Scientists develop new graphene material dialysis membrane

(1) graphene grown on copper foil; (2) peeling graphene from copper foil using polycarbonate support sheets; (3) scientists using interfacial polymerization to seal large numbers of cracks and defects in graphene (4) etching a hole of a specific size in the graphene using an oxygen plasma.

Dialysis is a process in which a filter membrane is used to filter material molecules from a solution to make it a more dilute solution. In the medical field, dialysis, also known as dialysis, is often used for blood purification. In addition, dialysis is also used for drug filtration and purification, removing impurities from chemical solutions, and using dialysis membranes to isolate specific molecules for medical diagnosis.
At present, commercial dialysis membranes are less efficient in separating filter molecules, mainly due to their structure: these dialysis membranes are relatively thick, and the filtration pores on the dialysis membrane are also dense, making it difficult for the targeting molecules to pass through quickly. Dialysis membrane.
Recently, engineers at the Massachusetts Institute of Technology (MIT) have successfully produced a highly functional dialysis membrane with a thickness of only 20 nm using graphene sheets, a single-layer carbon atom material, for nanometer-sized aqueous molecules. Rapid filtration is currently 10 times faster than dialysis membrane filtration. Moreover, the dialysis filtration efficiency of the graphene sheet itself is 100 times that of the conventional filter membrane.
Piran Kidambi, a postdoctoral fellow at MIT, said that graphene is now widely used in electronics and other technologies, and our research and development has further led graphene technology to thin film technology, especially laboratory-scale separation processes and blood dialysis.
Kidambi said: Because graphene is very thin, it is very fast to dilute with it. When the material molecules pass through the graphene dialysis membrane, unlike the conventional dialysis membrane, it is required to pass through the porous structure which is thick and has a sharp path.
Kidambi is the first author of the study and the results are published in the journal Advanced Materials. The other six co-authors are from MIT, including Rohit Karnik, professor of mechanical engineering, and Jing Kong, associate professor of electrical engineering.
The researchers first used chemical vapor deposition to grow a layer of graphene on the copper foil, then peeled off the copper foil, transferred the graphene sheet to the support sheet of the polycarbonate material, and the polycarbonate support sheet was distributed large enough. The pores allow any molecule to pass. The polycarbonate support sheet acts as a bracket to prevent curling of the ultra-thin graphene sheets.
Then, the staff used oxygen plasma technology to etch micropores on the graphene dialysis membrane, so that molecules of a certain size can be selectively filtered by the graphene film. Oxygen plasma is a technique in which oxygen is pumped into a plasma chamber to etch materials.
By adjusting the parameters of the oxygen plasma, we can control the density and size of the micropores. Among them, an oxygen radical combines with one carbon atom of graphene and reacts more rapidly, thereby generating carbon dioxide and escaping. The vacancy left by the missing carbon atoms is a micropore. The staff found that the longer the graphene sheets were exposed to the oxygen plasma, the larger the micropores were constructed and the more dense they were. A very small hole can be constructed with an exposure time of around 45-60 seconds.
Subsequently, the researchers placed the graphene dialysis membrane in a dilution chamber and tested the dialysis membranes with different pore sizes and pore distributions. The inlet side of the dilution chamber was injected with a mixed solution of molecules of different sizes, including potassium chloride (0.66 nm wide), vitamin B12 (1-1.5 nm), and lytic enzyme (4 nm). At the outlet of the dilution chamber is a dilute solution. The worker then measured the flow rate of the molecules as they penetrated each layer of graphene film.
The study found that the microporous dialysis membrane can filter out the macromolecular L-tryptophan, while the potassium chloride directly permeates. Macroporous dialysis membranes can pass directly through macromolecular materials.
At the same time, the staff also compared the filtration effect of the current commercial dialysis membrane. The comparison results show that the filtration speed of the graphene dialysis membrane is 10 times faster than that of the ordinary dialysis membrane.
According to Kidambi, the micropores etched on the polycarbonate support sheet account for only 10% of the total support area, which limits the filtration of certain molecular materials to some extent. But the filtration performance of only the 10% area is much higher than the current dialysis membrane performance. ( Compile: China Superhard Materials Network )