Abstract
Structural properties of carbonized cellulose were explored to conjugate the outcomes from various characterization techniques, namely X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy. All these techniques have evidenced the formation of graphene stacks with a size distribution. Cellulose carbonized at 1000 and 1800 °C at a heating rate of 2 °C/min showed meaningful differences in Raman spectroscopy, whereas in XRD, the differences were not well pronounced, which implies that the crystallite sizes calculated by each technique have different significations. In the XRD patterns, the origin of a specific feature at a low scattering angle commonly reported in the literature but poorly explained so far, was identified. The different approaches used in this study were congruous in explaining the observations that were made on the cellulose-derived carbon samples. The remnants of the basic structural unit (BSU) are developed during primary carbonization. Small graphene-based crystallites inherited from the BSUs, which formerly developed during primary carbonization, were found to coexist with larger ones. Even if the three techniques give information on the average size of graphenic domains, they do not see the same characteristics of the domains; hence, they are not identical, nor contradictory but complementary. The arguments developed in the work to explain which characteristics are deduced from the signal obtained by each of the three characterization techniques relate to physics phenomena; hence, they are quite general and, therefore, are valid for all kind of graphenic materials.
Highlights
Carbonaceous materials derived from biomass have a wide range of applications, ranging from aqueous and gaseous pollutant adsorption [1,2] and catalysis [3,4,5], to energy storage [6,7]
X-ray diffraction (XRD) patterns are routinely used for carbon characterization and provide parameters, such as Lc and La which are usually both calculated by the Scherrer equation through
The two XRD profiles of the carbonised cellulose samples in Figure 1 differ in the background intensity, and differ slightly in the intensity, width, and positions of the peaks upon the temperature increase
Summary
Carbonaceous materials derived from biomass have a wide range of applications, ranging from aqueous and gaseous pollutant adsorption [1,2] and catalysis [3,4,5], to energy storage [6,7]. The carbonization of a non-graphitizable material, such as cellulose, results in the formation of stacked graphenes lacking the long-range near-parallel extension (otherwise designated as the local molecular orientation (LMO)) [8], which is necessary for the solid to crystallize into genuine graphite. In this regard, there is some misinterpretation or confusion in the literature due to the fact that using a graphitization process (i.e., a heattreatment above 2200 ◦ C up to 3000 ◦ C) does not compulsorily result in obtaining carbon materials with the structure of genuine graphite [9]. One important traditional way of measuring graphitization is by measuring the value of the spacing between graphene layers using the 2θ position of the 00l diffraction peaks in the XRD patterns [14]
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