Figure 4 . The morphology of HP-HKUST-1/PES membrane (A, B: SEM
images of the membrane cross-section; C, D: EDS analysis).
The size of the hierarchical pore structure and the specific surface
area of the HP-HKUST-1/PES membrane are determined by the BET analysis
with the results shown in Figure 5(A) . It can be seen that the
N2 adsorption-desorption isotherm of the HP-HKUST-1/PES
membrane shows a classical I curve26. The isotherm of
HKUST-1/PES membrane demonstrate a typical microporous adsorption
characteristic at a relative pressure of P/P0 < 0.8 and the
quantity adsorbed increased rapidly if a relative pressure of P/P0
> 0.8, since the mesopores and marcopores between the
nanoparticles are existed. In contrast, the N2adsorption-desorption isotherm of HP-HKUST-1/PES membrane shows a
classical type IV with a wide hysteresis loop, indicating the presence
of abundant microporous structures and mesoporous
structure27. At low relative pressures of P/P0
< 0.4, monolayer adsorption dominates and the adsorption
capacity increases rapidly to saturation due to the high adsorption
capacity of the abundant microporous structure. At high relative
pressures of P/P0 > 0.4, multilayer adsorption and
mesoporous adsorption appears, and the adsorption capacity increased
again after saturation. Also, a significant hysteresis loopback exists
in the desorption process, owing to the capillary coalescence of
N2 molecules in the mesopores. The closure of the
adsorption-desorption isothermal curve indicates that no close pores
exited in HKUST-1/PES membrane with stable pore structure. Besides, it
can be deduced that compared with HKUST-1/PES membrane, a richer and
more tunable layered porous structure for HP-HKUST-1/PES membrane is
performed. From Figure 5(B) , it can be seen that the
HP-HKUST-1/PES membrane contains a wide pore size distribution range
from 8 to 40 nm not observed in the HKUST-1/PES membrane, except for
micropores with diameters of 0.8-1.2 nm. The specific surface areas and
pore volumes of HKUST-1 membrane and HP-HKUST-1 membrane are illustrated
in Table 1 . It can be seen that the volume of the mesopores
increased significantly, if the membrane is immobilized with HP-HKUST-1.
It can be calculated that the ratio of mesopore volume
(Vmeso) to micropore volume (Vmicro) for
HP-HKUST-1/PES membrane was about 3 times higher than that of
HKUST-1/PES membrane, although the BET surface area and total pore
volume decreased.