Surface Redox Potential Research Articles

A 2D-0D-2D Sandwich Heterostructure toward High-Performance Room-Temperature Gas Sensing.

The construction of two-dimensional (2D) van der Waals (vdW) heterostructures over black phosphorus (BP) has been attracting significant attention to better utilize its inherent properties. The sandwich of zero-dimensional (0D) noble metals within BP-based vdW heterostructures can provide efficient catalytic channels, modulating their surface redox potentials and therefore inducing versatile functionalities. Herein, we realize a 2D WS2-Au-BP heterostructure, in which Au nanoparticles are connected between BP and WS2 via ionic bonds. The ultralow conduction band minimum position, the reduced adsorption energies of O2, and the increased dissociation barrier energy of O2- into 2O contribute greatly to improving the long-term stability of BP in the air. The formation of heterostructures can reduce the potential barrier energy in target gas molecules, thus enhancing the absorption energy and charge transfer. Taking the paramagnetic NO2 gas molecules as a representative, a stable response magnitude of 2.11 to 100 ppb NO2 is achieved for 80 days, which is far larger than the initial responses of most BP-based materials. A practical gas sensing system is also developed to demonstrate its real-world implementation. This work provides a promising demonstration of 0D noble metal within 2D BP-based vdW heterostructure for simultaneously improving the long-term stability and room-temperature reversible gas sensing.

Correlation between biological activity and physicochemical properties of sodium dodecylbenzenesulfonate in aqueous solutions

The purpose of this study was to establish a correlation between the effect of the pollutant content on the dimensional and physicochemical characteristics of the investigated solutions and its effect on aquatic organisms. To this end, the surface tension, electrical conductivity, pH, and redox potential of aqueous solutions of sodium dodecylbenzenesulfonate were measured in a wide concentration range (10–710–2 М). The change in the size and number of optical inhomogeneities was investigated using the small-angle reflection method in the micron range. In addition, the behavior of aquatic biological objects (Daphnia Magna) was studied in the investigated solutions. It was shown that the investigated concentration dependences (including the behavior of biological objects) are non-linear: they have either a stepped character or clearly expressed extremes and are well correlated with each other. A comfortable concentration range of sodium dodecylbenzenesulfonate for daphnia (all daphnia are active within 58 hours of the experiment) was established (0.018–0.037 mM). The correlation and nature of the concentration dependences indicate that at critical concentrations, structural rearrangements occur in sodium dodecylbenzenesulfonate solutions, not only the formation of micelles and pre-micelles, but also structural rearrangements of the solvent (water) itself. Thus, it has been experimentally shown that the change in the structure of water during interaction with pollutants can significantly affect both the physicochemical properties of aqueous solutions and the behavior of aquatic biological objects.

Effects of C/Mn Ratios on the Sorption and Oxidative Degradation of Small Organic Molecules on Mn-Oxides

Manganese (Mn) oxides have a high surface area and redox potential that facilitate sorption and/or oxidation of organic carbon (OC), but their role in regulating soil C storage is relatively unexplored. Small OC compounds with distinct structures were reacted with Mn(III/IV)-oxides to investigate the effects of OC/Mn molar ratios on Mn-OC interaction mechanisms. Dissolved and solid-phase OC and Mn were measured to quantify the OC sorption to and/or the redox reaction with Mn-oxides. Mineral transformation was evaluated using X-ray diffraction and X-ray absorption spectroscopy. Higher OC/Mn ratios resulted in higher sorption and/or redox transformation; however, interaction mechanisms differed at low or high OC/Mn ratios for some OC. Citrate, pyruvate, ascorbate, and catechol induced Mn-oxide dissolution. The average oxidation state of Mn in the solid phase did not change during the reaction with citrate, suggesting ligand-promoted mineral dissolution, but decreased significantly during reactions with the other compounds, suggesting reductive dissolution mechanisms. Phthalate primarily sorbed on Mn-oxides with no detectable formation of redox products. Mn-OC interactions led primarily to C loss through OC oxidation into inorganic C, except phthalate, which was predominantly immobilized in the solid phase. Together, these results provided detailed fundamental insights into reactions happening at organo-mineral interfaces in soils.

Electrocatalytic Biomass Upgrading of Furfural using Transition-Metal Borides via Density Functional Theory Investigation.

Electrocatalytic biomass upgrading has proven to be an effective technique for generating value-added products. Herein, the design and development of furfural upgrading using transition-metal borides (MBenes) with simultaneous production of hydrogen are presented. Using density functional theory, the stabilities, selectivities, and activities of 13 MBene candidates are systematically evaluated for furfural upgrading. This research suggests that Fe2 B2 can serve as a promising electrocatalyst for the formation of furoic acid (FAC), with a limiting potential of -0.15V, and 5-hydroxy-2(5H)-furanone (HFO), with a limiting potential of -0.93V. Furthermore, Fe2 B2 and Mn2 Fe2 are shown to exhibit favorable limiting potentials of -1.35 and -1.36V, respectively, for producing 6-hydroxy-2.3-dihydro-6H-pyrano-3-one (HDPO), indicating that they may also serve as electrocatalysts.Based on Sabatier's principle, a descriptor (φ) of material properties is developed for screening catalysts with high catalytic activity considering the electronegativities and d-electron number of metals. Additionally, surface redox potential, electronic properties, and charge-density differences are determined for Fe2 B2 , which is estimated to exhibit high catalytic activity for the oxidation of furfural to FAC and HFO.

Enhanced Efficiency of Dye-Sensitized Solar Cells Based on Polymer-Assisted Dispersion of Platinum Nanoparticles/Carbon Nanotubes Nanohybrid Films as FTO-Free Counter Electrodes.

In this study, polymer-assisted dispersants are used to stabilize the nanohybrids of platinum nanoparticles (PtNPs)/carbon nanotubes (CNTs) through non-covalent bond forces. These dispersants aim to replace the florine-doped tin oxide (FTO) glass in traditional dye-sensitized solar cells (DSSCs) as counter electrodes. The large specific surface area, high conductivity, and redox potential of PtNPs/CNT nanohybrids are used as the basis to utilize them as the counter electrode material to fabricate a dye-sensitized solar cell. The conductivity results indicate that the resistance of the PtNP/CNT nanohybrid film can be reduced to 7.25 Ω/sq. When carbon nanotubes are mixed with platinum nanoparticles at a weight ratio of 5/1, the photoelectric conversion efficiency of DSSCs can reach 6.28%. When using the FTO-containing substrate as the counter electrode, its conversion efficiency indicates that the micro-/nano-hybrid material formed by PtNPs/CNTs also exhibits an excellent photoelectric conversion efficiency (8.45%) on the traditional FTO substrate. Further, a large-area dye-sensitive cell is fabricated, showing that an 8 cm × 8 cm cell has a conversion efficiency of 7.95%. Therefore, the traditional Pt counter electrode can be replaced with a PtNP/CNT nanohybrid film, which both provides dye-sensitive cells with a high photoelectric conversion efficiency and reduces costs.

Role of Wettability on the Adsorption of an Anionic Surfactant on Sandstone Cores.

We investigate the dynamic adsorption of anionic surfactant C14-16 alpha olefin sulfonate on Berea sandstone cores with different surface wettability and redox states under high temperature that represents reservoir conditions. Surfactant adsorption levels are determined by analyzing the effluent history data with a dynamic adsorption model assuming Langmuir isotherm. A variety of analyses, including surface chemistry, ionic composition, and chromatography, is performed. It is found that the surfactant breakthrough in the neutral-wet core is delayed more compared to that in the water-wet core because the deposited crude oil components on the rock surface increase the surfactant adsorption via hydrophobic interactions. As the surfactant adsorption is satisfied, the crude oil components are solubilized by surfactant micelles and some of the adsorbed surfactants are released from the rock surface. The released surfactant dissolves in the flowing surfactant solution, thereby resulting in an overshoot of the produced surfactant concentration with respect to the injection value. Furthermore, under water-wet conditions, changing the surface redox potential from an oxidized to a reduced state decreases the surfactant adsorption level by 40%. We find that the decrease in surfactant adsorption is caused not only by removing the iron oxide but also by changing the calcium concentration after the core restoration process (calcite dissolution and ion exchange as a result of using EDTA). Findings from this study suggest that laboratory surfactant adsorption tests need to be conducted by considering the wettability and redox state of the rock surface while recognizing how core restoration methods could significantly alter the ionic composition during surfactant flooding.

New insights into MnOOH/peroxymonosulfate system for catalytic oxidation of 2,4-dichlorophenol: Morphology dependence and mechanisms

Sulfate radical-based advanced oxidation processes (SR-AOPs) have received increasing attention as viable technology for recalcitrant organics removal from polluted waters. As for heterogeneous catalyst, it is crucial to reveal the effect of morphology on its catalytic activity and mechanism, providing guidelines for rational design of morphology-dependent catalysts. Hence, in this study, we selected manganese oxyhydroxide (MnOOH) as the peroxymonosulfate (PMS) activator and synthesized different morphological MnOOH with the same crystal structure. The catalytic activity of MnOOH follows: nanowires > multi-branches > nanorods. Different morphological MnOOH had different physical and chemical characterization such as specific surface area, Lewis sites, ζ-potential and redox potential, which played positive roles in catalytic activity of MnOOH as PMS activator. Unexpectedly, it was found that ζ-potential was more crucial than specific surface area, redox potential and Lewis sites. Notably, nanowires exhibited higher positive zeta potential, which was favor of promoting interfacial reactivity between HSO5− and surface of MnOOH. Furthermore, •OH, SO4•−, O2•− and 1O2, were involved in the MnOOH/PMS system. Moreover, the cycle of Mn (III)/Mn (II) accelerated MnOH+ formation. This study provided a new understanding of manganese-catalyzed peroxymonosulfate activation and elucidated the relationships between morphology of catalyst and its catalytic activity.

Toward efficient photocatalytic pure water splitting for simultaneous H2 and H2O2 production

Although overall water splitting with particulate photocatalysts is considered as an ideal means towards solar-to-hydrogen conversion, practical application of the promising technique is greatly inhibited by the congenital defects including H2/O2 separation and unfavorable four-electron kinetics. In this context, photocatalytic overall water splitting for simultaneous H2 and H2O2 generation via a two-electron pathway can readily address these issues. Here, we report a novel CoxNiyP cluster incorporated P-doped g-C3N4 photocatalyst (CoxNiyP-PCN) by a two-step phosphating method that presents such unique behavior for pure water splitting into stoichiometric H2 and H2O2. The highest H2 evolution rate reaches 239.3 μmol h−1 g−1, achieved over the CoNiP–PCN photocatalyst, which is among the best reported activities for overall water splitting. It is found that both P and the cluster cocatalyst are critical to the remarkably improved photocatalytic activity. Specifically, P as a substitution of C in PCN introduces a positive charge center (P+), reinforcing the chemical connection between PCN and CoNiP, in a form of P+-Pδ--Coδ+/Niδ+. This unique bridging effect, together with the extended light absorption by P doping and optimized surface redox potential by cocatalyst integration, stimulates efficient vectorial charge transfer between PCN and CoNiP and subsequent surface mass exchange. On the other hand, we also demonstrate that the well satisfied band structure of PCN can facilitate the two-electron reaction pathway. This work not only has implications for the potential use of CoNiP–PCN as potential photocatalyst for solar H2 production, but also offers a new idea for pure water slitting in particulate system.

Extracellular Electron Uptake by Two Methanosarcina Species

Author(s): Yee, Mon Oo; Snoeyenbos-West, Oona; Thamdrup, Bo; Ottosen, Lars DM; Rotaru, Amelia-Elena | Abstract: Direct electron uptake by prokaryotes is a recently described mechanism with a potential application for energy and CO 2 storage into value added chemicals. Members of Methanosarcinales, an environmentally and biotechnologically relevant group of methanogens, were previously shown to retrieve electrons from an extracellular electrogenic partner performing Direct Interspecies Electron Transfer (DIET) and were therefore proposed to be electroactive. However, their intrinsic electroactivity has never been examined. In this study, we tested two methanogens belonging to the genus Methanosarcina, M. barkeri and M. horonobensis, regarding their ability to accept electrons directly from insoluble electron donors like other cells, conductive particles and electrodes. Both methanogens were able to retrieve electrons from Geobacter metallireducens via DIET. Furthermore, DIET was also stimulated upon addition of electrically conductive granular activated carbon (GAC) when each was co-cultured with G. metallireducens . However, when provided with a cathode poised at −400 mV (vs. SHE), only M. barkeri could perform electromethanogenesis. In contrast, the strict hydrogenotrophic methanogen, Methanobacterium formicicum , did not produce methane regardless of the type of insoluble electron donor provided ( Geobacter cells, GAC or electrodes). A comparison of functional gene categories between the two Methanosarcina showed differences regarding energy metabolism, which could explain dissimilarities concerning electromethanogenesis at fixed potentials. We suggest that these dissimilarities are minimized in the presence of an electrogenic DIET partner (e.g. Geobacter ), which can modulate its surface redox potentials by adjusting the expression of electroactive surface proteins.

RGO‐ZnSe Photocatalyst towards Solar‐Light‐Assisted Degradation of Tetracycline Antibiotic Water Pollutant

AbstractIt is well known that – mainly, three processes govern the photocatalytic activity – the first one being the exciton formation after absorption of light, the second one is the charge separation and migration and the third one is the surface redox potential. In this study, an effective charge transfer and migration of photo generated electrons and holes from Zinc Selenide (ZnSe) to Reduced Graphene Oxide (RGO) have been reported. Further, these photocatalysts are evaluated by tetracycline (TC) photodegradation under simulated solar light irradiation. The ZnSe decorated RGO photocatalysts have been successfully synthesized using a one‐step solvothermal reaction. X‐ray diffraction, Scanning electron microscopy, Transmission electron microscopy, High‐resolution transmission electron microscopy, Raman and Fourier‐transform infrared spectroscopy are used to characterize the RGO‐ZnSe composite. Ultraviolet–visible spectroscopy and scavenger experiments are used to explore the photocatalysis mechanism of the water pollutant antibiotic TC. The main active species in TC photodegradation was found to be hole (h+). Furthermore, this work initiated a promising and effective photocatalyst, the RGO–ZnSe nanocomposites. Hence these nanocomposites could be potentially used for the degradation of organic pollutants.

Designing biochar properties through the blending of biomass feedstock with metals: Impact on oxyanions adsorption behavior

Metal-blending of biomass prior to pyrolysis is investigated in this work as a tool to modify biochar physico-chemical properties and its behavior as adsorbent. Six different compounds were used for metal-blending: AlCl3, Cu(OH)2, FeSO4, KCl, MgCl2 and Mg(OH)2. Pyrolysis experiments were performed at 400 and 700 °C and the characterization of biochar properties included: elemental composition, thermal stability, surface area and pore size distribution, Zeta potential, redox potential, chemical structure (with nuclear magnetic resonance) and adsorption behavior of arsenate, phosphate and nitrate. Metalblending strongly affected biochars' surface charge and redox potential. Moreover, it increased biochars' microporosity (per mass of organic carbon). For most biochars, mesoporosity was also increased. The adsorption behavior was enhanced for all metal-blended biochars, although with significant differences across species: Mg(OH)2-blended biochar produced at 400 °C showed the highest phosphate adsorption capacity (Langmuir Qmax approx. 250 mg g−1), while AlCl3-blended biochar produced also at 400 °C showed the highest arsenate adsorption (Langmuir Qmax approx. 14 mg g−1). Significant differences were present, even for the same biochar, with respect to the investigated oxyanions. This indicates that biochar properties need to be optimized for each application, but also that this optimization can be achieved with tools such as metal-blending. These results constitute a significant contribution towards the production of designer biochars.

Comparative metatranscriptomics reveals extracellular electron transfer pathways conferring microbial adaptivity to surface redox potential changes

Some microbes can capture energy through redox reactions with electron flow to solid-phase electron acceptors, such as metal-oxides or poised electrodes, via extracellular electron transfer (EET). While diverse oxide minerals, exhibiting different surface redox potentials, are widely distributed on Earth, little is known about how microbes sense and use the minerals. Here we show electrochemical, metabolic, and transcriptional responses of EET-active microbial communities established on poised electrodes to changes in the surface redox potentials (as electron acceptors) and surrounding substrates (as electron donors). Combination of genome-centric stimulus-induced metatranscriptomics and metabolic pathway investigation revealed that nine Geobacter/Pelobacter microbes performed EET activity differently according to their preferable surface potentials and substrates. While the Geobacter/Pelobacter microbes coded numerous numbers of multi-heme c-type cytochromes and conductive e-pili, wide variations in gene expression were seen in response to altering surrounding substrates and surface potentials, accelerating EET via poised electrode or limiting EET via an open circuit system. These flexible responses suggest that a wide variety of EET-active microbes utilizing diverse EET mechanisms may work together to provide such EET-active communities with an impressive ability to handle major changes in surface potential and carbon source availability.

In-situ mass-electrochemical study of surface redox potential and interfacial chemical reactions of Li(Na)FePO4 nanocrystals for Li(Na)-ion batteries

In this work, an in-situ experimental mass-electrochemical investigation of the LiFePO4 (LFP) and NaFePO4 (NFP)electrolyte interfacial chemical reactions and surface redox potential is achieved by adopting electrochemical quartz crystal microbalance (EQCM) to monitor the mass change trend. In organic electrolyte, LFP (NFP) cathode's mass decreases/increases during the charge/discharge process because of deintercalation/intercalation of Li (Na) ions, which is an normal phenomenon which is generally known. However, the mass-potential curve for LFP nanocrystals in aqueous electrolyte show an anomalous mass change interval (AMCI) around 3.42V (vs. Li/Li+) where the cathode's mass increase in the charging process and mass decrease in the discharging process, which doesn’t obey the normal law of mass change. Through density functional theory (DFT) calculations, we gain a microscopic picture of the solid-liquid interface structure with a reconstructed LFP (010)/H2O and NFP (010)/H2O interface. Taken together, it's concluded that the surface redox potential of LFP is around 3.31V, which is lower than the bulk potential (3.42V) and the desolvation/solvation rate of surficial Li-ion is lower than the bulk Li-ion diffusion rate. While for NFP, it's surface redox potential is almost the same as the bulk one.

Electrochemical and spectroscopic studies of pyrite–cyanide interactions in relation to the depression of pyrite flotation

Cyanide is the most commonly used depressant to reject pyrite as a gangue mineral at alkaline pH in differential flotation. However, the depression mechanism of cyanide still remains uncertain. The depression effect has been proposed as the preferential adsorption of cyano species on pyrite, which has, however, not been confirmed experimentally. It is also believed that cyanide inhibits the chemisorption of thiol collectors due to the decrease of surface redox potential. In order to clarify the controversial depression mechanisms, the interactions between pyrite and cyanide at pH 10 were investigated in this study. Preferential adsorption of cyanide on pyrite rather than the decrease of surface redox potential was determined to be the depression contributor. Surface cyanoferric species were identified, both electrochemically and spectroscopically, on pyrite surface in the presence of cyanide, inhibiting the oxidation of pyrite and the oxidation/chemisorption of xanthate. This study provides new insights into the depression of pyrite flotation by cyanide.

Conservation of Waterlogged Convict-built Wooden Road Blocks with PEG 3350 and Luviskol K-90®

Earthworks associated with widening of the Great Eastern Highway in Perth, Western Australia, unearthed an original section of the convict-built wooden road that linked Perth to Guildford, built between 1865 and 1867. An emergency in situ analysis of the timbers was conducted using surface pH and redox potential profiles, along with degradation depths using a pointed stainless steel probe. The water content of the wooden blocks was determined under laboratory conditions. The combination of probe depths and water content showed that the jarrah (Eucalyptus marginata) blocks were moderately waterlogged and significantly affected by brown rot fungus at the outer margins. Recoverable timbers were block lifted by Belmont Council workers using standard archaeological techniques and wrapped in high density black polyethylene builders' membrane and stored in the council yard for 3 weeks, under 30 cm of mulch. Conservation treatment took place in a covered annex of the Belmont museum and involved saturating the blocks with sprayed solutions of PEG 3350 and Luviskol K-90®. Consolidation and impregnation took 1 year of weekly treatment before 6 months of slow air drying. The consolidated surfaces were brush cleaned of sandy soil debris and the dried blocks placed in temporary Perspex® covered show cases with ventilation holes to facilitate water evaporation until equilibrium is reached.

Heterostructured Au/Pd-M (M = Au, Pd, Pt) nanoparticles with compartmentalized composition, morphology, and electrocatalytic activity.

The synthesis, processing, and galvanic exchange of three heterostructured nanoparticle systems is described. The surface accessibility and redox potential of a Au/Pd-Ag dumbbell nanoparticle, where a Au/Pd core/shell region, and a silver region make up the domains, was used to prepare the new nanostructures with controlled composition, morphology, and microstructure. Results indicate that the silver domain was particularly susceptible to galvanic displacement, and was exchanged to Au/Pd-M (M = Au, Pd, Pt). Interestingly, the dumbbell morphology remained after exchange, and the silver region was transformed to hollow, parachute, or concentric domains respectively. The morphology and microstructure change was visualized via TEM and HRTEM, and the composition changes were probed via STEM-EDS imaging and XPS. The electrocatalytic activity of the Au/Pd-M towards methanol oxidation was studied, with results indicating that the Au/Pd-Pt nanoparticles had high activity attributed to the porous nature of the platinum domains.

Morphology and surface properties of LiVOPO4: a first principles study

First principles calculations were used to investigate the surface energies, equilibrium morphology, surface redox potentials, and surface electrical conductivity of LiVOPO4. Relatively low-energy surfaces are found in the (100), (010), (001), (011), (111), and (201) orientations of the orthorhombic structure. Thermodynamic equilibrium shape of the LiVOPO4 crystal is built with the calculated surface energies through a Wulff construction. The (001) and (111) orientations are the dominating surfaces in the Wulff shape. Similar calculations for VOPO4 display a larger decrease in surface energies for the (100) surface rather than those in the other surfaces. It suggests that the Wulff shape of LiVOPO4 is closely related to the chemical environment around. Surfaces (100), (010) and (201) present lower Li surface redox potentials in comparison with the bulk material. Therefore, the Li migration rate on surfaces could be effectively increased by maximizing the exposure of these low redox potential surfaces. In addition, lower surface band gaps are found in all orientations compared to the bulk one, which indicates that electrical conductivity can be improved significantly by enlarging surfaces with relatively low band gaps in the particle. Therefore, synthesizing (201) and (100) nanosheets will greatly improve the electrochemical properties of the material.

In situ evaluation of model copper-cast iron canisters for spent nuclear fuel: a case of microbiologically influenced corrosion (MIC)

The Swedish method for disposal of spent nuclear fuel in a deep geological repository (KBS-3) relies on the stability of the granitic bed-rock and two engineered barriers: a copper-cast iron canister and highly compacted bentonite clay. In order to develop a better understanding of the internal corrosion processes that could take place if a leak were to occur in the outer copper canister, five miniaturised copper cast iron canisters were installed at a depth of 450 m at the Äspö Hard Rock Laboratory, in Sweden. The experiments differed in the density of the surrounding bentonite buffer, as well as in the number and position of leak points that were introduced in the copper shell. Several electrochemical techniques (e.g. AC impedance, linear polarisation resistance and electrochemical noise) were used to monitor the corrosion of different components of the experiment. Copper specimens were installed for post-test evaluation of the rate of general corrosion, localised corrosion and stress corrosion cracking (SCC). In addition, mechanical and environmental parameters, such as surface strain, hydrostatic pressure, redox potential, pH, water chemistry, dissolved gases, and microbial numbers, diversity, and activity were measured regularly. After five years of in situ exposure one of the canisters was retrieved and analysed to characterise and evaluate the corrosion processes that had occurred during the experiment. Extensive sulphide production by sulphate reducing bacteria led to rapid corrosion of iron, and the formation of iron sulphide deposits on the copper and iron electrodes disturbed the electrochemical measurements. This paper describes the various analyses that were carried out on the model canister and summarises the conclusions that can be drawn.

Bio-inspired morphological evolution of zinc oxide nanostructures on a tunable enzyme platform

Diamine oxidase is a copper-containing enzyme with interesting structural dynamics sensitive to environmental conditions. The present work explores the applicability of the system as a tunable platform for the shape and size selective synthesis of zinc oxide nanoparticles under ambient conditions. Significant changes in the nanoscale morphology of ZnO have been observed, using scanning electron microscopy, with respect to changes in pH and gas atmosphere of the medium. More specifically, hexagonal plates of nanoscale ZnO were formed at pH below the isoelectric point of the enzyme and spherical particles at alkaline pH. Interestingly the average particle size of ZnO nanostructures increases with increasing oxygen content at acidic pH while the opposite trend is noticed at alkaline pH. The observations are explained on the basis of changes in the enzyme's surface charge, conformation and redox potential using a combination of techniques like zeta potential measurements, FTIR spectroscopy, fluorescence spectroscopy, open circuit potential studies and cyclic voltammetry. Thus the present work demonstrates the applicability of an enzyme as a dynamic bio-template for the synthesis of a multitude of ZnO nanostructures which are expected to add newer insight into bottom-up fabrication of oxide nanostructures.

Microbial population and functional dynamics associated with surface potential and carbon metabolism.

Microbial extracellular electron transfer (EET) to solid surfaces is an important reaction for metal reduction occurring in various anoxic environments. However, it is challenging to accurately characterize EET-active microbial communities and each member's contribution to EET reactions because of changes in composition and concentrations of electron donors and solid-phase acceptors. Here, we used bioelectrochemical systems to systematically evaluate the synergistic effects of carbon source and surface redox potential on EET-active microbial community development, metabolic networks and overall electron transfer rates. The results indicate that faster biocatalytic rates were observed under electropositive electrode surface potential conditions, and under fatty acid-fed conditions. Temporal 16S rRNA-based microbial community analyses showed that Geobacter phylotypes were highly diverse and apparently dependent on surface potentials. The well-known electrogenic microbes affiliated with the Geobacter metallireducens clade were associated with lower surface potentials and less current generation, whereas Geobacter subsurface clades 1 and 2 were associated with higher surface potentials and greater current generation. An association was also observed between specific fermentative phylotypes and Geobacter phylotypes at specific surface potentials. When sugars were present, Tolumonas and Aeromonas phylotypes were preferentially associated with lower surface potentials, whereas Lactococcus phylotypes were found to be closely associated with Geobacter subsurface clades 1 and 2 phylotypes under higher surface potential conditions. Collectively, these results suggest that surface potentials provide a strong selective pressure, at the species and strain level, for both solid surface respirators and fermentative microbes throughout the EET-active community development.