1 research outputs found
Positively Charged Polyamine Nanofiltration Membrane for Precise Ion–Ion Separation
Positively charged nanofiltration (NF) membranes offer
enormous
potential for lithium–magnesium separation, hard water softening,
and heavy metal removal. However, fundamental performance limitations
for these applications exist in conventional polyamide-based NF membranes
due to the negatively charged surface and low ion–ion selectivity.
We hereby innovatively develop an advanced positively charged polyamine-based
NF membrane built by the nucleophilic substitution of bromine and
amine groups for precise ion–ion separation. Specifically,
polyethylenimine (PEI) and 1,3,5-tris(bromomethyl)benzene (TBB) are
interfacially polymerized to generate an amine-linked PEI-TBB selective
layer with an ultrathin thickness of ∼95 nm, an effective pore
size of 6.5 Ã…, and a strong positively charged surface with a
zeta potential of +20.9 mV at pH 7. The PEI-TBB composite membrane
achieves a water permeance of 4.2 L·m–2·h–1·bar–1, various divalent salt
rejections above 90%, and separation factors above 15 for NaCl/MgCl2 and LiCl/MgCl2 mixed solutions. A three-stage
NF process is implemented to achieve a Mg2+/Li+ mass ratio sharply decreasing from 50 to 0.11 with a total separation
factor (SLi,Mg) of 455. Furthermore, the
polyamine-based NF membrane exhibits excellent operational stability
under continuous filtration and high operational pressure, demonstrating
great application potential for precise ion–ion separation