Nano-sponges with potential for rapid wastewater treatment
Efficient adsorbents for industrial wastewater treatment are important to minimize potential environmental damage. In particular, as an important group of industrial pollutants, organic dyes are usually highly soluble in water, non-degradable, and many are toxic to carcinogenic. Changxia Li and Freddy Kleitz of the Faculty of Chemistry at the University of Vienna, together with colleagues, have now presented a new approach to design an innovative composite material, consisting of a nanoporous, ultra-thin covalent organic framework (COF) anchored on graphene, which is highly efficient. is in filtering organic pollutants from water. The study is published in Angewandte Chemistry.
“There are several ways today, including activated carbon filters, to purify water, but there is still room for improvement in the efficiency or adsorption capacity of the applications,” said lead author and postdoctoral researcher Changxia Li.
Freddy Kleitz’s group at the Institute of Inorganic Chemistry-Functional Materials is developing new nanoporous materials. Porous materials have a much larger total surface area than a non-porous material for the same volume and thus can accumulate a particularly large number of molecules on the surfaces during adsorption.
Highly porous COF as a new class of materials
Covalent organic frameworks (COFs) are a relatively new class of materials. They are particularly porous, while at the same time having a low density and low weight. Covalent means that their chemical bonds are formed through electron pairs between atoms.
The dyes that the researchers studied in their aqueous model solution were about 0.8 to 1.6 nanometers in size. “We developed a new method to form COF in a relatively environmentally friendly way, using water. As such, we were able to develop small ‘sponges’, with designed pore sizes and pore shapes in the nanometer range, as well as a tuned negative surface charge , which was highly selective in pulling the positively charged target molecules, that is, our dyes, out of the water,” the researchers said, “Just like the sponge soaks up the water, only in our case it’s the contaminants.”
A backbone made of graphene
When using COF powder in bulk, the inner pores of the material are often inaccessible to contaminants due to pore blockage at the outer edge, especially for large contaminant molecules. The new composite material developed by the researchers offers a thoroughly permeable structure: for this purpose, the researchers cultured COF on thin layered graphene nanosheets. The combination of graphene – in itself a 2D layer of carbon atoms – and the COF layer, which is up to two nanometers thick, resulted in a compact, open 3D structure. The ultra-thin COF layer could expose more adsorption sites than the bulk COF powder.
On the other hand, the larger, honeycomb-like pores of the graphene network support the transport of water through the filter material. “The large pores of the graphene network in combination with the ultra-thin COF layer with a large number of adsorption sites therefore enable a particularly fast and efficient wastewater treatment,” the researchers said. Because of graphene’s relatively low material input and the ability to reuse the composite material — after the pollutants have been washed out — as a filter, the development is also relatively cost-efficient, they said.
Water clusters in hydrophobic crystalline porous covalent organic structures
Changxia Li et al, Ultra-thin covalent organic framework anchored on graphene for enhanced removal of organic pollutants, Angewandte Chemie International Edition (2022). DOI: 10.1002/anie.202206564
Quote: Nano-sponges with potential for rapid wastewater treatment (2022, Aug. 3), retrieved Aug. 3, 2022 from https://phys.org/news/2022-08-nano-sponges-potential-rapid-wastewater-treatment.html
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