Mechanistic study on direct synthesis of carbon nanotubes from cellulose by means of microwave pyrolysis

Abstract

Abstract This paper investigates the impact of biomass components (i.e. cellulose and lignin) on direct production of carbon nanotubes (CNTs) from renewable biomass by means of microwave pyrolysis at low temperature. Palm Kernel Shell (PKS) was treated using two methods to isolate its bio-components, i.e. cellulose and lignin. The treated PKS samples were then pyrolyzed under microwave at 600 °C. Scanning electron microscopy (SEM) analysis revealed the formation of a large number of CNTs on the surface of cellulose bio-chars, while no CNTs were formed from lignin under the same pyrolysis conditions. It was inferred that cellulose was the component responsible for the formation of CNTs during microwave pyrolysis of biomass. High-resolution transmission electron microscope (HRTEM) analysis revealed that CNTs formed under such conditions had a multiwall structure. Raman spectroscopy analysis showed that the carbon order of CNTs increased when cellulose was used instead of the raw biomass for the synthesis of CNTs. Further analysis of the volatiles showed that unlike lignin, the volatile matter derived from cellulose were rich in monosaccharides such as D-Glucopyranose and glucopyranose which were postulated to have acted as an effective carbon source for the formation of CNTs. Self-extrusion of volatiles rich in monosaccharides and hydrocarbons during pyrolysis of cellulose, followed by the condensation and re-solidification of volatiles on the softened cellulose particles at elevated temperatures was proposed as the mechanism of formation of CNTs. The findings of this study may pave the way for the development of an effective, sustainable, and low-cost method for large scale production of CNTs from renewable biomass.