Inhibition of phenolic compounds from entering condensed freshwater by surfactant-modified evaporators during solar-driven seawater desalination

Abstract

Seawater desalination based on air–water interfacial solar heating is considered to be one of the effective methods to solve the freshwater shortage crisis in islands. However, the high temperature of the air–water interface unavoidably makes volatile organic compounds (VOCs) such as phenolic compounds volatilize into the condensed freshwater, resulting in freshwater pollution. In this work, solar evaporators with different photothermal materials such as carbon black, MoS2 and carbon nanotubes were modified with cetyl trimethyl ammonium bromide (CTAB) and were applied for both solar evaporation and inhibition of phenolic compounds from entering condensed freshwater. The distillation rates (RD) of 10 phenolic compounds could be significantly reduced. For example, the RD value of phenol was reduced from 77% to 4.6%, which was mainly due to the electrostatic force between the quaternary ammonium group of CTAB and phenol, the binding effect of CTAB micelle on phenol, as well as the hydrogen bond between phenol and air-laid cloth in the evaporator. In addition, the phenolic compounds with the boiling point above 230 °C have RD values all below 10%, while the RD values of phenolic compounds with the boiling point below 230 °C are significantly correlated with n-octanol/water partition coefficient (logKow) values with a correlation coefficient R2 of 0.915. This work demonstrates that the CTAB-modified solar evaporators can be used for clean condensed freshwater production during solar-driven seawater desalination.