Research subject: Solar desalination based on interfacial evaporation has emerged as a promising strategy for mitigating global freshwater shortages due to its high solar-to-vapor conversion efficiency, low environmental footprint, and suitability for remote or off-grid deployment. However, salt accumulation at the evaporation interface, particularly from highly soluble species, significantly reduces vapor generation and undermines long-term system stability. Therefore, developing self-cleaning structures capable of maintaining continuous water transport while preventing salt crystallization is essential for practical field operation.
Research approach: This study develops a self-cleaning solar evaporator based on engineered sycamore wood and systematically evaluates its desalination performance. For this purpose, four systems are designed and fabricated, including a reference sample without artificial channels and three systems incorporating vertical channels with diameters of 1.0, 1.5, and 2.0 mm, which are evaluated under controlled one-sun irradiation using NaCl solutions representative of seawater (3.5 wt.%) and highly saline water (20 wt.%). Water transport behavior, ion migration mechanisms, and condensate quality are assessed through continuous evaporation experiments and ion concentration analyses for Na⁺, Mg²⁺, K⁺, and Ca²⁺. Additionally, operational stability is examined through multi-cycle repeatability tests.
Main results: The WSE-1.5 device exhibits the highest steady evaporation rates, achieving 2.48 and 2.04 kg.m⁻².h⁻¹ in 3.5 wt.% and 20 wt.% NaCl solutions, respectively. This favorable performance is attributed to the ion exchange between the natural microchannels of the wood, which contain higher concentrations of salt ions, and the drilled millimeter-scale channels with lower concentrations. The difference in hydraulic conductivity between these pathways drives salt migration from the millimeter-scale channels to the microchannels and subsequently into the bulk water. The engineered structure also maintains timely water replenishment at the evaporation surface, ensuring stable vapor production. The condensate quality meets World Health Organization (WHO) and Environmental Protection Agency (EPA) potable water standards, with significantly reduced concentrations of Na⁺, Mg²⁺, K⁺, and Ca²⁺. Repeatability tests confirm that WSE-1.5 retained its performance after 15 cycles with negligible degradation. Overall, the proposed wood-based evaporator offers an efficient, robust, and cost-effective solution for desalinating saline waters in challenging environments.