Micro-Raman spectroscopy and Petrography for unraveling the complex heterogeneous physicochemical structures of biochar from the scale of bulk to micro: A comparison and discussion
Dezhi Chen , Zhou Fang , Yufan Wei , Jun Xu , Kai Xu , Long Jiang , Yi Wang , Sheng Su , Song Hu , Jun Xiang
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引用次数: 0
Abstract
This study produced biochar from coconut shells and corncobs through pyrolysis under a nitrogen atmosphere with temperatures ranging from 350℃ to 1400℃. The surface regions of the biochar were characterized at the micro-scale using a combination of micro-Raman spectroscopy and petrography. Extensive data from both methods were compared and correlated from the scale of bulk to micro- levels. The results indicate that for bulk structures, the average random reflectance (Rf) increases and Raman parameter α decreases with temperature, indicating a higher thermal maturity and lower C-H, C-O etc. structures. However, AD/AG, A(VR+VL+GR)/AD and A(VR+VL+GR)/AG exhibit significant inflection points at specific temperatures. These inflection points are linked to key structural transformations: aromatization at 600 ℃ and graphitization at 1000 ℃. At microscale, biochar contains pores of varying shapes and sizes (approximately 5–100μm) with ash deposits embedded within them. These features significantly influence the heterogeneity in Rf measurements, resulting in a broaden distribution of Rf as the pyrolysis process progressed. Besides, micro-Raman spectroscopy shows that biochar particles with higher substituent and side-chain abundances have a tendency towards preferential reactivity. Furthermore, the chemical structural distribution of biochar became more concentrated and focused below 1000 ℃. However, biochar undergoes heterogeneous graphitization at 1000 ℃, and the distribution of aromatic rings and graphite structure becomes even more dispersed between 1000 ℃-1400 ℃. The correlations between the results of petrographic method and micro-Raman at the bulk and micro-scale have been set up and discussed, and it can provide guidance for the comprehensive characterization of the heterogeneous structure of biochar.
期刊介绍:
The Journal of Analytical and Applied Pyrolysis (JAAP) is devoted to the publication of papers dealing with innovative applications of pyrolysis processes, the characterization of products related to pyrolysis reactions, and investigations of reaction mechanism. To be considered by JAAP, a manuscript should present significant progress in these topics. The novelty must be satisfactorily argued in the cover letter. A manuscript with a cover letter to the editor not addressing the novelty is likely to be rejected without review.