How we transport water in our bodies inspires new water filtration method – from UT Austin


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Artificial water channels enable fast and selective water permeation through water-wire networks Credit: Erik Zumalt, Cockrell School of Engineering, The University of Texas at Austin

A multidisciplinary group of engineers and scientists has discovered a new method for water filtration that could have implications for a variety of technologies, such as desalination plants, breathable and protective fabrics, and carbon capture in gas separations. The research team, led by Manish Kumar in the Cockrell School of Engineering at The University of Texas at Austin, published their findings in the latest issue of Nature Nanotechnology.

The study, which brought together researchers from UT Austin, Penn State University, the University of Tennessee, Fudan University and the University of Illinois at Urbana-Champaign, was initially inspired by the way our cells transport water throughout the body and began as an attempt to develop artificial channels for transporting water across membranes. The aim was to mimic aquaporins, essential membrane proteins that serve as water channels and are found in certain cells. Aquaporins are fast and efficient water filtration systems. They form pores in the membranes of cells in various parts of the body—eyes, kidneys and lungs—where water is in greatest demand.

Kumar and the team didn’t manage to mirror the aquaporin system exactly as planned. Instead, they discovered an even more effective  process. Unlike the body’s individual aquaporin cells, which function effectively independent of one another, the membranes developed by Kumar’s research group didn’t work well alone.

But, when he combined several of them to create networks of “water wires,” they were highly effective at  and filtration. Water wires are densely connected chains of water molecules that move exceptionally fast, like a train and its individual cars.

“We were trying to copy the already complicated water transport process used by aquaporins and stumbled upon an entirely new, and even better, method,” said Kumar, an associate professor in the Cockrell School’s Department of Civil, Architectural and Environmental Engineering. “It was completely serendipitous. We had no idea it would happen.”

These networks of artificial membranes could prove useful for separating salt from water, a filtration process that is currently inefficient and costly. The new membrane has shown impressive desalination properties, exhibiting far more selective salt and presumably other contaminant removal when compared with existing processes.

“Our method is a thousand times more efficient than current desalination processes in terms of its selectivity and permeability,” Kumar said. “For every 10,000 saltwater molecules that pass through current desalination systems, one salt molecule might not be filtered out. With our new  technology, one salt molecule for every 10 million water molecules would not be filtered out, while maintaining a  transport rate comparable to or better than current membranes.”

For his entire career, Kumar has focused on developing materials and processes that take the functionality of biological molecular models and apply them into engineering scales.

“It is difficult to even effectively mimic the complexities of how the human body works, especially at the molecular level,” he said. “This time, however, nature was the starting point for an even greater discovery than we could have ever hoped for.”


Explore further

Self-assembling, biomimetic membranes may aid water filtration


More information: Woochul Song et al, Artificial water channels enable fast and selective water permeation through water-wire networks, Nature Nanotechnology (2019). DOI: 10.1038/s41565-019-0586-8

Journal information: Nature Nanotechnology

Development of ultrathin durable membrane for efficient oil and water separation – Kobe University


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Researchers have succeeded in developing an ultrathin membrane with a fouling-resistant silica surface treatment for high performance separation of oil from water. Furthermore, this membrane was shown to be versatile; it was able to separate water from a wide variety of different oily substances.

Researchers led by Professor MATSUYAMA Hideto and Professor YOSHIOKA Tomohisa at Kobe University’s Research Center for Membrane and Film Technology have succeeded in developing an ultrathin membrane with a fouling-resistant silica surface treatment for high performance separation of oil from water.

Furthermore, this membrane was shown to be versatile; it was able to separate water from a wide variety of different oily substances.

These results were published online in the Journal of Materials Chemistry A on October 3 2019.

Introduction

The development of technology to separate oil from water is crucial for dealing with oil spills and water pollution generated by various industries. By 2025, it is predicted that two thirds of the world’s population won’t have sufficient access to clean water. Therefore the development of technologies to filter oily emulsions and thus increase the amount of available clean water is gaining increasing attention.

Compared with traditional purification methods including centrifugation and chemical coagulation, membrane separation has been proposed as a low cost, energy efficient alternative. Although this technology has been greatly developed, most membranes suffer from fouling issues whereby droplets of oil get irreversibly absorbed onto the surface. This leads to membrane pore blocking, subsequently reducing its lifespan and efficiency.

One method of mitigating the fouling issues is to add surface treatments to the membrane. However, many experiments with this method have encountered problems such as changes in the original surface structure and the deterioration of the treated surface layer by strong acid, alkaline and salt solutions. These issues limit the practical applications of such membranes in the harsh conditions during wastewater treatment.

Research Methodology

In this study, researchers succeeded in developing a membrane consisting of a porous polyketone (PK) support with a 10 nano-meter thick silica layer applied on the top surface. This silica layer was formed onto the PK fibrils using electrostatic attraction- the negatively charged silica was attracted to the positively charged PK.

The PK membrane has a high water permeance due to its large pores and high porosity. The silicification process- the addition of silica on the PK fibrils- provides a strong oil-repellent coating to protect the surface modified membrane from fouling issues.

Another advantage of this membrane is that it requires no large pressure application to achieve high water penetration. The membrane exhibited water permeation by gravity- even when a water level as low as 10cm (with a pressure of approx. 0.01atm) was utilized. In addition, the developed membrane was able to reject 99.9% of oil droplets- including those with a size of 10 nanometers. By using this membrane with an area of 1m2, 6000 liters of wastewater can be treated in one hour under an applied pressure of 1atm. It was also shown to be effective at separating water from various different oily emulsions.

As mentioned, the silification provided a strong oil repellent coating. Through the experiments carried out on the membrane to test its durability against fouling, it was discovered that oil did not become adsorbed onto the surface and that the oil droplets could be easily cleaned off. This membrane showed great tolerance against a variety of acidic, alkaline, solvent and salt solutions.

Conclusion

The ultrathin membrane developed by this research group has demonstrated efficient separation of water from oily emulsions, in addition to anti-fouling resistance. Technology to separate emulsions is indispensable in the fight against water pollution and clean water shortages. It is hoped that this development could be utilized in the treatment of industry waste water.

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Story Source:

Materials provided by Kobe UniversityNote: Content may be edited for style and length.


Journal Reference:

  1. Lei Zhang, Yuqing Lin, Haochen Wu, Liang Cheng, Yuchen Sun, Tomoki Yasui, Zhe Yang, Shengyao Wang, Tomohisa Yoshioka, Hideto Matsuyama. An ultrathin in situ silicification layer developed by an electrostatic attraction force strategy for ultrahigh-performance oil–water emulsion separationJournal of Materials Chemistry A, 2019; 7 (42): 24569 DOI: 10.1039/C9TA07988B

Nanocrack Coating Enhances Performance of Membranes for Water Filtration, Fuel Cells


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A team of researchers with members from institutions in South Korea and Australia has developed a coating for membranes used in fuel cells and many other applications that allows it to continue to perform at a high level even as temperatures rise and humidity drops to levels that normally cause performance to suffer.

In their paper published in the journal Nature, the team describes their coating, how it works and the different materials that can be improved through its use. Jovan Kamcev and Benny Freeman with the University of Texas at Austin have published a News & Views article in the same journal issue describing the work done by the team and the many ways that the membrane coating has been successfully tested.

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A hydrophobic coating layer provides a self-controlled mechanism for water conservation using nanometre-sized cracks (nanocracks) tuned by membrane swelling behaviour in response to external humidity conditions, which act as nanovalves. …more

Membranes are a critical part of machines that rely on ionic or size separation—some well-known applications are water filtration efforts, energy generation in fuel cells and flow batteries and by reverse electrodialysis. Though useful, membranes also have a reputation of being rather fragile, resulting in expensive repairs, replacement or performance degradation.

One such example is that most membranes need to be kept moist to work properly, which can become problematic in certain environments. Water filtration in a hot Middle Eastern desert, for example, suffers when temperatures soar and humidity levels drop. In this new effort, the research team reports that they have developed a coating for membranes that works similarly to stomatal pores in a cactus plant—the pores open to allow for taking in carbon dioxide during times of higher humidity, such as at night and then close again as the humidity levels drop during the heat of the day.

The membrane coating is made by placing a thin layer of fluorine-related material that is water repellant over the membrane, in a low-humidity environment—under high humidity conditions, nanocracks appear in the material, allowing the water in the air to pass through to the membrane below. But, as temperatures rise and drop, the material tightens, closing the gaps where the cracks exist, preventing the water in the from evaporating. Kamcev and Benny Freeman report that the has been tested successfully on a wide variety of applications under various environmental conditions, and that thus far, it has proven able to protect delicate membranes in severe environments, allowing for their use in a much broader range to applications.

Explore further: Self-assembling, biomimetic membranes may aid water filtration

More information: Chi Hoon Park et al. Nanocrack-regulated self-humidifying membranes, Nature (2016). DOI: 10.1038/nature17634

Abstract
The regulation of water content in polymeric membranes is important in a number of applications, such as reverse electrodialysis and proton-exchange fuel-cell membranes. External thermal and water management systems add both mass and size to systems, and so intrinsic mechanisms of retaining water and maintaining ionic transport1, 2, 3 in such membranes are particularly important for applications where small system size is important.

For example, in proton-exchange membrane fuel cells, where water retention in the membrane is crucial for efficient transport of hydrated ions1, 4, 5, 6, 7, by operating the cells at higher temperatures without external humidification, the membrane is self-humidified with water generated by electrochemical reactions5, 8. Here we report an alternative solution that does not rely on external regulation of water supply or high temperatures. Water content in hydrocarbon polymer membranes is regulated through nanometre-scale cracks (‘nanocracks’) in a hydrophobic surface coating.

These cracks work as nanoscale valves to retard water desorption and to maintain ion conductivity in the membrane on dehumidification. Hydrocarbon fuel-cell membranes with surface nanocrack coatings operated at intermediate temperatures show improved electrochemical performance, and coated reverse-electrodialysis membranes show enhanced ionic selectivity with low bulk resistance.

 

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