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BiOI is a promising photoelectrocatalyst for oxidation reactions. However, the limited photoelectrocatalytic (PEC) activity necessitates the development of new strategies to modify its surface chemistry and thus enhance functional properties. Herein, we present a simple method to increase photocurrent in a BiOI‐based photoanode by exfoliating microspheres of the oxyhalide produced through hydrothermal synthesis. Following exfoliation in isopropanol, the resulting layered BiOI‐based colloid contains a greater variety of species, including Bi2O2CO3, I3−, IO3−, Bi5+, and hydroxides, compared to the original BiOI. These additional species do not directly enhance the PEC oxygen evolution reaction (OER) performance. Instead, they are consumed or converted during PEC OER, resulting in more active sites on the photoelectrode and reduced resistance, which ultimately improves the water oxidation performance of the exfoliated BiOI. Over long‐term chronoamperometry, the exfoliated BiOI demonstrates a photocurrent twice as high as that of the BiOI microspheres. Analysis of the species after PEC OER reveals that the combination of IO3−, Bi5+, and I3− species on the BiOI is beneficial for charge transfer, thus enhancing the intrinsic PEC properties of the BiOI. This study offers new insights into the role of surface chemistry in determining PEC performance, aiding the optimization of 2D materials‐based photoelectrocatalysts. [ABSTRACT FROM AUTHOR]

An X-ray analysis of exfoliated MoS2, produced by means of microwave-assisted liquid-phase exfoliation (LPE) from bulk powder in 1-methyl-2-pyrrolidone (NMP) or acetonitrile (ACN) + 1-methyl-2-pyrrolidone (NMP) solvents, has revealed distinct structural differences between the bulk powder and the microwave-exfoliated samples. Specifically, we performed X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements to identify the elements of our exfoliated sample deposited on a Si substrate by drop-casting, as well as their chemical state and its structural crystalline phase. In the exfoliated sample, the peaks pattern only partially resemble the theoretical Miller indices for MoS2. In contrast, the bulk powder's spectrum shows the characteristic peaks of the 2H polytype of MoS2, but with some broadening. Notable is the retention of partial crystallinity in the post-exfoliation phases, specifically in the normal-to-plane orientation, thus demonstrating the effectiveness of microwave-assisted techniques in producing 2D MoS2 and attaining desirable properties for the material. XPS measurements confirm the success of the exfoliation procedure and that the exfoliated sample retains its original structure. The exfoliation process has been optimized to maintain the structural integrity of MoS2 while enhancing its surface area and electrochemical performance, thereby making it a promising material for advanced electronic and optoelectronic applications ranging from energy storage to sensing devices under ambient conditions. [ABSTRACT FROM AUTHOR]

Graphene-based chemical sensors hold promise across diverse applications owing to their exceptional sensitivity and selectivity. However, achieving their long-term durability and reusability while preserving high sensitivity remains a significant challenge, particularly in harsh environments where exposure to strong chemicals is inevitable. This paper presents a novel approach to address this challenge by synergistically integrating liquid-phase exfoliated graphene (LPEG) with polytetrafluoroethylene (PTFE) within a single sensing strip. Through a comprehensive experimental investigation, we demonstrate the fabrication of highly durable and reusable chemical leak detection sensors by combining LPEG and PTFE. Furthermore, we explore the sensing mechanism, highlighting the roles of LPEG and PTFE in enhancing sensitivity and selectivity, along with durability and reusability. Performance evaluation reveals the sensors' robustness against mechanical and chemical degradation, coupled with excellent recyclability. This innovative approach holds promise for applications in environmental monitoring, industrial safety, and healthcare, thus advancing the field of graphene-based chemical leak detection sensors. [ABSTRACT FROM AUTHOR]

The fabrication of few-layer borophene (BP) from bulk boron (b-B) is of great importance and still a scientific challenge due to the complex structure and crystallinity of b-B. Herein, we propose a novel technique to prepare a few-layer BP on a large scale with a large lateral size in a well-controlled manner. For this, we employed the Hummers' method-assisted liquid-phase exfoliation. In the first step, the chemical exfoliation of the b-B as a precursor was performed by the modified Hummers' method. After chemical exfoliation, mechanical delamination was employed by using an immersion sonicator. Finally, BP sheets were collected with dimensions ranging from several hundred nanometers to a few micrometers and an average thickness of 4.2 nm. We envision that the proposed low-cost, flexible, and large-scale production method will provide unique advantages for the application of few-layer BP in the realization of highperformance electronics, optoelectronics, flexible devices, sensing systems, energy conversion, and storage devices. [ABSTRACT FROM AUTHOR]

Photosynthetic reaction center (pRC) purified from Rhodobacter sphaeroides 2.4.1 purple bacteria was deposited on a graphene carrier exfoliated from the liquid phase and layered on the surface of SiO2/Si substrate for optoelectronic application. Light-induced changes in the drain-source current vs. gate voltage are demonstrated. Dried photosynthetic reaction centers/graphene composite on SiO2/Si shows a photochemical/-physical activity, as a result of interaction with the current flow in the graphene carrier matrix. The current changes are sensitive to light, due to the contribution from the charge separation in the pRC, and to the applied gate and drain-source voltages.

Disulfide zirconium (ZrS2) is a two-dimensional (2D) transition metal disulfide and has given rise to extensive attention because of its distinctive electronic structure and properties. However, mass production of high quality of ZrS2 nanosheets to realize their practical application remains a challenge. Here, we have successfully exfoliated the bulk ZrS2 powder with the thickness of micron into single and few-layer nanosheets through liquid-phase exfoliation in N-methylpyrrolidone (NMP) assisted via aliphatic amines as intercalators. It is found that the exfoliation yield is as high as 27.3%, which is the record value for the exfoliation of ZrS2 nanosheets from bulk ZrS2 powder, and 77.1% of ZrS2 nanosheets are 2–3 layers. The molecular geometric size and aliphatic amine basicity have important impact on the exfoliation. Furthermore, the ZrS2 nanosheets have been used as catalyst in the electrocatalytic dinitrogen reduction with the NH3 yield of 57.75 μg h−1 mgcat.−1, which is twice that by ZrS2 nanofibers reported in literature and three times that by the bulk ZrS2 powder. Therefore, the liquid phase exfoliation strategy reported here has great potential in mass production of ZrS2 nanosheets for high activity electrocatalysis.

The green exfoliation of graphite using the serum from skim natural rubber latex, with some left-over ammonia, was investigated. The methods proposed to increase the exfoliation yield included varying the graphite concentration from 10 to 25 mg/ml of serum, using smaller graphite powders obtained from the sedimentation of a graphite precursor, and increasing rotor speed of a homogenizer. The two former cases were performed in an ultrasonic bath. In the first case, using 10 mg of graphite/ml of serum gave the maximum yield of 0.70%. In the second case of using graphite suspended in the supernatant after 15-min settling as starting material in exfoliation, the yield was increased to 0.74% at the graphite concentration of 25 mg/ml. In the last case, using the homogenizer probe at 5,400 rpm for 20 min gave the yield up to 10.5%. Based on Raman spectroscopy, all these exfoliated products were multilayer graphene-based materials and could be comparable to the commercial graphene-based product. [ABSTRACT FROM AUTHOR]

Graphene-based chemical sensors hold promise across diverse applications owing to their exceptional sensitivity and selectivity. However, achieving their long-term durability and reusability while preserving high sensitivity remains a significant challenge, particularly in harsh environments where exposure to strong chemicals is inevitable. This paper presents a novel approach to address this challenge by synergistically integrating liquid-phase exfoliated graphene (LPEG) with polytetrafluoroethylene (PTFE) within a single sensing strip. Through a comprehensive experimental investigation, we demonstrate the fabrication of highly durable and reusable chemical leak detection sensors by combining LPEG and PTFE. Furthermore, we explore the sensing mechanism, highlighting the roles of LPEG and PTFE in enhancing sensitivity and selectivity, along with durability and reusability. Performance evaluation reveals the sensors’ robustness against mechanical and chemical degradation, coupled with excellent recyclability. This innovative approach holds promise for applications in environmental monitoring, industrial safety, and healthcare, thus advancing the field of graphene-based chemical leak detection sensors.

Photosynthetic reaction center (pRC) purified from Rhodobacter sphaeroides 2.4.1 purple bacteria was deposited on a graphene carrier exfoliated from the liquid phase and layered on the surface of SiO2/Si substrate for optoelectronic application. Light-induced changes in the drain-source current vs. gate voltage are demonstrated. Dried photosynthetic reaction centers/graphene composite on SiO2/Si shows a photochemical/-physical activity, as a result of interaction with the current flow in the graphene carrier matrix. The current changes are sensitive to light, due to the contribution from the charge separation in the pRC, and to the applied gate and drain-source voltages. [ABSTRACT FROM AUTHOR]

During water electrolysis, adding an electrocatalyst for the hydrogen evolution reaction (HER) is necessary to reduce the activation barrier and thus enhance the reaction rate. Metal chalcogenide-based 2D nanomaterials have been studied as an alternative to noble metal electrocatalysts because of their interesting electrocatalytic properties and low costs of production. However, the difficulty in improving the catalytic efficiency and industrializing the synthetic methods have become a problem in the potential application of these species in electrocatalysis. Liquid-phase exfoliation (LPE) is a low-cost and scalable technique for lab- and industrial-scale synthesis of 2D-material colloidal inks. In this work, we present, to the best of our knowledge, for the first time a systematic study on the surfactant-assisted LPE of bulk Bi2S3 crystalline powder to produce nanosheets (NSs). Different dispersing agents and LPE conditions have been tested in order to obtain colloidal low-dimensional Bi2S3 NSs in H2O at optimized concentrations. Eventually, colloidally stable layered nano-sized Bi2S3 suspensions can be produced with yields of up to ~12.5%. The thus obtained low-dimensional Bi2S3 is proven to be more active for HER than the bulk starting material, showing an overpotential of only 235 mV and an optimized Tafel slope of 125 mV/dec. Our results provide a facile top-down method to produce nano-sized Bi2S3 through a green approach and demonstrate that this material can have a good potential as electrocatalyst for HER. [ABSTRACT FROM AUTHOR]

Large-scale production of graphene nanosheets (GNSs) has led to the availability of solution-processable GNSs on the commercial scale. The controlled vacuum filtration method is a scalable process for the preparation of wafer-scale films of GNSs, which can be used for gas sensing applications. Here, we demonstrate the use of this deposition method to produce functional gas sensors, using a chemiresistor structure from GNS solution-based techniques. The GNS suspension was prepared by liquid-phase exfoliation (LPE) and transferred to a polyvinylidene fluoride (PVDF) membrane. The effect of non-covalent functionalization with Co-porphyrin and Fe-phthalocyanines on the sensor properties was studied. The pristine and functionalized GNS films were characterized using different techniques such as Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and electrical characterizations. The morphological and spectroscopic analyses both confirm that the molecules (Co-porphyrin and Fe-phthalocyanine) were successfully adsorbed onto the GNSs surface through π-π interactions. The chemiresistive sensor response of functionalized GNSs toward the low concentrations of nitrogen dioxide (NO2) (0.5–2 ppm) was studied and compared with those of the film of pristine GNSs. The tests on the sensing performance clearly showed sensitivity to a low concentration of NO2 (5 ppm). Furthermore, the chemical modification of GNSs significantly improves NO2 sensing performance compared to the pristine GNSs. The sensor response can be modulated by the type of adsorbed molecules. Indeed, Co-Por exhibited negative responsiveness (the response of Co-Por-GNS sensors and pristine GNS devices was 13.1% and 15.6%, respectively, after exposure to 0.5 ppm of NO2). Meanwhile, Fe-Phc-GNSs induced the opposite behavior resulting in an increase in the sensor response (the sensitivity was 8.3% and 7.8% of Fe-Phc-GNSs and pristine GNSs, respectively, at 0.5 ppm NO2 gas). [ABSTRACT FROM AUTHOR]

The recent advent of two-dimensional (2D) materials has had a ground-breaking impact on science and technology. To exploit in technology their unique thickness-dependent physicochemical properties, the large-scale production of 2D materials is mandatory, but it represents an open challenge still due to various pitfalls and severe limitations including the toxicity of state-of-the-art solvents. Thus, liquid-phase exfoliation based on green and bioderived solvents represents an ideal methodology for massive production. This is particularly crucial for introducing 2D materials in technological applications such as the production of drinking water and agri-food industrial processes. Here, we assessed the production of 2D nanosheets (specifically, graphene, WS2, MoS2) with liquid-phase exfoliation assisted by eco-friendly solvents, with a comparative evaluation of green solvents in terms of the yield and, moreover, the aspect ratio, defectivity, and crystalline quality of the produced nanosheets. In particular, we focus on the most promising green solvents in terms of the yield and the crystalline quality of the produced nanosheets: Polarclean, Iris, and Cyrene, which were compared with acetone/water mixtures, isopropyl alcohol (IPA), triethanolamine (TEA), aqueous solutions of urea, and an ethanol/water mixture as well as two toxic solvents largely used for the production of 2D nanosheets: N-methyl-2-pyrrolidone (NMP) and N, N-dimethylformamide (DMF). Remarkably, the density of defects was particularly low in the liquid-phase exfoliation with Polarclean, as indicated by the Raman spectrum of graphene, with the I(D)/I(G) ratio below 0.1. Furthermore, Polarclean and Iris also enable ink-jet printing with functional inks of 2D materials based on green solvents due to their low dynamic viscosity at room temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] The superiority of graphitic carbon nitride (g-C 3 N 4) nanosheet results from its large specific surface area, which can be achieved by exfoliation of the bulk layered structure. Liquid-phase exfoliation (LPE) is the best-known method for the synthesis of two-dimensional (2D) g-C 3 N 4 nanosheets. However, experimental investigations do not allow for a molecular-level understanding of the process. Molecular dynamics (MD) simulations are expected to provide microscopic insights and quantitative evaluation of the energy consumption during LPE, thus facilitating the search of effective solvents for the LPE of 2D materials. MD simulations are carried out to simulate the LPE process by performing potential of mean force calculations for the separation of two stacked g-C 3 N 4 nanosheets. Free energy of exfoliation is evaluated and compared among nine common solvents with distinct molecular structures. The most probable path for the exfoliation process is identified. The free energy of exfoliation is found to correlate directly with the solvent free energy of a single g-C 3 N 4 nanosheet. The solvation is enthalpy-driven and affected by the mobility of the solvent molecules around the nanosheet. Based on the MD results, several strategies are proposed to guide the selection of solvents for effective LPE. [ABSTRACT FROM AUTHOR]

Grinding-assisted liquid-phase exfoliation is a widely used method for the preparation of two-dimensional nanomaterials. In this study, N-methylpyrrolidone and acetonitrile, two common grinding solvents, were used during the liquid-phase exfoliation for the preparation of MoS2 nanosheets. The morphology and structure of MoS2 nanosheets were analyzed via scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The effects of grinding solvents on the gas-sensing performance of the MoS2 nanosheets were investigated for the first time. The results show that the sensitivities of MoS2 nanosheet exfoliation with N-methylpyrrolidone were 2.4-, 1.4-, 1.9-, and 2.7-fold higher than exfoliation with acetonitrile in the presence of formaldehyde, acetone, and ethanol and 98% relative humidity, respectively. MoS2 nanosheet exfoliation with N-methylpyrrolidone also has fast response and recovery characteristics to 50–1000 ppm of CH2O. Accordingly, although N-methylpyrrolidone cannot be removed completely from the surface of MoS2, it has good gas sensitivity compared with other samples. Therefore, N-methylpyrrolidone is preferred for the preparation of gas-sensitive MoS2 nanosheets in grinding-assisted liquid-phase exfoliation. The results provide an experimental basis for the preparation of two-dimensional materials and their application in gas sensors. [ABSTRACT FROM AUTHOR]

[Display omitted] Transition metal dichalcogenides (TMDs), like other two-dimensional layered materials beyond graphene, have gained enormous interest in recent years owing to their distinct electronic and optical properties, and potential applicability in areas such as sensing, nanoelectronics and catalysis. Surfactant-assisted exfoliation is commonly used to prepare aqueous dispersions of TMD nanosheets, but a clear picture of the TMD and surfactant features that influence the dispersion process is still lacking. In this work, we present a systematic study of the dispersibility of MoS 2 , WS 2 and MoSe 2 in aqueous medium using a cationic (cetyltrimethylammonium bromide, CTAB) and an anionic (sodium cholate, SC) dispersant, in a wide concentration range (seven orders of magnitude) and resorting to a carefully controlled sonication-centrifugation procedure. We present detailed, high precision dispersibility curves (concentration of dispersed TMD versus concentration of surfactant used), together with zeta potential and pH measurements, allowing insight into the influence of the type of metal and chalcogen, surfactant charge and surfactant concentration, on the effectiveness of the exfoliation and stabilization. The metal (Mo vs. W) influences the dispersibility at low surfactant concentrations, while the chalcogen (S vs. Se) plays a more significant role as the surfactant concentration is increased, alongside the surfactant charge. Structural characterization by scanning electron microscopy (SEM), Raman spectroscopy and atomic force microscopy (AFM) shows that the methodology applied yields well-exfoliated nanosheets with controlled mean lateral dimension (≈ 100 nm) and thickness (≤5 layers). Finally, the type of ionic surfactant (cationic vs. anionic) and its concentration play a pivotal role in the profile of the dispersibility curves, leading us to propose two types of master curves with distinct regions of phase behavior. [ABSTRACT FROM AUTHOR]

Measuring relative humidity is important for a myriad of industries, including production, agriculture, environmental monitoring, and medicine. Thin-film, fast-response sensors are particularly interesting for wearable applications, such as monitoring breathing. We report on humidity sensors made from graphene deposited as a thin film by the Langmuir-Blodgett (LB) method from three types of graphene in solution. We demonstrate humidity sensing and respiration monitoring from graphene made by bath sonication, probe sonication, and electrochemical exfoliation. We characterize the morphology and chemical composition of the three film types and compare their performance as sensors. We conclude that although all three types can be used for sensing, they each have their particular advantages and drawbacks. [ABSTRACT FROM AUTHOR]

The paper presents the investigation results of the morphology of carbon nanoparticles formed during liquid-phase exfoliation of thermally expanded graphite in tert-butanol. The thermally expanded graphite used in this work was obtained by thermal expansion of graphite nitrate with acetic and formic acids in the thermal shock mode at 500°C and 900°C. Initial cointercalate was shown by powder X-ray diffraction analysis to be the mixture of the II^nd and the IV^th stage intercalation compounds. It has been established by transmission electron microscopy that dispersions of carbon nanoparticles formed during the exfoliation of thermally expanded graphite in tert-butanol via sonication contain mainly few-layer graphenes, the planar dimensions of which reach 8 μm. The influence of the conditions for thermally expanded graphite obtaining on the morphology of resulting carbon nanoparticles is discussed. Dispersions based on thermally expanded graphite obtained at a lower temperature, in addition to few-layer graphenes, also contain a significant amount of amorphous carbon particles with planar sizes up to 100 nm.

The flourishing of the Internet of Things (IoT) in recent years creates a huge demand for various humidity sensors, since the humidity is closely related to our daily life. Transparent humidity sensors have great application prospects in the fields such as smart furniture and human-machine interface. However, it is difficult for devices made from traditional moisture sensitive materials to have both high optical transparency and sensitive humidity response. Herein, we developed a novel humidity sensor based on 2D MoO3-x nanosheets, in which the nanosheets were liquid-phase exfoliated from α-MoO3 powder. With the assistance of ethyl cellulose, a high concentration dispersion of oxygen-deficient MoO3-x nanosheets can be easily prepared by probe sonicating. The as-prepared humidity sensor shows a transmittance as high as 86% in visible range. Under a constant bias, the current of the sensor increases monotonically over a broad RH range from 11% to 95%. Moreover, the fast response and recovery speed in the subsecond timescale (0.12 s and 0.53 s) enables the transparent humidity sensor to work as a real-time device in the expiration monitoring system. This work demonstrates a promising application of 2D MoO3-x nanosheets and opens up a new avenue for designing transparent humidity sensors.

To date, multiple graphene@MXene hybrids have been reported via various synthesis approaches, but almost all the graphene@MXene hybrids inevitably used the reduced graphene oxide that prepared by chemical oxidation/reduction method, which generally involved the complex and dangerous operation procedure, and the highly toxic chemical reagent. How to prepare graphene@MXene hybrid through a simple, safe and eco-friendly synthetic route is highly desired. Compared with traditional synthesis technology, ultrasound synthesis strategy displays the merits of simplicity, low cost and environment protection. Herein, MXene (Ti3C2Tx) nanoflakes coupled with graphene nanosheets (graphene@MXene) were prepared in N-methylpyrrolidone (NMP) by simple ultrasound-assisted liquid-phase exfoliation method for the first time. Besides, the effect of types of solvent with different viscocity, sonication temperature and sonication duration time on the property of graphene@MXene hybrids were systematacially investigated. It is found the liquid-phase exfoliated graphene owned excellent electron transfer ability and the MXene (Ti3C2Tx) nanoflakes possessed outstanding adsorption property, the as-synthesized graphene@MXene hybrid exhibited significant signal synergistic enhancement effect toward the oxidation of hazardous veterinary drug residue compound (chlorpromazine) and food additives (rhodamine B). Based on this, a novel and sensitive electrochemical sensor was fabricated, the linear detection ranges were 5 nM to 0.5 μM for chlorpromazine with sensitivity of 1090 µA μM−1 cm−2, and 10 nM to 2.5 μM for rhodamine B with sensitivity of 440 and 102.14 µA μM−1 cm−2. Besides, the detection limits were evaluated to be as low as 1.25 nM and 2.45 nM for chlorpromazine and rhodamine B, respectively.

In recent years, interest in the liquid-phase exfoliation (LPE) of layered crystals has been growing due to the efficiency and scalability of the method, as well as the wide range of practical applications of the obtained dispersions based on two-dimensional flakes. In this paper, we present a comparative study of as-grown and liquid-phase exfoliated GaSe1−xSx flakes. Bulk GaSe1−xSx crystals with x ~ 0, 0.25, 0.5, 0.75, 1 were synthesized by melting stoichiometric amounts of gallium, selenium, and sulfur particles in evacuated ampoules. X-ray diffraction analysis showed that the crystal structure does not change considerably after LPE, while the analysis of the Raman spectra revealed that, after liquid-phase processing in IPA, an additional peak associated with amorphous selenium is observed in selenium-rich GaSeS compounds. Nevertheless, the direct and indirect transition energies determined from the Kubelka-Munk function for LPE crystals correlate with the band gap of the as-grown bulk GaSeS crystals. This finding is also confirmed by comparison with the data on the positions of the photoluminescence peak. [ABSTRACT FROM AUTHOR]

Electroconductive composites of graphene and cellulose nanocrystals (CNC) were prepared by direct exfoliation of natural flake graphite in CNC suspensions. Using the scalable high-shear exfoliation method, we show that the environmentally friendly CNC is an excellent graphene stabilizer as we prepared aqueous graphene-CNC dispersions with a high concentration (4.0 mg ml−1) and yield (4.0%) after only 2 h exfoliation time. With this fast and facile method, we exfoliated graphite using CNC with different amounts of negatively charged sulfate ester groups. We found that the graphene concentration is proportional to zeta potential of the CNC suspension suggesting that electrostatic repulsion plays a key role in graphene stabilization. Albeit the insulating nature of CNC, the spray-coated composite films were electrically conductive with conductivity up to 280 S m−1, depending on the CNC amount. Cyclic voltammetry measurements showed a reversible redox response for the Fe(CN)63-/4− couple proving that the electron transfer was efficient in the composite film. Furthermore, biocompatibility studies with photosynthetic microorganisms revealed no toxic effects as the cells maintained their photosynthetic performance and growth when placed in direct contact with the composite. The cytocompatibility, electroactivity and good water-stability make the composite film a promising anode for bioelectrochemical applications.

Abstract Large‐scale production of two‐dimensional (2D) materials still is a crucial point toward its practical applications. Violet phosphorus (VP) with a wide bandgap accelerates and broadens the potential applications of elemental phosphorus in optoelectronics. Here, we demonstrate the scalable production of solution‐processable violet phosphorus flakes stably dispersed in several solvents. The exfoliated VP flakes exhibit thickness‐dependent visible photoluminescence characteristics, which covers the shortcoming of black phosphorus. Meanwhile, the VP‐based field‐effect transistor reveals relatively competitive electrical properties to other liquid‐phase exfoliated 2D materials. Our study paves the way for a wide range of applications of optical devices, energy storage, catalysis, and sodium batteries based on large‐scale VP flakes.

[Display omitted] • Liquid phase exfoliation (LPE) using surfactants in solvent environment for mass production of graphene and CNT has attracted much attention. • The ideal dispersion of graphene and CNT by the molecular engineering of surfactants and as a result of improving the quality of molecular interactions in an exfoliation system will be discussed to reach the maximum amount. • The physical chemistry parameters including interactions that are essential for the design and development of efficient exfoliation and dispersion systems will be highlighted, experimentally and computationally. One of the main challenges in obtaining outstanding physicochemical properties of graphene and carbon nanotubes (CNTs) is overcoming strong interactions between graphene single-layer and single nanotubes. Due to their excellent potential for large-scale manufacturing, surfactant-based dispersion and liquid phase exfoliation (LPE) technologies have lately attracted a lot of interest. The present review includes recently conducted experimental and computational studies on the LPE, dispersion, and stabilization of CNTs and nanoscale graphene, as well as characteristic parameters involved in exfoliation, dispersion, and stabilization mechanisms using surfactants. Molecular engineering of surfactants may be possible to achieve an optimum exfoliation and dispersion system for achieving desirable graphene and CNTs. This would increase the quality of molecular interactions. For the purpose of creating effective exfoliation and dispersion systems, this review focused on physico-chemical characteristic parameters and component interactions, both empirically and conceptually. [ABSTRACT FROM AUTHOR]

Previously, the preparation of graphene often required one or more of strong acid oxidants, reduction temperatures above 1000 ℃,expensive metal catalysts, and accompanied by the problems of low efficiency, high and heavy pollution. Our work provided a novel strategy for low-temperature vacuum preparation of high-quality graphene. Anhydrous AlCl3 and FeCl3 were used as bi-intercalants to prepare stage-1 graphite intercalation compounds (AlCl3-FeCl3-GICs) with accordion-like structure. Vacuum treatment of stage-1 AlCl3-FeCl3-GICs at a relatively low temperature of 180 ℃, low-boiling-point AlCl3 was heated and vaporized to further stretch the graphite sheet to obtain worm-like expanded graphite. The expanded graphite could maintain a loose structure under atmospheric conditions and was not collapsed. The effect of van der Waals force between the sheets of adjacent graphite layers was greatly weakened, which made the expanded graphite easily to be exfoliated. High-quality graphene was obtained by ultrasonic treatment of expanded graphite in solvent using liquid-phase exfoliation method. The preparation process of expanded graphite did not use strong oxidants, and was carried out in an anhydrous and oxygen-free environment. The reaction temperature was also controlled within 180 ℃. The overall preparation conditions were relatively mild and environmentally friendly. The preparation of graphene by the liquid-phase method could avoid the destruction of the graphene lattice structure as much as possible. The scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) were used to observe the microscopic morphology of graphene, and the X-ray powder diffraction (XRD) instrument, ray photoelectron spectroscopy (XPS) instrument and Raman spectrometer were used to characterize the microstructure of graphene. The results show that the prepared graphene has extremely low defects, the sp2 lattice structure still maintains a high degree of regularity, and most graphene layers are within three.

MoO3 is a versatile two-dimensional transition metal oxide having applications in areas such as energy storage devices, electronic devices and catalysis. To efficiently utilize the properties of MoO3 arising from its two-dimensional nature exfoliation is necessary. In this work, the exfoliation of MoO3 is carried out in 2-butanone for the first time. The achieved concentration of the dispersion is about 0.57 mg·mL−1 with a yield of 5.7%, which are the highest values reported to date. These high values of concentration and yield can be attributed to a favorable matching of energies involved in exfoliation and stabilization of MoO3 nanosheets in 2-butanone. Interestingly, the MoO3 dispersion in 2-butanone retains its intrinsic nature even after exposure to sunlight for 24 h. The composites of MoO3 nanosheets were used as an electrode material for supercapacitors and showed a high specific capacitance of 201 F·g−1 in a three-electrode configuration at a scan rate of 50 mV·s−1.

Abstract Vanadium disulfide (VS2), a typical layered transition‐metal dichalcogenide, has drawn extensive attention in energy storage devices, catalysts as well as sensors due to its intriguing electronic peculiarities, whereas its chemiresistive gas sensing properties have seldom been investigated. In this contribution, first the ammonia sensing properties of VS2 nanosheets (NSs)‐based chemiresistive gas sensor are reported. VS2 NSs are synthesized through facile liquid‐phase exfoliation, and their crystal structure, micromorphology, and elemental component are characterized. Density functional theory calculation has revealed that VS2 (100) is highly affinitive to ammonia molecule, and sufficient electron transfers from ammonia to VS2, which implies VS2 NSs possess high potential for ammonia sensing. The computational results are verified by gas sensing measurement that the resistance of VS2 NSs remarkably increases upon injecting ammonia gas at low working temperature of 40 °C. Additionally, the VS2 NSs exhibit superb selectivity to ammonia. The probable mechanism for ammonia sensing can be that ammonia molecule absorbed at edge sites of VS2 NSs transfers electron to p‐type VS2 NSs, reduces hole concentration in the NSs, and thus leads to resistance enhancement of VS2 NSs.

Abstract There is a great interest to use carbon-based material like graphene and graphene oxide in biomedical applications due to its flexibility to be functionalized with bio-active molecules. Herein, graphene and graphene-based nanocomposites were biosynthesized by liquid-phase exfoliation of graphite using aqueous extract of Parthenium hysterophorous (P-H) as a surfactant. A set of five thin film samples of graphene was prepared from graphene suspension by vacuum filtration method. Samples were characterized by UV-vis spectroscopy, Raman spectroscopy, SEM, and XRD, which revealed successful synthesis of graphene. Graphene/P-H(G/P-H) nanocomposites comprising varied ratios of graphene and P-H were prepared and their antibacterial activity was investigated by agar well diffusion method. The experimental results indicated that G/P-H nanocomposite have higher antibacterial activity than graphene alone, and bioactivity of G/P-H nanocomposite was found to be controlled by the fraction of graphene in the composite.

In this work, the photocatalytic activity of layered GaSe flakes obtained by liquid-phase exfoliation of bulk crystals was tested on the photodegradation of an organic dye under UV irradiation. The initial bulk GaSe crystals were synthesized by stoichiometric fusion method. Investigation of the structure and composition showed that as-grown crystal corresponds to β-polytype of GaSe. Analysis of the kinetics of the decomposition MB molecules showed that the obtained flakes demonstrate good photocatalytic activity in the UV range. The efficiency of the dye photodegradation was 86% within 3 hours under UV irradiation. [ABSTRACT FROM AUTHOR]

A liquid exfoliation method is an indispensable productive approach, inhibited by our breakdown to measure nanosheet concentration, estimation, and thickness. The light scattered by MoS2 nanosheets in liquid solvents, viz., dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone, and ethanol results in optical extinction spectra which determines the optoelectronic properties. All samples were characterized by X-ray diffraction, scanning electron microscopy, and UV–Vis spectroscopy for determining their structure, morphology, and optical properties, respectively. The minimum estimated number of layers was found to be 15 in DMSO as solvent. The liquid-phase method can be employed to a wide range of 2D material including MoSe2, WS2, and WSe2. [ABSTRACT FROM AUTHOR]

Germanium selenide attracts emerging attention for applications in high-performance field-effect transistors and photodetector, due to its unique photoelectric performances and tunable bandgap. Herein, the germanium selenide-reduced graphene oxide (GeSe-RGO) hybrid is successfully synthesized by loading liquid-phase exfoliated GeSe nanosheets on the 2D graphene via a hydrothermal reduction process. It is demonstrated that the photoresponse performance of the photoelectrochemical (PEC) device constructed by the synthesized GeSe-RGO hybrid is significantly enhanced in comparison to the one built by the sole GeSe nanosheets. The results of the PEC tests display the photocurrent density can reach to 8.45 μA/cm2 at the bias of 0.8 V, which is approximately 4 times that of sole GeSe nanosheets. Meanwhile, with the increase of illumination intensity, the photocurrent density of the GeSe-RGO photodetector almost presents a linear increase. When the illumination intensity is 90 mW/cm2, the photoresponsivity value is up to 116 μA/W. In addition, the GeSe-RGO hybrid shows a durable photoresponse capability under the bias of 0 V, revealing that such a hybrid has the excellent self-powered ability in the PEC system. There is no evident degradation on the photoresponsive performance of GeSe-RGO photodetector after 50 light on-off cycling, indicating the good stability of the hybrids. The enhanced performance of the GeSe-RGO hybrid is attributed to the outstanding photoresponsive capability of RGO and the effective separation of photo-generated electron-hole pairs. Our work indicates that the GeSe-RGO hybrid has great prospects for future applications in PEC-type photodetector devices. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) MoTe2 nanomaterials have emerged as a promising candidate for constructing excellent supercapacitors due to their high capacitive performance. Recent studies have revealed that MoTe2 has broad prospects as an active material in supercapacitors, although its strict requirements in terms of the external environment and complex preparation process remain serious obstacles to its practical application. Toward this end, MoTe2 nanosheets (NSs) were prepared by a facile and inexpensive liquid-phase exfoliation approach for the fabrication of MoTe2 electrodes. The results show that the MoTe2 NSs exhibit significantly improved electrochemical performance, with a specific capacitance (859 F g−1) more than three times that of bulk MoTe2 (271 F g−1) at a current density of 1 A g−1. In addition, the MoTe2-based electrode showed excellent cycle stability and maintained excellent specific capacitance (92.7% of the initial value) after 1000 cycles under the working condition of a current density of 10 A g−1. This study describes a fundamental investigation on the energy storage and conversion properties of 2D layered materials. [ABSTRACT FROM AUTHOR]

Phosphorene is a new two-dimensional material that has recently attracted much attention owing to its fascinating electrical, optical, thermal and chemical properties. Here, we report on high-quality exfoliation of black phosphorus nanosheets, with controllable size produced in large quantities by liquid-phase exfoliation using N-methyl-2-pyrrolidone (NMP) as a solvent under ambient conditions. The as-synthesized few layers show a great potential for solar energy conversion based on the optical results shown in this work.

Graphene can be produced using several methods. One of the most successful production methods in terms of scale-up is liquid-phase exfoliation (LPE). With this method, the solvent employed during exfoliation is a critical parameter. In the present study, hexagonal graphite powders were micromechanically exfoliated using a low-energy ball mill, and the expanded graphite was then obtained from the micromechanically exfoliated graphite. Finally, the graphenes were synthesized using LPE. N-Methyl-2-pyrrolidone (NMP) and N,N-dimethylformamide (DMF) were the most successful solvents used for producing graphene by the LPE method. Naphthalene and sodium dodecyl sulfate (SDS) were added to these solvents to improve production efficiency. The chemicals yielding the best results were determined by analyzing the graphenes. While 3–5-layer graphenes were produced in all liquid media, the amount of high-quality graphenes differed among samples. The most efficient graphene was obtained in the samples produced using NMP + SDS liquid media. The production efficiency obtained in these samples as a result of the exfoliation process was 25%. The samples produced with NMP were more successful than those produced with DMF. [ABSTRACT FROM AUTHOR]

Aim: The present study aims to apply the facile liquid-phase exfoliation (LPE) strategy to fabricate 2D organic materials and thus to broaden the family of biocompatible and multifunctional 2D materials. Materials & methods: 2D material-organic melanin and cellulose nanosheets were synthesized from black sesame hull using LPE. Photoluminescence and photothermal properties of the nanosheets were assessed, as well as stability and cell killing ability. Results: The prepared 2D nanoplatform exhibited broad and multiple photoluminescent emission bands. It also demonstrated efficient photothermal cancer therapy with excellent biocompatibility. Conclusion: The present study could open an avenue in exfoliating organic materials using the LPE strategy. This could make the fabrication of multifunctional 2D organic materials more efficient and broaden the family of biocompatible 2D nanomaterials. [ABSTRACT FROM AUTHOR]

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The use of stabilizer with designer structures can effectively promote graphite exfoliation in common solvents to render functionalized graphene desirable for their various applications. Herein, a hyperbranched polyethylene copolymer, HBPE@Py@Acryl, simultaneously bearing multiple pyrene terminal groups and pendant acryloyl moieties has been successfully synthesized from ethylene with a Pd-diimine catalyst based on unique chain walking mechanism. The unique structural design of the HBPE@Py@Acryl makes it capable of effectively promote graphite exfoliation in a series of common, low-boiling-point organic solvents, e.g. CHCl 3 , to render stable graphene dispersions with concentrations effectively adjustable by changing feed concentrations of graphite and polymer or sonication time. Meanwhile, it can be irreversibly adsorbed on the exfoliated graphene surface based on the π-π interactions between them to concurrently render acryloyl-functionalized graphene free of structural defects, with majority (92.7%) of them having a thickness of 2–3 layers. This allows us to obtain graphene electrothermal films simply by filtration and UV irradiation, which exhibit outstanding stability in use. The action mechanism of the HBPE@Py@Acryl as stabilizer for promoting graphite exfoliation and the role of UV irradiation on improving the stability in use of resulting graphene films have been elucidated. [ABSTRACT FROM AUTHOR]

Liquid-phase exfoliation (LPE) is a widely used and promising method for the production of 2D nanomaterials because it can be scaled up relatively easily. Nevertheless, the yields achieved by this process are still low, ranging between 2% and 5%, which makes the large-scale production of these materials difficult. In this report, we investigate the cause of these low yields by examining the sonication-assisted LPE of graphene, boron nitride nanosheets (BNNSs), and molybdenum disulfide nanosheets (MoS2 NS). Our results show that the low yields are caused by an equilibrium that is formed between the exfoliated nanosheets and the flocculated ones during the sonication process. This study provides an understanding of this behaviour, which prevents further exfoliation of nanosheets. By avoiding this equilibrium, we were able to increase the total yields of graphene, BNNSs, and MoS2 NS up to 14%, 44%, and 29%, respectively. Here, we demonstrate a modified LPE process that leads to the high-yield production of 2D nanomaterials.

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.

Realizing the efficacy of the liquid-phase exfoliation technique to obtain a greater quantity of graphene, this study demonstrates a cost-effective technique of bio-surfactant-assisted liquid-phase exfoliation of few-layer graphene (FLG) with a low defect ratio. An ultrasonic bath without any toxic chemicals or chemical modification was employed to exfoliate the graphene at room temperature. Several state-of-the-art characterization techniques such as TEM, AFM, XRD UV-Vis, and Raman spectroscopy were used to confirm the presence of the graphene. The dispersion exhibits a typical Tyndall scattering to the red laser beam. After a 7-h sonication of the dispersion, followed by a centrifugation frequency of 500 rpm for half an hour, the graphene concentration was found to be 1.2 mg/mL. The concentration decreases monotonically with an increase in the frequency, as a higher frequency causes sedimentation of the larger flakes or removes the adsorbed surfactant molecules from the graphene structures that collapse the graphene sheets into the graphite. The presence of an amino acid head-group in the surfactant facilitated exfoliation in an aqueous solution at well below the critical micelle concentration (CMC) of the surfactant. The product demonstrates all characteristic features of an FLG system. The TEM and AFM image reveals large-area graphene with a wrinkle-free surface; these morphological properties are confirmed by XRD and Raman spectroscopy. This study suggests that a sonication-induced process with a biocompatible surfactant can produce a cheap, large-surface-area graphene system for a wide range of applications. Moreover, the use of a probe sonicator as an alternative to the bath-type sonicator, together with the demonstrated technique, may reduce the time needed, and leads to a manifold increase in the yield.

Graphene is a honeycomb hexagonal two-dimensional (2D) crystal nanomaterial with a thickness of only 0.334 nm. It has been widely used and studied because of its ultra-thin 2D nano-characteristics and excellent electrical, thermal, optical, and mechanical properties. With the continuous in-depth study of graphene, the liquid-phase dispersion of graphene has also achieved breakthroughs. This review summarizes the research progress of the liquid-phase exfoliation mechanism, exfoliation method, stable dispersion mechanism, and dispersion method of graphene in recent years. The research situations of the Hamaker constant theory in exfoliation mechanism and Hansen solubility coefficient theory in stable dispersion mechanism are mainly discussed. The shortcomings of the research are summarized and analyzes the graphene liquid phase dispersed in the important challenge in the future. The stable dispersion method of graphene is also summarized. In the future, the π-π interaction will be the most potential method for studying graphene stabilization.

In liquid-phase exfoliation for the production of 2D nanomaterials fluid forces are used to gently overcome adhesive interlayer forces, leading to single- or few-layer 2D nanomaterials. Predicting accurately the critical fluid shear rate for exfoliation is a crucial challenge. By combining notions of fluid mechanics and fracture mechanics, we analyze a mathematical model of exfoliation, focusing on the π − peel regime in which bending forces are much smaller than the applied hydrodynamic forces. We find that in this regime the shear rate is approximately proportional to the adhesion energy, independent of the bending rigidity of the exfoliated sheet, and inversely proportional to the size a of a (assumed pre-existing) material flaw. The model appears to give values comparable to those obtained in wet ball milling, but to overestimate the shear rate values reported for turbulent exfoliation (by rotor mixing or microfluidization). We suggest that for turbulent exfoliation a “cleavage model” may be more appropriate, as it gives a stronger dependence on a and smaller critical shear rates.

Liquid-phase exfoliation was employed to fabricate BN nanoplatelets (BNNPs) with the assistance of an additional shear force from Fe 3 O 4 nanoparticles. Iron-oxide nanoparticles vibrated between BN layers and bulk BN particles were exfoliated into nanoplatelets. A thermally conductive composite was fabricated by the incorporation of the resultant BNNP into an epoxy matrix. After exfoliation, BNNP exhibited better dispersion in the polymer composite compared to bulk BN due to the reduced mean interparticle distances. Thus, the introduction of BNNP enables the decrease in the thermal percolation threshold via the formation of heat flow paths and enhancement of the thermal conductivity by 480% with the addition of a filler content of 30 wt%. [ABSTRACT FROM AUTHOR]

We report an industrially viable promising approach to produce micrometer-sized multilayer graphene nanoplatelet powder (MGNP) in a scalable quantity via microwave-assisted exfoliation of graphite (MEG) and fragmented into MGNP through liquid-phase exfoliation in the co-solvent mixture by kitchen mixer (KM). KM allows rapid delaminating MEG into MGNP by shear force dominated exfoliation. Majority of MGNPs are with a diameter of few micrometers and thickness is in nanometers. MGNP are crystalline with very limited defects was confirmed by Raman measurements and transmission electron microscopy. This process transforms, more than 86% of graphite flakes into MGNP. This advanced approach opens a new pathway to produce MGNP in bulk quantity as it is feasible, rapid, and cost-effective. [ABSTRACT FROM AUTHOR]