A polyelectrolyte hydrogel coated loofah sponge evaporator based on Donnan effect for highly efficient solar-driven desalination

Abstract

Solar desalination is considered an efficient way to alleviate the global shortage of freshwater resources. However, the salt accumulation on the surface of solar absorbers drastically reduces light absorption and steam evaporation efficiency, especially in highly concentrated brines. Herein, inspired by the salt rejection mechanisms of the mangrove trees, a sodium polyacrylate carbonized loofah (PAAS-CLF) was designed using the biomass porous loofah sponge as the matrix, modified with sodium polyacrylate (PAAS) hydrogel coating for solar-driven desalination. The loofah sponge coated PAAS hydrogel as a substrate could obtain a naturally high porosity. Moreover, relying on the negatively charged PAAS hydrogel rich in –COO– groups, it could confine Na+ to induce the Donnan effect, thus reducing the diffusion of salt ions into the water supply layer and avoiding salt accumulation fundamentally. The PAAS-CLF had high water evaporation rates of 1.83 kg m−2h−1 with an efficiency of 94.54% attained under 1 sun. More notably, the evaporator maintained stable water evaporation rates over 1.45 kg m−2h−1 in salt water with a broad range of salinity (35–200 g kg−1), and no salt accumulation was observed during the long-time evaporation. Therefore, this work provides an approach of the flexible application using environmentally friendly biomass sponge composite polyelectrolyte hydrogel for salt-resistant evaporator in solar desalination and concentrated brine treatment.