Highly salt-resistant and efficient dynamic Janus absorber based on thermo-responsive hydroxypropyl cellulose

Recent advances in interfacial solar steam generation have made direct solar desalination a promising approach for providing cost-effective and environmentally friendly clean water solutions. However, developing highly effective, salt-resistant solar absorbers for long-term desalination at high efficiencies and evaporation rates remains a significant challenge. We present a Janus hydrogel-based absorber featuring a surface modified with thermo-responsive hydroxypropyl cellulose (HPC) and a hydrogel matrix containing photothermal conversion units, MXene, specifically designed for long-term seawater desalination. At the lower critical solution temperature, HPC undergoes phase separation, which results in the formation of a rough hydrophobic surface. This process creates a Janus evaporator structure that exhibits a high evaporation rate, excellent salt resistance, and long-term stability. Consequently, the hydrogel absorbers achieve an impressive evaporation rate (3.11 kg m^-2 h^-1) under one-sun irradiation. Salt residues are deposited only at the edges of the super-hydrophilic bottom. This process ensures long-term evaporator stability for continuous solar evaporation (>30 hours) in simulated seawater at an average evaporation rate of ∼2.58 kg m^-2 h^-1. With its unique structural design, achieved via a straightforward design process, the flexible Janus absorber serves as an efficient, salt-resistant, and stable solar steam generator for direct solar desalination.