Galaxy Technology Empire

July 1st.

Huang Haojie and a group of researchers from the Seawater Desalination Research Institute are discussing some issues with seawater desalination technology.

Theoretical calculations prove that graphene can be used in seawater desalination, and the single-layer nanopore two-dimensional membrane produced has ultra-high selective separation efficiency compared with traditional seawater desalination membranes.

However, the grain boundaries existing inside large-area graphene will reduce the mechanical properties of graphene. The process of introducing nanopores will further reduce the mechanical properties, causing the separation film to easily undergo local rupture, greatly reducing the separation efficiency and separation selectivity.

Of course, this problem is nothing to Galaxy Technology, and atomic manipulation technology can perfectly solve this problem.

Current graphene desalination membranes are divided into two categories.

One type is the single-atom-thick nanoporous film studied by the team of MIT professor Rohit Karnik.

However, the mechanical strength of single-atom-thick graphene is weak, so the graphene used in experimental studies is supported by polymer films.

And sub-nanometer pores are directly introduced into graphene through high-energy electron beam bombardment or oxygen plasma etching. The pore size distribution range is wide, which greatly reduces the separation efficiency, so it cannot be applied in practice.

Another category is the graphene oxide film studied by the team of Andre Geim, a professor at the University of Manchester and winner of the Explosives Physics Prize.

Graphene oxide is easy to mass-produce, but after the graphene oxide film is immersed in the solution, the graphene oxide sheets will absorb water and expand the interlayer spacing, reducing the seawater desalination efficiency. Therefore, existing research work mainly focuses on how to control graphene oxide. The interlayer spacing between ene sheets.

In addition, there are also relevant research results in China.

That is a binary structure graphene film that combines graphene nanosieves and carbon nanotubes. This film combines the selective separation efficiency of the former with the strength advantages of the latter.

Single-atom-thick nanoporous two-dimensional materials have minimal water transmission resistance and maximum water penetration flux, making them ideal materials for constructing ultra-thin and efficient seawater desalination membranes.

However, applying ultrathin 2D materials to actual seawater desalination faces two major difficulties.

The first is how to prepare large-area, crack-free nanoporous two-dimensional films with excellent mechanical strength and flexibility.

The second is how to introduce sub-nanometer pores with high density and uniform pore size distribution inside the film to achieve efficient and selective passage of water molecules and effective interception of salt ions/organic molecules.

Regarding the first problem, carbon nanotubes have excellent mechanical properties and are similar in structure to graphene, and the two can interact through π-π bonds and van der Waals forces.

The carbon nanotube film formed by overlapping carbon nanotubes is a porous network structure (average pore diameter 300 nanometers) film, which not only perfectly matches the structure of graphene, but also does not affect water permeability.

Therefore, domestic research institutions thought of combining nanopore graphene with carbon nanotubes to make up for the shortcomings of the former.

They first grew a single layer of graphene on copper foil, and then covered some areas on it with a network of interconnected carbon nanotubes. After the copper foil was etched away, a graphene film supported by carbon nanotubes was obtained.

In order to obtain high-density sub-nanometer pores with uniform pore size distribution, they grew a layer of mesoporous silicon oxide with uniform pore size distribution (average pore size 2 nanometers) on the surface of graphene as a mask, and used oxygen plasma etching to remove the mesoporous silicon oxide. Graphene within pores.

The longer the oxygen plasma etching time is, the more graphene is etched away and the larger the pore size of the graphene is.

In this way, the pore size of the graphene nanosieve can be controlled by adjusting the oxygen plasma etching time. When the etching time is controlled at 10 seconds, the pore diameter is 0.63 nanometers, which can effectively allow water molecules with a diameter of 0.32 nanometers to pass through and block salt ions with a diameter of 0.7 nanometers.

This kind of film can be suspended, bent, and stretched without polymer support without obvious cracks.

Test and calculation results show that the new film can withstand 380.6MPa stress and has a Young's modulus of 9.7GPa, which is three times that of a carbon nanotube film and equivalent to 2.4 times the tensile stiffness and 10,000 times the bending strength of a nanohole graphene film. Stiffness.

So, they made a large and strong graphene mesoporous film.

So what about its filtering performance?

Within 10 seconds, the permeability of the etched graphene nanosieve/carbon nanotube film can reach 20.6 liters per square meter per hour per atmosphere.

After 24 hours of penetration, the salt ion rejection rate is greater than 97%.

Compared with the commercial cellulose triacetate desalination membrane, the water permeability of the new graphene nanosieve/carbon nanotube membrane is increased by 100 times, and the anti-pollution ability is stronger.

And because it is not restricted by the internal concentration polarization effect, the membrane can still maintain a high water permeability in a high-concentration salt environment.

The new graphene nanosieve/carbon nanotube film made by domestic research institutions does not require polymer support, is strong and durable, and has multiple advantages of permeability efficiency.

Of course, this seawater desalination technology is not without its problems, that is, it is difficult to mass produce. If the mass production problem is solved, it can be applied on a large scale.

When Huang Haojie set his sights on graphene seawater desalination technology, he recruited this domestic research team.

"Dr. Yuan, are there any other problems with your seawater desalination membrane?"

Hearing Huang Haojie's words, Yuan Quan smiled and replied:

"There is no big problem. With the help of atomic manipulation technology, the composite film of graphene and carbon nanotubes has already achieved preliminary mass production, and the quality of our film is very strong."

She really admired Huang Junjie. Atomic manipulation technology was definitely a revolutionary technology.

If the graphene carbon nanotube composite film developed by her previous team has a seawater desalination efficiency of 1 per square meter; then the graphene carbon nanotube film produced using atomic manipulation technology has a seawater desalination efficiency of 10 per square meter.

The reason why there is such a big gap is that there are no defects in graphene-carbon nanotube composite films made with atomic manipulation technology.

Although this new type of film is also a graphene carbon nanotube composite film, its strength is nearly ten times stronger. The increase in strength can increase the atmospheric pressure to force the desalination of seawater to accelerate.

Currently, one square meter of membrane can produce 80 cubic meters of fresh water per hour and 700,000 cubic meters of fresh water per year.

In other words, if we want to achieve an annual output of 40 billion cubic meters of fresh water, we only need 57,000 square meters of membrane.

Of course, the service life of this film is about 4100 hours, which is equivalent to needing to be replaced every six months.

The production cost of this seawater desalination film is about 1,500 yuan per square meter.

Calculating this, a factory with an annual output of 40 billion cubic meters of fresh water needs to purchase 171 million yuan in seawater desalination membranes every year.

Of course, Huang Haojie would not sell it to a seawater desalination plant at cost price. After all, this company is dominated by the national team, and the ex-factory price of the film will be at least five times higher.

Including other electricity bills and the like, the annual operating cost of a factory with an annual output of 40 billion cubic meters of fresh water is about 1.2 billion yuan.

The equivalent operating cost per cubic meter is 0.03 Chinese yuan. Adding in equipment, infrastructure, and transportation costs, the cost per cubic meter of fresh water can be reduced to about 0.17 Chinese yuan.

The current water charges for various industries are: residential water: 2.80 yuan/cubic meter; administrative water: 3.90 yuan/cubic meter; industrial and commercial water: 4.10 yuan/cubic meter;

Water used in hotels, restaurants, catering industries, etc.: 4.60 yuan/cubic meter; water used in the bathing industry: 60 yuan/cubic meter; water used in the car washing industry and purified water: 40 yuan/cubic meter; water used in agriculture: 0.60 yuan/cubic meter.

Even for agricultural water, there is still a 400% profit margin.

Of course, due to the nature of this enterprise, except for agricultural water, the remaining water is wholesaled to various cities for use, and the wholesale price is 0.5 Chinese yuan per cubic meter.

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