3.2. Characterization of duckweed bio-char
3.2.1. Pore structure of duckweed bio-char
In general, development of pores during biomass pyrolysis is controlled primarily by the devolatilization of organic moieties, but also by the deposition of carbonaceous products (coke) formed by the condensation of volatile matter that can block the pores [30]. One should also factor in gasification of char carbon by pyrolysis gases, which leads to opening and/or enlarging the surface pores. Due to the combined effect of the above processes, pyrolysis conditions significantly affect the extent of pore formation in chars [31]. For example, at relatively low temperatures (400–600 °C), increasing temperature may result in an increased pore volume in the bio-char samples. On the other hand, at higher temperatures, condensation of volatiles can block and significantly reduce the total pore volume in the sample. The observed decrease in the micropore volume at high temperatures can be attributed to gasification of char - leading to increased macropore volume. Thus, high sweep gas flow rates and high heating rates can restrict pore development.