Fishing ions: this review provides a comprehensive analysis of different approaches in utilizing capacitive deionization (CDI) for selective ion separations and ion removal.
The global society
is in a transition, where dealing with climate
change and water scarcity are important challenges. More efficient
separations of chemical species are essential to reduce energy consumption
and to provide more reliable access to clean water. Here, membranes
with advanced functionalities that go beyond standard separation properties
can play a key role. This includes relevant functionalities, such
as stimuli-responsiveness, fouling control, stability, specific selectivity,
sustainability, and antimicrobial activity. Polyelectrolytes and their
complexes are an especially promising system to provide advanced membrane
functionalities. Here, we have reviewed recent work where advanced
membrane properties stem directly from the material properties provided
by polyelectrolytes. This work highlights the versatility of polyelectrolyte-based
membrane modifications, where polyelectrolytes are not only applied
as single layers, including brushes, but also as more complex polyelectrolyte
multilayers on both porous membrane supports and dense membranes.
Moreover, free-standing membranes can also be produced completely
from aqueous polyelectrolyte solutions allowing much more sustainable
approaches to membrane fabrication. The Review demonstrates the promise
that polyelectrolytes and their complexes hold for next-generation
membranes with advanced properties, while it also provides a clear
outlook on the future of this promising field.
We present a novel microfluidic EDGE (Edge based Droplet GEneration) device with regularly spaced micron-sized partitions, which is aimed at upscaling of o/w emulsion preparation. By this means, remarkably higher pressure stability was obtained, and two orders of magnitude higher droplet formation frequency was achieved compared to regular EDGE devices. Interestingly, we observed two different monodisperse droplet formation regimes for plateaus that were 2 micrometres in height, and to the best of our knowledge, no other microfluidic device has this ability. The average diameters of the droplets were 9 and 28 μm, both with a coefficient of variation (CV) below 5%. Based on the experimental throughput and a plausible mass parallelization scenario, the amount of hexadecane that can be emulsified is estimated to be between 6 and 25 m(3) m(-2) h(-1) depending on the required droplet size. With its high throughput potential and ability to produce uniform droplets of two different sizes, the partitioned EDGE device is promising for industrial emulsion production.
Capacitive deionization (CDI) is
a desalination technique that
can be applied for the separation of target ions from water streams.
For instance, mono- and divalent cation selectivities were studied
by other research groups in the context of water softening. Another
focus is on removing Na
+
from recirculated irrigation water
(IW) in greenhouses, aiming to maintain nutrients. This is important
as an excess of Na
+
has toxic effects on plant growth by
decreasing the uptake of other nutrients. In this study, we investigated
the selective separation of sodium (Na
+
) and magnesium
(Mg
2+
) in MCDI using a polyelectrolyte multilayer (PEM)
on a standard grade cation-exchange membrane (Neosepta, CMX). Alternating
layers of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate)
(PSS) were coated on a CMX membrane (CMX-PEM) using the layer-by-layer
(LbL) technique. The layer formation was examined with X-ray photoelectron
spectroscopy (XPS) and static water contact angle measurements (SWA)
for each layer. For each membrane, i.e., the CMX-PEM membrane, CMX
membrane, and for a special-grade cation-exchange membrane (Neosepta,
CIMS), the Na
+
/Mg
2+
selectivity was investigated
by performing MCDI experiments, and selectivity values of 2.8 ±
0.2, 0.5 ± 0.04, and 0.4 ± 0.1 were found, respectively,
over up to 40 cycles. These selectivity values indicate flexible switching
from a Mg
2+
-selective membrane to a Na
+
-selective
membrane by straightforward modification with a PEM. We anticipate
that our modular functionalization method may facilitate the further
development of ion-selective membranes and electrodes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.