Novel Pyrolytic Carbon Membranes Containing Silica: Preparation and Characterization

Abstract

A new class of pyrolytic carbon membranes containing silica (C−SiO2) has been prepared by the pyrolysis of copolyimides consisting of two phases and characterized. To control micropores in the C−SiO2 membrane, the polyimide copolymer precursors were synthesized via two building blocks that consisted of a carbon-rich phase and a silicon-rich phase. The carbon-rich block consisted of pyromellitic dianhydride and oxydianiline, and the silicon-rich block was oligomeric organosiloxane. These C−SiO2 membranes were characterized by FT-IR spectroscopy, X-ray diffraction, ESCA, FE-SEM, AFM, and TEM. These analyses revealed that the C−SiO2 membranes have an asymmetric structure in which the top surface consists of a SiO2-rich phase in a continuous carbon matrix and the bottom surface is mainly a carbon-rich phase. In a molecular probe study using small molecules (He, O2, N2, and CO2) having sizes from 2.6 to 3.64 A, the C−SiO2 membranes exhibited an outstanding molecular sieving capability, together with a high gas...