Continuous Synthesis of Double-Walled Carbon Nanotubes with Water-Assisted Floating Catalyst Chemical Vapor Deposition.

Liyu Dong,Branden E Leonhardt,Richard Liang,Jin Gyu Park,Songlin Zhang

doi:10.3390/nano10020365

Abstract

Double-walled carbon nanotubes (DWCNTs) were synthesized and continuously collected using a water-assisted floating catalyst chemical vapor deposition (FCCVD) method. Differing from the conventional water-assisted synthesis in which water vapor is one part of the carrier gas mixture, we included de-ionized water in the catalyst system, which achieved a more uniform and controlled distribution for efficient DWCNT production. Using a water-assisted FCCVD process with optimized conditions, a transition from multi- to double-walled CNTs was observed with a decrease in diameters from 19–23 nm to 10–15 nm in tandem with an elevated Raman IG/ID ratio up to 10.23, and corroborated from the decomposition peak shifts in thermogravimetric data. To characterize the mechanical and electrical improvements, the FCCVD-CNT/bismaleimide (BMI) composites with different water concentrations were manufactured, revealing high electrical conductivity of 1720 S/cm along the bundle alignment (collection) direction, and the nano-indentation tests showed an axial reduced modulus at 65 GPa. A consistent value of the anisotropic ratio at ~3 was observed comparing the longitudinal and transverse properties. The continuous capability of the presented method while maintaining high quality is expected to result in an improved DWCNT mass production process and potentially enhance the structural and electrical applications of CNT nanocomposites.

Highlights

Since the discovery of carbon nanotubes (CNTs) in 1991 [1], CNTs have been studied intensively because of their exceptionally high mechanical [2,3], electrical [3], and thermal properties
As experimentally verified by Yamada et al using ‘Ball-chemical vapor deposition (CVD)’ [27], water selectively reacted with the amorphous carbon, and the coating removal revived the catalyst activity, which considerably elevated the synthesis efficiency
Continuous synthesis and collection of CNTs based on the floating catalyst chemical vapor deposition (FCCVD) process were performed with various catalyst modifications

Summary

Introduction

Since the discovery of carbon nanotubes (CNTs) in 1991 [1], CNTs have been studied intensively because of their exceptionally high mechanical [2,3], electrical [3], and thermal properties. Transferring these properties into bulk products requires the development of efficient and reliable CNT synthesis methods. The conventional chemical vapor deposition (CVD) synthesis method [6] relies on the carbon decomposition on a pre-deposited substrate with transition metal catalyst (e.g., Fe, Co, and Ni). Requiring remarkably lower synthesis temperatures (700–1300 ◦C), the CVD method has been broadly used in laboratory and industrial environments

Methods

Results

Conclusion