Application of confocal Raman microscopy on the structure of sludge-based biochar

Confocal Raman microscopy method was utilized to analyze the structure changes of sludge-based biochar prepared at different pyrolysis temperatures (500~900℃). The results showed that there was a strong correlation between the fluorescence interference of Raman signal and the physicochemical properties of biochar. The Raman drift coefficient decreased with the pyrolysis temperature increasing, which was consistent with the changing trend of the volatile content, H/C and O/C ratio of sludge-based biochar. The correlation indices of the drift coefficient with the volatile content and the H/C ratio were 0.97 and 0.94, respectively, which revealed that the change of drift coefficient could be utilized to evaluate the change of volatile content and H/C ratio of biochar. In addition, the ratio of characteristic peak of biochar (D/G ratio) in the Raman spectra enhanced with the pyrolysis temperature increasing, which could represent the increasing process of the disorder degree of sludge-based biochar. The ratio of the valley region (V) to the D peak (IV/ID ratio) decreased with the pyrolysis temperature increasing, indicating that the proportion of defective fused aromatic ring structures increased. In addition, the ratio of ID1/IG1obtained by peak fitting was unobvious, while ID2/IG2 showed an increasing trend. The trend confirmed that the defects and amorphous structures were formed by the depositing compounds on the surface of carbon from low molecule fracture of side chain group. The ratio of IG1/IG2 decreased with the pyrolysis temperature increasing, indicating that the ratio of order to disorder of bond angle decreased following the increasing pyrolysis temperature. Therefore, Raman spectroscopy could be applied to characterize the sludge-based biochar, and reflect the evolution of its microstructure. © 2022 Chinese Society for Environmental Sciences. All rights reserved.