  Ultrasonic agitation is a proven method for breaking down layered materials
such as MoS2 into single or few layer nanoparticles. In this experiment, MoS2
powder is sonicated in isopropanol for an extended period of time in an attempt
to create particles of the smallest possible size. As expected, the process
yielded a significant quantity of nanoscale MoS2 in the form of finite layer
sheets with lateral dimensions as small as a few tens of nanometers. Although
no evidence was found to indicate a larger the longer sonication times resulted
in a significant increase in yield of single layer MoS2, the increased
sonication did result in the formation of several types of carbon allotropes in
addition to the sheets of MoS2. These carbon structures appear to originate
from the breakdown of the isopropanol and consist of finite layer graphite
platelets as well as a large number of multi-walled fullerenes, also known as
carbon onions. Both the finite layer graphite and MoS2 nanoplatelets were both
found to be heavily decorated with carbon onions. However, isolated clusters of
carbon onions could also be found. Our results show that liquid exfoliation of
MoS2 is not only useful for forming finite layer MoS2, but also creating carbon
onions at room temperature as well.
