Polyester fibre sphere solar evaporator for efficient interfacial solar desalination

Interfacial solar-driven desalination (ISDD) offers a promising solution to global freshwater shortages. Challenges such as complex manufacturing, high costs, low evaporation rates, and poor salt resistance have hindered its adoption. This study introduces a spherical solar evaporator, PPy-PFS, created by coating polyester fibre spheres (PFS) with polypyrrole (PPy) via solution immersion. The black PPy-PFS achieves an evaporation rate of 2.10 kg m –2 h –1 under 1 sun. With strong water supply and storage, it maintains a stable rate of 1.61 kg m –2 h –1 in 25 wt% saltwater. Long-term indoor tests (30 days, 8 h per day) show PPy-PFS's durability in desalinating 20 wt% saltwater. Producing 1 m 2 of PPy-PFS costs about 25.97 $, with a cost-effectiveness of 80.86 g h –1 USD –1 . Outdoor tests reveal that 1 m 2 of PPy-PFS can produce around 10 kg of freshwater daily from 20 wt% saltwater. Continuous evaporation of highly concentrated saltwater results in salt crystallization, achieving zero liquid discharge (ZLD). This simply designed, cost-effective, efficient, and salt-resistant PPy-PFS evaporator provides a potential strategy for mitigating freshwater shortages.