Effective Solar Thermal Evaporator with High Rejection on Ammonium Wastewater Treatment Enabled by Donnan Effect

Abstract

Solar photothermal interfacial evaporation technique can greenly and effectively obtain pure water, being promising to relieve worldwide water resource scarcity. However, there exist the volatile organic compounds in wastewater, such as, some macromolecules (e.g. phenol) and small molecules (e.g. NH4+), owing to the remarkable similarity in polarity and hydraulic radius between small ammonium ions and water molecules. This makes it challenging to efficiently separate freshwater from ammonium ions during the evaporation process using solar thermal materials. Here, we design an ingenious structure to firmly encapsulate the positively charged poly(ionic liquid) fragments inside the gel, realizing a positively charge-assisted effective solar evaporator with Donnan repulsion. High-quality freshwater can be obtained through the electrostatic repulsion effect, achieved with the assistance of positively charged materials (CNT100-LP3). Besides, possesses an excellent tensile stress of 0.8 MPa and tensile strain of 412%, enabling it stable cycle performance even in harsh environment. Consequently, the evaporation rate of 3.32 kg m−2 h−1 at 1 kW m−2 illumination is obtained, and the retention rate of ammonium can reach up to 97% in the treatment of high-concentration ammonium wastewater, which provides a new strategy for the inhibition of volatile small-molecule pollutants, and it is of great significance as a guide for the future development of solar steam generation.

Keywords: solar steam generation, ammonium rejection, low water evaporation enthalpy, purification water, Donnan exclusion