Green production of pristine graphene using fluid dynamic force in supercritical CO2

•A green preparation of graphene was developed by shear mixer and supercritical CO2.•The fluid dynamic force was main reason of exfoliation of graphite into graphene.•66% of the defect-free exfoliated graphene sheets were less than trilayer.•Flexible transparent and conductive graphene film on the PET was fabricated.

A green and scalable method was presented for the production of pristine graphene by the exfoliation of graphite using a shear mixer in supercritical CO2. The resulting graphene flakes were characterized by transmission electron microscopy, Raman spectroscopy and atomic force microscopy. The synergistic effects of the fluid dynamic force coupled with the supercritical CO2 actualized the exfoliation of graphite into graphene. The total exfoliation yield reached 63.2%. Up to 79% of the produced graphene was less than five layers, of which monolayer, bilayer and trilayer represented 27%, 25% and 14%, respectively. The average lateral size of the resulting graphene was 5 μm. The Raman spectrum reveals that the graphene was defect free. The prepared graphene was utilized to fabricate flexible, transparent and conductive films on a PET substrate through a vacuum filtration and dry transfer method. The transparency of the film reached 83%, the resistance was 0.83 kΩ/sq, and there was minimal variation, even after the film was bent more than 500 cycles.

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