Synthesis of Super-Long Carbon Nanotubes from Cellulosic Biomass under Microwave Radiation.

Joy Esohe Omoriyekomwan,Jian Zhang,Jianglong Yu,Arash Tahmasebi

doi:10.3390/nano12050737

Abstract

This study reports a novel method for synthesizing super-long carbon nanotubes (SL-CNTs) from cellulose via a microwave treatment process without an external catalyst. CNTs with a length of 0.7–2 mm were obtained via microwave treatment of cellulose biochar temperatures of 1200–1400 °C. Scanning electron microscope (SEM), together with high-resolution transmission electron microscope (HRTEM) results, were used to investigate the changes in the length and morphology of CNTs with respect to treatment temperature. The morphology of CNTs changed from twisted, curved, and threadlike to straight structures. The average length of CNTs after microwave pyrolysis at 600 °C was approximately 600–1800 nm, which after microwave treatment at 1300 °C and 1400 °C increased to about 1–2 mm. X-ray diffractometer (XRD) results confirmed the crystalline structure of CNTs with two prominent peaks at 2θ = 26.3° and 2θ = 43.2° correlating with the graphite (002) and (100) reflections. The ID/IG ratio obtained from Raman spectra of the CNTs decreased to the lowest value of 0.84 after microwave treatment at 1400 °C, implying a high degree of carbon order. The presence of Fe and trace amounts of other elements were confirmed by the energy-dispersive X-ray spectrometer (EDS) and were postulated to have catalyzed the growth of CNTs. The mechanism of the SL-CNTs growth under microwave treatment was proposed and discussed.

Highlights

Accepted: 21 January 2022After their discovery in 1991 [1], carbon nanotubes (CNTs), one of the many allotropic forms of carbon, have been extensively studied
These results suggested that the presence of inherent metallic species in biomass may have catalyzed the growth of the CNTs under high-temperature microwave treatment conditions [24]
Super-long carbon nanotubes (SL-CNTs) with lengths of up to 2 mm were successfully synthesized from cellulose biomass via microwave treatment without any catalyst or external carbon source

Summary

Introduction

Accepted: 21 January 2022After their discovery in 1991 [1], carbon nanotubes (CNTs), one of the many allotropic forms of carbon, have been extensively studied. The use of CNTs in various electrical, lightweight, and high-strength applications is advantageous due to their unique properties, such as high tensile strength and high modulus, as high as 150 GPa and a 1 TPa, respectively [3,4,5] Despite these unique properties, carbon nanotubes still have significant drawbacks, such as small dimensions and high cost, and non-sustainable synthesis methods that hinder their full potential [2]. Carbon nanotubes have been successfully synthesized using various methods, such as laser ablation [6], chemical vapor deposition (CVD) [2,7,8,9], arc-discharge [10], catalytic chemical vapor deposition (CCVD), and plasma-enhanced chemical vapor deposition (PECVD) [3,11,12] These methods usually necessitate using metallic catalysts (e.g., Ni, Mo, Fe, Co, etc.) [13,14,15], substrate [16], and hydrocarbons as carbon sources (e.g., ethane, methane, acetylene, xylene, or a mixture of these) [17]. Catalyst deactivation during the synthesis of CNTs limits their growth and subsequently hinders their practical

Methods

Results

Conclusion