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A sieve for molecules

RUB, Kramer

Researchers have long tried to use graphene, which is made of carbon, as a kind of sieve. But it has no pores. Now a team has found an alternative material that provides the holes on its own.

Researchers from Bielefeld, Bochum and Yale have succeeded in producing a layer of two-dimensional silicon dioxide. This contains natural pores and can therefore be used like a sieve for molecules and ions. Scientists have been searching for such materials for some time, as they could help desalinate seawater or be used in new types of fuel cells. The team describes the fabrication process in the journal Nano Letters, published online Jan. 19, 2022. The teams led by Dr. Petr Dementyev of Bielefeld University, Prof. Dr. Anjana Devi of Ruhr University Bochum and Prof. Dr. Eric Altman of Yale University collaborated on the work.

When two-dimensional materials are pierced with high precision, they can be used to screen out specific ions or molecules. Researchers have repeatedly tried to use graphene, a material made of carbon atoms, for this purpose. Since it has no natural pores, they have to be inserted artificially. But it is difficult to create holes of a defined size in graphene without permanently damaging the material, which breaks easily. This is because it loses too much stability due to the perforation. Consequently, an alternative had to be found. In the current work, the research team took advantage of the fact that the crystal lattice of two-dimensional silicon dioxide naturally has openings. They showed that these openings can be used to separate certain gases.

"Silicon dioxide naturally has a very high density of tiny pores that could not be created in artificial membranes," says Petr Dementyev of the Bielefeld-based Physics of Supramolecular Systems and Surfaces group. "Unlike graphene, the pores are all nearly the same size. And there are so incredibly many that the material behaves like a fine-mesh sieve for molecules."

2D silica has been known since 2010. However, its production was very expensive and only possible on a small scale. The researchers from Bochum, Bielefeld and Yale brought together expertise from materials chemistry, chemical engineering and chemical physics to devise a new manufacturing process. They used what is known as atomic layer deposition to deposit a single layer of silicon dioxide on a gold surface. Using a high-pressure process, the researchers transferred the layer to its two-dimensional form and then characterized it in detail spectroscopically and microscopically. They then studied the gas flow through the 2D membrane in a vacuum chamber.

While evaporated water and evaporated alcohol were able to pass through the silica layer, the gases nitrogen and oxygen were retained. "Materials like this with selective permeability are in high demand in industry," says Anjana Devi. However, before the 2D silica can be used in practice, it is important to evaluate exactly how many different molecules can attach to or penetrate the surface of the material. 

"We expect our results to be important for materials science worldwide," sums up Anjana Devi of the Inorganic Materials Chemistry group in Bochum. "Such 2D membranes could help at the forefront of sustainable development, for example in the field of energy conversion or storage."

adapted from RUB, Julia Weiler
Project meeting

General assembly 2021

All members of the RDPCI are cordially invited to attend this year's full meeting of the Reserch Department Plasmas with Complex Interactions. It will be held on Dec. 15, 2021 at 1 p.m. via zoom.

Conversion of substances

DFG approves second funding period of the CRC 1316

Plasmas for the Systems for material conversion are an important component in the utilization and storage of decentrally generated renewable energies. The Collaborative Research Center 1316 (CRC 1316) "Transient Atmospheric Pressure Plasmas - from Plasma to Liquids to Solids" is dedicated to combining atmospheric pressure plasmas with catalysis to develop the most flexible solutions possible for this material conversion. "They should be scalable, controllable and robust against external influences, such as impurities in the starting materials," explains Prof. Dr. Achim von Keudell, spokesman of the CRC. 

The first funding period of the CRC 1316 was dedicated to the elucidation of transient phenomena in atmospheric pressure plasmas as well as interfacial processes at the surface of catalysts. Here, the focus was on three systems: the plasma-catalytic conversion of gases, the combination of plasmas with electrolysis at the interface between liquid and solid, and plasma-assisted biocatalysis, in which enzymes very selectively produce new molecules. The researchers were able to make great progress in these areas: For example, they achieved precise control of the formation of reactive particles in these plasmas. They were also able to gain a deeper understanding of the atomic and molecular surface processes in these systems. 

In the second funding period, these findings will be brought together to make the best possible use of the interplay between a plasma with its reactive particles and a catalytically active surface. There are many further questions in this regard, since in traditional catalysis, for example, stable molecules are essentially reaction partners, whereas in plasma catalysis, reactive particles or highly excited species can accelerate or suppress a specific reaction path. On this basis, the first prototype plants for plasma catalysis, plasma electrolysis and plasma biocatalysis are to be developed. 

In addition to the RUB as the host university, researchers from the University of Ulm, the Jülich Research Center and the Fritz Haber Institute in Berlin are involved in the CRC.

Research funding

Approval for Jun.-Prof. Golda's DAAD project

In collaboration with Dr. Claire Douat from the institute GREMI in Orléans, France, Jun.-Prof. Judith Golda has submitted a DAAD project on the diagnostics and application of plasma radiation as a CO source for sterilization in wound healing. This has now been approved by the DAAD for 1.1.2022.
The aim of the project is to investigate the production pathways and the role of the CO molecule in the plasma treatment of biological material. To study CO generation in CAPs, two well-characterized plasma sources will be used that have complementary operating principles: A radial kHz-dielectric barrier discharge with direct contact of the plasma including ions, electrons, and strong electric fields with the treated substrate; and a coplanar RF discharge where only the field-free plasma effluent containing reactive species and plasma-generated photons reaches the substrate. This project will explore possible synergistic effects between CO and plasma-generated species such as electric fields, ions and electrons, photons, and other neutral radicals. The two complementary plasma sources will be used to distinguish the effects of indirect and direct plasma treatment on the impact of plasma-produced CO on bacteria. The plasma sources used here will be characterized with CO2 admixture to ensure that the amount of CO produced is below the toxicity limit. Parameter variations will be used to determine the optimal CO production conditions.
The project includes travel expenses to address the planned research questions.

Link to the group: https://piplab.rub.de

CONFERENCE

Japan Workshop

A workshop between CRC1316 and Japanese universities/research institutions will take part between November 29th and December 3rd, 2021. The organizers are Prof. Czarnetzki, Satoshi Hamaguchi, Jan Kuhfeld and two PhD students from Nagoya University. Further information can be found here.

Please note that the deadline is already October 27, 2021. Active participation is by invitation only, but passive participation is completely open. Participants must register in any case.