Imperfect graphene's "gorgeous turn"

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â– Chinese and foreign graphene dynamics

The preparation of high-quality graphene materials is like woven cloth. Researchers should "finely work" on this monoatomic film composed of hexagonal honeycomb-shaped carbon atoms, while ensuring high quality is not easy. The superiority of graphene is due to its perfect structure. Once the structure is destroyed, even a very small damage will lead to a significant decline in its performance. Therefore, defective graphene is difficult to use in the preparation of high-end precision products such as transistors. However, graphene, which is as imperfect as “coarse cloth”, has great potential in terms of decontamination and environmental protection, and purification of the environment.

No longer worried about oil spills

Referring to the 2010 US Gulf of Mexico oil spill, I am afraid that it is still worrying. At that time, it was a headache and helplessness. The effect of seawater oil removal was not good enough to curb the damage caused by oil spills to the marine ecology.

Two years later, the internationally renowned journals Advanced Materials and Advanced Functional Materials reported a graphene-based adsorbent with ultra-efficient adsorption characteristics. The material can be used to clean up offshore crude oil leaks, chemical pollution, adsorbed pollutants up to 800 times its own quality, and can be recycled more than 20 times. AOL and other media believe that this graphene sponge structure may become the first industrial application of graphene, and has great application prospects in chemical and environmental protection.

The Science and Technology Daily reporter interviewed Professor Sun Litao, the leader of the study and director of the Southeastern University-FEI Napymi Demonstration Center. He said that they use a pulverized graphene material to make a porous sponge-like structure, and through various methods to achieve the regulation of its microstructure, in order to optimize the adsorption performance and mechanical properties of graphene sponge. After research, they found for the first time that graphene sponge has ultra-high-efficiency adsorption characteristics, and it can absorb oil and other organic substances without water absorption. It has been successfully used to quickly remove oil leakage at sea and achieve efficient separation of oil and water. In addition, by firmly bonding graphene and a commercial sponge, a graphene-based composite sponge having strong mechanical strength can be obtained. The sponge is combined with a negative pressure system to achieve continuous oil-water separation, greatly improving separation efficiency and reducing the cost of use.

The graphene sponge assembled from the defective graphene sheet has a large accommodation space and a high porosity. The graphene material in the entire sponge accounts for less than 1% of the volume and can be recycled. In order to further reduce the cost of materials, they also prepared carbon aerogels using waste cotton or waste paper as precursors. It has been tested and its effect on adsorption and recycling of various organic liquids is good, and trial production has been achieved.

Let the sea water quickly become fresh water

Graphene is called "magic material" with its unique mechanical and electrical properties, but its interaction with water is confusing: graphene surface repels water, but the capillary channel of graphene film immersed in water allows water to be fast penetration. The “briefing” relationship between graphene and water has fascinated scientists.

The University of Manchester collaborated with the research team of the University of Science and Technology of China to explore the mechanism by theoretical analysis and molecular simulation. It was found that the graphene oxide film in the water environment can form a channel of about 0.9 nm wide when intimately contacted with water. Ions or molecules of this size can pass quickly, while the "big head" is completely blocked. This screening effect not only requires very precise ion size requirements, but is thousands of times faster than conventional concentration diffusion. This finding reasonably explains the experimental results, also known as the "ion sponge effect."

Using a computer to simulate the rapid filtering of ions by graphene nanochannels, it is found that the interaction between graphene and ions causes ions to accumulate in the nanochannels, thereby promoting the rapid diffusion of ions. If the size of the capillary channel in the graphene film is further compressed by mechanical means, and the pore size is controlled, the salt in the seawater can be efficiently filtered. This means that it is expected to become a filter device that will desalinate a cup of seawater into drinking water in a matter of minutes.

The internationally authoritative academic journal Science has published the results of this research. In the review, it is believed that graphene oxide films are of great significance in many separation applications, such as achieving rapid desalination and purification of seawater. With this feature, the future of human beings turning the sea into a huge reservoir may no longer be a fantasy.

Expected to be a weapon

At present, most of the filter materials that play a key role in some anti-fog masks and air purifiers rely on the electrostatic principle to adsorb PM2.5. However, when the mist is exhaled in the water vapor or the nose and mouth, these electrostatic effects are weakened or even disappeared, thereby reducing the effect of blocking PM2.5 and making these filter materials ineffective.

Graphene has an extremely high specific surface area and excellent chemical stability, and has great potential in air purification. Conventional filters are difficult to produce ultra-small pore sizes by existing processes. Sun Litao told reporters in an interview that his research team combined graphene oxide with traditional filter materials and successfully prepared a graphene oxide-based filter material that can efficiently remove bismuth. Since the removal of PM2.5 by the filter material is purely physical barrier, it is not affected by moisture and has long-term stability.

In addition, the defective graphene skeleton is very thin and has a large number of pores. Therefore, the porous filter membrane assembled by the inner pores is staggered in the vertical and horizontal directions, thereby ensuring that the filter material can effectively retain PM2 when the pore diameter is larger than 2.5 μm. .5, while ensuring the lower respiratory resistance of the filter material, solving the problem of poor breathing of most anti-fog masks.

Defective graphene is not perfect, but researchers have unearthed its inherent potential, enabling it to achieve its gorgeous turn, and to show its talents in environmental protection and decontamination.

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