3D thermoresponsive hydrogel with enhanced water uptake and active evaporation for effective interfacial solar steam generation

To mitigate the global water shortage problem, interfacial solar steam generation (ISSG) technology, an eco-friendly desalination technology, has been actively studied. ISSG technology could be appropriate for practical seawater desalination technology when achieving a high evaporation rate. Hydrogels have been used as platforms for solar absorbers because they can provide high evaporation rates. This study proposes a thermoresponsive polypyrrole/alginate/poly(n-isopropylacrylamide) (PAP) hydrogel composed of alginate, poly(N-isopropylacrylamide) (PNIP), and polypyrrole (PPy) for ISSG. The proposed PAP hydrogel has high water absorption and releases water rapidly, which can facilitate active evaporation. Additionally, the PAP hydrogel was fabricated into a three-dimensional (3D) structure to maximize the total area of the water–air interface and in turn maximize solar evaporation. The effect of the 3D geometric shape on the solar evaporation rate was investigated by varying its aspect ratio. The experimental results indicate that a hydrogel with a high aspect ratio gives rise to a progressively higher evaporation rate. The highest evaporation rate was 4.145 kg m−2 h−1 under 1 sun irradiation (solar intensity of 1 kW m−2). To confirm the evaporation rate on the top and side surfaces in a 3D form, a ratio calculation based on the aspect ratio was also performed.