Construction of lignin crosslinked nanocellulose 3D-printed solar evaporators for efficient seawater desalination via hydroxyl-yne click chemistry

Developing lignin-nanocellulose-based solar evaporators is crucial for sustainable seawater desalination, yet challenges remain, including limited photothermal efficiency, weak water transport, and lignin leaching that compromises structural integrity. Herein, a 3D-printed solar evaporator was fabricated by covalently crosslinking alkali lignin (AL) and TEMPO-oxidized cellulose nanofibers (TOCN) via hydroxyl-yne click chemistry using dipropiolate-terminated polyethylene glycol (DA-PEG) as a green crosslinker. The resulting lignin-DA-PEG-nanocellulose (LPNC) inks showed excellent shear-thinning behavior suitable for Direct Ink Writing (DIW), enabling precise fabrication of highly porous, interconnected foams that promoted directional water transport. The optimized LPNC-3 porous foam retained 190.50 ± 31.25 mg AL per 1000 mg TOCN, showing efficient lignin immobilization and structural stability. It exhibited a high water absorption rate (1147.2 ± 65.7 %), strong alkali resistance with minimal lignin leaching (2.2 ± 0.3 %), and enhanced photothermal efficiency with reduced water evaporation enthalpy (1781 ± 50 J·g^-1). Under 1 sun (1 kW·m^-2) illumination, the evaporator achieved a high evaporation rate of 1.64 kg·m^-2·h^-1 and 88.09 % solar-to-vapor efficiency. It maintained stable performance over 10 cycles and effectively desalinated artificial seawater to meet WHO standards. This study offers a green and efficient strategy to enhance the durability and performance of lignocellulose-based solar evaporators for practical water purification applications.