Preparation And Proton Conductivity Of MOP@MOFs Composites

The highly ordered and tunable structural features of Metal-Organic Frameworks(MOF s)materials facilitate the study of proton transport pathways and mechanisms in MOFs and also provide theoretical feasibility for the design of novel proton-conducting materials.Based on this,in this paper,metal-organic polyhedra(MOP)with proton carriers and proton sources were encapsulated into the pores of MOFs,and then the modified MOFs composites were used as the reinforcing phase to co-blend with the Sulfonated polyether ether ketone(SPEEK)matrix to prepare composite membranes in order to improve the comprehensive performance of SPEEK membranes.The details are as follows:(1)Firstly,two methods,impregnation and in situ growth,were used to encapsulate MOP-1 with abundant amino groups into a MOF(DUT-68)without any proton source and proton carrier.The results showed that the structural stability of MOP-1@DUT-68 synthesized by the in situ growth method was better,and the MOP-1 loading was about 18%higher than that of MOP-1?DUT-68 obtained by the impregnation method,and MOP-1 could be more stably encapsulated in the pores of DUT-68,resulting in the proton conductivity of MOP-1@DUT-68 at 98%RH and 80℃ reached 1.14 ×10-3 S·cm-1,which is 3 orders of magnitude higher than DUT-68 under the same conditions and 11 times higher than that of MOP-1 ?DUT-68.More importantly,the in situ growth encapsulation method can break through the size limitation of the host and guest molecules,and the molecules encapsulated into the pores of MOFs are less likely to leak.In contrast,the impregnation method can only be used to encapsulate some guest molecules whose size is smaller than the pore size of the cage of MOFs due to the size limitation and is prone to leakage.(2)To further improve the proton conductivity,the acid-functionalized MOP-3 was encapsulated into MOL-101-NH2 by in situ growth,and the-NH2 on its ligand could form an acid-base pair with the-SO3H on MOP-3,and then,the protonated 5-sulfoisophthalic acid was anchored to MIL-101-NH2 by electrostatic interaction,and then introduced Cu(OAc)2·H2O into MIL-101-NH2,assembling with the ligands to form the MOP-3.The MOP-3@MIL-101-NH2 composites were obtained after being assembled.The introduction of MOP-3 increased the proton concentration,and the formation of acid-base pairs between the host and guest molecules could participate in the construction of hydrogen bonding networks,providing sites for proton transport and thus expanding the proton transport channels,resulting in a proton conductivity of MOP-3@MIL-101-NH2 of 2.55 ×10-3 S·cm1 at 98%RH and 368 K,which is 6.39 times higher than that of MIL-101-NH2.(3)Sulfonated polyetheretherketone(SPEEK)was selected as the membrane substrate,and MOP-1@DUT-68(M1@D)and MOP-3@MIL-101-NH2(M3@M)composites were blended with SPEEK matrix to obtain M1@D/SPEEK and M3@M/SPEEK composite membranes.Due to the proton source brought by the introduction of MOFS·composites and the formation of acid-base pairs by-NH2 on the composites and-SO3H on the SPEEK membranes,the host-guest molecules synergistically promoted the formation of hydrogen bonding networks,and the proton conductivity of M1@D/SPEEK-7 and M3@M/SPEEK-7 at 98%RH and 343 K reached 1.69×10-1 and 3.54×10-1 S·cm-1,respectively,which were 9.4 and 19.7 times that of the pure SPEEK film(1.80 ×10-2 S·cm-1),respectively.Moreover,the thermal stability,dimensional stability,mechanical properties,oxidation stability and hydrolysis resistance of the composite film were better than the pure SPEEK film.