Atmospheric water harvesting on MIL-100(Fe) upon a cyclic adsorption process

Abstract

The main objective of this study was the design of an efficient adsorptive process to extract water from thin air, based on MIL-100(Fe), which is a promising material in water adsorption-related processes. Indeed, equilibrium and dynamic studies were performed to evaluate the suitability of this adsorbent. CO2, N2, and O2 adsorption equilibrium isotherms were measured at three different temperatures, and CO2 was the gas that presented a higher affinity towards MIL-100(Fe). H2O adsorption equilibrium isotherms follow a Type VI isotherm, showing two steps (0.21 < P/Po < 0.30 and 0.36 < P/Po < 0.40) attributed to the presence of two different cavities (25 and 29 Å) on its structure. The obtained data were regressed against adsorption equilibrium isotherm models (Langmuir model, Dual Ising-Single Langmuir model, and Polanyi's potential theory). The H2O adsorption dynamic behavior was in agreement with the expected from the H2O vapor adsorption equilibrium isotherms. Furthermore, the dynamic adsorption behavior of water adsorption in fixed-bed experiments was well predicted by the developed model. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analysis revealed a high regeneration capability during the adsorption/desorption cycles. Additionally, the structure remains stable during the water vapor contact and after exposure at different temperatures. Temperature Swing Adsorption (TSA) process, with a column volume of 0.35 m3, allowed maximum H2O productivity of 86.8 l·day−1 for MIL-100(Fe).