Sonication-assisted Exfoliation Research Articles

MoS2 nanosheets based label-free colorimetric aptasensor for Escherichia coli O157: H7 detection

The aggregation behavior of large-scale two-dimensional molybdenum disulfide (MoS2) nanosheets prepared by sonication-assisted exfoliation in environmental friendly 45% ethanol/water mixture under different conditions (e.g., salt concentration, cation valence and nanosheets size) had been examined to make them more appropriate for biological sensing application. Adjustment of sonication time and centrifuging speed could be utilized to select MoS2 nanosheets with various concentrations and sizes. Higher concentrations of salt and cations with higher valence were more effective to aggregate MoS2 nanosheets and settle them than their counterparts, which could be attributed to the perturbation of attractive van der Waals forces and repulsive Coulombic interactions. Moreover, the ethanol in mixture was capable of assisting MoS2 nanosheets to resist this aggregation initiated by salt but it would disturb the stability of aptamer functionalized MoS2 nanosheets in salt solution. The interplay of Escherichia coli O157: H7 (E. coli O157:H7) aptamer functionalized MoS2 nanosheets and salt was then inspired to develop a high sensitive detection method of E. coli O157:H7. The introduction of target bacteria induced MoS2 nanosheets to be exposed to cations, and promoted the aggregation and sedimentation behavior of MoS2 nanosheets. The change in extinction of MoS2 nanosheets had a linear relationship with E. coli O157:H7 concentration in a range of 500–5000 CFU/mL with a detection limit of 116 CFU/mL. This proposed colorimetric sensor expands the application scope of MoS2 nanosheets and shows its promising potential as an alternative tool for bacteria detection in food and water quality monitoring.

Solution-Processed 2D Transition Metal Dichalcogenides: Materials to CMOS Electronics

ConspectusTwo-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) have demonstrated exceptional potential as materials for future complementary metal-oxide-semiconductor (CMOS) technology. This is primarily because of their atomic thickness and excellent electrical and mechanical properties. With advancements in fabrication technology, electronic devices based on 2D TMD materials have rapidly progressed from isolated units for scientific experimentation to integrated circuits with practical applications. Among the different production methods, the solution-processing of 2D TMD nanomaterial dispersions offers the distinct advantages of low-temperature processing and cost-effective manufacturing for large-scale flexible and wearable electronics. A wide range of 2D nanoflake inks with versatile electronic properties can be assembled into atomic-thick thin films with dangling-bond-free van der Waals interfaces between adjacent nanoflakes. Furthermore, direct printing techniques can easily integrate multifunctional devices, such as n-type and p-type transistors, into CMOS devices and more complex integrated circuits. Despite these benefits and previous accomplishments, the field of solution-processed CMOS electronics using 2D TMD semiconducting materials is in its early stages of development and requires further research. One of the current challenges is the production of scalable and high-purity 2D semiconductor mono- and few layers with large lateral sizes and narrow thickness distribution. The field-effect mobility of solution-processed 2D TMD transistors remains lower than that of the transistors manufactured using mechanical exfoliation and chemical vapor deposition methods. In particular, limited research has been conducted on solution-processed p-type 2D TMD transistors. As a result, solution-processed CMOS devices using n-type and p-type 2D TMD transistors are scarce. In this Account, we provide an overview of the recent progress in the field of solution-processed CMOS electronics employing 2D TMD materials. First, we introduce the basic liquid exfoliation methods, such as sonication-assisted exfoliation and molecular intercalation methods, that are commonly utilized to prepare 2D TMD dispersions. In addition, we discuss the production of monolayer 2D materials, which serve as the building blocks for fabricating atomic-thick thin films. Subsequently, we review the typical techniques for depositing 2D inks, including spin coating, drop casting, and inkjet printing. Furthermore, we outline the thin-film patterning process for each technique, which is crucial for integrating multifunctional materials in CMOS devices. Subsequently, we focus on the recent advancements in solution-processed 2D TMD transistors. Furthermore, we explore the various factors that can improve the performance of the devices with regard to charge transport and charge traps. Afterward, we highlight notable applications of solution-processed CMOS technology, such as logic circuits and ring oscillators. Finally, we provide an overview of the challenges and opportunities in the development of solution-processed 2D materials and the integration of multifunctional devices for the advancement of CMOS electronics. This Account aims to provide a comprehensive guide for readers, offering both a broad overview and an in-depth insight into solution-processed 2D material-based electronics, covering a wide range of topics from the preparation of 2D TMD ink to device fabrication and CMOS applications. Therefore, this Account is expected to drive further progress and advancements in this field and promote the realization of practical applications.

Fully Integrated Photodetector Array Based on an Electrochemically Exfoliated, Atomically Thin MoS2 Film for Photoimaging

Despite the widespread interest in MoS2-based photodetectors over the past few years, use of a high-performance photoimaging device remains a major challenge due to the low yield and poor quality of the MoS2 film. In this paper, we demonstrate a simple method to fabricate a high-performance fully integrated photodetector array based on a large-area atomically thin MoS2 film for photoimaging. Here, the film is constructed by spin-coating of the MoS2 nanosheets, which are acquired via electrochemical intercalation and sonication-assisted exfoliation. By precisely controlling this process, semiconducting few-layered MoS2 nanosheets with pure phase can be obtained. High-performance photodetectors have been achieved for the TFSI-treated MoS2 film, as the responsivity reaches 1080 A/W, and the response/recovery time improved to 56/62 ms with high stability during the repeated on/off test. The overall performance is much better than that of previously reported photodetectors based on liquid-exfoliated MoS2 nanosheets. Furthermore, a fully integrated photoimaging device with a crossing structure and an effective pixel density of 460/cm2 has been fabricated based on the MoS2 film, and shows great potential for shape imaging with cross-talk suppression. We believe this work provides an approach to exploit the photodetector and image sensor based on layered materials.

Auto-oxidation of exfoliated MoS2 in N-methyl-2-pyrrolidone: from 2D nanosheets to 3D nanorods

We have therefore introduced a novel preparation route for MoO3 nanorods from exfoliated 2H-MoS2 via the auto-oxidation of a mixture of N-methyl-2-pyrrolidone and water via the sonication-assisted exfoliation of MoS2.

Facile exfoliation of MoS2 powders into nanosheets with excellent fluorescence quenching performance of perovskite

MoS2 nanosheets of pure semi-conducting hexagonal phase (2H-phase) have lots of potential applications due to their unique and novel property, and the fluorescence resonance energy transfer is very easy to happen between zero-dimensional (0D) perovskite quantum dots and two-dimensional (2D) MoS2 nanosheets. Herein, we demonstrate that a facile and green method to fabricate MoS2 nanosheets by sonication-assisted exfoliation of MoS2 powders in pure water after a hydrothermal reaction. The experimental results confirm that MoS2 ultrathin sheets obtained from powders are monolayer and few-layer 2H-phase nanosheets with size of 100–300 nm. Interestingly, the as-prepared MoS2 nanosheets have excellent performance to quench the fluorescence of CsPbBr3 quantum dots. It can provide a new way for us to explore energy resonance transfer between 0D quantum dots and 2D layered materials.

Dispersion of Few-Layer Black Phosphorus in Binary Polymer Blend and Block Copolymer Matrices

Exfoliated black phosphorus (bP) embedded into a polymer is preserved from oxidation, is stable to air, light, and humidity, and can be further processed into devices without degrading its properties. Most of the examples of exfoliated bP/polymer composites involve a single polymer matrix. Herein, we report the preparation of biphasic polystyrene/poly(methyl methacrylate) (50/50 wt.%) composites containing few-layer black phosphorus (fl-bP) (0.6–1 wt.%) produced by sonicated-assisted liquid-phase exfoliation. Micro-Raman spectroscopy confirmed the integrity of fl-bP, while scanning electron microscopy evidenced the influence of fl-bP into the coalescence of polymeric phases. Furthermore, the topography of thin films analyzed by atomic force microscopy confirmed the effect of fl-bP into the PS dewetting, and the selective PS etching of thin films revealed the presence of fl-bP flakes. Finally, a block copolymer/fl-bP composite (1.2 wt.%) was prepared via in situ reversible addition–fragmentation chain transfer (RAFT) polymerization by sonication-assisted exfoliation of bP into styrene. For this sample, 31P solid-state NMR and Raman spectroscopy confirmed an excellent preservation of bP structure.

Scalable preparation of water-soluble ink of few-layered WSe2 nanosheets for large-area electronics**Project supported by the National Natural Science Foundation of China (Grant Nos. 51771224, 51772087, and 51471185), the National Key R&D Program of China (Grant Nos. 2016YFJC020013 and 2018FYA0305800), and Fujian Institute of Innovation, Chinese Academy of Sciences.

Few-layer two-dimensional (2D) semiconductor nanosheets with a layer-dependent band gap are attractive building blocks for large-area thin-film electronics. A general approach is developed to fast prepare uniform and phase-pure 2H-WSe2 semiconducting nanosheets at a large scale, which involves the supercritical carbon dioxide (SC-CO2) treatment and a mild sonication-assisted exfoliation process in aqueous solution. The as-prepared 2H-WSe2 nanosheets preserve the intrinsic physical properties and intact crystal structures, as confirmed by Raman, x-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscope (STEM). The uniform 2H-WSe2 nanosheets can disperse well in water for over six months. Such good dispersivity and uniformity enable these nanosheets to self-assembly into thickness-controlled thin films for scalable fabrication of large-area arrays of thin-film electronics. The electronic transport and photoelectronic properties of the field-effect transistor based on the self-assembly 2H-WSe2 thin film have also been explored.

A dual-criterion optimization for sulfonated asphalt-assisted aqueous phase exfoliation to prepare graphene suitable for protective coating of aluminium

In this work, we aimed to prepare graphene with high concentration (CG) or quality (indicated by ID/IG) by sonication-assisted exfoliation in aqueous sulfonated asphalt (SAS) solution. The highest CG can reach 0.181 mg ml−1, while the smallest ID/IG is only 0.331 in the investigated range. Meanwhile, we observed that CG and ID/IG changed in the opposite trend with the increase of SAS concentration, and reached their extreme values simultaneously. This was attributed to SAS’s agglomeration-induced redistribution of total energy absorbed by graphite between exfoliation and crushing. The graphene size was mainly within 100–400 nm and most of layer number was <5. The stabilization of graphene dispersion comes from the electrostatic repulsion between negatively charged SAS groups adsorbed on the graphene sheets. As the protective coating of aluminium, the graphene with relative small (for H2SO4 solution) or large (for NaCl solution) size, relative high defect content and annealing at proper temperature can improve the anticorrosion performance of graphene.

Electrochemical sensor study of TiO2 nanoparticle–graphene composite produced by mechanical milling and sonication-assisted exfoliation

TiO2 nanoparticle-decorated graphene was produced by mechanical milling of TiO2 powder with graphite followed by sonication of the nanocomposite in the presence of sodium lauryl sulfate surfactant. Sonication led to the exfoliation of graphite to produce TiO2 nanoparticle–graphene composite. The as-prepared TiO2–graphite nanocomposite was characterized using X-ray diffraction and scanning electron microscopy and the exfoliated TiO2–graphene nanocomposite was analyzed using Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The results indicated the formation of faceted titanium dioxide particles with an average size of ~ 200 nm. Thickness of the few layered graphene sheets was found to be 2 + 0.8 nm. The glassy carbon electrode coated with the TiO2 nanoparticle–graphene composite was used to detect potassium ferricyanide (K3FeCN6) by cyclic voltammetric method. TiO2 nanoparticle–graphene-coated surface demonstrated improved response with enhanced current for K3FeCN6 detection.

Equipartition of Energy Defines the Size-Thickness Relationship in Liquid-Exfoliated Nanosheets.

Liquid phase exfoliation is a commonly used method to produce 2D nanosheets from a range of layered crystals. However, such nanosheets display broad size and thickness distributions and correlations between area and thickness, issues that limit nanosheet application potential. To understand the factors controlling the exfoliation process, we have liquid-exfoliated 11 different layered materials, size-selecting each into fractions before using AFM to measure the nanosheet length, width, and thickness distributions for each fraction. The resultant data show a clear power-law scaling of nanosheet area with thickness for each material. We have developed a simple nonequilibrium thermodynamics-based model predicting that the power-law prefactor is proportional to both the ratios of in-plane-tearing/out-of-plane-peeling energies and in-plane/out-of-plane moduli. By comparing the experimental data with the modulus ratio calculated from first-principles, we find close agreement between experiment and theory. This supports our hypothesis that energy equipartition holds between nanosheet tearing and peeling during sonication-assisted exfoliation.

Effect of Frequency and Number of Piezoelectric Probes in Sonication-assisted Exfoliation of Graphite Layers into Graphene Oxide

Effect of Frequency and Number of Piezoelectric Probes in Sonication-assisted Exfoliation of Graphite Layers into Graphene Oxide

Understanding Surfactant Stabilization of MoS2 Nanosheets in Aqueous Dispersions from Zeta Potential Measurements and Molecular Dynamics Simulations

The sonication-assisted exfoliation of MoS2 in aqueous media in the presence of ionic surfactants to give stable dispersions is an attractive procedure for obtaining single or few-layered nanosheet...

Enhanced dispersion of boron nitride nanosheets in aqueous media by using bile acid-based surfactants

Facile noncovalent surface functionalization of hydroxylated boron nitride nanosheet (BNNS-OH) was attempted through the sonication-assisted exfoliation of h-BN in aqueous media in the presence of bile acid-based surfactants such as sodium cholic acid (SC) or sodium deoxycholic acid (SDC), resulting in SC- or SDC-BNNS-OH dispersion with high up to 2 mg ml−1 and enhanced dispersion stability due to the increased negative zeta potential. While prepared SC-BNNS-OH revealed multi-layered BNNS structures, the large lateral sizes of hundreds nanometers and clear h-BN lattice structures are very promising for the preparation and application of water-processable BNNS-based nanomaterials. It is regarded that noncovalent functionalization of BNNS-OH based on σ-π interaction between with σ-rich bile acid-based amphiphiles and π-rich BNNS is very effective to formulate multi-functional BNNS-based nanomaterials or hybrids that can be utilized in various applications where both the pristine properties of BNNS and the extra functions are simultaneously required.

Probing Graphene–Surfactant Interactions in Aqueous Dispersions with Nuclear Overhauser Effect NMR Spectroscopy and Molecular Dynamics Simulations

Sonication-assisted exfoliation of graphite in aqueous solutions of ionic surfactants is an attractive, scalable route for the production of defect-free graphene. The interaction of surfactant chains with graphene is crucial both to the process and to the stability of the dispersion. We use 1H nuclear Overhauser effect (NOE) NMR techniques and classical molecular dynamics (MD) simulations to probe the molecular nature of these interactions in graphene dispersions stabilized by the cationic surfactant cetyltrimethylammonium bromide. We show that the surfactant chains are quasi-bound to the graphene sheets undergoing rapid exchange with the free surfactant ligands in the bulk, but what is surprising is the observation of NOE interactions between groups that are separated by more than 5 A along the chain. MD simulations provide the key to interpreting these observations; these interactions are a consequence of the arrangement of the quasi-bound surfactant chains that allows segments of different chains to co...

Synthesis of ZnO Nanocrystal–Graphene Composite by Mechanical Milling and Sonication-Assisted Exfoliation

A ZnO nanocrystal–graphene composite was synthesized by a two-step method involving mechanical milling and sonication-assisted exfoliation. Zn metal powder was first ball-milled with graphite powder for 30 h in water medium. This ball-milled mixture was then subjected to exfoliation by sonication in the presence of sodium lauryl sulfate surfactant to produce graphene decorated with spherical agglomerates of ultrafine nanocrystalline ZnO. The presence of a few layers of graphene was confirmed by Raman spectroscopy and atomic force microscopy measurements. The size, phase identity and composition of the ZnO nanocrystals was determined by transmission electron microscopy measurements.

Graphene/Na carboxymethyl cellulose composite for Li-ion batteries prepared by enhanced liquid exfoliation

In the present work, we report a sonication-assisted exfoliation method of graphene preparation enhanced by the use of microwave heating and “green” exfoliant – sodium carboxymethyl cellulose (NaCMC). Introducing microwave heating during sonication of graphite dispersions in aqueous solutions of NaCMC results in the formation of graphene dispersions with concentration as high as 4.29mg/ml. It is found that drying the dispersions results in the formation of graphene/NaCMC composites with graphene content up to 38.65wt%. A study of the composite with High Resolution Transmission Electron Microscopy and Raman Spectroscopy reveals the formation of few-layer graphene approximately below five layers. The as-prepared graphene/NaCMC composite shows higher capacities than commercial graphite in Li-ion half cells reaching 397mAh/g(graphene). Also, when the composite is used with a nanosilicon (33wt%) in a Li-ion half cell high initial reversible capacities of 1611mAh/g(Si) with good cyclability and rate capability have been reached.

High-rate production of few-layer graphene by high-power probe sonication

Graphene can be obtained via sonication-assisted liquid-phase exfoliation, but the production rate of few-layer graphene (FLG) is still low. A high-power probe sonicator was used in this study to improve the production rate of FLG, and its performance was optimized by controlling processing parameters such as the initial graphite concentration, surfactant concentration and liquid volume. By optimizing processing parameters, production rate of FLG dispersions in N-methyl-2-pyrrolidone (NMP) were greater than 1 g/h, which is the best value achieved in the sonication-assisted exfoliation process. In the case of liquid exfoliation in water/surfactant solution, production rate of FLG was achieved approximately 0.28 g/h. Our work here demonstrates that graphene concentration in a probe-sonication process does not depend on the shape of vessel, and it is predictable by power law models.

Development of a highly active electrocatalyst via ultrafine Pd nanoparticles dispersed on pristine graphene.

A unique synthesis was developed to immobilize Pd nanoparticles on pristine graphene (PG) sheets via a facile supercritical carbon dioxide route. Pristine graphene was obtained by sonication-assisted exfoliation of graphite in an organic solvent. Finely dispersed worm-like Pd nanoparticles are homogeneously deposited on the hydrophobic graphene surfaces. The combination of pristine graphene sheets and well-dispersed Pd nanoparticles provided large electrochemically active surface areas (ECSA) for both direct formic acid fuel cell (DFAFC) and methanol fuel cell (DMFC). The ECSA values are more than twice as large as those of reduced graphene oxide and carbon nanotube based counterparts or six times those of conventional XC-72 carbon black. Significant enhancements were also observed in the electrocatalytic activity and stability measurements. The excellent electrochemical property of Pd/PG is attributable to the well-preserved graphene structure that ensures electrical conductivity and stability of the composite. Its large surface area also allows for the deposition of small size and high dispersion of the Pd nanoparticles. This straightforward synthesis offers a new pathway for developing highly active electrocatalysts based on pristine graphene with fully optimized properties.

A novel aptamer sensor based on layered tungsten disulfide nanosheets and Au nanoparticles amplification for 17β-estradiol detection

The required routine monitoring of the endocrine-disrupting compounds in real samples demands for cost-effective, selective and sensitive detection methods. Layered tungsten disulfide (WS2) nanosheets are a type of two-dimensional, covalent-network solid material with remarkable structural and electronic properties that have attracted increasing interest in recent years. In this work, WS2 nanosheets are prepared by a one-step sonication-assisted exfoliation method and characterized using X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. A novel aptamer-based label-free electrochemical biosensor for 17β-estradiol is fabricated with the aptamers immobilized on the WS2 nanosheets/Au nanoparticle-modified glassy carbon electrode through Au–S interaction. After blocking with bovine serum albumin, the aptamer probe is then bound with the addition of 17β-estradiol to form the estradiol/aptamer complex on the electrode surface, which leads to a significant decrease in peak current. The change in the peak current has a good linear relationship with 17β-estradiol concentration in the range of 1.0 × 10−11 to 5.0 × 10−9 M, with a detection limit of 2.0 × 10−12 M (3σ/S). The aptamer sensor exhibits high sensitivity and remarkable reproducible analytical performance, and has been successfully applied for the determination of 17β-estradiol in serum and water samples with the recovery of 96.0–104.2%. The layered WS2 nanosheet/Au nanoparticle film thus, acts as an efficient platform for the assembling of bio-probes and will be extended to other analytes such as protein and DNA and RNA electrochemical biosensing.

Dispersion of graphene in organic solvents and their use for improving efficiency of dye- and quantum dot-sensitized solar cells

Pristine graphene was directly suspended in a variety of organic media, which are used either as electrolyte solvents or deposition media in sensitized solar cells. Dispersion occurred directly through sonication-assisted exfoliation of graphite powder, without adopting the oxidative approach involving intermediate formation of graphene oxide and its subsequent reduction. The concentration of the thus dispersed graphene was relatively low, in the order of a few tens of micrograms per ml, but it was very effective in increasing the efficiency of sensitized solar cells. Dispersed graphene was first deposited on solid substrates and was extensively characterized by TEM, SEM, XPS and Raman spectroscopy. Also dispersed graphene has been introduced in liquid-electrolyte and gel-electrolyte dye-sensitized solar cells by means of sulfolane/3-methoxypropionitrile mixtures and in quantum dot sensitized solid-state solar cells by means of chlorobenzene-based suspensions. Increase of cell efficiency in the presence of the above tiny quantities of graphene was very large, particularly in the case of solid state cells where more than 3-fold increase of efficiency was observed.