MMMs were fabricated by doctor blading of DMF-based solutions of polysulfone (PSU) and MIL-116(Ga)-formate, giving the corresponding MMMs with 5, 10, 15, and 20 wt.% loading as well as a pure polysulfone membrane was prepared. The films are casted onto a soda-lime glass slide using a micrometre adjustable knife and are then dried in a vacuum furnace at 120 °C. distribution over a large area, and the zoomed in area shows that there is no agglomeration. The particles are freely "floating" in the polymer and the polymer is highly transparent after casting. c) SEM image of a druse-like particle that has been cracked-open during SEM preparation of the MMM (breaking the MMM after freezing with liquid N 2 ). The particle shows nanoscopic lose particulate in the middle, while densified crystalline needles form a hollow-shell particle. d) A schematic of the hollow-sphere druselike particle, separating CH 4 from He. It further shows the surface of MIL-116(Ga) with the dangling -COOH groups forming H-bridges to the sulfone groups of PSU , offering important polymer-filler interaction.