High Exfoliation Research Articles

Green production of functionalized few-layer borophene decorated with cerium-doped iron oxide nanoparticles for repeatable hydrogen peroxide detection

Functionalized few-layer borophene (FFB) was prepared using gallnut extract and coffee waste extract as natural exfoliating and stabilizing agents in an environmentally friendly ultrasonic and high shear exfoliation. Here, a facile precipitation method was employed to grow iron oxide nanoparticles doped with cerium (Ce-FeONPs) onto the surface of FFB. This intriguing combination of materials yielded Ce-FeONPs nanoparticles that exhibited exceptional peroxidase-like activity, efficiently catalyzing the conversion of 3,3′,5,5′-tetramethylbenzidine (TMB) to a blue oxidized TMB (oxTMB) in the presence of hydrogen peroxide (H2O2). Additionally, the introduction of FFB contributes a reducibility effect to the catalytic oxidation of TMB, facilitating the restoration of the oxTMB to TMB. Thus, FFB-Ce-FeONPs showcase intriguing properties encompassing both oxidative and reductive characteristics, suggesting their potential as a reagent for repeated detection of H2O2. Moreover, a colorimetric sensing system enabled the liner detection of H2O2 spanning a concentration range from 0.08 to 1 mM, with a detection limit of 0.03 mM. Noteworthily, FFB-Ce-FeONPs demonstrated sustained efficacy over ten successive recycling cycles, as indicated by consistent slopes and observable color changes. In summary, this work reports the first application of nanoenzymes in repetitive H2O2 detection. Even after ten multiple cycles, the detection limit remains virtually unaltered, underscoring the robustness and enduring effectiveness of the engineered nanomaterial. The proposed simultaneous oxidation and reduction strategies for detecting H2O2 showed a commendable capability in ten cycles of H2O2 detection, thus providing a promising approach in the field of H2O2 detection.

Boron nitride nanosheets from high shear exfoliation for high-performance thermal conductivity films

Boron nitride nanosheets (BNNSs) with intrinsically ultra-high thermal conductivity have attracted more and more attention and various methods have been proposed to prepare BNNSs-based thermally conductive adhesives. In this work, a liquid phase shear exfoliation process was proposed to prepare BNNSs. BNNSs can be directly prepared by exfoliating h-BN particles dispersed in isopropanol at a controlled rotational speed range of 16,000–22,000 rpm and the maximum yield of BNNSs is up to 32.1%. After the BNNSs were modified with polydopamine (M-BNNSs), the dispersion performance of BNNSs in water was significantly improved. BNNSs were incorporated into a cellulose nanofiber-based adhesive, and the highly thermally conductive films were prepared by a flow-delay process. A tested in-plane thermal conductivity of up to 23.23 W·m−1·K−1 and excellent mechanical properties are demonstrated and thermal infrared images provide a more visual representation of the high thermal conductivity and heat dissipation properties of the film, indicating the promising application of the film in the field of thermal conductivity.

High yield exfoliation of sub-micron hexagonal boron nitride using a solvent free method

Schematic of intercalation and exfoliation of submicron hBN.

Exploring the Role of Molecular Intercalants in Electrochemical Production of Graphene-Based 2D Materials

Since the discovery of graphene, two-dimensional (2D) materials have gained extensive attention due to the unique material properties from their reduced dimensionality. Numerous techniques have been thoroughly investigated for the fabrication of graphene-based 2D materials. Among them, electrochemical synthesis is one of the most promising approaches for the large-scale production of 2D materials with tunable properties [1-3]. Especially, intercalation of various ions/molecules electrochemically driven in between the graphene sheets plays the key role in the synthesis of single or few-layer 2D materials. However, the influence of molecular intercalants is still poorly understood.In this work, we studied different types of intercalants (i.e., ClO4 -, PF6 -, BF4-, HSO4 -) and explored the inserting process of molecular anions in-between the weekly-bonded layered materials driven by electrochemistry. Combining the cyclic voltammetry, XRD, Raman and density functional theory computation modeling, we can monitor the intercalation behavior of different anions and evaluate the contribution of intercalants in the high-yield production of graphene by electrochemical exfoliation. By optimizing the use of certain molecular intercalants, high exfoliation yield (>80 %) of graphene nanosheets with moderate oxidation damage and good electrochemical stability was achieved assisted by electrochemical exfoliation. Our study provides new insights into the electrochemical production of graphene-based 2D materials and suggests that the introduction of molecular intercalants is a promising tool for the controlled synthesis of layered 2D materials.Reference:(1) Xia, Z. Y.; Pezzini, S.; Treossi, E.; Giambastiani, G.; Corticelli, F.; Morandi, V.; Zanelli, A.; Bellani, V.; Palermo, V. The Exfoliation of Graphene in Liquids by Electrochemical, Chemical, and Sonication-Assisted Techniques: A Nanoscale Study. Advanced Functional Materials 2013, 23 (37), 4684-4693. DOI: 10.1002/adfm.201203686.(2) Xia, Z. Y.; Maccaferri, G.; Zanardi, C.; Christian, M.; Ortolani, L.; Morandi, V.; Bellani, V.; Kovtun, A.; Dell'Elce, S.; Candini, A.; et al. Dispersion Stability and Surface Morphology Study of Electrochemically Exfoliated Bilayer Graphene Oxide. Journal of Physical Chemistry C 2019, 123 (24), 15122-15130. DOI: 10.1021/acs.jpcc.9b03395.(3) Cao, J. Y.; He, P.; Mohammed, M. A.; Zhao, X.; Young, R. J.; Derby, B.; Kinloch, I. A.; Dryfe, R. A. W. Two-Step Electrochemical Intercalation and Oxidation of Graphite for the Mass Production of Graphene Oxide. Journal of the American Chemical Society 2017, 139 (48), 17446-17456. DOI: 10.1021/jacs.7b08515.

Optimization of Anodizing Condition for Mg-14mass%Li-3mass%Al Alloy

Mg-Li system alloys also has excellent cold-workability compared to commercial hcp-structured Mg alloys. However, Mg-Li alloys have poor corrosion resistance because not only that is Mg-based alloy but Li as a major alloying element is a less noble metal. For example, Mg-Li alloy sheet indicates high corrosion rate and exfoliation corrosion as a result of long-term corrosion test. The authors reported Mg-14 mass%Li-3 mass%Al alloy has the highest corrosion resistance in β-type solid solution alloy. Even though the optimized alloy composition, the alloy does not have enough corrosion resistance for practical use. In this study, anodized coating on Mg-Li alloy using phosphate solution was investigated. Anodizing of Mg-Li alloy facilitates the dissolution of substrate because of high Li concentration in this alloy. Therefore, the anodizing conditions were widely examined. As a result, the coating with approximately 15-20 μm of the surface layer was successfully formed. The surface layer was composed of MgAl2O4 and some phosphorus compounds. The thickness of anodized layer varied with the anodizing conditions. The dense surface layer was formed at a certain anodizing voltage and the corrosion resistance of anodized Mg-Li alloys was improved. However, the surface has some cracks and large flaky compounds. The formation mechanism of dense layer during anodizing were discussed.

Reaction mechanism of exfoliation degree and high temperature surface oxidation metamorphism of 2D Ti3C2Tx on thermal decomposition of various energetic materials

Achieving higher and faster energy release processes is a major research goal for energetic materials (EMs). Typically, EMs enhance their overall performance by incorporating catalysts. The novel two-dimensional layered MXenes, such as Ti3C2Tx, have shown significant potential as additives for ammonium perchlorate (AP). However, there is limited research on the impact of the exfoliation degree and high temperature oxidation of Ti3C2Tx MXene catalyst on the pyrolysis and combustion of different types of EMs. In this study, ultrathin Ti3C2Tx (U–Ti3C2Tx) MXene with a high exfoliation degree of approximately 20–80 nm was obtained through hydrofluoric acid (HF) etching, dimethyl sulfoxide (DMSO)-assisted layer expansion and ultrasonic peeling. The catalytic performance of MXenes on the thermal decomposition of three types of EMs (dihydroxylammonium 5, 5′-bistetrazole-1, 1′-diolate (TKX-50), cyclotetramethylene tetranitroamine (HMX), and AP) was evaluated. Results showed that 4 wt% U–Ti3C2Tx can reduce the decomposition peak of TKX-50 by 33.6 °C and decreases the high temperature decomposition (HTD) peak of AP by 45.5 °C, indicating superior catalytic performance compared to non-exfoliated Ti3C2Tx MXene. However, it had insignificant effect on HMX. Surface chemical analysis, electrochemical characterization, thermal decomposition of gaseous products analysis and material studio simulation all confirmed that high exfoliation U–Ti3C2Tx MXene exhibited better stability and electrical conductivity, facilitating the acceleration of the H+ transfer process and rapid gas release from EMs. Additionally, ignition tests demonstrated that high exfoliation U–Ti3C2Tx could effectively participate in the ignition process of EMs. The characterization and thermal analysis of Ti3C2Tx products after high temperature and oxidation treatment indicated that the catalytic activity is weakened due to high temperature crystal collapse and surface oxidation to TiOx metamorphism. This study provides new insights for the application of MXene catalysts in EMs.

The effect of controlled intercalation on the mechanical performances and dimensional accuracy of material extrusion additive manufactured poly(lactic acid)/organo-montmorillonite nanocomposites

Although the material extrusion-based 3D printing (MEX-3DP) has the ability to construct functional complex nanocomposites based on two-dimensional (2D) nanomaterials, however, the interplay of exfoliation degree of 2D materials and MEX-3DP parameters has not been elucidated, which seriously limits the further design and application of MEX-3DP 2D materials towards low-cost device fabrication. In this report, we use the well-studied organo-montmorillonite (MMT) as model materials and systematically studied the effect of various intercalation degrees on the mechanical and geometrical performance of MEX-3DP organo-MMT reinforced poly (lactic acid) nanocomposites. It was elucidated that, different from traditional injection moulding process, the best performance of MEX-3DP samples is obtained from completely exfoliated organo-MMT. The effect of the intercalation degrees is correlated with the melt flowability, thermal expansion and the resulting voids size that essential for MEX-3DP processes. The structure and rheology analysis demonstrate that the high exfoliation degree of 2D materials is essential to compensate the weak interfacial bonding or shrinkage-induced poor mechanical properties. The findings provide a detailed insight into the 2D materials exfoliation on the MEX-3DP quality, which is meaningful for engineers willing to design MEX-3DP functional 2D materials, for next generation disruptive technologies and applications.

Enhanced esterification performance by SO42−/ZrO2 anchored Nb2O5 nanotube

SO42-/ZrO2 anchored Nb2O5 nanotubes (SO42-/ZrO2@Nb2O5-NT) are prepared via the high temperature calcination, proton exchange, exfoliation, recombination, and impregnation processes. The structures and anchoring model can be confirmed by XRD, HRTEM, and FT-IR technologies. The acidic properties and specific surface area are characterized by NH3-TPD and N2 adsorption–desorption isotherms. The catalytic performances are evaluated via an esterification reaction of acetic acid and n-butanol. The results show that SO42-/ZrO2@Nb2O5-NT have stronger acid strength and higher acid content than that of Nb2O5-NT. The optimal esterification scheme is as follows: catalyst dosage is 11 wt.%, molar ratio of alcohol to acid is 2.7:1, reaction temperature is 118 ℃, and reaction time is 7 h. The esterification rate can be reached up to 92.31% over SO42-/ZrO2@Nb2O5-NT. We have rationalized esterification performance of these selected catalysts in light of structure–property relationships, which gives useful insight for the development and application of next generation esterification catalyst.

Straightforward Strategy Toward In Situ Water-Phase Exfoliation and Improved Interfacial Adhesion to Fabricate High-Performance Polypropylene/Graphene Nanocomposites.

Graphene is a potential candidate for achieving high-performance and multifunctional polypropylene (PP) composites. However, the complex manufacturing process and low dispersibility of graphene, as well as poor interfacial adhesion between graphene and polypropylene chains, stifle progress on large-scale production and applications of graphene/polypropylene composites. Here, we develop a strategy of maleic anhydride grafted polypropylene (MAPP) latex-assisted graphene exfoliation and melt blending to address the key challenges facing in industrial production. The surface property of the graphitic precursor is well-designed to achieve a high graphene exfoliation yield of ∼100% and induce abundant hydrogen bonding between the obtained mild-oxidized graphene (MOG) sheets and MAPP chains. Therefore, the MAPP-modified MOG can homogeneously disperse in the PP matrix and exhibits an excellent interfacial compatibility with the polymer. The addition of 5 wt % MOG results in simultaneous increase in the initial decomposition temperature, crystallization temperature, tensile strength, and Young's modulus by 43.2, 11.4 °C, 21.5, and 50.7%, respectively, and the electrical conductivity increases to 0.02 S·m-1. This work illustrates a practical solution to low-cost, eco-friendly, and feasible industrial production of graphene/PP composites through synchronous exfoliation and interfacial modification of graphene.

Exfoliating kaolin to ultrathin nanosheets with high aspect ratio and pore volume: A comparative study of three kaolin clays in China

A revised intercalation-assisted liquid exfoliation method is proposed to exfoliate three typical kaolin clays (Beihai, Longyan and Suzhou) in China. By combining intercalation, ball milling, ultrasound and freeze-drying technologies, the ultrathin kaolin nanosheets with large lamellar size (1–2 μm), low thickness (∼10 nm), high aspect ratio (∼130) and large pore volume (∼0.3 cm3/g) were obtained. A large number of kaolinite monolayer structures were observed in AFM images, indicating high exfoliation efficiency. The morphology, crystal structure and microstructures of kaolin samples during the intercalation and exfoliation processes are studied in detail by high resolution XRD, SEM, BET and AFM analysis. The mechanism for effective intercalation, exfoliation and stabilization of kaolin clays is clarified. The ultrathin kaolinite nanosheets slightly curved after exfoliation process were found to form some porous structures between the kaolin nanolayers, providing plenty of interlayer spacing for functional loading or interfacial binding. These ultrathin kaolin nanosheets might have the advantages to improve the adhesion ability, loading capacity, and mechanical properties of kaolin-based composite materials.

Scalable high yield exfoliation for monolayer nanosheets

Although two-dimensional (2D) materials have grown into an extended family that accommodates hundreds of members and have demonstrated promising advantages in many fields, their practical applications are still hindered by the lack of scalable high-yield production of monolayer products. Here, we show that scalable production of monolayer nanosheets can be achieved by a facile ball-milling exfoliation method with the assistance of viscous polyethyleneimine (PEI) liquid. As a demonstration, graphite is effectively exfoliated into graphene nanosheets, achieving a high monolayer percentage of 97.9% at a yield of 78.3%. The universality of this technique is also proven by successfully exfoliating other types of representative layered materials with different structures, such as carbon nitride, covalent organic framework, zeolitic imidazolate framework and hexagonal boron nitride. This scalable exfoliation technique for monolayer nanosheets could catalyze the synthesis and industrialization of 2D nanosheet materials.

High conversion continuous flow exfoliation of 2D MoS2.

We report a low-cost and highly efficient process for exfoliating of MoS2 using an energy efficient vortex fluidic device (VFD). This method is high in green chemistry metrics in avoiding the use of auxiliary substances, and the process is scalable, with a conversion of as received MoS2 into 2D sheets at ∼73%.

Molten-salt etching synthesis of delaminatable MXenes.

A LiF-involved molten-salt etching method is proposed for yielding delaminatable MXenes with comparable quality and supercapacitive performance to those made by solution etching. This approach combines the benefits of molten-salt etching in processability with high exfoliation efficiency of solution-based etching method.

Indium doping-assisted monolayer Ga2O3 exfoliation for performance-enhanced MOSFETs.

Monolayer (ML) Ga2O3 with outstanding properties is promising for advanced nanodevice applications; however, its high exfoliation energy makes obtaining it challenging. In this study, we propose a more efficient solution to obtain ML Ga2O3 by exfoliation from indium-doped bulk β-Ga2O3. The exfoliation efficiency with the assistance of In-doping and the doping influence on the stability and structural and electronic properties of ML Ga2O3 are systematically studied using first-principles calculations. The exfoliation energy of ML Ga2O3 is found to be reduced by 28% and is of the same order of magnitude as that of typical van der Waals (vdWs) 2D materials. Besides, excellent stability is preserved for ML Ga2O3 at extremely high In doping concentration by phonon spectrum and ab initio molecular dynamics inspections. The bandgap of ML Ga2O3 decreases from 4.88 to 4.25 eV with increased In concentration, and the modification of the VBM converts ML Ga2O3 to a direct bandgap semiconductor. With the suppression of ZA mode phonon scattering, the pristine and In-doped ML Ga2O3 exhibit high electron mobility, whereas the strong electron-phonon coupling (EPC) effect significantly decreases the hole mobility. Finally, the transfer characteristics of 5 nm MOSFETs based on the pristine and In-doped ML Ga2O3 with varied In concentrations are simulated based on the non-equilibrium Green's function (NEGF) formalism. The Ion for HP has a maximum of 3060 μA μm-1 at In doping concentration of 5% and is triple that of the pristine ML Ga2O3 for LP at In doping concentration of 20%. The FOMs of n-type MOSFETs based on the In-doped ML Ga2O3 and typical 2D materials are compared and shows huge potential for sub-5 nm applications. Our study applies a new strategy for obtaining ML Ga2O3 and can also improve the device performance at the same time.

Enhanced photoresponse of InxMo1-xS2 (X = 0.05 and 0.1) nanosheets for PEC type photodetector

Transition metal chalcogenides (TMDCs) have great potential in the field of solid state photodetectors and photoelectrochemical (PEC) type photodetector owing to high carrier mobility and suitable energy band gap. Two dimensional MoS2, most intensively investigated member of TMDCs, has shown excellent photoresponsivity in the visible range owing to excitonic transition and suitable electronic structure. Herein, we demonstrate the PEC photodetector based on InxMo1-xS2 nanosheets. High yield liquid phase exfoliation techniques have been employed for the synthesis of InxMo1-xS2 nanosheets. InxMo1-xS2 nanosheets have hexagonal lattice structure with highly crystalline behavior and X-ray diffraction confirms the doping of indium in 2H–MoS2. PEC type detectors show 582 μA/W and 107 μA/W photoresponsivity for In0.05Mo0.95S2 and In0.1Mo0.9S2 nanosheets by optimized concentration of indium. Present investigation advocates the significant development in the field of opto-electronics and photoelectrochemical cells for generation clean energy.

Effect of exfoliation degree on the performance of montmorillonite nanosheets

Montmorillonite (MMT) is easily exfoliated into two-dimensional(2D) nanosheets, which are widely used to prepare functional composites. However, there are few studies on the differences in the performance of MMT nanosheets (MMTNS) with different exfoliation degrees, which seriously limits the further breakthrough in the preparation of high-performance MMTNS based materials. In this work, some representative performance of MMTNS with different exfoliation degrees was investigated, and the performance was closely related with making functional composites. The exfoliation degrees of MMTNS were controlled by different ultrasonic exfoliation powers. The performance of MMTNS was studied by the measurements of atomic force microscopy (AFM), Zeta potential, turbidity, viscosity, scanning electron microscopy (SEM) and molecular dynamics simulation. The results show that MMTNS with high exfoliation degree had more negative electrical sites exposed and stronger repulsive potential energy between particles, which exhibited high surface negative electricity and excellent dispersion stability. Moreover, the MMTNS with high exfoliation degree had better gelling property. It can be seen that the “house-of-cards” structure in the structure after gelation of MMTNS with high exfoliation degree was more intensive. Also, with the increase of MMTNS exfoliation degree, its adsorption capacity for organic matter was better and its reaction with organic was more active. These findings might be helpful to select the suitable MMTNS for making functional composites by controlling its exfoliation degree.

Preparation of multi-function graphene materials through electrode-distance controlled electrochemical exfoliation

Preparation of graphene materials with different microstructures is of great significance for the specific applications in various areas. Here, a modified electrochemical exfoliation method with controlled electrode distance is proposed to prepare exfoliated graphene, graphene quantum dots, and graphene oxide (EGr, EGQD, and EGO). Compared with electrolysis at a fixed location, the modified electrode distance can effectively tune the insertion speed and direction, as well as the kinetic rates of exfoliation processes. Specifically, at a short electrode distance of 3 cm, it produced high-quality EGr with the size above 5 μm and thickness below 5 layers; when the electrode distance increased to 30 cm, EGQD with the size below 5 nm was produced. Further, the distance between 3 and 30 cm facilitates producing EGO with ca. 15% O content. In addition, it is found that the reaction temperature, optimized electrolyte, and controlled potential can further optimize the exfoliation processes, which can achieve a high exfoliation rate of ca. 2000, 140, and 1500 g h−1 for EGr, EGQD, and EGO preparation in an industrial-scale system, respectively. These modified graphene materials can be directly applied in various areas. For example, EGr can act as an effective component to increase one order of the dielectric property of PVDF; EGQD can effectively generate a PL spectrum at ca. 550 nm; EGO can facilely form a conductive and flexible film through self-assembly.

Viscous Solvent-Assisted Planetary Ball Milling for the Scalable Production of Large Ultrathin Two-Dimensional Materials.

Ball milling is a widely used method to produce graphene and other two-dimensional (2D) materials for both industry and research. Conventional ball milling generates strong impact forces, producing small and thick nanosheets that limit their applications. In this study, a viscous solvent-assisted planetary ball milling method has been developed to produce large thin 2D nanosheets. The viscous solvent simultaneously increases the exfoliation energy (Ee) and lowers the impact energy (Ei). Simulations show a giant ratio of η = Ee/Ei, for the viscous solvent, 2 orders of magnitude larger than that of water. The method provides both a high exfoliation yield of 74%, a high aspect ratio of the generated nanosheets of 571, and a high quality for a representative 2D material of boron nitride nanosheets (BNNSs). The large thin BNNSs can be assembled into high-performance functional films, such as separation membranes and thermally conductive flexible films with some performance parameters better than those 2D nanosheets produced by chemical exfoliation methods.

Low Temperature Heating of Silver‐Mediated Exfoliation of MoS2

AbstractThe need for high‐quality large‐scale monolayers of layered materials pushes the development of scalable gold‐mediated exfoliations. Gold proves to be a suitable adhesive for exfoliation of several 2D materials. However, the extension to other noble metals remains underwhelming as gold outperforms all previously studied metals by a large margin. This is attributed to compromised stability against oxidation and surface contamination of less noble metals, leading to nonideal interfaces for exfoliation. The closest competitor to gold is silver, where gold still leads by a factor 100 regarding exfoliated layer size. In this work, a silver‐mediated exfoliation process performing on par with gold is presented. The combination of freshly cleaved silver surfaces with a low‐temperature annealing is found to be crucial. The exfoliation yield shows a dependence with annealing temperature, leading to loss in exfoliation performance for higher temperature. Raman studies indicate inhomogeneous strain for the MoS2/Ag interface at these temperatures, which hints at the competing factors of thermal activation versus oxidation of silver. Finally, a transfer process is implemented to promote silver to a fully functional exfoliation substrate. Ultimately, heating up exfoliations tips the strict balance between interfacial interactions and surface contaminations toward robust high monolayer yield exfoliation as demonstrated for silver.

Simultaneous exfoliation and functionalization of large-sized boron nitride nanosheets for enhanced thermal conductivity of polymer composite film

Hexagonal boron nitride nanosheets (BNNS) are of considerable interest as building fillers to hybridize with other organic components to create thermal conductive frameworks. However, it is still a challenge to prepare functionalized BNNS with high aspect ratio and good dispersibility. Here, a unique method based on temperature pretreatment and glucose-assisted mechanical agitation is developed to achieve a high actual exfoliation yield (47%) of BNNS with high aspect ratio and few lattice defects. The resultant BNNS are covalently grafted with hydroxyl groups and well dispersed in water for storage. Density functional theory investigation and experimental work are carried out to illustrate the mechanism of exfoliation and functionalization of hexagonal boron nitride (h-BN). The high contact area of the adjoined high aspect ratio nanosheets easily causes less phonon scattering and more payload transfer. Accordingly, at the BNNS loading of 20 wt%, the BNNS/polyvinyl alcohol (PVA)/chitosan (CS) film presents a high thermal conductivity of 38.21 W m−1 K−1 in the in-plane direction and excellent tensile strength of 128.3 MPa. In addition, this new scalable exfoliation strategy can be motivating for fabricating other two-dimensional materials including graphene, tungsten disulfide (WS2), and molybdenum disulfide (MoS2).