Hierarchically porous sponge with low evaporation enthalpy for high-efficiency solar desalination: robust salt resistance and mechanical durability

The advancement of sustainable solar-driven interfacial evaporation systems for seawater desalination continues to be hindered by intrinsic trade-offs among rapid water transport, effective salt rejection, and mechanical robustness in conventional photothermal materials. In this study, a hierarchically porous   poly(vinyl alcohol)-propionaldehyde-glutaraldehyde sponge (PVPG)   was synthesized via a mixed-acetal reaction. The three-dimensionally interconnected hierarchical pore network significantly enhanced capillary-driven water transport. The PVPG/CB/CMC sponge (PCB) was fabricated by integrating hydrophobic carbon black (CB) and hydrophilic sodium carboxymethyl cellulose (CMC) into the PVPG sponge. The hydrophobic-hydrophilic synergy between CB and CMC optimized water state and reduced the evaporation enthalpy of water. This enabled the evaporator to achieve an impressive evaporation rate of 3.56 kg m −2 h −1 under 1 sun irradiation. Simultaneously, spontaneous salt crystallization inhibition through the Donnan effect ensured that the system maintained a long-term evaporation rate of 3.08 kg m −2 h −1 even in 20 wt% high-salinity brine. Importantly, covalent crosslinking between CMC and the sponge matrix endowed the composite with exceptional mechanical durability, preserving structural integrity after 100 compression cycles, thereby addressing the brittleness limitation commonly observed in polyelectrolyte-based evaporators. This innovative architecture establishes a new framework for designing robust solar evaporators that integrate high efficiency, salt resistance, and structural stability, providing a practical solution for applications in challenging marine environments.