Non-linear thermogravimetric mass spectrometry of carbon materials providing direct speciation separation of oxygen functional groups

Pascal Düngen,Robert Schlögl,Saskia Heumann

doi:10.1016/j.carbon.2018.01.047

Abstract

Thermogravimetric mass spectrometry (TG-MS) is an established way to analyze oxygen containing surface functional groups of carbon materials. Thermal stabilities and structures of functional groups influence their decomposition temperatures and products (CO, CO2). In this work, a non-linear procedure with isothermal steps is presented enabling a separation of functional groups by different decomposition temperatures. Nitrosulfuric acid functionalized carbon materials like multi-walled carbon nanotubes (MWCNT) and graphite were used to design the temperature program. Comparative studies of linear and non-linear heating experiments in argon and hydrogen containing atmosphere were performed to state the benefits and limits of both methods. The distinct advantage of non-linear thermal analysis is demonstrated by an application-oriented experiment where only selected functional groups are consumed.

Highlights

Multi-walled carbon nanotubes (MWCNT) are highly desired materials for numerous applications
Thermal decomposition of oxidized carbon materials combined with simultaneous detection of released gaseous products enables the determination of different thermal stabilities of functional groups
Specific surface areas were determined by N2 sorption experiments and analyzed by Brunauer-Emmet-Teller (BET) theory showing type II hysteresis for graphite and type IV for MWCNT

Summary

Introduction

Multi-walled carbon nanotubes (MWCNT) are highly desired materials for numerous applications. Due to their unique structure they combine graphitic properties like high conductivity, thermal and mechanical stability with high surface area (250 m2/g) [1e4]. The functional groups on the surface of the supporting MWCNT can influence the stability of the compound material. To describe the interaction between metal catalysts and functional groups, or to determine the catalytic activity of the carbon material itself, it is necessary to qualitatively and quantitatively identify functional groups and describe the changes to such groups before and after their use in a catalytic reaction [11,12]. The reaction temperature applied during this catalytic test already changes the composition of functional groups and influences the quantification [14]

Methods

Results

Conclusion