Solar interfacial evaporation hydrogel with distributed packaging of phase change materials for continuous desalination

Abstract

Solar-driven interfacial evaporation (SDIE) is now widely recognized as a promising solution to the global freshwater crisis. This recognition stems from its low energy consumption and environmentally friendly characteristics. However, the performance is hampered by variations in solar intensity due to daily cycles and weather changes, significantly affecting evaporation rates and freshwater yield. One of the most effective strategies for addressing this issue is to integrate solar energy storage materials with SDIE. In this study, we integrated a phase change energy storage material (Na₂SO₄·10H₂O) into a solar evaporator encapsulated within a dual-network hydrogel composed of sodium alginate and polyacrylamide. Additionally, Chinese ink was utilized as a light absorber to improve the efficiency of photo-thermal conversion. This hydrogel-based evaporator effectively stores surplus solar energy and releases latent heat, enabling continuous and efficient seawater desalination even under low-light conditions. Experimental findings indicate that the evaporation rate was highly 2.72 kg·m⁻²·h⁻¹ under 1 sun, and the evaporation efficiency was 92.8 %. Notably, the phase change material exhibits significant heat storage capacity, with a phase change latent heat of 181.42 J·g⁻¹. Consequently, In the absence of solar radiation, the evaporation rate remains sustained at 1.25 kg·m⁻²·h⁻¹, representing a 16.8 % increase in freshwater production compared to hydrogels lacking phase change materials. Moreover, the hydrogel-based evaporator demonstrates robust performance in purifying total dissolved solids (TDS) and major salt ions from seawater, showcasing exceptional durability under high acid-base and salinity conditions. This study underscores a promising pathway towards sustainable and efficient desalination processes utilizing intermittent renewable solar energy.