As-prepared Nanosheets Research Articles

Fluorescence Sensing of Glutathione Based on the In-Situ Growth of Carbon Dots-Manganese Dioxide Nanosheets

Blue fluorescent carbon dots with high purity were synthesized through a one-step hydrothermal method using citric acid and ethylenediamine as raw materials and then purification by column chromatography. In-situ controllable synthesis was used to prepare carbon dots-manganese dioxide (CDs-MnO2) nanosheets, with carbon dots as the seed, potassium permanganate as the manganese source and sodium citrate as the reducing agent. The as-prepared nanosheets were characterized by transmission electron microscopy, absorption spectroscopy, and fluorescence spectroscopy. It was found that MnO2 can be degraded by Glutathione (GSH) through a redox reaction, which restores the fluorescence of CDs. A new method for determining GSH was constructed using CDs-MnO2 fluorescence sensing. The method is simple and sensitive, with linear ranges of 0.1-5 μM and 10-60 μM, respectively, and a lowest detection limit of 0.034 μM. The method was successfully used for the determination of GSH in human serum, with satisfactory recoveries in the range of 98.9-100.1%.

Synthesis of CuCo2S4 nanosheets and its application in dye-sensitized solar cells

CuCo2S4, a ternary sulfide and an eco-friendly thiospinel that occurs naturally as a mineral named Carrollite, has been synthesized successfully in ambient conditions at low temperatures using ultrasonication. It has yet to be reported, but the nanosheet structure obtained from the ultrasonication synthesis method employed as a counter electrode in the dye-sensitized solar cells (DSSCs) has been demonstrated. The purity, crystallinity, morphology, and structure were explored thoroughly through the medium of XRD, SEM, TEM, SAED, and EDAX, and along with this, the presence of metal sulfide bond was investigated with the FT-IR and Raman spectra, which altogether confirmed the formation of CuCo2S4 nanosheet. The as-prepared nanosheets of CuCo2S4 have shown excellent homogeneity, as expected. Also, the presence of sulfur in the synthesized CuCo2S4, which is a highly polarizable atom and of a smaller size exhibiting a higher surface area, demonstrates higher electrocatalytic activity when fabricated as a counter-electrode in DSSCs by providing an incredible short circuit current density of 31.05 mA cm−2, open circuit potential of 735 mV with good fill factor value which altogether resulted in the power conversion efficiency of 10.21 % nearer to DSSC fabricated with Platinum counter electrode under the same conditions.

Engineering nitrogen vacancies and cyano groups into C3N4 nanosheets for highly efficient photocatalytic H2O2 production

Thermal oxidation of bulky carbon nitride (C3N4, CN) to expose more active sites is an important method to improve the activity of the as-prepared CN nanosheets. Unfortunately, the yield of thermal oxidation is low. Herein, we report dual-deficient CN (DDCN) ultrathin nanosheets engineered with nitrogen vacancies and cyano groups by two-step bottom-up thermal polymerization of belt-like melamine with a high yield of 65%. Featured with abundant exposed active sites, short charge migration distance, wide visible-light absorption, quick charge separation/transfer, enhanced oxygen adsorption ability and 2e oxygen reduction reaction selectivity, the DDCN exhibits a high H2O2 production rate of ∼1031 μmol g1 h1, which is 19.5 times that of CN (53 μmol g1 h1) under visible light irradiation (λ ≥ 420nm). Specifically, the apparent quantum yield (AQY) of DDCN reached 10.7% at 420nm. This study provides a facile dual-defect engineering method to develop highly efficient ultrathin CN-based photocatalysts.

Changing Cinnamaldehyde Skeleton Achieves Antibacterial Nanoswitch.

Changeable substituent groups of organic molecules can provide an opportunity to clarify the antibacterial mechanism of organic molecules by tuning the electron cloud density of their skeleton. However, understanding the antibacterial mechanism of organic molecules is challenging. Herein, we reported a molecular view strategy for clarifying the antibacterial switch mechanism by tuning electron cloud density of cinnamaldehyde molecule skeleton. The cinnamaldehyde and its derivatives were self-assembled into nanosheets with excellent water solubility, respectively. The experimental results show that α-bromocinnamaldehyde (BCA) nanosheets exhibits unprecedented antibacterial activity, but there is no antibacterial activity for α-methylcinnamaldehyde nanosheets. Therefore, the BCA nanosheets and α-methylcinnamaldehyde nanosheets achieve an antibacterial switch. Theoretical calculations further confirmed that the electron-withdrawing substituent of the bromine atom leads to a lower electron cloud density of the aldehyde group than that of the electron-donor substituent of the methyl group at the α-position of the cinnamaldehyde skeleton, which is a key point in elucidating the antimicrobial switch mechanism. The excellent biocompatibility of BCA nanosheets was confirmed by CCK-8. The mouse wound infection model, H&E staining, and the crawling ability of drosophila larvae show that as-prepared BCA nanosheets are safe and promising for wound healing. This study provides a new strategy for the synthesis of low-cost organic nanomaterials with good biocompatibility. It is expected to expand the application of natural organic small molecule materials in antimicrobial agents.

Metallic layered VSe2 saturable absorber based single- and dual-wavelength ultrafast fiber laser

Vanadium selenide (VSe2) is a special two-dimensional (2D) transition metal dichalcogenide (TMD) material with metallic properties similar to graphene, which has been proved to have saturable absorption properties and used in mode-locked fiber lasers. As an excellent saturable absorber (SA) material, VSe2 has advantage of ultrafast carrier recovery time and broadband optical response range. However, the potential application of VSe2 in the field of ultrafast photonics has not been fully developed so far. In this work, the as-prepared VSe2 nanosheets were deposited on tapered fiber by optical deposition to obtain VSe2 SA. By inserting VSe2 SA into an Er-doped fiber laser, the mode-locked pulses with a central wavelength of 1574.4 nm can be obtained. The pulse width of the laser is measured to be ∼680 fs which is narrowest in the reported VSe2 SA-based lasers. In addition, the unique dual-wavelength mode-locked pulse is also obtained by further adjusting intracavity dispersion and polarization. This kind of dual-wavelength pulse is valuable in high order harmonic generation enhancement, terahertz wave generation, dense wavelength division multiplexing, dual-frequency comb and other applications. Our results show that metallic VSe2 is of great potential value in ultrafast fiber laser.

Binder-Free Two-Dimensional Few-Layer Titanium Carbide MXene Ink for High-Performance Symmetric Supercapacitor Device Applications

A heightened interest in developing MXene (Ti3C2Tx) for energy storage is evident in binder-free MXene ink being directly applied to current collector Ni-foam. Moreover, 2D titanium carbide MXene, with a few layers of nanostructure, has been prepared for symmetric supercapacitor device applications. As-prepared MXene nanosheets exist in two forms: dried powder and ink, achieved through wet-chemical etching and dimethyl sulfoxide delamination from the MAX (Ti3AlC2) phase. This comparative study of electrode devices involves (i) MX-dry powder with binder/additive electrodes and (ii) binder-free MXene inks with directly applied MX-conductive inks. The surface morphological images of pure MX-powder/ink display few layers, and material analysis reveals the good crystalline nature of delaminated MXene (Ti3C2Tx) inks. The electrochemical symmetric supercapacitor device performances of pure MXene powder and binder-free directly applied/coated MXene (Ti3C2Tx) ink, in terms of cyclic voltammetry (CV) and impedance spectroscopy (EIS), exhibit galvanostatic charge–discharge (GCD) curves that show high specific capacitance (Csp) at 105.75 F/g at a current density of 1 A/g. A comparison of active material electrodes demonstrated excellent cycle stability. Hence, in this work, we confirmed the superior capacitive behavior of binder-free MXene ink (MX-I) compared to conductive additives with polymeric binders included in MXene electrodes.

DNA Framework-Templated Fabrication of Ultrathin Electroactive Gold Nanosheets.

Generally, two-dimensional gold nanomaterials have unique properties and functions that offer exciting application prospects. However, the crystal phases of these materials tend to be limited to the thermodynamically stable crystal structure. Herein, we report a DNA framework-templated approach for the ambient aqueous synthesis of freestanding and microscale amorphous gold nanosheets with ultrathin sub-nanometer thickness. We observe that extended single-stranded DNA on DNA nanosheets can induce site-specific metallization and enable precise modification of the metalized nanostructures at predefined positions. More importantly, the as-prepared gold nanosheets can serve as an electrocatalyst for glucose oxidase-catalyzed aerobic oxidation, exhibiting enhanced electrocatalytic activity (~3-fold) relative to discrete gold nanoclusters owing to a larger electrochemical active area and wider band gap. The proposed DNA framework-templated metallization strategy is expected to be applicable in a broad range of fields, from catalysis to new energy materials.

Facile and efficient preparation of hemicellulose-assisted MoS2 nanosheets via green liquid-phase exfoliation method

A facile, environmental-friendly and efficient exfoliation process has been reported to produce MoS2 nanosheets at room temperature via liquid-phase exfoliation method using hemicellulose as an assistant in aqueous solution. It is found that bulk MoS2 has been successfully exfoliated into few-layered MoS2 nanosheets. The non-polar sites of hemicellulose can firmly adhere to MoS2 surface, whereas the hydrophilic branches can facilitate the dispersion, resulting in the effective exfoliation in aqueous solution. The exfoliated dispersions of MoS2 nanosheets are homogeneous and highly stable over 7 months, even stored at ambient conditions. The optical properties of exfoliated MoS2 nanosheets were investigated by UV–Vis, and the morphological characterizations were examined by SEM, TEM, AFM, XRD and Raman. The results show that the hemicellulose-assisted MoS2 nanosheets produced by 10 mg/ml initial concentration have approximately 8–9 layers. Also, the surface-enhanced Raman scattering (SERS) capability of as-prepared MoS2 nanosheets is observable with the enhancement factor (EF) of about 4 × 104, indicating that the hot-spots can be generated on nanosheets. It demonstrates a plausible application of exfoliated MoS2 nanosheets as a SERS substrate as well as a great potential for other solution-based device fabrication. This present liquid-phase exfoliation method is a green, simple and effective process for mass production of MoS2 nanosheets.

Convenient preparation of expanded graphite and graphite nanosheets as well as improvement of electrical conductivity of polyurethane by filling graphite nanosheets

Expandable graphite precursors were firstly prepared by the oxidative intercalation of natural flake graphite powders with mean lateral particle sizes of 25–100 μm in concentrated sulfuric acid solutions using Ca(ClO)2 as an oxidant. Higher oxidative intercalation extent increased the thermal expansion of expandable graphite to obtain expanded graphite with a larger volume ratio of 162 mL⋅g−1. Graphite nanosheet samples were facilely and eco-friendly prepared by sand milling of expanded graphite in an aqueous solution. The thicknesses of as-prepared graphite nanosheets could be decreased from 15–20 to 4.8–5.5 nm with the prolonging of sand milling time from 4 to 12 h. As compared with polyurethane/natural flake graphite composite films, the electric conductivity of polyurethane/graphite nanosheet composite films was increased by 6 orders of magnitude at a lower filler content of 5 wt%. The filling of graphite nanosheets endows polyurethane with good electrical conductivity.

Ultra-large Sn3O4 nanosheets with Sn2+ defect for highly efficient hydrogen sensing

Hydrogen (H2) is the cleanest energy but also dangerous, thus the real-time detection of H2 leakage is crucially important. Herein, we develop ultra-large micro-sized Sn3O4 nanosheet hierarchies via a facile hydrothermal method using polyvinyl pyrrolidone as a regulating agent. Structural analyses reveal the as-prepared Sn3O4 nanosheets are single-crystalline with {010}-facet exposure and Sn2+-deficiency. When examined as gas sensing materials, the {010}-faceted Sn2+-deficient Sn3O4 nanosheets demonstrate highly efficient H2 sensing with excellent selectivity/response (two times higher than those for NO2, SO2, H2S, and H2O) and stability upon long-term testing (over 37 days). The sensor displays fast response /recovery times of 9.4/24 s to 10 ppm H2 at a low working temperature of 150 °C, and even well responds to 50 ppb H2 with a theoretical limit of detection (LOD) of 0.54 ppb. The excellent H2 sensing performance of the Sn3O4 nanosheets has been verified by the first-principle calculation based on density functional theory (DFT), suggesting that the Sn2+-deficient {010} surface of Sn3O4 provides abundant adsorption sites for hydrogen molecules. Moreover, we demonstrate the practical application of Sn3O4 sensor embedded into a miniaturized deployable module, which realizes the real-time on-line H2 monitoring with excellent repeatability and selectivity for long-term operation.

Sn3O4 nanosheets with N-doped carbon coating for high performance lithium storage

Tin-based oxides are promising anode materials for lithium ion batteries (LIBs) in virtue of their many advantages including high capacity, abundant reserves and environmental friendliness. Yet, previous studies mainly focus on the SnO2-based anodes for lithium storage. Considering that the mixed valence and layered crystal structure of Sn3O4 may lead to better lithium storage properties, Sn3O4-based anode material is designed and synthesized through a facile hydrothermal method in this work. The as-prepared Sn3O4 nanosheets are coated with N-doped carbon layers (∼15 nm) on both sides through dopamine polymerization and subsequent polydopamine carbonization to solve the issues of poor intrinsic electronic conductivity and drastic volume change during LiSn alloying/dealloying, which have hindered their application in LIBs. With the structural and composition advantages brought by the thick N-doped carbon layers, the Sn3O4@NC nanosheets delivered a remarkable reversible capacity (1222 mAh g−1 after 50 cycles at 200 mA g−1) and excellent rate performance when applied in LIB as anode material, owing to the improved electrical conductivity and strengthened structure stabilities. Importantly, we demonstrate a convenient strategy to realize carbon coating in the fabrication of Sn3O4-based anode materials, which could inspire the development of other Sn3O4-based anode materials with excellent lithium storage properties.

Barium Lanthanum Oxide Nanosheets in Photocatalytic and Forensic Applications: One-Pot Synthesis and Characterization.

The present work elucidates the fabrication of Barium Lanthanum Oxide nanosheets (BaLa2O4 NSs) via a simple one-pot precipitation method. The acquired results show an orthorhombic crystal system with an average crystallite size of 27 nm. The morphological studies revealed irregular-shaped sheets stacked together in a layered structure, with the confirmation of the precursor elements. The diffused reflectance studies revealed a strong absorption between 200 nm and 350 nm, from which the band-gap energy was evaluated to be 4.03 eV. Furthermore, the fluorescence spectrum was recorded for the prepared samples; the excitation spectrum shows a strong peak at 397 nm, attributed to the 4F7/2→4G11/2 transition, while the emission shows two prominent peaks at 420 nm (4G7/2→4F7/2) and 440 nm (4G5/2→4F7/2). The acquired emission results were utilized to confirm the color emission using a chromaticity plot, which found the coordinates to be at (0.1529 0.1040), and the calculated temperature was 3171 K. The as-prepared nanosheets were utilized in detecting latent fingerprints (LFPs) on various non-porous surfaces. The powder-dusting method was used to develop latent fingerprints on various non-porous surfaces, which resulted in detecting all the three ridge patterns. Furthermore, the as-synthesized nanosheets were used to degrade methyl red (MR) dye, the results of which show more than 60% degradation at the 70th minute. It was also found that there was no further degradation after 70 min. All the acquired results suggest the clear potential of the prepared BaLa2O4 NSs for use in advanced forensic and photocatalytic applications.

CuMnO2 nanosheets for high performance aqueous Zn-ion batteries

Zinc-ion batteries based on aqueous electrolytes have great advantages over organic ones. Here, CuMnO2 nanosheets with a thickness of about 10 nm have been prepared by a hydrothermal method assisted by nitrilotriacetic acid. Benefiting from its layered structure and unique two-dimensional (2D) nanosheets, the as-prepared CuMnO2 nanosheets are a good host for fast zinc ion transport, high capacity, and reversible electrochemical reactions, as well as excellent cycling stability. Specifically, a zinc storage capacity of 299.1 mAh g−1 at 0.2 A g−1 and stable cycling (189.9 mAh g−1 after 300 cycles), fast diffusion kinetics of Zn-ions (1.52 × 10−13 cm2 s−1), and good rate capabilities (78 mAh g−1 even at 2.0 A g−1) are achieved. This work suggests a potential candidate cathode for zinc-ion batteries.

Detection of human serum albumin using a rare-earth nanosheet fluorescent probe based on intensity and lifetime signals

Human serum albumin (HSA) is an important biomarker for early disease diagnosis. Therefore, the detection of HSA in biological samples is important. In this study, for the sensitive detection of HSA, a fluorescent probe based on Eu(III)-doped yttrium hydroxide nanosheets was designed and sensitized by α-thiophenformyl acetone trifluoride as an antenna. The morphology and structure of the as-prepared nanosheet fluorescent probe were studied by transmission electron microscopy and atomic force microscopy. A detailed investigation of the fluorescence properties of the as-obtained nanosheet probe revealed that the Eu(III) emission intensity was linearly and selectively enhanced by the consecutive addition of HSA. Furthermore, the lifetime signal of this probe was enhanced with increasing concentration. The sensitivity of the nanosheet probe to HSA is discussed based on the results of ultraviolet–visible, fluorescence, and infrared spectral analyses, the findings demonstrate that the nanosheet fluorescent probe we prepared is a highly sensitive and selective tool for detecting HSA concentration with a high intensity and a large lifetime change.

Fabrication of zwitterionic polymer-functionalized MXene nanosheets for anti-bacterial and anti-biofouling applications

Marine biological pollution is a worldwide problem that poses a significant challenge in marine engineering. MXene nanosheets and zwitterionic polymers are promising materials for marine anti-biofouling and have attracted much attention. Herein, we self-assembled the polydopamine layer on the surface of MXene nanosheets (MXene-PDA), and then introduced the zwitterionic polymer (PEIS) by Michael addition reaction onto the PDA layer to obtain the zwitterionic polymer-functionalized MXene nanosheets (MXene-PEIS). The as-prepared MXene-PEIS exhibits excellent antifouling performance through the cooperative antifouling effect between the MXene nanosheets and the zwitterionic polymer PEIS (the antibacterial rate improved by 88 % and there was a 98 % decrease in microalgae adhesion density). Moreover, the nanocomposite antifouling coatings (MXene-PEIS/SP) were obtained by blending the as-prepared MXene-PEIS nanosheets with self-polishing coatings. The results show that MXene-PEIS/SP coatings have good antifouling performance due to the synergy between MXene, PEIS, and self-polishing coatings.

Modulate the metallic Sb state on ultrathin PdSb-based nanosheets for efficient formic acid electrooxidation

Incorporation of oxophilic metals into Pd-based nanostructures has shown great potential in small molecule electrooxidation owing to their superior anti-poisoning capability. However, engineering the electronic structure of oxophilic dopants in Pd-based catalysts remains challenging and their impact on electrooxidation reactions is rarely demonstrated. Herein, we have developed a method for synthesizing PdSb-based nanosheets, enabling the incorporation of the Sb element in a predominantly metallic state despite its high oxophilic nature. Moreover, the Pd90Sb7W3 nanosheet serves as an efficient electrocatalyst for the formic acid oxidation reaction (FAOR), and the underlying promotion mechanism is investigated. Among the as-prepared PdSb-based nanosheets, the Pd90Sb7W3 nanosheet exhibits a remarkable 69.03% metallic state of Sb, surpassing the values observed for the Pd86Sb12W2 (33.01%) and Pd83Sb14W3 (25.41%) nanosheets. X-ray photoelectron spectroscopy (XPS) and CO stripping experiments confirm that the Sb metallic state contributes the synergistic effect of their electronic and oxophilic effect, thus leading to an effective electrooxidation removal of CO and significantly enhanced FAOR electrocatalytic activity (1.47 A mg−1; 2.32 mA cm−1) compared with the oxidated state of Sb. This work highlights the importance of modulating the chemical valence state of oxophilic metals to enhance electrocatalytic performance, offering valuable insights for the design of high-performance electrocatalysts for electrooxidation of small molecules.

Monodisperse covalent organic nanosheets by in-situ oxidation method for efficient ion/molecule separation

Two-dimensional (2D) covalent organic nanosheets (CONs) are layered crystalline porous polymers comprising periodically extended graphene-like structures, and have great application potential in membrane separation field due to the advantages of abundant optional monomers, tunable pore size and structure, facilely-tailored functionality and pre-designed properties. However, unlike graphene oxide (GO) membranes, it is hard to directly prepare 2D CON membranes by vacuum filtration because of the difficulties in preparation of ultra-thin, large-sized and well-dispersed 2D CONs. Herein, an improved buffering interlayer interface method was proposed to realize a facile one-step synthesis of GO-like CON oxides by using H2O2 as an in-situ oxidant in the buffer layer. The stereoscopic fulcrum-oxygen sites introduced into the structure of CONs lead to weaken interactions between CON layers and increased hydrophilicity, which contributes to subsequent preparation of monodisperse nanosheets. The membranes fabricated with the as-prepared monodisperse nanosheets can realize high-efficiency transport of metal ions with a precise charge-discriminated group separation ability and efficient ion rejection. The strategy of in-situ oxidation to prepare monodisperse CONs proposed in this study provides a valuable approach for the preparation of novel functionalized CONs and the achievement of fast membrane separation performance.

The Preparations of Fluorographene Nanosheets and Research in Tribological Properties in High Vacuum.

In this study, fluorographene nanosheets (FG nanosheets) were prepared via the solvent-ultrasonic exfoliation method. The fluorographene sheets were observed using field-emission scanning electron microscopy (FE-SEM). The microstructure of the as-prepared FG nanosheets was characterized by X-ray diffraction (XRD) and a thermal analyzer (TG). The tribological properties of FG nanosheets as an additive in ionic liquids in high vacuum were compared to that of ionic liquid (IL) with graphene (IL-G). The wear surfaces and transfer films were analyzed via an optical microscope, Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The results show that FG nanosheets can be obtained from the simple solvent-ultrasonic exfoliation method. The prepared G nanosheets are a sheet, and the longer the ultrasonic time is, the thinner the sheet is. Ionic liquids with FG nanosheets had low friction and a low wear rate under high vacuum conditions. The improved frictional properties were attributed to the transfer film of FG nanosheets and more formation film of Fe-F.

Enhancing Electrochemical Nitrate Reduction to Ammonia over Cu Nanosheets via Facet Tandem Catalysis.

Electrochemical conversion of nitrate (NO3 - ) into ammonia (NH3 ) represents a potential way for achieving carbon-free NH3 production while balancing the nitrogen cycle. Herein we report a high-performance Cu nanosheets catalyst which delivers a NH3 partial current density of 665 mA cm-2 and NH3 yield rate of 1.41 mmol h-1 cm-2 in a flow cell at -0.59 V vs. reversible hydrogen electrode. The catalyst showed a high stability for 700 h with NH3 Faradaic efficiency of ≈88 % at 365 mA cm-2 . In situ spectroscopy results verify that Cu nanosheets are in situ derived from the as-prepared CuO nanosheets under electrochemical NO3 - reduction reaction conditions. Electrochemical measurements and density functional theory calculations indicate that the high performance is attributed to the tandem interaction of Cu(100) and Cu(111) facets. The NO2 - generated on the Cu(100) facets is subsequently hydrogenated on the Cu(111) facets, thus the tandem catalysis promotes the crucial hydrogenation of *NO to *NOH for NH3 production.

High performance δ-Bi2O3 nanosheets transformed Bi2S3 nanoflakes interconnected nanosheets as negative electrode for supercapacitor applications

Progress of negative electrode for supercapacitors (SCs) is most important topic of the recent advanced technological era for the next generation energy storage devices and applications. Bismuth oxide (δ-Bi2O3) with high specific capacitance has emerged as a promising negative electrode material for SCs. Herein, a facile two-step synthesis strategy has been proposed to fabricate Bi2S3 nanoflakes interconnected nanosheets electrode by the conversion of electro-deposited as-prepared δ-Bi2O3 nanosheets followed by hydrothermal route. From the comparison study, it is concluded that Bi2S3 nanoflakes interconnected nanosheets exhibit ultrahigh specific capacitance (565 F g−1 at 1 A g−1) and exceptional cycling stability (∼98% retention after 2000 cycles) as a negative electrode material. Meanwhile, δ-Bi2O3 nanosheets electrode has only reached to 474 F g−1 at 1 A g−1 with poor retention of ∼46%. The improved and better performance of Bi2S3 nanoflakes interconnected nanosheets electrode is attributed to high conductivity due to sulfurization. The current fabrication strategy would provide valuable insights to prepare Bi-based nano-materials for high-performance energy storage technologies and beyond.