Sunlight-Driven Heating/Cooling of Flexible MOFs for Energy-Saving Propane Adsorption

Temperature swing adsorption is essential to purifying raw materials/separating products in a broad range of industrial applications, but periodic heating/cooling of the adsorption bed is energy- and time-consuming. This work reports a sunlight-driven temperature swing system with flexible metal–organic frameworks (FMOFs) for C3H8 adsorption, integrating the wavelength-selective utilization of sunlight and the thermoresponsive gate-opening effect of MOFs to minimize the energy consumption of heating and cooling adsorbents. During adsorption, the hierarchically porous poly(vinylidene fluoride-co-hexafluoropropene) [P(VdF-HFP)HP] coating is covered on the top of the adsorption bed, acting as a radiative cooler to efficiently reduce adsorption temperature under sunlight radiation. Molecular-pocket-shaped pores of FMOFs are open under this temperature, and C3H8 can diffuse into these specific pores, interacting with adsorption sites. For desorption, the adsorption beds are turned upside down in which adsorbents are directly exposed to sunlight for heating and releasing C3H8. Under this temperature, the molecular-pocket-shaped pores of FMOFs are closed, which coordinate with heating for efficient desorption. The results demonstrate the adsorption/desorption cycles within only a range of 20 °C by this system, and real outdoor sunlight has also been applied to verify its feasibility in C3H8 capture.