In this study, custom-tailored
graphene oxide quantum dots (GOQD) were synthesized as functional
nanofillers to be embedded into the polyamide (PA) membrane for reverse
osmosis (RO) via interfacial polymerization (IP). The heterostructured
interface-functionalization of amine/sulfonic decoration on GOQD (N/S-d-GOQD)
takes place via the tuning of the molecular design. The embedded N/S-d-GOQD
inside the PA matrix contributes to facilitating water molecules quick
transport due to the more accessible capturing sites with higher internal
polarity, achieving a nearly 3-fold increase in water permeance when
compared to the pristine thin-film composite (TFC) membrane. Covalent
bonding between the terminal amine groups and the acyl chloride of
trimesoyl chloride (TMC) enables the formation of an amplified selective
layer, while the sulfonic part assists in maintaining a robust membrane
surface negative charge, thus remarkably improving the membrane selectivity
toward NaCl. As a result, the newly developed TFN membrane performed
remarkably high water permeance up to 5.89 L m–2 h–1 bar–1 without the compromising
of its favorable salt (NaCl) rejection ratio of 97.1%, revealing a
comparably high separation property when comparing to the state-of-the-art
RO membranes, and surpassing the permeability-selectivity trade-off
limits. Furthermore, we systematically investigated the GOQDs with
different surface decorations but similar configurations (including
3 different nanofillers of pristine GOQD, amine decorated GOQD (N-d-GOQD),
and N/S-d-GOQD) to unveil the underlying mechanisms of the swing effects
of internal geometry and polarity of the embedded nanofillers on contributing
to the uptake, and/or release of aqueous molecules within TFN membranes,
providing a fundamental perspective to investigate the impact of embedded
nanofillers on the formation of an IP layer and the overall transporting
behavior of the RO process.
A highly permselective nanofiltration
membrane was engineered via
zwitterionic copolymer assembly regulated interfacial polymerization
(IP). The copolymer was molecularly synthesized using single-step
free-radical polymerization between 2-methacryloyloxyethyl phosphorylcholine
(MPC) and 2-aminoethyl methacrylate hydrochloride (AEMA) (P[MPC-co-AEMA]). The dynamic network of P[MPC-co-AEMA] served as a regulator to precisely control the kinetics of
the reaction by decelerating the transport of piperazine toward the
water/hexane interface, forming a polyamide (PA) membrane with ultralow
thickness of 70 nm, compared to that of the pristine PA (230 nm).
Concomitantly, manipulating the phosphate moieties of P[MPC-co-AEMA] integrated into the PA matrix enabled the formation
of ridge-shaped nanofilms with loose internal architecture exhibiting
enhanced inner-pore interconnectivity. The resultant P[MPC-co-AEMA]-incorporated PA membrane exhibited a high water
permeance of 15.7 L·m–2·h–1·bar–1 (more than 3-fold higher than that
of the pristine PA [4.4 L·m–2·h–1·bar–1]), high divalent salt rejection of
98.3%, and competitive mono-/divalent ion selectivity of 52.9 among
the state-of-the-art desalination membranes.
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