Fabrication Of High Performance UiO-66 Gas Separation Membrane With Two-Dimensional Transition Metal Dichalcogenides As Metal Source

Membrane-based separation has attracted much attention because of its unique advantages such as low energy consumption,high operation efficiency,and relatively low cost.Zirconium-based MOF?Zr-MOF?membranes have become the focus of people's interest due to their tailorable pore aperture,adjustable adsorption behavior enabled by functional group decoration and ligand/cluster-missing defect regulation as well as extraordinary chemical/thermal stability.In recent years,most researches have been devoted to improving their applications including gas separation,pervaporation,nanofiltration and electrochemical ion separation.Nevertheless,it has remained a great challenge to further improve the separation performance of Zr-MOF membranes due to very limited available zirconium sources and heating modes.Conventionally,the difficulty in complete avoidance of undesired adverse reactions makes it impossible to accurately control nucleation and growth kinetics of Zr-MOF crystals on porous substrates under solvothermal conditions.Although adopting post-modification may improve their separation performance to a certain extent through intercrystalline defect patching,we prefer to improve the intrinsic separation performance of polycrystalline Zr-MOF membrane via simple optimization of the microstructure.In this study,we mainly conducted the following research:1)we first reported the use of layered ZrS₂ as zirconium source of Zr-MOF powders.The obtained powder exhibited a typical octahedral morphology,high crystallinity and ideal thermal stability.We verified the feasibility of layered ZrS₂ as a zirconium precursor.2)Moreover,by combining layered ZrS₂ precursor with tertiary solvothermal growth,we successfully prepared polycrystalline UiO-66 membrane exhibiting unprecedented CO₂/N₂selectivity on porous?-Al₂O₃ substrate.This UiO-66 membrane prepared under the optimal conditions showed preferential infiltration of CO₂(permeation:3.8×10^-8 molm^-2s^-1Pa^-1),resulting in an unprecedented ideal separation selectivity of CO₂/N₂?31.3?,which was higher than other unmodified polycrystalline MOF membranes measured under the same conditions.In addition,the membrane also possed a high long-term operating stability,and the penetration rate and selectivity of CO₂/N₂ did not decrease significantly within 24 h.3)On the one hand,the use of layered ZrS₂,a representative of transition-metal dichalcogenides?TMDC?,as zirconium source during was found to be indispensable for improving the selectivity of the CO₂/N₂ gas pair of UiO-66 membrane;on the other hand,tertiary solvothermal growth was conducted and proved essential for reducing grain boundary defects.As far as we know,the CO₂/N₂ selectivity reported in this study was the highest among all pristine polycrystalline MOF membranes measured under ambient conditions.Last but not least,our study highlighted the importance of concurrent metal source and fabrication process innovation in performance enhancement of polycrystalline MOF membranes.