Molecular cages sift ‘heavy’ water from near-identical H₂O

Host: Nick Petrić Howe

Welcome back to the Nature Podcast. This week: how to separate ‘heavy’ water from regular water.

Host: Benjamin Thompson

And how crowd data could help engineers give bridges a structural check-up. I’m Benjamin Thompson

Host: Nick Petrić Howe

And I’m Nick Petrić Howe.

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Host: Nick Petrić Howe

Before we get into the show, I just wanted to mention that this is our 750^th episode of the Nature Podcast.

Host: Benjamin Thompson

Amazing, right? Another big milestone for us. I’ve been here since episode 500, and time has absolutely flown by since then, and we have covered some amazing things on the podcast. And to everyone listening right now, whether this is your first show or your 750^th, thank you so much for listening. Anyway, back to our regularly scheduled podcast. Nick, what’s up first today?

Interviewer: Nick Petrić Howe

Well, I’ve been looking into a new way to get ‘heavy’ water. Now, heavy water is very similar to regular old H₂O. It’s just a bit heavier, as the name suggests. This is because it’s composed of a different isotope of hydrogen – deuterium – which is like hydrogen but with an extra neutron. These minor differences between the two so-called isotopologues makes it really quite difficult to separate regular water, H₂O, from its heavier counterpart, D₂O. But a paper in Nature has a new solution. Now, you may be wondering, why do people even want heavy water? Well, it’s useful for a whole range of things, like nuclear energy production, drug design and it’s even used in nutritional studies. In fact, it is considered so valuable that during World War II, a facility for producing heavy water was destroyed to disrupt enemy plans. Whilst we can get heavy water, the current methods of production are very energy intensive, so better methods would be useful to cut costs, and that’s where this new Nature paper comes in.

Interviewee: Cheng Gu

In this Nature paper, we provided a new separation mechanism for water isotopologues without significant energy consumption.

Interviewer: Nick Petrić Howe

This is Cheng Gu, one of the authors of the new paper. Now, we’ve talked about how similar the two isotopologues – heavy water and regular water – are, but there’s one interesting difference. They diffuse at very slightly different rates – not different enough to be useful under regular circumstances, but Cheng’s idea was to harness this slight difference and amplify it. The way he and his team did this was by building a series of tiny molecular cages that were connected by even tinier windows. Now, these cages are rigid, but the windows are flexible and can change size with temperature, so they can let different things move through more or less easily as you change the temperature. The idea was that, at the right temperature, water and heavy water would move through at different rates, based on their slight difference in diffusion rates. And indeed, Cheng and his colleagues found that, at room temperature, the slightly lighter H₂O hopped more easily through this set of windows and cages.

Interviewee: Cheng Gu

Their slight differences in the diffusion rates were amplified. So, for example, in our materials, the diffusion rates of H₂O were eightfold that of D₂O.

Interviewer: Nick Petrić Howe

This much faster diffusion allowed Cheng and his colleagues to separate the water from heavy water, and in a way that’s much more energy efficient than any previous methods. For one thing, the conditions needed are easily achievable.

Interviewee: Randy Snurr

I certainly think there is the potential here for a practical process for obtaining heavy water. And one thing that's really attractive is that their method works at room temperature.

Interviewer: Nick Petrić Howe

This is Randy Snurr, nanopore researcher and author of an expert-written article in Nature on the new paper. Randy is excited about the advantages of this work over older techniques, such as quantum sieving, that uses quantum effects to separate heavy and normal water through tiny pores.

Interviewee: Randy Snurr

The quantum sieving only kicks in at very low temperatures, so like around the temperature of liquid nitrogen, for example, 77 Kelvin. And of course, it's expensive to get down to those temperatures, so if they can separate the heavy water from ordinary water at room temperature, it's a really attractive aspect of this work.

Interviewer: Nick Petrić Howe

So, the problem of separating heavy water has been solved once and for all, right?

Interviewee: Randy Snurr

I doubt it. I think it's a significant step, but scaling this up to some sort of industrial process will certainly require additional work.

Interviewer: Nick Petrić Howe

Cheng agrees that more work is needed before this new paper can be used in industry, but he thinks it’s an achievable goal.

Interviewee: Cheng Gu

We are confident that some more materials will be developed with higher performance and lower costs, guided by our mechanism, to finally challenge the current industrial separation techniques.

Interviewer: Nick Petrić Howe

In addition to the potential for this technique to be used for heavy water production, Cheng is also excited about the other opportunities it opens up. If it can be used to separate one such set of similar molecules, then a potentially similar methodology, using a slightly different structure with different sized windows, could be set up to separate all sorts of other things.

Interviewee: Cheng Gu

Our work provided a new mechanism of diffusion regulation to successfully achieve efficient separation of water isotopologues at room temperature. This rationale can be more broadly suitable for use with diverse adsorbents for the efficient discrimination of isotopologues, thereby inspiring the researchers to be involved in this urgent and challenging field of isotopologues separation to promote understanding and utilising isotopes, thus causing a huge ripple effect, I think.

Interviewer: Nick Petrić Howe

That was Cheng Gu, from the South China University of Technology. You also heard from Randy Snurr, from Northwestern University in the US. To find out more about this paper, check out a link to it and a link to a News and Views article written by Randy in the show notes.

Host: Benjamin Thompson

Coming up, how researchers are using data from mobile phones to check the health of the Golden Gate Bridge. Right now, though, it’s time for the Research Highlights, read by Shamini Bundell.

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Shamini Bundell

Dancers might be able to feel the beat, even if they can’t hear it. That’s the suggestion from a study showing that concertgoers groove more energetically when the bass is turned up – even though the low-frequency sounds aren’t actually audible. Researchers in Canada set up their own electronic music concert for this experiment, and brought in around 60 people to come and dance. They gave them headbands to track their movement and played music with and without low-frequency sounds. On average, the audience moved almost 12% more when the bass speakers were turned on compared to when they were off. They were likely sensing the sounds through the vestibular system, which controls balance and spatial orientation. And the authors suggest that feeling the beat might increase the urge to dance. You can groove along to that research in Current Biology.

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Shamini Bundell

Sand dunes in the desert aren’t static. They move with the wind. Unfortunately, as the climate changes in the future, so will the wind, which could lead to dunes moving and expanding, with potential impacts on roads, railways, fields and homes. Researchers in the UK examined how local wind patterns, simulated by climate models, would change small desert dunes and sand seas around the world, looking at a worst-case emissions scenario. They found that nearly three-quarters of the world’s desert dune area could experience changes, in many cases resulting in increased dune movements and in some places resulting in bigger dune fields. The researchers say that climate-driven dune changes should be taken into account when planning the development of infrastructure, industry and cities. Read more in Nature Climate Change.

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Host: Benjamin Thompson

Next up, reporter Adam Levy is looking at how the power of the crowd could bridge a vital gap.

Interviewer: Adam Levy

It’s hard to think of a piece of infrastructure that’s more essential than a bridge. These bottlenecks of transportation keep our world moving. Here's engineer Thomas Matarazzo.

Interviewee: Thomas Matarazzo

They’re really essential to modern societies. We need bridges to exchange goods, services and for people to be able to connect with each other.

Interviewer: Adam Levy

And so, keeping these connections alive and healthy is vitally important, but monitoring the health of bridges is also a tricky business that requires long, skilled investigations, or high-tech expensive monitoring. But what if it didn't require either and could be handled by something as simple as a bunch of smartphones? Well, that's the idea Thomas has been exploring in a paper out recently in Communications Engineering. I called him up, and he started out by telling me just how important it is to keep bridges up and running.

Interviewee: Thomas Matarazzo

Bridges are expensive and they're not straightforward to maintain, and they're very critical to a functioning transportation system. If you have one bridge that is suddenly unavailable, then that could potentially make it impossible to get from city A to city B, right? And bridges don't necessarily have a way of communicating with us or telling us if there's a problem. But without monitoring them, there is no way to know for certain what the exact condition of a bridge is.

Interviewer: Adam Levy

So, up till now, if engineers would like to check up on the health of a bridge, how would one actually go about that?

Interviewee: Thomas Matarazzo

Essentially, it's a visual inspection. You will have professional engineers surveying the entire bridge, looking at critical components, doing visual examinations of them, looking for cracks, looking for corrosion. And so, it's a very thorough inspection by a professional engineer. This is overall a great method. And some of the big shortcomings that we see with visual inspections are that they don't happen frequently enough and that visual inspections can be subjective or miss visual cues of damage.

Interviewer: Adam Levy

I suppose one way of overcoming some of those limitations is to place sensors actually on a bridge to measure a lot of the things that maybe the eye can't see and measure things over time. Why is this sometimes not a practical approach?

Interviewee: Thomas Matarazzo

This is, overall, a very effective approach, in terms of getting the information. The problem with the sensor network is that it's not scalable. We have over 600,000 bridges in the US and to have to purchase a sensor network and maintain that sensor network and have folks that are able to correctly analyse that data could be a very expensive endeavour.

Interviewer: Adam Levy

You actually set out to investigate the health of perhaps the most famous bridge in the entire world, which is the Golden Gate Bridge in California. And you set out to investigate this using crowdsourcing. Can you explain how something so complex could possibly be sourced from a crowd?

Interviewee: Thomas Matarazzo

It really is not intuitive because everything I just told you suggests that you need this high-tech, sophisticated, expensive sensor technology to measure the dynamic properties of bridges. And so, it was really only over the course of a decade of research that led us to that point where we were ready to make that scientific hypothesis and perform this test of simply, what if we use smartphones in moving vehicles? If we collected enough of this ‘low-quality’ data, would the information we have be comparable to the past studies that have used high-quality data on this bridge? Smartphones have about a dozen sensors in them, and one of the sensors available is an acceleration sensor. We're also using GPS to keep track of the position of the phone as it's travelling over the bridge.

Interviewer: Adam Levy

Now, how accurate are the results you end up getting from the ‘low-quality’ data out of these smartphones?

Interviewee: Thomas Matarazzo

In some cases, the estimates we were getting from the smartphone data was impressively accurate. Overall, the errors were very low. In all cases, we saw errors that were below 3%. This type of accuracy is really desirable. The reason why we're able to get such high accuracy is by aggregating the different datasets that we've collected. Maybe on one data set, a car is driving fast, another dataset, the car is driving slow. As you aggregate the data, you're able to see more what's in common among these datasets and what's in common with these datasets are the bridge vibrations.

Interviewer: Adam Levy

Now, you didn't actually detect any defects which, of course, is good news for the Golden Gate Bridge. But do we know if this approach can actually detect defects when it needs to?

Interviewee: Thomas Matarazzo

So, what we're going to be looking for are important dynamic properties that will change if there are structural defects. And so, modal frequencies are a really important dynamic property of bridges. And they really opened the door to other types of dynamic features and properties with which we can reliably predict condition based on vibration data.

Interviewer: Adam Levy

How big could the benefits of this approach actually be in terms of the lifespan of bridges?

Interviewee: Thomas Matarazzo

We put together some analysis to quantify the potential benefits of this plan. If you started to use crowdsourced data immediately as soon as a bridge was built, over the course of the lifespan of that bridge, the information that you have from crowdsourced data could add over 14 years of service to that bridge without any additional costs.

Interviewer: Adam Levy

Now, you actually used Uber, the ride-sourcing app, to collect this data. Why use a private company's app? And does this actually create any challenges to piggyback off this?

Interviewee: Thomas Matarazzo

One of the exciting things about ride-sourcing companies is that they've collected an abundance of data just to help their everyday business operate. And so, these are large, pre-existing datasets that are out there, and their potential for providing important information on bridges has been completely untapped. So, the idea here is that these datasets exist, and there's a huge potential here for these types of datasets to just be repurposed and produce important dynamics information of bridges.

Interviewer: Adam Levy

What then would actually be your hope for how this kind of crowdsourced data on bridges could change how we monitor the health of bridges in the first place?

Interviewee: Thomas Matarazzo

I think, fundamentally, the first thing we are hoping for is widespread adoption. The ideal case is we have an automatic system that can detect potential abnormalities that may not yet be visible to the naked eye, and that we start to think about visual inspections in terms of instead of this huge endeavour where you have a few individuals looking over every component of the bridge, it's more of a check-in because we have assurance from the two years of data that we've been collecting.

Host: Nick Petrić Howe

That was Thomas Matarazzo from the US Military Academy, West Point in the United States. To find out more about that paper, we'll put a link to it, along with a link to the special issue of Communications Engineering that is part of, in the show notes.

Interviewer: Benjamin Thompson

Finally on the show, the UN’s Climate Change Conference, COP27, kicked off a few days ago in Egypt. And as we speak, thousands of people, including world leaders, scientists and activists are coming together to continue negotiations aimed at reigning in global warming. To find out what’s been happening and what to expect, I’m joined on line by Jeff Tollefson who covers all things climate here at Nature. Jeff, thank you so much for joining me today.

Interviewee: Jeff Tollefson

Thank you, Ben.

Interviewer: Benjamin Thompson

We're recording this on Tuesday afternoon UK time, and the conference proper began yesterday. What's been happening so far? We've already seen a speech from the UN secretary-general António Guterres, who said that we're on a highway climate to hell, and we're in the fight of our lives and we're losing.

Interviewee: Jeff Tollefson

Yeah, I mean, it's just kicking off. These are early days. But there are a few things that we do know. Going into the conference of course, as the secretary-general has mentioned, we have a lot of science suggesting that the world is way behind on their commitments, and we are headed for much more warming than world leaders have committed to under the 2015 Paris agreement. So, that's kind of the basic backdrop. The question is what happens at this meeting and why does it matter? That's a little bit of a complex question. This isn't like last year at COP26. The actual discussion over emissions reductions is a little bit more complex. Countries are setting up for a big review that is scheduled to end next year. So, this is a little bit of an off year. But as the secretary-general says, there's no such thing as an off year when it comes to climate change and carbon emissions.

Interviewer: Benjamin Thompson

And emissions reduction is, of course, paramount in terms of doing something about climate change. But another thing that seems front and centre this year relates to finance.

Interviewee: Jeff Tollefson

Yeah, so finance is always important. The wealthy countries of the world have committed US$100 billion per year, a long time ago, and have failed to make good on that promise. So, that's kind of a perennial issue. This year, there will be a new focus on climate impacts. So, the finance that's been out there thus far has mostly gone to mitigation efforts to curb emissions, promote renewable energy, this kind of thing and then for adaptation, basically efforts to help countries prepare for global warming. But what happens when you have a big storm? What happens when you have a big drought? Those are unavoidable impacts and they cost money. So, we had massive flooding in Pakistan and Bangladesh this year, drought in Africa, various things going on all around the world that cost money. And low-income countries are basically saying we didn't cause this problem and yet we're experiencing the impacts. We want you to pay for those impacts. It's called ‘loss and damage’, and it was actually just this week formally voted on to the agenda in Sharm El-Sheikh in Egypt. So, we're going to have the first kind of set of formal negotiations over this.

Interviewer: Benjamin Thompson

And in some quarters, this is a very controversial idea, and certainly in several cases, wealthy nations who perhaps bear the greatest responsibility for global warming are pushing back against paying compensation to countries who don't.

Interviewee: Jeff Tollefson

Yeah, absolutely. I mean, the biggest fear among wealthy countries – the US is kind of leading this charge but I think it's probably more or less true everywhere – the biggest fear is that wealthy countries don't want to write a blank cheque that would put them on the hook for any number of problems that are going to arise in the future. But the thing is that it's not really the future anymore. The future is already here. We're seeing these impacts today and we can calculate them, and the science has evolved around this front, to the point where scientists are now able to kind of make estimates of how much global warming is contributing to many natural disasters. So, that's the question: is there some kind of negotiation where wealthy countries might agree to help pay for these damages? Is there a way around this political impasse?

Interviewer: Benjamin Thompson

And you say negotiations are about to start then. What are people you've spoken to saying about the likelihood or finding a resolution?

Interviewee: Jeff Tollefson

Yeah, I don't think anybody knows, frankly. There have been some proposals put out there, but whether you can get everybody on board for a singular solution is really unclear. I don't think it's going to get resolved this year, so we have to think about COP27 as the starting place for this discussion.

Interviewer: Benjamin Thompson

And if that's one of the major things that will be discussed at the conference, Jeff, what else should we be looking out for? I mean, lots of pledges were made at the last COP. Is there going to be a stock-taking aspect to this from last year, do you think?

Interviewee: Jeff Tollefson

Well, they're starting that process. So, there's a formal kind of stock take that's scheduled to complete in 2023. So, the discussions now are about how that process is going to work. There are some countries that have stepped forward with new climate commitments. There was a call at Glasgow for countries to come forward and update their pledges voluntarily this year. So, we'll see. There may be new announcements. We just don't quite know yet on that front. That said, one early indication, we had an election in Brazil. Former president Lula has been re-elected, and his team is already at work at COP27, negotiating an alliance among tropical rainforest nations, so I think the talks right now involve the Democratic Republic of the Congo and Indonesia. Among those three you’ve got the bulk of the world's tropical forests, and deforestation has been a long-time issue. There have been a lot of commitments. Those commitments have generally not been followed through on and the question now is whether these countries can collaborate, devise a plan that might allow for money to flow and for policies be put in place that would actually reduce deforestation. So, that's another thing to watch. We'll see how that evolves during the COP.

Interviewer: Benjamin Thompson

And obviously, Jeff, you speak to a lot of folk ahead of the conference and while it's going on – researchers and policymakers and what have you. What's the sense that you've got of what people are hoping from COP27, and how does it compare to what did happen at COP26 maybe?

Interviewee: Jeff Tollefson

Well, some people have referred to this COP as the implementation COP, and I think that's what people want to see. In some ways, COP26 was about increasing ambition, which is to say increasing political commitments. But what I think everybody in the world is waiting for, certainly scientists and environmentalists and people who want to see progress on global warming, is implementation. This will be the twenty-seventh of these COPs, and emissions just keep going up, and this year is likely to be no different. We had a brief dip during the pandemic but then emissions started to rise again. So, really, what everybody's hoping for is action. And there's one last question on the agenda at this COP. There's a new kind of mechanism that they're trying to create that would allow countries to share information and share best practices, if you will, and maybe devise ways to kind of accelerate action on the ground. It's not clear what that looks like. But that's one of the questions that people will be addressing here. But regardless of what comes of that, I think that's the question that looms over this process. Is it actually accomplishing anything? Are governments going home from these meetings and implementing policies that will actually reduce emissions, that will close down coal plants, that will increase investments for renewable energy? And any hint that we can get out of these meetings that governments will take them seriously and go home and do what needs to be done, I think is what people are hoping for.

Interviewer: Benjamin Thompson

Nature’s Jeff Tollefson there. For the latest news on what’s going on at COP, look out for links in the show notes.

Host: Nick Petrić Howe

That’s all for this week. As always, you can keep in touch with us on Twitter – we’re @NaturePodcast. Or you can send us an email to podcast@nature.com. I’m Nick Petrić Howe.

Interviewer: Benjamin Thompson

And I’m Benjamin Thompson. Thanks for listening.