An advanced structural characterization of templated meso-macroporous carbon monoliths by small- and wide-angle scattering techniques

Abstract

This study is dedicated to link the nanoscale pore space of carbon materials, prepared by hard-templating of meso-macroporous SiO 2 monoliths, to the corresponding nanoscale polyaromatic microstructure using two different carbon precursors wthat generally exhibit markedly different carbonization properties, i.e., a graphitizable pitch and a non-graphitizable resin. The micro-and mesoporosity of these monolithic carbon materials was studied by the sorption behavior of a relatively large organic molecule (p-xylene) in comparison to typical gas adsorbates (Ar). In addition, to obtain a detailed view on the nanopore space small-angle neutron scattering (SANS) combined with in situ physisorption was applied, using deuterated p-xylene (DPX) as a contrast-matching agent in the neutron scattering process. The impact of the carbon precursor on the structural order on an atomic scale in terms of size and disorder of the carbon microstructure, on the nanopore structure, and on the template process is analyzed by special evaluation approaches for SANS and wide-angle X-ray scattering (WAXS). The WAXS analysis shows that the pitch-based monolithic material exhibits a more ordered microstructure consisting of larger graphene stacks and similar graphene layer sizes compared to the monolithic resin. Another major finding is the discrepancy in the accessible micro/mesoporosity between Ar and deuterated p-xylene that found for the two different carbon precursors, pitch and resin, which can be regarded as representative carbon precursors in general. These differences essentially indicate that physisorption using probe gases such as Ar or N 2 can provide misleading parameters if to be used to appraise the accessibility of the nanoscale pore space.

On the Highly Ordered Graphene Structure of Non-Graphitic Carbons (NGCs)—A Wide-Angle Neutron Scattering (WANS) Study

“…The WAXS/WANS of NGCs is the superposition of interlayer scattering caused by the stacking, and the intralayer scattering caused by the graphene layers themselves. Assuming that a higher temperature results in growth and higher order in both, the graphene layers and in the layer stacking [20,[37][38][39][40][41][42][43], overall, the reflections of samples get sharper with higher treatment temperature. For instance, PF-R 1000 showed broad reflections, while PF-R 3000 exhibits sharper reflections (Figure 5).…”

“…A widely used approach for WAXS was proposed by Shi et al in 1993 [31], followed by other procedures by Azuma in 1998 [32] and Fujimoto and Shiraishi in 2001 [33]. Finally, in 2002, Ruland and Smarsly published an advanced approach for analyzing the WAXS of NGCs [34] that has already been successfully used in several studies [20,[35][36][37][38][39][40][41][42]. Typical WAXS/WANS data and the general idea of the approach of Ruland and Smarsly are shown in Figure 2.…”

OctCarb—A GNU Octave Script for the Analysis and Evaluation of Wide-Angle Scattering Data of Non-Graphitic Carbons

“…Hence, Raman spectroscopy and wide-angle X-ray/neutron scattering (WAXS/WANS) are commonly used to obtain quantitative structural parameters of NGCs. While Raman spectroscopy is mainly used to determine the average extension L a of the graphene layers, WAXS/WANS allows for precisely determining a significant number of different structural parameters describing the NGC microstructure [19][20][21][22][23][24][25][26][27][28]. Recently, we discussed and compared the determination of L a by these two methods, applied on a systematic series of carbons, and a procedure was presented for thorough characterization of NGCs based on Raman spectroscopy only [29,30].…”