Sustainable Water Recycling in Arid Greenhouses: Low-Cost Approaches Using Radiation Cooling Synergies

The technology of atmospheric water harvesting, which relies on passive daytime radiative cooling, offers a viable method to obtain clean and circulating water for greenhouses in arid areas. However, efficient radiative cooling materials often entail complex structures or high costs. This study addresses the sustainability challenge of water circulation in arid-region greenhouses by proposing a low-cost water harvesting solution based on synergistic radiative cooling and bionic structures. A composite cooling material with a production cost of only 5.23 USD/m² was developed using simple spray-coating techniques. The material achieved a maximum temperature reduction of 9.7 °C below ambient temperature at night. Through heterogeneous wettability patterning, the maximum water collection capacity reached 7.53 L·m^–2·day^–1 (work for 6 h every day) under stable laboratory conditions and 4.08 L·m^–2·day^–1 in greenhouse environments during nighttime. Post-3-month testing revealed minimal performance degradation, with material emissivity showing a mere 1% decrease and hydrophobic surface contact angle variation remaining within 5%. This research provides a cost-effective, durable, and sustainable water harvesting strategy for agricultural greenhouses in arid regions.