Water Technologies by Interface Engineering
Seth Darling – Argonne National Laboratory
Driven by climate change, population growth, development, urbanization, and other factors, water crises represent one of the greatest global risks in the coming decades. Advances in materials represent a powerful tool to address many of these challenges. Understanding—and ultimately controlling—interfaces between materials and water are pivotal. In this presentation, Dr. Darling will lay out the challenges and present several examples of work in his group based on ALD materials engineering strategies for addressing applications in water. In each instance, manipulation of interfacial properties provides novel functionality, ranging from selective transport to energy transduction to pollution
0:00:01 Hi, my name is Seth Darling. I work at Argonne National Laboratory where I'm the director of the 0:00:06 Center for Molecular Engineering and I also direct an energy Frontier Research center called um use 0:00:12 advanced materials for energy water systems. And today I'll be talking about ways that we can use A. 0:00:18 L. D. And related methods to advanced water technologies. So we're all aware of just how essential 0:00:27 is water is in our daily lives. We all need it to survive of course and for sanitation and other 0:00:32 purposes. But in fact water is actually much more important to our society than you may realize from 0:00:38 this direct interaction we have with it every day. You need water to make just about anything. All 0:00:46 of the raw materials we use from paper to plastic to rubber, cotton all require tremendous amounts 0:00:53 of water to manufacture. What that means is that the goods that are made from these things, the 0:00:58 phone in your pocket, the clothes that you're wearing, the chair that you're sitting on. all of 0:01:02 these things require tremendous amounts of water. So as the world continues to develop, each 0:01:09 individual's water footprint is growing dramatically. Even electricity requires water to generate. 0:01:15 So demand is skyrocketing around the world and yet supplies are under increasing threat due to 0:01:22 climate change, unsustainable use, pollution and so on. So As you can see from these projections 0:01:29 published in the New York Times back in 2019, water stress is all over the place and it is expanding 0:01:36 going forward and we'll continue to do so. This is literally one of the biggest threats we face as a 0:01:41 society Over the next century or two. Okay, now there are all kinds of things we need to do to 0:01:48 address those challenges involving policy and infrastructure and so on. But there are also many 0:01:53 opportunities for science and technology to address these water challenges and many of these science 0:02:01 and technology opportunities come down to water solid interfaces the place where materials meet 0:02:08 water or more generally Aquarius fluids. This is what controls the performance and properties of 0:02:14 membranes and sensors ands orbits and issues like fouling. So many of the underlying component 0:02:22 technologies in water treatment processes rely on what happens in water solid interfaces. At the 0:02:29 same time, water solid interfaces are rather poorly understood. There is this wonderful quote from 0:02:36 the great scientist Wolfgang Pauli, who said God made the bulk surfaces were invented by the Devil. 0:02:43 And this is because, you know, while there's still plenty to learn of course about bulk solid 0:02:48 materials in bulk liquids fluids, there is much more to be learned about the interface between them 0:02:53 because it is so much more complex where those bulk properties become disrupted for both the solid 0:02:59 material and the fluid. This is actually the mission of our Energy Frontier Research Center, amused 0:03:06 where we have a collection of fantastic researchers from Argon National Laboratory where it's 0:03:10 headquartered a number of faculty members from the University of Chicago as well as some from 0:03:15 Northwestern University. All focused on this question of water solid interfaces and trying to 0:03:20 understand them more clearly in terms of absorption and reactivity and transport and ultimately how 0:03:26 that understanding can deliver better technologies. So I'm gonna give you examples from my own group 0:03:34 where we use primarily tools like L. D. And related methods to manipulate these interfaces, these 0:03:40 water solid interfaces. And we're gonna start with some examples from the world of membranes. 0:03:44 Membranes are one of the wonderful ways in which and treat water but they are particularly prone to 0:03:52 the scourge of fowling. Fowling is basically where stuff dunks up on a surface and this is 0:03:58 ubiquitous and water systems. Water systems are notorious for fouling membranes are particular 0:04:03 challenge in this context, because of course, membranes are porous materials and you need water to 0:04:08 transport through the membrane in the context of water treatment. And so as those pores get dunked 0:04:13 up with stuff, of course, it is harder for the water to pass through and ultimately it won't at all. 0:04:18 And one of the most problematic Fallon's is oil and particularly oils like crude oil, which tend to 0:04:24 stick very aggressively to surfaces and follow them up. So you can see that as an example here, 0:04:32 here's pictured a piece of a polymer membrane. This is a commercial polymer membrane with some crude 0:04:39 oil on it. That's that black blob there in the center. And as you'll see when this is submerged 0:04:44 under the water, the oil remains firmly adhered on that interface, it won't come off. You can rinse 0:04:48 it and backflow and so on. It will not release from the surface. If you take that same polymer 0:04:55 membrane and tailor the interface using A. L. D. But not changing the poorest nature of the material 0:05:04 so it can still perform a separation. You can see here. The difference in its resistance to fouling 0:05:10 the crude oil on the surface just lifts right off leaving behind a pristine membrane. So why does 0:05:16 this happen? Well, here's some snapshots from some molecular dynamics simulations performed by a 0:05:22 collaborator at Argon. Uh Subaru, pictured in the corner where they've taken some amorphous slabs of 0:05:29 various metal oxides. And here we're picturing aluminum oxide, titanium dioxide and tin dioxide uh 0:05:35 with water liquid liberating over the surface and dynamical fashion. And you can see just by eye 0:05:42 from these snapshots that the aluminum oxide has very little water near the interface. But the 0:05:46 titanium and tin oxides have these tightly bound hydration layers. You can see it as well here in 0:05:52 the correlation functions on the right Where there are actually two tightly browned hydration layers 0:05:57 on both the titanium and tin oxide and only very weakly bound water with the aluminum oxide. And 0:06:03 it's actually that tightly bound water that delivers this fouling resistance. Because the water is 0:06:10 bound so tightly, the oil cannot actually touch the oxide and therefore it can never foul it or not, 0:06:16 never, but will be less prone to fouling it so released so much more easily when it's just exposed 0:06:20 to some water. Now, what I was showing you was some static videos of kind of uh gently placing a 0:06:29 fouled membrane in in water. The question is, can this actually prevent fouling during a real 0:06:34 filtration or separation process. And here I need to introduce the two geometries, the two common 0:06:40 geometries used infiltration to better understand these experiments and these are dead infiltration. 0:06:46 Which is what we most often do in research labs where you're pushing the entire feed stream down 0:06:53 through your membrane with of course, hoping to filter out the things that you're trying to target. 0:06:59 That is actually not typically the way that filtration is done in industry, the way it's done much 0:07:04 more commonly in industry as so called cross flow filtration, where the feed stream is running 0:07:09 parallel to the surface of the membrane and the trans membrane pressure is sufficient enough for the 0:07:15 in this case water to pass through the membrane and the salutes to be blocked. The reason that cross 0:07:20 flow is usually used in industry is because that sheer force associated with the tangential flow 0:07:25 will tend to remove these Fallon's that might get stuck on the surface or at least remove some of 0:07:32 them. Now, I'm going to show you an example using debt infiltration. The reason for this is because, 0:07:37 as I just described, fouling occurs much more aggressively in a dead end system, so it's easier to 0:07:42 probe your anti fouling technology um, when fouling is happening more aggressively. So what we have 0:07:50 here is a dead end cell with a crude oil in water emulsion, which you can see picture being pushed 0:07:56 down through the membrane and in this case the oil droplets and that emotion are larger than the 0:08:02 poor side, so they get filtered out as you can see in the feed and permeate solutions there. The 0:08:07 problem is, as you can see pictured on the right, the flux of water going through this polymer 0:08:13 membrane plummets very rapidly because of fouling with the oil. And even if you rinse it with water, 0:08:19 you get no recovery of that flux again because it has been fouled. But if you take that same 0:08:26 membrane and replace it with one that's been coated with one of those eld oxides that has the 0:08:31 tightly bound hydration layers, you get very different performance. You can see here with this tin 0:08:36 oxide that the flux will still decline because it's in a dead end geometry. And we're just kind of 0:08:42 collecting oil droplets near the surface. But when you rinse this with water, you recover your flux 0:08:47 because it's not actually touched the oxide. It's not fouled the interface and it will just rinse 0:08:52 right away. So really simple treatment for that interface that can give you a significant 0:08:58 improvement in performance. Now, that might get you really encouraged about what L do can L. D. Can 0:09:05 do for membranes but there is a catch here which is that commercial polymer membranes are made from 0:09:11 many different chemistries. Many different polymers. This is not an exhaustive list here, but these 0:09:16 are some of the most common polymers used to make membranes. And some of these polymers have 0:09:22 functional groups that are good at binding those LD precursors to give you a nice coating on your 0:09:27 interface. Things like poly ether cellphone for example, which has the cell phone groups or maybe 0:09:32 the carbonell groups you might find uh and some other polymers. But many of the most common polymers 0:09:38 used to make membranes like P. V. D. F. Or polypropylene have no such functional groups. There's no 0:09:44 way to easily new create an L. D. Con formal coating on these membranes and thereby you can't get 0:09:50 all of these advantages that I showed you in that previous example. But we've developed a pretty 0:09:57 simple solution to this problem which is to use one step before you do the A. L. D. And that is 0:10:03 dipped coding in a solution of a molecule like tannic acid. So tannic acid is pictured there it 0:10:09 looks like kind of a complex molecule. It's actually a naturally occurring uh compound that's found 0:10:14 in tree bark and other places. Uh And tannic acid is not particularly unique or magical here. It's 0:10:22 just an example of a molecule that has the features we're looking for which is minorities that will 0:10:27 bind to those types of polymers that don't have the right functional groups like polypropylene or P. 0:10:32 V. D. F. Because it is hydrophobic uh minorities. But it also has functional groups like carbonell 0:10:38 groups that will bind the L. D. Precursors. So it acts as kind of a bridge between the membrane and 0:10:44 the L decoding. So you can take your A P. V. D. F. Membrane, simply dip it in a solution of tannic 0:10:49 acid and then proceed with A. L. D. Like normal. And you should be able to get all of that same 0:10:54 functionality I showed. But now with basically any pollen remember. So here's an example of a bunch 0:10:59 of little coupons of polymer membranes that have been dip coated in tannic acid and then with 0:11:07 various numbers of A L. D. Cycles. And the brown color you see is indicative of the oxide coating 0:11:13 forming on the on the membrane. You can see in the pristine column the left most column that even 0:11:19 after, you Know 50 or 70 eight LD cycles, you're barely seeing any oxide forming on the surface 0:11:24 because again there aren't inherently binding groups for the L. D. Precursors on this membrane. But 0:11:31 even with a modest pre treatment with tannic acid, we can start getting good L. D. Codings with 0:11:36 relatively low numbers of cycles and you take those same pieces of membrane, you just dunk them in 0:11:41 water because remember what we're trying to do is to create that hydra filic surface that will bind 0:11:46 protective water layers. And here you can see that while the native membrane doesn't really get wet 0:11:52 easily by water. With a simple pre treatment with tannic acid, just a few A. L. D. Cycles will start 0:11:58 making your membrane hydra filic. And so just like before you can put these into a dead infiltration 0:12:05 cell in this case the gray data are from a membrane that we tried to code using A. L. D. But did not 0:12:11 pre treat and you get that big drop influx that does not recover. Whereas the one that's been pre 0:12:16 treated so therefore has a good l decoding on it. Now has this beautiful recovery of flux with water 0:12:22 rinsing just like we saw before. Now that's a really effective way to extend the operational 0:12:30 lifetime of your membrane and a fowling environment. But it will still ultimately failed because 0:12:35 that is an example of what's called a passive anti fouling strategy meaning it's just trying to 0:12:40 prevent Fallon's from touching the surface. At some point they will and once they have nuclear 0:12:46 waited on the surface they can spread you'll lose that protective hydration layer and the membrane 0:12:51 will become fouled. So to be more aggressive ultimately you're going to need something that will 0:12:57 break down those felons degrade them into smaller pieces that will then go back into the water. And 0:13:03 one of the great ways to do that is using potala sis. One category of which is photo callouses. 0:13:08 We're using light to drive the reactions. So infotech Attallah sis, you're shining your your light 0:13:13 on generally a semiconductor generating electrons and holes. And when you're in water in an inquest 0:13:20 environment, both electrons and holes will react with that water and species in the water to produce 0:13:26 a variety of reactive species like super oxide radicals, hydrogen peroxide. Um the holes can create 0:13:34 hydroxyl radicals for example. And these all will attack organic substances like oil and break them 0:13:42 down into smaller fragments and ideally all the way down even to basically fully mineralized carbon 0:13:49 dioxide and water. So if those organic substances or Fallon's, that will cause them to detach from 0:13:57 your surface. Now, one of the most common, probably the most common photo catalyst used in this 0:14:04 context is titanium dioxide. And that's because it offers all kinds of really great advantages. It's 0:14:09 earth abundant. It's nontoxic. It's stable and water of course, that's important here. And it's very 0:14:13 effective at creating reactive oxygen species roos even under ambient conditions, you don't have to 0:14:19 heat it up or apply pressure or what have you. There is though, one drawback to titanium dioxide and 0:14:26 that is that it requires an ultraviolet light to activate it because it has a relatively large band 0:14:31 gap about three electron volts. That means you need UV light and that doesn't mean it's useless. You 0:14:37 can of course use UV lamps and this is done. But that increases the expense. And also makes it more 0:14:43 difficult to use in, say, developing world applications where you don't necessarily have access to 0:14:48 electricity, let alone ultraviolet lights. In that case. What would be really nice is if you could 0:14:54 get the same type of functionality of T I O two but with visible like and what would be really great 0:15:01 is if you could even use sunlight which of course is free and plentiful. So how do you take catalyst 0:15:09 like T. I. 02 and make it sensitive to visible light? One of the great ways to do that is with 0:15:14 doping and one of the dough opens that's particularly effective in this regard is nitrogen. You can 0:15:20 just put a little bit of nitrogen into your T. I. 02 and that will make it sensitive to visible 0:15:25 light because it places states in the gap. So you can see pictures here of three membranes. Uh 0:15:31 pristine membrane on the left, one that was coded by A. L. D. With regular T. I. 02 in the middle 0:15:37 and then one with the doped T. I. 02 on the right. And by I you can see that that membrane with the 0:15:43 nitrogen doping has this sort of yellowy orange color which tells you it's absorbing visible light. 0:15:49 And the U. V. Spectra here confirmed that where you're picking up this whole part of the kind of the 0:15:53 blue into the green part of the spectrum. Whereas the regular tho to only absorbs out in the in the 0:16:01 ultraviolet. So now you can take a membrane like this and just shine visible light on it sunlight or 0:16:06 simulated sunlight and perform focus palaces and water. So here's the concentration plotted, for 0:16:12 example of just organic molecule and water over time with light shining on the membrane system. In 0:16:20 water with just the starting membrane you get no degradation of that organic. But with the nitrogen 0:16:27 duty I owe to you can see this nice photo catalytic activity where it's progressively degrading the 0:16:33 organic species in the water. And you can use this to make a membrane that will actively degrade 0:16:39 foul in such that it can be self cleaning. So here again, we're plotting the flux of water going 0:16:44 through the membrane over time. And we're starting with the lights off because we don't want any 0:16:48 photo ca palaces to happen at the beginning here And there are two membranes whose data are plotted 0:16:54 here, one that we coated with regular T. I. O. Two and one that's been coated with nitrogen doped T 0:16:59 I. 02 So we have some initial water flux in these membranes. And now we're going to intentionally 0:17:05 foul them. We're introducing a protein here called bovine serum albumin, which is known to stick 0:17:10 aggressively to these membranes. And you can see the flux drops significantly at some point when 0:17:16 we've dropped it down to, you know, somewhere, say below half of where it started or so. Uh we 0:17:21 remove that talent and we reintroduce clean pure water. And here you can see there's no recovery in 0:17:28 the flux because this is truly foul. This is a irreversibly fouled membrane, it wasn't just kind of 0:17:34 loosely attached to the surface. Now, all we do is turn on the lights. And what you can see is 0:17:42 there's this phenomenal recovery in the flux from the nitrogen doped sio two just with visible light 0:17:48 shining on the membrane. This is in situ in in Operandi even in the filtration cell that this is 0:17:54 happening now, that's a severely fouled membrane that is showing self cleaning. Of course, in most 0:18:00 real filtration processes, you're not gonna have that much foul and present, it will be. There is 0:18:04 more of a dilute or trace contaminant in your in your feed stream. So, here's maybe a more realistic 0:18:12 setting where we've given it just a constant exposure to the foul UNt. But at a lower concentration. 0:18:17 And as you can see here, as long as you keep the lights on this nitrogen doped sio two membrane can 0:18:24 stabilize its flux higher than 95% of its original flux value, more or less indefinitely. I'm only 0:18:30 showing five hours here, of course. But um you can see it's it's gotten flat and in principle this 0:18:35 could have an indefinite operational lifetime under this type of a fowling environment. As long as 0:18:41 the lights are on. 0:18:45 Here's another application for membranes. This is a photo from a wastewater treatment plant. And if 0:18:51 you ever go to a wastewater treatment plant, you'll see a lot of tanks that look like this. This is 0:18:55 an aerobic digestion tank and that frothiness you see on the surface because of a bunch of bubbles 0:19:01 that are being added to the tank through aeration generation process. The reason they had the 0:19:07 bubbles is because there are microbes living in the water that degrade the pollutants that are in 0:19:12 the water and their metabolism is such that they're feeding on all of this waste. They need extra 0:19:17 oxygen to keep going there aerobic microbes and so they have to add that oxygen in the form of air 0:19:23 bubbles through the water in order to keep it working effectively. And this is a huge energy expense 0:19:29 in water treatment. It's actually the largest energy consumption in one of these plants. As these 0:19:34 aeration in the aerobic digestion tanks. So if you can make those that aeration process more 0:19:40 efficient, there'll be a huge energy efficiency gain in water treatment. And the way you make 0:19:46 operation more efficient is to make the bubbles smaller because a smaller bubble has more surface 0:19:51 area to volume ratio. So more of the oxygen will get into the water and not release at the surface 0:19:56 back into the atmosphere. So to make smaller bubbles, we're going to make a special type of membrane 0:20:04 called a Janice membrane. Janice membrane is one that has different properties on its two faces, 0:20:09 like the roman God Janice. And there are many different ways to make Janice membranes and they're 0:20:14 useful for many different types of things. I'm just going to show you an example here from 0:20:18 generation and specifically we're going to make a type of Janice membrane where the properties are 0:20:24 moving in a Gradient from one face to the other. Now those properties can be any two different 0:20:29 properties positive charge or negative charge. Hydrophobic city and hydra Felicity or what have you. 0:20:35 Okay. Uh in this case we're going to be playing some tricks with the A. L. D. To not get a perfectly 0:20:42 can formal and uniform coding throughout the poorest membrane material but rather to create a 0:20:47 gradient by getting the right um diffusion conditions for the L. D. Precursors going down through 0:20:55 the porous material. So here you can see a cross section of a porous membrane uh where the blue over 0:21:01 laid on the micrografx. Here is the aluminum signal going down through that cross section. And you 0:21:07 can see the gradient there with your I. Uh And what's cool with A L. D. Is that you can actually 0:21:12 tune the shape of that gradient. We can make it steeper by using more L. D. Cycles like you're 0:21:17 seeing here. Or we can even move kind of the location of the curve down through the depth of the 0:21:23 membrane by playing with for example, pressure or temperature. So we have really arbitrary control 0:21:30 over the shape of what that gradient looks like of the inorganic material going down through the 0:21:34 member cross section. Just to show you can actually make a Janice membrane this way here's the same 0:21:40 membrane top and bottom and you can see the water droplets on the backside which was not coated. Uh 0:21:46 You still have that hydrophobic city where the water balls up and on the front face where we exposed 0:21:51 it to the metal oxide. We now have a hydra filic surface where the water droplets spread out. So why 0:21:58 did we do this? The idea is we're gonna pressurize air up through the column, into the water through 0:22:06 the membrane and in the native membrane which is hydrophobic everywhere. Uh It's also arrow filic. 0:22:13 It likes air so as the air bubble starts to come up through the poor in the membrane, it's going to 0:22:17 spread out on the surface of the membrane which likes the air more than the water. And so you're 0:22:22 gonna end up with this really big uh bubble of air that will eventually release from the surface 0:22:28 when it has enough buoyancy from being big enough. The idea of the Janice membrane is we've made 0:22:33 just that top surface there hydro filic so that now is the air starts to come out of the membrane. 0:22:39 Water will undercut it because it's hydra filic and sarah phobic and then it will release when it's 0:22:44 a much smaller and here I'll just play them side by side. You can see the polymer membrane on the 0:22:50 left before it was treated has these very large bubbles. And the one on the right that we've turned 0:22:55 into a Janice membrane now releases very small bubbles, thereby giving you more oxygen in your water 0:22:59 for the same energy input. Mhm. So let's move on to our next example outside of membranes now into 0:23:08 something called steam generation. And most of the folks working in this field of steam generation 0:23:14 talk about this in the context of desalination through distillation, which may very well be a useful 0:23:20 and very interesting technological application. Uh one that really motivates me in this field is a 0:23:26 little bit different, which is pictured here. This is evaporation ponds at a mining operation. This 0:23:32 is an aerial photograph, there are buildings and roads and in the shot there to give you a sense for 0:23:36 scale. These are huge evaporation ponds, very common in mining operations are also in hydraulic 0:23:43 fracturing operations, where you get massive amounts of waste water generated in the process and 0:23:49 that water is filthy, it has salts in it, it might have radionuclides, it can have organic materials 0:23:54 and all kinds of stuff which make it not safe or legal to dump it into a waterway or in many cases 0:24:01 to re inject it back into the ground. So instead, what they have to do is just wait for it to 0:24:05 evaporate. And this is a huge challenge in in all of these industries because evaporation is slow. 0:24:13 Much of the heat involved with the sun shining down on these evaporation ponds is just lost to the 0:24:18 surrounding environment not going into evaporation. The question is, can we make that more efficient? 0:24:23 So, in an evaporation or even distillation process very energy intensive. Because you're heating up 0:24:29 this huge bath of water takes a huge amount of energy to break all those hydrogen bonds and then 0:24:34 ultimately drive it into the vapor. And if you're distilling it, you'll of course then re condense 0:24:38 the purified water. The idea here is you're using a plentiful renewable source though sunlight. So 0:24:45 it's not pulling energy off the grid, but we still don't want to heat up the entire bath of water 0:24:49 because again, that'll get lost to the surrounding environment. What we want to do instead is to 0:24:54 place a material at the interface. The air water interface, that is a photo thermal material that 0:24:59 will convert light to heat very efficiently. And the idea then, is all of that energy gets focused 0:25:07 right where it needs to be, where the evaporation happens at the air water interface. But you need 0:25:12 that material to do lots of things. It's got to absorb a big part of the solar spectrum, efficiently 0:25:17 convert that light to heat, prevent the heat from being lost down to the water bath below. Its got 0:25:22 to transfer the heat to the water to evaporate it at the interface. You need water to transport up 0:25:27 through it. So it's got to be porous, effectively needs to be buoyant so it floats on the surface. 0:25:32 Obviously it has to be water stable and you saw the scale on that picture, it's better be low cost 0:25:37 and scalable or what's the point here? That's a lot of requirements for material. But it turns out 0:25:43 folks are finding lots of ones that work Well, one that we've discovered works well. It's actually a 0:25:47 very old material, chinese calligraphy ink which is just a natural material made by burning wood 0:25:52 under certain conditions and formulating it with some other natural materials. And you can get this 0:25:57 nice black material that can be coded easily on surfaces. You can see here the chinese character for 0:26:02 for water under thermal imaging with sunlight shining on it gets quite hot. Not surprisingly, 0:26:08 because it's black. It's a carbon nano material. But there is one thing that this chinese ink 0:26:15 doesn't have, which is water stability. In fact water is the solvent and in chinese things. So of 0:26:19 course it's going to disperse in water. So if you were to take some porous material code on your 0:26:25 chinese ink, put it on the water. It just dissolves back off the surface and disperses. So here's 0:26:30 where L. D. Can come to the rescue again, you just coat your porous material with the chinese ink. 0:26:35 It can be a membrane, a sponge piece of fabric. What have you would even works and then you overcoat 0:26:40 it with an optically transparent metal oxide film, like titanium dioxide, for example, that 0:26:47 encapsulates it and secures it on the surface so that it won't disperse when it's placed in water. 0:26:53 And you can see how effective this is here. Here's beakers of water with thermal imaging. One just 0:26:58 on the top row is just a beaker of water that gets kind of lukewarm when exposed to sunlight. 0:27:02 Whereas if you put one of these photo thermal l destabilized materials at the top, you get all that 0:27:08 thermal energy focused right where you want it to be at the air water interface, big jump in 0:27:13 temperature and much faster evaporation of water for the same energy input. So this can dramatically 0:27:19 increase the efficiency of this process. The last example I want to show relates to another way to 0:27:26 treat water which is orbits and specifically the one we want to target here is oil spill pollution, 0:27:34 huge challenge. This is a photo from deepwater horizon, but of course oil spills happen in water 0:27:38 bodies all the time. There have been many major ones just this past year and literally thousands of 0:27:43 them happen every year of different scales and most of the soil never gets cleaned up. That that 0:27:49 does is most often just burned in place, turning a water pollution problem into an air pollution 0:27:54 problem. What would be great as if you could have absorbent that would selectively soak that oil up 0:27:59 out of the water and then it will be even greater as if you could reuse your absorbent because 0:28:06 otherwise you'd have to have enough of it to scale to the size of the spill, which is of course 0:28:09 completely impractical. And something like deepwater horizon, you want to be able to capture the oil, 0:28:14 recover the oil and then reuse this orbit and keep going back for more. So here we're going to use a 0:28:20 variant of L. D. Called sequential infiltration synthesis for those who aren't familiar with it. Uh 0:28:27 The idea here is you're dealing with a substrate that is porous to the L. D. Precursors, like a 0:28:32 polymer. The space between the chains is as uh sufficient for the molecules to diffuse through. So 0:28:40 instead of kind of the millisecond and military type pressures and times you use an L. D. With 0:28:45 little pulses that might form an inorganic film on top of your polymer substrate and S. I. S. We use 0:28:52 typically larger times higher pressures. So the integrated exposure is much larger and allows those 0:28:58 precursors to diffuse down into the polymer film. And if you have functional groups that will bind 0:29:03 them, you can form a composite material. And classic example is try method aluminum and water just 0:29:11 like an L. D. But with a polymer with functional groups that will bind the Try method aluminum like 0:29:15 carbonell groups that you might find in something like PM. Emma. And you can see here in this cross 0:29:20 section of a P. M. A film, you can actually grow aluminum oxide in this case inside of the film 0:29:25 rather than as a coating on top of it. Okay, so here we're going to take a polymer like polyurethane, 0:29:32 which you might be sitting on right now. It's used in seat cushions, which does not like oil more 0:29:37 than water. In fact like oil and water about the same. We're going to do S. I. S. On this to grow a 0:29:42 metal oxide uh down into all those little fibers that make up the phone. And then we're gonna use 0:29:49 that as an anchor for a silent ization reaction to attach molecules that have the properties that we 0:29:55 want in this case being Olio filic, oil loving and hydrophobic water heater. And I'll show you a 0:30:02 video here where you can see this uh in action. We've got a uh sponge that we've treated in the way 0:30:10 I just described. And this is oil and water. We just died. The oil blue to make it a little bit 0:30:16 easier to see and hear is an oil spill. A small one, admittedly. And you'll see what the sponge can 0:30:22 do it selectively and rapidly grabs the oil. So that's great because it was only a filic. You wanna 0:30:28 be able to recover the oil, which is easy by simply squeezing it. And then as I said, you want to be 0:30:34 able to reuse yours orbit, which you'll see right here. And the beauty of this uh technology is that 0:30:41 you can do this over and over again. Uh you can just keep squeezing it like a kitchen sponge and 0:30:46 reusing this orbit repeatedly. We actually don't know what the limits on reusability here are 0:30:52 because unfortunately, Ed the postdoc here gets tired of doing this experiment before we see any 0:30:58 drop in performance. So certainly dozens or 100 times maybe even more than that. We can't say for 0:31:04 sure. Now we have scaled up this technology for testing at a tank like this and I'm just going to 0:31:11 show in the interest of time to videos side by side. Uh, we'll start with the one on the right. 0:31:16 We've actually taken this olio sponge as we call it out onto the open ocean and the pacific ocean. 0:31:22 There's a place where oil leaks out of the sea floor naturally and forms a sheen on the surface of 0:31:27 the ocean, which you can see there, that kind of rainbow pattern. And you'll see in a moment a big 0:31:32 pad made out of that olio sponge, which we drag across the oil sheen and it'll pick it right up off 0:31:38 the surface. Um So this works out on the open water and oil sheen by the way is almost impossible to 0:31:45 clean up. Otherwise you can see the oil on the surface of the pad on the left. Now, if you look at 0:31:51 that video, you can see a whole bunch of those pads which have been submerged under the surface of 0:31:57 the water. That is a cloud of crude oil being exposed underneath the water in the water column, as 0:32:04 it's called, exposed to a big wall of olio sponge for a period of time. And then that crane you see 0:32:11 picture there is used to lift that wall out of the water. We can take the pads then off of their 0:32:17 frame, put them through this ringer and squeeze out the fluid that was captured. And the question is, 0:32:22 do we actually get any oil? Of course, you'll have some water in the sponge because it was submerged 0:32:26 in the water. But did you actually get any oil? Which is a different physical challenge than 0:32:31 cleaning oil off the surface And you can't tell him that shot. But here in the next one, you can see 0:32:37 that is brown water coming out of there because we did in fact pull oil out of the water, um which 0:32:43 was the first ever example of cleaning crude oil out of the water column. So we're excited about 0:32:48 that, showing you examples from membranes and catalysts and solar steam ins orbits. But there are 0:32:54 many other ways in which controlling water solid interfaces can help with water technologies that I 0:32:59 didn't have time to talk about sensors and fighting corrosion and so on. Again, it all comes down to 0:33:04 these water solid interfaces and L'd and related tools are a great way to come call them. Whole 0:33:10 bunch of folks contributed to the work that I showed you hear the one individual I really want to 0:33:14 highlight as my colleague and friend, Jeff Allam, who for my money, is the best LD scientists in the 0:33:20 world. And I'm really lucky to have him as a as a longtime collaborator uh and he worked on pretty 0:33:25 much everything that I showed you here today. Funders are along the bottom of the screen and with 0:33:31 that I want to thank you so much for your attention finished in learning more about water. Feel free 0:33:35 to check out. The only book ever written by three sevenths Water is available from booksellers near 0:33:42 you. And the website for our Energy Frontier Research Center is pictured there. Thanks so much.