Bioinspired photothermal polyaniline composite polyurethane sponge: interlayer engineering for high-concentration seawater desalination

High-performance, salt-resistant, and stable wood-based solar evaporator equipped with sodium alginate-based functional skin

Harnessing renewable solar energy for photothermal evaporation and seawater desalination holds significant potential for alleviating freshwater scarcity. However, evaporators reported recently often suffer from limitations in environmental compatibility, salt resistance, and stability. Herein, we report a green and straightforward approach to fabricate a dual-layer solar evaporator (STF-wood) by equipping wood-based materials with a sodium alginate-based photothermal skin. The functional skin, synthesized through the chelation of tannic acid (TA), sodium alginate (SA), and Fe3+, not only exhibits excellent photothermal conversion efficiency but also forms a dense network that restricts the movement of free water, thereby enhancing the localized heat effect. Moreover, the positively charged surface of the skin can prevent the passage of salt ions through the Donnan effect, demonstrating superior salt resistance. STF-wood is capable of operating stably in seawater with an evaporation rate of 1.92 kg m-2 h-1 and maintains a similar rate even after undergoing 5-hour ultrasonic treatment. This work presents a sustainable and efficient solution to compensate for the shortcomings of environmental compatibility and operational stability for solar evaporator.

Self-Generating Zwitterionic Polyurethane Foam for Solar-Driven Water Evaporation in Complex Environments

Solar-driven water evaporation has attracted increasing attention as an environmentally friendly method of water purification/desalination. However, the presence of biofouling and oil-fouling agents in natural water induces channel plugging and significantly decreases its efficiency. In this study, a self-generating zwitterionic polyurethane foam (ZPF) is fabricated by grafting a silylated hydrolysis-induced zwitterionic telomer (Si-HIZ), further spraying TiN/PDMS on the top as a solar evaporation device. The TiN/PDMS serves as a photothermal converter, and the ZPF serves as a water pump. The foam exhibits excellent evaporation performance, with a water evaporation rate of 1.51 kg m-2 h-1 and a photothermal conversion efficiency of 98.56%. When used underwater, the foam forms a hydration layer that effectively inhibits biofilm formation in the channels, allowing solar-driven water evaporation to occur normally after cocultivating in a bacterial suspension (Escherichia coli, Staphylococcus aureus, and Pseudomonas sp.) for 4 days. Moreover, it exhibits good anti-oil-fouling performance (underwater-oil contact angle = 151°) and resists 20 wt % NaCl solutions in solar-driven water evaporation. These results demonstrate that hydrolysis-induced zwitterionic polymers are promising materials for designing water purification/desalination devices, introducing new avenues for applications in complex environments.

Green Synthesis of Polyurethane Sponge-Grafted Calcium Alginate with Carbon Ink Aerogel with High Water Vapor Harvesting Capacity for Solar-Driven All-Weather Atmospheric Water Harvesting

Atmospheric water harvesting (AWH) technology is a new strategy for alleviating freshwater scarcity. Adsorbent materials with high hygroscopicity and high photothermal conversion efficiency are the key to AWH technology. Hence, in this study, a simple and large-scale preparation for a hygroscopic compound of polyurethane (PU) sponge-grafted calcium alginate (CA) with carbon ink (SCAC) was developed. The PU sponge in the SCAC aerogel acts as a substrate, CA as a moisture adsorber, and carbon ink as a light adsorber. The SCAC aerogel exhibits excellent water absorption of 0.555-1.40 g·g-1 within a wide range of relative humidity (40-80%) at 25 °C. The SCAC aerogel could release adsorbed water driven by solar energy, and more than 92.17% of the adsorbed water could be rapidly released over a wide solar intensity range of 1.0-2.0 sun. In an outdoor experiment, 57.517 g of SCAC was able to collect 32.8 g of clean water in 6 h, and the water quality meets the drinking water standards set by the World Health Organization. This study suggests a new approach to design promising AWH materials and infers the potential practical application of SCAC aerogel-based adsorbents.

Facile Preparation of Hydrogel-Coated Surfaces with Antifouling and Salt Resistance for Efficient Solar-Driven Water Evaporation

Hydrogel-based evaporators are a promising strategy to obtain freshwater from seawater and sewage. However, the time-consuming and energy-consuming methods used in hydrogel preparation, as well as their limited scalability, are major factors that hinder the development of a hydrogel-based evaporator. Herein, a facile and scalable strategy was designed to prepare a hydrogel-coated evaporator to realize efficient solar-driven water evaporation. The hydrogel coating layer is composed of a robust 3D network formed by tannic acid (TA) and poly(vinyl alcohol) (PVA) through a hydrogen bond. With the assistance of TA surface modifier, carbon black (CB) is uniformly distributed within the hydrogel matrix, endowing the coating with remarkable photothermal properties. In addition, Fe3+ is deposited on the surface of the hydrogel coating through metal coordination with TA, further improving the light absorption of the coating. Due to the synergistic effect of CB and Fe3+, the hydrogel-coated foam exhibited excellent photothermal properties. The water evaporation rate reached 3.64 kg m-2 h-1 under 1 sun irradiation. Because of the hydration ability of PVA hydrogel and the large porous structure of the foam, the hydrogel-coated foam demonstrated excellent antifouling performance and salt resistance. This study provides a facile method for designing and manufacturing high-performance solar-driven water evaporation materials.