Expanded Graphite-Polyurethane Foams for Water-Oil Filtration.

Area of Science:

• Materials Science
• Environmental Engineering
• Chemical Engineering

Background:

• Effective separation of oil-in-water mixtures and emulsions is crucial for environmental protection and resource recovery.
• Conventional methods often involve high energy consumption or secondary pollution.
• Developing advanced materials for efficient and sustainable oil-water separation remains a significant challenge.

Purpose of the Study:

• To engineer porous foams with underwater oleophobic properties using expanded graphite and waterborne polyurethane.
• To investigate the influence of fabrication methods on foam structure and oil-water separation performance.
• To evaluate the efficiency, reusability, and potential for practical application of the developed foams.

Main Methods:

• Solvent-free fabrication of porous foams by combining expanded graphite with waterborne polyurethane (PUEGr).
• Introduction of calcium carbonate during fabrication to create foams with varied pore structures (PUEGr_t).
• Characterization of foam properties, including pore size distribution, hydrophilicity/oleophilicity in air, and oleophobicity underwater.
• Testing of gravity-driven filtration for separating surfactant-free oil-in-water mixtures and emulsions.

Main Results:

• Both PUEGr and PUEGr_t foams exhibited interconnected porous networks, hydrophilicity/oleophilicity in air, and underwater oleophobicity.
• PUEGr foams achieved 96.85% oil rejection and a flow rate of 9988 L m⁻² h⁻¹ for 10% oil-in-water mixtures.
• PUEGr_t foams showed higher efficiency (99.99%) but lower flow rate (8547 L m⁻² h⁻¹) for mixtures, and superior emulsion separation (98.28% efficiency).
• Foams demonstrated excellent reusability and performance stability under harsh conditions.

Conclusions:

• The developed expanded graphite/waterborne polyurethane foams are effective 3D filters for gravity-driven oil-water separation.
• Tailoring pore size through fabrication methods allows for optimization of separation efficiency and flow rate.
• The solvent-free, reusable, and energy-efficient nature of these foams highlights their significant potential for practical environmental applications.