Modification of pore structure in activated carbons by heat treatment with thermoplastic resins

Three activated carbons having different surface areas, coconut-shell based (AC-C), pelletized (AC-P) and bamboo-derived (AC-B) were modified by mixing them with four thermoplastic precursors, poly(vinyl alcohol) (PVA), hydroxy propyl cellulose (HPC), citric acid (CiA) and fluorine-containing polyimide (FPI), followed by heat treatment at 900°C for 1 h. The porous structures of the modified activated carbons were characterized by nitrogen adsorption and SEM. It was found that the thermoplastic precursors modified the porous structure of AC-B more significantly compared with the other two: AC-P and AC-C. PVA, HPC, and CiA modification resulted in the reduction of surface area of AC-B, which is attributed to a different modification of the micropore structure; PVA eliminated all micropores, HPC eliminated ultra-micropores preferentially, and CiA decreased the volume of ultra-micropores, whereas it increased that of super-micropores. On one hand, the addition of 30 mass% CiA to AC-B resulted in an increase in external surface area by 170 %. On the other hand, the modifier FPI increased the surface area by increasing ultra-micropores to approximately twice that of the original activated carbons. By the selection of modifier, the distribution of micropore size in the substrate-activated carbons can be modified, either by decreasing or by increasing ultra-micropores.