Highly charged hydrogel with enhanced donnan exclusion toward ammonium for efficient solar-driven water remediation

Developing solar-driven photothermal materials with superior rejection capability toward volatile ammonium (NH4+) is a huge challenge but rather important for agricultural/municipal wastewater remediation. Herein, different from common hierarchical porosity designs, a positive charge-assisted Janus hydrogel evaporator with enhanced Donnan exclusion toward ammonium is uniquely achieved without sacrificing the water evaporation capability. The ammonium diffusion resistance of the so-fabricated Janus evaporator is significantly increased by optimizing the charge density and diffusion distance, yielding a high ammonium rejection rate up to 95%, which is never reported before. Meanwhile, the Janus evaporator also yields a water evaporation rate up to 3.3 kg m(-2)h(-1) for the natural wastewater via partial amorphization of cellulose I alpha allomorph, which is similar to 3 times faster than the previous photothermal materials for intercepting volatile phenol molecules. This work points out new avenues for the application of photothermal materials in separating freshwater from small volatile molecules using clean solar energy.

Automated summary

Developing solar-driven photothermal materials with superior rejection capability toward volatile ammonium is crucial for wastewater remediation. The Janus hydrogel evaporator achieved enhanced Donnan exclusion toward ammonium without sacrificing water evaporation capability, significantly increasing ammonium rejection rate and water evaporation rate for natural wastewater. This work opens up new possibilities for using photothermal materials to separate freshwater from small volatile molecules using clean solar energy.