Ultrathin Two-dimensional Nanosheets Research Articles

Microwave-induced phase engineering of copper sulfide nanosheets for rechargeable magnesium batteries

Phase controlling in transition metal dichalcogenides has been considered as a powerful route to regulate their chemical and electronic property for energy-related application yet is still subject to limited efficient fabrication method. We herein report a microwave-assisted strategy to synthesize CuxS nanosheets with tunable phases as high-performance cathode materials for rechargeable magnesium batteries. By precisely controlling the microwave irradiation time, the ultrathin two-dimensional CuxS nanosheets with graphene-like morphologies can be selectively prepared. The electrochemical measurements show that the specific capacities of different CuxS nanosheets strongly depend on their crystallographic structure and comply with a decreasing tendency of Cu1.7S > CuS > Cu1.9S. The multiphase Cu1.7S nanosheets delivers a capacity of 153.0 mAh g − 1 at 300 mA g − 1, significantly higher than that 100.8 and 84.8 mAh g − 1 of CuS and Cu1.9S counterparts. Moreover, Cu1.7S nanosheets display an excellent rate capability at various high current densities. Our work found that tuning the phase composition of CuxS could improve its electrochemical performances for rechargeable magnesium batteries. In addition, we offer a facile strategy to fabricate multiphase two-dimensional metal sulfide materials with great potential applications for energy devices.

Green preparation of porous hierarchical TiO2(B)/anatase phase junction for effective photocatalytic degradation of antibiotics.

In this study, porous hierarchical bronze/anatase phase junction TiO2 assembled by ultrathin two-dimensional nanosheets was prepared by a novel, green and simple deep eutectic solvent-regulated strategy. Due to its structural features, the TiO2 sample exhibited enhanced photocatalytic activities for multiple kinds of antibiotics, including ofloxacin, ciprofloxacin and chloramphenicol.

Ultrathin two-dimensional phosphorus and nitrogen Co-doped carbon nanosheet as efficient oxygen reduction electrocatalyst

Developing metal-free electrocatalysts with high performance towards oxygen reduction reaction (ORR) is critical for the commercialization of fuel cell technologies and metal-air batteries. Herein, we develop an effective and rational strategy to synthesize an ultrathin two-dimensional (2-D) carbon nanosheet (P–NCNS) with more exposed N and P doping sites as ORR electrocatalyst. This strategy adopts ice/salt dual-template to construct an ultrathin 2-D porous carbon nanosheet using gelatin as C/N precursor, and employs red P as P dopant to achieve controllable doping of heteroatoms. Red P also acts as a pore-forming agent to create abundant porosity on 2-D carbon surface through the activation of P-containing species. The resulting carbon nanosheet exhibits an ultrathin thickness of 1–2 nm, a large specific surface area (499.5 m2 g−1) and a well-defined micro/mesoporous structure, showing more exposed and abundant N, P doping sites that are accessible to the ORR reactants. As a result, P–NCNS shows an outstanding ORR performance both in alkaline and acidic electrolyte. More attractively, P–NCNS was used as the cathode electrocatalyst for a primary zinc-air battery showing good performance and long-term stability. This strategy offers a new insight for the design and synthesis of high-performance non-precious metal electrocatalyst for ORR.

Effect of ROS generation on highly dispersed 4-layer O-Ti7O13 nanosheets toward tumor synergistic therapy

Ultra-thin two-dimensional nanosheets have attracted increasing attention due to their great application prospects in nanomaterial science and biomedicine. Herein, we report the preparation of exfoliated raw and oxidized 4-layer Ti7O13 (O-Ti7O13) and their ability to produce reactive oxygen species (ROS). The results show that O-Ti7O13 nanosheets can effectively produce ROS induced by X-ray irradiation. The 4-layer nanosheets can quickly load doxorubicin (DOX) within 5 min with a high loading rate to obtain a novel nanodrug system through their electrostatic adsorption capacity, and they exhibit a sustained release behavior. In this way, chemotherapy, radiation therapy and photodynamic therapy effectively combine for cancer synergistic treatment. We evaluated the cytotoxicity, cellular uptake and intracellular location of the O-Ti7O13 nanosheet-based drug delivery system in A549 lung cancer cells. Our results show that the O-Ti7O13/DOX complex is more cytotoxic to A549 cells than free DOX since a low concentration of loaded DOX (10 μg/mL) with a low dose of X-rays can cause the complete apoptosis of tumor cells. This work reveals that the therapeutic effect of DOX-loaded O-Ti7O13 nanosheets is strongly dependent on their loading mode, and the effects of chemotherapy and photodynamic therapy are enhanced under X-ray irradiation, which allows O-Ti7O13 nanosheet use as a photo-activated drug carrier. This work provides a new strategy for preparing 2D metal oxide nanosheets toward biomedical applications.

Ultra-thin two-dimensional nanosheets for in-situ NIR light-triggered fluorescence enhancement

Ultra-thin two-dimensional (2D) nanosheets of Zn-based metal -organic framework (MOF) were prepared from the precursor [Zn(bpydc) (H2O)·H2O]n (bpydc = 2,2′-bipyridine-5,5′-dicarboxylate), by using a liquid phase ultrasonic stripping technique. The atomic thickness and the abundant oxygen atoms making the nanosheets are well dispersed in various solvents, exhibiting unique fluorescence responses to solvents of different polarities. Adding on, by loading on the ytterbium ion (Yb3+)-sensitized hexagonal phase up-converting nanoparticles (UCNPs, sodium yttrium fluoride (NaYF4): 20 mol% Yb3+, 1 mol% erbium (Er3+ ions)) on the surfaces of nanosheets, the in-situ near infrared (NIR) light (980 nm) triggered luminescence enhancement has been observed, suggesting the favorable application foreground in biomedical science, super-capacitors, and electronic devices.

An ultrathin polydiacetylene nanosheet as dual colorimetric and fluorescent indicator for lysophosphatidic acid, a cancer biomarker

Ultrathin two-dimensional (2D) nanosheets have been considered as one of the powerful platforms for chemical sensing of biomolecules. However, few 2D nanosheets with intrinsic chromatism exist for the specific and effective detection of some biomarkers. Here, we report a novel ultrathin chromic polydiacetylene (PDA) nanosheet via the self-assembly and photopolymerization of an amphiphilic guanidinium-capped diacetylene monomer (PCDA-Gu). The PDA-Gu nanosheets exhibit specific combination of lysophosphatidic acid (LPA), a biomarker for ovarian cancer, based on the synergistic salt-bridge interactions and hydrophobic interactions between the PDA-Gu nanosheets and LPA, and induced both color and fluorescence change. The linear correlation between the colorimetric response (CR) (or fluorescence intensity) and the concentration of LPA enable effective quantitative analysis of LPA in the biologically relevant low concentration range. Owing to their chromic properties and ultrathin lamellar structure, the PDA-Gu nanosheets have opportunity to act as a powerful indicator for LPA.

Hydrogen Sensors Based on MoS2 Hollow Architectures Assembled by Pickering Emulsion.

For rapid hydrogen gas (H2) sensing, we propose the facile synthesis of the hollow structure of Pt-decorated molybdenum disulfide (h-MoS2/Pt) using ultrathin (mono- or few-layer) two-dimensional nanosheets. The controlled amphiphilic nature of MoS2 surface produces ultrathin MoS2 NS-covered polystyrene particles via one-step Pickering emulsification. The incorporation of Pt nanoparticles (NPs) on the MoS2, followed by pyrolysis, generates the highly porous h-MoS2/Pt. This hollow hybrid structure produces sufficiently permeable pathways for H2 and maximizes the active sites of MoS2, while the Pt NPs on the hollow MoS2 induce catalytic H2 spillover during H2 sensing. The h-MoS2/Pt-based chemiresistors show sensitive H2 sensing performances with fast sensing speed (response, 8.1 s for 1% of H2 and 2.7 s for 4%; and recovery, 16.0 s for both 1% and 4% H2 at room temperature in the air). These results mark the highest H2 sensing speed among 2D material-based H2 sensors operated at room temperature in air. Our fabrication method of h-MoS2/Pt structure through Pickering emulsion provides a versatile platform applicable to various 2D material-based hollow structures and facilitates their use in other applications involving surface reactions.

Hierarchical core–shell heterostructures of ZnIn2S4 nanosheets on electrospun In2O3 nanofibers with highly enhanced photocatalytic activity

Well-designed heterostructure semiconductor photocatalysts can improve the activity of photocatalytic reactions. In this work, we constructed a series of hierarchical ZnIn2S4/In2O3 heterostructures by growing ultrathin two-dimensional ZnIn2S4 nanosheets onto one-dimensional In2O3 electrospun nanofibers and used them as photocatalysts for the efficient photoreduction of toxic Cr(VI). This structural design increased the specific surface area, promoted the separation of photogenerated electrons and holes, and provided more active sites for the catalytic reactions. Under visible light irradiation, the optimized ZnIn2S4/In2O3 photocatalyst showed the highest photocatalytic performance with 100% reduction efficiency for Cr(VI) (50 mg/L) within 90 min, which is much higher than pure In2O3 and ZnIn2S4. Additionally, the recycling tests and X-ray diffraction (XRD) characterization indicated the stability of the ZnIn2S4/In2O3 photocatalyst, making it a promising candidate for environmental remediation applications. Finally, the two active species (e˗ and ·O2˗) participating in the photoreduction process were determined via trapping experiments and electron spin resonance (ESR) spectroscopy. Finally, a possible mechanism for the ZnIn2S4/In2O3 heterojunction photocatalytic system was carefully determined.

Formation of Hierarchical FeCoS2 -CoS2 Double-Shelled Nanotubes with Enhanced Performance for Photocatalytic Reduction of CO2.

Hierarchical FeCoS2 -CoS2 double-shelled nanotubes have been rationally designed and constructed for efficient photocatalytic CO2 reduction under visible light. The synthetic strategy, engaging the two-step cation-exchange reactions, precisely integrates two metal sulfides into a double-shelled tubular heterostructure with both of the shells assembled from ultrathin two-dimensional (2D) nanosheets. Benefiting from the distinctive structure and composition, the FeCoS2 -CoS2 hybrid can reduce bulk-to-surface diffusion length of photoexcited charge carriers to facilitate their separation. Furthermore, this hybrid structure can expose abundant active sites for enhancing CO2 adsorption and surface-dependent redox reactions, and harvest incident solar irradiation more efficiently by light scattering in the complex interior. As a result, these hierarchical FeCoS2 -CoS2 double-shelled nanotubes exhibit superior activity and high stability for photosensitized deoxygenative CO2 reduction, affording a high CO-generating rate of 28.1 μmol h-1 (per 0.5 mg of catalyst).

Solution-processable two-dimensional ultrathin nanosheets induced by self-assembling geometrically-matched alkane

Two-dimensional (2D) nanomaterials have attracted much interest as promising candidates for next generation energy storage, electronics and catalytic applications, due to their unique topology and electronic structure. However, the development of an operable and versatile solution processing technique for simple fabrication of high-quality 2D nanosheets continues to present a significant challenge. Here, an ultrathin indium sulfide nanosheet is synthesized via a simple solution-phase reaction involving two steps: i) thermal decomposition of precursors to form a crystal nucleus; ii) growth of 2D nanosheets in a mixture of amino ligand and alkane solvent. The alkane, matching the amino ligand structure in terms of geometry, could assemble with the ligand to form a soft template and thus induce a 2D arrangement of the nucleus. Moreover, the chemical inertness of the alkane facilitated rotation of crystal seeds, resulting in anisotropic growth of the nanosheet. We further demonstrated that the geometrically matched alkane-assisted solution processing reaction could be applied to synthesize various 2D metal chalcogenides. Functionally, the acquired indium sulfide nanosheets, which possess high photoelectric activity, were introduced for fabrication of photoelectrodes capable of efficient photoelectrochemical water splitting. Our work opens up a new perspective toward the construction and potential applications for various 2D nanomaterials.

Build 3D Nanoparticles by Using Ultrathin 2D MOF Nanosheets for NIR Light-Triggered Molecular Switching.

The coordination interactions between transition-metal ions (Cu2+, Ag+) and sulfur atoms on ultrathin two-dimensional (2D) nanosheets of spin-crossover (SCO) metal-organic frameworks {[Fe(1,3-bpp)2(NCS)2]2}n (1,3-bpp = 1,3-di(4-pyridyl)propane), which constructed the ultrathin 2D nanosheets into three-dimensional (3D) nanoparticles, have made a profound effect on the SCO performance. Compared with 2D nanosheets, both the intraligand π-π* transition band and the metal-to-ligand charge transition band from the d(Fe) + π(NCS) to π*(1,3-bpp), for the 3D nanoparticles, have shown dramatic blue-shifts; meanwhile, the d-d transition band for the high-spin (HS) state Fe(II) ions has been generated, suggesting significantly the influence of 3D assemble-caused dimensional changes on the solid-state SCO performance of ultrathin 2D nanosheets. More importantly, by loading on the ytterbium ion (Yb3+)-sensitized hexagonal phase upconverting nanoparticles in the aqueous colloidal suspension, the near infrared (NIR) light (980 nm) triggered HS (high spin) to LS (low spin) state transitions have been observed, demonstrating the achievement of challenging target of NIR light-triggered molecular conversion under environment conditions.

Facile synthesis of large-area ultrathin two-dimensional supramolecular nanosheets in water

Synthesizing large-area ultrathin two-dimensional (2D) nanostructures in aqueous media has received considerable increasing attention but remains a big challenge. Herein, we report a facile method for the synthesis of two unprecedented large-area ultrathin 2D supramolecular nanosheets via ionic self-assembly in water. Upon consideration of electrostatic interaction and repulsive effect, deprotonated tetrakis(4-carboxyphenyl)porphyrin (TCPP) or Fe(III) tetra(4-carboxyphenyl)porphine chloride (TCPP(Fe)) as connection vertex and protonated bis(2-dimethylaminoethyl) ether (BDMAEE) unit as bridging edge connect with each other to form few-layer 2D nanosheet with a thickness of ~ 1.8–1.9 nm, while the lateral size can close to one hundred micrometers. Moreover, the well-dispersed 2D TCPP(Fe)-BDMAEE with heme-like active center displays intrinsic peroxidase-like catalytic activity, which can be used to detect hydrogen peroxide. The present facile strategy highlights new opportunities in constructing large-area ultrathin 2D supramolecular nanomaterials and paves the avenue to expand their potential applications.

Highly selective NO2 chemiresistive gas sensor based on hierarchical In2O3 microflowers grown on clinoptilolite substrates

Hierarchical In2O3 microflowers (HIMF) were prepared via a simple one-step hydrothermal method on the surface of the clinoptilolite substrate (CS). Structural characterizations were investigated by various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectric spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The results demonstrated that the HIMF were comprised of abundant ultrathin two-dimensional nanosheets with a width of about 500 nm and the thickness of approximately 20 nm. The high-yield HIMF with a hexagonal phase were loose and uniformly distributed on the surface of the CS. The CS accompanied with the HIMF was made into a gas sensor to test NO2 sensing properties. It indicated that the gas sensor exhibited excellent NO2 sensing performance of low operating temperature, fast response, high selectivity and good reversibility. The outstanding NO2 sensing properties of the HIMF could be ascribed to its unique hierarchical structure and the synergistic effect of the CS. The possible formation process and sensing mechanism of the HIMF were proposed. The results show a potential prospect for using the natural porous mineral as the substrate to synthesize high-performance sensing material.

Ruthenium Complex-Incorporated Two-Dimensional Metal-Organic Frameworks for Cocatalyst-Free Photocatalytic Proton Reduction from Water.

Ultrathin two-dimensional (2D) nanosheets with efficient light-driven proton reduction activity were obtained through the exfoliation of novel metal-organic frameworks (MOF), which were synthesized by using a bis(4'-carboxy-2,2':6',2″-terpyridine) ruthenium complex as a linker and 3d transition-metal (Mn, Co, Ni, and Zn) anions as nodes. The nanosheet of the Ni2+ node exhibits a photocatalytic hydrogen evolution rate of 923 ± 40 μmol g-1 h-1 at pH = 4.0, without the presence of any cocatalyst or cosensitizer. A combined experimental and theoretical study suggests a reductive quenched pathway for the photocatalytic hydrogen evolution by the nanosheet. The transition-metal nodes at the edge of the nanosheets are proposed as the active sites. Density functional theory (DFT) calculations attributed the different catalytic activities of the nanosheets to the discrepancy of H adsorption free energy at various transition-metal nodes.

Confinement preparation of hierarchical NiO-N-doped carbon@reduced graphene oxide microspheres for high-performance non-enzymatic detection of glucose

Here, hierarchical NiO-N-doped carbon@reduced graphene oxide (NiO-NC@rGO) microspheres have been fabricated by a confinement preparation process. Ni-based coordination polymer@rGO as precursor were synthesized by a simple hydrothermal method. Subsequently, NiO-NC microspheres were formed under the cover of rGO by pyrolysis. Morphology characterizations showed NiO-NC-rGO microspheres with a hierarchical structure based on ultrathin two-dimensional nanosheets. Most importantly, such microspheres exhibited excellent performances for the detection of glucose. The NiO-NC-rGO modified glassy carbon electrode (NiO-NC-rGO/GCE) was used as working electrode to establish a glucose sensor based on electrochemical technique. The main performance parameters of such glucose sensor are presented as follows. The sensitivity is 4254 μA mM−1 cm−2; The detection limit is 70.9 nM; The linear detection range is 0.5 μM − 20.0 μM (R = 0.9998). The structural and compositional advantages of NiO-NC@rGO have been considered in this work. On the one hand, the abundant active sites can be provided by the hierarchical structure of microspheres for the adsorption of the target molecules. On the other hand, the synergy of NiO, NC and rGO is the key design element of the ternary materials.

Construction of Z-scheme heterojunction of PANI-Ag-CN sandwich structure with efficient photocatalytic hydrogen evolution

In this work, we report a sandwich structure of PANI-Ag-CN photocatalyst, which is stacked layer by layer with g-C3N4 and PANI ultra-thin two-dimensional nanosheets and Ag nanoparticles are embedded as interlayers. The Z-scheme heterojunction can be formed in this sandwich structure of PANI-Ag-CN photocatalyst, where Ag nanoparticles act as the charge transfer intermediate, leading to the annihilation of the holes of g-C3N4 and the electrons of PANI, and thus the strong reductive electrons and the strong oxidative holes can be left at the CB of g-C3N4 and VB of PANI, respectively. Meanwhile, the short charge transfer and the large number of active sites on the ultra-thin two-dimensional nanosheets are proved beneficial for to the photocatalytic hydrogen evolution from water. The PANI-Ag-CN photocatalyst exhibits an increased hydrogen evolution activity of 5048 μmol·g−1·h−1, which is 43.52-fold higher than that of g-C3N4 and 58.02-fold higher than that of bulk g-C3N4. Moreover, the photocurrent of PANI-Ag-CN is 1.9 × 10−6 A/cm2, which is 5.94 times higher than that of g-C3N4.

Metal-organic framework-based CO2 capture: From precise material design to high-efficiency membranes

A low-carbon economy calls for CO2 capture technologies. Membrane separations represent an energy-efficient and environment-friendly process compared with distillations and solvent absorptions. Metal-organic frameworks (MOFs), as a novel type of porous materials, are being generated at a rapid and growing pace, which provide more opportunities for high-efficiency CO2 capture. In this review, we illustrate a conceptional framework from material design and membrane separation application for CO2 capture, and emphasize two importance themes, namely (i) design and modification of CO2-philic MOF materials that targets secondary building units, pore structure, topology and hybridization and (ii) construction of crack-free membranes through chemical epitaxy growth of active building blocks, interfacial assembly, ultrathin two-dimensional nanosheet assembly and mixed-matrix integration strategies, which would give rise to the most promising membrane performances for CO2 capture, and be expected to overcome the bottleneck of permeability-selectivity limitations.

Ultrathin two-dimensional polydopamine nanosheets for multiple free radical scavenging and wound healing.

Novel 2D polydopamine nanosheets were successfully prepared by using a simple but effective "bottom-up" synthesis method. The ultrathin polydopamine nanosheets exhibit excellent multiple free radical scavenging activities including DPPH˙ and ABTS˙+ free radicals, especially O2˙-. Full-thickness skin defect regeneration was accelerated by treatment with the nanosheets.

Construction of uniform SnS2/ZnS heterostructure nanosheets embedded in graphene for advanced lithium-ion batteries

Lithium-ion batteries have been broadly used in energy storage systems and power batteries. However, the current research on LIBs anodes still faces key problems such as low specific capacity, limited cycle life and low initial coulombic efficiency, which limit its commercial applications. In order to solve these issues, SnS2/ZnS heterostructure nanosheets are synthesized on a reduced graphene oxide (expressed as SnS2/ZnS-rGO) derived from ZnSn(OH)6 through the solution sulfidation method. This composite has the features of two-dimensional ultrathin nanosheets and heterostructure, which can shorten Li+ diffusion distance, and provide additional charge transfer driving force. The three-dimensional (3D) SnS2/ZnS-rGO electrode represents high specific capacity (1458.3 mA h g−1 at 0.2 A g−1) and outstanding cycle stability of 4000 cycles (432.4 mA h g−1 at 10 A g−1). This unique lithium storage mechanism has been studied by in-situ and ex-situ XRD techniques in detail. This work not only provides a feasible method for the preparation of bimetallic sulfides, but also gives a novel application prospect for the new self-built high energy density anode.

Ultrathin nickel phosphide nanosheet aerogel electrocatalysts derived from Ni-alginate for hydrogen evolution reaction

Transition metal phosphides (TMPs) have been regarded as an alternative to Pt-based catalysts for hydrogen evolution reaction (HER) on account of their high performance and low cost. The ultrathin two-dimensional (2D) nanosheets of TMPs can expose abundant active sites and facilitate the transfer of mass/charge to enhance HER performance. However, the synthesis of ultrathin 2D nanosheets of TMPs is still a great challenge. Herein, we reported a novel and scalable strategy to prepare 2D ultrathin nickel phosphide nanosheets (∼2.5 nm) by using alginate as precursor through ice-templating process. The role of ice-templating is that the growth of the ice crystals would squeeze Ni-alginate into 2D nanosheets, and then forming Ni-alginate aerogels. The three-dimensional (3D) interconnected porous network of aerogels was advantageous to reduce the lattice strains of subsequent oxidation and phosphorization process. It is the key step to prepare 2D ultrathin nickel phosphides (Ni2P and Ni5P4) nanosheets. As expected, all the prepared Ni5P4 nanosheet aerogels displayed remarkable HER performance in 1 M KOH electrolyte. Especially, due to their ultrathin 2D nanosheets and high P percentage, the Ni5P4-500-350 sample with excellent long-term stability exhibits a low overpotential of 147 mV at current density of 10 mA cm−2 and a low Tafel slope of 57 mV dec−1.