JACS: controlling the size separation of graphene oxide (go) nano layer by directional freezing technology

Graphene and its derivatives have attracted much attention due to their many wonderful applications Due to its unique two-dimensional (2D) arrangement of carbon atoms, it has excellent electronic, electrical, optical and mechanical properties The function and properties of graphene oxide (go) based materials are determined by the transverse size and size distribution of go nano sheets For example, go with a smaller lateral size has enhanced antimicrobial activity For the preparation of conductive fillers and films, go with large transverse size is very necessary However, go nanoflakes usually have a wide size distribution due to the random chemical stripping process, which is the most widely used method for mass production of go The effect of freezing rate on the size distribution (source: Journal of the American Chemical Society) was studied by scientists from the Institute of chemistry, Chinese Academy of Sciences, Tsinghua University and Beijing University of Aeronautics and Astronautics The research results of the size separation of go nano tablets by directional freezing of go aqueous dispersion with controlled rate were reported for the first time They found that when 0.10 mg / ml of go dispersion was used to adjust the freezing rate from 0.2 to 45.0 μ MS-1, a narrow size distribution of go nano tablet could be obtained In this range, the size of go nanoflakes increases from several nanometers to tens of microns with the decrease of freezing rate The size separation mechanism of go nanoflakes is based on the following facts: 1) the adsorption of go nanoflakes on the ice crystal surface is due to the unique arrangement of hydroxyl groups on the base surface of go nanoflakes, which is conducive to the preferential formation of hydrogen bonds between go nanoflakes and ice crystals 2) The delamination of go nanoflakes occurs at the front of ice growth because of the Brownian motion of the growing ice crystals and go nanoflakes and the forces generated by their interactions The researchers further proved that the narrow size distribution of go nano chips can be directly used as ink for the required rheological behavior, and the three-dimensional (3D) porous structure with adjustable pore diameter can be printed out by these inks Summary of the 3D printed modulus function and structural photos (source: Journal of the American Chemical Society) For the first time, researchers from China reported that the size separation of the go nano tablets was controlled by controlling the directional frozen go aqueous dispersion When the growth rate of ice crystal front is appropriate, go nano layer will be stratified in the ice crystal growth front Due to the formation of hydrogen bond between the go nano sheet and ice crystal, the narrow size distribution of go nano sheet is adsorbed on the ice crystal surface Because the rheological behavior of go dispersions can be adjusted by changing the lateral size of go nano chips in the dispersions, the narrow size distribution of go dispersions after size separation can be used as the ink paper link for printing the 3D structure of adjustable aperture: http://pubs.acs.org/doi/10.1021/jacs.7b05490