Membrane Separations
membrane-based separations necessary for global water security
Escalating populations, rapid industrialization, and climate change have imposed unprecedented pressures on global resources—with expanding water and energy demands at the heart of these pressures. Achieving global water security necessitates the treatment of underutilized sources (e.g., seawater and wastewater), for which pressure-driven desalination technologies are particularly well-suited. In these technologies, the membrane is the critical component and requires material breakthroughs to realize paradigm-shifting performance. Attempts to improve performance have been inconsequential over the last several decades—a result of our poor understanding of nanofluidic transport. During my PhD research, I sought to elucidate synthesis–structure–performance relationships in conventional- and novel-material based membranes, contextualizing how these fundamental relationships can be exploited to improve practical water treatment processes.
Overall, my interests are in transport phenomena unique to extremely confined environments that are relevant to real-world water purification technologies. These fundamental relationships are critical for the bottom-up development of ultra-efficient membranes. I believe new approaches for studying nanoconfined phenomena that radically contrast the traditional Edisonian approach are necessary to guide membrane design and provide insight that may lead to next-generation membranes for desalination.
Schematic illustration of various membrane properties, treatments, and process conditions that influence membrane performance characteristics, such as water and salt permeance (A and B, respectively). Image taken from C.L. Ritt et al., J. Membr. Sci. (2022).
Illustration of fully solvated perchlorate ion (ClO4-) interacting with a cellulosic polymer chain. Numbers represent the net charges of the functional groups. Images adapted from C.L. Ritt et al., Sci. Adv. (2022).
Ion Selectivity
designing ion-selective materials require novel approaches
For water treatment purposes, ultraselective membranes can enable precise control over the makeup of permeate and brine streams for complex feed solutions. This level of control could enable more sustainable water treatment by tailoring the treatment to the desired end use and would substantially reduce chemical and energy consumption, ultimately lowering the treatment cost for water production. In addition, fit-for-purpose membranes could improve resource recovery efforts (e.g., lithium recovery), sensor devices, and proton selectivity in fuel cells and water electrolyzers.
During my PhD, I employed machine learning to reveal the importance of electrostatics for ion-ion selectivity in complex, nanoporous polymeric environments. Leveraging new data-driven approaches for studying ion transport may be an essential step toward designing ion-selective materials.
Nanofluidics
Solid-state nanofluidic devices as model systems
We lack a holistic understanding of many fundamental transport mechanisms that occur in nanoporous systems. This is particularly prevalent for charge-based phenomena. In industrially relevant polymer-based systems where charge can greatly influence performance (e.g., membranes used for desalination), the sensitivity of polymeric matrices to their environment makes it difficult to deconvolute highly coupled transport phenomena and extract useful insight. Conversely, solid-state devices offer well-defined and precisely controlled platforms for studying nanofluidic ion transport.
Illustration of solid-state nanofluidic device, which is composed of an array of 20-nm high, 4-μm wide, and 20-μm long nanochannels that separate the cis and trans reservoirs where electrolyte solutions are exchanged. The optical topographic image (right) shows the nanochannels prior to etching. Image taken from C.L. Ritt et al., ACS Nano (2022).
Conceived plant nanobionic approach, where nanoparticles that can catalyze pollutant metabolism are multiplexed with near-infrared (nIR) fluorescent nanosensors within plant leaves. The resulting nanobionic system can enable real-time monitoring of pollutants as they appear and are subsequently degraded. Images in the figure are adapted from T.T.S. Lew et al., Adv. Mater. (2021) & E. Voke et al., ACS Sensors (2021).
Plant Nanobionics
plant nanobionics can accelerate the development of phytoremediation technologies
There are over 5 million brownfield sites globally that require remediation and redevelopment. While many approaches exist to address this issue, traditional brownfield remediation technologies possess a high carbon footprint and are often hindered by their high cost. Phytoremediation is an inherently carbon negative process that is self-sustaining, cheap, and can address a wide variety of environmental contaminants. However, the current generation of phytoremediators are slow and limited to select growth conditions, leaving this process viable only for low-value lands.
Plant nanobionics is an emerging field that imparts non-native functions to plants by introducing nanoparticles. This approach benefits from its applicability to any wild-type plant without the need of genetic engineering, which is only applicable to a narrow range of plant species.
Plant nanobionic approaches can be used to develop next-generation phytoremediators that (i), remove contaminants quickly and selectively, (ii), store contaminants at high capacities, (iii), metabolize contaminants beyond their natural limits, (iv), possess stimuli responsive features, and (v), can autonomously monitor contaminants as they appear in the environment.