Double-layered hydrogels based on phase change material and pen ink for continuous and efficient solar-driven seawater desalination

A novel double-layered hydrogel based on the polyacrylamide matrix, pen ink, and phase-change microcapsules was developed to construct a hydrogel-based evaporator for efficient and continuous seawater desalination. The n-eicosane (core)@crystalline TiO2 (shell) phase-change material microcapsules was fabricated by using an interfacial polycondensation method, and the resulting phase-change microcapsules obtained a considerably high latent-heat capacity of 187 J·g−1. The upper layer of the hydrogel exhibits a high solar absorptivity of over 90 % due to the introduction of pen ink as a solar absorber, which helps the hydrogel-based evaporator to gain an excellent capability to absorb and convert photothermal energy. A high evaporation efficiency of 93.89 % was obtained for the developed hydrogel-based evaporator along with a high evaporation rate of 1.85 kg·m−2·h−1 under one-sun illumination. The phase-change microcapsules dispersed in the lower layer of the hydrogel can act as a latent heat storage unit to store a great quantity of photothermal energy through melting phase change by the PCM core. This imparts a consecutive evaporation capability to the developed hydrogel-based evaporator. As a result, the water production was increased by 11 % under 50-min one-sun illumination for and 50-min non-illumination.