Electrically conductive 3D-printed metal-organic framework-based material for water harvesting

In recent decades, water availability has emerged as a global concern, emphasizing the need for fast, cost-effective, and durable solutions, especially in response to climate change. Airborne moisture and water droplets constitute a substantial freshwater source, especially in arid, low-humidity environments typical of deserts. Atmospheric water harvesting (AWH) using metal-organic frameworks (MOFs) is gaining traction for localised and decentralised applications, such as small-scale plants near freshwater-scarce areas. Electric swing adsorption (ESA) is a potential method for rapidly regenerating adsorbents. However, the effective use of ESA technology depends on three key requirements: high water capture capacity, good electrical conductivity of the adsorbent material, and low energy consumption for rapid water release. Traditional MOFs lack electrical conductivity. Herein, an electrically conductive MOF/graphite monolith was developed using carboxymethylcellulose (CMC) and kaolin as binders and shaped via direct ink writing (DIW). The monolith, shaped as a rectangular prism with a square cross-section and approximately 49 parallel channels, was evaluated for its water vapour adsorption capabilities and regeneration using Joule heating. Water adsorption equilibrium isotherms were measured at 286, 303, and 323 K under pressures up to 12.2, 23.5, and 23.1 mbar, respectively. While graphite and binders influenced water adsorption capacity, the material maintained a high affinity for water. Joule heating of the pre-saturated monolith achieved 323 K within 220 seconds with an electrical power input of 12.5 W. Finally, cyclic adsorption/desorption experiments demonstrated that heating the adsorbent to 323 K while passing a pure N 2 stream is sufficient for complete regeneration.