Bio-based chitosan/pulp fiber/carbon nanotubes sponge-like porous hydrogel for solar interfacial evaporation

A porous hydrogel was fabricated via freeze-crosslinking without freeze-drying. • Pulp fibers replace costly nanocellulose as a low-cost reinforcing skeleton. • Pulp fibers reinforce the chitosan network against collapse during evaporation. Solar interfacial evaporation holds great promise for seawater desalination and wastewater treatment, yet the development of low-cost, efficient, and structurally stable evaporators remains challenging. Herein, a sponge-like porous hydrogel (CAFC) was fabricated from chitosan (CS), pulp fibers (PF), and carbon nanotubes (CNTs) through glutaraldehyde (GA) cross-linking and freeze-induced pore formation. The Schiff-base cross-linked CS network provided structural integrity, while the PF scaffold facilitated water transport and CNTs enabled efficient light harvesting and photothermal conversion. The optimized CAFC-4 hydrogel exhibited over 90% light absorption across 250–2500 nm and achieved a water evaporation rate of 2.66 kg m⁻² h⁻¹ with a solar evaporation efficiency of 84.4% under 1 sun irradiation. Even in 10 wt% NaCl solution, CAFC-4 maintained an evaporation rate of 1.93 kg m⁻² h⁻¹ and showed stable performance during cyclic and continuous evaporation tests. The evaporator also effectively purified wastewater containing methylene blue and Orange I, with no characteristic absorption peaks of the dyes observed in the UV–vis spectra of the collected water. Under natural sunlight, CAFC-4 achieved a maximum evaporation rate of 2.06 kg m⁻² h⁻¹ during outdoor simulated seawater desalination, with rejection efficiencies exceeding 99.9% for the major salt ions. These results demonstrate a simple and scalable strategy for constructing low-cost, biomass-based solar evaporators for water purification and desalination. Download: Download high-res image (233KB) Download: Download full-size image