Abstract
ZIF-8 membranes were fabricated by a two-step procedure consisting of (1) a flexible and simple spray coating process to deposit uniform ZnO layers on different supports and (2) subsequent solvent-free transformation of the ZnO layers into dense ZIF-8 membranes by a vapor-solid reaction. The spray coating offered superior flexibility regarding the choice of support and yielded even and homogeneous ZnO layers with thicknesses of 5-10 mu m on non-porous crude steel plates, porous alpha-Al2O3 and porous stainless steel discs. The texture of the ZnO layer did not depend on the texture of the underlying support. The conversion of the ZnO to ZIF-8 via vapor-solid reaction of gaseous 2-mlm and ZnO was performed without the use of a solvent and no further activation or seeding was applied. Except the spray coated ZnO, no further zinc species were added to synthesize the ZIF-8 layers. The particle size, morphology and the degree of intergrowth were tunable by adjusting the temperature of the vapor-solid reaction in a range of 25-130 degrees C. The variation of the reaction time for the fabrication of membranes on alpha-Al2O3 discs at 80 degrees C resulted in well-intergrown layers without visible defects. The ideal gas selectivities increased with increasing temperature and the best membrane showed a H-2 permeance of 2.3.10(-8 )mol m(-2) s(-1) Pa-1 at 100 degrees C and ideal selectivities of H-2/CO2, H-2/N-2 and H-2/CH4 of 5.4, 7.1 and 9.5.