrs) is considered in more detail. Predicted γ-ray emission from the nova super-remnant around RS Oph is discussed in the context of its observability by satellite experiments (i.e. Fermi-LAT) as well as current and future Cherenkov telescopes.

Metabolic Performance and Fate of Electrons during Nitrate-Reducing Fe(II) Oxidation by the Autotrophic Enrichment Culture KS Grown at Different Initial Fe/N Ratios.

Autotrophic nitrate-reducing Fe(II)-oxidizing (NRFeOx) microorganisms fix CO2 and oxidize Fe(II) coupled to denitrification, influencing carbon, iron, and nitrogen cycles in pH-neutral, anoxic environments. However, the distribution of electrons from Fe(II) oxidation to either biomass production (CO2 fixation) or energy generation (nitrate reduction) in autotrophic NRFeOx microorganisms has not been quantified. We therefore cultivated the autotrophic NRFeOx culture KS at different initial Fe/N ratios, followed geochemical parameters, identified minerals, analyzed N isotopes, and applied numerical modeling. We found that at all initial Fe/N ratios, the ratios of Fe(II)oxidized to nitratereduced were slightly higher (5.11 to 5.94 at Fe/N ratios of 10:1 and 10:0.5) or lower (4.27 to 4.59 at Fe/N ratios of 10:4, 10:2, 5:2, and 5:1) than the theoretical ratio for 100% Fe(II) oxidation being coupled to nitrate reduction (5:1). The main N denitrification product was N2O (71.88 to 96.29% at Fe/15N ratios of 10:4 and 5:1; 43.13 to 66.26% at an Fe/15N ratio of 10:1), implying that denitrification during NRFeOx was incomplete in culture KS. Based on the reaction model, on average 12% of electrons from Fe(II) oxidation were used for CO2 fixation while 88% of electrons were used for reduction of NO3- to N2O at Fe/N ratios of 10:4, 10:2, 5:2, and 5:1. With 10 mM Fe(II) (and 4, 2, 1, or 0.5 mM nitrate), most cells were closely associated with and partially encrusted by the Fe(III) (oxyhydr)oxide minerals, whereas at 5 mM Fe(II), most cells were free of cell surface mineral precipitates. The genus Gallionella (>80%) dominated culture KS regardless of the initial Fe/N ratios. Our results showed that Fe/N ratios play a key role in regulating N2O emissions, for distributing electrons between nitrate reduction and CO2 fixation, and for the degree of cell-mineral interactions in the autotrophic NRFeOx culture KS. IMPORTANCE Autotrophic NRFeOx microorganisms that oxidize Fe(II), reduce nitrate, and produce biomass play a key role in carbon, iron, and nitrogen cycles in pH-neutral, anoxic environments. Electrons from Fe(II) oxidation are used for the reduction of both carbon dioxide and nitrate. However, the question is how many electrons go into biomass production versus energy generation during autotrophic growth. Here, we demonstrated that in the autotrophic NRFeOx culture KS cultivated at Fe/N ratios of 10:4, 10:2, 5:2, and 5:1, ca. 12% of electrons went into biomass formation, while 88% of electrons were used for reduction of NO3- to N2O. Isotope analysis also showed that denitrification during NRFeOx was incomplete in culture KS and the main N denitrification product was N2O. Therefore, most electrons stemming from Fe(II) oxidation seemed to be used for N2O formation in culture KS. This is environmentally important for the greenhouse gas budget.

Disclosing the synergistic mechanisms of azo dye degradation and bioelectricity generation in a microbial fuel cell

Microbial fuel cell (MFC) with cost-effective aerobic biocathode was developed for further treatment of azo dye intermediates into less harmful products in a single system. The fate of electrons in MFC for azo dye decolourisation and bioelectricity generation were explored via a series of studies including the effects of azo dye concentration, organic loading, external resistance and hydraulic retention time. The addition of low concentration of New Coccine (NC) (25 mg/L) improved 17% of the power density to 20.13 ± 0.37 W/m3. The internal resistance decreased from 50 to 32 Ω. As dye concentration increases, the decolourisation efficiency maintained over 90% (200 mg/L NC), whereas, power density dropped to 10.83 ± 1.21 W/m3. The increase of NC to higher concentration hindered the bioelectricity production, as both anode and azo dye molecules were competing for electrons. More electrons were utilized for decolourisation than bioelectricity generation as decolourisation efficiency improved, but power density dropped with the increase of organic loading. Lower external resistance allowed greater electron transfer, thus it enhanced the overall power performance. Higher power density (15.12 ± 1.12 W/m3) and normalized energy recovery (76 Wh/kg COD) were achieved at the lowest external resistance of 100 Ω. Both decolourisation and power performances were improved with 2 days HRT. The intermediate products from decolourisation and mineralization processes were identified, and the degradation pathway of NC has been proposed based on the UV–Vis, HPLC and GC–MS results.

A photo-(electro)-catalytic system illustrating the effect of lithium ions on titania surface energetics and charge transfer

We describe the effect of Li+ on photoinduced charge transfer at TiO2 in acetonitrile solutions at open circuit (photocatalytic conditions) or under potential control. Using 2-propanol and 4-nitrobenzaldehyde as probe scavengers of holes and electrons, respectively, we aim to demonstrate the importance of tuning the chemical role of electrons and holes through control of surface and interface properties.Adsorption of Li+ in the dark causes a positive shift of the TiO2 bands as revealed by cyclic voltammetry and Mott–Schottky analysis. Likewise, there is clear evidence that dark adsorption of 2-propanol brings about a redistribution of the bandgap states.Electrochemical measurements show that, upon illumination, the charge of photo-accumulated electrons is compensated by Li+ that can undergo insertion at the surface/subsurface region, which prevents a negative shift of the bands and has important consequences on the overall photo(electro) catalytic processes. Concerning the fate of electrons, 4-nitrobenzaldehyde is selectively reduced to 4-aminobenzaldehyde probing that electron transfer specifically involves the NO2 moiety while reduction of the aldehyde functional group is observed only at much more negative potentials than Efb and is cation insensitive.Regarding the fate of photogenerated holes, the effect of Li+ is evident in the change of the mechanism of 2-propanol oxidation, as revealed by both electrochemical and EPR experiments. Adsorption as alcoholate occurs in the dark but it is strongly inhibited on pre-illuminated TiO2 in the presence of Li+.

Determination of the electron lifetime in nanocrystalline dye solar cells by open-circuit voltage decay measurements.

Fate of electrons: Kinetic measurements of open-circuit voltage decay in nanocrystalline TiO2 dye-sensitized solar cells reveal major features of the electron lifetime and recombination mechanisms in these solar cells. The lifetime dependence on the photovoltage is exponential in broad terms (see picture), ranging from three decades to 20 ms to 20 s, when the photovoltage decreases by about 0.6 V.