Capturing of atmospheric water in arid areas by iron hygroscopic hydrogel for agricultural automation
In response to extreme weather conditions,such as deserts and plateaus with scarce precipitation,agricultural development is deeply constrained by the environment.However,the scientific use of moisture and solar energy can effectively alleviate the problem of insufficient crop yields.Here,through the coordination of Fe 3d electron empty orbits with N/O lone electron pairs,active sites for water adsorption are formed,and then these sites construct a hygroscopic hydrogel to capture atmospheric water.The hydrogel is composed of nanoparticles(around 5 nm)with a porous structure;the diameter of the pores is 1-100 μm.The hydrophilicity test result shows that the contact angle is 10.2°,suggesting a super hydrophilic surface of the Fe hydrogel.The X-ray diffraction data indicates that the hydrogel has a weak crystallinity;only two peaks are observed for the dehydrated hydrogel.When the hydrogel absorbs moisture,the peak located at 14° disappears.Place the anhydrous hydrogel in an ambient environment,which can absorb moisture at a rapid rate.The adsorption equilibrium curve shows that the hydrogel can capture 1.16 times its own weight of moisture at 15℃and 60％relative humidity(RH),and the water uptake values are 0.82 and 3.50 g/g at 30％RH and 90％RH,respectively.Besides,the hydrogel achieves full dehydration only at 40℃,which is lower than most adsorbents,such as silica gel and calcium chloride,implying minimal energy consumption for reuse.Before moisture harvesting,the hydrogel is in a film structure,while in the hydrous state,it will transform into a liquid.Through adsorption and desorption cycle tests,the hydrogel remains stable for more than 60 cycles.During the process of adsorption and desorption,the structural changes do not affect the water uptake,proving its well-developed self-healing ability.By integrating the hydrogel into a water production assembly,atmospheric water can be collected.The results show that the concentration of all ions in the liquid water reaches the WHO drinking water standard.The content of Fe and ethanolamine is around 0.08 and 0.01 mg/L,respectively,proving that the collected water can be used for agricultural irrigation.Designing the agricultural automatic water supplement system with hydrogel,it couples with the temperature sensor,humidity sensor,and photosensitive sensor to monitor the shed environment in real time,so as to automatically control the plant growth environment.The hydrogel harvests moisture from the air and transfers the gaseous water to liquid.With the aid of solar energy,the liquid water can be desorbed and stored in a tank.The water can accurately flow to the roots of plants through the flowing pipeline and spray device.The experimental results display that the hydrogel-embedded greenhouse can increase the RH from 55％to 88％,reaching the standard for plant growth.When sowing pea seeds,which can grow in low humidity environments,the peas continued to grow over 30 cm after automatic irrigation with atmospheric water in an arid area.In all,our designed automatic agricultural system is capable of collecting freshwater from the atmosphere to irrigate crops,reducing agriculture's dependence on freshwater and helping to alleviate water scarcity in arid areas.
hygroscopic hydrogelatmospheric wateratmospheric water harvestingarid regionssmart farmsolar energy
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