Fabrication of a Novel Covalent Organic Framework Membrane and Its Gas Separation Performance

Herein, we employ 2,5-dimethoxyterephthalaldehyde (DMTA) containing ether oxygen group in the structure as the construction unit to react with tetra-(4-anilyl)-methane (TAM) through Schiff-based condensation reaction in a Teflon-lined autoclave to synthesize a novel three-dimensional covalent organic framework named DMTA-COF. Furthermore, the condensation reaction was confirmed by Fourier transform infrared spectroscopy (FT-IR). The crystal structure of DMTA-COF was analyzed by the powder X-ray diffraction (PXRD) measurement in conjunction with structural simulation. The morphology, thermal stability, porosity and pore distribution of DMTA-COF were measured by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and N-2 adsorption-desorption at 77 K. The high affinity for CO2 adsorption was also confirmed by low pressure CO2 sorption. Considering the relatively small pore size and the strong CO2 adsorption interaction of DMTA-COF due to an abundant of ether oxygen group and imine linkage, we synthesized one continuous supported DMTA-COF membrane for H-2/CO2 separation. In our study, the porous Al2O3 support surface was first coated with polyaniline (PANI) and was then further functionalized with aldehyde groups by reaction with DMTA at 150 degrees C for 1 h. Finally, in situ growth of the COP membrane utilizing the covalent linkage yielded a novel continuous DMTA-COF membrane. X-ray diffraction (XRD) result indicated that the DMTA-COF membrane was pure phase and had high crystallinity. From SEM characterization, we could see that the DMTA-COF membrane was compact and well intergrowth and adhered to the support tightly. Gas separation performance results shown that DMTA-COF membrane had a high H-2 permeance and selectivity of H-2/CO2. For DMTA-COF membrane, the 1:1 binary mixture gas separation factors of H-2/CO2 calculated as the gas molar ratios in permeate and retentate side was 8.3 at room temperature and atmospheric pressure. And H-2/CO2 separation factor of DMTA-COF membrane exceeded the corresponding Knudsen coefficient (4.7), with H-2 permeance of up to 6.3 X 10(-7) mol.m(-2).s(-1).Pa-1. Because of its outstanding characteristics, the novel DMTA-COF membrane is expected to be widely used in the field of H-2 purification and separation.