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

Area of Science:

• Materials Science
• Environmental Science
• Chemical Engineering

Background:

• Solar-driven interfacial evaporation is a promising sustainable water treatment method.
• Salt accumulation significantly reduces efficiency in marine and hypersaline environments.

Purpose of the Study:

• To develop advanced hydrogel evaporators with tunable surface charges for enhanced performance in saline water.
• To investigate the impact of surface charge modulation on evaporation rate and salt resistance.

Main Methods:

• Synthesis of covalent organic framework (COF)/graphene hydrogels with controlled anionic, cationic, and zwitterionic functionalities.
• Molecular-level tuning of surface charge by adjusting building block ratios during COF synthesis.
• Performance evaluation of hydrogel evaporators in various saline concentrations under solar irradiation.

Main Results:

• Hetero-charged and zwitterionic hydrogels demonstrated increased water evaporation rates in seawater compared to pure water.
• The optimized hetero-charged hydrogel achieved an evaporation rate of 3.23 kg m⁻² h⁻¹ in 3.5 wt.% saline water, exceeding pure water performance by 12%.
• The hydrogel exhibited excellent salt resistance, maintaining performance in up to 20 wt.% brine.

Conclusions:

• Controllable surface charge modulation in COF/graphene hydrogels is an effective strategy to overcome salt accumulation limitations in solar evaporation.
• These materials show significant potential for efficient desalination and treatment of diverse wastewaters in challenging environments.