Flexible and Highly Efficient Bilayer Photothermal Paper for Water Desalination and Purification: Self-Floating, Rapid Water Transport, and Localized Heat

In view of the sustainable and environmentally friendly characteristics of solar energy, solar water evaporation has been identified as a promising approach to mitigate the global water crises. However, it is still a great challenge to develop a portable, flexible, scalable, and high-performance solar water evaporation material. Herein, a bilayer-structured solar water evaporation material consisting of a top multiwalled carbon nanotube (MWCNT) layer and a bottom polyphenylene sulfide/fibrillated cellulose (PPS/FC) paper was fabricated via a simple vacuum filtration technology for efficient solar water evaporation. The MWCNT layer performs as a light absorber with a high solar absorptance (∼93%) in the wavelength range from 400 to 1200 nm and good light-to-heat conversion capability, while the bottom layer (porous network-structured PPS/FC paper) exhibits excellent water transporting ability, high temperature stability, and good thermal insulating capability (0.0467 W m^-1 K^-1). Benefiting from the above advantages, an attractive water evaporation rate of 1.34 kg m^-2 h^-1 was achieved with near ∼95% efficiency under 1 sun irradiation (1 kW m^-2). Moreover, the MWCNTs@PPS/FC paper maintains high solar evaporation efficiency after several cycles, indicating long-term durability and good reusability. Moreover, the collected clean water using the MWCNTs@PPS/FC paper from seawater of different salinities, simulated wastewater samples with different pH values or containing heavy metal ions, as well as industrial dyes, satisfy the drinkable water standard (defined by WHO), demonstrating excellent seawater desalination and wastewater purification capability. The advanced performances of the MWCNTs@PPS/FC paper could inspire novel paradigms of solar-driven water evaporation technologies in drinkable water collection.