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Fonds National Suisse de la Recherche Scientifique (FNSRS) 2021

Adsorption on tailored nanostructures and the rational design of hydrogels for atmospheric water harvesting

Atmospheric Water Harvesting Hydrogels

Titre : Adsorption on tailored nanostructures and the rational design of hydrogels for atmospheric water harvesting

Numéro  : 194367

Début/Fin : 01.03.2021 - 28.02.2023

Requérant  : Graeber Gustav
Institution de Recherche : Department of Mechanical Engineering Massachusetts Institute of Technology

Résumé partiel
Providing sufficient fresh water to the world’s population is one of the key challenges of the 21st century. Especially for arid, rural regions without access to liquid water and without reliable infrastructure, decentralized, sorption-based atmospheric water harvesting (AWH) is a promising method to address water scarcity. Current research on sorption materials for AWH focusses on hygroscopic salts, metal organic frameworks (MOFs) and, recently, hydrogels. Despite the intense research effort, sorbents are missing that combine operation at low relative humidity, with a large water uptake, low regeneration temperatures and fast sorption rates. Overall, it is not sufficiently understood how to rationally design the sorbent for best AWH performance, including all aspects of material, component and system level challenges. Due to their easily tunable properties, low cost and scalability, hydrogels are attractive candidate materials for our project.In the proposed project, we aim to develop a sorption material with unique tailored nanostructures, a hierarchical topography and sponge-like properties for AWH applications. We envision that a nanotextured hydrogel can be the ideal candidate for AWH, since tailored nanostructures in the material enable vapor liquification based on capillary condensation, while the hydrogel acts as a sponge that swells and holds large quantities of the condensed liquid water. Simultaneously, hydrogels can be tuned to quickly release the incorporated water triggered by an external stimulus such as a temperature increase. We will systematically study the synthesis of nanotextured hydrogels and investigate how the hydrogel properties affect the AWH performance.We will synthesize millimeter-sized hygroscopic hydrogel spheres with a hierarchical network of microchannels and nanopores. The envisioned hydrogel topography spanning over three orders of length scales enhances vapor transport kinetics due to facile vapor diffusion between the spheres and in the microchannels, while simultaneously allowing for enhanced vapor liquefication within the nanopores due to capillary condensation. To achieve this specific topography, we will systematically vary the hydrogel composition and synthesis parameters such as the synthesis temperature, the concentration of cross-linker, solvents, and monomer, and also explore variations in the functional groups. We will characterize the resulting changes in the material properties by measuring density, pore size distribution, and equilibrium water vapor uptake as a function of relative humidity and temperature. We will test the samples with the most promising material properties in an AWH prototype system to assess the resulting system performance measured by the achievable daily water production. We will characterize the synthesized hydrogels with respect to their structure by scanning electron microscopy and test the wettability with a goniometer. We will measure the adsorption characteristics by thermogravimetric vapor analysis.

Mots clés : Hydrogels ; Wetting ; Atmospheric water harvesting ; Capillary condensation ; Sponges ; Nanostructures ; Adsorption

Fonds National Suisse de la Recherche Scientifique

Page publiée le 20 août 2022