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.