Polyacrylonitrile nanofiber membranes modified with ionically crosslinked polyelectrolyte multilayers for the...

Area of Science:

• Materials Science
• Polymer Chemistry
• Separation Science

Background:

• Nanofiltration membranes are crucial for water purification and separation processes.
• Developing membranes with enhanced flux and selectivity remains a key challenge.
• Layer-by-layer (LbL) assembly offers a versatile method for fabricating thin film composite membranes.

Purpose of the Study:

• To fabricate and characterize nanofiltration membranes using LbL assembly of branched polyethylenimine (BPEI) and polyacrylic acid (PAA) on a polyacrylonitrile (PAN) nanofibrous support.
• To investigate the influence of polyacrylic acid's degree of ionization (DI) and pH on BPEI/PAA multilayer film growth.
• To evaluate the separation performance (flux and rejection) of the modified nanofiber membranes.

Main Methods:

• Fabrication of nanofiltration membranes via LbL assembly of BPEI and PAA on PAN nanofibrous mats.
• Estimation of PAA's degree of ionization (DI) using FTIR spectroscopy.
• Characterization of multilayer film growth under varying DI and pH conditions.
• Performance testing of the membranes for pure water flux and MgSO4 rejection at a specific pressure.

Main Results:

• BPEI/PAA multilayer growth was dependent on PAA's DI and pH, with exponential growth observed at DI < 30% or pH < 3.5.
• A 1100 nm thick separation layer was formed using 15 bilayers of BPEI/PAA.
• The modified PAN nanofiber membranes exhibited a strong negative charge above pH 4.5.
• The membrane with 15 BPEI/PAA bilayers achieved a pure water flux of 19.7 Lm⁻²h⁻¹ and 98.7% MgSO4 rejection at 4 bar.

Conclusions:

• The study successfully developed high-performance nanofiltration membranes using LbL assembly of BPEI/PAA on PAN nanofiber mats.
• The optimized membrane demonstrated significantly higher flux and salt rejection compared to those on conventional supports.
• The enhanced performance is attributed to the combined high charge density and porosity of the nanofiber support and the BPEI/PAA multilayers.