Crossly charged microfluidic device for spontaneous filtration without an external power supply

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Conventional microfluidic desalination requires external power sources.
• Developing energy-efficient water purification methods is crucial for global water security.

Purpose of the Study:

• To investigate a spontaneous filtration method for desalination.
• To evaluate the performance of a novel filtration device using charged precursor mixtures.
• To demonstrate salt rejection without relying on external power.

Main Methods:

• A filtration device with main (1 mm depth) and shallow (400 μm depth) channels was designed.
• Highly charged precursor mixtures were injected into the device.
• Filtration performance was assessed using a fluorescent dye and various salt solutions (CaCl2, NaCl, CaSO4, Na2SO4).
• Particle migration was observed and compared with simulation data.

Main Results:

• The device achieved salt rejection rates of 3.16% for CaCl2, 30.13% for NaCl, 43.74% for CaSO4, and 36.32% for Na2SO4.
• Donnan exclusion theory explained the observed salt rejection trends.
• Charged species and microparticles migrated toward the main channel centerline due to highly charged surfaces.
• Observed particle migration behavior aligned with simulation results.

Conclusions:

• The proposed spontaneous filtration method effectively separates salts from water without external power.
• The technique shows significant potential for desalinating brackish and salty surface water.
• The findings support the application of Donnan exclusion principles in passive water treatment technologies.