Chlorosulfuric acid-assisted production of functional 2D materials

Abstract

The use of two-dimensional materials in bulk functional applications requires the ability to fabricate defect-free 2D sheets with large aspect ratios. Despite huge research efforts, current bulk exfoliation methods require a compromise between the quality of the final flakes and their lateral size, restricting the effectiveness of the product. In this work, we describe an intercalation-assisted exfoliation route, which allows the production of high-quality graphene, hexagonal boron nitride, and molybdenum disulfide 2D sheets with average aspect ratios 30 times larger than that obtained via conventional liquid-phase exfoliation. The combination of chlorosulfuric acid intercalation with in situ pyrene sulfonate functionalisation produces a suspension of thin large-area flakes, which are stable in various polar solvents. The described method is simple and requires no special laboratory conditions. We demonstrate that these suspensions can be used for fabrication of laminates and coatings with electrical properties suitable for a number of real-life applications.

Hexagonal boron nitride exfoliation and dispersion

“…Several works that functionalized hBN with hydroxyl groups produced sheets between 2–3 nm thick and 1.5–3 μm in lateral size. 87–91,93,94 Protonating hBN with chlorosulfonic acid also produced large sheets of several micrometers in lateral size and few layers, 109–111 with the largest one reported with 2 nm thickness and 24.5 μm of length, obtained by stirring for 72 h in the CSA. 110 A few more works using intercalating agents and thermal expansion consistently produced 1–2.5 nm thick sheets with lateral lengths from 0.6 μm.…”

“…110 Finally, in 2021, Gudarzi and coworkers modified the exfoliation method in CSA by adding pyrene to non-covalently functionalize hBN with pyrene sulfonic acid and make the resulting dispersion more compatible in ambient conditions. 111 The resulting material consisted of large 6–7 layer sheets with a mean lateral size of 4 μm which were dispersible in various polar solvents. The dispersions were used to produce a two-layer hBN–graphene laminate through sequential vacuum filtration.…”

“…The dispersions were used to produce a two-layer hBN–graphene laminate through sequential vacuum filtration. 111…”

Machine learning enhanced electrical impedance tomography for 2D materials

“…For experimental evaluation, we chose a graphene laminate film, which was prepared using a liquid-phase exfoliated graphene suspension, details can be found elsewhere [62]. A 1 cm by 1 cm, 35 μm thick graphene sample was fabricated with 64 contacts; the high number was chosen to test the selection ability of the A-ESA.…”

Ultimate Charge Transport Regimes in Doping-Controlled Graphene Laminates: Phonon-Assisted Processes Revealed by the Linear Magnetoresistance

“…At the same time, charge transport across the boundaries of nanosheets remains the main limiting factor for the film conductivity, especially in laminates produced from layered van der Waals materials, 15−20 implemented exfoliation chemistry and postprocessing, relative twist angle between the crystals, residually trapped intercalants, and packing density. 19,21−23 Here, we study the graphene laminates produced by chlorosulfuric acid-assisted liquid phase exfoliation, 24 shown to deliver large aspect ratio (∼10 3 ) high-quality nanosheets of graphene. In particular, we perform magnetotransport characterization of multiple solution-processed laminates with the same structural properties but different charge carrier types and doping densities controlled by the postprocessing annealing.…”