Liquid-phase Exfoliation Method Research Articles

Study of the Hydrogen Evolution Reaction on Macroscopic Snse-Based Photoelectrodes

Conversion of solar energy to valuable chemicals by using photoelectrochemical (PEC) techniques such as water splitting, carbon dioxide reduction reaction (CO2RR) and nitrogen reduction reaction (N2RR), are promising methods to solve the issues of energy crisis and global warming [1-2]. Two-dimensional (2D) and layered semiconductors, for example, transition metal chalcogenides (TMCs), metal oxides and MXenes have attracted great attention for PEC applications because of their unique properties, such as high carrier mobility, tunable bandgap, anisotropic carrier transport, and high specific surface area [3]. Our review indicates that, i) 2D and layered semiconductors can be applied for different PEC applications, both in oxidation and reduction reactions, and have ability to give higher performance in water reduction (i.e., hydrogen evolution reaction, HER) than in the other ones. ii) TMCs have been the most studied material with higher performance than the others. However, high PEC performance was achieved only on single crystal TMCs or in microelectrochemical cells, implying a limitation in the scalability of this solar energy conversion approach [4]. There is a clear need to study macroelectrodes prepared from polycrystalline semiconductors and identify the opportunities and barriers for their applications. In our study [5], tin(II) selenide (SnSe) was used as a photoelectrode for PEC HER since it has not been widely investigated for this PEC application. We fabricated SnSe macroscopic photocathodes by depositing SnSe flakes, made from commercial SnSe crystals using a liquid phase exfoliation (LPE) method, on glassy carbon. The as-received SnSe crystals were exfoliated in isopropanol/water mixtures (IPA/H2O) and pure IPA, respectively. Pure IPA was found to be the optimal solvent to prepare flakes and for achieving the highest PEC activity. An additional size separation to make three different size fractions of SnSe crystals served to further optimize the LPE process. Electrodes prepared from the largest flakes showed the highest photocurrent density of 2.44 ± 0.65 mA cm–2 at –0.74 V vs. RHE. The photodeposited Pt co-catalyst on SnSe surface further accelerated the PEC HER activity to 4.39 ± 0.15 mA cm–2. Intensity modulated photocurrent spectroscopy results manifested that the Pt co-catalyst enhanced the charge transfer process and suppressed charge carrier recombination. Overall, the solvent for exfoliation, the edge density of SnSe nanoflakes, immobilization method, and Pt co-catalyst affected the PEC HER performance of SnSe. These results indicate the merit of employing SnSe electrodes for PEC HER and inspire us to explore other photoelectrocatalytic reactions on the macroscopic exfoliated SnSe electrodes.

Generation of Bright-Dark soliton pairs in mode-locked fiber laser based on WSe2/MoSe2 heterojunction

In this study, the WSe2/MoSe2 heterojunction was fabricated by liquid-phase exfoliation (LPE) method with a modulation depth of 11.39 % and saturable intensity of 0.246 GW/cm2. The WSe2/MoSe2 heterojunction was used as a saturable absorber (SA) to achieve bright-dark soliton pairs modulation in Er-doped fiber laser (EDFL)successfully. Stable bright-dark soliton pairs, with a repetition frequency of 4.459 MHz, were successfully generated using a pump power of 218.8 mW. The central wavelengths were found to be at 1564.16 nm and 1564.98 nm with the peak-to-peak spacing of 0.82 nm. The single-pulse energy was determined to be 0.7 nJ. The experimental results demonstrate the exceptional nonlinear saturable absorption characteristics of the WSe2/MoSe2 heterojunction. These findings offer valuable insights for future research on bright-dark soliton pairs utilizing this material.

VTe2: Broadband Saturable Absorber for Passively Q-Switched Lasers in the Near- and Mid-Infrared Regions.

In this study, we demonstrate the fabrication of a novel 2D transition metal dichalcogenide, VTe2, into a saturable absorber (SA) by using the liquid phase exfoliation method. Furthermore, the first-principles calculations were conducted to elucidate the electronic band structures and absorption spectrum. The nonlinear optical absorption properties of VTe2 at 1.0, 2.0, and 3.0 μm were measured using open-aperture Z-scan and P-scan methods, which showed saturation intensities and modulation depths of 95.57 GW/cm2 and 9.24%, 3.11 GW/cm2 and 7.26%, and 15.8 MW/cm2 and 17.1%, respectively. Furthermore, in the realm of practical implementation, the achievement of stable passively Q-switched (PQS) lasers employing SA composed of few-layered VTe2 nanosheets has manifested itself with broadband operating wavelengths from 1.0 to ∼3.0 μm. Specifically, PQS laser operations from near-infrared to mid-infrared with pulse durations of 195 and 563 ns for 1.0 and 2.0 μm solid-state lasers, respectively, and 749 ns for an Er3+-doped fluoride fiber laser at 3.0 μm were obtained. Our experimental results demonstrate that VTe2 is a potential broadband SA device for achieving PQS lasers. To the best of our knowledge, this is the first demonstration of using VTe2 as an SA in PQS lasers in the near- and mid-infrared regions, which highlights the potential of VTe2 for future research and applications in optoelectronic devices.

Efficient Fluoride Removal from Aqueous Solution Using Graphene/Ce Composite Supported on Activated Carbon

Background: More than 260 million people worldwide are affected by excess fluoride (F- > 1.5 mg/L) in their drinking water. Fluorosis of the teeth and skeleton, among other health issues, is caused by it. Objective: The aim of this study is to evaluate the fluoride removal from contaminated water using graphene-based new adsorbent material. Method: Graphene (G) was prepared by a facile liquid-phase exfoliation method. CeO2 nanoparticles (NPs) were synthesized by the co-precipitation method. G was treated with CeO2 NPs in a probe sonicator to generate G/Ce material in solution. Finally, the impregnation evaporation process synthesized the G/Ce supported on activated carbon composite (G/Ce/AC). Results: FE-SEM analysis shows that the crumpling and scrolling sheets of G, the nanosized spherical shape of CeO2 NPs and a thick layer of nano-sized spherical particles has built up on the surface of graphene in G/Ce/AC composite. After conversion to G/Ce/AC Composite, the specific surface area of graphene was increased from 3.08 to 485.3621 m2/g. The adsorption of fluoride on G/Ce/AC was investigated using batch systems (effects of pH, contact time, adsorbent dosage and the initial fluoride concentration), adsorption isotherm and kinetic studies. The pseudo-second order was the one that best described the kinetic data, while the Langmuir isotherm best described the equilibrium data with a maximum adsorption capacity equal to 27.9 mg/g. Conclusion: Therefore, the results show that the G/Ce/AC composite was well synthesized and has excellent fluoride adsorption capacity compared to other materials already evaluated for this purpose.

Phytic Acid-Promoted Exfoliation of Black Phosphorus Nanosheets for the Fabrication of Photothermal Antibacterial Coatings.

Medical device-associated infections (MDAI) caused by planktonic pathogens are of serious concern worldwide due to the emergence of drug resistance resulting from continuous overuse or misuse of antibiotics. Therefore, the design of non-antibiotics-based treatment for MDAI is of crucial importance. Black phosphorus (BP), a novel 2D material, has recently received much attention owing to its remarkable physical, chemical, mechanical, and functional features. However, the intricacy of the fabrication process has severely hampered the development of BP in prospective applications. In this study, a simple and eco-friendly liquid-phase exfoliation method of phytic acid (PA)-promoted exfoliation of BP nanosheets (PA@BP NSs) is developed for their potential application in antibacterial photothermal therapy. To impart the antimicrobial effects, the polydimethylsiloxane surfaces are functionalized with quaternized polymer (polyquaternium-2 or PQ) and PA@BP NSs, leading to the formation of PA-BP-PQ composite coatings. In addition to the contact-killing antibacterial effect of the cationic PQ, the PA-BP-PQ coating exhibits remarkable near-infrared irradiation-triggered bactericidal effects with low cytotoxicity both in vitro and in vivo. This study proposes a simple liquid-phase exfoliation technique for the fabrication of BP NSs and a one-step approach for the construction of PA-BP-PQ composite coatings for bi-modal (contact-killing and photothermal) antimicrobial therapy.

High-efficient photocatalytic degradation of multiple pollutants by CdPS3 nanosheets

Photocatalytic degradation technique is an effective route for degrading the polluting sources by using photocatalysts. In recent years, van der Waals material based photocatalysts has been drawing more and more attention due to their excellent photodegradation performance. In this research, we have developed a type of highly efficient layered photocatalyst, CdPS3 nano flakes prepared by the liquid-phase exfoliation method. We compared different photodegradation rates of rhodamine B (RhB) by using photocatalysts of CdPS3 ground bulk powder and CdPS3 nanosheets exfoliated by three different dispersants, i.e., N-methyl pyrrolidone (NMP), deionized (DI) water and sodium cholate (SC). For a complete degradation of RhB (80 mL, 100 mg/L), the SC-exfoliated CdPS3 nanosheets exhibited the highest degradation efficiency within 15 min. These SC-exfoliated nanosheets also demonstrated good potential for degrading methylene blue (MB), potassium dichromate (PD), tetracycline (TC) and methyl orange (MO). The strong dark adsorption and dye-sensitized photocatalytic properties of CdPS3 nanosheets could both contribute to high degradation efficiencies of RhB and MB, synergistically. Capture experiments revealed that superoxide radicals dominated the degradations of these pollutants. Additionally, for PD and MO, hydroxyl radicals and holes were also important active species in the photodegradation redox reactions.

Synthesis of Black Phosphorene/P-Rich Transition Metal Phosphide NiP3 Heterostructure and Its Effect on the Stabilization of Black Phosphorene

Black phosphorus (BP), as a direct band gap semiconductor material with a two-dimensional layered structure, has a good application potential in many aspects, but the surface state of it is extremely unstable, especially that of single-layer black phosphorus. In this study, BP crystals and two-dimensional black phosphorus (2D BP) are prepared by a mechanical ball-milling–liquid-phase exfoliation method. The X-ray diffraction (XRD) spectrum and high-resolution transmission electron microscopy (HRTEM) results showed that red phosphorus (RP) successfully turned to BP by the mechanical ball-milling method. The spectrophotometric analysis has detected absorption peaks at 780 nm, 915 nm, and 1016 nm, corresponding to single, double, and three-layer BP bandgap emission. A simple solvothermal strategy is designed to synthesize in-plane BP/P-rich transition metal phosphide (TMP) heterostructures (BP/NiP3) by defect/edge-selective growth of NiP3 on the BP nanosheets. HRTEM analysis indicates that the metal ions are preferentially deposited on the defects of 2D BP such as edges and unsaturated sites, forming a 2D BP/NiP3 in-plane heterojunction.

Transient heat transfer studies of aluminium graphene nanocomposite heat spreaders using digital interferometry

The thermal runaway caused by poor thermal management of batteries is one of the main challenges being faced by electric vehicles (EVs). An energy-saving, passive method for efficient thermal management of two and three wheeler battery packs is the use of aluminum (Al) heat spreaders with superior thermal conductivity, in conjunction with natural air cooling. Thermal conductivity of the (Al) heat spreaders can be enhanced by incorporation of graphene flakes. The present work focuses on extensive heat transfer studies of Al graphene nanocomposite (AGNC) heat spreaders with enhanced heat transfer capability. Few layered graphene (FLG) was synthesized by the liquid phase exfoliation method and characterized by X-Ray diffraction (XRD) analysis, Transmission electron microscopy (TEM), and Confocal Raman spectroscopy. AGNC heat spreaders were made by powder metallurgy. Mach-Zehnder interferometric (MZI) technique was employed to analyse the heat dissipation characteristics of AGNC heat spreaders, which infact is the novelty here. The slope of the local heat flux curve obtained by MZI was found to be less in the case of AGNC heat spreaders as compared to Al heat spreader indicating more uniform heat dissipation for AGNC heat spreaders. Transient heat transfer studies showed 63 % enhancement in the heat dissipation for AGNC heat spreader as compared to pure Al heat spreader. The transient temperature distribution was also visualized using Infrared (IR) thermography and the results show more uniform temperature distribution in the case of AGNC heat spreaders. The better phonon transport across the grain boundaries loaded with FLGs could be the reason for faster heat transport in AGNC heat spreaders.

Large-energy mode-locked Er-doped fiber laser based on indium antimonide as a modulator

Large energy mode-locked pulsed fiber lasers have great potential, especially for a wide range of applications in human eye safety lidar. In our work, we have obtained stable large-energy mode-locking pulse phenomena by making saturable absorbers (SA) from indium antimonized (InSb). InSb-SA was obtained by liquid-phase exfoliation method. A large energy mode-locked pulse of 10.89 nJ was obtained at a pump pulse of 620 mW and a repetition frequency of 469 kHz, with an output power of 5.09 mW. Our research shows that InSb has more advantages compared with commonly used optical modulators. The experimental results can provide a reference for future research on large-energy mode-locked pulses.

Liquid phase exfoliation of MoSe2: Effect of solvent on morphology, edge confinement, bandgap and number of layers study

In this study, a facile and scalable method for synthesizing MoSe2 nanomaterial via a sonication-assisted liquid-phase exfoliation method is proposed. This study shows the successful synthesis of few-layered MoSe2 in various solvents including DI water, ethanol, N-Methyl-2-pyrrolidone (NMP), Dimethylformamide (DMF) and Dimethylsulfoxide (DMSO). The exfoliated nanosheets have remarkably different properties than bulk MoSe2 which were studied using Field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and UV–Vis spectroscopy to investigate their morphology, functional groups, structure and optical properties, respectively. The mean values of the number of layers from an optical extinction spectrum based on the effect of edge and quantum confinement were also calculated. Moreover, the exfoliated material using this method has potential application in energy storage as demonstrated by the electrochemical performance of the bulk and exfoliated materials.•Successful synthesis of the few-layer MoSe2 from bulk MoSe2 using liquid phase exfoliation method in various solvents•The investigation of the effect of solvent on the number of layers and optical properties of MoSe2

Two-dimensional perovskite NdNb2O7 for high-performance UV photodetectors by a general exfoliation and assembly strategy

Two-dimensional (2D) oxide perovskites show great promise as candidates for future optoelectronic devices. For the first time, we have successfully exfoliated 2D perovskite NdNb2O7 (NNO) nanosheets by a solid-state calcination and liquid-phase exfoliation method. The individual NNO nanosheet photodetector (PD) demonstrates outstanding performance in detecting UV light (260 nm, 3 V), including high responsivity (62 AW−1), high detectivity (6.7 *1012 Jones), high spectral selectivity (R260/R400= 9000), fast response speed (0.1/7.8 ms) and long-term stability. Furthermore, through a simple interface self-assembly technique, we have successfully achieved orderly and flat films of NNO nanosheets. The resulting film exhibits high transparency (>75 %) in the visible light range. The NNO film device demonstrates excellent performance after undergoing numerous bending tests. This work not only presents a new candidate for high-performance and high-stability UV photodetectors but also introduces a general exfoliation and assembly strategy.

Ab-Initio and Experimental Study of the Electronic and Optical Properties of Layered 2D Molybdenum Disulphide

Molybdenum disulphide (MoS2) in its two-dimensional (2D) mono- to few layers is applied in numerous photonic applications owing to its wide bandgap. In this work, the electronic and optical properties of monolayer MoS2 were successfully investigated by ab initio study through density functional theory (DFT) calculation and experimental work. A 2D monolayer MoS2 model was simulated using CASTEP in the framework of plane-wave pseudopotential. The simulated bandgap is 1.7 eV which is interestingly close to those determined bandgap of MoS2 prepared through the liquid-phase exfoliation method. This confirmed the successful formation of 2D layered MoS2 in the proposed fabrication process. The MoS2 model also predict well the experimentally derived absorption range which has a significant peak at around ~600 nm wavelength ascribed to the excitonic property.

Entropy-driven liquid-phase exfoliation of non-Van-Der-Waals crystals into nanoplatelets

Liquid-phase exfoliation (LPE) methods have revolutionized the production of two-dimensional (2D) materials from layered crystals, employing techniques such as ultrasonic degradation, mechanical exfoliation, and electrochemical exfoliation. However, the exfoliation of three-dimensional (3D) crystals that are nonlayered and non-Van-Der-Waals presents both challenges and opportunities. This study introduces an atomistic biaxial shear-normal strain entropy analysis to comprehend and design the LPE process specifically for such materials. By analysing the atomistic compressive biaxial shear-normal strain induced during LPE in 3D crystals, we establish a strain–stress-entropy relationship and derive a general exfoliation rate equation. We validate our model by comparing it to literature-based alloy exfoliation tests and conducting new Mg(OH)2 LPE (ball milling) experiments. The results not only confirm the applicability of the derived equation but also provide valuable insights into the exfoliation process. The implications of these findings are substantial, as they open new possibilities in various applications by informing the selection of 3D crystals and facilitating the design and optimization of LPE processes.

Probing the Magnetic Properties of Boron-Doped Graphenic-Based Carbon Materials

Graphenic carbon (GC) has been successfully synthesized from biomass (coconut shell charcoal) using the liquid phase exfoliation method. The dopants, in the form of light atoms such as boron (B-GC), were introduced with the aim of improving their magnetic properties. X-ray diffraction was used to identify the GC and B-GC, and the results show broad peaks around 24° and 43°, indicating the presence of graphene-like carbon structure. The bonding structure was also analyzed using X-ray photoelectron (XPS). It reveals the main bonds in GC consist of sp2, sp3, and C=O. While the B-GC sample shows an additional bond, namely the B-C bond, as an indicator of the successful doping process of B into the GC structure. Both GC and B-GC show weak room temperature ferromagnetism. Furthermore, these findings show that introducing boron atoms into the graphenic structure can improve magnetization.

Dual-wavelength amplified spontaneous emission from interface-engineered polymer films using atomically thin red coral

Naturally available two-dimensional (2D) materials having van der Waal's heterostructure are an impetus for generating amplified spontaneous emission (ASE) from dye-based polymer films. Under continuous wave (CW) laser pumping, the problem of scatterer mobility due to induced thermal gradient can be mitigated by such films. In this work, liquid-phase exfoliation (LPE) method has been used to synthesize 2D red coral (2D-RC) from its bulk form. In order to obtain CW-pumped ASE from a rhodamine B (RhB) dye mixed polyvinyl alcohol (PVA) film, 2D-RC has been used as a passive scatterer. Dual-wavelength ASE at ∼591 nm and ∼626 nm has been obtained by designing a step on the film and by introducing film-glass interfaces. Enhanced ASE has been obtained by designing a film-based Fabry-Pérot (FP) cavity in addition to the interfaces. Far-field diffraction patterns obtained due to induced optical non-linearity and thermal lensing in the system have been used to demonstrate scatterer ability by comparing with other commonly used passive scatterers. Thus, dual-wavelength ASE from dye-mixed polymer films has been demonstrated by means of interface engineering and induced step using the newly synthesized van der Waal's heterostructure, namely 2D-RC, as a passive scatterer which may pave the way towards further exciting NLO effects based applications.

Direct Observation of Photon Induced Giant Band Renormalization in 2D PdSe2 Dichalcogenide by Transient Absorption Spectroscopy.

Insight into fundamental light-matter interaction as well as underlying photo-physical processes is crucial for the development of novel optoelectronic devices. Palladium diselenide (PdSe2 ), an important representative of emerging 2D noble metal dichalcogenides, has gain considerable attention owing to its unique optical, physical, and chemical properties. In this study, 2D PdSe2 nanosheets (NSs) are prepared using the liquid-phase exfoliation method. A broadband carrier relaxation dynamics from visible to near-infrared bands are revealed using a time-resolved transient absorption spectrometer, giving results that indicate band filling and bandgap renormalization (BGR) effects in the 2D PdSe2 NSs. The observed blue-shift of the transient absorption spectra at the primary stage and the subsequent red-shift can be ascribed to this BGR effect. These findings reveal the many-body character of the 2D TMDs material and may hold keys for applications in the field of optoelectronics and ultrafast photonics.

Production Methods and Energy Applications of Borophene

Two dimensional materials have unique physical, chemical and electrical properties. Many theoretical studies on borophene revealed important possible properties, such as metallicity, transparency, conductivity and chemical activity; due to vacancies present in its structure. It was first synthesized in 2015 and experimental studies on this new exciting 2D material is few in number. It was found that many of these studies still focus on expensive and sophisticated production methods such as Molecular Beam Epitaxy (MBE) and Chemical Vapor Deposition (CVD). Although graphene, first of these 2D materials, is being studied more than two decades, it could not do the expected impact on energy industry due to lack of production methods in industrial scale. In this review, it was intended to build a narrative on the experimental production methods and resulting structures of borophene rather than theoretical background. It was found that liquid phase exfoliation method to synthesize borophene sheets might be the most promising method to upscale borophene production. Theoretical, computational and experimental studies suggested that β12 and χ3 borophene structures were stable and could be produced by sonochemical exfoliation method. In addition, possible uses in energy applications and some future prospects were also discussed. Borophene produced this way, might be used in batteries, supercapacitors hydrogen evolution (HER) and oxygen evolution (OER) reactions.

High performance 1.9 µm passively Q-switched bulk laser with germanene as a saturable absorber.

Germanene is an analog of graphene, and its independent novel low-bending honeycomb structure gives outstanding advantages such as environmental stability and significant low-frequency optical absorbance. In this paper, the few-layer germanene was successfully prepared by the liquid phase exfoliation method. The saturable absorption characteristics of germanene in the infrared waveband were detected by the open-aperture Z-scan method. With germanene as a saturable absorber, a high-performance passively Q-switched bulk laser was realized at 1.9 µm. The shortest pulse width of 60.5 ns was obtained from continuous-wave pumping, corresponding to a single pulse energy of 6.7 µJ and peak power of 110 W. By utilizing the pulse pumping style with a repletion rate of 10 Hz, the single pulse energy and peak power increased to 45.8 µJ and 328 W, respectively, which exceeded all two-dimensional SA materials reported before. This research manifests that germanene is an excellent SA material for mid-infrared solid-state lasers.

Broadband nonlinear absorption properties of TiS2 nanosheets

Titanium disulfide (TiS2) is a typical transition-metal dichalcogenides (TMDs) with a layered structure similar to graphene, exhibiting remarkable photoelectric properties. In this study, TiS2 nanosheets were exfoliated successfully by liquid-phase exfoliation method. And the NLA properties of TiS2 nanosheets from ultraviolet to near-infrared were investigated by using an open-aperture Z-scan method. The results demonstrate that TiS2 nanosheets own excellent NLA characteristics in near infrared waveband. The excellent optical nonlinear properties of TiS2 nanosheets provide the possibility for practical applications of the TiS2 nanosheets in optical limiting fields especially in infrared waveband.

Excellent ultraviolet optical limiting properties of Se nanosheets

Selenium (Se) is located in the fourth period of the periodic table in group VIA (element 34). In this experiment, three different solvents (isopropyl alcohol, N-methyl-2-pyrrolidone, and ethanol) were used to prepare the two-dimensional Se nanosheets, which were manufactured by the liquid phase exfoliation method with a thickness of 3.35–4.64 nm and a transverse scale of several hundred nanometers. The nonlinear absorption properties at 355, 532, and 1064 nm were studied using the open aperture Z-scan technique. Final results showed that Se nanosheets exhibited optical limiting (OL) effect in all three wavebands and three solvents, and had large two-photon absorption coefficients, especially in ultraviolet (UV) waveband. Which proved that Se nanosheets had great potential application as excellent OL materials in UV waveband. Our research broadens the path for the semiconductor field of Se, inspires the application of Se in nonlinear optics field.