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Graphene blessing! New nano "sponge" can efficiently filter organic pollutants in water


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Efficient adsorbents for industrial wastewater treatment are important to minimize potential environmental damage. Especially for organic dyes, as a kind of important industrial pollutants, they usually have high water solubility, non degradability, and many have carcinogenicity. Li Changxia and Freddy Kratz of the school of chemistry of the University of Vienna and their colleagues have now proposed a new method to design innovative composite materials, which are composed of nano porous ultra-thin covalent organic frameworks (COF) on graphene and can be used to efficiently filter organic pollutants in water. The study was published on Angewandte Chemie.

Source: Angewandte Chemie International Edition (2022)

"There are several methods to purify water today, including activated carbon filters, but there is still room for improvement in application efficiency or adsorption capacity," said Li Changxia, the first author and post doctoral researcher.


Freddy kleitz of the Functional Materials Research Institute of the Institute of inorganic chemistry is developing new nano porous materials. For the same volume, the porous material has a much larger total surface area than the non porous material, so a particularly large number of molecules can be accumulated on the surface during the adsorption process.

Covalent organic framework (COF) is a relatively novel material. They are particularly porous while being low in density and light in weight. Covalence means that their chemical bonds are formed by electron pairs between atoms.


The dye size studied by the researchers in their aqueous model solution was about 0.8 to 1.6 nm. "We have developed a new method of using water to form COF in a relatively environmentally friendly manner. Therefore, we are able to develop a small 'sponge', whose designed pore size and pore shape are in the nanometer range, and the adjusted negative surface charge is very selective when the positively charged target molecules (that is, our dyes) are pulled out of the water," the researchers said "Just like a sponge absorbs water, it is a pollutant only in our case."


When bulk COF powder is used, due to the blockage of pores at the outer edge, the inner pores of the material often no longer contact with pollutants, especially for large pollutant molecules. The new composite developed by the researchers provides a completely permeable structure: for this purpose, the researchers cultured COF on thin graphene nanosheets. Graphene itself is a combination of a 2D carbon atom layer and a COF layer up to 2 nm thick, forming a compact and open 3D structure. The ultrathin COF layer can expose more adsorption sites than the bulk COF powder.

On the other hand, the larger honeycomb pores in the graphene network support the transport of water through the filter material.


The large pores of the graphene network are combined with the ultra-thin COF layer with a large number of adsorption sites, so that particularly fast and efficient wastewater treatment can be realized. Since the material input of graphene is relatively low, and the composite material can be reused as a filter after the pollutants are washed away, the development is also relatively cost-effective.