Characterization of Various Noncovalent Polyphenol-Starch Complexes and Their Prebiotic Activities during In Vitro Digestion and Fermentation.

This study explores the structural characterization of six noncovalent polyphenol-starch complexes and their prebiotic activities during in vitro digestion and fermentation. Ferulic acid, caffeic acid, gallic acid, isoquercetin, astragalin, and hyperin were complexed with sweet potato starch (SPS). The polyphenols exhibited high binding capacity (>70%) with SPS. A partial release of flavonoids from the complexes was observed via in vitro digestion, while the phenolic acids remained tightly bound. Molecular dynamics (MD) simulation revealed that polyphenols altered the spatial configuration of polysaccharides and intramolecular hydrogen bonds formed. Additionally, polyphenol-SPS complexes exerted inhibitory effects on starch digestion compared to gelatinized SPS, owing to the increase in resistant starch fraction. It revealed that the different complexes stimulated the growth of Lactobacillus rhamnosus and Bifidobacterium bifidum, while inhibiting the growth of Escherichia coli. Moreover, in vitro fermentation experiments revealed that complexes were utilized by the gut microbiota, resulting in the production of short-chain fatty acids and a decrease in pH. In addition, the polyphenol-SPS complexes altered the composition of gut microbiota by promoting the growth of beneficial bacteria and decreasing pathogenic bacteria. Polyphenol-SPS complexes exhibit great potential for use as a prebiotic and exert dual beneficial effects on gut microbiota.

Structural, in vitro digestion, and fermentation characteristics of lotus leaf flavonoids.

Bioaccessibility and bioactivity of flavonoids in lotus leaves are related to their characteristics in gastrointestinal digestion and colonic fermentation. The aim of this study is to investigate the stability of lotus leaf flavonoids (LLF) in simulated gastrointestinal digestion, and its modulation on gut microbiota in vitro fermentation. Results showed that LLF mainly consisted of quercetin-3-O-galactoside, quercetin-3-O-glucuronide, quercetin-3-O-glucoside, and kaempferol-3-O-glucoside. These flavonoids kept stability with only a small fraction degraded in simulated gastric and intestinal fluids. In vitro fermentation, LLF stimulated the growth of Actinobacteria and Firmicutes, inhibited the growth of Proteobacteria, and induced the production of fermentation gases and short-chain fatty acids. Interestingly, supplementation of soluble starch significantly improved the utilization of LLF by the intestinal flora. These results revealed that LLF shaped a unique biological web with Lactobacillus and Bifidobacterium spp. as the core of the biological network, which would be more beneficial to gut health.

Sonoprocessing of wetting of SiC by liquid Al: A thermodynamic and kinetic study.

The sonoprocessing of droplet spreading during the wetting process of molten aluminum droplets on SiC ceramic substrates at 700 °C is investigated in this paper. When wetting is assisted by a 20 kHz frequency ultrasonic field, the wettability of liquid metal gets enhanced, which has been determined by the variations in thermodynamic energy and wetting kinetics. Wetting kinetic characteristics are divided into two stages according to pinning and depinning states of substrate/droplet contact lines. The droplet is static when the contact line is pinning, while it is forced to move when the contact line is depinning. When analyzing the pinning stage, high-speed photography reveals the evidence of oxide films being rapidly crushed outside the aluminum droplet. In this work, atomic models of spherical Al core being wrapped by alumina shell are tentatively built, whose dioxide microstructures are being transformed from face-centered cubic into liquid at the atomic scale. At the same time, the wetting experiment reveals that the oxide films show changes in the period of sonoprocessing from 3rd to 5th second. During the ultrasonic spreading behavior in the late stage, there is a trend of evident expansion of the base contact area. The entire ultrasonic process lasts for no longer than 10 s. With the aid of ultrasonic sinusoidal waves, the wettability of metal Al gets a rapid improvement. Both molecular dynamic (MD) investigations and the experiments results reveal that the precursor film phenomenon is never found unless wetting is assisted by ultrasonic treatments. However, the precursor film appears near the triple line after using ultrasonics in the droplet wetting process, whose formation is driven by ultrasonic oscillations. Due to the precursor film, the ultrasonic wetting contact angle is lower than the non-ultrasonic contact angle. In addition, the time-variant effective ultrasonic energy has been quantitatively evaluated. The numerical expressions of thermodynamic variables are well verified by former ultrasonic spreading test results, which altogether provide an intrinsic explanation of the fast-decreasing contact angle of Al/SiC.

Atomic-scale imaging of CH3NH3PbI3 structure and its decomposition pathway.

Understanding the atomic structure and structural instability of organic-inorganic hybrid perovskites is the key to appreciate their remarkable photoelectric properties and understand failure mechanism. Here, using low-dose imaging technique by direct-detection electron-counting camera in a transmission electron microscope, we investigate the atomic structure and decomposition pathway of CH3NH3PbI3 (MAPbI3) at the atomic scale. We successfully image the atomic structure of perovskite in real space under ultra-low electron dose condition, and observe a two-step decomposition process, i.e., initial loss of MA+ followed by the collapse of perovskite structure into 6H-PbI2 with their critical threshold doses also determined. Interestingly, an intermediate phase (MA0.5PbI3) with locally ordered vacancies can robustly exist before perovskite collapses, enlightening strategies for prevention and recovery of perovskite structure during the degradation. Associated with the structure evolution, the bandgap gradually increases from ~1.6 eV to ~2.1 eV. In addition, it is found that C-N bonds can be readily destroyed under irradiation, releasing NH3 and HI and leaving hydrocarbons. These findings enhance our understanding of the photoelectric properties and failure mechanism of MAPbI3, providing potential strategies into material optimization.

A Simple High Power, Fast Response Streaming Potential/Current-Based Electric Nanogenerator Using a Layer of Al2O3 Nanoparticles.

Harvesting energy from ambient moisture and natural water sources is currently of great interest due to the need for standalone self-powered nano/micro-systems. In this work, we report on the development of a cost-effective nanogenerator based on a carbon paper-Al2O3 nanoparticle layer-carbon paper (CAC) sandwich structure, where the 3D Al2O3 layer is deposited via vacuum filtration. This type of device can produce an open-circuit voltage (UOC) of up to 4 V and a short-circuit current (ISC) of ∼18 µA with only an 8 µL water droplet applied. To our knowledge, this is the highest voltage yet reported from a single moisture/water-induced electricity nanogenerator using solid oxides and carbon-based materials. A remarkable output power of 14.8 µW can be reached with an optimized resistive load. An LED with a working voltage of 3-3.2 V can operate for a short time with the power from a single CAC device exposed to one 8 µL water droplet. Furthermore, a CAC generator adsorbing as little as 2 µL water droplets every 3 min can also give a UOC of 3.63 V. We show that CAC devices provide a robust electrical output over more than 200 wet-dry cycles without any deterioration in performance. These units demonstrate much promise as cost-effective electricity generators for harvesting energy from natural sources like rainwater, tap water, snow runoff, and dew. The response time of CAC devices can be as fast as 10-100 ms, making them ideal for applications as self-powered water detectors. The generation of power in this device arises from the streaming current. To assist in the optimization of these devices, we have analyzed how their response is related to such factors as layer thickness, time interval between application of water droplets, and the volume of each water droplet.

Antimony nanocrystals self-encapsulated within bio-oil derived carbon for ultra-stable sodium storage.

Integrating carbon-coating and nanostructuring has been considered as the most promising strategy to accommodate the dramatic volume expansion represented by high-capacity antimony (Sb) upon sodiation. Suitable coating source and synthetic strategy that are both economical and strong are yet to be explored. In this regard, by using renewable bio-oil as carbon source and self-wrapping precursor, robust Sb@C composite anode with Sb nanoparticles homogeneously impregnated into the cross-linked 2D ultrathin carbon nanosheets is developed via a facile NaCl template-assisted self-assembly and followed carbothermal reduction method. Such judiciously crafted interconnected macroporous framework can mitigate of mechanical stress and alleviate the volume change of inner Sb, guaranteeing high-performance sodium-ion battery anode. At a current density of 0.1 A g-1, ultrahigh reversible capacity of 520 mAh g-1 can be achieved. Notably, a stable capacity of 391 mAh g-1 is even retained after 500 cycles at 1 A g-1. Such a facile and cost-effective synthetic method is promising for high-performance sodium-ion batteries.

Surface activation towards manganese dioxide nanosheet arrays via plasma engineering as cathode and anode for efficient water splitting.

Developing high-efficiency, low-cost electrocatalysts for water splitting is important but challenging. Two-dimensional nanosheet manganese dioxide (MnO2) arrays are promising candidates for the design and development of advanced catalysts because of their large surface area. Here, a feasible solution to improve the catalytic activity of MnO2 materials via decorating the active sites on the surface is proposed. With the help of plasma engineering, we successfully enabled surface activity of the MnO2 nanosheets by decorating P or Fe species together with rich vacancies on the surface. The decorated P (P-MnO2) or Fe (Fe-MnO2) species were highly beneficial for the absorption of protons and OH- respectively, and rich oxygen vacancies induced the formation of stable Mn3+, which contributed to electron and charge transfer. Thus, increased electrochemically active specific areas, accelerated charge transfer, and a proper surface electronic structure could be achieved. On the basis of this activation strategy, the fabricated P-MnO2 and Fe-MnO2 showed excellent catalytic performance for the hydrogen evolution and oxygen evolution reactions. To our knowledge, the performance of P-MnO2 and Fe-MnO2 outperformed most MnO2-based electrocatalysts in the field of electrocatalytic water splitting. Surface activation of two-dimensional MnO2 materials by decorating active species via plasma treatment can provide a feasible route for modulating the performance of earth-abundant electrocatalysts for practical applications.

Direct Observation of Li Migration into V5S8: Order to Antisite Disorder Intercalation Followed by the Topotactic-Based Conversion Reaction.

Two-dimensional transition-metal dichalcogenides hold great potential in rechargeable lithium-ion batteries. Their electrochemical properties are closely related to the structural evolutions during lithium-ion migration. Understanding these migration/reaction mechanisms is important to help improve battery performance. Herein, we report the real-time and atomic-scale observation of phase transitions during the lithiation and delithiation for V5S8 via in situ electron diffraction and high-resolution transmission electron microscopy techniques. We find that the phase transformation proceeds via a sequence of order to antisite disorder intercalation and topotactic-based conversion reaction. During the intercalation reaction, the lithium ion destroys the orderings of the interstitial V with the formation of Li/V antisite. Such a reaction is found to be reversible, i.e., the extraction of lithium from LixV5S8 leads to the recovery of V orderings. The conversion reaction involves heterogeneous nucleation of Li2S with 3-20 nm nanodomains, which maintain the crystallographic integrity with LixV5S8. These findings elucidate the complex interactions between the lithium ion and host V5S8 during ionic migration in solids, which should be helpful in understanding the relationship between phase transformation kinetics and battery performance.

General Decomposition Pathway of Organic-Inorganic Hybrid Perovskites through an Intermediate Superstructure and its Suppression Mechanism.

Organic-inorganic hybrid perovskites (OIHPs) have generated considerable excitement due to their promising photovoltaic performance. However, the commercialization of perovskite solar cells (PSCs) is still plagued by the structural degradation of the OIHPs. Here, the decomposition mechanism of OIHPs under electron beam irradiation is investigated via transmission electron microscopy, and a general decomposition pathway for both tetragonal CH3 NH3 PbI3 and cubic CH3 NH3 PbBr3 is uncovered through an intermediate superstructure state of CH3 NH3 PbX2.5 , X = I, Br, with ordered vacancies into final lead halides. Such decomposition can be suppressed via carbon coating by stabilization of the perovskite structure framework. These findings reveal the general degradation pathway of OIHPs and suggest an effective strategy to suppress it, and the atomistic insight learnt may be useful for improving the stability of PSCs.

Fe doped Ni5P4 nanosheet arrays with rich P vacancies via phase transformation for efficient overall water splitting.

Proper vacancy engineering is considered as a promising strategy to improve intrinsic activity, but it is challenging to construct rich vacancies by a simple strategy. Herein, Fe doped Ni5P4 nanosheet arrays with rich P vacancies are developed via a facile phase transformation strategy. Based on systematic investigations, we have demonstrated that an optimized surface electronic structure, abundant active sites and improved charge transport capability can be effectively achieved by vacancy engineering. Consequently, Fe doped Ni5P4 with rich vacancies show remarkable catalytic performances with 94.5 mV for the hydrogen evolution reaction (HER) and 217.3 mV for the oxygen evolution reaction (OER) at 10 mA cm-2, respectively, as well as good durability. When directly employed as working electrodes, the as-obtained Fe doped Ni5P4 with rich vacancies can attain 10 mA cm-2 at a low voltage of 1.59 V. This work demonstrates a feasible strategy for rationally fabricating electrocatalysts with rich vacancies via a simple phase transformation.

Engineering Se vacancies to promote the intrinsic activities of P doped NiSe2 nanosheets for overall water splitting.

Element doping is a general and effective approach to modify the electrocatalytic performances, but the low intrinsic activity in each electroactive site still limits the further improvements. Herein, we provide an effective strategy by simultaneously introducing P doping and Se vacancies to enhance the intrinsic activities in NiSe2 nanosheet arrays (A-NiSe2|P) through Ar plasma treatment. Owing to the increased active sites and enhanced electrical conductivity, the resulted A-NiSe2|P shows the enhanced hydrogen evolution performances. Theoretical calculations reveal that introduction of Se vacancies plays a significant role in lowering the adsorption free energy of H* in Ni, Se and P sites, leading to promoted intrinsic activities in A-NiSe2|P. Further, A-NiSe2|P as bifunctional electrocatalysts only needs 1.62 V to reach 10 mA cm-2 for overall water splitting. Our study and understanding of A-NiSe2|P may highlight the importance of element doping and vacancies in enhancing the catalytic activities in overall water splitting.

Metallization and Diffusion Bonding of CoSb3-Based Thermoelectric Materials.

CoSb3-based skutterudite alloy is one of the most promising thermoelectric materials in the middle temperature range (room temperature-550 °C). However, the realization of an appropriate metallization layer directly on the sintered skutterudite pellet is indispensable for the real thermoelectric generation application. Here, we report an approach to prepare the metallization layer and the subsequent diffusion bonding method for the high-performance multi-filled n-type skutterudite alloys. Using the electroplating followed by low-temperature annealing approaches, we successfully fabricated a Co-Mo metallization layer on the surface of the skutterudite alloy. The coefficient of thermal expansion of the electroplated layer was optimized by changing its chemical composition, which can be controlled by the electroplating temperature, current and the concentration of the Mo ions in the solution. We then joined the metallized skutterudite leg to the Cu-Mo electrode using a diffusion bonding method performed at 600 °C and 1 MPa for 10 min. The Co-Mo/skutterudite interfaces exhibit extremely low specific contact resistivity of 1.41 µΩ cm2. The metallization layer inhibited the elemental inter-diffusion to less than 11 µm after annealing at 550 °C for 60 h, indicating a good thermal stability. The current results pave the way for the large-scale fabrication of CoSb3-based thermoelectric modules.

Microstructure Evolution and Mechanical Properties of Melt Spun Skutterudite-based Thermoelectric Materials.

The rapid solidification of melt spinning has been widely used in the fabrication of high-performance skutterudite thermoelectric materials. However, the microstructure formation mechanism of the spun ribbon and its effects on the mechanical properties are still unclear. Here, we report the microstructure evolution and mechanical properties of La-Fe-Co-Sb skutterudite alloys fabricated by both long-term annealing and melt-spinning, followed by sintering approaches. It was found that the skutterudite phase nucleated directly from the under-cooled melt and grew into submicron dendrites during the melt-spinning process. Upon heating, the spun ribbons started to form nanoscale La-rich and La-poor skutterudite phases through spinodal decomposition at temperatures as low as 473 K. The coexistence of the micron-scale grain size, the submicron-scale dendrite segregation and the nanoscale spinodal decomposition leads to high thermoelectric performance and mechanical strength. The maximum three-point bending strength of the melt spinning sample was about 195 MPa, which was 70% higher than that of the annealed sample.

Plasma-induced surface reorganization of porous Co3O4-CoO heterostructured nanosheets for electrocatalytic water oxidation.

Herein, porous Co3O4-CoO heterostructured nanosheets are constructed by plasma treatment. The density-functional theory calculations demonstrate that constructing Co3O4-CoO heterostructures modify the electronic structure to achieve enhanced electrical conductivity, but also boost the charge transfer to realize enhanced surface reactivity. Contributing to the short ion diffusion path, the rich electroactive surface sites and enhanced charge transfer capability, the resulting Co3O4-CoO nanosheet arrays possess the low overpotential of 270 mV at 10 mA cm-2 and the low Tafel slope of 49 mV dec-1. This work provides a novel strategy to construct heterostructured nanosheet arrays by surface reorganization for cost-effective OER electrocatalyst.

Joining Alumina and Sapphire by Growing Aluminium Borate Whiskers In-Situ, and the Whiskers' Orientation Relationship with the Sapphire Substrate.

Bonding between polycrystal alumina and sapphire with (0001), (10 1 ¯ 0), (11 2 ¯ 0), (1 1 ¯ 02) orientations is successfully achieved by growing aluminium borate whiskers in the joint. The morphology of the whiskers in the joint is characterised by (Scanning Electron Microscopy) SEM. The relationship between the growing direction of the aluminium borate whiskers and the orientation of the sapphire substrate is investigated. The effect of the growing direction of the aluminium borate whiskers on the mechanical properties of the joint is discussed. The results show that the whiskers on the sapphire with (10 1 ¯ 0) orientation grow perpendicular to the surface of the substrate while the whiskers show a random growth on the other substrates. It is found that there is an orientation relationship between the whiskers (220) and sapphire (10 1 ¯ 0) and the morphology of the whiskers has great influence on the mechanical properties of the joint. The joint between polycrystal alumina and sapphire with (10 1 ¯ 0) orientation exhibits the highest strength, which reaches 26 MPa.

Constructing MoS2/CoMo2S4/Co3S4 nanostructures supported by graphene layers as the anode for lithium-ion batteries.

With the increasing energy demand, it is very urgent to develop new anode materials for lithium ion batteries (LIBs). Designing nanostructures and constructing multicomponent metal sulfides are vital for enhancing the electrochemical performance. This study reports a new synthetic method to construct MoS2/CoMo2S4/Co3S4 nanostructures supported by graphene. A key step in the process, high temperature annealing, promotes the interdiffusion of metal sulfides to form multicomponent metal sulfides and establishes a strong C-S bond between the MoS2/CoMo2S4/Co3S4 nanostructure and graphene. The unique nanostructure and synergistic effects between the conductive graphene and the MoS2/CoMo2S4/Co3S4 nanostructure endows the material with good lithium storage. As a result, it exhibits a good rate performance (360 mA h g-1 at 10 A g-1) and a high specific capacity (770 mA h g-1 at 0.2 A g-1). This study provides a unique method to construct promising anode materials for the application of LIBs.

Rich P vacancies modulate Ni2P/Cu3P interfaced nanosheets for electrocatalytic alkaline water splitting.

Constructing well-defined interfaces is vital to improve the electrocatalytic properties, but the studies on transition-metal-interface electrocatalysts with rich vacancies are rarely reported. Here, rich P vacancies to modulate Ni2P/Cu3P interfaced nanosheets for overall water splitting is demonstrated. We conduct a series of experimental parameters to adjust the nanostructures of Ni2P/Cu3P, and to get insight into the synergistic effects of interfaces and P vacancies on the catalytic activities. Notably, Ni2P/Cu3P with rich P vacancies shows the lowest overpotential requirements of 88 and 262 mV at 10 mA cm-2 towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The good activity is ascribed to abundant electroactive sites, electric field effect at the interfaces and tuning the electron structure by P vacancies. In addition, as bifunctional electrode, Ni2P/Cu3P with rich P vacancies allows for a low water-splitting voltage of 1.60 V at 10 mA cm-2. This work may open up a new route for efficient electrocatalysts through the synergistic effects of interfaces and vacancies.

Transmission electron microscopy of organic-inorganic hybrid perovskites: myths and truths.

Organic-inorganic hybrid perovskites (OIHPs) have attracted extensive research interest as a promising candidate for efficient and inexpensive solar cells. Transmission electron microscopy (TEM) characterizations that can benefit the fundamental understanding and the degradation mechanism are widely used for these materials. However, their sensitivity to the electron beam illumination and hence structural instabilities usually prevent us from obtaining the intrinsic information or even lead to significant artifacts. Here, we systematically investigate the structural degradation behaviors under different experimental factors to reveal the optimized conditions for TEM characterizations of OIHPs by using low-dose electron diffraction and imaging techniques. We find that a low temperature (-180 °C) does not slow down the beam damage but instead induces a rapid amorphization for OIHPs. Moreover, a less severe damage is observed at a higher accelerating voltage. The beam-sensitivity is found to be facet-dependent that a (1 0 0) exposed CH3NH3PbI3 (MAPbI3) surface is more stable than a (0 0 1) surface. With these guidance, we successfully acquire the atomic structure of pristine MAPbI3 and identify the characterization window that is very narrow. These findings are helpful to guide future electron microscopy characterizations of these beam-sensitive materials, which are also useful for finding strategies to improve the stability and performance of the perovskite solar cells.

In situ synthesis of core-shell vanadium nitride@N-doped carbon microsheet sponges as high-performance anode materials for solid-state supercapacitors.

Vanadium nitride (VN) with high conductivity exhibits the potential promising as anode materials for supercapacitors, but VN suffered the obvious performance fading due to the dissolution of VN in aqueous electrolyte. In this work, we solve these problems through realizing 3D structural VN microsheets shelled with N-doped carbon layer (VN@NC) by introducing melamine as nitrogen source and PVP as carbon source. The as-prepared VN@NC electrode display high capacitance of 368 F g-1 and good rate property. A solid-state asymmetric supercapacitor (ASC) with NiCo2O4 nanowires as cathode materials and VN@NC as anode materials was fabricated. The ASC device exhibits the high energy density of 65.3 W h kg-1, and good cycling stability (92% capacitance retention) after 4000 cycles. Moreover, the ASC device shows good mechanical flexibility with negligible capacitance loss after 1000 bending cycles.

A free-standing manganese cobalt sulfide@cobalt nickel layered double hydroxide core-shell heterostructure for an asymmetric supercapacitor.

Rational design of self-supported electrode materials is important to develop high-performance supercapacitors. Herein, a free-standing MnCo2S4@CoNi LDH (MCS@CN LDH) core-shell heterostructure is successfully prepared on Ni foam using the hydrothermal reaction and electrodeposition. In this architecture, the inner MnCo2S4 nanotube provides an ultra-high electrical conductivity and the CoNi LDH nanosheets can offer more electrochemical active sites for better faradaic reactions. Moreover, the core-shell heterostructure can also maintain the structural integrity during the processes of continuous charge/discharge. The MCS@CN LDH electrode displays a satisfactory specific capacitance of 1206 C g-1 and excellent cycling performance with ∼92% retention after 10 000 cycles. In addition, an asymmetric supercapacitor (ASC), in which MCS@CN LDH and N-doped rGO are used as the positive electrode and the negative electrode, was assembled which exhibits an energy density of 48.8 W h kg-1 with superior cycling stability, indicating the potential of this electrode in practical energy storage.