Showing papers by "Hua Zhang published in 2019"

Recent Progress in Graphene-Based Noble-Metal Nanocomposites for Electrocatalytic Applications.

Abstract: The fast industrialization process has led to global challenges in the energy crisis and environmental pollution, which might be solved with clean and renewable energy. Highly efficient electrochemical systems for clean-energy collection require high-performance electrocatalysts, including Au, Pt, Pd, Ru, etc. Graphene, a single-layer 2D carbon nanosheet, possesses many intriguing properties, and has attracted tremendous research attention. Specifically, graphene and graphene derivatives have been utilized as templates for the synthesis of various noble-metal nanocomposites, showing excellent performance in electrocatalytic-energy-conversion applications, such as the hydrogen evolution reaction and CO2 reduction. Herein, the recent progress in graphene-based noble-metal nanocomposites is summarized, focusing on their synthetic methods and electrocatalytic applications. Furthermore, some personal insights on the challenges and possible future work in this research field are proposed.

MOF-Based Hierarchical Structures for Solar-Thermal Clean Water Production.

Abstract: Solar-thermal water evaporation, as a promising method for clean water production, has attracted increasing attention. However, solar water evaporators that exhibit both high water vapor generation ability and anti-oil-fouling ability have not been reported. Here, a unique metal-organic-framework-based hierarchical structure, referred to as MOF-based hierarchical structure (MHS), is rationally designed and prepared, which simultaneously displays a high solar absorption and a superhydrophilic and underwater superoleophobic surface property. As a proof-of-concept application, a device prepared from the MHS can achieve a high solar-thermal water evaporation rate of 1.50 kg m-2 h-1 under 1 sun illumination. Importantly, the MHS also possesses an excellent anti-oil-fouling property, ensuring its superior water evaporation performance even in oil-contaminated water. The high solar-thermal water evaporation rate and anti-oil-fouling property make the MHS a promising material for the solar-thermal water production.

Ultrasensitive 2D Bi2O2Se Phototransistors on Silicon Substrates

Abstract: 2D materials are considered as intriguing building blocks for next-generation optoelectronic devices. However, their photoresponse performance still needs to be improved for practical applications. Here, ultrasensitive 2D phototransistors are reported employing chemical vapor deposition (CVD)-grown 2D Bi2 O2 Se transferred onto silicon substrates with a noncorrosive transfer method. The as-transferred Bi2 O2 Se preserves high quality in contrast to the serious quality degradation in hydrofluoric-acid-assisted transfer. The phototransistors show a responsivity of 3.5 × 104 A W-1 , a photoconductive gain of more than 104 , and a time response in the order of sub-millisecond. With back gating of the silicon substrate, the dark current can be reduced to several pA. This yields an ultrahigh sensitivity with a specific detectivity of 9.0 × 1013 Jones, which is one of the highest values among 2D material photodetectors and two orders of magnitude higher than that of other CVD-grown 2D materials. The high performance of the phototransistor shown here together with the developed unique transfer technique are promising for the development of novel 2D-material-based optoelectronic applications as well as integrating with state-of-the-art silicon photonic and electronic technologies.

Surface-charge-mediated Formation of H-TiO2@Ni(OH)2 Heterostructures for High-Performance Supercapcitors

Abstract: Supercapacitors or ultracapacitors are promising for efficient energy storage applications, owing to their high power density, high charge-discharge rates, and long cycle life performance. To achieve this goal, a large specific surface area, an high electronic conductivity and a fast cation intercalation de-intercalation process are generally required in the design and preparation of materials for high-performance supercapacitors. Recently, core-shell heterostructures with multifunctionalities are regarded as one of promising materials for supercapacitors or ultracapacitors applications. In particular, one-dimensional (1D) core-shell heterostructures have sparked great scientific and technological interests due to their high versatility and applicability as the essential components in nanoscale electronics, catalysis, chemical sensing, and energy conversion storage devices. Various metal metal oxide, metal metal, metal oxide metal oxide and metal oxide conductive polymers so far have been investigated. Transition metal hydroxide oxide Co3O4, Co(OH)2, MnO2, Mn(OH)2, NiO, Ni(OH)2 and their compounds storing energy by surface faradaic (redox) reactions were generally integrated with conducting scaffold to build core-shell structure. Intensive studies show that an enlarged active surface area of transition metal hydroxide oxide enables a promoted surface redox reaction and enhanced electrochemical performance. Therefore, controllable synthesis of a hierarchically porous construction with high surface areas is critically important for energy storage.

Self-gating in semiconductor electrocatalysis

Abstract: The semiconductor–electrolyte interface dominates the behaviours of semiconductor electrocatalysis, which has been modelled as a Schottky-analogue junction according to classical electron transfer theories. However, this model cannot be used to explain the extremely high carrier accumulations in ultrathin semiconductor catalysis observed in our work. Inspired by the recently developed ion-controlled electronics, we revisit the semiconductor–electrolyte interface and unravel a universal self-gating phenomenon through microcell-based in situ electronic/electrochemical measurements to clarify the electronic-conduction modulation of semiconductors during the electrocatalytic reaction. We then demonstrate that the type of semiconductor catalyst strongly correlates with their electrocatalysis; that is, n-type semiconductor catalysts favour cathodic reactions such as the hydrogen evolution reaction, p-type ones prefer anodic reactions such as the oxygen evolution reaction and bipolar ones tend to perform both anodic and cathodic reactions. Our study provides new insight into the electronic origin of the semiconductor–electrolyte interface during electrocatalysis, paving the way for designing high-performance semiconductor catalysts. The semiconductor–electrolyte interface dominates the behaviour of semiconductor electrocatalysts. Inspired by ion-controlled electronics a universal self-gating phenomenon is now proposed to explain transport modulation during electrocatalytic reaction.

Synthesis of PdM (M = Zn, Cd, ZnCd) Nanosheets with an Unconventional Face-Centered Tetragonal Phase as Highly Efficient Electrocatalysts for Ethanol Oxidation

Abstract: Recently, crystal-phase engineering has been emerging as a promising strategy to tune the physicochemical properties of noble metal catalysts and further improve their catalytic performance. However, the synthesis of noble metal catalysts with an unconventional crystal phase as well as desired composition and morphology still remains a great challenge. Herein, a series of PdM (M = Zn, Cd, ZnCd) nanosheets (NSs) with thickness less than 5 nm have been synthesized via a facile one-pot wet-chemical method. In particular, different from the conventional face-centered cubic (fcc) phase, PdM NSs possess an unconventional face-centered tetragonal (fct) phase. As a proof-of-concept application, the fct PdZn NSs exhibit significantly enhanced mass activity and stability in ethanol oxidation reaction, compared to the pure Pd NSs and commercial Pd black catalyst.

Synergistic additive-mediated CVD growth and chemical modification of 2D materials.

Abstract: Research on 2D materials has recently become one of the hottest topics that has attracted broad interdisciplinary attention. 2D materials offer fascinating platforms for fundamental science and technological explorations at the nanometer scale and molecular level, and exhibit diverse potential applications for future advanced nano-photonics and electronics. The chemical vapor deposition (CVD) technique has shown great promise for producing high-quality 2D materials with superior electro-optical performance. However, it is difficult to synthesize continuous single-crystal 2D materials with large domain sizes and good uniformity due to the low vapor pressure of their precursors. It has been observed that the addition of selected synergistic additives to the CVD process under mild conditions can result in uniformly large-area and highly crystalline monolayer 2D materials with exceptional optical/electrical properties. Moreover, the 2D material-based devices chemically modified by synergistic additives can achieve superior performances compared to those previously reported. In this review, we compare several typical synergistic additive-mediated CVD growth processes of 2D materials, as well as their superior properties, and provide some perspectives and challenges for the future of this emerging research field.

The Dominant Energy Transport Pathway in Halide Perovskites: Photon Recycling or Carrier Diffusion?

Abstract: Photon recycling and carrier diffusion are the two plausible processes that primarily affect the carrier dynamics in halide perovskites, and therefore the evaluation of the performance of their photovoltaic and photonic devices. However, it is still challenging to isolate their individual contributions because both processes result in a similar emission redshift. Herein, it is confirmed that photon recycling is the dominant effect responsible for the observed redshifted emission. By applying one- and two-photon confocal emission microscopy on Ruddlesden–Popper type 2D perovskites, of which interplane carrier diffusion is strictly suppressed, the substantial PL redshift (72 meV) is well reproduced by the photon transport model. A comparison of 3D bulk CH3NH3PbBr3 single crystal to 2D perovskite by depth-resolved two-photon PL spectra reveals the contribution of carrier diffusion on energy transport at a distance beyond diffusion length is constantly negligible, though the carrier diffusion indeed exists in the 3D crystal. The investigation resolves the fundamental confusion and debate surrounding the issue and provides significant insights into carrier kinetics in perovskites, which is important for future developments in solar cells and other optoelectronic devices.

Progressively Exposing Active Facets of 2D Nanosheets toward Enhanced Pseudocapacitive Response and High-Rate Sodium Storage.

Abstract: Sodium-ion batteries are gradually regarded as a prospective alternative to lithium-ion batteries due to the cost consideration. Here, three kinds of tin (IV) sulfide nanosheets are controllably designed with progressively exposed active facets, leading to beneficial influences on the Na+ storage kinetics, resulting in gradient improvements of pseudocapacitive response and rate performance. Interestingly, different forms of kinetics results are generated accompanying with the morphology and structure evolution of the three nanosheets. Finally, detailed density functional theory simulations are also applied to analyze the above experimental achievements, proving that different exposed facets of crystalline anodes possess dissimilar Na+ storage kinetics. The investigation experiences and conclusions shown in this work are meaningful to explore many other proper structure design routes toward the high-rate and stable metal-ions storage.

Optical and electrical properties of two-dimensional palladium diselenide

Abstract: © 2019 Author(s). Two-dimensional (2D) noble-metal dichalcogenides exhibit exceptionally strong thickness-dependent bandgaps, which can be leveraged in a wide variety of device applications. A detailed study of their optical (e.g., optical bandgaps) and electrical properties (e.g., mobilities) is important in determining potential future applications of these materials. In this work, we perform detailed optical and electrical characterization of 2D PdSe2 nanoflakes mechanically exfoliated from a single-crystalline source. Layer-dependent bandgap analysis from optical absorption results indicates that this material is an indirect semiconductor with bandgaps of approximately 1.37 and 0.50 eV for the monolayer and bulk, respectively. Spectral photoresponse measurements further confirm these bandgap values. Moreover, temperature-dependent electrical measurements of a 6.8-nm-thick PdSe2 flake-based transistor show effective electron mobilities of 130 and 520 cm2 V-1 s-1 at 300 K and 77 K, respectively. Finally, we demonstrate that PdSe2 can be utilized for short-wave infrared photodetectors. A room-temperature specific detectivity (D) of 1.8 × 1010 cm Hz1/2 W-1 at 1 μm with a band edge at 1.94 μm is achieved on a 6.8-nm-thick PdSe2 flake-based photodetector.

Heterostructured TiO2 Spheres with Tunable Interiors and Shells toward Improved Packing Density and Pseudocapacitive Sodium Storage

Abstract: Insertion-type anode materials with beneficial micro- and nanostructures are proved to be promising for high-performance electrochemical metal ion storage. In this work, heterostructured TiO2 shperes with tunable interiors and shells are controllably fabricated through newly proposed programs, resulting in enhanced pseudocapacitive response as well as favorable Na+ storage kinetics and performances. In addition, reasonably designed nanosheets in the extrinsic shells are also able to reduce the excess space generated by hierarchical structure, thus improving the packing density of TiO2 shperes. Lastly, detailed density functional theory calculations with regard to sodium intercalation and diffusion in TiO2 crystal units are also employed, further proving the significance of the surface-controlled pseudocapacitive Na+ storage mechanism. The structure design strategies and experimental results demonstrated in this work are meaningful for electrode material preparation with high rate performance and volume energy density.

Aging amorphous/crystalline heterophase PdCu nanosheets for catalytic reactions.

Abstract: Phase engineering is arising as an attractive strategy to tune the properties and functionalities of nanomaterials. In particular, amorphous/crystalline heterophase nanostructures have exhibited some intriguing properties. Herein, the one-pot wet-chemical synthesis of two types of amorphous/crystalline heterophase PdCu nanosheets is reported, in which one is amorphous phase-dominant and the other one is crystalline phase-dominant. Then the aging process of the synthesized PdCu nanosheets is studied, during which their crystallinity increases, accompanied by changes in some physicochemical properties. As a proof-of-concept application, their aging effect on catalytic hydrogenation of 4-nitrostyrene is investigated. As a result, the amorphous phase-dominant nanosheets initially show excellent chemoselectivity. After aging for 14 days, their catalytic activity is higher than that of crystalline phase-dominant nanosheets. This work demonstrates the intriguing properties of heterophase nanostructures, providing a new platform for future studies on the regulation of functionalities and applications of nanomaterials by phase engineering.

Quest for p-Type Two-Dimensional Semiconductors.

Abstract: Two-dimensional (2D) semiconductors have demonstrated great potential in modern nanotechnologies across a variety of research fields, including (opto-)electronics, spintronics, and electro-/photocatalysis. Interestingly, the vast majority of 2D semiconductors, such as the widely explored transition-metal dichalcogenides, are n-type or ambipolar. The search for p-type 2D semiconductors in the past decade has succeeded in identifying only a few promising candidate materials. In this Perspective, we discuss various strategies to obtain p-type conduction in normally n-type or ambipolar 2D semiconductors and, more importantly, the direct synthesis of p-type 2D semiconductors such as black phosphorus, 2D tellurium, and, most recently, α-MnS.

Stiff micelle-crosslinked hyaluronate hydrogels with low swelling for potential cartilage repair.

Abstract: Pluronic F127 diacrylate (F127DA) nano-micelle crosslinked methacrylated hyaluronic acid (MeHA) hydrogels (NMgels) with strong compressive properties have been demonstrated in our previous study. The current study further focuses on how the F127DA micelles and long-term swelling affect the mechanical performance of hydrogels from the view of in vitro/in vivo applications. Co-contributions of the F127DA micelles and MeHA to the compression performance are first investigated through mechanical analysis and cyclic loading/unloading tests before and after swelling. The optimized NMgel with F127DA micelles of 15 wt% and MeHA of 1.5 wt% (F15H1.5) exhibits a low swelling ratio and a well-maintained network in pH = 7.4 phosphate buffered saline. The abundant hydration significantly affects the initial mechanical properties of the hydrogels. After swelling, the compressive strength, modulus and fracture energy of F15H1.5 NMgel decrease from ∼3.44 MPa, ∼312 kPa and ∼407.5 kJ m-3 to 0.59 MPa, ∼55 kPa, and ∼81.8 kJ m-3, respectively. The energy dissipation of the first loading-unloading cycle dramatically decreases from ∼21.5 kJ m-3 to ∼6.0 kJ m-3 as well. Nevertheless, the gel still retains excellent stiffness, toughness and self-recovery due to the dense and strong micelle linkages. In vivo studies show that the implantation of F15H1.5 hydrogel in thyroid cartilage defects of rabbit larynx effectively promotes the regeneration of cartilage after 8 weeks. These results indicate that the stiff NMgel is a promising cartilage tissue engineering scaffold for the regeneration of cartilage in vivo.

Effect of pre-existing {101¯2} extension twins on mechanical properties, microstructure evolution and dynamic recrystallization of AZ31 Mg alloy during uniaxial compression

Abstract: AZ31 Mg alloy plates were pre-compressed at room temperature along the transverse direction (TD) to introduce { 10 1 ¯ 2 } extension twinning. Mechanical properties, microstructure evolution and dynamic recrystallization (DRX) mechanisms of twinned samples containing pre-existing twins during uniaxial compression were investigated and compared to those of as-received samples. The results indicated that compared to that of as-received sample compressed along the rolling direction (RD), the yield stress of twinned sample was dramatically increased at from room temperature to 200 °C. In contrast, when compressing along the normal direction (ND), the yield stress of twinned sample was greatly decreased at from room temperature to 200 °C. With the further increase of temperature, the as-received and twinned samples exhibited similar compression flow curves and obvious DRX had taken place. Continuous dynamic recrystallization (CDRX) was the main DRX mechanism in the as-received sample compressed along ND at 200 °C. Twin assisted DRX besides CDRX was also initiated in the as-received sample compressed along RD and in the twinned sample compressed along ND or RD at 200 °C. DRX mechanism was changed to discontinuous dynamic recrystallization (DDRX) in the as-received and twinned samples with the further increase of temperature.

In-plane anisotropic properties of 1T′-MoS2 layers

Abstract: Crystal phases play a key role in determining the physicochemical properties of a material. To date, many phases of transition metal dichalcogenides have been discovered, such as octahedral (1T), distorted octahedral (1T'), and trigonal prismatic (2H) phases. Among these, the 1T' phase offers unique properties and advantages in various applications. Moreover, the 1T' phase consists of unique zigzag chains of the transition metals, giving rise to interesting in-plane anisotropic properties. Herein, the in-plane optical and electrical anisotropies of metastable 1T'-MoS2 layers are investigated by the angle-resolved Raman spectroscopy and electrical measurements, respectively. The deconvolution of J1 and J2 peaks in the angle-resolved Raman spectra is a key characteristic of high-quality 1T'-MoS2 crystal. Moreover, it is found that its electrocatalytic performance may be affected by the crystal orientation of anisotropic material due to the anisotropic charge transport.

Elemental Segregation in Multimetallic Core-Shell Nanoplates.

Abstract: In this work, we report an element segregation phenomenon in two-dimensional (2D) core-shell nanoplates, subsequently resulting in the formation of yolk-cage nanostructures after selective electrochemical etching. By using PtCu nanoplates as templates, PtCu@Pd core-shell nanoplates are formed. Interestingly, during the growth of Ru on the PtCu@Pd core-shell nanoplates, due to the selective element diffusion, PtCuPd@PdCu@Ru nanoplates are obtained. After selectively etching of PdCu in PtCuPd@PdCu@Ru using electrochemical method, the PtCuPd@Ru yolk-cage nanostructures are obtained. As a proof-of-concept application, this unique nanostructure shows superior electrocatalytic activity and stability toward the methanol oxidation reaction as compared to the PtCu nanoplates and commercial Pt/C catalyst.

Bioaccumulation and Health Risk Assessment of Heavy Metals in the Soil–Rice System in a Typical Seleniferous Area in Central China

Abstract: Heavy metals are rich in seleniferous areas; however, the bioaccumulation and health risk of heavy metals are poorly understood, given the fact that selenium (Se) can inhibit the phytotoxicity and bioavailability of many heavy metals. The present study investigated the bioaccumulation of heavy metals in the soil-rice system in the Enshi seleniferous area of central China. Soils were contaminated by Mo, Cu, As, Sb, Zn, Cd, Tl, and Hg caused by the weathering of Se-rich shales. Among these heavy metals, Cd and Mo had the highest bioavailability in soils. The bioavailable fractions of Cd and Mo accounted for 41.84 and 10.75% of the total Cd and Mo in soils, respectively. Correspondingly, much higher bioaccumulation factors (BAFs) of Cd (0.34) and Mo (0.46) were found in rice, compared with those of other heavy metals (Zn 0.16, Cu 0.05, Hg 0.04, and Sb 0.0002). For the first time-to our knowledge-we showed that the uptake of Hg, Cd, and Cu by rice could be inhibited by the presence of Se in the soil. The probable daily intake (PDI) of Se, Cd, Mo, Zn, and Cu through consumption of local rice was 252 ± 184, 314 ± 301, and 1774 ± 1326 μg/d; and 7.4 ± 1.68 and 0.87 ± 0.35 mg/d, respectively. The high hazard quotients (HQs) of Mo (1.97 ± 1.47) and Cd (5.22 ± 5.02) suggested a high risk of Cd and Mo for Enshi residents through consumption of rice. Environ Toxicol Chem 2019;38:1577-1584. © 2019 SETAC.

Synthesis of MoX 2 (X = Se or S) monolayers with high-concentration 1T′ phase on 4H/fcc-Au nanorods for hydrogen evolution

Abstract: Controlled synthesis of transition metal dichalcogenide (TMD) monolayers with unusual crystal phases has attracted increasing attention due to their promising applications in electrocatalysis. However, the facile and large-scale preparation of TMD monolayers with high-concentration unusual crystal phase still remains a challenge. Herein, we report the synthesis of MoX2 (X = Se or S) monolayers with high-concentration semimetallic 1T′ phase by using the 4H/face-centered cubic (fcc)-Au nanorod as template to form the 4H/fcc-Au@MoX2 nanocomposite. The concentrations of 1T′ phase in the prepared MoSe2 and MoS2 monolayers are up to 86% and 81%, respectively. As a proof-of-concept application, the obtained Au@MoS2 nanocomposite is used for the electrocatalytic hydrogen evolution reaction (HER) in acid medium, exhibiting excellent performance with a low overpotential of 178 mV at the current density of 10 mA/cm2, a small Tafel slope of 43.3 mV/dec, and excellent HER stability. This work paves a way for direct synthesis of TMD monolayers with high-concentration of unusual crystal phase for the electrocatalytic application.

Microbiome and Metabolome Analyses of Milk From Dairy Cows With Subclinical Streptococcus agalactiae Mastitis-Potential Biomarkers.

Abstract: The microbial ecosystem in the udders of dairy cows directly influences the flavor and quality of milk. However, to our knowledge, no published research has analyzed the complex relationship between the udder microbiome and its associated metabolism in animals with subclinical mastitis. We identified the bacterial species and measured relative population numbers in the milk of cows with subclinical Streptococcus agalactiae mastitis (GBS) and compared this information to that from the milk of healthy cows. Metabolite profiles were determined to investigate correlations between the milk microbiota and metabolic factors in healthy vs. GBS dairy cows. Six milk samples from GBS cows and six from healthy cows were subjected to 16S rRNA gene sequencing to identify the microbial species using a MiSeq high-throughput sequencing apparatus. The metabolites present in the milk were identified by gas chromatography time-of-flight mass spectrometry. Both principal component analysis and orthogonal partial least squares discriminant analysis indicated that the metabolites were well-separated from each other in the milk samples from the two groups. GBS dramatically altered microbial diversity, and the GBS group had significantly fewer Proteobacteria, Actinobacteria, and Acidobacteria than the CON group, with greater relative abundance of Firmicutes (p < 0.01). Several bacterial genera, such as Streptococcus, were significantly more abundant in milk from the GBS group than in milk from the CON group, and there was a tendency for greater abundance of Turicibacter (p = 0.07) and Enterococcus spp. (p = 0.07) in the GBS group. The levels of five milk metabolites were significantly higher in the GBS group than in the CON group: phenylpyruvic acid, the homogentisic acid: 4-hydroxyphenylpyruvic acid ratio, the xanthine: guanine ratio, uridine and glycerol. Metabolic pathway analysis of the different metabolites revealed that the following were enriched in both groups: galactose metabolism; pentose and glucuronate interconversion; starch and sucrose metabolism; alanine, aspartate and glutamate metabolism; arginine biosynthesis; citrate cycle (TCA cycle); D-glutamine and D-glutamate metabolism; and the neomycin, kanamycin, and gentamicin biosynthesis pathways. Several typical metabolites were highly correlated with specific ruminal bacteria, such as Streptococcaceae, Lachnospiraceae, Lactobacillaceae and Corynebacteriaceae, demonstrating the functional correlations between the milk microbiome and associated metabolites. These findings revealed that the milk microbiota and metabolite profiles were significantly different between the two groups of cows, raising the question of whether the microbiota associated with the bovine mammary gland could be related to mammary gland health. There was also a relationship between milk quality and the presence of spoilage bacteria. Other bacterial taxa should be investigated, as related information may provide insights into how perturbations in milk metabolomics profiles relate to differences in milk synthesis between healthy cows and those with subclinical mastitis.