Transparent cellulose-lignin films containing Fe³⁺ with high UV absorption for thermal management

In this paper, cellulose-lignin films containing Fe³⁺ were prepared by the codissolution-precipitation method, and the films have high transparency as well as high UV absorption. In this process, kraft lignin chelates with Fe³⁺ and then bonds with cellulose through hydrogen bonding, evenly distributing within the film. The morphological results showed that the kraft lignin chelated with Fe³⁺ bound tightly linked to cellulose within the Fe@cellulose-lignin composite films. The addition of Fe³⁺ made the composite film (C-Fe_-0.7-L) maintain a high transmittance of 66.9 % at 600 nm with excellent UV absorption. Excellent UV absorption performance, completely shielded from both Ultraviolet A (UVA), Ultraviolet B (UVB), and Ultraviolet C (UVC), and improved the thermal stability of the film. Under 100 mW cm^-2 solar irradiation, the temperature of C-Fe_-0.7-L rose rapidly to 60.7 °C. Based on this property, solar energy is transformed into kinetic energy, which realizes the photothermal conversion of solar energy. This work realizes the use of transparent films for energy utilization.