The passive capture of clean water from humid air without reliance on bulky equipment and high energy has been a substantial challenge and has attracted significant interest as a potential environmentally friendly alternative to traditional water harvesting methods. Metal-organic frameworks (MOFs) offer a high potential for this application due to their structural versatility which permits scalable, facile modulations of structural and functional elements. Although MOFs are promising materials for water harvesting, little research has been done to address the microstructure-adsorbing characteristics relationship with respect to the dynamic adsorption-desorption process. In this article, we present a parametric study of nine hydrolytically stable MOFs with diverse structures for unraveling fundamental material properties that govern the kinetics of water sequestration in this class of materials as well as investigating overall uptake capacity gravimetrically. The effects of temperature, relative humidity, and powder bed thickness on the adsorption-desorption process are explored for achieving optimal operational parameters. We found that Zr-MOF-808 can produce up to 8.66 L_H2O kg⁻¹_MOF day⁻¹, an extraordinary finding that outperforms any previously reported values for MOF-based systems. The presented findings help to deepen our understanding and guide the discovery of next-generation water harvesting materials.

Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are two perfluoroalkyl substances that have been shown to result in several adverse health effects, including birth defects, kidney/testicular cancer, as well as liver and thyroid damage. The surfactant nature of PFOS and PFOA in water makes these compounds extremely difficult to remove from drinking water. In this paper, an efficient method to remove PFOS and PFOA from drinking water using linear fluorinated silane-functionalized aluminum oxide hydroxide (γ-AlOOH) nanowhiskers was developed. Filters functionalized with linear fluorinated silanes containing 13–17 fluorine atoms were able to remove >90% of the PFOS/PFOA at a very high flux of 1223 L/m²·h. However, due to the hydrophobicity of these linear fluorinated silanes, high pressure drop was also noted across the membrane thickness during the filtration process. To reduce the back-pressure drop, linear fluorinated silanes with appended hydrophilic poly(ethylene glycol) units were synthesized, and it was further demonstrated that the new hydrophilic linear fluorinated silane dramatically reduced the pressure drop of the γ-AlOOH filter while maintaining 99.9% PFOS and PFOA reduction. Adsorption tests were performed to understand the removal mechanism.

An untethered, soft robot using liquid crystal elastomer (LCE) actuators, onboard power, and wireless Bluetooth control was developed. LCE actuators were thermally triggered using Joule heating and demonstrated an ∼5 N force pull capacity per LCE. A >20% repeatable strain was demonstrated over >100 cycles with minimal loss of strain at high cycle numbers. The LCE actuators were horizontally oriented to maximize conversion of LCE contraction to overall robot movement. A battery and control board were integrated into the body of the robot, which allowed for Bluetooth control of the LCE on/off cycle. System level programming and design were implemented to offset the slow recovery associated with LCE actuators. The multiple LCE actuator legs were programmed to allow individual control of on/off cycles for each leg. LCE leg actuation was alternated between inner and outer legs to provide horizontal movement with minimized loss of motion during the LCE recovery cycle by actuating one set of legs during the recovery cycle of the other set for a maximum movement speed of 1.27 cm/min. Path control was also demonstrated by turning the robot by actuating two LCE legs on one side of the robot. The robot was able to pull up to 1400 g in ideal frictional conditions, allowing the possibility of payload transport, additional battery storage, or onboard sensors. Additional design considerations are discussed to further improve overall robot speed in the future by combining system and material level design considerations.