Freeze-drying assisted liquid exfoliation of BiFeO_(3) for pressure sensing

Breaking up bulk crystals of functional materials into nanoscale thinner layers can lead to interesting properties and enhanced functionalities due to the size and interface effects.However,unlike the van der Waals layered crystals,many materials cannot be exfoliated into thin layers by liquid exfoliation.BiFeO_(3) is a piezoelectric ceramic material,which is commonly synthesized as bulk crystals,limiting its wider applications.In this contribution,a freeze-drying assisted liquid exfoliation method was adopted to fabricate thin-layered BiFeO_(3) nanoplates with lateral sizes of up to 500 nm and thicknesses of 10−20 nm.The freeze-drying process showed a vital role in the preparation process by imposing stress on the dispersed BiFeO_(3) crystals during the liquid-to-solid-to-gas transition of the solvent.Such stress resulted in lattice strains in the freeze-dried BiFeO_(3) crystals,which enabled their further exfoliation under subsequent ultrasonication.Considering the intrinsic piezoelectric effect of BiFeO_(3),pressure sensors based on bulk and thin-layer BiFeO_(3) were also fabricated.The pressure sensor based on BiFeO_(3) nanoplates exhibited a largely enhanced sensitivity with a wider working range than the bulk counterpart,because of the stronger piezoelectric effect induced and the extra electrical charges at abundant interlayer interfaces.We suggest that the freeze-drying assisted liquid exfoliation method can be applied to other non-van der Waals crystals to bring about more functional material systems.

Solvothermal-assisted liquid-phase exfoliation of large size and high quality black phosphorus

Black phosphorus(BP),especially for BP nanosheets,with unique layered structure among two dimensional(2D)materials has attracted much attention due to its outstanding physical properties,such as ultra-high mobility,in-plane anisotropic properties.However,the small horizontal-size of reported BP limits its applications in the integrated circuit or some functional devices.In this work,a solvothermalassisted liquid-phase exfoliation technique is firstly employed for preparing large size and high-quality BP nanosheets.In the high-polar acetonitrile solvent,solvothermal treatment weakens the Van der Waals forces of block BP.Together with the subsequently ultrasonic processing,effective exfoliation of large size and high-quality BP nanosheets are realized.The TEM,AFM and Raman results indicate that the prepared BP nanosheets are high quality with an average thickness of about 2 nm,and the horizontalsize is up to 10μm.This facile and effective method for exfoliated BP nanosheets provides a promising strategy for the exfoliation of other 2D materials.

Extensive study of optical contrast between bulk and nanoscale transition metal dichalcogenide semiconductors

A remarkable refinement in the optical behavior of two-dimensional transition metal dichalcogenides(TMDs)has been brought to light when cleaved from their respective bulks.These atomically thin direct bandgap semiconductors are highly responsive to optical energy which proposes the route for futuristic photonic devices.In this manuscript,we have substantially focused on the optical study of MoS_(2)and WS_(2)nanosheets and comparative analysis with their bulk counterparts.The synthesis of nanosheets has been accomplished with liquid exfoliation followed by fabrication of thin films with drop-casting technique.X-ray diffraction and field emission scanning electron microscopy affirmed the morphology,whereas,UV-visible spectroscopy served as the primary tool for optical analysis.It was observed that several parameters,like optical conductivity,optical band-gap energy etc.have enhanced statistics in the case of exfoliated nanosheets as compared to their respective bulks.Some researchers have touched upon this analysis for MoS_(2),but it is completely novel for WS_(2).We expect our work to clearly distinguish between the optical behaviors of nanoscale and bulk TMDs so as to intensify and strengthen the research related to 2D-layered materials for optoelectronic and photovoltaic applications.

Review of the role of ionic liquids in two-dimensional materials

Ionic liquids(ILs)are expected to be used as readily available“designer”solvents,characterized by a number of tunable properties that can be obtained by modulating anion and cation combinations and ion chain lengths.Among them,its high ionicity is outstanding in the preparation and property modulation of two-dimensional(2D)materials.In this review,we mainly focus on the ILs-assisted exfoliation of 2D materials towards large-scale as well as functionalization.Meanwhile,electric-field controlled ILs-gating of 2D material systems have shown novel electronic,magnetic,optical and superconducting properties,attracting a broad range of scientific research activities.Moreover,ILs have also been extensively applied in various field practically.We summarize the recent developments of ILs modified 2D material systems from the electrochemical,solar cells and photocatalysis aspects,discuss their advantages and possibilities as“designer solvent”.It is believed that the design of ILs accompanying with diverse 2D materials will not only solve several scientific problems but also enrich materials design and engineer of 2D materials.

Facile Exfoliation of Two-Dimensional Crystalline Monolayer Nanosheets from an Amorphous Metal-Organic Framework

The large-scale preparation ofmonolayer two-dimensional(2D)material remains a great challenge,which hinders its real-world applications.Herein,we report a novel layered metal–organic framework(MOF),IPM-1,whichwas synthesized froma cage-like organic linker,with extremely weak interlaminar interaction.When subjected to external disturbance,IPM-1 degenerated into an intermediate state between the crystalline and amorphous phase,in which the layers retain the inplane two-dimensional periodic structure but aremisaligned in the third dimension,leading to the loss of apparent porosity and crystallinity.This amorphous IPM-1 is readily exfoliated at gramscale into crystalline 2D nanosheets with a thickness of 1.15 nm,excellent thickness homogeneity,lateral size up to 10μm,and restored microporosity.IPM-1 nanosheets exhibit high chemical stability and catalytic activity in the oxidation of alcohol,combining the advantages of both homogeneous and heterogeneous catalyst.This work underscores that MOFs without apparent crystallinity can be ideal precursors for the successful preparation of 2D crystalline monolayer nanosheets.

Design and fabrication of NiFe_(2)O_(4)/few-layers WS_(2) composite for supercapacitor electrode material

Few-layers WS_(2) was obtained through unique chemical liquid exfoliation of commercial WS_(2).Results showed that after the exfoliation process,the thickness of WS_(2) reduced significantly.Moreover,the NiFe_(2)O_(4) nanosheets/WS_(2) composite was successfully synthesized through a facile hydrothermal method at 180°C,and then proven by the analyses of field emission scanning electron microscopy,X-ray diffraction,and X-ray photoelectron spectroscopy.The composite showed a high specific surface area of 86.89 m^(2)·g^(−1) with an average pore size of 3.13 nm.Besides,in the threeelectrode electrochemical test,this composite exhibited a high specific capacitance of 878.04 F·g^(−1) at a current density of 1 A·g^(−1),while in the two-electrode system,the energy density of the composite could reach 25.47 Wh·kg^(−1) at the power density of 70 W·kg^(−1) and maintained 13.42 Wh·kg^(−1) at the higher power density of 7000 W·kg^(−1).All the excellent electrochemical performances demonstrate that the NiFe_(2)O_(4) nanosheets/WS_(2) composite is an excellent candidate for supercapacitor applications.

Tunable nitrogen crafted 2D-graphene nano-hybrid from industrial expansive and ecological approach as robust cathode microporous layer to improve performance of a direct methanol fuel cell

In this work, the excess water-stagnation issue in the high current region in direct methanol fuel cells(DMFCs) is resolved by using atomic precision modulated nitrogen-crafted graphene(NG) in the cathode microporous layer by utilizing simplistic,industrial-expansive and ecological strategy. Few-layer 2D-graphene(~2–5 nm thickness) is prepared by bath sonication approach from abundant feedstock-graphite and is treated with nitric acid to yield 1.8 wt.% uniformly dispersed nitrogen containing NG. Specifically, 1:4 weight ratio NG:carbon-black(CB) hybrid architecture, displays 0.252 V in 370 mA cm^(-2) with the peak power density of 93.4 mW cm^(-2), improving cell power density by 45.6% compared with standard one at 60℃ and 1 mol/L methanol/oxygen conditions at ultra-low catalyst loadings and displaying exceptional stability. Atomic insights into NG reveal that interplay between bonding configurations, altered hydrophobic/hydrophilic porosity of graphene(10.6% less wettability from contact angle and 13.1% high electrode porosity measurements) contribute to the better mass-transport-porogenic effect(16.3% high oxygen-permeability), mildly affecting the electron pathway(6.5% reduced in-plane electrical conductivity),overall significantly improving cell performance. Altogether, this work delivers multiple advantages, i.e., the usage of material from facile, sustainable and cost-effective routes, while improving DMFC performance with potential industrial promise.

NiPS_(3)quantum sheets modified nitrogen-doped mesoporous carbon with boosted bifunctional oxygen electrocatalytic performance

Electrocatalysts for oxygen reduction reactions(ORR)and oxygen evolution reactions(OER)are highly crucial and challenging toward the energy storage and conversion technologies such as fuel cells,metal-air batteries and water electrolysis.To replace noble-metal based catalysts and boost catalytic performance of carbon-based materials,we initially develop the nickel,phospho rus,sulfur and nitrogen co-modified mesoporous carbon(NiPS_(3)@NMC)as a bifunctional oxygen electrocatalyst.The perfo rmance for ORR(half-wave potential at 0.90 V)and OER(10 mA cm^(-2)at 1.48 V)surpasses those of Pt/C coupled with IrO_(2)catalysts and most of the non-precious metal based bifunctional electrocatalysts reported in related literature.Moreover,the electrochemical durability is also confirmed by accelerated durability tests(ADTs)and long-term chronoamperometry(CA)tests.We demonstrated that the interfacial effect between NiPS_(3)quantum sheets(QS s)and NMC substrates by thermal activation contributed to the enhanced oxygen electrode bifunctionality with more active sites,due to the electrons-donating from nickel,phosphorus and sulfur elements and relatively enriched pyridinic type N.Such excellent overall performance highlights the potential application of NiPS3 QSs and NMC composites as the materials on energy conversion and storage.

Review of fabrication methods of large-area transparent graphene electrodes for industry

Graphene is a two-dimensional material showing excellent properties for utilization in transparent electrodes;it has low sheet resistance,high optical transmission and is flexible.Whereas the most common transparent electrode material,tin-doped indium-oxide(ITO)is brittle,less transparent and expensive,which limit its compatibility in flexible electronics as well as in low-cost devices.Here we review two large-area fabrication methods for graphene based transparent electrodes for industry:liquid exfoliation and low-pressure chemical vapor deposition(CVD).We discuss the basic methodologies behind the technologies with an emphasis on optical and electrical properties of recent results.State-of-the-art methods for liquid exfoliation have as a figure of merit an electrical and optical conductivity ratio of 43.5,slightly over the minimum required for industry of 35,while CVD reaches as high as 419.

High yield production of ultrathin fibroid semiconducting nanowire of Ta2Pd3Se8

Immediately after the demonstration of the high-quality electronic properties in various two dimensional(2D)van der Waals(vdW)crystals fabricated with mechanical exfoliation,many methods have been reported to explore and control large scale fabrications.Comparing with recent advancements in fabricating 2D atomic layered crystals,large scale production of one dimensional(1D)nanowires with thickness approaching molecular or atomic level still remains stagnant.Here,we demonstrate the high yield production of a 1D vdW material,semiconducting Ta2Pd3Se8 nanowires,by means of liquid-phase exfoliation.The thinnest nanowire we have readily achieved is around 1 nm,corresponding to a bundle of one or two molecular ribbons.Transmission electron microscopy(TEM)and transport measurements reveal the as-fabricated Ta2Pd3Se8 nanowires exhibit unexpected high crystallinity and chemical stability.Our low-frequency Raman spectroscopy reveals clear evidence of the existing of weak inter-ribbon bindings.The fabricated nanowire transistors exhibit high switching performance and promising applications for photodetectors.