Structural Flexibility in Activated Carbon Materials Prepared under Harsh Activation Conditions.

Fabiano Gomes Ferreira De Paula,Francisco Rodríguez-Reinoso,Joaquín Silvestre-Albero,Paulo Fernando Ribeiro Ortega,Manuel Martínez-Escandell,Ignacio Campello-Gómez

doi:10.3390/ma12121988

Abstract

Although traditionally high-surface area carbon materials have been considered as rigid structures with a disordered three dimensional (3D) network of graphite microdomains associated with a limited electrical conductivity (highly depending on the porous structure and surface chemistry), here we show for the first time that this is not the case for activated carbon materials prepared using harsh activation conditions (e.g., KOH activation). In these specific samples a clear structural re-orientation can be observed upon adsorption of different organic molecules, the structural changes giving rise to important changes in the electrical resistivity of the material. Whereas short chain hydrocarbons and their derivatives give rise to an increased resistivity, the contrary occurs for longer-chain hydrocarbons and/or alcohols. The high sensitivity of these high-surface area carbon materials towards these organic molecules opens the gate towards their application for sensing devices.

Highlights

Activated carbon materials have experienced a renovated interest in the last few years in fields such as electrochemical energy storage, sensing devices, etc. [1,2,3,4,5,6]
The selection of these samples prepared from a different precursor, and using a different activation procedure will allow a pre-evaluation of the structural flexibility in activated carbon materials
Experimental results described above have shown that activated carbon materials prepared under harsh activation conditions (e.g., KOH activation) can exhibit intrinsic structural re-structuring upon hydrocarbon adsorption, preferentially for long chain molecules

Summary

Introduction

Activated carbon materials have experienced a renovated interest in the last few years in fields such as electrochemical energy storage (supercapacitors and batteries), sensing devices, etc. [1,2,3,4,5,6]. One of the basic criteria to identify the optimum carbon material for these applications (in terms of capacity, sensitivity, and selectivity) concerns the perfect knowledge of i) the porous structure of the synthesized carbon (presence of micropores and mesopores), ii) the surface chemistry (presence of functional groups on the carbon surface), and iii) the inner carbon structure (e.g., graphitization degree, size of the graphite microdomains, etc.) These characteristics will define among others the selective adsorption and electrochemical response (sensitivity) of the activated carbon devices. This manuscript aims to evaluate potential structural changes in activated carbon materials upon adsorption by combining XRD and Raman spectrometry To this end, different carbon materials, coming from lignocellulosic or petroleum residues, and prepared under different chemical activation routes (low and high temperature, and different activating agents), will be compared. The effect of these structural changes in the final resistivity of the activated carbon material will be discussed

Experimental Section

Effect of the Carbon Precursor

Effect of The Activation Temperature

Raman Spectrometry for Samples LACC-K 700 and PAC-K 700

Electrical Conductivity Measurements

Conclusions