Prestrain Guided Yield of Large Single-Crystal Nickel Foils with High-Index Facets.

Single-crystal metal foils with high-index facets are currently being investigated owing to their potential application in the epitaxial growth of high-quality van der Waals (vdW) film materials, electrochemical catalysis, gas sensing and other fields. However, the controllable synthesis of large single-crystal metal foils with high-index facets remains a great challenge because high-index facets with high surface energy are not preferentially formed thermodynamically and kinetically. Herein, single-crystal nickel foils with a series of high-index facets are efficiently prepared by applying prestrain energy engineering technique, with the largest single-crystal foil exceeding 5×8 cm2 in size. In terms of thermodynamics, the internal mechanism of prestrain regulation on the formation of high-index facets is proposed. Molecular dynamics simulation is utilized to replicate and explain the phenomenon of multiple crystallographic orientations resulting from prestrain regulation. Additionally, large-sized and high-quality graphite films are successfully fabricated on single-crystal Ni(012) foils. Compared to the polycrystalline nickel, the graphite/single-crystal Ni(012) foil composites show more than five-fold increase in thermal conductivity, thereby showing great potential applications in thermal management. This study hence presents a novel approach for the preparation of single-crystal nickel foils with high-index facets, which is beneficial for the epitaxial growth of certain two-dimensional materials. This article is protected by copyright. All rights reserved.

Multi-scale simulation of proton diffusion in dislocation cores in BaZrO3.

Dislocations are important for their effects on the chemical, electrical, magnetic, and transport properties of oxide materials, especially for electrochemical devices such as solid fuel cells and resistive memories, but these effects are still under-studied at the atomic level. We have developed a quantum mechanical/molecular mechanical (QM/MM)-based multiscale simulation program to reveal the diffusion properties of protons on 〈100〉 edge dislocations in BaZrO3 perovskite oxide. We find that the large free space and the presence of hydrogen bonds in the dislocation core structure lead to significant trapping of protons. The diffusion properties of protons in dislocation cores were investigated, and no evidence of pipeline diffusion was found from the calculated migration energy barriers, which not only did not accelerate ion diffusion but rather decreases the conductivity of ions. The proton diffusion properties of Y-doped BaZrO3 (BZY), with a dislocation core structure (BZY-D) and with a grain boundary structure (BZY-GB) were also compared. In all three structures, local lattice deformation occupies an essential part in the proton transfer and rotation processes. The change in bond order is calculated and it is found that the interaction with oxygen and Zr ions during proton transfer and rotation controls the energy barrier for local lattice deformation of the O-B-O motion, which affects the proton diffusion in the structure. Our study provides insight into proton diffusion in dislocations in terms of mechanical behavior, elucidates the origin of the energy barrier associated with proton diffusion in dislocations, and provides guidance for the preparation and application of proton conductors.

Novel insights into lattice thermal transport in nanocrystalline Mg3Sb2 from first principles: the crucial role of higher-order phonon scattering.

Zintl phase Mg3Sb2, which has ultra-low thermal conductivity, is a promising anisotropic thermoelectric material. It is worth noting that the prediction and experiment value of lattice thermal conductivity (κ) maintain a remarkable difference, troubling the development and application. Thus, we firstly included the four-phonon scattering processes effect and performed the Peierls-Boltzmann transport equation (PBTE) combined with the first-principles lattice dynamics to study the lattice thermal transport in Mg3Sb2. The results showed that our theoretically predicted κ is consistent with the experimentally measured, breaking through the limitations of the traditional calculation methods. The prominent four-phonon scatterings decreased phonon lifetime, leading to the κ of Mg3Sb2 at 300 K from 2.45 (2.58) W m-1 K-1 to 1.94 (2.19) W m-1 K-1 along the in (cross)-plane directions, respectively, and calculation accuracy increased by 20%. This study successfully explains the lattice thermal transport behind mechanism in Mg3Sb2 and implies guidance to advance the prediction accuracy of thermoelectric materials.

Strain-resilient electrical functionality in thin-film metal electrodes using two-dimensional interlayers.

Flexible electrodes that allow electrical conductance to be maintained during mechanical deformation are required for the development of wearable electronics. However, flexible electrodes based on metal thin-films on elastomeric substrates can suffer from complete and unexpected electrical disconnection after the onset of mechanical fracture across the metal. Here we show that the strain-resilient electrical performance of thin-film metal electrodes under multimodal deformation can be enhanced by using a two-dimensional (2D) interlayer. Insertion of atomically-thin interlayers - graphene, molybdenum disulfide, or hexagonal boron nitride - induce continuous in-plane crack deflection in thin-film metal electrodes. This leads to unique electrical characteristics (termed electrical ductility) in which electrical resistance gradually increases with strain, creating extended regions of stable resistance. Our 2D-interlayer electrodes can maintain a low electrical resistance beyond a strain in which conventional metal electrodes would completely disconnect. We use the approach to create a flexible electroluminescent light emitting device with an augmented strain-resilient electrical functionality and an early-damage diagnosis capability.

Ultrasensitive detection of nucleic acids using deformed graphene channel field effect biosensors.

Field-effect transistor (FET)-based biosensors allow label-free detection of biomolecules by measuring their intrinsic charges. The detection limit of these sensors is determined by the Debye screening of the charges from counter ions in solutions. Here, we use FETs with a deformed monolayer graphene channel for the detection of nucleic acids. These devices with even millimeter scale channels show an ultra-high sensitivity detection in buffer and human serum sample down to 600 zM and 20 aM, respectively, which are ∼18 and ∼600 nucleic acid molecules. Computational simulations reveal that the nanoscale deformations can form 'electrical hot spots' in the sensing channel which reduce the charge screening at the concave regions. Moreover, the deformed graphene could exhibit a band-gap, allowing an exponential change in the source-drain current from small numbers of charges. Collectively, these phenomena allow for ultrasensitive electronic biomolecular detection in millimeter scale structures.

A novel concept for syngas biomethanation by two-stage process: Focusing on the selective conversion of syngas to acetate.

Thermal gasification of nonrenewable and renewable sources produces syngas, containing CO, H2, CO2 and N2. Anaerobic conversion of syngas to CH4 is a promising way to replace natural gas. However, the high N2 content (>50%) in syngas would result in the low CH4 content in the biogas and CO in syngas also had serious inhibition on methanogens. The present study proposed a two-stage anaerobic process for syngas biomethanation, and syngas was first anaerobically converted to acetate by mixed culture, which could be further converted to methane easily without the negative effects of N2 and CO. The results showed that mesophilic condition was more suitable for the conversion of syngas to acetate compared to thermophilic and ambient conditions at pH 5.5 considering the higher acetate yield and syngas conversion rate. Although CO was efficiently converted at thermophilic condition, it was mostly converted to H2, which was then converted to acetate. CO was much easier to be converted compared to H2. Further study showed that pH 6.5 and 7.5 were optimal for selective conversion of syngas to acetate. The other products including butyrate and ethanol were also detected in relatively higher amounts at pH 4.5 and 9.5. Although pH 5.5 and 8.5 had relatively lower syngas conversion rates compared to pH 6.5 and 7.5, they might inhibit methanogens naturally without adding methane inhibitors. Finally, batch experiments showed that the acetate concentration had obvious inhibition on syngas conversion when the acetate concentration was higher than 2 g/L.

Thermophilic Alkaline Fermentation Followed by Mesophilic Anaerobic Digestion for Efficient Hydrogen and Methane Production from Waste-Activated Sludge: Dynamics of Bacterial Pathogens as Revealed by the Combination of Metagenomic and Quantitative PCR Analyses.

Thermophilic alkaline fermentation followed by mesophilic anaerobic digestion (TM) for hydrogen and methane production from waste-activated sludge (WAS) was investigated. The TM process was also compared to a process with mesophilic alkaline fermentation followed by a mesophilic anaerobic digestion (MM) and one-stage mesophilic anaerobic digestion (M) process. The results showed that both hydrogen yield (74.5 ml H2/g volatile solids [VS]) and methane yield (150.7 ml CH4/g VS) in the TM process were higher than those (6.7 ml H2/g VS and 127.8 ml CH4/g VS, respectively) in the MM process. The lowest methane yield (101.2 ml CH4/g VS) was obtained with the M process. Taxonomic results obtained from metagenomic analysis showed that different microbial community compositions were established in the hydrogen reactors of the TM and MM processes, which also significantly changed the microbial community compositions in the following methane reactors compared to that with the M process. The dynamics of bacterial pathogens were also evaluated. For the TM process, the reduced diversity and total abundance of bacterial pathogens in WAS were observed in the hydrogen reactor and were further reduced in the methane reactor, as revealed by metagenomic analysis. The results also showed not all bacterial pathogens were reduced in the reactors. For example, Collinsella aerofaciens was enriched in the hydrogen reactor, which was also confirmed by quantitative PCR (qPCR) analysis. The study further showed that qPCR was more sensitive for detecting bacterial pathogens than metagenomic analysis. Although there were some differences in the relative abundances of bacterial pathogens calculated by metagenomic and qPCR approaches, both approaches demonstrated that the TM process was more efficient for the removal of bacterial pathogens than the MM and M processes.IMPORTANCE This study developed an efficient process for bioenergy (H2 and CH4) production from WAS and elucidates the dynamics of bacterial pathogens in the process, which is important for the utilization and safe application of WAS. The study also made an attempt to combine metagenomic and qPCR analyses to reveal the dynamics of bacterial pathogens in anaerobic processes, which could overcome the limitations of each method and provide new insights regarding bacterial pathogens in environmental samples.

Anaerobic granular sludge for simultaneous biomethanation of synthetic wastewater and CO with focus on the identification of CO-converting microorganisms.

CO is a main component of syngas, which can be produced from the gasification of organic wastes and biomass. CO can be converted to methane by anaerobic digestion (AD), however, it is still challenging due to its toxicity to microorganisms and limited knowledge about CO converting microorganisms. In the present study, anaerobic granular sludge (AGS) was used for the simultaneous biomethanation of wastewater and CO. Batch experiments showed that AGS tolerated CO partial pressure as high as 0.5 atm without affecting its ability for synthetic wastewater degradation, which had higher tolerance of CO compared to suspended sludge (less than 0.25 atm) as previously reported. Continuous experiments in upflow anaerobic sludge blanket (UASB) reactors showed AGS could efficiently convert synthetic wastewater and CO into methane by applying gas-recirculation. The addition of CO to UASB reactor enhanced the hydrogenotrophic CO-oxidizing pathway, resulted in the increase of extracellular polymeric substances, changed the morphology of AGS and significantly altered the microbial community compositions of AGS. The microbial species relating with CO conversion and their functions were revealed by metagenomic analysis. It showed that 23 of the 70 reconstructed genome bins (GBs), most of which were not previously characterized at genomic level, were enriched and contained genes involved in CO conversion upon CO addition. CO-converting microorganisms might be taxonomically more diverse than previously known and have multi-functions in the AD process. The reductive tricarboxylic acid (TCA) cycle in combination with the oxidation of the CO was probably crucial for CO utilization by the majority of the GBs in the present study.

MoS2 heterostructure with tunable phase stability: strain induced interlayer covalent bond formation.

The structural phase transition in MoS2 promises applications in novel nanoelectronic devices. Elastic strain engineering can not only serve as a potential route for phase transition engineering, but also reveal potential ferroelastic behavior of MoS2 nanostructures. However, the elastic strain required for phase transition in monolayer MoS2 is far beyond its elastic limit, thus inhibiting the experimental realization. In this study, employing density functional theory calculations, we uncover that by forming heterostructure with buckled 2D materials, such as silicene, germanene and stanene, the critical phase transition strain required in monolayer MoS2 can be drastically reduced. Particularly when MoS2 forms sandwiched structures with silicene or stanene, the uniaxial and biaxial critical strain can be reduced to ∼0.06 and ∼0.03, respectively, which is well below the experimental elastic limit. This theoretical study not only proposes an experimental achievable strategy for flexible phase transition design in MoS2 nanostructure, but also identifies those MoS2 heterostructures as 2D candidates for potential shape memory devices and pseudoelasticity applications.

Methane potentials of wastewater generated from hydrothermal liquefaction of rice straw: focusing on the wastewater characteristics and microbial community compositions.

BACKGROUND: Hydrothermal liquefaction (HTL) has been well studied for the bio-oil production from biomass. However, a large amount of wastewater with high organic content is also produced during the HTL process. Therefore, the present study investigated the methane potentials of hydrothermal liquefaction wastewater (HTLWW) obtained from HTL of rice straw at different temperatures (170-320 °C) and residence times (0.5-4 h). The characteristics (e.g., total organic content, organic species, molecular size distribution, etc.) of the HTLWW were studied, and at the same time, microbial community compositions involved in AD of HTLWW were analyzed. RESULTS: The highest methane yield of 314 mL CH4/g COD was obtained from the sample 200 °C-0.5 h (HTL temperature at 200 °C for 0.5 h), while the lowest methane yield 217 mL CH4/g COD was obtained from the sample 320 °C-0.5 h. These results were consistent with the higher amounts of hard biodegradable organics (furans, phenols, etc.) and lower amounts of easily biodegradable organics (sugars and volatile fatty acids) present in sample 320 °C-0.5 h compared to sample 200 °C-0.5 h. Size distribution analysis showed that sample 320 °C-0.5 h contained more organics with molecular size less than 1 kDa (79.5%) compared to sample 200 °C-0.5 h (66.2%). Further studies showed that hard biodegradable organics were present in the organics with molecular size higher than 1 kDa for sample 200 °C-0.5 h. In contrast, those organics were present in both the organics with molecular size higher and less than 1 kDa for sample 320 °C-0.5 h. Microbial community analysis showed that different microbial community compositions were established during the AD with different HTLWW samples due to the different organic compositions. For instance, Petrimonas, which could degrade sugars, had higher abundance in the AD of sample 200 °C-0.5 h (20%) compared to sample 320 °C-0.5 h (7%). The higher abundance of Petrimonas was consistent with the higher content of sugars in sample 200 °C-0.5 h. The higher Petrimonas abundance was consistent with the higher content of sugars in sample 200 °C-0.5 h. The genus Syntrophorhabdus could degrade phenols and its enrichment in the AD of sample 320 °C-0.5 h might be related with the highest content of phenols in the HTLWW. CONCLUSIONS: HTL parameters like temperature and residence time affected the biodegradability of HTLWW obtained from HTL of rice straw. More hard biodegradable organics were produced with the increase of HTL temperature. The microbial community compositions during the AD were also affected by the different organic compositions in HTLWW samples.

iTRAQ quantitative proteomic analysis reveals the pathways for methanation of propionate facilitated by magnetite.

Methanation of propionate requires syntrophic interaction of propionate-oxidizing bacteria and hydrogenotrophic methanogens, which is referred to as interspecies electron transfer. The present study showed that 10 mg/L conductive magnetite enhanced the methane production rate from propionate by around 44% in batch experiments, and both direct interspecies electron transfer and interspecies H2 transfer were thermodynamically feasible with the addition of magnetite. The methanation of propionate facilitated by magnetite was also demonstrated in a long-term operated continuous reactor. The methane production rate from acetate by the enriched mixed culture with magnetite was higher than that without magnetite, while similar methane production rates were found from H2/CO2 by the enriched mixed culture with and without magnetite. The ability to utilize molecular H2 indicated interspecies H2 transfer played a role in the enriched culture with magnetite, and propionate-oxidizing bacteria relating with interspecies H2 transfer were also detected by metagenomic sequencing. Metagenomic sequencing analysis also showed that Thauera, possibly relating with direct interspecies electron transfer, were enriched with the addition of magnetite. iTRAQ quantitative proteomic analysis, which was used in mixed culture for the first time, showed that magnetite induced the changes of protein expression levels involved in various pathways during the methanation of propionate. The up-regulation of proteins involved in propionate metabolism were found, and they were mainly originated from propionate-oxidizing bacteria which were not reported to be capable of direct interspecies electron transfer until now. Cytochrome c oxidase was also revealed as the possible protein relating with direct interspecies electron transfer considering its up-regulation with the addition of magnetite and origination from Thauera. Most of the up-regulated proteins in methane metabolism were originated from Methanosaeta, while most of the enzymes with down-regulated proteins were originated from Methanosarcina. However, the up-regulated proteins relating with hydrogenotrophic methanogenesis were originated from neither Methanosaeta nor Methanosarcina, indicating they were not involved in direct interspecies electron transfer. The hydrogenotrophic methanogens, e.g. Methanospirillum, Methanosphaerula et al., might be involved in direct interspecies electron transfer. Overall, the present study showed that both direct interspecies electron transfer and interspecies H2 transfer were present during methanation of propionate facilitated by magnetite.

Mesophilic and thermophilic alkaline fermentation of waste activated sludge for hydrogen production: Focusing on homoacetogenesis.

The present study compared the mesophilic and thermophilic alkaline fermentation of waste activated sludge (WAS) for hydrogen production with focus on homoacetogenesis, which mediated the consumption of H2 and CO2 for acetate production. Batch experiments showed that hydrogen yield of WAS increased from 19.2 mL H2/gVSS at 37 °C and pH 10-80.1 mL H2/gVSS at 55 °C and pH 10. However, the production of volatile fatty acids (mainly acetate) was higher at 37 °C and pH 10 by comparison with 55 °C and pH 10. Hydrogen consumption due to homoacetogenesis was observed at 37 °C and pH 10 but not 55 °C and pH 10. Higher expression levels of genes relating with homoacetogenesis and lower expression levels of genes relating with hydrogen production were found at 37 °C and pH 10 compared to 55 °C and pH 10. The continuous experiment demonstrated the steady-state hydrogen yield of WAS was comparable to that obtained from batch experiments at 55 °C and pH 10, and homoacetogenesis was still inhibited. However, the steady-state hydrogen yield of WAS (6.5 mL H2/gVSS) was much lower than that (19.2 mL H2/gVSS) obtained from batch experiments at 37 °C and pH 10 due to the gradual enrichment of homoacetogens as demonstrated by qPCR analysis. The high-throughput sequencing analysis of 16S rRNA genes showed that the abundance of genus Clostridium, containing several homoacetogens, was 5 times higher at 37 °C and pH 10 than 55 °C and pH 10.

Doping-Induced Tunable Wettability and Adhesion of Graphene.

We report that substrate doping-induced charge carrier density modulation leads to the tunable wettability and adhesion of graphene. Graphene's water contact angle changes by as much as 13° as a result of a 300 meV change in doping level. Upon either n- or p-type doping with subsurface polyelectrolytes, graphene exhibits increased hydrophilicity. Adhesion force measurements using a hydrophobic self-assembled monolayer-coated atomic force microscopy probe reveal enhanced attraction toward undoped graphene, consistent with wettability modulation. This doping-induced wettability modulation is also achieved via a lateral metal-graphene heterojunction or subsurface metal doping. Combined first-principles and atomistic calculations show that doping modulates the binding energy between water and graphene and thus increases its hydrophilicity. Our study suggests that the doping-induced modulation of the charge carrier density in graphene influences its wettability and adhesion [corrected]. This opens up unique and new opportunities for the tunable wettability and adhesion of graphene for advanced coating materials and transducers.

The unexpected non-monotonic inter-layer bonding dependence of the thermal conductivity of bilayered boron nitride.

Hexagonal boron nitride (BN) and its bilayer form are very fascinating two-dimensional materials that have attracted tremendous interest recently. Their realistic applications in emerging nanoelectronics usually quest for manipulating the thermal transport properties in a precise manner. Using nonequilibrium molecular dynamics simulations, we herein studied the effect of inter-layer covalent bonding on the thermal conductivity of bilayered BN. We found that the in-plane thermal conductivity of bilayered BN, which can be largely tuned by introducing covalent bonding between the two BN layers, depends not only on the inter-layer bonding density, but also on the detailed topological configuration of the inter-layer bonds. For randomly distributed inter-layer bonding the thermal conductivity of bilayered BN decreases monotonically with inter-layer bonding density, the same behavior already found for bilayered graphene. However, for regularly arranged inter-layer bonding the thermal conductivity of bilayered BN surprisingly possesses a non-monotonic dependence on the inter-layer bonding density. This non-intuitive non-monotonic dependence is further explained by performing spectral energy density analysis, where the peak and valley values of the thermal conductivity are governed by different mechanisms. These results suggest the application of inter-layer covalent bonding in designing nanoscale devices with precisely tunable thermal conductivities.

Community dynamics of prokaryotic and eukaryotic microbes in an estuary reservoir.

This study demonstrates both prokaryotic and eukaryotic community structures and dominant taxonomies in different positions of the greatest estuary reservoir for drinking water source in the world in four seasons of one year using 454 pyrosequencing method with total of 312,949 16S rRNA and 374,752 18S rRNA gene fragments, including 1,652 bacteria OTUs and 1,182 fungus OTUs. During winter and spring, the community composition at the phylum level showed that microorganisms had similar structures but their quantities were different. Similarly, obvious changes at the genus level were observed among the samples taken in winter and spring between summer and fall. Microorganisms located the reservoir inlet were founded to be different from those in rear at both phylum and genus level. Air temperature had a stronger effect than sampling location on the microbial community structure. Total nitrogen and dissolved oxygen were algae-monitoring indicators during the whole year. Moreover, Bacillus was an efficient indicator during summer and autumn for bacteria OTUs.