Graphene quantum dots, graphene oxide, carbon quantum dots and graphite nanocrystals in coals

Abstract

Six coal samples of different ranks have been used to prepare single-layer graphene quantum dots (S-GQDs). After chemical oxidation and a series of centrifugation separation, every coal could be treated into two fractions, namely, CoalA and CoalB. According to the characterization results of TEM, AFM, XRD, Raman and FTIR, CoalA was revealed to be mainly composed of S-GQDs, which have an average height of about 0.5 nm and an average plane dimension of about 10 nm. The obtained S-GQDs showed excitation-dependent fluorescence and excellent electrochemiluminescence. CoalB was found to be some other carbon-based nanomaterials (CNMs), including agglomerated GQDs, graphene oxide, carbon quantum dots and agglomerated carbon nanocrystals. Generally, low-ranked coals might be more suitable for the preparation of S-GQDs. The production yield of S-GQDs from the six investigated coals decreased from 56.30% to 14.66% when the coal rank increased gradually. In contrast, high-ranked coals had high production yield of CoalB and might be more suitable for preparing other CNMs that were contained in CoalB, although those CNMs were difficult to separate from each other in our experiment.

Extraction and Characterization of Preformed Mixed Phase Graphene Sheets from Graphitized Sub-Bituminous Coal

“…The research on the abundant source of carbon-coal-reveals that it contains graphite-like clusters and poly-aromatic structures similar to sp 2 bonding properties of graphene [6,7,10,11]. It also reveals that carbon in coal has turbostratic structure that of graphite and amorphous carbon and this could be separated by simple method like chemical oxidation [7,11]. These nanocrystallites of coal are confined to a small area and hence very tedious to extract.…”

“…Physical approach such as mechanical exfoliation, lithography and other approaches such as hydrothermal treatment, electrochemical oxidation, proton ablation and chemical oxidation have been used for the synthesis of graphene [4,5]. However, most of the above stated precursors and production methods are too expensive and are optimized for the production of graphene with a homogenous sp 2 phase [6,7]. For applications, defect is introduced in graphene which enhances its property and this could be extrinsic, intrinsic or mixed phase of sp 2 -sp 3 carbon network.…”

An Electrochemiluminescent Biosensor Based on Interactions between a Graphene Quantum Dot−Sulfite Co‐reactant System and Hydrogen Peroxide

“…[17] Briefly, 0.5 g dried coal sample was refluxed with 100 mL 6 mol · L À1 HNO 3 at 130 8C for 12 h, and the resultant suspension was cooled to room temperature. The obtained suspension was centrifuged (2770 g) for 30 min to collect the supernatant.…”

Production of yellow-emitting carbon quantum dots from fullerene carbon soot

“…These methodologies can be mainly classified into two categories, namely, the "top-down" and "bottom-up" methods. The former includes laser ablation [12][13][14], plasma treatment [15], electrochemical oxidation [16][17][18][19], and acid-refluxing [20][21][22][23][24][25][26][27][28][29][30][31], while the latter is mainly focused on pyrolysis using simple heating and hydrothermal or microwave treatment [32][33][34][35]. Among these methods, the acid-refluxing of raw carbon materials offers a large-scale production of CQDs as it only needs simple instruments and can be easily scaled-up using standard industrial equipment.…”

“…Among these methods, the acid-refluxing of raw carbon materials offers a large-scale production of CQDs as it only needs simple instruments and can be easily scaled-up using standard industrial equipment. Theoretically, nearly all carbon-rich resources such as carbon nanotubes (CNTs) [20], carbon fibers [21], activated carbon [22], coals [23][24][25], petroleum coke [26][27][28], and carbon soot [29][30][31] can be used as the starting materials. For the large-scale production of CQDs, CNTs and carbon fibers can be ideal candidates if their prices can be further lowered in the future.…”