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An Unexpected Transformation of Organic Solvents into 2D Fluorescent Quantum Dots During Ultrasonication Assisted Liquid Phase Exfoliation
摘要： Ultrasonication within organic solvents is widely used to exfoliate layered materials and produce two-dimensional (2D) nanostructures. Several 2D materials synthesized by such liquid phase exfoliation (LPE) approaches are reported to exhibit photoluminescence. In these approaches, it is presumed that while the 2D nanostructures are derived from the layered parent material undergoing delamination, the organic solvent serves as a dispersing medium. However, in this study, we show that the organic solvent also contributes towards formation of 2D nanostructures that are optically active. We show that that bare organic solvent, when exposed to ultrasonication, transforms into 2D photoluminescent carbon quantum dots (CQDs) that display blue, cyan, green, and yellow emissions depending upon the excitation wavelength. Although this finding is intuitive, it has remained unacknowledged in the design of experiments which require ultrasonication of layered materials in organic solvents. Our results suggest that optical properties of dispersions obtained by LPE embody a contribution not only from the 2D nanostructures derived from the layered material but also from the 2D CQDs that are formed as a natural result of the liquid medium being exposed to ultrasonication. We anticipate that this new physical insight would form an important addition to the guidelines for exfoliation and help in rightly inferring the optical properties of the 2D material dispersions produced by these methods.
关键词： 2D nanostructures,Carbon quantum dots,Organic solvents,Liquid phase exfoliation,Ultrasonication,Photoluminescence
更新于2025-09-11 14:15:04
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Dewetting of monolayer water and isopropanol between MoS2 nanosheets
摘要： Understanding dewetting of solvent molecules confined to layered material (LM) interfaces is crucial to the synthesis of two-dimensional materials by liquid-phase exfoliation. Here, we examine dewetting behavior of water and isopropanol/water (IPA/H2O) mixtures between molybdenum disulfide (MoS2) membranes using molecular dynamics (MD) simulations. We find that a monolayer of water spontaneously ruptures into nanodroplets surrounded by dry regions. The average speed of receding dry patches is close to the speed of sound in air. In contrast, monolayer mixtures of IPA/H2O between MoS2 membranes slowly transform into percolating networks of nanoislands and nanochannels in which water molecules diffuse inside and IPA molecules stay at the periphery of islands and channels. These contrasting behaviors may explain why IPA/H2O mixtures are much more effective than H2O alone in weakening interlayer coupling and exfoliating MoS2 into atomically thin sheets.
关键词： molecular dynamics simulations,liquid-phase exfoliation,isopropanol/water mixtures,two-dimensional materials,layered material interfaces,dewetting,solvent molecules,MoS2 membranes
更新于2025-09-10 09:29:36
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Exfoliation behavior of van der Waals strings: case study of Bi <sub/>2</sub> S <sub/>3</sub>
摘要： The family of crystals constituting covalently bound strings, held together by van der Waals forces, can be exfoliated into smaller entities, similar to crystals made of van der Waals sheets. Depending on the anisotropy of such crystals, and the spacing between their strings in each direction, van der Waals sheets or ribbons can be obtained after the exfoliation process. In this work, we demonstrate that ultra-thin nanoribbons of bismuth sulfide (Bi2S3) can be synthesized via a high power sonication process. The thickness and width of these ribbons are governed by the van der Waals spacings around the strings within the parent crystal. The lengths of the nanoribbons are initially limited by the dimensions of the starting bulk particles. Interestingly, these nanoribbons change stoichiometry, composition and are elongated when the duration of agitation increases, due to Ostwald ripening. An application of the exfoliated van der Waals strings is presented for optical biosensing using photoluminescence of Bi2S3 nanoribbons, reaching detection limits of less than 10 nM L-1 in response to bovine serum albumin. The concept of exfoliating van der Waals strings could be extended to a large class of crystals for creating bodies ranging from sheets to strings, with optoelectronic properties different from that of their bulk counterparts.
关键词： bio-sensing,photo luminescence,van der Waals strings,bismuth sulfide,liquid phase exfoliation,Bi2S3,Ostwald ripening
更新于2025-09-10 09:29:36
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High-Yield and Damage-free Exfoliation of Layered Graphdiyne in Aqueous Phase
摘要： The two-dimensional carbon material graphdiyne (GDY) holds great promise as a semiconductor and porous material, however, exfoliation of bulk GDY into single- or few-layered GDY in the aqueous phase remains a challenge. We report an efficient method for the damage-free exfoliation of bulk GDY into single- or few-layered GDY with high yield in an aqueous solution of inorganic salts (e.g., Li2SiF6). This was confirmed by spherical-aberration-corrected scanning transmission electron microscopy, scanning/transmission electron microscopy, atomic force microscopy, Fourier transform infrared/Raman spectroscopy, X-ray photoelectron spectroscopy. The method gives high exfoliation efficiency (75 wt %) without creating additional structural defects or oxides in the exfoliated GDY. Theoretical calculations suggest that non-covalent adsorption of the anion, diffusion of the cation, and subsequent repulsive forces between adjacent flakes are the main driving force for the efficient exfoliation.
关键词： non-covalent adsorption,carbon materials,graphdiyne,surface chemistry,liquid-phase exfoliation
更新于2025-09-09 09:28:46
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Direct Liquid Phase Exfoliation of Graphite to Produce Few-Layer Graphene by Microfluidization
摘要： Graphene has attracted a great number of attentions due to the excellent physical and chemical properties. For the convenience of investigations and applications, it is crucial to produce the grapheme with high-quality and high-yield by an easy-obtained method. In this research, a promising method is demonstrated to produce a high-concentration few-layer graphene (FLG) dispersion by direct micro?uidization in water/surfactant systems. The effects of surfactant selection, chamber pressure and micro?uidization cycles on the graphitic material exfoliation ef?ciency are systematically studied. The FLG concentration and the quality of the as-prepared FLG were determined by a series of characterizations. The graphene dispersions, with an average lateral size of 0.6 (cid:2)m and a few-layer structure, were stabilized by surfactants at a high concentration of up to 1.7 mg/mL and = 0.07–0.56, C/O ～ 19(cid:3)36) within a processing time of a few hours. This method should facilitate the mass production of high-quality graphene by liquid-phase exfoliation and promote the industrial application of graphene.
关键词： High Concentration,Few-Layer Graphene,Micro?uidization,Liquid Phase Exfoliation,Aqueous Graphene Dispersion
更新于2025-09-09 09:28:46
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Atomically Thin 2D‐Arsenene by Liquid‐Phased Exfoliation: Toward Selective Vapor Sensing
摘要： Phosphorene and antimonene, single- or few-layered (FL) semiconductor materials, have recently attracted enormous attention due to their unique properties, provided by their extreme thinness. Here, a liquid-phase exfoliation (LPE) procedure to prepare FL arsenene, another member of pnictogens, assisted by sonication and without any additional surfactant is reported. The exfoliation process is performed in various solvents. Among those, N-methylpyrrolidone is found to provide the highest concentration of stable arsenene sheets. Spectroscopic and microscopic analyses confirm the formation of high-quality few-layer arsenene nanosheets with large lateral dimensions. An application of this material for construction of vapor sensor based on electrochemical impedance spectroscopy is demonstrated. The device detects selectively methanol or acetone vapors depending on the selected resonance frequency. The results are highly reproducible, and the vapor sensor has long-term stability.
关键词： centrifugation,arsenic,2D arsenene,vapor sensors,liquid-phase exfoliation
更新于2025-09-04 15:30:14