Room-temperature synthesis of various allotropes of carbon nanostructures (graphene, graphene polyhedra, carbon nanotubes and nano-onions, n-diamond nanocrystals) with aid of ultrasonic shock using ethanol and potassium hydroxide

The exploration of the synthesis methods of sp(2) and sp(3) carbon nanomaterials under ambient conditions is very meaningful towards their industrial applications. The existing bottom-up synthesis methods usually need high temperature or high pressure conditions. We report a facile and environmentally-friendly approach enabling the synthesis of almost all types of known carbon nanostructures at room temperature and under atmosphere pressure. They include both sp(3)-structured n-diamond (not cubic diamond) nanocrystals and sp(2)-structured graphene, defective multiwalled carbon nanotubes, defective carbon nano-onions as well as graphene polyhedra. The reaction of ethanol and potassium hydroxide at ambient conditions yields n-diamond nanocrystals. To synthesize the sp(2) carbon nanomaterials, the assistance of the ultrasonic shock at the early stage of crystallization is necessary to ensure the formation of the carbon ring nucleation seeds. The synthetic yields of n-diamond nanocrystals, graphene polyhedra, defective carbon nano-onions, and graphene are estimated to be 0.37%, 0.30%, 0.04%, and 0.01% (carbon mass ratio), respectively, and all of them have good crystallinity. These results improve our understanding of the low-temperature crystal growth process of the carbon nanostructures. (C) 2021 Elsevier Ltd. All rights reserved.