Liquid-phase Shear Exfoliation Research Articles

Liquid-phase shear exfoliation combined with hydrothermal processing for the preparation of graphene nanosheet/AlOOH nanofiber composite powder to enhance high-temperature performance of MgO-carbon castable

Flake graphite (FG) poses challenges for incorporation into castables due to its hydrophobic nature. In this paper, a strategy combining liquid-phase shear exfoliation (LPSE) with hydrothermal processing was proposed to produce hydrophilic graphene nanosheet/AlOOH nanofiber (GN/ANF) composite powders to address this issue. Under optimal shear exfoliation conditions, the yield of graphene nanosheets (GNs) reached up to 57%. Following a straightforward hydrothermal treatment, the water contact angle of as-prepared GN/ANF composite powders decreased to 53.1°, compared to 103.6° of the original FG. Benefiting from the hydrophilic properties of the composite powders and the homogeneous dispersion of GNs in MgO castables, the sample containing 0.5 wt% GNs exhibited better high-temperature performance than its counterparts. Relative to the control specimen, the slag corrosion index of the sample containing 0.5 wt% GNs decreased from 0.60 to 0.13, while the thermal shock resistance increased by approximately 2.8 times.

Experimental Study on Green Concrete using Graphene

The paper considers methods for concrete modification using low-layer graphene and grapheme oxide. It was found that graphene oxide and low-layer graphene obtained by liquid-phase shear exfoliation significantly increase the strength of concrete. In our opinion, low-layer graphene has better prospects since it is cheaper and its production technology is environmentally friendly. The viability and future of graphene largely depends on the availability of such a method that allows mass production of high-quality graphene at an affordable price. In this regard, liquid- phase separation of graphite with the formation of low-layer graphene, which can be used to modify concrete, turned out to be a competitive solution. The following main tasks were formulated in order to solve the organizational problems of low- layer grapheme industrial production: reducing the concentration of low-layer grapheme in concrete; increasing the concentration of low-layer graphene in suspension; developing an industrial technology for the production of concentrate with a high content of low- layer graphene; conducting full-scale experimental studies to determine the optimal concentration of low-layer graphene in concrete.

Improving the technology and equipment for industrial production of nanoplates by liquid-phase shear exfoliation of layered crystals

For the production of nanoplates from layered crystals by liquid-phase shear exfoliation, patent-protected technologies and equipment have been developed. The main difference between the proposed technologies and equipment from the known ones is that the exfoliation process is possible only by shearing in continuous operation. Particular interest in liquid-phase exfoliation can be explained by the following advantages of this technology in relation to others: chemical reagents are used in minimal amounts (3–4 mLL–1) as surfactants to prevent agglomeration of nanoplates that are formed during exfoliation; as a rule, one of the components of the created structural or functional material serves as a liquid dispersion medium; material and energy costs are much less than when using other technologies; this technology is easily scalable. The kinetics of the exfoliation process has been studied and it has been established that the concentration of nanoplate-layered crystals mainly depends on the total path of particles traveled by them in the exfoliation zone, i.e. in the zone of contact of the movable blades with the inner surface of the stator. A mathematical model has been developed for the distribution of nanoplates in a liquid, and the critical concentration of agglomeration of these plates in a liquid has been determined. A cascade technology for the production of nanoplates and a method for calculating the main regime and geometric parameters of rotary devices with moving blades are proposed.

Relationship between the shape of particles of initial graphite and graphene plates during liquid-phase shear exfoliation

Relationship between the shape of particles of initial graphite and graphene plates during liquid-phase shear exfoliation

Organic salt-assisted liquid-phase shear exfoliation of expanded graphite into graphene nanosheets

How to improve the efficiency of liquid-phase shear exfoliation (LPSE) for mass production of large-size graphene nanosheets still remains an ongoing challenge. In this work, we have developed a LPSE method using a rotor-stator mixer. It is quite simple and efficient by exfoliation of expanded graphite (EG) in N-methyl-2-pyrrolidone (NMP) with the assistance of organic salts including sodium citrate, potassium citrate and sodium tartrate. The LPSE of EG in NMP can provide improved yields, up to 6 times as high as values from exfoliation of natural flake graphite (NFG). The additive of organic salts in NMP can make a further improvement in graphene yields, 1.5 times higher than that obtained only in NMP. Remarkably, the yields of the as-exfoliated graphene are as high as 10% under optimal conditions, and up to 50% after multiple-cycle exfoliation. Organic salts in LPSE act as analogue grinding aids enhancing the applied shear forces and thus contributing to the improved efficiency of LPSE, but they do not intercalate into the interplanar spaces of graphite. This facile LPSE method should have excellent potential in the large scale production of graphene nanosheets for numerous applications.

Continuous and semi-continuous industrial production of lubricants modified with graphene nanostructures

This article proposes one of the options for the production of graphene-containing suspensions and their modification of lubricants. It is based on the technology of obtaining graphene nanostructures by the method of liquid-phase shear exfoliation of graphite. The proposed technological scheme can operate in both semi-continuous and continuous modes. The main advantages of this technology are simplicity and reliability of equipment, as well as environmental friendliness of production.

Improved efficiency of liquid-phase shear exfoliation of expanded graphite with mica plates as bifunctional additives

Liquid-phase shear exfoliation (LPSE) is a potential method of large-scale production of good-quality graphene.

Production of Graphene-Containing Suspensions for Liquid-Phase Shear Exfoliation of Graphite

A method and device for obtaining graphene-containing suspensions by liquid-phase shear exfoliation of graphite in a continuous mode have been developed. The comparison of the intensities of the process of exfoliation of graphite in the periodic and continuous modes was carried out and it was found that the intensity of the exfoliation process in the continuous mode is higher than in the periodic one. The limiting concentration of graphene structures in a suspension is reached 1.5 times faster when using an apparatus operating in a continuous mode than in a periodic mode, and its numerical value is greater (by at least 25 %).

Scalable Preparation of Low-Defect Graphene by Urea-Assisted Liquid-Phase Shear Exfoliation of Graphite and Its Application in Doxorubicin Analysis.

The mass production of graphene is of great interest for commercialization and industrial applications. Here, we demonstrate that high-quality graphene nanosheets can be produced in large quantities by liquid-phase shear exfoliation under ambient conditions in organic solvents, such as 1-methyl-2-pyrrolidinone (NMP), with the assistance of urea as a stabilizer. We can achieve low-defect graphene (LDG) using this approach, which is relatively simple and easily available, thereby rendering it to be an efficient route for the mass production of graphene. We also demonstrate the electrochemical sensing of an LDG-modified electrode for the determination of doxorubicin (DOX). The sensor shows an enhanced electrocatalytic property towards DOX, leading to a high sensitivity (7.23 × 10−1 μM/μA) with a detection limit of 39.3 nM (S/N = 3).

Phase-Inversion Polymer Composite Separators Based on Hexagonal Boron Nitride Nanosheets for High-Temperature Lithium-Ion Batteries.

By preventing electrical contact between anode and cathode electrodes while promoting ionic transport, separators are critical components in the safe operation of rechargeable battery technologies. However, traditional polymer-based separators have limited thermal stability, which has contributed to catastrophic thermal runaway failure modes that have conspicuously plagued lithium-ion batteries. Here, we describe the development of phase-inversion composite separators based on carbon-coated hexagonal boron nitride (hBN) nanosheets and poly(vinylidene fluoride) (PVDF) polymers that possess high porosity, electrolyte wettability, and thermal stability. The carbon-coated hBN nanosheets are obtained through a scalable liquid-phase shear exfoliation method using ethyl cellulose as a polymer stabilizer and source of the carbon coating following thermal pyrolysis. When incorporated within the PVDF matrix, the carbon-coated hBN nanosheets promote favorable interfacial interactions during the phase-inversion process, resulting in porous, flexible, free-standing composite separators. The unique chemical composition of these carbon-coated hBN separators implies high wettability for a wide range of liquid electrolytes. This combination of high porosity and electrolyte wettability enables enhanced ionic conductivity and lithium-ion battery electrochemical performance that exceeds incumbent polyolefin separators over a wide range of operating conditions. The hBN nanosheets also impart high thermal stability, providing safe lithium-ion battery operation up to 120 °C.

Environmentally friendly technology for the modification of lubricants with graphene nanostructures

Nanomaterials, and in particular graphene, significantly increase the basic tribological characteristics of lubricants. One of the most effective ways to quickly use laboratory results on an industrial scale is to modify traditional lubricants with graphene concentrates. The research results showed that in order to solve this problem successfully, it is necessary to create graphene concentrate and distribute it evenly over the total volume of the lubricant. It is necessary that the concentrate be prepared on the same basis as the lubricant. In the present work, previous studies on the mechanical activation and exfoliation of graphite in a core drum mill, liquid-phase shear exfoliation in a rotary apparatus with moving blades, and the homogenization of graphene nanostructures in lubricants using a rotary mixer are combined. Changes were made to the design of the main components, taking into account the use of this technology in the industry. The presented technology is environmentally friendly, since only oil and graphite are used and there are no harmful wastes that must be disposed of.

Kinetics of liquid-phase shear exfoliation of graphite in synthetic oils

Lubricants modified with nanosized particles are of great interest to science and industry, since they have much better tribological characteristics compared to traditional lubricants. One of the most promising nanoparticles is graphene, which has an extremely low coefficient of friction, is very wear-resistant and environmentally friendly. Today, the main problem for the development of a new nano-lubricant is the creation of an environmentally friendly and cheap technology for the industrial production of graphene suspensions or graphene concentrates for the modification of traditional lubricants. The article describes the process of liquid-phase shear exfoliation of graphite in a rotary apparatus with moving blades, in synthetic oils. The kinetic dependences of the exfoliation process, i.e. the dependence of the concentration of graphene nanostructures in suspension over time at different values of the process parameters. It has been experimentally proved that using a stator-rotor mixer with moving blades, it is possible to obtain graphene nanostructure concentrations of at least 2 mg / ml.

Improving functional and environmental performance of Portland cement-based materials by graphene nanostructures

Nanoparticles can accelerate cement hydration due to their high activity compacting microstructure, and consequently increase the strength. For the industrial production of concrete modified with nanoscale particles, it is necessary to develop an environmentally friendly and cheap technology for the industrial production of nanoparticles. The article presents the results of increasing the operational characteristics of concrete by adding graphene nanostructures obtained by liquid-phase shear exfoliation of graphite. This environmentally friendly technology requires energy costs, at least ten times less than technologies that use ultrasonic treatment of the suspension. Our industrial partner set a specific task: to find the minimum concentration of graphene structures in relation to cement, at which the compressive strength of cement-sand mix increases by 30%. It was experimentally established that at concentrations of graphene nanostructures with respect to cement not more than 0.02%, the compressive strength increases by at least 30%.

Production of few-layer and multilayer graphene by shearing exfoliation of graphite in liquids

The article describes the process of liquid-phase shear exfoliation of graphite in a rotary apparatus with moving blades, in water and I-20A oil (Rosneft, Russia) used as a liquid. The linear dependence of the process intensity on the shear rate and graphite concentration in the initial suspension are established in the paper. To increase the share of graphene converted into graphene plates, it has been proposed to reduce periodically the concentration of graphene plates in suspension by adding pure liquid. It was found that the exfoliation rate of graphite is directly proportional to the concentration of graphite in the initial suspension and the rotor speed. The resulting graphene-containing oil-based suspension was used to modify greases.

Production of graphene concentrates based on synthetic oils in rod drum mills

The article presents the results of the refinement of the mathematical model of the process of liquid-phase shear exfoliation of graphite and experiments on the production of graphene concentrates based on synthetic oils in a rod drum mill. The model parameters were identified and its adequacy to the real process was experimentally confirmed. It is given the dependence of the coefficient of light absorption, which characterizes the average integral value of graphene layers in suspension particles and their concentration on the processing time.

Calculation of parameters of the rotary apparatus for the production of graphene concentrate based on synthetic oils

This article presents the results of a study of the process of liquid-phase shear exfoliation of graphite in oil. The result is a suspension containing graphene structures. It was experimentally established that when designing industrial devices, the concentration of graphene structures in oil can be considered directly proportional to the following parameters: graphite concentration in the initial suspension; rotor radius; rotational speed; number of moving blades; suspension processing time. A relationship, allowing to calculate the performance or parameters of industrial rotary devices based on the results of experiments on a laboratory setup, was obtained.

The use of concrete and epoxy resin, modified with few-layer graphene for the production, repairs, and strengthening of concrete beams

The paper deals with the modification of concrete and epoxy resin with a 2D carbon material (2DCM) obtained by liquid-phase shear exfoliation of graphite. It was experimentally established that the three-point bending strength of graphene-modified samples (0.05 wt.% of graphene in cement) in 1.5 times greater than that of pristine (unmodified) concrete. The water absorption of concrete modified with the 2DCM was found to decrease by 3 times. A method, differing from the known ones where few-layered graphene is obtained directly in the hardener through shear exfoliation of graphite, was developed for modifying the ED-20 epoxy resin using the 2DCM. It allowed us to increase the Charpy impact strength by 25-30 %. The tensile and bending strength were increased by 10 %. The test results of the restored beams after breaking at three-point bending, as well as on the adhesion of the reinforcing fabric to concrete, revealed a synergistic effect while using the concrete and epoxy resin modified with the 2DCM.

The novel and facile preparation of 2DMoS2@C composites for dye adsorption application

In this work, we proposed a convenient strategy for preparing the MoS2-based adsorbents by combining liquid-phase shear exfoliation and annealing. We selected carboxymethylcellulose sodium (CMC) as the additive to promote the exfoliation of bulk MoS2 in the pollution-free ethanol/water mixture system. The results showed that the addition of appropriate CMC increased the viscosity of the suspension and prevented 2D MoS2 nanosheets agglomeration to improve the shear-exfoliating effect. By optimizing the operating conditions, the average lateral dimension and average layer number of 2D MoS2 nanosheets were around 100 nm and around 4 layers, respectively. The composites of 2D MoS2 nanosheets and porous carbon (2DMoS2@C) were obtained after annealing the composites of 2D MoS2 nanosheets and CMC. Furthermore, the adsorption behaviors of 2DMoS2@C for the removal of rhodamine B (RhB) and methylene blue (MB) were investigated. Interestingly, the 2DMoS2@C exhibited superior performance towards MB removal than towards RhB removal because of the pore structure and dye molecular size. The theoretical adsorption capacity of 2DMoS2@C for MB removal calculated by the Langmuir isotherm model could get 272 mg/g. The adsorption mechanism of 2DMoS2@C was also analyzed in detail. This is a facile, efficient and economical method for preparing adsorbents based on 2D materials.

High‐Throughput Continuous Production of Shear‐Exfoliated 2D Layered Materials using Compressible Flows

2D nanomaterials are finding numerous applications in next-generation electronics, consumer goods, energy generation and storage, and healthcare. The rapid rise of utility and applications for 2D nanomaterials necessitates developing means for their mass production. This study details a new compressible flow exfoliation method for producing 2D nanomaterials using a multiphase flow of 2D layered materials suspended in a high-pressure gas undergoing expansion. The expanded gas-solid mixture is sprayed in a suitable solvent, where a significant portion (up to 10% yield) of the initial hexagonal boron nitride material is found to be exfoliated with a mean thickness of 4.2 nm. The exfoliation is attributed to the high shear rates (γ˙ > 105 s-1 ) generated by supersonic flow of compressible gases inside narrow orifices and converging-diverging channels. This method has significant advantages over current 2D material exfoliation methods, such as chemical intercalation and exfoliation, as well as liquid phase shear exfoliation, with the most obvious benefit being the fast, continuous nature of the process. Other advantages include environmentally friendly processing, reduced occurrence of defects, and the versatility to be applied to any 2D layered material using any gaseous medium. Scaling this process to industrial production has a strong possibility of reducing the cost of creating 2D nanomaterials.

Layered franckeite and teallite intrinsic heterostructures: shear exfoliation and electrocatalysis

Naturally occurring van der Waals heterostructures (vdWH) undergo liquid-phase shear exfoliation and are applied in electrocatalytic energy reactions.