External Electron Research Articles

Nonlinear finite element analysis of electromechanical behaviors in a piezoelectric semiconductor beam

In this paper, a one-dimensional beam model with extensional, flexure and shearing deformations for a piezoelectric semiconductor fiber is established based on the first-order beam theory and nonlinear electric current constitutive relation. To solve such a nonlinear beam model under transverse and axial forces, a finite element method is proposed together with an iterative process. Throughout numerical case studies, effects of the external forces and initial electron concentration are investigated on electromechanical fields. It is shown that the applied forces have a great influence on the distribution of electron concentration, which can freely regulate the electron transport in piezoelectric semiconductors.

Unrevealing the role of metal oxide nanoparticles on biohydrogen production by Lactobacillus delbrueckii

The positive interaction between Clostridium sp. and lactic acid-producing bacteria (Lactobacillus sp) is commonly seen in various high-rate hydrogen production systems. However, the exact role of the hydrogen production ability of Lactobacillus sp in a dark fermentation production system is rarely studied. Lactobacillus delbrueckii was herein used for the first time, to the best of the author’s knowledge, to demonstrate biohydrogen production under anaerobic conditions. At first, the pH condition was optimized, followed by the addition of nanoparticles for enhanced biohydrogen production. Under optimized conditions of pH 6.5, substrate concentration 10 g/L, and 100 mg/L of NiO/Fe2O3, the maximum hydrogen yield (HY) of 1.94 mol/mol hexose was obtained, which is 18 % more than the control. The enhanced H2 production upon the addition of nanoparticles is supported via the external electron transfer (EET) mechanism, which regulates the metabolic pathway regulation with increased production of acetate and butyrate and reduced formation of lactate.

Microbial Interactions in Electroactive Biofilms for Environmental Engineering Applications: A Role for Nonexoelectrogens.

Microbial electrochemical systems have gained much attention over the past decade due to their potential for various environmental engineering applications ranging from energy production to wastewater treatment to bioproduction. At the heart of these systems lie exoelectrogens-microorganisms capable of exporting electrons generated during metabolism to external electron acceptors such as electrodes. The bacterial biofilm communities on these electrodes are dominated by exoelectrogens but are nonetheless extremely diverse. So far, within the field, the main focus has been on the electroactive bacteria. However, to broaden our understanding of these communities, it is crucial to clarify how the remaining inhabitants of electrode-respiring biofilms contribute to the overall function of the biofilm. Ultimately, such insights may enable improvement of microbial electrochemical systems by reshaping the community structure with naturally occurring beneficial strains.

Tailorable Tetrahelical Bundles as a Toolkit for Redox Studies.

Oxidoreductases have evolved over millions of years to perform a variety of metabolic tasks crucial for life. Understanding how these tasks are engineered relies on delivering external electron donors or acceptors to initiate electron transfer reactions. This is a challenge. Small-molecule redox reagents can act indiscriminately, poisoning the cell. Natural redox proteins are more selective, but finding the right partner can be difficult due to the limited number of redox potentials and difficulty tuning them. De novo proteins offer an alternative path. They are robust and can withstand mutations that allow for tailorable changes. They are also devoid of evolutionary artifacts and readily bind redox cofactors. However, no reliable set of engineering principles have been developed that allow for these proteins to be fine-tuned so their redox midpoint potential (Em) can form donor/acceptor pairs with any natural oxidoreductase. This work dissects protein-cofactor interactions that can be tuned to modulate redox potentials of acceptors and donors using a mutable de novo designed tetrahelical protein platform with iron tetrapyrrole cofactors as a test case. We show a series of engineered heme b-binding de novo proteins and quantify their resulting effect on Em. By focusing on the surface charge and buried charges, as well as cofactor placement, chemical modification, and ligation of cofactors, we are able to achieve a broad range of Em values spanning a range of 330 mV. We anticipate this work will guide the design of proteinaceous tools that can interface with natural oxidoreductases inside and outside the cell while shedding light on how natural proteins modulate Em values of bound cofactors.

Production of medium chain fatty acids through co-fermentation of food waste and sewage sludge without external electron donors

Effective biowaste treatment with renewable bioenergy production has become attractive. In this study, chain-elongation (CE) technology was applied to convert food waste (FW) and sewage sludge (SS) into high value-added medium chain fatty acids (MCFAs) by co-fermentation, which not only reduces environmental pollution but also recovers valuable resources. Five groups of batch co-fermentation experiments were performed using FW and SS at different ratios (FW/SS based on chemical oxygen demand, COD) without external electron donors (EDs) to investigate the effects of different FW/SS ratios on the production of MCFAs. The results showed that 100 % FW (FW/SS=1:0) achieved the highest n-caproate concentration (396.37 ± 35.98 mg COD/L), followed by 75 % FW (FW/SS=3:1) (384.42 ± 28.00 mg COD/L). Moreover, 75 % FW (FW/SS=3:1) had higher n-caproate specificity (11.22 ± 3.81 %) than 100 % FW (7.52 ± 0.68 %). Thus, a semi-continuous co-fermentation experiment at a FW/SS ratio of 3:1 was performed for 90 days to explore the feasibility of long-term MCFAs production without external EDs. The results showed that the maximum MCFAs concentration, specificity, and production rate were 10441.31 mg COD/L, 58.20 %, and 250.59 mg COD/L·d−1, respectively. Among the three MCFAs, n-caproate was the most abundant, accounting for 60.28 %. Microbial community analysis revealed that four lactate-producing bacteria (Bifidobacterium, Olsenella, Atopobium, and Proteiniphilum) co-occurred with Caproiciproducens, developing a CE system driven by lactate as the ED. This study provides new insights into the recovery of resources from FW and SS.

AAPM WGTG51 Report 374: Guidance for TG-51 reference dosimetry.

Practical guidelines that are not explicit in the TG-51 protocol and its Addendum for photon beam dosimetry are presented for the implementation of the TG-51 protocol for reference dosimetry of external high-energy photon and electron beams. These guidelines pertain to:(i)measurement of depth-ionization curves required to obtain beam quality specifiers for the selection of beam quality conversion factors, (ii)considerations for the dosimetry system and specifications of a reference-class ionization chamber, (iii)commissioning a dosimetry system and frequency of measurements, (iv)positioning/aligning the water tank and ionization chamber for depth ionization and reference dose measurements, (v)requirements for ancillary equipment needed to measure charge (triaxial cables and electrometers) and to correct for environmental conditions, and (vi)translation from dose at the reference depth to that at the depth required by the treatment planning system. Procedures are identified to achieve the most accurate results (errors up to 8% have been observed) and, where applicable, a commonly used simplified procedure is described and the impact on reference dosimetry measurements is discussed so that the medical physicist can be informed on where to allocateresources.

Pengaruh Penambahan Nanopartikel ZnO Terhadap Morfologi Nanokomposit TiO2/ZnO

The photoanode layer which is generally an oxide semiconductor material plays an important role in dye-sensitized solar cells. Photoanode facilitate electron transfer from dye to external circuit and electron injection from the dye. Photoanode should have a high surface area as well as high pore size to accommodate the dye sensitizer capacity optimally. To improve the function of TiO2-based photoanode, it can be done by adding ZnO nanoparticles. The characterization results showed that the addition of nanoparticles did not change the structure of each component, ZnO had a hexagonal wurtzite structure while TiO2 had a tetragonal structure in the anatase phase. The surface morphology of ZnO, TiO2 and TiO2/ZnO nanocomposites is quite homogeneous with spherical particles. The addition of ZnO nanoparticles affects the specific surface area and pore volume of TiO2/ZnO nanocomposites. Compared to the specific surface area and pore volume of TiO2, the addition of ZnO nanoparticles increased the specific surface area by 68% and the specific pore volume to three times the TiO2 pore volume

Propylene Polymerization Performance with Ziegler-Natta Catalysts Combined with U-Donor and T01 Donor as External Donor

In propylene (C3) polymerization with Ziegler-Natta catalyst, not only internal donor but also external donor is very important to make isotactic polypropylene (PP) with higher yield. Most propylene-based polymers have been commercially produced with Ziegler-Natta catalysts combined with dialkyl-dialkoxy silane compounds (R2Si(OR)2) such as C-donor, P-donor, and D-donor as external donors. In this paper, we will introduce the propylene polymerization performance with aminosilane compounds, i.e., diethylamino triethoxy silane (U-donor) and bis(ethylamino) di-cyclopentyl silane (T01 donor), as external donor in Ziegler–Natta catalyst. The polymerization screening experiments were conducted using some triethoxyalkylsilanes compounds (1–7) and performances were compared with U-donor. The polymerization results of the binary donor system show improvement in stereoregularity. These aminosilane compounds exhibit high hydrogen response in propylene polymerization and high copolymerization performance of propylene (C3) and ethylene (C2) in ICP production compared with dialkyl-dialkoxy silane compounds. While using methanol as an additive along with external electron donor, as a serendipitous, the copolymerization activity, block ratio, EPR (ethylene-propylene rubber) content improve significantly for U-donor as compared with T01 donor and C-donor.

Extracellular electron transfer capability of oral pathogens Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis

Polymicrobial oral biofilms, which consist of fermentative-bacteria, are associated with periodontitis, gingivitis and cause systemic diseases1. Unlike aerobic-respiration, fermentation does not require electron acceptors like O2; and redox-cycling of biological electron-carriers, like NADH, drives the intracellular oxidation and reduction of organic-substrates2. Thus, the energy gain is potentially lower than that of respiratory metabolism; however, the high pathogenic activity in anaerobic conditions remained ambiguous3. Afew studies have shown that fermentative gut microbes are capable ofreducing external electron acceptors viaextracellular electron transfer (EET)4-7. EET, a phenomenon initially found in environmental-bacteria, where metabolically generated electrons are transferred to external electron-acceptors through an outer-membraneredoxprotein complex8-9. Thus, the pathogens colonization in the human microbiome may be supported by their EET capability and is important to explore such potentiality. Here, we electrochemically characterized oral-biofilm pathogens Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis, to examine their EET ability with lactate/glucose. Both strains showed current production on an electrode surface, associated with consumption of substrate10. The addition of antibiotics that suppress the biosynthesis of membrane or protein showed a significant current decrease, demonstrating that current production reflects the cellular-activity. Further, transmission-electron-microscopy of 3,3‡-diaminobenzidine (DAB) stained cells revealed the presence of redox-enzymes on the cell-membrane suggesting a potential EET mechanism via membrane proteins9. These results could be a basis to reevaluate human oral pathogens from an electroactive point of view. The identified EET activity of the two strains can be utilized for an effective test for assessing the impact of antibacterial compounds on the pathogen cellular-activity on an electrode11.

From trash to treasure: Microbial conversion of palladium contaminants into valuable Pd nanoparticles by Bacillus thuringiensis Y9

Microbial reduction is a sustainable approach for both environmental remediation and recycling of precious metals from waste. Bacteria-mediated reduction of palladium ions (Pd2+) in wastewater under mild conditions is such a strategy. However, external electron donors are usually required for palladium bioreduction. Herein, a novel gram-positive bacterium, Bacillus thuringiensis Y9 (B. thuringiensis Y9), was found to reduce Pd2+ to palladium nanoparticles (Pd-NPs) with endogenous electron donors. Transcriptomic analyses revealed 443 and 439 differentially expressed genes response to palladium treatment under anaerobic and aerobic conditions, respectively. It was found the genes encoding NADH-quinone oxidoreductase, dehydrogenases, cytochrome c reductase, cytochrome c oxidase, quinone cycle and ribE in B. thuringiensis Y9 have strong positive relationship to palladium reduction. The removal efficiencies of palladium by B. thuringiensis Y9 are as high as 93 mg g−1 under anaerobic conditions and 60 mg g−1 under aerobic conditions. Hydrogenase also plays vital role in the bioreduction process. The maximum Pd removal ratio of 99.18% was obtained with the primary influencing factors using response surface methodology (RSM). Our study provides a novel and sustainable strategy for Pd recovery from wastewater. The transcriptome data are valuable for understanding the global bioreduction mechanism of the microbial conversion of palladium.

Second harmonic helicity and Faraday rotation in gated single-layer 1T′−WTe2

Single-layer of 1T$'$ phase of WTe$_2$ provides a rich platform for exotic physical properties such as nonlinear Hall effect and high-temperature quantum spin hall transport. Utilizing a continuum model and diagrammatic method, we calculate the second harmonic conductivity of monolayer 1T$'$-WTe$_2$ modulated by an external vertical electric field and electron doping. We obtain a finite helicity and Faraday rotation for the second harmonic signal in response to linearly polarized incident light in the presence of time-reversal symmetry. The second harmonic signal's helicity is highly controllable by altering the bias potential and serves as an optical indicator of the nonlinear Hall current. Our study motivates future experimental investigation for the helicity spectroscopy of two dimensional materials.

Polyhydroxyalkanoate-driven current generation via acetate by an anaerobic methanotrophic consortium

Anaerobic oxidation of methane (AOM) is an important microbial process mitigating methane (CH4) emission from natural sediments. Anaerobic methanotrophic archaea (ANME) have been shown to mediate AOM coupled to the reduction of several compounds, either directly (i.e. nitrate, metal oxides) or in consortia with syntrophic bacterial partners (i.e. sulfate). However, the mechanisms underlying extracellular electron transfer (EET) between ANME and their bacterial partners or external electron acceptors are poorly understood. In this study, we investigated electron and carbon flow for an anaerobic methanotrophic consortium dominated by ‘Candidatus Methanoperedens nitroreducens’ in a CH4-fed microbial electrolysis cell (MEC). Acetate was identified as a likely intermediate for the methanotrophic consortium, which stimulated the growth of the known electroactive genus Geobacter. Electrochemical characterization, stoichiometric calculations of the system, along with stable isotope-based assays, revealed that acetate was not produced from CH4 directly. In the absence of CH4, current was still generated and the microbial community remained largely unchanged. A substantial portion of the generated current in the absence of CH4 was linked to the oxidation of the intracellular polyhydroxybutyrate (PHB) and the breakdown of extracellular polymeric substances (EPSs). The ability of ‘Ca. M. nitroreducens’ to use stored PHB as a carbon and energy source, and its ability to donate acetate as a diffusible electron carrier expands the known metabolic diversity of this lineage that likely underpins its success in natural systems.

Order-of-magnitude enhancement in photocurrent generation of Synechocystis sp. PCC 6803 by outer membrane deprivation

Biophotovoltaics (BPV) generates electricity from reducing equivalent(s) produced by photosynthetic organisms by exploiting a phenomenon called extracellular electron transfer (EET), where reducing equivalent(s) is transferred to external electron acceptors. Although cyanobacteria have been extensively studied for BPV because of their high photosynthetic activity and ease of handling, their low EET activity poses a limitation. Here, we show an order-of-magnitude enhancement in photocurrent generation of the cyanobacterium Synechocystis sp. PCC 6803 by deprivation of the outer membrane, where electrons are suggested to stem from pathway(s) downstream of photosystem I. A marked enhancement of EET activity itself is verified by rapid reduction of exogenous electron acceptor, ferricyanide. The extracellular organic substances, including reducing equivalent(s), produced by this cyanobacterium serve as respiratory substrates for other heterotrophic bacteria. These findings demonstrate that the outer membrane is a barrier that limits EET. Therefore, depriving this membrane is an effective approach to exploit the cyanobacterial reducing equivalent(s).

Electron Weibel instability induced magnetic fields in optical-field ionized plasmas

Generation and amplification of magnetic fields in plasmas is a long-standing topic that is of great interest to both plasma and space physics. The electron Weibel instability is a well-known mechanism responsible for self-generating magnetic fields in plasmas with temperature anisotropy and has been extensively investigated in both theory and simulations, yet experimental verification of this instability has been challenging. Recently, we demonstrated a new experimental platform that enables controlled initialization of highly nonthermal and/or anisotropic plasma electron velocity distributions via optical-field ionization. Using an external electron probe bunch from a linear accelerator, the onset, saturation, and decay of the self-generated magnetic fields due to electron Weibel instability were measured for the first time to our knowledge. In this paper, we will first present experimental results on time-resolved measurements of the Weibel magnetic fields in non-relativistic plasmas produced by Ti:Sapphire laser pulses (0.8 μm) and then discuss the feasibility of extending the study to a quasi-relativistic regime by using intense CO2 (e.g., 9.2 μm) lasers to produce much hotter plasmas.

Identification and characterization of a prokaryotic 6-4 photolyase from Synechococcus elongatus with a deazariboflavin antenna chromophore.

Synechococcus elongatus, formerly known as Anacystis nidulans, is a representative species of cyanobacteria. It is also a model organism for the study of photoreactivation, which can be fully photoreactivated even after receiving high UV doses. However, for a long time, only one photolyase was found in S. elongatus that is only able to photorepair UV induced cyclobutane pyrimidine dimers (CPDs) in DNA. Here, we characterize another photolyase in S. elongatus, which belongs to iron-sulfur bacterial cryptochromes and photolyases (FeS-BCP), a subtype of prokaryotic 6–4 photolyases. This photolyase was named SePhrB that could efficiently photorepair 6–4 photoproducts in DNA. Chemical analyses revealed that SePhrB contains a catalytic FAD cofactor and an iron-sulfur cluster. All of previously reported FeS-BCPs contain 6,7-dimethyl-8-ribityllumazine (DMRL) as their antenna chromophores. Here, we first demonstrated that SePhrB possesses 7,8-didemethyl-8-hydroxy-5-deazariboflavin (8-HDF) as an antenna chromophore. Nevertheless, SePhrB could be photoreduced without external electron donors. After being photoreduced, the reduced FAD cofactor in SePhrB was extremely stable against air oxidation. These results suggest that FeS-BCPs are more diverse than expected which deserve further investigation.

Efficient hydrodeoxygenation of lignocellulose derivative oxygenates to aviation fuel range alkanes using Pd-Ru/hydroxyapatite catalysts

Bimetallic Pd-Ru/ hydroxyapatite (HAP) catalysts were developed together with Zirconium phosphate (ZrP) to prepare aviation fuel range hydrocarbons by one-pot HDO from lignocellulose-derived C15 oxygenate. The effects of the catalyst composition, reaction time, initial H2 pressure and reaction temperature on the HDO were explored. 84.24% C8-C15 alkanes could be obtained by Pd0.6-Ru1.8/HAP at 150 °C, 4 MPa H2. The HDO pathway and the stability of the catalyst were also investigated. To explore the synergy of bimetals and the efficiency of the catalysts, a series of characterizations were conducted. The results verified that the bimetallic catalyst had a better adsorption capacity for the substrate, and the ruthenium external electron density raised due to the introduction of palladium, thereby enhancing the hydrodeoxygenation activity of the catalyst.

Enhanced straw fermentation process based on microbial electrolysis cell coupled anaerobic digestion

The low quality and yield of methane severely hinder the industrial application of straw biogas fermentation, and no effective solution has been found so far. In this study, a novel method was developed when a microbial electrolysis cell (MEC) was coupled with normal anaerobic fermentation to enhance methane yield and purity. The fermentation process achieved a methane purity of more than 85%, which is considerably higher than that of previously published reports. With microbial stimulation and an electric current, the degradation of fibers has been greatly enhanced. The MEC system substantially improved the yield and purity of biogas, bringing a new path to the synthesis of methane by carbon dioxide and hydrogen ions in solution under electron irradiation. Electrochemical index analysis showed extra methane synthesis, due to the external circuit electron transfer. The results of the gas chromatography and solid degradation rate showed that the carbon source of extra methane was CO 2 produced during normal fermentation and additional volatile solid degradation. These results show that the MEC considerably enhanced the quality and yield of methane in the straw fermentation process, providing insights into normal anaerobic fermentation.

Medium-chain carboxylates production from co-fermentation of swine manure and corn stalk silage via lactic acid: Without external electron donors

Environmental issues caused by untreated animal manure and crop straws require the development of resource recovery from waste through a circular economy approach. Swine manure and corn stalks as the main agricultural biomass can be a renewable resource to produce biofuels and chemicals, and they have been successfully converted into methane via anaerobic digestion. However, the revenue from methane has been relatively low. This study aimed to convert swine manure and corn stalk silage into a high-value medium-chain carboxylic acid (MCCA) through a temperature-phased two-stage bioprocess. The carbohydrates in these streams, which were first converted to lactic acid (LA) rich solution at thermophilic condition, were then fermented to MCCA by mesophilic chain elongation without addition of external e-donors. In this study, thermophilic condition enhanced the LA fermentation and shifted the dominant product spectrum from volatile fatty acid (VFA) to LA. The average LA concentration was 8.4 gCOD/L at thermophilic, which was improved by 3.4 times compared with that achieved at mesophilic condition. For the chain-elongating bioreactor, the LA-rich broth was successfully converted into MCCA. Moreover, the maximum productivities of MCCA and n-caproate were 1890 and 1290 mg COD/L/d, respectively, at pH 6.0 with an LA loading rate of 2.1 g COD/L/d. Maintaining an appropriate LA/VFA ratio and mild pH was necessary to overcome the acrylate pathway and drive LA conversion toward n-caproate instead of propionate. In addition, Pseudoramibacter and Caproiciproducens became the dominant community, with a relative abundance of 45.6% and 9.7%, respectively.

Medium-chain fatty acids production from carbohydrates-rich wastewater through two-stage yeast biofilm processes without external electron donor addition: Biofilm development and pH impact

The production of medium-chain fatty acids (MCFAs) is considered promising for carbon resource recovery from waste streams. However, a large quantity of external electron donors are often required, causing great cost and environmental impact. Therefore, in this study, a two-stage technology was developed to produce MCFAs from carbohydrate-rich wastewater without external electron donor addition, with the biofilm development and pH impact being explored. Stage I aimed at converting organics into ethanol and a yeast biofilm reactor is innovatively applied. The results showed that the yeast biofilm could quickly form on carriers with steady-state thickness reaching 50–200 μm. However, the attachment of yeast biofilm was weak at the initial stage so that the violent turbulence should be avoided during operation. The polyurethane foam was the most suitable for yeast biofilm development among the tested carriers, as evidenced by the highest ethanol production, accounting for 74.2% of soluble organics. The Nakaseomyces was the main fungal genus in the steady-state biofilm, while lactic acid bacteria were also developed, resulting in lactate and acetate production. In Stage II, the yeast biofilm reactor effluent was applied for MCFA production at different pH (5–8). However, the MCFA production selectivity was significantly affected by pH, with 65.2% at pH of 5 but decreasing substantially to 3.0% at pH of 8. Both the microbial and electron transfer efficiency analysis suggested that mildly acidic pH can promote the electron transfer from ethanol toward the chain elongation process instead of its excessive oxidation. Thus, if conditions of online extraction or microbial tolerance permit, a lower pH should be recommended for Stage II in the developed technology as well as other ethanol-based MCFA production process. This is a conceptual study that eliminated external electron donor addition in MCFAs production and provide a sustainable and reliable way in carbon resources recovery.

Thiosulfate as external electron donor accelerating denitrification at low temperature condition in S0–based autotrophic denitrification biofilter

This study was carried out to determine the inhibition of low temperature on the performance of S0–based autotrophic denitrification (S0–SAD) biofilter, and proposed to enhance the nitrate removal efficiency with thiosulfate as external electron donor. With the decline of temperature from 30 °C to 10 °C at 0.25 h of empty bed contact time (EBCT), the nitrate removal rate presented a logarithmical drop, and the effluent nitrate dramatically increased from 9.19 mg L−1 to 15.13 mg L−1. EBCT was prolonged until 0.33 h for 20 °C, 0.66 h for 15 °C and 1.5 h for 10 °C, respectively, to maintain the effluent nitrate below 10 mg L−1. Such excessive variation of EBCT for different temperature is undoubtedly incredible for practical engineering. Thiosulfate, as the external electron donor, was adopted to compensate the efficiency loss during temperature decrease, which significantly prompted nitrate removal rate to 0.59, 0.53 and 0.31 kg N m−3 d−1 at 20 °C, 15 °C and 10 °C conditions, respectively, even at a short EBCT of 0.25 h. It not only acted as compensatory electron donor for nitrate removal, but also promoted the contribution of elemental sulfur via accelerating the DO consumption and extended larger effective volume of S0–layer for denitrification. Meanwhile, the significant enrichment of Sulfurimonas and Ferritrophicum provided biological evidences to the enhancement process. However, the incomplete consumption of thiosulfate was observed especially at EBCT of 0.25 h and 10 °C, and the thiosulfate runoff needs to be concerned in case of contaminating the effluent. Herein, approximately extending EBCT to 0.66 h and decreasing thiosulfate dosage were conducted simultaneously, thereby achieving 100% thiosulfate utilization efficiency and expected nitrate removal. This study provided a fundamental guidance to design and operate S0–SAD biofilter in response to seasonal temperature variation for practical engineering.