Characterization of nanoparticles of biochars from different biomass

•Properties of nanoparticles extracted from biochars were investigated.•Nano-biochars were compared with their macro-counterparts.•Properties of nano-biochars differ from the properties of their macro-counterparts.

The research on biochar is focused primarily on the estimation of biochar as a “macro” fraction, and not much attention is devoted to its fractions with finer particles. The aim of the study was to characterize the physicochemical properties of biochar nanoparticles (biochar-NPs). The properties of the biochar-NPs were also compared to the properties of initial biochars. The results of this study indicate that the properties of biochar-NPs differ from the properties of their macro-counterparts. The differences were observed in the pH, cation exchange capacity, content of particular elements, and aromaticity/polarity not only based on the type of biochars, but also the regularities in the differences between their macro- and nano-forms. The nano-biochars had a larger surface area and smaller pore sizes than the corresponding macro-biochars and were characterized by a higher negative zeta potential and greater diversity of crystalline forms than the macro-biochar. Moreover, nano-biochar had significantly lower levels of C, H, and N compared to macro biochars.