Structural and textural characterization of Brassica carinata biochar to investigate its potential industrial applications

Biochar, a low-cost, and carbon-rich product of the thermal decomposition of biomass under oxygen-limited conditions and at relatively low temperatures, has recently been identified as a promising porous material with a wide range of industrial applications. In the present study, a comprehensive analysis of proximate, ultimate, nutrient profile, structural, and textural properties of a biochar derived from two Ethiopian indigenous Brassica carinata cultivars was conducted. The characterization of the biochar was achieved by employing a variety of well-established methods, including proximate analysis (moisture, volatile matter, ash content, and fixed carbon), ultimate analysis (C, S, and O content), atomic oxygen to carbon ratio (O/C), morphological and elemental composition analysis through scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). Furthermore, a combination of mercury intrusion porosimetry (MIP), dynamic vapor sorption (DVS), and gas adsorption methods such as nitrogen and krypton gas adsorption, were used for an in-depth study of the porous structure. SEM morphological characterization showed that the biochar surfaces showed multiple pores of diverse sizes and shapes. EDS elemental composition analysis revealed that sodium, aluminium, and silicon were not detected, but potassium, calcium, magnesium, and iron were all present in noticeable amounts. Furthermore, ultimate analysis showed that the most prevalent elements were carbon (86 wt.%) and oxygen (10.41‒9.77 wt.%), while sulphur was present in negligible concentrations. MIP analysis demonstrated that the porosities of the biochars varied from 62.68 to 69.99 wt.%, with the Holetta-1 biochar showing the highest porosity. The superior porosity of Holetta-1, as confirmed via MIP analysis, yielded higher values for bulk volume (2.36 mL g− 1), skeletal volume (1.65 mL g− 1), and total intrusion volume (1.65 mL g− 1) compared to the Yellow Dodolla. The most frequent pore diameters were 172.46 μm for Yellow Dodolla and 111.42 μm for Holetta-1. The MIP log differential pore diameter distributions were observed to vary from 18 to 411 μm and 10 to 411 μm, respectively, for Yellow Dodolla and Holetta-1. Despite the biochars’ low specific surface areas (0.17–0.21 m² g⁻¹), krypton sorption was a suitable technique for its characterization compared to DVS and nitrogen sorption methods. In conclusion, the characterization studies confirmed that this carbon-rich porous material possesses unique and valuable properties, with these attributes position it as a promising alternative for diverse industrial applications, contributing to the development of a bio-based circular economy.