Solar-driven polypyrrole-decorated polyester filter cotton for efficient desalination and zero liquid discharge

Interfacial solar evaporation technology (ISET) holds significant promise for mitigating freshwater scarcity through solar-driven desalination. However, the advancement of solar evaporators that employ straightforward methods to enhance the evaporation rate (ER), improve salt resistance, and facilitate the collection of salt crystals poses a considerable challenge for ISET. In this study, we developed a photothermal material (PTM) named polypyrrole-polyester filter cotton (PPy-PFC), achieved by coating polypyrrole (PPy) onto polyester filter cotton (PFC) using a simple solution immersion technique. The PPy-PFC effectively reduces the enthalpy of water evaporation, resulting in an impressive ER of 2.44 kg m⁻² h⁻¹ under 1-solar intensity. The polyester fiber bundle (PFB) incorporates vertical water supply channels and acts as a water pump. When multiple PFBs are employed to deliver water to the PPy-PFC, it can consistently evaporate 20 wt% saltwater with an ER of 1.95 kg m⁻² h⁻¹. This remarkable salt resistance performance is attributed to the ample water supply delivered by the multiple PFBs, which facilitates the diffusion backflow of salt ions. Additionally, by positioning a single PFB at the center of the PPy-PFC, a unidirectional saltwater-flowing evaporator is constructed. Crystallized salt forms around the single PFB with a radius of 1.5 cm, achieving zero liquid discharge (ZLD). This study presents a novel strategy for designing solar evaporators that improve ER by reducing the enthalpy of water evaporation, enhancing salt resistance through sufficient water supply, and enabling the collection of salt crystals via the establishment of a unidirectional saltwater-flowing channel.