CNT/PVA-PVA double-layer hydrogel interfacial evaporators for stable solar desalination and water purification

Abstract

Hydrogel-based solar interface evaporation technology efficiently concentrates photothermal heat at the solid–liquid–gas interface to enable effective seawater desalination, offering a promising solution to the global freshwater crisis and thus attracting extensive attention. However, the high evaporation rate is limited by its water transport capacity and salt tolerance. This work presents a wetting-gradient bilayer structured solar-driven hydrogel evaporator (B-CPVA) featuring a relatively hydrophobic upper layer (carbon nanotubes-polyvinyl alcohol B-CPVA) for efficient broadband solar absorption and high photothermal conversion, combined with a hydrophilic bottom layer (PVA) to facilitate rapid water transport. The proportion of carbon nanotubes to PVA of the upper layer was modified to enable consistent solar thermal energy conversion and sustained high-efficiency water evaporation. The B-CPVA evaporator exhibits a high evaporation rate of 2.40 kg m⁻² h⁻¹ with an efficiency of 92.85% when exposed to simulated seawater under 1.0 sun illumination. In addition, the NaCl crystals formed on the B-CPVA surface can be fully dissolved in approximately 53 minutes, achieving effective salt removal through a self-cleaning mechanism. The organic solutions (MO and RhB) treated with this evaporator became colorless and transparent, and UV-visible spectroscopy revealed the complete disappearance of characteristic absorption bands. confirming the excellent pollutant purification ability of this material, which provides a highly efficient solution for solar desalination applications.