Biomass-Derived Microporous Carbon Materials with an Open Structure of Cross-Linked Sub-microfibers with Enhanced Adsorption Characteristics

摘要

Moringa oleifera seed shells exhibit a unique structure of cross-linked sub-microfibers (0.5-1.5 mu m diameter) with a well-connected macroporous network. Controlled pyrolysis (500-800 degrees C) and cyclic activation of the precursor provided a porous carbon material with a structure that minimizes mass-transfer constraints. Under both slow (10 degrees C/min(-1)) and flash pyrolysis, the structure was preserved, while a significant microporosity was developed. By flash pyrolysis (700-800 degrees C), a material with enhanced characteristics for potential application as a molecular sieve (S-DA = 450-470 m(2) g(-1), and S-BET = 5 m(2) g(-1)) was obtained. Cyclic activation of carbonized shells, consisting of an oxygen chemisorption stage (180 C) followed by a desorption stage in an inert atmosphere (450-900 degrees C), resulted in a controlled development of microporosity upon successive activation cycles. After 10 activation cycles, respective S-DA and S-BET values of 1172 and 761 m(2) g(-1) were obtained. Higher development of the surface area and a wider distribution of micropores was observed when the desorption stage was carried out at 900 degrees C. The development of the surface area was achieved at low burnoff (22-33%), thus preserving the structure of the material. Thanks to its unique structure, the material obtained exhibited enhanced characteristics for gas sorption as a result of diminished mass-transfer limitations, assessed through the kinetics of carbon dioxide adsorption runs at ambient conditions.