Intermediate gel coating on macroporous Al2O3 substrate for fabrication of thin carbon membranes

To fabricate carbon membranes based on a low-cost macroporous Al2O3 substrate, a pretreatment called “intermediate gel coating” on the substrate was introduced. It can be carried out simply by coating the substrate with an AlOOH sol and drying to form a gel layer. The PFA (polyfurfuryl alcohol) was synthesized and coated on the gel-modified Al2O3 substrate, and the carbon membranes were obtained after a carbonization treatment. Scanning electron microscopy (SEM), thermogravimetry (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and pore-size analysis were conducted in material characterization, and the permeation performances of the carbon membranes were tested with H2, N2, O2 and CO2. Upon the substrate surface modification for fabrication of carbon membranes, such an intermediate gel coating method is superior to the traditional sol–gel treatment because the intermediate gel layer effectively prevented the PFA from penetrating into the macroporous substrate during coating and carbonization treatments so that a thin and uniform carbon layer can be created. The resulting carbon membranes exhibited promising gas permeability and permselectivity.