A pH-stable positively charged composite nanofiltration membrane with excellent rejection performance

Area of Science:

• Materials Science
• Chemical Engineering
• Membrane Technology

Background:

• Developing stable and high-performance nanofiltration (NF) membranes is crucial for water treatment and separation processes.
• Existing membranes often suffer from degradation in harsh pH conditions, limiting their applicability.
• Positively charged membranes are desirable for specific separation tasks, such as removing negatively charged pollutants.

Purpose of the Study:

• To develop a novel, pH-stable, positively charged composite NF membrane with enhanced rejection performance.
• To investigate the effect of monomer composition on membrane structure and performance.
• To evaluate the long-term stability of the developed membrane in acidic and alkaline environments.

Main Methods:

• Interfacial polymerization of polyethyleneimine (PEI) and piperazine (PIP) in the aqueous phase with cyanuric chloride (CC) in the organic phase on a polysulfone (PSF) ultrafiltration (UF) substrate.
• Characterization of membrane morphology, chemical structure, and rejection performance.
• Long-term immersion tests in strong acidic (pH 1) and alkaline (pH 13) solutions.

Main Results:

• A novel positively charged composite NF membrane was successfully fabricated with excellent rejection capabilities.
• The membrane exhibited remarkable pH stability, with no significant changes in morphology, chemistry, or performance after 30 days in extreme pH conditions.
• The rejection performance could be tuned by adjusting the mass ratio of PEI to PIP, indicating control over the active layer structure.

Conclusions:

• The developed polyamide composite NF membrane demonstrates superior pH stability and excellent rejection performance.
• Mixing piperazine (PIP) with polyethyleneimine (PEI) creates a more compact active layer, enhancing membrane properties.
• The tunable nature of the membrane's rejection performance offers potential for tailored separation applications.