Surface characterisation and classification of microwave pyrolysed maple wood biochar

•Structural change of biochar under experimental microwave pyrolysis conditions.•Classification showed reflectance increased with decreasing biochar porosity.•Increasing pyrolysis temperature resulted in irregularity in biochar surface.•FTIR profiles showed lower functional group activity with increasing temperature.

Maple wood biochars produced by microwave pyrolysis were analysed and compared in relation to their physical properties such as porosity and reflectance of chars. The aim of this research was to investigate the feasibility of the selection of relevant wavelengths in Visible/Near Infra-Red spectroscopy by combining Maximum R2 (MAXR) with Multiple Linear Regressions (MLR) method to build a predictive model. The porosity and yield data of the resulting biochars were used to test the model. Based on the spectral information, different mathematical techniques were used to group the biochars based on their physical properties. Scanning electron microscopy imaging of the biochar samples showed that pyrolysis temperature and doping ratio played a major role in the formation of microporous structures within the biochars formed due to the devolatilisation process during microwave pyrolysis. The FTIR analysis was consistent with the scanning electron microscopy conclusions, indicating evidence of aliphatic group stretching with increase in temperature and doping ratio. The FTIR profile of the control (fresh maple wood) sample had a more complex spectrum. With increase in pyrolysis temperature, functional group activities decreased indicating breaking up of weaker bonds.