Room Temperature Formation of Carbon Onions via Ultrasonic Agitation of MoS2 in Isopropanol

TL;DR

This study demonstrates that ultrasonic agitation of MoS2 in isopropanol at room temperature produces nanoscale MoS2 and novel carbon onions, revealing a new method for synthesizing these carbon structures alongside layered MoS2.

Contribution

The paper introduces a novel room temperature ultrasonic method to produce carbon onions during MoS2 exfoliation in isopropanol, expanding the applications of liquid exfoliation techniques.

Findings

Ultrasonic agitation yields nanoscale MoS2 sheets.

Formation of carbon onions and other carbon allotropes during sonication.

Carbon onions decorate MoS2 nanosheets and can form isolated clusters.

Abstract

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.