Ultrathin two-dimensional materials for photo- and electrocatalytic hydrogen evolution

Sustainable hydrogen production via photocatalytic, electrocatalytic, and synergetic photoelectrocatalytic processes has been regarded as an effective strategy to address both energy and environmental crises. Due to their unique structures and properties, emerging ultrathin two-dimensional (2D) materials can bring about promising opportunities to realize high-efficiency hydrogen evolution. This review presents a critical appraisal of advantages and advancements for ultrathin 2D materials in catalytic hydrogen evolution, with an emphasis on structure–activity relationship. Furthermore, strategies for tailoring the microstructure, electronic structure, and local atomic arrangement, so as to further boost the hydrogen evolution activity, are discussed. Finally, we also present the existing challenges and future research directions regarding this promising field.     

Interface affected zone for optimal strength and ductility in heterogeneous laminate

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The core-shell structured Fe-based amorphous magnetic powder cores with excellent magnetic properties

The Fe-based soft magnetic amorphous powder cores (AMPCs) with excellent comprehensive magnetic properties were successfully designed and fabricated using the core-shell structured FeSiBCCr/TiO₂ composite powders. The influence of the concentration of water (H₂O) for the magnetic performance of the AMPCs has been systematically studied based on careful analysis of the process of nucleation and growth of TiO₂ under different H₂O concentration in the reaction system. The growth process for the TiO₂ coating layer with the H₂O concentration in the range of 0.01–0.02 ml/g corresponds to the heterogeneous nucleation phase, while the mixing phase of heterogeneous and homogeneous nucleation occurs when the concentration of H₂O increases to 0.03 ml/g. Optimized soft magnetic properties have been achieved for the AMPCs with H₂O concentration of 0.02 ml/g, including high permeability of 81.5 with a high frequency stability up to 10 MHz, high quality factor of 102 at 530 kHz, low core loss of 42 mW/cm³ at 500 kHz for B_m = 0.01 T, and better DC-bias property of 52% at a bias field of 100 Oe due to the uniform and proper thickness insulation coating layer, which can be used to produce miniature magnetic components for applications in medium and high-frequency fields.     

Energy transduction ferroic materials

Ferroic materials and multiferroics, characterized by their ferroic orders, provide an efficient route for the coupling control of magnetic, mechanical, and electrical subsystems in energy transduction, which aims at converting one form of energy into another. A surge of interest in the ferroic coupling effect has stemmed from its potential use as a new versatile route for energy transduction. Here, the recent progress on the use of (multi)ferroic materials is reviewed, with special emphasis on the fundamental mechanisms that dictate the energy transduction process, including piezoelectricity, pyroelectricity, electrocaloric, magnetostriction, magnetocaloric, elastocaloric, magnetoelectricity, and emerging spin-charge conversion. Research on energy transduction ferroic materials paves the way for ubiquitous energy harvesting through magneto-mechano-electric-thermal coupling mechanisms. Finally, a summary and the future prospective directions of this field are discussed.     

Fluid eddy induced piezo-promoted photodegradation of organic dye pollutants in wastewater on ZnO nanorod arrays/3D Ni foam

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Direct Z-scheme photocatalysts: Principles,synthesis, and applications

The properly designed semiconductor photocatalysts are promising materials for solving the current serious energy and environmental issues because of their ability of using sunlight to stimulate various photocatalytic reactions. Especially, the constructed direct Z-scheme photocatalysts, mimicking the natural photosynthesis system, possess many merits, including increased light harvesting, spatially separated reductive and oxidative active sites, and well-preserved strong redox ability, which benefit the photocatalytic performance. This review concisely compiles the recent progress in the fabrication, modification, and major applications of the direct Z-scheme photocatalysts; the latter include water splitting, carbon dioxide reduction, degradation of pollutants, and biohazard disinfection. It finishes with a brief presentation of future challenges and prospects in the development of direct Z-scheme photocatalytic systems.     

Effect of 2–6 at.% Mo addition on microstructural evolution of Ti-44Al alloy

In order to understand the effect of Mo alloying on the microstructural evolution of TiAl alloy, the as-cast microstructure, heat treated microstructure characteristic, and hot compression microstructure evolution of Ti-44 A1 alloy have been studied in this work. The as-cast microstructure morphology changes from(γ+α_2)lamellar colony and β/β_0+γ mixture structure to β/β_0 phase matrix widmannstatten structure,when Mo content increases from 2 at.% to 6 at.%. Affected by the relationship between β phase and αphase, the angles between the lamellar orientation and the block β/β_0 phase are roughly at 0°, 45° and90°. Comparing with heat treatment microstructure, the hot compression microstructure contains lessβ/β_0 phase, however, the β/β_0 phase containing 2 Mo alloy and 3 Mo alloy hot compressed at 1275 ℃ has the inverse tendency. In addition,(α_2 +γ) colony is decomposed by the discontinuous transformation.     

Piezoelectric properties in two-dimensional materials: Simulations and experiments

The piezoelectric effect, discovered in 1880 by Jacques and Pierre Curie, effectively allows to transduce signals from the mechanical domain to the electrical domain and vice versa. For this reason, piezoelectric devices are already ubiquitous, including, for instance, quartz oscillators, mechanical actuators with sub-atomic resolution and microbalances. However, the ability to synthesize two-dimensional (2D) materials may enable the fabrication of innovative devices with unprecedented performance. For instance, many materials which are not piezoelectric in their bulk form become piezoelectric when reduced to a single atomic layer; moreover, since all the atoms belong to the surface, piezoelectricity can be effectively engineered by proper surface modifications. As additional advantages, 2D materials are strong, flexible, easy to be co-integrated with conventional integrated circuits or micro-electromechanical systems and, in comparison with bulk or quasi-1D materials, easier to be simulated at the atomistic level. Here, we review the state of the art on 2D piezoelectricity, with reference to both computational predictions and experimental characterization. Because of their unique advantages, we believe 2D piezoelectric materials will substantially expand the applications of piezoelectricity.     

Practical strategy to produce ultrafine ceramic glaze: Introducing a polycarboxylate grinding aid to the grinding process

In this work, a polycarboxylate comb-like polymer was used as grinding aid for ceramic slurry, and the effect of addition of this grinding aid on ceramic process property was highlighted. The grinding efficiency of the polycarboxylate grinding aid (PG) in terms of the particle size distribution and specific surface of unit volume of the ceramic slurry being ground were investigated. Consequently, the PG that was synthesized via free radical polymerization under the condition of an APEG/AA/MA molar ratio of 0.3:1:1, an initiator dosage of 5 wt%, and a reaction time of 6 h at 90 °C, provided better grinding efficiency than those of the triethanolamine and other commercial grinding aids. Specifically, with a dosage of 0.21% and 2 h of grinding, the d₉₇ and d₅₀ of ceramic slurry decreased from 13.956 μm and 2.043 µm to 3.739 µm and 0.561 µm, respectively. The cumulative distribution, frequency distribution and SEM results exhibited a uniform particle size distribution for ceramic ground with PG-C. Furthermore, the sintering experiment indicated that a lower processing temperature was capable of producing ultrafine ceramic. These improvements indicated the potential application of the PG as an efficiency ceramic grinding aid, which further facilitating the preparation of uniform ultrafine slurry by a sand mill.     

Controllable preparation of antimony powders by electrodeposition in choline chloride-ethylene glycol

Antimony powders with different morphologies have been prepared by electrodeposition at 313–353 K and 10–50 mA·cm^?2 in 0.1 mol·L^?1 SbCl₃ + ChCl-EG solution. The electrochemical behavior of Sb(III) on titanium electrode are studied by cyclic voltammetry. Results show that the electrochemical reduction of Sb(III) in SbCl₃ + ChCl-EG solution is a quasi-reversible process via a one-step reaction and the apparent activation energy is 50.723 kJ·mol^?1. The effects of current density and temperature on current efficiency and specific energy consumption are also investigated. The current efficiency increases with the increasing of current density and temperature. The specific energy consumption increased with the increase of current density, while decreased with the raising of temperature. When the current density is 40 mA·cm^?2 at 353 K, the current efficiency and specific energy consumption are up to 97.89% and 1251.277 kW·h·t^?1, respectively. The morphology and phase of the products are analyzed by FESEM and XRD. It demonstrates that the deposition products are pure antimony powders and their preferred crystal plane is (0 1 2). The pineal, wheat grain, badminton, dendritic, and cluster-like antimony powders can be prepared by controlling electrodeposition parameters. The particles size range of antimony powders are 0.21–261.05 μm.     

Synthesis of porous nanododecahedron Co3O4/C and its application for nonenzymatic electrochemical detection of nitrite

Porous nanododecahedron of Co₃O₄/C has been synthesized by calcination of the ZIF-67 in air at 400 °C and then be used as electrode material for fabricating a highly sensitive and low overpotential sensor of nitrite ion (NO₂^?). The structure and morphology characterization show that ZIF-67 behaves as an ideal sacrificial template for preparing Co₃O₄/C with regular shape. The two components of Co₃O₄ and carbon are uniformly distributed in the composite. Electrochemical analysis shows that the excellent electrocatalysis performance toward the oxidation of NO₂^? is based on the synergy of Co₃O₄ and carbon in the nanocomposite. At NO₂^? concentration from 2 nM to 8 mM, a fast response time within 3 s is revealed and 1.21 nM of detection limit is achieved. The sensor is also reliable to analysis of NO₂^? existed in the real samples of soil leaching liquid and macrophage supernate.     

Mechanochemical synthesis of BiSI and Bi19S27I3 semiconductor materials

With regard to the intensive investigations of bismuth oxyhalides as promising photocatalysts, much expectation may be put on the corresponding chalcohalides but little is known due to difficulty in the synthesis. In this report, BiSI and Bi₁₉S₂₇I₃ were synthesized by one-step mechanochemical method without heating and aqueous operations and the products were characterized by X-ray diffraction crystallography, Raman spectroscopic analysis, X-ray photoelectron spectroscopy analysis, photoluminescence spectra and UV–visible DRS. The new method allowed the simple syntheses of pure bismuth chalcohalides without observable existences of impurity phases. The crystal structures of BiSI and Bi₁₉S₂₇I₃ were orthorhombic, with the absorption band gaps of 1.80 and 1.14 eV for BiSI and Bi₁₉S₂₇I₃, respectively. Bi-rich compound is considered to be beneficial to the photochemical property of chalcohalides. After overcoming the difficulty in the synthesis, our research would offer new strategy to exploit the potentials of V-VI-VII compounds, particularly of sulfides, as promising semiconductors to compete the corresponding counterparts of oxides.     

Keystroke dynamics enabled authentication and identification using triboelectric nanogenerator array

Cyber security has become a serious concern as the internet penetrates every corner of our life over the last two decades. The rapidly developing human–machine interfacing calls for an effective and continuous authentication solution. Herein, we developed a two-factor, pressure-enhanced keystroke-dynamics-based security system that is capable of authenticating and even identifying users through their unique typing behavior. The system consists of a rationally designed triboelectric keystroke device that converts typing motions into analog electrical signals, and a support vector machine (SVM) algorithm-based software platform for user classification. This unconventional keystroke device is self-powered, stretchable and water/dust proof, which makes it highly mobile and applicable to versatile working environments. The promising application of this novel system in the financial and computing industry can push cyber security to the next level, where leaked passwords would possibly be of no concern.     

Recent advances in emerging 2D nanomaterials for biosensing and bioimaging applications

The great success of graphene throws new light on discovering more two-dimensional (2D) layered nanomaterials that stem from atomically thin 2D sheets. Compared with a single element of graphene, emerging graphene-like 2D materials composed of multiple elements that possess more versatility, greater flexibility and better functionality with a wide range of potential applications. In this review, we provide insights into the rapidly emerging 2D materials and their biosensing and bioimaging applications in recent three years, including 2D transition metal nanomaterials, graphitic nitride materials, black phosphorus, and emerging 2D organic polymers. We first briefly highlight their unique 2D morphology and physicochemical properties and then focus on their recent applications in electrochemical biosensing, optical biosensing and bioimaging. The challenges and some thoughts on future perspectives in this field are also addressed.     

Enhanced photocatalytic degradation performance of organic contaminants by heterojunction photocatalyst BiVO4/TiO2/RGO and its compatibility on four different tetracycline antibiotics

Photocatalytic performance of four tetracycline antibiotics using BiVO₄/TiO₂/RGO composites was investigated. To make full use of catalysis, optimum preparation conditions involved RGO content, solution pH and hydrothermal temperature on the structure forming of BiVO₄/TiO₂/RGO composites were investigated. Subsequently, the obtained visible light-driven photocatalyst was used to degrade four kinds of tetracycline antibiotics involved tetracycline (TC), chlortetracycline (CTC), oxytetracycline (OTC) and doxycycline (DXC) for wastewater treatment. Results showed that BiVO₄/TiO₂/RGO photocatalyst exhibited excellent photocatalytic activity and high compatibility due to the enhanced separation efficiency of photo-generated carriers with high reduction and oxidation capability. The degradation process of four kinds of tetracycline antibiotics was traced and detected through identifying intermediates produced in the reaction system. And a possible catalytic mechanism for BiVO₄/TiO₂/RGO photocatalyst was put forward based on band gap structure of BiVO₄ and TiO₂.     

Computational design and property predictions for two-dimensional nanostructures

Recent success in isolating and growing various two-dimensional (2D) materials with intriguing properties has pushed forward the search for new 2D nanostructures with novel properties. Current experimental trial-and-error methods face the fundamental challenges of low efficiency and a lack of clear guidelines. In contrast, based on state-of-the-art first-principles calculations and well-developed structural prediction algorithms, computational simulations can not only predict an increasing number of new 2D materials with desirable properties but also suggest their possible synthesis routes. Among them, many predictions, such as the growth of monolayer boron sheets (borophene), piezoelectricity in molybdenum disulfide (MoS₂), ferroelectricity in tin telluride (SnTe), topological defects in transition metal dichalcogenides, Dirac cones in borophene, and high carrier mobility and mobility anisotropy in black phosphorene, have been verified by experiments, showing the accuracy of computational approaches, as well as their power in facilitating experimental exploration in 2D flatland. To date, the rapid expansion in theoretical work has generated a large number of very important results, but the overall picture of recent progress, current challenges, and future opportunities is rarely discussed. Accordingly, this review aims at providing information about current trends and future perspectives for 2D materials research. To achieve this, the review is organized as follows: (1) discussion of structural predictions in 2D materials using borophene as an example; (2) predictions of the electronic, optical, mechanical, and magnetic properties in various 2D materials; (3) discussion of the influence of defects on the structures and properties of 2D materials; and (4) evaluation of current progress in computational simulations and perspectives for future development.     

Light-induced ultrafast proton-coupled electron transfer responsible for H2 evolution on silver plasmonics

Light-driven proton-coupled electron transfer (PCET) reactions on nanoplasmonics would bring temporal control of their reactive pathways, in particular, prolong their charge separation state. Using a silver nano-hybrid plasmonic structure, we observed that optical excitation of Ag-localized surface plasmon instigated electron injection into TiO₂ conduction band and oxidation of isopropanol alcoholic functionality. Femtosecond transient infrared absorption studies show that electron transfer from Ag to TiO₂ occurs in ca. 650?fs, while IPA molecules near the Ag surface undergo an ultrafast bidirectional PCET step within 400?fs. Our work demonstrates that ultrafast PCET reaction plays a determinant role in prolonging charge separation state, providing an innovative strategy for visible-light photocatalysis with plasmonic nanostructures.     

Investigation on flow characteristics of ice slurry in horizontal 90° elbow pipe by a CFD-PBM coupled model

Elbow pipes are important components for ice slurry pipeline transport. However, the flow characteristics of ice slurry in elbow are far from fully being understood, especially the influence of ice particle kinetics on ice particle size distribution (PSD). This study is intended to provide a better understanding of the behavior of ice slurry flow in elbow pipe. A CFD-PBM coupled model is employed to investigate the flow characteristics of ice slurry in horizontal 90° elbow pipe. The quadrature method of moments is utilized to solve the population balance equations. Based on the revised model, the flow characteristics of ice slurry in the horizontal 90° elbow pipe are investigated. The simulation results show that in the range of calculations, the pressure drop of elbow pipe is increased with the increase of velocity and ice packing fraction (IPF). An adverse pressure gradient is formed due to the change in flow direction. The emergence of secondary flow is caused by the centrifugal force. It makes the ice particles gather on the outer wall of the elbow section. The ice diameter increases along the flow direction due to the aggregation. The evolution of particle size distribution (PSD) is not significant. However, aggregation and stratification cannot be ignored in the process of long distance transport of ice slurry. The results are of significance for guiding the safety design and operation of ice slurry transportation.     

Eggshell nano-particle potential for methyl violet and mercury ion removal: Surface study and field application

A nano-scale sorbent was produced from eggshell wastes for sorption of Hg(II) and methyl violet (MV) from aqueous solutions and real wastewaters. The properties of the nano-particles were fully determined using SEM, DLS, FTIR, XRD, BET, TGA, AFM, EDAX, mapping, and TEM analyses. The adsorbent structure mainly contained carbonate and silica. The effects of influential parameters including temperature, contact time, initial contaminants concentration, sorbent dose, and initial pH on the removal efficiency were investigated. The maximum sorption efficiency of Hg(II) and MV occurred at pH of 6 and 9 and temperatures of 25 °C and 55 °C, respectively. Freundlich model could be interpreted the equilibrium data of the sorption process of both contaminants. The maximum sorption capacity of Hg(II) and MV using eggshell nano-particles was obtained as 116.27 mg/g and 123.45 mg/g, respectively. The dynamic behavior of the process was studied using two kinetic models. The sorption system performance was also examined and t_1/2 were determined as 4.34 min for Hg(II) and 4.97 min for MV. The sorption process of Hg(II) and MV was exothermic and endothermic, respectively. Effective sorption after seven cycles and successful treatment of landfill leachate and textile wastewater with eggshell nano-particles confirms its adequacy.     

Study on decolorization of Rhodamine B by raw coal fly ash catalyzed Fenton-like process under microwave irradiation

Coal fly ash (CFA) catalyzed Fenton-like process was studied under microwave (MW) irradiation for the decolorization of Rhodamine B (RhB) wastewater. The physical-chemical properties of CFA were characterized, including the specific surface area, micromorphology, chemical and crystal components, and the distribution and chemical valence of metallic elements. The metallic oxidants in the CFA indicate CFA can work as Fenton-like catalyst and MW-absorbent simultaneously. The results reveal OH is more significant in the decolorization of RhB than HO₂ and O₂^?. The generation of more OH in the MW-Fenton-like process (293–326 K) than that in the conventional heated Fenton-like process (326 K) reflects the function of hot spot effect and possible non-thermal effect of MW. Under the optimum condition ([H₂O₂] 2 mmol L^?1, [CFA] 15 g L^?1, pH 3, P_MW 0.1 kW), the decolorization rate reaches 91.6% after 20 min. The intrinsic kinetic model of RhB decolorization is $-\frac{\mathrm{d}{C}_{\mathrm{R}\mathrm{h}\mathrm{B}}}{\mathit{dt}}={1.76\times 10}^{-4}·C_{\mathrm{R}\mathrm{h}\mathrm{B}}·C_{{\mathrm{H}}_2{\mathrm{O}}_2}^{1.89}·C_{\mathrm{C}\mathrm{F}\mathrm{A}}^{1.97}-\mathrm{d}{\mathrm{C}}_{\mathrm{R}\mathrm{h}\mathrm{o}\mathrm{d}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{B}}/\mathrm{d}\mathrm{t}=1.76\times {10}^{-4}·{\mathrm{C}}_{\mathrm{R}\mathrm{h}\mathrm{o}\mathrm{d}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{B}}·{\mathrm{C}}_{{\mathrm{H}}_2{\mathrm{O}}_2}^{1.89}·{\mathrm{C}}_{\mathrm{c}\mathrm{o}\mathrm{a}\mathrm{l}\mathrm{f}\mathrm{l}\mathrm{y}\mathrm{a}\mathrm{s}\mathrm{h}}^{1.97}$. The loss of catalytic metallic elements causes the decline of catalytic capacity of CFA. The energy consumption (4313.3 kW·h kg^?1 RhB) is a limitation for the MW-Fenton-like process, which can be overcame by the safe application of nuclear energy. The intermediates and the path of RhB decolorization were detected and proposed, respectively.