Graphene oxide is highly desired for printing electronics, catalysis, energy storage, separation membranes, biomedicine, and composites. However, the present synthesis methods depend on the reactions of graphite with mixed strong oxidants, which suffer from explosion risk, serious environmental pollution, and long-reaction time up to hundreds of hours. Here, we report a scalable, safe and green method to synthesize graphene oxide with a high yield based on water electrolytic oxidation of graphite. The graphite lattice is fully oxidized within a few seconds in our electrochemical oxidation reaction, and the graphene oxide obtained is similar to those achieved by the present methods. We also discuss the synthesis mechanism and demonstrate continuous and controlled synthesis of graphene oxide and its use for transparent conductive films, strong papers, and ultra-light elastic aerogels.
Ultrathin, lightweight, high‐strength, and thermally conductive electromagnetic interference (EMI) shielding materials with high shielding effectiveness (SE) are highly desired for next‐generation portable and wearable electronics. Pristine graphene (PG) has a great potential to meet all the above requirements, but the poor processability of PG nanosheets hinders its applications. Here, efficient synthesis of highly aligned laminated PG films and nacre‐like PG/polymer composites with a superhigh PG loading up to 90 wt% by a scanning centrifugal casting method is reported. Due to the PG‐nanosheets‐alignment‐induced high electrical conductivity and multiple internal reflections, such films show superhigh EMI SE comparable to the reported best synthetic material, MXene films, at an ultralow thickness. An EMI SE of 93 dB is obtained for the PG film at a thickness of ≈100 µm, and 63 dB is achieved for the PG/polyimide composite film at a thickness of ≈60 µm. Furthermore, such PG‐nanosheets‐based films show much higher mechanical strength (up to 145 MPa) and thermal conductivity (up to 190 W m−1 K−1) than those of their MXene counterparts. These excellent comprehensive properties, along with ease of mass production, pave the way for practical applications of PG nanosheets in EMI shielding.
It is crucial to align two-dimensional nanosheets to form a highly compact layered structure for many applications, such as electronics, optoelectronics, thermal management, energy storage, separation membranes, and composites. Here we show that continuous centrifugal casting is a universal, scalable and efficient method to produce highly aligned and compact two-dimensional nanosheets films with record performances. The synthesis mechanism, structure control and property dependence of alignment and compaction of the films are discussed. Significantly, 10-μm-thick graphene oxide films can be synthesized within 1 min, and scalable synthesis of meter-scale films is demonstrated. The reduced graphene oxide films show super-high strength (~660 MPa) and conductivity (~650 S cm−1). The reduced graphene oxide/carbon nanotube hybrid-film-based all-solid-state flexible supercapacitors exhibit ultrahigh volumetric capacitance (407 F cm−3) and energy density (~10 mWh cm−3) comparable to that of thin-film lithium batteries. We also demonstrate the production of highly anisotropic graphene nanocomposites as well as aligned, compact films and vertical heterostructures of various nanosheets.
Graphite film has many remarkable properties and intriguing applications from energy storage, electromagnetic interference (EMI) shielding, and thermal management to ultraviolet lithography. However, the existing synthesis methods require an extremely high processing temperature of ∼3000 °C and/or long processing time of typically hours. Here, we report an ultrafast synthesis of tens of nanometer-thick high-quality graphite films within a few seconds by quenching a hot Ni foil in ethanol. The vertical growth rate can reach over 64 nm s −1 , which is more than 2 orders of magnitude higher than those of the existing methods. Moreover, the films show excellent electrical conductivity (∼2.6 × 10 5 S/m) and mechanical strength (∼110 MPa) comparable to or even better than those synthesized by chemical vapor deposition. As an example, we demonstrate the potential of these graphite films for effective EMI shielding, which show a record absolute shielding effectiveness of 481,000 dB cm 2 g −1 , outperforming all the reported synthetic materials.
The
strong quantum confinement effect as well as abundant edges
and oxygen functional groups enable nano-graphene oxide (NGO) a variety
of intriguing applications such as catalysis, bioimaging, drug delivery
and photovoltaic devices. However, the development of NGO is severely
hindered because of the difficulty in controlled mass production.
Here, we report the efficient synthesis of NGO with a high yield of
∼40 wt % by water electrolytic oxidation of glassy carbon (GC).
The NGO shows a high oxidation degree (C/O atomic ratio, ∼1.4)
and excellent dispersion stability. Moreover, its size can be easily
tuned by the graphitization degree of GC, which enables the controlled
synthesis of NGO with average size of 4, 8, and 13 nm and different
oxygen functional groups. As metal-free catalysts, the 13 nm sized
NGO is found to be beneficial for the oxidative coupling reaction
of benzylamine, while the 4 nm sized NGO shows a conversion rate of
88 times higher than 13 nm sized NGO for the oxidation reaction of
benzene. In addition, the water electrolytic oxidation mechanism of
graphitic materials is systematically studied. It is found that sulfuric
acid has a protective effect on the graphite electrode during the
water electrolytic oxidation process, and 50 wt % sulfuric acid solution
well balances the protection and oxidation processes, leading to the
highest oxidation efficiency and production rate.
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