Preparation and evaluation of modified cyanobacteria-derived activated carbon for H2 adsorption

A series of porous carbon sorbents obtained by carbonization and activation by KOH/ZnCl2 of the abundant waste material cyanobacteria was utilized for the adsorption of H-2. During experiments to determine the optimal activation parameters, the activation time had little effect, whereas the KOH/C and ZnCl2/C mass ratios and activation temperature had a significant impact on adsorption performance. Samples activated by KOH exhibited better adsorption characteristics (such as higher values of S-BET, V-total, V-micro, etc.) than those activated by ZnCl2. In particular, ACK-2-8, which had an S-BET of 1951 m(2) g(-1), displayed H-2 uptake capacities of nearly 17.3 mg g (-1) at similar to 196 degrees C and 1 bar. In addition, for evaluation of the H-2 adsorption performance, N-doped and P-doped porous carbons were synthesized using HNO3, NH3 $ H2O and H3PO4, respectively, to modify the abovementioned cyanobacteria-derived activated carbon ACK-2-8, and exhibited H-2 adsorption amounts that were 16.8%, 31.8%, and 45.7% higher, respectively, than those of undoped ACK-2-8. Furthermore, it was remarkable that P-doping in conjunction with a moderately high SBET enhanced the uptake of H-2 by ACK-2-8-2, which had a smaller SBET than ACK-2-8-3 but the best uptake capacity of up to 25.2 mg g(-1), and thereby showed that the relationship between the H-2 adsorption capacity and SBET of these materials was scarcely linear and was therefore noticeably different from previously reported results for the uptake of H-2 by other carbon sorbents. Hence, it is probable that the considerable H-2 adsorption properties of the material with a moderate SBET have great potential applications for hydrogen capture or storage.