Raman Spectroscopy for Characterizing Porous carbon

Abstract: Porous carbon obtained from low cost and abundant biomass has gained attention as renewable material feedstock. In this study, porous carbon biochar produced through pyrolysis was investigated by Raman spectroscopy to disclose the structural properties. The measured samples were in form of pellets (identified as WP, 139, 233, 226), and lumber wood (Pine, a softwood type and Beech, a hardwood type). The resulted spectra, which consisted of two broadened overlapped peaks were fitted with two Gaussian curves. The intensity ratio of the curves (ID/IG) were calculated to analyse the aromaticity of the samples. The aromaticity represents the proportion of the total C phases (amorphous and crystalline) within the samples. The result indicates that the aromaticity of the samples increased as the pyrolysis temperature was raised. Furthermore, the biochar obtained for higher temperature had larger crystalline surface area, which is indicated by La (crystalline length). The La values obtained were around 9-10 Å and exhibit a highly disordered structure with turbostratic arrangement. As complementary, the data from Raman measurements were also compared with elemental analysis results to show the amount of carbon content in the samples. The results from elemental analysis present that the higher temperature will produce higher carbon proportion in the samples. Thereby, both Raman spectroscopy and elemental analysis give similar trends for evaluating the structure of the samples. In comparison with a soot sample, biochar exhibits less carbonization since the aromaticity and crystalline surface area (defined by La) of the soot have higher values. The Raman signal increases for higher laser power and detector integration acquisition time. However, high power and long acquisition time promote fluorescence background. Thus, moderate laser power and integration time was preferably chosen for reliable Raman measurements.