Hydrothermally obtained α-MnO2 nanowire characterizations confirm the tetragonal crystalline structure that is several micrometers long and 20–30 nm in diameter with narrow distributions in their dimensions. The absorption calculated from diffuse reflectance of α-MnO2 occurred in the visible region ranging from 400 to 550 nm. The calculated band gap with Quantum Espresso using HSE approximation is ~2.4 eV for the ferromagnetic case, with a slightly larger gap of 2.7 eV for the antiferromagnetic case, which is blue-shifted as compared to the experimental. The current work also illustrates the transformations that occur in the material under heat treatment during TGA analysis, with the underlying mechanism. Electrochemical studies on graphite supports modified with α-MnO2 compositions revealed the modified electrode with the highest electric double-layer capacitance of 3.444 mF cm−2. The degradation rate of an organic dye—rhodamine B (RhB)—over the compound in an acidic medium was used to examine the catalytic and photocatalytic activities of α-MnO2. The peak shape changes in the time-dependent visible spectra of RhB during the photocatalytic reaction were more complex and progressive. In two hours, RhB degradation reached 97% under sun irradiation and 74% in the dark.
In the present work, the potential of wastewater procured from a local treatment plant situated in Hunedoara in order to produce biogas was assessed in anaerobic co-digestion process. Finding appropriate combinations of feedstocks involved in the process represents a key factor in obtaining high biogas amounts and also high quality of biogas. Therefore, a case study was carried out in a lab-scale installation for biogas production using a suspension consisting of wastewater, animal (cow and chicken) slurry and degraded corn. The wastewater and animal slurry were selected as the main feedstock, providing for the microbial community required in the anaerobic digestion, in a volume ratio of 3:1 animal slurry to wastewater. Moreover, the feedstocks were subjected to several characterization methods: determination of total content of carbon, hydrogen and nitrogen and the content of volatile matter using European Standards. The process was performed in thermophilic conditions and controlled mixing of the suspension for a period of 24 days. The performances were appreciated by monitoring the amount of the produced biogas and the main gaseous components of the biogas: CH4, CO2 and H2S.
The effect of germanium trapezoidal profile shape on the direct current (DC) current gain (βF), cut-off frequency (fT) and maximum oscillation frequency (fMAX) of silicon-germanium (SiGe) hetero-junction bipolar transistors (HBTs) has been investigated. The energy balance (EB), hydrodynamic (HD) and drift-diffusion (DD) physical transport models in SILVACO technology computer aided design (T-CAD) simulator were used. It was found that the current gain values using energy balance model are higher than hydrodynamic and much higher than those corresponding to drift-diffusion. Moreover, decreasing the germanium gradient slope towards the collector side of the base enhances the maximum oscillation frequencies using HD and EB models whilst, they remain stable for DD model.
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