Kinetics of Water Vapor Adsorption and Desorption in MIL-101 Metal–Organic Frameworks

Abstract

The adsorption−desorption isotherms and relaxation curves of water in chromium terephthalate metal−organic frameworks (MOFs), MIL-101, were measured by the gravimetric method at 298 K and 1 atm. The obtained isotherms were compared to those obtained by the volumetric method, which showed good agreement. The measured isotherms exhibited three-step and two-step curves during adsorption and desorption, respectively. The hysteresis between adsorption and desorption isotherms was not pronounced, and the difference in relative humidity between the adsorption and desorption isotherms was 0.05−0.10 at identical adsorbed mass. Regarding the water adsorption relaxation curves, when the relative humidity was varied stepwise from 0.40 to 0.47 and the water supply rate was small, the relaxation curves could be fitted to two straight lines, indicating that, initially, the middle cages filled with water, followed by the large cages at a different adsorption rate. When the relative humidity was changed stepwise from 0.40 to 0.90 and the water supply rate was large, the relaxation curves could be fitted to a single straight line until the equilibrium state, and the relaxation time was about 40 s. The kinetics of water transport inside MIL-101 is strongly dependent on its unique pore structure and hydrophilicity−hydrophobicity spatial distribution.

A Thermal Management Strategy for Electronic Devices Based on Moisture Sorption-Desorption Processes

“…This can be ascribed to the fact that the vapor transport on the gas side at the air-coating interface is the rate-controlling step of the desorption process. 26 Namely, as outlined and validated in the previous literature, 27 the influence of solid-side diffusion and local disequilibrium between the free and adsorbed moisture, deemed as proportional to the coating thickness, are negligible in our experiments (more details in Note S2). Under this circumstance, the desorption rate of the coating layers can be expressed by a simplified model:…”

Polydimethyl siloxane/MIL-101 Composites for Enhanced Toluene Adsorption in the Presence of Humidity

“…37,64 Water adsorption isotherm for MIL-101 displays a distinct two-step process, firstly from 40 to 45% P/P 0 , and secondly, from 45 to 50% P/P 0 which confirms the presence of two mesoporous cages with different aperture sizes. 38 After 0.25 hr coating time, the promising MIL-PDMS-Sigma-0.25 exhibited a 10% higher uptake in its Type-V water uptake isotherm compared with the pristine form, whilst also exhibiting a 10% increase in the isotherm inflection point from 45 to 55% P/P 0 . 65 The inflection in P/P 0 is defined as the point when water adsorption uptake rises steeply due to their complete occupation inside the smaller pore cavity and an indicator of their transfer into the mesoporous cages beyond the P/P 0 .…”

“…MIL-101 is a MOF with high surface area, ready tunability, excellent hydrothermal stability 26,27 and is frequently studied for VOC capture. [28][29][30][31] Consistent with these characteristics, MIL-101 also showed high water adsorption capacity, implying high hydrophilicity [32][33][34][35][36][37][38] and lack of native hydrophobicity desired for VOC removal in humid environments. Suggested surface modification strategies to increase MOF's hydrophobicity include ligand functionalization with hydrophobic moieties, 39,40 in-situ hydrophobization 41 and post-synthetic modification (PSM).…”

Green Electro-Synthesized MIL-101(Fe) and Its Aspirin Detoxification Performance Compared to MOF-808

“…In MIL-101(Fe), the absorption comes from water molecules coordinated with the iron trimeric unit, while in the ligand comes from the -OH from the carboxylic moieties. Yanagita et al [52] has proven that MIL-101 is able to absorb water from humidity at room temperature and atmospheric pressure. Therefore, even after previous activation, MIL-101(Fe) still contains water due to the presence of water molecules coordinated with the central of Fe(III) and also because of the possibility of adsorption of water molecules in the air after the activation process.…”