Abstract
Demand for rapid and massive-scale exfoliation of bulky graphite remains high in graphene commercialization and property manipulation. We report a procedure utilizing “preformed acidic oxidizing medium (PAOM)” as a modified version of the Hummers’ method for fast and reliable synthesis of graphene oxide. Pre-mixing of KMnO4 and concentrated H2SO4 prior to the addition of graphite flakes enables the formation of effectively and efficiently oxidized graphene oxide (EEGO) featured by its high yields and suspension homogeneity. PAOM expedites diffusion of the Mn-oxidants into the graphite galleries, resulting in the rapid graphite oxidation, capable of oxidizing bulky graphite flakes (~0.8 mm in diameter) that can not be realized by the Hummers’ method. In the scale-up tests, ten-time amount of graphite can be completely exfoliated by PAOM without need of extended reaction time. The remarkable suspension homogeneity of EEGO can be exploited to deposit ultra-flat coating for wafer-scale nanopatterning. We successfully fabricated GO optical gratings with well-defined periodicity (300 nm) and uniform thickness (variation <7 nm). The combination of the facile and potent PAOM approach with the wafer-scale patterning technique may realize the goal for massive throughput graphene nanoelectronics.
Highlights
That the resultant GO which we define as the effectively and efficiently oxidized graphene oxide (EEGO) was featured by a bright yellow color reflecting its high degrees of oxidation[6]
We demonstrate that the ability of EEGO to remain highly dispersive can lead to controllable fabrication of wafer-size superfine optical gratings
The EEGO product prepared by preformed acidic oxidizing medium (PAOM) displays the brightest yellow color among all the others, suggesting that graphite is subjected to substantial oxidation, and its production is proven to be reproducible
Summary
That the resultant GO which we define as the effectively and efficiently oxidized graphene oxide (EEGO) was featured by a bright yellow color (due to the loss of electronic conjugation) reflecting its high degrees of oxidation[6]. The conventional Hummers’ method requires several hours and even days depending on the graphite flake size[10,11,12]. Because such effective oxidation weakened the van der Waals forces and facilitated the exfoliation process, EEGO was well dispersed in water permitting it to be uniformly casted onto substrates in the form of thin films. All the GO samples were washed and filtrated with HCl aqueous solution (37% HCl:DI water = 10:100 mL) several times, followed by dialysis in water to reach neutral pH conditions under aqueous environment These GO samples were subjected to a 6000 rpm centrifuge for 10 min. The precipitates were only analyzed by XRD and the supernatants were collected for various analyses (see below)
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