# Engineering Charge Heterogeneity in COF/Graphene Hydrogels for Salt‐Resistant Solar Evaporation

## TL;DR

A new COF/graphene hydrogel with engineered charge heterogeneity enables efficient and salt-resistant solar water evaporation, even in highly saline conditions.

## Contribution

The design of hetero-charged COF/graphene hydrogels with spatially separated ionic domains for enhanced salt resistance and evaporation rates in saline water.

## Key findings

- Hetero-charged hydrogels achieve an evaporation rate of 3.23 kg m⁻² h⁻¹ in 3.5 wt.% saline water, 12% higher than in pure water.
- The hydrogel maintains strong salt resistance even in 20 wt.% brine due to suppressed salt crystallization.
- The material shows potential for treating diverse wastewaters beyond desalination.

## Abstract

Solar‐driven interfacial evaporation technology offers a sustainable solution for water treatment, however, its efficiency in marine environments is often hindered by salt accumulation. Here, a series of covalent organic framework (COF)/graphene hydrogels with controllable charge distributions is reported, including homo‐ and hetero‐charged as well as zwitterionic surface functionalities. By adjusting the ratio of anionic and cationic building blocks during COF synthesis, the surface charge of the hydrogel evaporator is continuously modulated at the molecular level. The hetero‐charged and zwitterionic hydrogels enable faster water evaporation in seawater than in pure water by reducing the evaporation enthalpy. In particular, the hetero‐charged hydrogel achieves an evaporation rate of up to 3.23 kg m−2 h−1 in 3.5 wt.% saline water, 12% higher than that in pure water, and maintains strong salt resistance even in 20 wt.% brine. Beyond desalination, the hydrogel exhibits high potential for treating diverse wastewaters, providing a scalable platform for sustainable water treatment in complex environments.

Hetero‐charged COF/graphene hydrogel (HCG‐1) with spatially separated cationic and anionic domains is engineered to achieve salt‐resistant solar evaporation. This unique charge architecture regulates Na⁺ and Cl− distribution, promotes intermediate‐water formation and effectively suppresses salt crystallization, enabling stable solar evaporation in saline water at rates exceeding those in pure water.