Liquid-phase Exfoliation Method Research Articles

Functionalized boron nanosheets with near-infrared-triggered photothermal and nitric oxide release activities for efficient antibacterial treatment and wound healing promotion.

The spread of bacterial resistance is a rising serious threat to global public health, and has created an urgent need for the development of a new generation of antibacterial nano-agents to take the place of antibiotics. In this work, a multifunctional nanoplatform based on boron nanosheet (B NS)-coated quaternized chitosan (QCS) and the nitric oxide (NO) donor N,N'-di-sec-butyl-N,N'-dinitroso-1,4-phenylenediamine (BNN6) (B-QCS-BNN6) was prepared via a liquid-phase exfoliation and electrostatic adsorption method. The 2D B NSs could convert near-infrared (NIR) light into heat energy as well as assemble positively charged QCS and BNN6 to trap negatively charged bacteria, and the positive charge made it easily captured by bacteria, increasing the opportunities for NO diffusion to the bacterial surface. The B-QCS-BNN6 nanoplatform not only exhibited photothermal therapy (PTT) efficacy but could also control NO release precisely after stimulation with an 808 nm laser for the rapid and effective treatment of typical Gram-negative and Gram-positive bacteria. The enhanced PTT/NO antibacterial function achieved >99.9% inactivation of bacteria within 5 min. Furthermore, this synergetic antibacterial strategy could also be conveniently employed for highly efficient disinfection of a methicillin-resistant Staphylococcus aureus (MRSA) infected wound and promotion of the reconstruction of damaged tissues for in vivo MRSA-infected wound therapy.

Ta4C3 MXene as a saturable absorber for femtosecond mode-locked fiber lasers

Ta4C3 as one of the MXene has been widely investigated in the application of materials chemistry, biomedicine, electrochemical energy storage and other fields. However, the study of its optical properties and applications remains rare. In this work, few-layer Ta4C3 MXene are prepared and its optical properties and applications are systematically investigated. We develop few-layer Ta4C3 MXene through the liquid phase exfoliation (LPE) method, and prepare it as Ta4C3 saturable absorber (SA). To obtain femtosecond pulses, the Ta4C3-SA is inserted further to an erbium-doped fiber laser (EDFL) cavity. It is worth noting that in the experiment the EDFL composed of Ta4C3-SA can generate stable femtosecond pulses, and the spectral bandwidth and duration of the femtosecond pulses are 1559.6 nm and 350 fs, respectively. Meanwhile, the numerical simulation results consistent with the experimental results. The results reveal that Ta4C3 MXene has great application potential in nonlinear optics and ultrafast photonics.

Ternary Transition Metal Dichalcogenides for High Power Vector Dissipative Soliton Ultrafast Fiber Laser

Abstract2D ternary transition metal dichalcogenides (TMDCs) have been studied widely by researchers from the fields of nanotechnology to materials science because of the extraordinary chemical/physical characteristics, and significant potential in nanoscale device applications. Here, the application of NbxRe(1−x)S2 nanosheets in ultrafast photonics is studied. The few‐layer NbxRe(1−x)S2 nanosheets are fabricated through liquid phase exfoliation method and a NbxRe(1−x)S2‐microfiber device is constructed by depositing these nanosheets onto the tapered region of a microfiber. After incorporating the NbxRe(1−x)S2‐microfiber saturable absorber (SA) into a net positive dispersion Er‐doped fiber (EDF) laser cavity, the generation of stable dissipative soliton pulses with a pulse duration of 1.03 ps proved as polarization‐locked vector solitons upon further study. With pump power growing to 900 mW, the average output power increases to 116.9 mW without pulse splitting. Besides, the pulse width can be compressed to 149.6 fs outside the cavity by using a single‐mode fiber. Compared with previous works based on 2D materials‐based saturable absorbers, the NbxRe(1−x)S2‐based mode‐locked fiber laser proposed herein, reveals superior comprehensive performance.

Passively mode-locked Er-doped fiber laser based on a semi-metallic InBi saturable absorber

Two-dimensional (2D) materials have drawn great interest for their applications in mode-locking due to their unique optical nonlinearities. However, most of these 2D materials are semi-conductors. In this study, a new kind of semi-metal indium bismuth (InBi) is reported which is a topological nodal-line semi-metal with exotic physical properties. The InBi nanomaterials were prepared through a liquid phase exfoliation method with an average thickness of 32.8 nm. The saturable absorption property was measured and passive mode-locking operation was successfully achieved in the Er-doped fiber laser. It exhibited a modulation depth of 3.21%, a saturable intensity of 100 MW cm−2 and a pulse width about 859.97 fs corresponding to the central wavelength of 1562.27 nm and 3 dB bandwidth of 2.98 nm. The experimental results open a new avenue for the use of semi-metals InBi nanomaterials in lasers and photonics applications.

High-performance hole transport layer based on WS2 doped PEDOT:PSS for organic solar cells

In this work, we developed WS2 nanosheets (WS2 NS) doped into PEDOT:PSS (PEDOT:PSS/WS2 NS) as an efficient hole transport layer (HTL) for organic solar cells (OSCs). WS2 NS is obtained by a simple and cost-effective liquid-phase exfoliation (LPE) method. The results show that the PEDOT:PSS:WS2 NS anode interlayer has higher work function, reduced roughness and improved hole mobility. The devices based on PEDOT:PSS:WS2 NS interlayer show enhanced extraction and transportation of holes and improved fill factor and short-circuit current density. Based on PM6:Y6, the power conversion efficiency (PCE) increased from 14.35% to 15.67% after WS2 NS doping.

Optical pulse modulators based on layered vanadium diselenide nanosheets

The transition metal disulfides of VB group elements have gradually come into people’s field of vision owing to their two-dimensional structure and unique optical properties. Vanadium diselenide (VSe2) as a kind of transition metal diselenides, is competent for the applications of nonlinear saturable absorption. The dispersion of few-layer VSe2 is prepared by liquid phase exfoliation method. Clearly, it has an obvious layered structure, and the interlayer spacing is 0.31 nm. The VSe2 nanosheets are inserted into the Erbium-doped fiber laser through tapered deposition method and the measured modulation depth is 1.46%. A 1530.5 nm centered 851-fs pulse is observed with the 3.2 nm 3-dB spectral width. The experimental results show that the pulse is persistent under the power of 334 mW, with signal-to-noise ratio of 41 dB. And an up to 552.4 MHz modulation phenomenon is observed around 1560 nm, so is its frequency tunability. This is the first time that VSe2 is used to realize high frequency modulation in fiber laser. It is proved that VSe2 is expected to be a budding material of ultrafast optical modulation devices and widely used in the field of ultrafast photonics.

Two-Dimensional Gallium Sulfide as a Novel Saturable Absorber for Broadband Ultrafast Photonics Applications.

Two-dimensional (2D) gallium sulfide (GaS) offers a plethora of exceptional electrical and optical properties, allowing it to be used in a wide range of applications, including photodetectors, hydrogen generation, and nonlinear optical devices. In this paper, ultrathin 2D GaS nanosheets are synthesized using the liquid-phase exfoliation method, and the structure, morphology, and chemical composition of the as-prepared nanosheets are extensively investigated. After depositing 2D GaS nanosheets on side polished fibers, successful saturable absorbers (SAs) are fabricated for the first time. The realized modulation depths are 10 and 5.3% at 1 and 1.5 μm, respectively, indicating the wideband saturable absorption performance of the prepared SAs. By integrating GaS-SAs into three different wavelength-based fiber laser cavities, stable mode-locked pulses are achieved, having pulse durations of 46.22 ps (1 μm), 614 fs (1.5 μm), and 1.02 ps (2 μm), respectively. Additionally, different orders of harmonic mode-locked pulses with the highest repetition rate of 0.55 GHz (45th order) and Q-switched pulses with the shortest pulse duration of 2.2 μs are obtained in the telecommunication waveband. These findings suggest that 2D GaS has a lot of potential for broadband ultrafast photonics in nonlinear photonics devices.

Wavelength tunable Q-switched Er-doped fiber laser based on ZrSe2

We demonstrated a passively Q-switched Er-doped fiber laser based on the ZrSe2/PVA film. Here, the layer structure ZrSe2 platelets were produced by the liquid-phase exfoliation method. By means of nonlinear optical transmittance measurement, the modulation depth and saturation intensity of the ZrSe2/PVA SA were 31% and 4.75 MW/cm2, respectively. The Q-switched pulses revealed the highest repetition rate and pulse energy around 43.7 kHz and 139.8 nJ with the pump power at 346 mW. Based on the invisible filter, we produced the wavelength-tunable and dual-wavelength Q-switched pulses after insertion of the in-line polarizer inside the cavity. Through the proper adjustment of the polarization controller, a tuning wavelength of from 1544.3 to 1563.5 nm, a tuning range of around 19.2 nm, and the smallest tuning interval of around 1 nm have been achieved.

Saturable absorption and self-defocusing response of 2D monoelemental germanium nanosheets in broadband spectra.

Germanium has caused a research boom in recent years due to its high carrier mobility and good stability. Although germanium has been proven to have application potential in photodetectors and other fields, its nonlinear optical properties are rarely reported. Herein, we prepared 2D germanium nanosheets by liquid phase-exfoliation (LPE) method and studied its third-order nonlinear optical response. It is found that the germanium nanosheets exhibit a broadband nonlinear optical response such as it has a large nonlinear absorption coefficient αNL ≈ -0.87 cm GW-1 and a negative nonlinear refractive index n2 ≈ -6.30 × 10-13 cm2 W-1 at 1064 nm wavelength. The experimental results show the excellent nonlinear optical performance of germanium nanosheets and indicate that 2D germanium nanosheets have promising potential in a wide range of photonics device applications.

Stoichiometric modulation on optical nonlinearity of 2D MoS x Se2−x alloys for photonic applications

Abstract The composition-engineered band structures of two-dimensional (2D) ternary transition-metal dichalcogenides (TMDCs) semiconductor alloys directly dominate their electronic and optical properties. Herein, in this paper, a detailed theoretical and experimental study on the composition-dependent nonlinear optical properties of 2D MoS x Se2−x alloys was carried out. The first-principles calculations were performed to investigate the compositionally modulated properties of monolayer 2D MoS x Se2−x (x = 0.25, 0.5, 1.0, 1.5, and 1.75) in terms of the carrier effective mass, carrier density and mobility, as well as band-gaps. Furthermore, high-quality few-layered MoS x Se2−x (x = 0.2, 0.5, 1.0, 1.5, and 1.8) nanosheets were fabricated by using liquid phase exfoliation method. The third-order nonlinear optical response was investigated by open-aperture Z-scan technique, revealing composition-dependent saturable absorption, and light modulation properties, which were correlated to the theoretical calculations and further confirmed by using MoS x Se2−x nanosheets as saturable absorbers (SAs) for all-solid-state pulsed lasers. In particular, a mode-locked solid-state laser with pulse width of 227 fs was realized with MoS0.2Se1.8 as SA, for the first time to our best knowledge. Our work not only provides a comprehensive understanding of the compositionally and defectively modulated nonlinear optical responses of ternary TMDCs alloys, but also paves a way for the development of 2D materials-based novel optoelectronic devices.

Preparation of antimonene nanosheets and their thermoelectric nanocomposites

Having high stability, carrier mobility and band gap tunability, antimonene nanosheets hold promise for thermoelectric applications. However, due to low production yield and oxidization, relevant studies have focused on theoretical prediction and numerical simulation. We herein report a liquid-phase exfoliation method with a novel solvent system of amine-terminated polyether (Jeffamine ED 2003): ethanol = 1:4 (weight ratio) for preparation of antimonene nanosheets. This method not only effectively inhibited the oxidation of antimonene nanosheets but produced a low thickness of 2.0 ± 0.5 nm; a film consisting of the nanosheets exhibited an electrical conductivity of 1800.1 ± 97.4 S/cm and a thermoelectric power factor of 118.9 ± 5.6 μW m−1 K−2. An epoxy nanocomposite film containing 99 vol% antimonene nanosheets demonstrated sufficient mechanical resilience for assembling of a thermoelectric generator. With a human body temperature gradient of 11 °C, the generator created a voltage of 0.471 mV and a current of 21.578 μA, leading to a power output of 10.16 nW. This study also investigated the lithium-ion intercalation method as a benchmark for preparation of antimonene nanosheets.

Large-energy mode-locked Er-doped fiber laser based Cr2Si2Te6 as a modulator

Ultrafast photonic devices based on two-dimensional (2D) materials attract the attentions of researchers. In order to expand the range and diversity of ultrafast lasers and advanced photonics, it is necessary to explore new 2D materials with excellent nonlinear absorption properties. Ferromagnetic insulators (FIs) have the suitable band structure and they can be stripped into single layer structure easily, however, few related works have been reported. In this work, Cr2Si2Te6 (CST) thin film modulator was prepared through the method of liquid-phase exfoliation (LPE) and investigated its nonlinear optical properties and application in obtaining large energy mode-locking pulse output. The modulation depth and saturable intensity of the CST were 4.40% and 12.51 MW/cm2, respectively. Transferring it into the ring cavity, the all-fiber laser can generate a large energy pulse with a center wavelength of 1558.53 nm and a repetition frequency of 1.61 MHz. The energy of single pulse was 53.03 nJ. The maximum average output power was 85.54 mW under the pump power of 1659 mW. To our knowledge, the energy of single pulse is the highest among the reported all-fiber lasers with FIs saturable absorbers (SAs). Our experimental results proved that CST-SA has excellent modulation properties, which provides a basis for future research.

Nanostructure and functional group engineering of black phosphorus via plasma treatment for CO2 photoreduction

As an emerging two-dimensional (2D) semiconductor, black phosphorus (BP) has attracted great interest in photocatalytic CO2 reduction, but the performance is restricted by the low surface reactivity and poor stability. Exfoliating BP into the 2D structure is an effective method to increase the exposure of active sites. However, the intrinsic surface reactivity and stability cannot be improved, and, the widely used liquid-phase exfoliation method is time-consuming and laborious. In this work, we successfully exfoliates the bulk BP into ultrathin BP nanosheets with dense surface amino-functional groups (BP-NH2) using NH3 plasma treatment. The 2D structure can shorten the photo-excited charges migration distance and improve the exposure of surface-active sites. Furthermore, the amino-functional groups on ultrathin BP nanosheets can prevent the destruction of BP nanosheets in ambient air, favoring the charge separation, CO2 adsorption and activation during the catalytic process. Benefiting from integrated advantages of amino functional groups, the optimal BP-NH2 exhibits a photocatalytic CO2 reduction rate to CO of 27.6 μmol g−1 h−1 with a selectivity of 87.0 %, both of which are higher than those of pristine bulk BP. This work presents ideas for stabilizing BP and improving the CO2 reduction performance simultaneously.

A biodegradable polymer-assisted efficient and universal exfoliation route to a stable few layer dispersion of transition metal dichalcogenides

Quasi two-dimensional transition metal dichalcogenides (2D-TMDs) with 1–5 layers have been obtained by developing an effective and highly efficient bio-based polymer-solvent system by mild ultrasonication. The hydroxypropyl cellulose (HPC)/1-Butanol (BuOH) system was determined to be an universal polymer-solvent system to effectively exfoliate the bulk transition metal dichalcogenides (TMDs) MoS2, TiS2, WS2, NbS2 and MoSe2. The above process is significant as it is a room temperature liquid phase exfoliation method that leads to a stable dispersion of a few layer 2D-TMD having significant proportion (>50%) of exfoliated material which remains stable in suspension for several months.

Real-time quality monitoring and organic pollutants degradation of water using atomically thin Magnesiochromite

Here, we report the synthesis of atomically thin Magnesiochromite by an easily scalable liquid-phase exfoliation method. Two-dimensional (2D) MgCr2O4 was studied in detail by microscopy analysis. Thickness and average lateral dimensions of the 2D sheets, measured by atomic force microscopy were 4–5 nm and 100–350 nm respectively. Formation of atomically thin structure was also confirmed by Raman spectroscopy which also confirmed the phonon confinement along 2D. Catalytic activity of the 2D MgCr2O4 was studied under visible light and ultrasonic irradiation. Organic dye pollutants such as Methylene Blue, Methyl Orange, and Rhodamine B dye shows degradation efficiency of ∼98.6% within 20 min. The hydrophilic nature of the 2D catalyst is fruitfully utilized by the self-cleaning of cotton fabric and ∼67% decolorization was observed within 3 h of sunlight irradiation. Additionally, a smartphone-based colorimetric measurement technique was used to study the degradation efficiency of the catalyst making it cost efficient and user friendly.

Layered Metallic Vanadium Disulfide for Doubly Q-Switched Tm:YAP Laser with EOM: Experimental and Theoretical Investigations.

In the current study, layered metallic vanadium disulfide (VS2) is fabricated by a liquid-phase exfoliation method, and its microstructures as well as optical characteristics are investigated. Based on first-principles calculations, the band structure and density of the states of both bulk T-VS2 and monolayer H-VS2 are illustrated, showing the metallic behavior with a zero band gap. By using VS2 as the saturable absorber in a doubly Q-switched Tm:YAP laser with an EOM, the Q-switching laser pulses at 2 μm with 22 ns and 200 Hz are generated, corresponding to the single pulse energy of 755 μJ and the peak power of 34.3 kW. The coupled rate equations of the doubly Q-switched laser are given, and the numerical simulations agree with the experimental results. The results indicate that VS2 is a promising nanomaterial due to its nonlinear optical property. The doubly Q-switched laser demonstrates a high level of performance in reducing pulse width and enhancing pulse peak power.

Amplitude modulator of Multi-walled Carbon nanotubes/Chitin in the C-band region

In ultrafast all-optical signal processing, the all-optical method is crucial, and all-fiber technique offers a wide range of applications in optical communications. This study investigated the amplitude modulation using multi-walled carbon nanotubes (MWCNTs) embedded into chitin as saturable absorber (SA). The MWCNTs-chitin SA is fabricate using a liquid phase exfoliation method to reduce complexity and produce an excellent material quality. In this paper, an optical amplitude modulator produced a linear region with a regression line of the peak intensity at pump power range from 17.92 mW to 67.92 mW with modulation efficiency of 0.50 dB/mW.

Broadband and enhanced nonlinear optical modulation characteristics of CuBTC for pulsed lasers

Metal-organic frameworks (MOFs) materials with sufficient charge mobility and promising structural flexibility are appealing for compact optoelectronic nano devices. In this work, the nonlinear optical features of the MOFs-CuBTC were comprehensively investigated for the first time. The CuBTC saturable absorbers were synthesized via liquid-phase exfoliation (LPE) method and characterized for the morphology and structure. The nonlinear optical response of CuBTC was characterized by employing an open-aperture Z-scan technique, which showed the great nonlinear optical modulation potential for the pulsed laser. Thereby, the CuBTC saturable absorber was implemented in the stable passively Q-switched lasers with the operating wavelengths at ∼1 and ∼2 µm to verify its broadband modulation properties, which produced the shortest pulse durations of 131 and 346 ns, respectively. These investigations confirmed that CuBTC can be a promising modulation device candidate for generating short laser pulses in wide spectral regions.

Stretched-pulse generation in all-fiber mode-locked erbium-doped fiber laser using Lawsone dye saturable absorber

This paper describes the generation of mode locked pulses by an erbium-doped fiber laser (EDFL) cavity with a Lawsone dye saturable absorber (SA). The Lawsone SA is made of a piece of thin film, which is obtained using a liquid-phase exfoliation method. Characterization of the film reveals that its saturation intensity and modulation depth are 2.9 MW/cm2 and 12 % respectively. When the Lawsone SA is added to the EDFL cavity, a stable mode-locked pulse train is achieved at 1567.5 nm wavelength. The laser operates within a pump power of 33.6 mW to 43.3 mW at a repetition rate of 3.4 MHz and pulse width of 1.47 ps. The results indicate that the Lawsone dye can be used as a SA for laser pulse generation.

One-Pot Synthesis of Chlorophyll-Assisted Exfoliated MoS2/WS2 Heterostructures via Liquid-Phase Exfoliation Method for Photocatalytic Hydrogen Production.

Developing strategies for producing hydrogen economically and in greener ways is still an unaccomplished goal. Photoelectrochemical (PEC) water splitting using photoelectrodes under neutral electrolyte conditions provides possibly one of the greenest routes to produce hydrogen. Here, we demonstrate that chlorophyll extracts can be used as an efficient exfoliant to exfoliate bulk MoS2 and WS2 to form a thin layer of a MoS2/WS2 heterostructure. Thin films of solution-processed MoS2 and WS2 nanosheets display photocurrent densities of −1 and −5 mA/cm2, respectively, and hydrogen evolution under simulated solar irradiation. The exfoliated WS2 is significantly more efficient than the exfoliated MoS2; however, the MoS2/WS2 heterostructure results in a 2500% increase in photocurrent densities compared to the individual constituents and over 12 h of PEC durability under a neutral electrolyte. Surprisingly, in real seawater, the MoS2/WS2 heterostructure exhibits stable hydrogen production after solar illumination for 12 h. The synthesis method showed, for the first time, how the MoS2/WS2 heterostructure can be used to produce hydrogen effectively. Our findings highlight the prospects for this heterostructure, which could be coupled with various processes towards improving PEC efficiency and applications.