3 research outputs found
Molecular Dynamics Study of Carbon Nanotubes/Polyamide Reverse Osmosis Membranes: Polymerization, Structure, and Hydration
Carbon
nanotubes/polyamide (PA) nanocomposite thin films have become very
attractive as reverse osmosis (RO) membranes. In this work, we used
molecular dynamics to simulate the influence of single walled carbon
nanotubes (SWCNTs) in the polyamide molecular structure as a model
case of a carbon nanotubes/polyamide nanocomposite RO membrane. It
was found that the addition of SWCNTs decreases the pore size of the
composite membrane and increases the Na and Cl ion rejection. Analysis
of the radial distribution function of water confined in the pores
of the membranes shows that SWCNT+PA nanocomposite membranes also
exhibit smaller clusters of water molecules within the membrane, thus
suggesting a dense membrane structure (SWCNT+PA composite membranes
were 3.9% denser than bare PA). The results provide new insights into
the fabrication of novel membranes reinforced with tubular structures
for enhanced desalination performance
Effective Antiscaling Performance of Reverse-Osmosis Membranes Made of Carbon Nanotubes and Polyamide Nanocomposites
The antiscaling properties of multiwalled
carbon nanotube (MWCNT)–polyamide
(PA) nanocomposite reverse-osmosis (RO) desalination membranes (MWCNT–PA
membranes) were studied. An aqueous solution of calcium chloride (CaCl<sub>2</sub>) and sodium bicarbonate (NaHCO<sub>3</sub>) was used to precipitate
in situ calcium carbonate (CaCO<sub>3</sub>) to emulate scaling. The
MWCNT contents of the studied nanocomposite membranes prepared by
interfacial polymerization ranged from 0 wt % (plain PA) to 25 wt
%. The inorganic antiscaling performances were compared for the MWCNT–PA
membranes to laboratory-made plain and commercial PA-based RO membranes.
The scaling process on the membrane surface was monitored by fluorescence
microscopy after labeling the scale with a fluorescent dye. The deposited
scale on the MWCNT–PA membrane was less abundant and more easily
detached by the shear stress under cross-flow compared to other membranes.
Molecular dynamics simulations revealed that the attraction of Ca<sup>2+</sup> ions was hindered by the interfacial water layer formed
on the surface of the MWCNT–PA membrane. Together, our findings
revealed that the observed outstanding antiscaling performance of
MWCNT–PA membranes results from (i) a smooth surface morphology,
(ii) a low surface charge, and (iii) the formation of an interfacial
water layer. The MWCNT–PA membranes described herein are advantageous
for water treatment
Antiorganic Fouling and Low-Protein Adhesion on Reverse-Osmosis Membranes Made of Carbon Nanotubes and Polyamide Nanocomposite
We
demonstrate efficient antifouling and low protein adhesion of multiwalled
carbon nanotubes-polyamide nanocomposite (MWCNT-PA) reverse-osmosis
(RO) membranes by combining experimental and theoretical studies using
molecular dynamics (MD) simulations. Fluorescein isothiocyanate (FITC)-labeled
bovine serum albumin (FITC-BSA) was used for the fouling studies.
The fouling was observed in real time by using a crossflow system
coupled to a fluorescence microscope. Notably, it was observed that
BSA anchoring on the smooth MWCNT-PA membrane was considerably weaker
than that of other commercial/laboratory-made plain PA membranes.
The permeate flux reduction of the MWCNT-PA nanocomposite membranes
by the addition of FITC-BSA was 15% of its original value, whereas
those of laboratory-made plain PA and commercial membranes were much
larger at 34%–50%. Computational MD simulations indicated that
the presence of MWCNT in PA results in weaker interactions between
the membrane surface and BSA molecule due to the formation of (i)
a stiffer PA structure resulting in lower conformity of the molecular
structure against BSA, (ii) a smoother surface morphology, and (iii)
an increased hydrophilicity involving the formation of an interfacial
water layer. These results are important for the design and development
of promising antiorganic fouling RO membranes for water treatment