Creation of conductive MOF nanosheets on water – sciencedaily

Oil and water don’t mix, but what happens where oil and water meet? Or where air meets liquid? Unique reactions occur at these interfaces, which a team of Japan-based researchers used to develop the first successful construction of uniform, electrically conductive nanosheets needed for next-generation sensors and power generation technologies.

The research collaboration of Osaka Prefecture University, Japan Synchrotron Radiation Research Institute and the University of Tokyo published their approach on October 28 in Applied materials and interfaces ACS.

“We have known for a long time that oil forms a large, uniform film on the surface of the water – understanding and using this familiar phenomenon could lead to energy-saving processes,” said corresponding author Rie Makiura, associate professor in the materials department. Sciences, Osaka Prefecture University. “Using a combination of raw materials at a similar interface, we have succeeded in creating functional materials with advanced three-dimensional nanostructures that conduct electricity.”

These materials are metal-organic frameworks, which are microporous and composed of metal ions and highly organized organic linkers. Called MOFs, they have a myriad of potential applications from nanotechnology to life sciences, according to Makiura, but one unrealized property is holding them back from actual use – most manufactured MOFs do not conduct electricity well.

“In order to utilize the superior characteristics of conductive MOFs in applications such as sensors and energy devices, the fabrication and integration of ultrathin films with a defined pore size, well-controlled growth direction and film thickness are a necessity and have been actively researched. Makiura said.

Most of the earlier developments of MOF thin films involved exfoliating layers of larger crystals and placing them on a substrate. According to Makiura, however, this process is complicated and often results in thick, non-uniform leaves that are not very conductive. To develop ultra-thin and uniform conductive nanosheets, she and her team decided to reverse the approach.

They began to spread a solution containing organic linkers over an aqueous solution of metal ions. Once in contact, the substances begin to assemble their components in a hexagonal arrangement. For an hour, the arrangement continued as nanosheets form where liquid and air meet. After the formation of the nanosheets was completed, the researchers used two barriers to compress the nanosheets into a more dense and continuous state.

It’s a streamlined approach to producing incredibly thin nanosheets with highly organized crystal structures, according to Makiura. Researchers confirmed the uniform structure Going through X-ray microscopic and crystallographic analysis. The tightly ordered crystals visualized also indicated the electrical properties of the material, as the crystals were evenly in contact in each sheet, which also facilitated close contact between the sheets. The researchers tested this by transferring nanosheets to a silicon substrate, adding gold electrodes, and measuring conductivity.

“Although it was not easy to evaluate ultra-thin films, we were delighted to be able to prove that they had a three-dimensional nanostructure and high electrical conductivity,” said first author Takashi Ohata. , doctoral student supervised by Makiura.

Researchers are now studying how various parameters affect the morphology of nanosheets, with the goal of developing a controllable and adjustable methodology to create high-quality nanosheets with targeted electronic properties.

“Our versatile and simple bottom-up assembly of molecular building components suitable for the air / liquid interface in an extended architecture achieves the creation of a perfectly oriented and electrically conductive crystalline nanosheet,” said Makiura. “The new discovery further enhances the potential of air / liquid interfacial synthesis to create a wide variety of nanosheets for actual use in many potential applications, including for power generation devices and catalysts.”

Other contributors include Akihiro Nomoto, Department of Applied Chemistry, Osaka Prefecture University; Takeshi Watanabe and Ichiro Hirosawa, Japan Synchrotron Research Institute; Tatsuyuki Makita and Jun Takeya, Material Innovation Research Center and Department of Advanced Materials Science, University of Tokyo.

Funding Information This work was supported by Japan Society for the Promotion of Science KAKENHI Grant Numbers JP19H05715 (Grant-in-Aid for Scientific Research on Innovative Area: Aquatic Functional Materials), JP16H05968, JP16K13610, JP20H02551, JP21J13884 (Research Fellowship for Young Scientists), the Mazda Foundation and Masuya Kinen Kenkyu Shinko Foundation, Japan. Synchrotron X-ray diffraction experiments were performed on the beamlines BL19B2 and BL46XU, SPring-8 (2016B1862, 2017A1569, 2017B1899, 2018A1559, 2018A2065, 2018A2066, 2018B1802, 2018B1840, 2019A1771, 2019B1860, 2019B1857). X-ray photoelectron spectroscopy and transmission electron microscopy experiments were carried out at NAIST, with the support of the nanotechnology platform program (Synthesis of molecules and materials) of the Ministry of Education, Culture, of Sports, Science and Technology (MEXT), Japan (NPS17064).


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