COMMUNICATION © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 1603528 (1 of 5) Graphite-to-Graphene: Total Conversion Matat Buzaglo,* Ilan Pri Bar, Maxim Varenik, Liran Shunak, Svetlana Pevzner, and Oren Regev* M. Buzaglo, Dr. I. P. Bar, M. Varenik, L. Shunak, Prof. O. Regev Department of Chemical Engineering Ben-Gurion University of the Negev 84105 Beer-Sheva, Israel E-mail: matatbu@post.bgu.ac.il; oregev@bgu.ac.il Dr. S. Pevzner Department of Chemistry Nuclear Research Center Negev 84190, Israel Prof. O. Regev Ilse Katz Institute for Nanoscale Science and Technology Ben-Gurion University of the Negev 84105 Beer-Sheva, Israel DOI: 10.1002/adma.201603528 surface [17–19] and are therefore more likely to provide a stable protective covering. We examined diluents with an increasing conjugation degree and hence improved ability to form a planar conformation cov- ering the surface of the graphitic materials. We started from non-aromatic compounds (e.g., NaCl) and non-conjugated aromatics (e.g., polystyrene), and proceeded through semi- conjugated aromatics (e.g., dibenzo crown ether and diphe- nylbutadiyne) to fully conjugated aromatics (e.g., naphthalene, anthracene, and pyrene) (Figure 2). The more conjugated (and planar) the diluent, the stronger its adsorption to and protection of the graphitic surface from converting to amorphous carbon, as analyzed by thermogravimetric analysis (TGA) [20] (Figure 2b, and Section S3.1, Supporting Information). TGA parameters, such as T 1/2 , the temperature of the combustion step at which half of the total weight loss is reached (Section S3.1, Supporting Information), is correlated with both the graphene sheet dimen- sions (thickness and mean lateral dimension (MLD), Section S4, Supporting Information) and the defect density. [20] Additional TGA parameter is ΔT, the temperature range in which the gra- phene sheets burn (Sections S3.1 and S4, Supporting Informa- tion) is related to the polydispersity of the graphene products. [20] In addition to TGA, the graphene products were analyzed using both microscopy and spectroscopy techniques as pre- sented subsequently. The strong π–π interactions between the fully conjugated aromatic diluents and the graphitic surface resulted in the for- mation of large graphene sheets with narrow polydispersity (high T 1/2 and low ΔT values, respectively; Figure 2a), as well as in higher graphene content percentage in the product as opposed to milling with the other groups of diluents (Figure 2b, and Figure S2b, Supporting Information).The other diluents have weaker interactions with the graphitic surface and do not confer adequate protection during the milling process. The result was small-size graphene sheets, conversion to amor- phous carbon (lower graphene content percentage), and wider polydispersity (Figure 2). To establish a simple bulk characterization technique, we constructed a ΔT–T 1/2 thermal phase diagram (TPD) of a variety of commercial carbon-based powders of diverse particle sizes (as reflected in their T 1/2 values) and crystallinities, namely, activated carbon, graphene sheets, and GF (Section S1, Sup- porting Information). The TGA parameters of these powders were found to be located in distinct regions, or phases, in the TPD (Figure 3a): activated carbon in the 550–630 °C T 1/2 range, graphene sheets at 630–730 °C, and GF at 830–1000 °C. There- fore, this TPD may be used as a simple means for a morpho- logical classification of carbon-based bulk materials. In addition, we ball-milled pyrene (fully conjugated aromatic)-protected GF at various milling energies (rotational Graphene production has been intensively studied since its emergence in 2004, [1] to accelerate its entrance to the application field in a reasonable price and quality. The most suitable methods for graphene mass production are top-down mechanochem- ical approaches, such as sonication [2] and high-shear mixing. [3] However, these techniques are limited to liquid medium, which requires graphene stabilization, solvent removal, and results in very low yields (<3%). [2–4] Another top-down mechanochemical approach, ball milling, nowadays an established technique for producing nanomaterials, [5] is a good candidate for generating the shear and impact forces needed to produce graphene from graphite. This method has been used to produce graphene from graphite [6–11] in both wet (liquid media) and dry (solid media) milling. In these previous studies, the dry milling resulted in high content of amorphous carbon, [12] while the wet milling resulted in more crystalline products, but required extremely long milling procedures (milling time > 20 h). [8,13] Furthermore, in some cases, subsequent sonication was used to improve the relatively low yields. [9,10] In this study, graphite flakes (GF) were pre-mixed with solid diluents (Section S1, Supporting Information) to prevent re-aggregation of the obtained graphene sheets, [14–16] and to minimize the formation of amorphous carbon during the dry milling process. In the non-protected milling, there is a con- tinuous fragmentation leading to amorphous carbon formation (Figure 1, left panel), while in a diluent-protected milling, the diluent adsorbs part of the impact forces (low milling energies), and therefore enables the exfoliation into graphene sheets (due to shear forces), followed by their fragmentation at higher milling energies. Next, all the diluent is completely removed via filtration with suitable solvents, to obtain the graphene product (Figure S1 and Table S1, Supporting Information). As for the diluents’ chemistry, we focused on aromatic com- pounds, since they form π–π interactions with the graphitic www.advmat.de www.advancedsciencenews.com Adv. Mater. 2017, 29, 1603528