2.2 Cu/ZnO/Ti CMNR fabricated by flowing synthesis
The Ti membrane substrate was washed with the acetone, ethanol and deionized water successively after being polished by the sand paper, in order to remove the burrs, scratches, oil stains and impurities. Then, the Ti membrane substrate was immersed in the sodium hydroxide solution (10 mol·L-1) at 80 ℃ for 2 h, followed with dried at 80 ℃ for 2 h. After that, the Ti membrane substrate was modified by 3-aminopropyltrimethoxysilane (APTES), followed with Cu/ZnO immobilization. A typical modification and assembly process was shown in Figure 1: (1) The mixed solution of 95 wt% ethanol and APTES (8 g·L-1, 10 mL) 25 was permeating through the Ti membrane substrate with the flowrate of 5 mL·h-1, then dried at 80 ℃ for 2 h, so that the membrane was modified by APTES; (2) Zinc nitrate solution (0.845 mol·L-1, 5 mL) was permeating through the Ti membrane substrate with the flowrate of 1 mL·h-1, followed with dried at 80 ℃ for 2 h, so that Zn2+ was deposited in the pores of Ti membrane substrate; (3) 2-methylimidazole solution (2.151 mol·L-1, 5 mL) was permeating through the membrane with the flowrate of 1 mL·h-1, and coordinated with the Zn2+ deposited in the pores of Ti membrane, and then, ZIF-8 was synthesized and immobilized in the pores after being dried at 80 ℃ for 2 h; with repeating steps (2) and steps (3) several times,the loading amount of ZIF-8 could be increased effectively; (4) The ZIF-8/Ti membrane was washed with deionized water for several times to remove the unstable particles, and then dried at 80 ℃ for 2 h; (5) The copper nitrate solution (0.053 mol·L-1, 5 mL) was permeating through the ZIF-8/Ti membrane with the flowrate of 1 mL·h-1, and the Cu2+ was deposited stably and distributed uniformly in the membrane pores by ion-exchange between Cu2+ and Zn2+ in ZIF-8, followed with being dried at 80 ℃ for 2 h to form Cu2+/ Zn2+/Ti membrane; (6) The Cu2+/ Zn2+/Ti membrane obtained in step (5) was washed with deionized water and dried at 80 ℃ for 2 h to remove unstable particles; (7) Finally, the Cu/ZnO/Ti CMNR fabrication could be accomplished by reduced under 20% H2/N2 environment at 360 ℃ for 3 hours. During this process, ZIF-8 has been taken as a sacrificial intermediate. The above procedures from (1) to (6) were carried out in situ by means of the technological apparatus as shown in Figure S1, and the reduced and calcined procedure of (7) was achieved on the apparatus as shown in Figure S2.
For convenient comparison, the Cu/Ti membrane was fabricated without ZIF-8 as sacrificial intermediate, and the ZnO/Ti membrane was obtained by directly sintering the ZIF-8/Ti membrane under the air atmosphere as well.