Replacing petrochemical polymers with biomaterials for biodegradable mulch applications has attracted widespread attention. However, improving film performance and reducing costs remain an issue. In this work, we found that the synergistic effect of sodium alginate and quaternary lignin significantly improved the performance and reduced the cost of poly(vinyl alcohol) films. The water retention, ultraviolet (UV) resistance, heat collection, light transmission, mechanical properties, soil consolidation, and the degradation rates of the composite films were systematically studied. We found that the addition of lignin enabled the film to achieve complete UV resistance, while the sodium alginate synergistically improved the mechanical and water-holding properties of the film. The film improved soil slumping, and the water vapor permeability of the film was 109.2 g•m −2 •day −1 . The degradation of the film was facilitated by the self-degradation properties of sodium alginate and lignin, which degraded 55% after 50 days.

Interfacial evaporation using light-absorbing hydrogels offers efficient solar evaporation performance under natural sunlight, ensuring an affordable clean water supply. However, achieving light-absorbing hydrogels with durable and efficient utilization is still a challenge due to inevitable salt accumulation, a difficult-to-control surface morphology, and poor mechanical properties on the surfaces of hydrogel-based evaporators. In this work, a photothermal sponge-like hydrogel with a 3D interconnected porous structure was constructed using low-cost activated carbon as a photothermal material, as well as a double-network polymer chain as the basic skeleton using a simple foaming polymerization strategy. The sponge-like hydrogel evaporator showed tailored surface topography, adequate water transport, excellent elasticity and toughness, good salt rejection, and thermal localization properties. Under the irradiation of simulated sunlight (1.0 kW/m2), a high evaporation rate of 2.33 kg·m–2·h–1 was achieved. Furthermore, efficient salt self-cleaning behavior was achieved due to the fast ion diffusion within the 3D interconnected porous structures. Even in highly concentrated brine of 15 wt %, continuous and efficient water evaporation was still achieved. The excellent evaporation and salt rejection properties of this photothermal sponge-like hydrogel indicated its promising long-term sustainable utilization in seawater desalination.