A carbon fiber in which hexagonal carbon layers in the shape of a bottomless
cup
are stacked. At least part of edges of the hexagonal carbon layers are exposed
on an outer surface and an inner surface of the carbon fiber. The exposed large
ring end has an armchair edge, a zigzag edge, and a chiral edge on the circumference.
This carbon fiber has a high degree of activity on the exposed edges of the hexagonal
carbon layers and the surfaces of the carbon fiber. Therefore, the carbon fiber
can be used as various types of filters and the like.