Arginine-functionalised hydrogels as a novel atmospheric water-harvesting material

Atmospheric water harvesting is a versatile but underutilised source of potable water. In this study, a poly(HEMA-co-PEGMA) linear copolymer and PEGDMA-crosslinked hydrogel were post-functionalised using Steglich esterification to attach l-arginine onto HEMA side chains. The water-harvesting properties of the resulting polymers were then tested. The functionalised polymers had a water uptake of 130-150 mg g⁻¹ water after 24 hours. The thermal phase transitions were around 60-80 °C, however this can be easily adjusted by varying composition and degree of functionalisation. Notably, there was a significant decrease in the rate of water uptake after 2-3 hours. This property was further explored with a rapid cycling test, in which 70-minute water-harvesting cycles yielded 2 g water per gram of polymer after 24 hours. The data presented in this body of work showcases the water-harvesting potential of guanidinium moieties, as well as highlighting the broad scope of materials and synthetic methods that could be used for developing water-harvesting polymeric materials.