Effects of synthesis method, feedstock type, and pyrolysis temperature on physicochemical properties of biochar nanoparticles

Nowadays, biochar nanoparticles have been the subject of intense debates due to having conflicting influences on the environment. Therefore, acquiring knowledge about the contributing factors affecting their characteristics is all-important. This study aimed to investigate the effects of production techniques (sonication/centrifugation and hydrothermal using H2SO4/HNO3) of biochar nanoparticles derived from two feedstock types (corn (Zea mays L.) residues and Conocarpus erectus L. wood) and pyrolysis temperatures (400 degrees C and 700 degrees C) on their physicochemical properties. Furthermore, hydrodynamic size distribution, morphology, elemental compositions, aromaticity, polarity, pH, ash content, yield, zeta potential, specific surface area, pore volume, average pore diameter, and surface functional groups of biochar nanoparticles and bulk types were investigated. The results revealed that all biochar nanoparticles generated by the hydrothermal method had the most polarity (O/C), surface functional groups, stability (negative zeta potential), and surface area compare to those of nanoparticles prepared by the other method and even the bulk biochars. However, their aromaticity (H/C), pH, and ash contents were the least. The results also showed that woody biochar nanoparticles contained higher surface area, pore volumes, stability, polarity, and acidic functional groups than corn-based biochar nanoparticles, but lower yield and ash content, regardless of production approach type. In all samples, the elevation of pyrolysis temperature influenced their properties by reducing size, polarity, yield, and increase of surface area, pH, aromaticity, and ash content. Overall, biochar nanoparticle characteristics ultimately depend on production technique, pyrolysis temperature, and feedstock type. Moreover, considering each factor as a variable should be based on the type of application.