Three-level pore structure hydrogels for solar vapor generation

Photothermal evaporation materials have drawn attention owing to their high solar energy utilization. In this work, a series of three-level pore structure hydrogels (TLPSHs) consisting of polyvinyl alcohol (PVA), graphene oxide (GO) or reduced graphene oxide (rGO) are prepared. The hydrogel with PVA crosslinked with rGO shows the most promising properties mainly owing to its three-level pore structure being a combination of nanosized pores for low enthalpy water evaporation and a broad distribution of micronsized pores facilitating water transport into said nanosized pores. When varying the content of rGO/PVA between 5 and 15 wt%, the 10 wt% loading gives the highest water evaporation rate and energy conversion efficient owing to its microstructure combining intra water hydrogen disruption and water transport. The TLPSHs with 88 % porosity has more than 97 % sunlight absorption throughout the UV–Vis-NIR spectrum and stable evaporation rate (1.65 kg m^-2h⁻¹) under 1 sun irradiation. The hydrogel rejects salt by having a higher temperature than the surrounding seawater which causes salt to precipitate in the water rather than on the hydrogel evaporator when the saturation limit is reached. Lastly, the scalability and real life applicability is demonstrated through outdoor experiments on seawater.