Low temperature synthesized carbon nanotube superstructures with superior CO2 and hydrogen storage capacity

Carbon nanotubes (CNTs) may be prepared at a low temperature of 180 degrees C using carbon tetrachloride as carbon source and ferrocene/Ni as substrate/catalyst. The lowly graphitic CNTs have diameter of 180-300 nm and wall thickness of ca. 25 nm and are arranged into closely networked superstructures with surface area and pore volume of 470m(2) g(-1) and 0.39 cm(3) g(-1), respectively. On activation, the CNT superstructures yield highly porous CNT composites with surface area of 1479-3802m(2) g(-1) and pore volume of 0.83-2.98 cm(3) g(-1). Mild activation generates highly microporous (>= 95% microporosity) carbons that retain nanotubular morphology and which exhibit excellent CO2 uptake capacity; up to 4.8 mmol g(-1) at 1 bar and 19.5 mmol g(-1) at 20 bar and 25 degrees C, while at 0 degrees C they store 8.4 mmol g(-1) and 25.7 mmol g(-1) at 1 and 20 bar, respectively. More severe activation generates activated carbons with surface area and pore volume of up to 3802 m(2) g(-1) and 2.98 cm(3) g(-1), respectively, and which possess significant microporosity combined with mesoporosity resulting in exceptional total hydrogen storage of up to 7.5 wt% at -196 degrees C and 20 bar, rising to 9.7 wt% and 14.9 wt% at 40 bar and 150 bar, respectively, while at room temperature total uptake reaches 4.4 wt%. The porosity of the CNT superstructures can thus be tailored towards CO2 or hydrogen uptake applications.