Zeolitic imidazolate framework-8 nanoparticles coated composite hollow fiber membranes for CO2/CH4 separation

Metal-organic frameworks, particularly zeolitic imidazolate frameworks (ZIFs), are promising nanomaterials for gas separation applications owing to their controllable morphologies, high surface areas, low cost, and ease of synthesis. Here, we demonstrate coating of ZIF-8 nanoparticles (NPs) on the lumen of graphene oxide (GO)/ polysulfone (Psf) hollow fiber membranes (HFMs) augments carbon dioxide (CO2) and methane (CH4), commonly found in biogas with CO2 as an impurity, separation. GO/Psf HFMs were fabricated using the non solvent induced phase separation technique, in an in-house built pilot plant. Then, the ZIF-8 precursor solutions were passed through these HFMs for different time intervals in a sequential manner. To confirm ZIF-8 NPs coating, these HFMs were characterized for morphology, functionality, and microstructure. Further, pure gas separation studies carried out using ZIF-8 NPs coated HFMs exhibited CO2 permeance of 80.17 GPU and an ideal CO2/CH4 selectivity of 14.32, which is similar to 123% higher than the uncoated HFMs. In the mixed gas separation studies, CO2/CH4 selectivity of 30.66 was recorded for ZIF-8 NPs coated HFMs, which is 120% higher than the uncoated HFMs, with CO2 permeance of 50.89 GPU. Long-term stability studies with ZIF-8 NPs coated HFMs demonstrated that these membranes could perform gas separation for as long as 48 h without losing their performance. We have shown the CO2/CH4 separation performance of HFMs is significantly improved by ZIF-8 NPs coating, easily done by sequential flow of reagents. Thus, this study proves in-situ ZIF-8 NPs coated membranes have a great potential to separate CO2/CH4 mixtures with enhanced selectivity and longevity.