In situ characterization of functional groups of biochar in pyrolysis of cellulose

Heating rate, an important parameter in pyrolysis, not only impacts distribution of pyrolysis products, but also affects evolution of functionality of biochar and further application of the biochar. In this study, an in situ Diffuse Reflection Infrared Fourier Transform Spectra (DRIFTS) technique was used to probe transformation of functional groups of the biochar derived from pyrolysis of cellulose at varied heating rate of 5, 10, 15 and 20 °C/min, aiming to draw an overall picture for the change of functional groups of the biochar versus the heating rate and pyrolysis temperature. The results showed the abundance of -OH, CH and CO experienced a maximum in 410 to 450 °C, depending on the specific heating rates, and then decreased with further increasing temperature via the conversion routes including dehydration, dehydrogenation and cracking. This led to carbonization of the biochar with monotonous increase of abundance of =C-H and CC functionality. Formation of the =C-H had a very close correlation with the removal of -C-H and -OH, especially the -C-H. Cracking of CO was one of the decisive factors for formation of CC. Nevertheless, cracking of C-O-C was much more difficult to be removed than that of CO and -OH, deterring the carbonization and leading to the retainment oxygen in the biochar.