Room temperature hydrogen uptake in single walled carbon nanotubes incorporated MIL-101 doped with lithium: effect of lithium doping

Single walled carbon nanotubes incorporated hybrid MIL-101 (SWNT-MIL-101) was synthesised and lithium ions were doped into the framework at various Li⁺ ions concentrations. Hydrogen adsorption–desorption measurements were performed at 298 K up to 90 bar and the hydrogen uptake capacities were found considerably enhanced by the combined modification by single walled carbon nanotubes and lithium doping. Lithium naphthalenide (C₁₀H₇Li) was used to dope Li⁺ ions into the SWNT-MIL-101 framework. The concentration of lithium ions inside the framework was quantitatively determined by inductively coupled plasma analysis. Powder X-ray diffraction studies showed that the crystalline framework of MIL-101 was not disturbed by SWNT incorporation and Li doping. BET surface area analysis by N₂ adsorption at 77 K showed a decrease in BET surface and pore volume as the concentration of Li ions increases inside the framework. The present study showed that combined modification of MOFs by single walled carbon nanotube followed by lithium ion doping is effective in enhancing their hydrogen uptake capacities at ambient temperatures.