(168e) Tunable-Porosity Membranes for Water Treatment By Discrete Nanoparticle Assembly

Tunable-Porosity
Membranes For Water Treatment By

Discrete
Nanoparticle Assembly

Patrizia Marchetti ¹, Martin Mechelhoff ², Andrew G. Livingston ^1, *

¹Department of Chemical
Engineering, Imperial College London, South Kensington Campus,
London SW7 2AZ, UK

²Lanxess Deutschland GmbH
,Group Function Innovation & Technology, 51369 Leverkusen, Germany

* a.livingston@imperial.ac.uk

Thin
film composite (TFC) membranes are an important class of membranes, mainly used
for reverse osmosis and nanofiltration (NF) [1].
They consist of a
thin (submicron) separating ?barrier? on top of a chemically different porous
support. For aqueous
applications, they are usually prepared by interfacial polymerization of polyamide on a support-layer consisting of, for example,
polysulfone. The two main challenges with this procedure are the need for organic
solvents, such as n-hexane, and the difficulty in a precise control of the pore
size at nanometer scale. Colloidal assembly of polymeric nanoparticles
represents an interesting alternative to conventional fabrication procedures
for TFC membranes [2]. This approach permits the organization of nanomaterials,
acting as pre-structured building blocks, to create larger entities with new
properties. The production process is also more environmentally friendly, as
crosslinked organic nanoparticles can be easily handled in an aqueous solution
without the need for an organic solvent.

In
this work, a novel NF membrane was prepared by a facile single-step coating
procedure of highly crosslinked poly(styrene-co-butadiene) polymer
nanoparticles on top of a hydrophilic ultrafiltration support. The
nanoparticles employed were characterised by high chemical and mechanical
stability in extreme conditions, such as concentrated acid and base solutions
and a wide range of organic solvents. During membrane fabrication, the
nanoparticle surface loading was optimized, in order to avoid cracking during
the drying step and obtain a thin, defect-free membrane separation layer of 144
nm (Figure 1).

Figure 1. Thin Film Nanocomposite membrane
by nanoparticle assembly on top of polyacrylonitrile ultrafiltration support

The
membrane exhibited a significant charge rejection mechanism and low fouling
tendency, due to the high density of hydroxyl group functionalization on the
nanoparticle surface. Interestingly, upon heating above the glass transition
temperature (or minimum film formation temperature) the particles coalesced,
forming a rubber-like dense film. This was a consequence of deformation and
interpenetration of the nanoparticles, which in turn comprise a highly
crosslinked particle core and a more flexible and less dense outer shell. The
novel membrane formed by nanoparticle annealing showed a molecular weight
cut-off below 500 g mol^-1 and a viable water permeance of about 40 L
m^-2 h^-1 bar^-1, unlike membranes formed from conventional
linear rubber-like polymers, which usually have insignificant water permeance
of less than 0.4 L m^-2 h^-1 bar^-1. The
permeation pathways were found to be proportional to, and therefore tunable
with, the annealing temperature.

References

[1]
K. Peng Lee, T. C. Arnot, D. Mattia, J. Membr. Sci. 370 (2011) 1.

[2]
Q. Zhang,
S. Ghosh, S. Samitsu, X. Peng, I. Ichinose. J. Mater. Chem. 21 (2011)
1684.