2D Ultrathin Nanosheets Research Articles

High-Performance Broadband Photoelectrochemical Photodetectors Based on Ultrathin Bi2O2S Nanosheets.

Two-dimensional (2D) bismuth oxychalcogenide (Bi2O2X, X refers to S, Se, and Te) is one type of rising semiconductor with excellent electrical transport properties, high photoresponse, and good air stability. However, the research on 2D Bi2O2S is limited. In this work, ultrathin Bi2O2S nanosheets are synthesized by a facile and eco-friendly chemical synthesis method at room temperature. The thickness and lateral sizes are 2-4 nm and 20-40 nm, respectively. The 2D ultrathin Bi2O2S nanosheets have a broad absorption spectrum from ultraviolet (UV) to near-infrared (NIR). Photoelectrochemical (PEC) photodetectors based on 2D Bi2O2S nanosheets are fabricated by a simple drop-casting method. The 2D Bi2O2S-based PEC photodetectors show excellent photodetection performance with a broad photoresponse spectrum from 365 to 850 nm, a high responsivity of 13.0 mA/W, ultrafast response times of 10/45 ms, and good long-term stability at a bias voltage of 0.6 V, which are superior to most 2D material-based PEC photodetectors. Further, the 2D Bi2O2S PEC photodetector can function as a high-performance self-powered broadband photodetector. Moreover, the photoresponse performance can be effectively tuned by the concentration and the kind of electrolyte. Our results demonstrate that 2D Bi2O2S nanosheets hold great promise for application in high-performance optoelectronic devices.

Interfacial polarization regulation of ultrathin 2D nanosheets inducing high energy storage density of polymer-based nanocomposite with opposite gradient architecture

High discharge energy density (Udis) has been achieved via regulating the interfacial polarization of ultra-thin 2D Sr2Nb2O7 nanosheets (SNO NSs) and constructing opposite gradient architecture. To further increase the dielectric constant (εr) of SNO NSs and therefore motivate high interfacial polarization, core-shell structured 2D nanosheets include Sr2Nb2O7@TiO2 NSs and Sr2Nb2O7@BaTiO3 NSs are successfully prepared and utilized as fillers in poly(vinylidene fluoride) (PVDF)/ polymethyl methacrylate (PMMA) blend polymer matrix (BPM). In addition, opposite gradient architecture, include high polarization layer (PL), high insulating layer (IL) filled with large size BN nanosheets (BN NSs) and middle transition layer, are constructed to depress the electric breakdown strength (Eb) degradation. As expected, the SNO@BTO NSs filled films with an optimal composition achieve excellent Udis of 32.51 J cm−3 with charge-discharge efficiency (η) of 0.64 near the Weibull Eb of 651.52 MV m−1. This Udis value is the most prominent in dielectric polymer nanocomposites under equivalent applied electrical field. The opposite gradient architecture can effectively depress the Eb degradation by preventing the electric trees evolution, which is confirmed by finite element simulations. This work provides a novel paradigm to fabricate high Udis energy storage polymer-based nanocomposites filled with 2D nanofillers.

Composite Membrane of Poly(vinylidene fluoride) and 2D Ni(OH)2 Nanosheets for High-Performance Lithium-Ion Battery

For the first time, we explored the possibility of utilizing 2D nickel hydroxide nanosheets (NHNs) to prepare NHN/poly(vinylidene fluoride) composite membranes for battery separator applications. The effect of these ultrathin 2D nanosheets on the morphology, crystallization behaviors, porosity, electrolyte uptake ratio, ionic conductivity, and thermal stability of the composite membranes were systematically investigated. A low filler content of only 3 wt % NHNs into PVDF membranes not only promoted superior thermal stability (1.9% shrinkage at 130 °C for 0.5 h) but also led to a significant increase of β-phase content (85.0%), electrolyte affinity (327.6% uptake ratio), and ionic conductivity (1.5 mS cm–1). Strong interfacial interactions between 2D NHNs and polymer molecular chains are responsible for significant α to β crystalline phase conversion, benefiting to high ionic conductivity and electrochemical performance of cells. Moreover, in order to gain more insights for battery applications, this membrane was assembled and evaluated in Li/LiFePO4 half-cells, showing a good cycling performance and rate capability, with a capacity retention of 95.9% after 100 cycles at 2 C and a high specific capacity of 129.1 mAhg–1 at 2 C. Thus, this NHN/PVDF composite membrane could be a promising separator for next generation lithium-ion batteries requiring high safety and ultrafast rechargeability.

Defect engineering of ultrathin 2D nanosheet BiOI/Bi for enhanced photothermal-catalytic synergistic bacteria-killing

Optical antibacterial agents present great potential in eliminating infectious pathogens. It is of great significance to construct effective photonic antibacterial agents with outstanding light absorption properties. Herein, 2D engineering defect nanosheets BiOI/Bi with Bi decoration and defect engineering (BiOI-DE) are constructed to perform photonic sterilization. On the one hand, the rational designed BiOI-DE can effectively promote the broad-spectrum light absorption ability to enhance the light utilization rate. On the other hand, the substantive structure can simultaneously harvest the enhanced photonic carriers and thermal effect when irradiated with high penetration ability NIR, further exhibiting higher activity in killing Escherichia coli (E. coli) than that of single BiOI with poor light absorption. The sterilization efficiency is over 99%. Moreover, the causes of the photothermal effect are discussed, indicating that the change of BiOI bandgap and surface bismuth decoration displays a critical role in enhancing light absorption and creating heat energy. In the meantime, the structural advancement of BiOI-DE effectively improves the photocatalytic activity, the synergistic photothermal-catalytic process establishes a favorable condition for improving antibacterial performance. This system provides rational design and potential inspiration for high efficient antibacterial strategy by employing defect engineering approaches.

Monolayer Nanosheets Exfoliated from Cage-Based Cationic Metal-Organic Frameworks.

The rational design and preparation of monolayer metal-organic framework (MOF) nanosheets remain great challenges. Recently, we found that monolayer MOF nanosheets can be facially exfoliated on a large scale from pristine two-dimensional (2D) MOFs with substantially reduced interlaminar interaction. By employing cage-like bicyclocalix[2]arene[2]triazine tri-imidazole as the building block, a family of cationic two-dimensional metal-organic frameworks (2D MOFs) with steric layer were designed and prepared. The single crystal structures have clearly identified that only very weak and sparse distributed C-H···π interaction exists between adjacent layers.On the basis of density functional theory calculation, the interlayer interaction of these cage-based cationic 2D MOFs was estimated to be 1/46th of that of graphite. Due to the extremely weak interaction, these cationic 2D MOFs tend to degenerate into an "amorphous" state after being soaked in other solvents; they can be readily exfoliated into 1.1 nm thick monolayer nanosheets with a high degree of thickness homogeneity, large lateral size, and significantly enlarged surface area. This work has identified that a cage-like molecule is the ideal building block for 2D cationic MOFs and ultrathin nanosheets; It was futher confirmed that weakening the interlaminar interaction is an effective strategy for facilely producing monolayer nanosheets.

Ultrathin 2D nanosheets of transition metal (hydro)oxides as prospective materials for energy storage devices: A short review

The ultrathin two-dimensional (2D) transition metal oxides and hydroxides (TMO and TMH) nanosheets are attractive for creating high-performance energy storage devices due to a set of unique physical and chemical properties. Flat 2D structure of such materials provides a sufficient number of active adsorption centers, and the ultra-small thickness, on the order of several nanometers, provides fast charge transfer, which significantly improves electronic conductivity. This brief review summarizes recent progress in the synthesis of materials based on ultrathin 2D nanosheets for energy storage applications, including pseudocapacitors, lithium-ion batteries, and other rechargeable devices. The review also presents examples of representative work on the synthesis of ultrathin 2D nanomaterials based on TMO and TMH for various power sources. In conclusion, the article discusses possible prospects and directions for further development of methods and routes for the synthesis of ultrathin two-dimensional transition metal oxides and hydroxides.

Conversion of layered materials to ultrathin amorphous nanosheets induced by ball-milling insertion and pure-water exfoliation

A simple and universal two-step strategy, “ball-milling insertion and pure-water exfoliation”, to efficiently produce high quality ultrathin amorphous 2D nanosheets.

Two-dimensional ultra-thin nanosheets optimize the surface reaction dynamics and photo/pyro-generated carrier transfer of NaNbO3 for an efficient pyro-photo-electric catalytic system

We proposed a strategy that integrated an 2D ultra-thin (<5 nm) nanosheet Co(OH)2 layer on NaNbO3 to optimize the surface reaction dynamics and unobstructed photo/pyro-generated carrier transfer path for pyro-photo-electric catalytic system.

Ultrathin perovskite derived Ir-based nanosheets for high-performance electrocatalytic water splitting

2D ultrathin capping agent-free Ir-based nanosheets have been fabricated via a facile strategy by thermally treating ZnIr(OH)6 perovskite hydroxide, which can serve as promising electrocatalysts for overall water splitting.

Molten Salt Synthesis of Cofe Alloy Embedded in 2d Ultrathin N-Doped Porous Carbon Nanosheets for Efficient Cooperative Oxygen Electrocatalysis

Molten Salt Synthesis of Cofe Alloy Embedded in 2d Ultrathin N-Doped Porous Carbon Nanosheets for Efficient Cooperative Oxygen Electrocatalysis

Metal-organic framework-derived 2D layered double hydroxide ultrathin nanosheets for efficient electrocatalytic hydrogen evolution reaction.

A facile approach to synthesize a Pt-doped metal-organic framework (MOF)-derived layered double hydroxide (LDH), denoted as Pt@CuFe-LDHm, is developed. It consists of highly dispersed 2D nanosheets, and the excellent properties (high specific surface area and large porosity) inherited from CuFe(dobpdc) bestow it with superior catalytic properties. Pt@CuFe-LDHm shows low overpotentials of 33, 47 and 120 mV at 10 mA cm-2 with small Tafel slopes of 34.0, 50.2 and 85.6 mV dec-1 in 1.0 M KOH, 0.1 M KOH and 1.0 M PBS. This work paves the way for high-performance and durable HER electrocatalysts in alkaline and neutral electrolytes.

Oxygen vacancy-engineered ultrathin NiCo2O4 nanosheet arrays derived from MOFs as an advanced electrode for supercapacitors.

To overcome the poor electronic conductivity and slow ion transport of NiCo2O4, ultrathin nanosheet arrays with oxygen vacancies are constructed by a facile NaBH4 reduction method using a bimetallic MOF as the precursor. Benefiting from the advantages of highly exposed surface area and short paths for charge transport of ultrathin 2D nanosheets, as well as the improved electronic conductivity arising from oxygen vacancies, the optimal 0.1-Ov-NiCo2O4/NF electrode shows excellent electrochemical performance, largely outperforming pristine NiCo2O4/NF.

Synthesis of photoresponsive and photoemissive ultrathin 2D nanosheets of In2S3 achieved through a new single source molecular precursor.

Indium sulfide, a two-dimensional semiconductor material, has emerged as a promising candidate for cost-effective and sustainable solar cells. This report deals with the facile preparation of colloidal In2S3 with a new ultrathin nanosheet (NS) morphology. The synthesis was mediated through a new structurally characterized single source molecular precursor. The crystal structure, phase purity, and morphology of the NSs were thoroughly investigated by pXRD, Raman, XPS, and electron microscopic techniques. AFM studies revealed that the NSs have an average thickness of ∼1.76 nm. The optical studies confirm quantum confinement in the as-prepared NSs with a blue shift in the direct band gap, which lies in the optimal range suitable for solar cell application. Furthermore, photoluminescence studies indicate strong emission by these NSs in the blue region. The as-synthesized In2S3 NSs-based prototype photoelectrochemical cell exhibit high photostability and photoresponsivity, which make them suitable candidates for sustainable solar cells.

Regulation of morphology and electronic configuration of NiCo2O4 by aluminum doping for high performance supercapacitors

Morphology engineering and element doping are two effective strategies to boost the capacitive performance of electroactive materials. The morphology control through doping process is conducive to simplifying the preparation process. Herein, an aluminum-doped (Al-doped) strategy was used to prepare Al-doped NiCo2O4 nanosheet-wire structure (Al-NiCo2O4 NSW) by hydrothermal method and subsequent calcination. The nanosheet-wire structure was composed of one-dimensional (1D) nanowires and two-dimensional (2D) ultrathin nanosheets. 1D nanowires can provide efficient pathways for the electrons/ions transport. 2D nanosheets can enlarge the specific surface area and expose more active sites. The Al doping can change the electronic structure of NiCo2O4 with enhanced electrical conductivity as revealed by density functional theory (DFT) calculations. Meanwhile, a strong adsorption capacity of OH– was obtained on Al-NiCo2O4 NSW for redox reactions. The Al-NiCo2O4 NSW electrode demonstrated a high specific capacity of 1441C g−1 (2446F g−1) at 1 A g−1 and excellent cycling stability (87.6% capacity retention at 10 A g−1 for 5000 charge-discharge cycles). The assembled asymmetric supercapacitor manifested a superior energy density of 46.2 Wh Kg−1 at a power density of 800 W kg−1.

Flower-like MoS2 hierarchical architectures assembled by 2D nanosheets sensitized with SnO2 quantum dots for high-performance NH3 sensing at room temperature

Flower-like MoS2 hierarchical architectures assembled by ultrathin 2D nanosheets decorated with SnO2 quantum dots (QDs) were successfully prepared through a solvothermal method and used for room-temperature NH3 sensing detection. The morphology and structure of as-prepared hierarchical architectures were fully characterized, showing that SnO2 QDs with uniform particle size of 2–4 nm were uniformly distributed on the ultrathin nanosheets of MoS2 hierarchical architectures. SnO2 QDs@MoS2 composites based gas sensor exhibited a high response of 8.6 and short response/recovery times of 6 s/121 s to 100 ppm NH3 with good selectivity, excellent repeatability, and outstanding long-term stability at room temperature of 25 °C. Such highly enhanced response toward NH3 was ascribed to the synergistic effect between active SnO2 QDs with abundant dangling bonds and MoS2 nanosheets with large specific surface area and high carrier mobility. This work presented a potential room-temperature sensing material and revealed the underlying sensitization mechanism of the quantum dots, offering new ideas for the development of low-temperature gas sensors.

High-performance hybrid supercapacitors based on electrodeposited amorphous bimetallic nickel cobalt phosphide nanosheets

In this article, an amorphous bimetallic nickel cobalt phosphide (NiCoP) thin film composed of 2D nanosheets architecture was directly grown on Ni foam substrate by using one-step electrodeposition route and utilized as an efficient binder-free cathode for hybrid supercapacitors (HSCs). Particularly, the molar ratio of Ni/Co of the bimetallic NiCoP electrodes was systemically optimized for acquiring superior capacitive features. According to the synergistic advantages of ultrathin 2D nanosheets, good electrical conductivity of metal phosphides, and amorphous characteristics, the optimized bimetallic Ni0.5Co0.5P electrode exhibited the high specific capacity of 42.2 mA h g−1 at a current density of 1 A g−1, which was superior to the corresponding mono-metallic phosphides of NiP (38.8 mA h g−1) and CoP (21.5 mA h g−1). Moreover, an as-fabricated HSC device assembled with modified activated carbon anode and the Ni0.5Co0.5P cathode delivered not only an impressive specific capacity of 56.5 mA h g−1 at 1 A g−1, but also high energy density of 45.2 Wh kg−1 along with a power density of 800 W kg−1. Furthermore, the HSC device demonstrated good cycling stability with 86.7% capacity retention even after 10,000 cycles at 2 A g−1. Thereby, the facile and simple electrodeposition process and superior electrochemical performance of the electrodeposited NiCoP materials makes them as promising electrode materials for energy storage applications.

Controlled engineering of tunable 3D-BiOX (X = Cl, Br) hierarchical nanostructures via dopamine-mediated synergetic interactions for efficient visible-light absorption photocatalysis

Integration of surface tunable 3D-BiOX hierarchical nanostructures (HNS) from size and facet controlled ultra thin 2D-nanosheets in aqueous solutions under an environmental benign process is remains a challenge. Because of their visible light response is highly depending on structural characteristics and yet most fabrications are involved hydrothermal methods. Herein, a simple dopamine-mediated bioinspired approach is proposed to integrate surface tunable 3D-BiOCl, 3D-BiOBr and 3D-BiOCl0.875Br0.125 hierarchical microspheres assembled by ultra thin 2D-nanosheets in aqueous solutions under mild conditions. The biomolecule dopamine (DA.HX) here played a multiple role as reactant, template and halogen source for 3D-BiOX materials, and its amount precisely controlled surface textural properties and nanosheets thickness with exposed (001) facets. Interestingly, the interfacial surface chelate interactions of dopamine facilitated the band-edge shift towards visible range along with surface induced oxygen defect impurities, which effectively reduced their forbidden bandwidth for extended visible light absorptions and photoluminescence quenching with an efficient charge separations. The photocatalytic activities of resulting 3D-BiOX HNS have shown excellent Rhodamine B degradation provided by highly oxidative h+ and surface induced oxygen vacancies acted as e- trapping centers to generate highly active O2− radicals for selective benzyl alcohol oxidation with high photostability and recyclability than their bare BiOX materials.

Long-term catalytic durability in Z-scheme CdS@ 1T-WS2 heterojunction materials

This study aimed to improve the long-term durability of CdS catalysts by reducing the deterioration of catalytic activity caused by photocorrosion. An ultrathin 1T-WS2 2D nanosheet was introduced to enclose the CdS nanorods. The crystal defects in the wrapped CdS particles were reduced, and the WS2 sheet became thinner in the junction particle. The 2CdS@1WS2 junction particle exhibited the slowest decay time of the photoluminescence curve, and the photocurrent density increased by more than 3.5-fold in the junction particle than the single CdS particle. Eventually, the optimized 2CdS@1WS2 catalyst exhibited a high rate of H2 production of ≈3935 μmol g−1h−1 under simulated solar light irradiation with a quantum efficiency of 50%. Although the recycling experiment was repeated over 10 times using the 2CdS@1WS2 junction particle, the produced hydrogen amount did not decrease. This result is because CdS nanorods wrapped stably by the ultrathin WS2 nanosheets, which suppressed the photocorrosion of CdS, and furthermore, the 1T phase WS2 rapidly attracted photogenerated electrons from CdS, facilitating charge separation and inhibiting their recombination, thereby improving the catalyst activity. Finally, it was revealed that an effective Z-scheme charge transfer mechanism in the CdS@1T-WS2 junction particle follows during water splitting.

Study on mechanism of low-temperature oxidation of n-hexanal catalysed by 2D ultrathin Co3O4 nanosheets

Study on mechanism of low-temperature oxidation of n-hexanal catalysed by 2D ultrathin Co3O4 nanosheets

Ultrathin PdAuBiTe Nanosheets as High-Performance Oxygen Reduction Catalysts for a Direct Methanol Fuel Cell Device.

Ultrathin 2D metal nanostructures have sparked a lot of research interest because of their improved electrocatalytic properties for fuel cells. So far, no effective technique for preparing ultrathin 2D Pd-based metal nanostructures with more than three compositions has been published. Herein, a new visible-light-induced template technique for producing PdAuBiTe alloyed 2D ultrathin nanosheets is developed. The mass activity of the PdAuBiTe nanosheets against the oxygen reduction reaction (ORR) is 2.48 A mgPd -1 , which is 27.5/17.7 times that of industrial Pd/C/Pt/C, respectively. After 10000 potential cyclings, there is no decrease in ORR activity. The PdAuBiTe nanosheets exhibit high methanol tolerance and in situ anti-CO poisoning properties. The PdAuBiTe nanosheets, as cathode electrocatalysts in direct methanol fuel cells, can thus give significant improvement in terms of power density and durability. In O2 /air, the power density can be increased to 235.7/173.5mWcm-2 , higher than that reported in previous work, and which is 2.32/3.59 times higher than Pt/C.