Flash Reduction of Graphic Oxide to Graphene (28166)
INVENTOR: Jiaxing Huang, Laura Cote, Rodolfo Cruz Silva
INVENTION: A flash conversion process where photolytic exposure instantaneously converts graphene oxide (GO) to graphene. The process enables rapid formation of fused graphene/polymer composites from a random mixture of GO and polymer particles. Using a photo-mask, conducting graphene/polymer patterns can be readily produced on flexible substrates.
ADVANTAGES: A low temperature, chemical-free method for generating graphene from GO enabling the smooth formation of graphene/polymer composites.
SUMMARY: Graphite oxide (GO) is a promising precursor for the bulk production of graphene, due to its relatively low cost of synthesis and solvent processability, that make it attractive for graphene composites production. However, reduction of GO to graphene generally employs chemical agents or high temperature treatment, that bring significant processing challenges for making graphene-polymer composites from GO. Therefore, a low temperature, chemical-free method for generating graphene from GO is highly desirable. This invention provides a flash conversion process where GO can be photo-thermally reduced to graphene upon exposure to a pulsed Xenon flash at ambient conditions. The technique is rapid, versatile, scaleable and can be done with a simple flash unit.
GO was prepared using a modified Hummer’s method from graphite powders, isolated as a filter cake film, dried and ground into powder. Upon Xenon lamp exposure under ambient conditions, graphene was generated as indicated by color change (Figure 1). Exposure conditions were adjusted for optimal product properties. Analysis reveals complete GO conversion to fully exfoliated graphene comparable to material produced by chemical reduction. GO single layers and polystyrene colloids readily form aqueous suspensions and yield a random blend of polystyrene beads with GO films upon filtration. Flash irradiation converts GO to graphene fusing the polystyrene particles and GO in a continuous, conducting film (Figure 2). The conductivity of the flash produced graphene or its composite product can be easily tuned by the optical exposure dose employed.
Employing a photo-mask, conducting graphene domains are readily patterned on the insulating GO film. Flash patterning allows exposed areas to be removed directly by additional flashing utilizing the enhanced photothermal effect of graphene. Therefore, both patterning and etching can be performed in one system by increasing the dose of flash irradiation. Figure 3 displays interdigitated graphene electrodes fabricated on a flexible, 1.5 inch Nylon “wafer” upon flashing through a mask. A GO/polystyrene blend precursor was used to improve the resolution and mechanical durability of the patterned films. The exposed areas became conducting and more hydrophobic, while the protected areas remained insulating and hydrophilic, affording an all-organic, flexible sensor.
STATUS: A patent application has been filed and Northwestern seeks to develop the invention.
Figure 1. Graphite Oxide (GO) (a) converted to graphene (b) upon exposure to a photographic camera flash. The grids in the background are 1 mm × 1 mm. Flash conversion of GO to graphene is evident by the change in color (a, b) and was further studied by water contact angle (insets in a, b).
Figure 2. Flash conversion random GO/polymer particle blends. The SEM image (a) of blend film of GO sheets and polystyrene beads. (b) After flashing, polystyrene was fused with graphene to form homogeneous.composite. The inset is a low magnification SEM image of film before (left) and after (right) flash conversion. Scale bars in (a, b) and (inset) represent 3 and 500 μm respectively.
Figure 3. (a) Arrays of graphene/polystyrene interdigitated electrodes (IDE) fabricated on a 1.5 inch diameter GO/polystyrene thin film deposited on Nylon filter paper. Inset view of one IDE set. Contact pads 5 mm x 5 mm and electrode fingers 100 µm thick. An ammonia sensor fabricated using graphene IDEs with polyaniline as the selective layer. (b) Response from the metal-free, flexible sensor on exposure to 100 ppm of ammonia vapor.
