Few-layer Nanosheets Research Articles

Synergistic integration of MXene nanosheets with CdS@TiO2 core@shell S-scheme photocatalyst for augmented hydrogen generation

In order to ensure continuous and stable production of hydrogen (H2), the development of hierarchical nanostructures within a few-layer Mxene nanosheet, incorporating an ultrathin TiO2 shell material, is essential. This shell material plays a crucial role in maintaining the long-term stability of the core and preventing photo-corrosion, thus enabling uninterrupted H2 generation. To evaluate their potential as visible-driven photocatalysts for high H2 production, we conducted a comparative analysis of CdS cores covered with three different shell transition metal oxides (TiO2@NiO@ZnO), supported by Mxene. Structural and morphological characterizations through XRD and TEM confirmed the formation of pure CdS@TiO2@NiO@ZnO core–shell nanostructures, characterized by spherical shapes with a core diameter of 187 nm and a shell thickness of 19.2 nm. XPS experiments demonstrated the structural integrity of the individual elements within the nanocomposite, existing in their respective oxidation states within the core@shell structure. The hierarchical nanostructure exhibited optical characteristics with an absorption edge ranging from 480 to 580 nm. Among the three different shell materials, TiO2 displayed the highest photocatalytic activity under visible light irradiation, followed by NiO and ZnO. Based on our findings, the CdS@TiO2 core@shell photocatalyst supported by Mxene exhibited the highest efficiency, with a production rate of 16.2 mmol.h−1.g-1cat. This can be attributed to enhanced charge separation, the spatial distribution of carriers, and favorable structural properties. Our DFT calculations further supported the efficacy of coupling Mxene with CdS/TiO2, as it facilitated efficient water splitting, with CdS favoring H2O dissociation and Mxene favoring HER. These results highlight the potential of developing highly efficient photocatalysts for water splitting by integrating Mxene with CdS/TiO2. Additionally, The prepared CDTM (Mxene@CdS/TiO2) photocatalyst existing S-scheme heterojunction for efficient water splitting. This underscores the system's effective functioning across diverse sceneries, Overall, our study presents a feasible and effective strategy for constructing an S-scheme heterojunction system that utilizes photo charge carrier separation to enhance the utilization and conversion of solar energy.

PANI/Ti3C2Tx composite nanofiber-based flexible conductometric sensor for the detection of NH3 at room temperature

The rational design of sensing materials with distinct morphologies and compositions is important to construct outstanding flexible gas sensors. Herein, a mesh polyaniline (PANI)/Ti3C2Tx composite nanofiber-based flexible sensor was constructed by electrospinning of PANI and few-layer Ti3C2Tx nanosheets. Sensing results indicated that this novel PANI/Ti3C2Tx flexible sensor demonstrated much higher NH3 sensing response (2.3-fold improvement @ 20 ppm) in comparison with the sensor based on pure PANI nanofibers at 25 °C. Under different bending angles (maximum compression of 150°) and different bending times (maximum bending of 3200 times), the PANI/Ti3C2Tx flexible sensor maintained steady sensing behavior towards 20 ppm NH3, which reflected its good flexible bending stability. The PANI/Ti3C2Tx flexible sensor also exhibited good selectivity, repeatability, as well as good long-term stability. The improvement of NH3 sensing properties can be ascribed to the formation of Schottky junctions between PANI and Ti3C2Tx nanosheets, improved protonation degree of PANI, and the special three-dimensional mesh fiber structure. Our work revealed that the PANI/Ti3C2Tx composite nanofibers with interconnected mesh fiber structure have great potential to construct flexible NH3 sensors.

Restoring Piezoelectric Properties in 2D Zinc Oxide Nanosheets by Surface Modifications: Implications for Piezoelectric Nanogenerators

Nanoelectronic devices that are self-powered through the conversion of mechanical energy into electronic energy are of great interest for the fields of wearables and medical implants. The ability to find nanomaterials that have piezoelectric properties suitable for nanogenerators can be a challenge. Zinc oxide (ZnO) is a well-known material that has one of the highest piezoelectric tensors among tetrahedrally bonded semiconductors, due to its buckled noncentrosymmetric structure on the (0001) and (0001̅)] surfaces. However, this piezoelectric response is diminished in few-layered two-dimensional (2D) ZnO, as it loses it buckled structure and becomes graphitic. As a consequence, ultrathin 2D ZnO sheets are not suitable for nanoscale devices that rely on a piezoelectric response. In this work, we show that defects, specifically, zinc and oxygen vacancies, and adsorbed oxygen, can restore the wurtzite structure and piezoelectric response of free standing 2D ZnO sheets at specific thicknesses. Using density functional theory calculations, we show that both a 1 monolayer (ML) surface coverage of oxygen and a 25% concentration of zinc vacancies can restore the buckling in few-layer 2D ZnO nanosheets. For a 1.48 nm thick sheet with a 25% Zn vacancy concentration, an e33 value of 1.26 C/m2 can be achieved, which is 120% enhancement compared to the bulk value. These findings provide a methodology for screening piezoelectric properties of other materials and demonstrate that defects can be used to restore the wurtzite structure and dielectric properties of ultrathin 2D ZnO sheets that would allow them to be used in nanoscale piezoelectric devices.

Two-dimensional perovskite Pb2Nb3O10 photodetectors

For the first time, we report high-performance two-dimensional (2D) perovskite Pb2Nb3O10 photodetectors (PNO PDs). The few-layer PNO nanosheets are obtained successfully through a simple calcination and liquid exfoliation method. The individual PNO nanosheet devices with various structures (Au-PNO-Au, Au-PNO-Ti, Ti-PNO-Ti) are fabricated and investigated. The Au-PNO-Ti device exhibits a high rectification factor (∼102) owing to a large Schottky barrier difference between the PNO nanosheet and two asymmetric electrodes. Notably, the Au-PNO-Ti device shows excellent self-powered performance, including high responsivity (2.8 A/W), high detectivity (1.1 × 1012 Jones), and fast speed (0.2/1.2 ms) at 350 nm light illumination. This work not only suggests the performance of the PNO nanosheet PDs but also sheds light on the development of high-stability and high-performance devices based on 2D perovskite niobate in the future.

High-performance flexible nanogenerators based on piezoelectric hBN- induced polyvinylidene fluoride nanofibers

Flexible piezoelectric nanogenerators (PENGs) are promising candidates for clean energy harvesting and powering electronics, especially for low-power modules. In this study, a PENG has been fabricated by incorporating functionalized mono-/few-layered hexagonal boron nitride nanosheets (F-hBNNS) in a polyvinylidene fluoride (PVDF) polymeric matrix. The synthesized 2D nanosheets are well characterized using different spectroscopic and microscopic methods. The analysis showed successful exfoliation of hBN, which indicated less than three layers of hBN after exfoliation and sulfonated and carboxylated functionalization on the surface. Also, the piezoresponse force microscopy (PFM) tests revealed a 3 times higher piezoelectric coefficient for F-hBNNS compared to that of the non-functionalized hBN with the same number of layers. The synthesized F-hBNNS with piezo-flexoelectric properties boosted the energy harvesting performance of the electrospun PVDF-based fibrous mats 5.5 times. The open-circuit output voltage test showed 23 V at 4 Hz with a power density of 1.93 μW/cm2 at a resistance loading of 16 MΩ in a simple finger tapping. The fabricated PENGs showed no decline in voltage output over 1000 cycles of bending-unbending of a robotic finger. It is proposed that the enhanced performance is due to (i) the synergistic effects of the flexoelectric and piezoelectric properties of synthesized F-hBNNS in the PVDF matrix and (ii) the manipulation of the crystalline structure of the PVDF chains, which is increased to 90% β-phase crystallinity with 49.03% total degree of crystallinity. This study shows the compatibility of the fabricated PENGs with the human body's biomechanics for being used as an efficient energy source for wearable devices with low power consumption.

Exfoliation of a Two-Dimensional Metal–Organic Framework for Enhanced Photocatalytic CO2 Reduction

A two-dimensional metal-organic framework, FICN-12, was constructed from tris[4-(1H-pyrazole-4-yl)phenyl]amine (H3TPPA) ligands and Ni2 secondary building units. The triphenylamine moiety in the H3TPPA ligand readily absorbs UV-visible photons and sensitizes the Ni center to drive photocatalytic CO2 reduction. FICN-12 can be exfoliated into monolayer and few-layer nanosheets with a "top-down" approach, which exposes more catalytic sites and increases its catalytic activity. As a result, the nanosheets (FICN-12-MONs) showed photocatalytic CO and CH4 production rates of 121.15 and 12.17 μmol/g/h, respectively, nearly 1.4 times higher than those of bulk FICN-12.

Constructing sulfur and oxygen co-doped carbon nanosheets by tailoring poly tannic acid for fast and stable potassium storage

Carbonaceous material with excellent structural stability and low cost has always been deemed focus of pursuer, nevertheless it showed the sluggish dynamics and large volume expansion as the anode materials for potassium-ion batteries (PIBs). Herein, S, O co-doped ultra-thin carbon nanosheets (S/O-CNS) with enlarged interlayer spacing was synthesized through pyrolysis poly tannic acid with a sulfur-assisted carbonization strategy. Under the unique synthesis process, sulfur acts as a dopant and intercalating agent to acquire few-layer carbon nanosheets with large interlayer spacing (0.42 nm), while oxygen was in-situ doped into the carbon lattice and provides sites for sulfur doping. With the synergistic effects of the co-doping effect and heterostructure, S/O-CNS delivers an excellent reversible capacity of 375.6 mA h g−1 at 0.1 A g−1, an impressive rate performance of 159.9 mA h g−1 even at 10 A g−1 as well as outstanding cycle stability of 198.9 mA h g−1 after 700 cycles at 1.0 A g−1. Kinetics analysis indicates that the capacitance-controlled process plays a dominant role in K+ storage. The results prove that the enlarged interlayer spacing and abundant edge defects accelerate the ion diffusion kinetics. This dual-doping strategy provides a way to design high-performance carbonaceous materials for PIBs.

Boosting sulfate radical assisted photocatalytic advanced oxidative degradation of tetracycline via few-layered CoZn@MOF/GO nanosheets

A facile and robust protocol for the synthesis of CoZn@MOF/GO photocatalyst via hydrothermal route has been presented, and the method has resulted in the formation of CoZn@MOF/GO few-layer nanosheets. The as-prepared catalyst has shown improved degradation of tetracycline hydrochloride. A detailed investigation of the effect of various parameters such as pH, concentration, and catalyst load was carried out to ascertain the optimum reaction condition required for the maximum degradation of tetracycline. Also, presence of GO has improved the visible light assimilation, band gap restructuring and consequent photocatalysis. Radical scavenger and electron resonance studies revealed that presence of light, persulfate and oxygen were pivotal for the enhanced photocatalysis of TCn at CoZn@MOF/GO and to accomplish complete degradation of TCn. The synergism between catalytic, sulfate mediated and advanced photocatalytic process has been discussed, a systematic degradation pathway was analysed in detail and a plausible mechanism has been proposed.

Nonstationary thermophysical characterization of exfoliated graphite with carbon nanotubes composites

The sheet samples of thermally exfoliated graphite (TEG)–carbon nanotubes (CNT) composites (TEG-CNT-cs) were obtained by persulphate oxidation using chemical (CO) and electrochemical (anode) oxidation (ECAO). Electron microscopy reveals multi-layered structures of few-layer graphene nanosheets with folded and tubular-like fragments. The effective thermal diffusivity values were estimated by nonstationary photo-pyroelectric thermophysical characterization using the heat pulse and thermowave modulation methods. Comparison with other carbon (C-) based thermal management materials shows that TEG-CNT-cs exhibit thermal diffusivity, effusivity, and conductivity comparable with those of actual C–polymer- and C–C-composites. For TEG-CNT-cs, evaluated values of phonon mean free path (MFP) and relaxation time (RT) are in the ranges estimated for defective graphene. The values of diffusivity and effusivity, MFP, and RT are lower for denser TEG-CNT-cs obtained by ECAO and are higher for less dense TEG-CNT-cs obtained by CO. The obtained diffusivity and effusivity values designate TEG-CNT-cs as suitable thermal management materials.

Enhanced degradation of few-layer black phosphorus by fulvic acid: Processes and mechanisms

The oxidation of the emerging nanomaterial black phosphorus (BP) affected by pH and oxygen has been carefully documented. However, in natural waters, there is a large amount of chemically reactive organic matters like fulvic acid (FA), whose impacts on degradation and stability of few-layer BP or BP nanosheets (BPNS) are scarcely disclosed. Hence, we investigated the kinetics of BPNS degradation products (H2PO2−, HPO32−, and PO43−) in the presence of FA. The results showed that the apparent reaction rate constants of BPNS were 0.026, 0.050, and 0.060 d−1 under oxygen-and-light condition and 0.005, 0.016, and 0.023 d−1 under hypoxia-and-darkness condition at FA gradients of 0, 2.5, and 5 mgC/L, respectively. Microscopic observations, simple molecular simulation experiment, and density functional theory computation explained that FA significantly enhanced the degradation of P atoms on the BPNS surface through the indirect pathway of reducing the energy barrier of O2 dissociative adsorption and the direct pathway of chemical adsorption, which caused the P-P bond on the BPNS surface to break down and formed P-O bonds or C-P bonds. This study revealed for the first time the degradation mechanism of BPNS in the presence of FA, which is a chemical mechanism of the BPNS transformation behavior. It helps to make a more scientific risk assessment of BP in natural waters.

Ultrafast optical nonlinearity in natural van der Waals heterostructure nanosheets of franckeite

Franckeite, a natural van der Waals heterostructure with excellent physicochemical characteristics, has shown great potential for high-performance optoelectronic device. Here, the few-layer franckeite nanosheets have been prepared by liquid phase-exfoliation method successfully, and the nonlinear optical absorption and carrier dynamics behaviors of the nanosheets have been studied experimentally. The franckeite nanosheets show wavelength- and intensity-dependent nonlinear absorption characteristics, and exhibit ultrafast carrier dynamic process. The ultrafast optical nonlinearity in franckeite nanosheets has been further validated via an Er3+-doped fiber laser to deliver stable femtosecond pulse. The experimental results reveal that franckeite heterostructure nanosheets can be an ideal candidate in the design and manufacture of ultrafast nonlinear optoelectronic devices.

Fullerene Covalent Passivation of Black Phosphorus Nanosheets toward Enhanced Near-Infrared-II Photothermal Therapy

Photothermal therapy (PTT) triggered by near-infrared-II (NIR-II, 1000-1700 nm) light is developed as a potential tumor therapy technique with deeper tissue penetration capacity and higher allowable laser power density of the skin than NIR-I (750-1000 nm) biowindow. Black phosphorus (BP) with excellent biocompatibility and favorable biodegradability demonstrates promising applications in PTT but suffers from low ambient stability and limited photothermal conversion efficiency (PCE), and utilization of BP in NIR-II PTT is scarcely reported. Herein, we develop novel fullerene covalently modified few-layer BP nanosheets (BPNSs) with ∼9-layer thickness through an easy one-step esterification process (abbreviated BP-ester-C60), bringing about the dramatically enhanced ambient stability of BPNSs due to bonding of the hydrophobic C60 with high stability and the lone electron pair on the phosphorus atom. BP-ester-C60 is then applied as a photosensitizer in NIR-II PTT, delivering a much higher PCE than the pristine BPNSs. Under 1064 nm NIR-II laser irradiation, in vitro and in vivo antitumor studies reveal that BP-ester-C60 exhibits dramatically enhanced PTT efficacy with considerable biosafety relative to the pristine BPNSs. This is interpreted by the boost of NIR light absorption on account of the modulation of the band energy level resulting from intramolecular electron transfer from BPNSs to C60.

A Spear and Shield-Inspired Ar Plasma Safeguard Few-Layer Black Phosphore with Firefighting of Epoxy Resin.

Appearing as an innovative and efficient strategy, a facile strategy of a plasma ball mill is carried out to prepare few-layer black phosphorus nanosheets (BPNSs), for abating the fire risk of epoxy resin (EP). A spear and shield-inspired Ar plasma emergeed through a plasma ball mill to prevent Ar@BP nanosheets from oxidation compared with the preparation of BP nanosheets (MBPNSs) in a mechanical ball mill. The absorption coefficient in the synchrotron radiation spectrum is increased by 16.91%, indicating that BP is effectively protected by Ar proof. The Vienna ab initio simulation reveals that the combination of Ar@BP with oxygen cannot proceed spontaneously with the binding energy of 4.44eV. With the introduction of 1.5 wt% Ar@BP, the total heat release (THR), total smoke release (TSR), total smoke production(TSP), CO, and CO2 yield, compared with that of EP, are descended by 30.40%, 24.41%, 24.10%, 33.23%, and 37.60%, respectively, indicating excellent flame retardancy property. It is attributed to the condensed and gas phase function. Meanwhile, the tensile strength and elongation at break increase by 27.92% and 56.04%, respectively, with the incorporation of 1.5 wt% Ar@BP.

Simultaneous triple-effect on inhibiting the photogenerated carriers recombination of g-C3N4 for boosting solar H2 production at atmospheric pressure

Graphitic carbon nitride (g-C3N4) has been well known as one of the important organic semiconductor photocatalyst. However, its low photocatalytic activity greatly hampered its application, which relates to it fast recombination of photoexcited electrons and holes. In this work, conductive thermal oxidation catalysts with good photothermal property (Sm0.5Sr0.5CoO3 (SSC), La0.5Sr0.5CoO3 (LSC) and La0.5Sr0.5MnO3 (LSM)) were used to construct few-layer g-C3N4 based photocatalysts with simultaneously triple-effect on inhibiting the photogenerated carriers recombination. The stacking of g-C3N4 can be reduced by the thermal oxidation and the thickness of few-layer g-C3N4 nanosheets is about 1.5 nm on average, which shortens the migration distance of electrons. The heat converted by the photothermal effect of SSC can accelerate the migration of photogenerated electrons. In addition, the consumption of photogenerated holes can be transferred from g-C3N4 to SSC, further restraining the recombination of electron-hole pairs. The prepared few-layer g-C3N4 nanosheets with 1% addition of SSC exhibit a superior hydrogen evolution rate of 16,521.4 μmol g−1 h−1, which is 13.2 times higher than that of the bulk g-C3N4 at atmospheric pressure.

Enhanced Electrochemical Performance of Metallic CoS-Based Supercapacitor by Cathodic Exfoliation.

Two-dimensional nanomaterials hold great promise as electrode materials for the construction of excellent electrochemical energy storage and transformation apparatuses. In the study, metallic layered cobalt sulfide was, firstly, applied to the area of energy storage as a supercapacitor electrode. By a facile and scalable method for cathodic electrochemical exfoliation, metallic layered cobalt sulfide bulk can be exfoliated into high-quality and few-layered nanosheets with size distributions in the micrometer scale range and thickness in the order of several nanometers. With a two-dimensional thin sheet structure of metallic cobalt sulfide nanosheets, not only was a larger active surface area created, but also, the insertion/extraction of ions in the procedure of charge and discharge were enhanced. The exfoliated cobalt sulfide was applied as a supercapacitor electrode with obvious improvement compared with the original sample, and the specific capacitance increased from 307 F∙g-1 to 450 F∙g-1 at the current density of 1 A∙g-1. The capacitance retention rate of exfoliated cobalt sulfide enlarged to 84.7% from the original 81.9% of unexfoliated samples while the current density multiplied by 5 times. Moreover, a button-type asymmetric supercapacitor assembled using exfoliated cobalt sulfide as the positive electrode exhibits a maximum specific energy of 9.4 Wh∙kg-1 at the specific power of 1520 W∙kg-1.

Preparation and optical-electronic properties of thin films comprising P3HT and few-layer graphene nanosheets

The present work investigates the production of thin films from nanocomposites obtained by solution mixing a synthesized P3HT with different proportions of few-layered graphene (FLG) in chloroform and its influence on crystallography and light absorption in the visible region. Commercial FLG produced through exfoliation in the liquid phase assisted by a non-anionic surfactant was employed, being a material not yet tested for the production of nanocomposites, let alone to be applied in photovoltaic cells. The deposition of thin films was evaluated at low (1000 rpm) and high (2500 rpm) rotation speeds in a dynamic and static deposition process. In addition, the annealing heat treatment in the optimized thin films was evaluated. The results showed that the P3HT was synthesized with suitable molar mass, regioregularity, and thermal resistance as characterized by the analyses of gel permeation chromatography (GPC), 1H-nuclear magnetic resonance (1H NMR), and thermogravimetric analysis (TGA). The thin films produced showed that the FLG enlarged and strengthened the P3HT absorption, increasing the absorption region by up to 34 % in addition to improving the resolution of the absorption peaks favoring the π-π* transition, which is important for the photovoltaic effect. By the X-ray diffraction analysis, it can be suggested that incorporating the FLG improves the charge mobility as there was an increase in the crystallite size without changing the interplanar distance. Based on these results, it can be suggested that P3HT/FLG nanocomposites are promising for application in both the active and hole transport layers of solar cells.

Copper tungstate deposited reduced graphene oxide nanocomposite for highly efficient capacitive deionization

Copper tungstate (CuWO4) decorated 2-dimensional reduced graphene oxide (CWO/rGO) has been successfully fabricated via solvothermal synthesis at 180 °C for 12 h, and then utilized for capacitive deionization (CDI) applications. After deposition of 20 – 40 nm spherical CuWO4 nanoparticles onto few-layered rGO nanosheets, the specific surface area can be up to 338 m2 g−1 with abundant 2 – 10 nm mesopores, which can accelerate the ion transport to augment the electrochemical performance. The CWO/rGO nanocomposite also exhibits high specific capacitances of 380 and 327 F g−1 at 0.5 A g−1 and 5 mV s−1, respectively. Furthermore, the specific electrosorption capacity (SEC) of CWO/rGO is highly dependent on environmental parameters including NaCl concentration, flow rate, applied potential, and solution temperature. An excellent SEC of 54.1 mg g−1 is achieved when 1000 mg L-1 NaCl was used at 1.4 V. Both Faradaic and electric double layer capacitances contribute the electrosorption capacity to the CDI performance of CWO/rGO where CuWO4 provides electroactive sites and rGO enhances the electric conductivity as well as offers mesoporous channels for electrosorption of ions. Meanwhile, the high charge efficiency of 95 %, lower energy consumption of 0.32 kWh m−3, and long-term stability of 50 charging-discharging cycles make the CWO/rGO a potential material for brackish water desalination, which can elucidate on the development of highly efficient desalination technologies.

Ultrasonic exfoliated few-layer Ti2CTx nanosheets for high specific capacitive electrode

Ultrasonic exfoliated few-layer Ti2CTx nanosheets for high specific capacitive electrode

Microwave-assisted hydrothermal synthesis of Fe-doped 1T/2H-MoS2 few-layer nanosheets for efficient electromagnetic wave absorbing

Molybdenum disulfide (MoS2) has been considered as an excellent candidate for microwave absorption applications due to its appropriate electrical conductivity and large area size. However, the absorption efficiency and absorption bandwidth of single-phase MoS2 nanocomposites have been limited due to the weak electrical conductivity and magnetism. This paper proposes a feasible strategy to optimize the electromagnetic properties of MoS2 absorbent by Fe-doping. The MoS2 nanosheets with different Fe concentration have been synthesized a microwave-assisted hydrothermal process. Microstructure characterizations reveal that Fe dopants can facilitate the formation mixed 1T/2H phase MoS2 nanosheets. Owing to the improved permittivity and permeability properties, impedance matching, as well as attenuation characteristics originated from the doping effect and partial phase transformation, the Fe-doped 1T/2H-MoS2 nanosheets exhibit excellent electromagnetic wave absorbing properties. Its maximum reflection loss reaches − 60.03 dB at the matching thickness of 5.65 mm, and the effective absorption bandwidth below − 10 dB is 5.33 GHz. Such novel doping strategy provides a new insight for design and controlling the magneto-dielectric properties of MoS2 nanostructures.

Interlayer coupling, electronic and optical properties of few-layer silicon carbide nanosheets

Interlayer coupling, electronic and optical properties of few-layer silicon carbide nanosheets