High Yield Synthesis of Aspect Ratio Controlled Graphenic Materials from Anthracite Coal in Supercritical Fluids

Abstract

This paper rationalizes the green and scalable synthesis of graphenic materials of different aspect ratios using anthracite coal as a single source material under different supercritical environments. Single layer, monodisperse graphene oxide quantum dots (GQDs) are obtained at high yield (55 wt %) from anthracite coal in supercritical water. The obtained GQDs are ∼3 nm in lateral size and display a high fluorescence quantum yield of 28%. They show high cell viability and are readily used for imaging cancer cells. In an analogous experiment, high aspect ratio graphenic materials with ribbon-like morphology (GRs) are synthesized from the same source material in supercritical ethanol at a yield of 6.4 wt %. A thin film of GRs with 68% transparency shows a surface resistance of 9.3 kΩ/sq. This is apparently the demonstration of anthracite coal as a source for electrically conductive graphenic materials.

Supercritical Fluid‐Facilitated Exfoliation and Processing of 2D Materials

“…[175] The etching rate was observed to increase with water density above 0.1 g mL −1 . [178] ScH 2 O cutting down of large anthracite flakes started as early as 10 min. This anisotropic etching in combination with exfoliation in scH 2 O allows the scalable production of zigzag-edge-rich graphene nanosheets for electrochemical devices.…”

“…[144,241] Anthracite coal was demonstrated by Poulin and co-workers as a source of nanosheets using an scH 2 O process (374 °C, 22.1 MPa) that was mildly oxidizing. [144,241] Anthracite coal was demonstrated by Poulin and co-workers as a source of nanosheets using an scH 2 O process (374 °C, 22.1 MPa) that was mildly oxidizing.…”

“…[144,241] Anthracite coal was demonstrated by Poulin and co-workers as a source of nanosheets using an scH 2 O process (374 °C, 22.1 MPa) that was mildly oxidizing. [241] Sathish and co-workers also reported an scDMF process (450 °C) for creating 5 nm diameter BN QDs from h-BN. [241] These GO QDs were evaluated as labels in HeLa cells and found not to exhibit toxicity at up to 40 µg mL −1 and to provide a distinct blue fluorescence after 24-h incubation with these cells.…”

Facile and Efficient Fabrication of Bandgap Tunable Carbon Quantum Dots Derived From Anthracite and Their Photoluminescence Properties

“…Additionally, the cheapest price and substantial deposits of coal, in contrast to crystalline carbon such as graphene, carbon tubes and fullerenes, have attracted tremendous interest and efforts in developing preparation methods of CQDs from coal. Up to now, CQDs have been successfully prepared from coal by different methods (Ye et al, 2013;Dong et al, 2014;Hu et al, 2015Hu et al, , 2016Sasikala et al, 2016;Li et al, 2017;Liu X. et al, 2018;Saikia et al, 2019). Ye et al (2013) employed concentrated sulfuric acid and nitric acid to exfoliate CQDs from coal at 100 • or 120 • C for 24 h. Similarly, CQDs were obtained through refluxing coal in 5 M HNO 3 at 120 • C for 12 h (Dong et al, 2014).…”

“…However, there are some drawbacks to the above methods, such as the longer reaction time and the inherent difficulty in separation of CQDs from the mixture which contains a large amount of inorganic salts that formed during the neutralization phase via the addition of bases. Hence, in order to optimizing the preparation conditions of CQD from coal, selective depolymerization of coal in an oxidizing supercritical fluid was proposed by Sasikala et al (2016). They isolated CQDs in supercritical water under the conditions of 400 • C and 25 MPa within 2 h. Although this way could observably shorten the time to prepare CQDs, the unattainable reaction conditions hampered the large scale preparation of CQDs.…”