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I am very happy to have the opportunity to discuss with you such a familiar substance—water.

Water is a common substance, but for scientists, water is arguably one of the most complex substances in nature. So far, more scientific research is still needed to explore the nature of water, so water is a very strange world to us.

strange water

Water can be said to be everywhere. Traces of water can be found on the ground, underground, and even in outer space and outer planets. But the water is actually very strange, why do you say that?

The first example I want to take you to Antarctica to take a look.

The temperature in Antarctica is very low, and a lot of water will freeze. However, there are still many fishes living freely in such a cold place.

Why don’t fish freeze at such a low temperature?

After scientific research, it was found that there is a substance called antifreeze protein in the blood vessels of these fishes, which can inhibit water from turning into ice.

This is a very interesting phenomenon in nature, but it has not been known to everyone.

Actually, water has many other very strange properties.

For example, when most substances change from liquid to solid, their volume will decrease. But when water freezes, its volume will increase and its density will decrease, and the density of water will be the highest when it is 4°C.

This phenomenon is contrary to common sense.

In addition, if we do an experiment, put a bottle of hot water and a bottle of cold water in the refrigerator at the same time, you will find that hot water freezes faster than cold water.

This is also a very strange phenomenon.

In addition, there are also studies on freezing people, freezing organs, and organ refrigeration. In fact, it is similar to why fish don’t freeze.

One of the most important issues is that when freezing the human body, it is necessary to ensure that the water in the body cannot freeze. Once the water freezes, it may become a small ice ball, which will pierce the cell membrane and inactivate the organ.

Simply looking at the phenomenon of water freezing, in fact, there are many physical and chemical processes that are not known to everyone, and more in-depth scientific methods are needed to explore these issues.

Someone has concluded that water has more than 70 abnormal properties.

In addition to the heat shrinkage and cold expansion mentioned just now, that is, the abnormal density, there are many other characteristics such as high specific heat, high melting point, thermal conductivity, and tension.

These properties are still under research, and we still don’t fully understand what their inner mechanism is.

Therefore, on the 125th anniversary of the publication of Science, it raised 125 of the most challenging scientific questions of this century. One of the questions is “What is the structure of water”, which shows that the structure of water is actually The above is the most critical part of understanding the nature of water.

If we can understand the structure of water from the microscopic level, we will be able to better understand many of the characteristics of water and solve the problem of the century.

Quantum effect of water

Everyone knows that water is made of water molecules, so what do water molecules look like?

Like the one drawn in this picture.

The water molecule is actually very simple, just two hydrogens plus one oxygen to form a simple three-atom molecule. This is the chemical composition that we all know well.

However, we mentioned in an article published in “Science” four years ago that the structure of water is actually not that simple. Water has some quantum effects.

What is quantum effect?

In the classic image, simple water is two hydrogens and one oxygen. Even if you heat it up and add some disturbance, it is still in this configuration.

However, if we analyze with more precise means, we will find that hydrogen atoms have certain fluctuations in space, which means that they have no definite positions, but some probability distributions.

The spatial fluctuation phenomenon of hydrogen atoms will have a great impact on the structure and properties of water, including hydrogen bond interactions, which makes water exhibit some very abnormal characteristics.

As an example, if we don’t consider hydrogen atomsDue to the occasional quantum effect, many chemical reactions in our body may not occur at all, or at least slowed down by more than 1,000 times.

So, if there is no quantum effect of water, we humans may not exist, and all living things will not exist.

After our work came out, many businesses launched some “quantum water”, which is said to be a kind of water that is good for our health.

But what I want to say is that this quantum may not be another quantum. Every bottle of water you hold in your hand can be said to be quantum water. Because quantum effect is an attribute of water itself, this is a conceptual hype phenomenon.

Single water is so complicated, so if water and water are put together, is its structure more complicated?

There is an interaction between water and water. This interaction is called hydrogen bonding.

What is a hydrogen bond?

The oxygen in the water is negatively charged and the hydrogen is positively charged. When water molecules are put together, the positively charged hydrogen and the negatively charged oxygen will attract each other. This mutual attraction is the hydrogen bond.

It is like treating a water molecule as a person, just like people and people hand in hand, it becomes a water network structure.

Hydrogen bonds have many strange properties. For example, it has synergy. If the state of holding hands with another person changes, it will affect the state of a bunch of people around.

Hydrogen bonds are also flexible. If I let go of my hand, then I can easily hold hands with another person, so it has a very strange and very flexible feature.

In addition, Hydrogen bonds also have directionality. The hydrogen bond is always hydrogen to oxygenIn order to form a bond, if hydrogen points to hydrogen or oxygen points to oxygen, this bond will not be formed.

These three characteristics cause water to form a very complex network structure called a hydrogen bond network.

If we can figure out the structure of the hydrogen bond network, it is very possible to completely unravel the mystery of some abnormal properties of water, and even manipulate the properties of water.

Three phases of water

Everyone knows that water has three phases.

It is a solid and an ice phase at low temperatures. The water molecules in the ice phase are arranged in their own positions, forming a regular and orderly network structure. .

If the temperature of the ice is raised a little bit, it will melt. After melting, these water molecules will not be able to stay, they will go to other places, and even go to gaps, so they will become disordered. The liquid structure.

In the case of a liquid, water molecules are in a completely disordered state without any regularity, periodicity.

If the temperature rises further, the water molecules and the water molecules will gradually move away from each other, their bonds will be broken, and finally it will become a gaseous state without any interaction.

In the three phases of water, although the ice phase is relatively simple, so far, we have found that there are about 18 ice phases. Under different conditions, it exhibits different structures.

The liquid phase can be said to be the most complex phase in water so far. There is no theory or experiment that can answer the structure of the liquid phase.

In the past few decades, there have been a number of experiments and theories trying to answer this question, and many models have been proposed, such as the tetrahedral model, the chain loop model, the completely random chaotic model, but no A model can give a satisfactory answer.

So, until now, the structure of liquid water is still under intense debate.

It seems that the merchants have solved this problem. They already know what the structure of liquid water is, or that they can make the water molecules in the liquid water gather into small groups by some means, and then make the small groups easier to pass Our cell membranes are absorbed by the body and promote metabolism.

Unfortunately, this phenomenon or claim is still not scientifically supported and needs to be further confirmed.

So what shall we do?

The most direct way is to see the water molecules and be able to know where the water molecules areLocally, how it is arranged into a network structure, it has several water molecules in this network, this is my original intention of studying water.

I saw a real-space image of a single water molecule for the first time

In order to see the water molecules, we cannot use the common optical microscope, because its resolution is far from enough, so here is the introduction of scanning tunneling microscope, abbreviated as STM.

The scanning tunneling microscope was invented in 1981 by two Swiss scientists, Bining and Rohrer, who won the Nobel Prize in Physics in 1986. They could see the atomic structure of the surface with this microscope, which was a very remarkable achievement at the time.

Why can STM see atoms? Of course, it is not to look directly with the eyes. More vividly, it should be to perceive atoms and touch atoms like a blind person.

In real situations, instead of touching the atom with our hands, we take a very thin and sharp tip to get close to the atom. When the tip and the atom are close enough, there will be a very Local tunneling current is generated.

When scanning the surface, it can beThe atomic fluctuations on the surface are imaged. So, We don’t actually see the atom, but perceive it.

STM working principle

Many people have asked me, how sharp do you need to do this? Because what you want to see is an atom, not an ordinary matter.

Actually, for a moment, the diameter of the tip of the needle tip should be one thousandth of that of a human hair. This size is completely invisible under an optical microscope.

Not only that, even if you have a needle with such a small diameter, you still can’t guarantee that you can see the atoms. You must go through a very complicated method to modify some single atoms or modify a single molecule at the end of the tip, so that you can see very high Resolved image.

To use an image metaphor, the tip of a needle is like a large cloud behind a tornado, but it is precisely some of the most advanced atoms and molecules that are the most important factor in obtaining high-resolution images. This image closely reflects the true shape of the needle tip.

These are two scanning tunneling microscopes in our laboratory, or scanning probe microscopes.

In order to see water molecules, ordinary scanning tunneling microscopes are not enough. We have to drop it to more than 260 degrees below zero, which is very close to absolute zero.

In addition to low temperature, we must also put STM in a very high vacuum environment, the vacuum degree can be compared to the vacuum degree in the universe. This will hold the molecule firmly on the surface and prevent it from moving around.

In addition, due to the very high vacuum, the molecules in the surrounding atmosphere will not interfere with water molecules.

In such a pure environment, we can finally see the real-space image of a single water molecule for the first time, we can see many V-shaped structures.

If you stack the water structure, the microstructure you see is exactly the same as the water skeleton, not only the bond angles, but also the bond lengths.

This is the first time that humans can clearly see the structure of water molecules.

However, sometimes I see a strange image of water molecules.

For example, the image on the right is a black hole; the one on the left is actually water molecules.

Put the water molecule up, we will find that it is not the skeleton of the water molecule, but the electron cloud generated by the electrons around the water molecule. There are more electrons in bright places and fewer electrons in dark places, so an image that can be said to be exactly the same as a black hole is formed.

The size of these two substances may differ by more than 20 orders of magnitude. We have to feel that the natural world is so exquisite, and the two materials with such a large difference in scale are so consistent in the image.

the boundary of “ice”

Since we can see a single water molecule, what can we do?

We can play it slowly, raise it, or shoot it.

The first thing, we want to see what the ice looks like, and how the ice grows. This is a very basic concept, but no one actually knows what is going on.

If you go to the South Pole or North Pole, there is a lot of thick ice on the sea. This kind of iceis actually the substance formed by the piles of thousands of water.

Can you reduce such a thick layer of ice layer by layer, and finally reduce it to a single layer of ice. What is the structure of a single layer of ice? How did it grow? This will affect our understanding of the formation of thick ice.

Finally one day, we accomplished this thing. This work was just published in the journal Nature at the beginning of this year (2020).

We saw a high-resolution image of the atomic structure of a single layer of ice, and we can see that it is a honeycomb structure, which is exactly the same as the graphene honeycomb structure we are familiar with, so we call it a graphene-like structure.

In addition, its boundary is actually more complicated than the honeycomb structure, because it not only has a zigzag boundary composed of six rings, but also a complex boundary composed of five rings and seven rings. , We call it the “armchair” border.

After seeing this boundary, we can take photos of its growth state.

For example, for the jagged border, we found that it first grows a five circle in one positionThe ring and then the five-rings are further extended to form a series of five-rings in a queue, but there are some gaps between these five-rings.

What to do? The water molecule is very smart. It can be directly embedded in these gaps, bridging these five-rings together, like a bridge, and finally turning it into the initial six-ring state, which completes a growth .

This is the true growth state of the ice we see under the microscope.

Once we know how ice grows, we can tell materials scientists how to prepare some special materials to inhibit the formation of ice, or to promote ice formation.

This is one example. We made a material that looks the same on the top and bottom, but in fact we have done a special coating treatment on the upper and lower parts of this material, the upper is the anti-icing coating, the lower is the icing-promoting coating .

Put this material under water vapor, and then drop to a low temperature, and the water will start to condense and freeze on the surface.

A very rough and granular ice grows on the coating above, and a very flat layer of ice grows on the coating below. At this time, when the wind blows, the ice particles above are easily blown off, but the ice layer below will be firmly sucked on the surface, and it won’t be blown off.

We finally found that we can artificially control the behavior of materials to inhibit or promote icing, which actually has very important practical significance.

For example, studying the formation of ice and rain in the atmosphere.

The cold water freezes on the interface

Another example is anti-icing on the surface, preventing organs from being punctured by ice ballast when organs are refrigerated.

For the first time human beings have seen “salt water” at the atomic level

I just talked about pure water, but in fact, water interacts very interestingly with other substances.

One of these interactions is called “ionic hydration.” This word sounds very strange, but I will give you an example that everyone will find it very familiar.

If we pour a spoonful of salt directly into the water and shake it again, the salt will soon disappear, because the salt is dissolved in the water.

Why does the salt dissolve? From a microscopic point of view, it’s probably like this: Salt is sodium chloride, which is composed of chlorine and sodium.Soak the sodium chloride in water, the water molecules will slowly drag away the two ions of sodium and chloride, and the water molecules will be wrapped around the dragged ions, thus forming a cluster structure , This cluster structure is the ion hydrate, and this process is called the ion hydration process.

The process of ion hydration has been realized by chemists more than 100 years ago, but no one has really seen what ion hydrate looks like so far, is it possible to What is the configuration of water molecules around the ion? How many water is around the ion? In fact, these basic questions are difficult to answer.

We can clearly see under the microscope that a hydrate formed by one water and one ion, two water and one ion, three water, four water and other different numbers of water molecules can form strange things with one ion. The structure, and its configuration is also very interesting.

This can be said to be the first time we humans can see salt water clearly at the atomic level.

Actually, it is not so easy to want to see salt water.

Under normal circumstances, we put salt in water to dissolve it into ionic hydrates, but this method is not feasible for us.

We must artificially create a single ion hydrate with a needle so that the imaging becomessimple.

So we designed a very interesting method. We can use a needle tip to simulate the process of dissolving ions in water, artificially create ion hydrates containing different numbers of water molecules, and then take pictures.

In addition to seeing the state of water, we also found that when a certain number of water molecules are wrapped around the ion, the ion hydrate can diffuse very quickly on the surface, which is a very interesting magic number effect.

Only when a certain number of water molecules are encapsulated, the ion can obtain a relatively large velocity.

When the human body absorbs ions, the ions must pass through the ion channel to be absorbed by the human body, but the ion channel itself is very narrow, and it is an atomic-scale channel.

It’s anomalous that in fact, ions can pass through ion channels very efficiently.

Our work actually provides a very interesting understanding of whether ions are surrounded by a certain number of water molecules when they pass through the channel. Water molecules can help ions pass through the ion channel efficiently.

This actually provides a new idea for the interpretation of biological ion channels.

Water-Potential Clean Energy

Finally, I want to talk to you about energy.

Before we used a microscope to look at the water, so can we manipulate the water?

The answer is definitely yes.

We can decompose water, break its hydrogen-oxygen bond, and turn water into hydrogen and oxygen.

What is the meaning of producing hydrogen? Hydrogen is a very clean and highly efficient energy source. The combustion of hydrogen can generate a huge amount of energy.

At the same time, hydrogen becomes water after burning, and water can be decomposed into hydrogen, which can form a recyclable clean energy, and no pollution will be produced in this process.

If we have a way, can efficiently decompose water into hydrogen and oxygen, the world’s energy problem will be solved.

Junior high school chemistry taught us how to split water. When electricity is directly connected to the water, the water becomes hydrogen and oxygen. This is a very simple process.

But this process cannot be used for commercialization, and it cannot be used to generate energy.

Because the electrode materials are very expensive, platinum materials are used, and in addition, they must consume a huge amount of electricity. So people try every means to break through these two bottlenecks.

First of all, can we find some cheaper materials that are close to the efficiency of platinum electrodes to replace platinum so as to reduce costs.

Recently, we found that after some special treatment of molybdenum disulfide, its hydrolysis efficiency can be compared with platinum, but it is not yet fully compatible with platinum. This shows that after a series of efforts, We may find such materials to replace expensive platinum electrodes.

Another idea, because it consumes a lot of electricity, can we decompose water into hydrogen without electricity?

Many scientists are also working in this direction. For example, design some special catalysts to react with mixed liquid phases so that water can be directly decomposed into hydrogen without electricity. But unfortunately we have to heat it to a certain extent, and heating also consumes energy.

If heating is not required, is it possible to automatically decompose water at room temperature?

We can use sunlight. Sunlight has a lot of energy. If the catalyst is soaked in water, and the water will automatically decompose into hydrogen and oxygen under the sunlight, wouldn’t it be a very pleasant thing.

Unfortunately, the efficiency of photolysis of water is still very low, and further improvement and optimization are needed.

Today I showed you some of the characteristics of water.

In fact, water is also a very important substance in our living body. Without water, proteins cannot be folded; without water, chemical reactions in the human body will not occur, and humans will not exist.

From this, we can see that in terms of structure, water is a very soft substance, but in science it is a very difficult piece of bone.

Scientists have used the most advanced experimental and theoretical simulation methods to try to reach the atomic and molecular scales, hoping that through high-resolution research, they can reveal more of the mystery of water, so that water can better serve and benefit mankind.