Generation of H2O2 and halogenated by-products at the evaporator surface during seawater desalination based on air-water interfacial solar heating

Seawater desalination based on air-water interfacial solar heating has attracted significant attention in recent years. However, the “high temperature, high salinity, sunlight irradiation and enrichment of photosensitive substances” environment formed at the evaporator surface unavoidably enhances the photochemical reaction, which in the next step may lead to the production of active species and by-products. In this work, H₂O₂, as an important reactive oxygen species and a transit substance for reactive oxygen species such as ·OH, ¹O₂, and ·O₂⁻, was monitored during solar evaporation. The average H₂O₂ concentration at the evaporator surface was 2.24 mg·L⁻¹ with a maximum concentration of 5.0 mg·L⁻¹, which is significantly higher than the average H₂O₂ concentration in the ocean. The effects of the nitrate ions, halogen ions, iron ions, dissolved organic matter, and solar intensity on the generation of H₂O₂ concentrations were explored. Finally, halogenated by-products were detected at the evaporator surface when phenol, a model pollutant, was present in the feedwater. This work fills the knowledge gap in understanding the generation of H₂O₂ and the formation of halogenated by-products at the evaporator surface during solar evaporation.