Surface vs. bulk - how do the properties of Miscanthus rhizomes change when subjected to high temperature treatment?

This work is focused on the determination of differences in the composition of the surface and bulk of thermally treated Miscanthus rhizomes. The biomass samples were processed in a wide temperature range from 200 to 700°C. The surface of formed biochars was studied with the use of time-of-flight secondary ion mass spectrometry. The obtained results were compared with other analytical methods, such as: thermogravimetry, proximate and ultimate analysis, Fourier transform infrared spectroscopy, etc. The performed studies revealed more intense decomposition of lignocellulose on the surface than in the bulk of treated Miscanthus rhizomes, especially at low temperature range (200–300°C), which was related to the diffusion limitations of intermediates of thermal processing of biomass migrating towards the surface. On the other hand, a decomposition of the surface layers of the studied material finished at lower temperature, while the remaining lignocellulose could still react in the bulk. Generally, the obtained results may be helpful in selecting thermal treatment conditions that allow obtaining optimal surface properties of the created biochar and increasing the scope of its potential applications. • different composition of surface and subsurface layers of formed biochar. • decomposition of the surface layers of the studied biomass ends at about 500°C. • lignocellulose in the bulk still reacts at higher temperature. • thermal treatment facilitates mobility of metals in the biochar structure. • ToF-SIMS allows for comprehensive analysis of thermally treated biomass surface. [ABSTRACT FROM AUTHOR]