This process is repeated in a continuous manner thus ensuring a complete extraction process. The solvent returning to the bottom flask vaporizes again, effectively concentrating the soluble material in the flask and producing a freshly distilled solvent portion for the next extraction cycle (14−16) ( Figure S1 also see the Supporting Information Video). Once the extractor cup fills up to the level of the siphon tube, the solvent automatically drains into the bottom flask, carrying the soluble material with it. When the solvent in the bottom flask is heated to boiling temperature, the solvent vapor condenses in the reflux condenser at the top of the setup, filling the cup of the Soxhlet extractor containing the sample. In the extraction procedure, the sample is placed into the Soxhlet extractor fitted with a reflux condenser and mounted on top of a flask containing the desired solvent. Another common application of the apparatus in synthetic chemistry is for separation of a poorly soluble product from insoluble byproducts─a particularly arduous task frequently encountered when working with polycyclic aromatic compounds. (13) Soxhlet apparatus is indispensable in those cases where nearly complete extraction of a soluble material from the insoluble matrix is desired, for example, when extracting natural products from dilute sources. ![]() As explained below, both requirements are satisfied by removing the polymer in Soxhlet apparatus─a continuous (or, rather, an automated batch) solid–liquid extraction setup well known in organic, medicinal, and environmental chemistry. To address those limitations, we sought a simple experimental method that would minimize handling of the sample by the operator, while also providing a freshly distilled solvent for dissolving the polymer away. Our experience supports the literature observations, suggesting that mechanical handling during polymer removal and solvent impurities are two key factors limiting the quality of transferred graphene. (1) This leads to an unfortunate scenario where repeated washing of the 2D material to achieve more complete removal of the polymer results in greater mechanical damage and contamination by the impurities present in the solvent. More so, impurities present in organic solvents (such as acetone, isopropyl alcohol, etc.) used during the transfer processes could lead to surface contamination with a resultant negative effect on carrier mobility in graphene. attributed some of the damage to incomplete removal of the sacrificial polymer (PMMA) from the graphene film due to high adhesion potential between the two substances. Subsequently, avoiding transfer-induced damage is extremely challenging. one atom), care needs to be taken during the transfer process to prevent crack and wrinkle formation. (9−11) Due to the negligible thickness of graphene (ca. Extension of this process to other 2D materials would not only provide samples with superior intrinsic properties but also enhance their suitability for advanced technological applications.ĭifferent transfer procedures have been developed, but perhaps the most reliable technique available to date uses organic polymers (i.e., PMMA, PC, PVA, etc.) as the support layer. The new procedure is virtually effortless from the experimental point of view, utilizes much less solvent compared to the conventional washing procedure, and allows for easy scale-up. The amount of strain and doping was found to be similar, but the D-band, which is indicative of the defects, was less pronounced in the samples prepared by Soxhlet-assisted transfer. Compared to the conventional protocol, graphene produced by the current approach has a lower residual polymer content, leading to a root mean square roughness of only 1.26 nm. Excellent structural and morphological qualities of the material thus produced were confirmed using optical microscopy, atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. Here, we report a simple, economical, and highly efficient approach for obtaining pristine graphene on a suitable substrate (e.g., SiO 2/Si) by utilizing Soxhlet extraction apparatus for delicate removal of the polymer with a freshly distilled ultrapure solvent (acetone) in a continuous fashion. ![]() This contamination is usually due to incomplete polymer removal and also due to impurities present in organic solvents. Surface contamination experienced during polymer-assisted transfer is detrimental for optical and electrical properties of 2D materials.
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