This study highlights the separation of hydrogen from
H2–He mixture gas by a graphene-coated halloysite
nanoclay membrane.
The graphene-coated clay membrane along with its pure clay counterpart
is successfully developed and studied for gas separation using hydrogen
(H2)–helium (He) single and mixture gases. Hydrothermal
and nonhydrothermal methods were applied for the synthesis of a ″coated″
membrane on a porous alumina substrate from the graphene and halloysite
clay. To date, nanoporous zeolites are the potential materials for
gas separation based on a molecular sieving mechanism. A similar separation
mechanism for hydrogen and helium from mixture gases may not work
efficaciously due to the closeness of their kinetic diameter (H2: 2.89 Å and He: 2.6 Å). The presence of defects
and torn nanopores between graphene layers along with the different
surface charges of the inner and outer layer of halloysite nanotubes
facilitates the ″coated″ membrane to show an appreciable
H2/He separation factor of ∼4 using H2–He (1:1) mixture gas compared to 2.86 for the pure halloysite
membrane. The available charge layer of graphene also has a significant
contribution for this increased H2/He selectivity value.
The permeate flux of H2 and He through both the graphene-coated
clay membrane and pure clay membrane has also been noted. The permeate
flux of pure H2 and He was 2 × 10–7 and 1.3 × 10–7 mol m–2 s–1 Pa–1 for the clay membrane, whereas
for the ″coated″ clay membrane, the values changed to
0.1 × 10–7 and ∼0.05 × 10–7 mol m–2 s–1 Pa–1 at 100 kPa, respectively.