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Going small for big solutions: Sub-nanoparticle catalysts made from coinage elements as effective catalysts

Due to their small size, nanoparticles find varied applications in fields ranging from medicine to electronics. Their small size allows them a high reactivity and semiconducting property not found in the bulk states. Sub-nanoparticles (SNPs) have an extremely small diameter of around 1 nm, making them even smaller than nanoparticles. Almost all atoms of SNPs are available and exposed for reactions, and therefore, SNPs are expected to have extraordinary functions beyond the properties of nanoparticles, particularly as catalysts for industrial reactions. However, preparation of SNPs requires fine control of the size and composition of each particle on a sub-nanometer scale, making the application of conventional production methods near impossible.

To overcome this, researchers at the Tokyo Institute of Technology led by Dr. Takamasa Tsukamoto and Prof. Kimihisa Yamamoto previously developed the atom hybridization method (AHM) which surpasses the previous trials of SNP synthesis. Using this technique, it is possible to precisely control and diversely design the size and composition of the SNPs using a “macromolecular template” called phenylazomethine dendrimer. This improves their catalytic activity than the NP catalysts.

Now, in their latest study published in Angewandte Chemie International Edition, the team has taken their research one step further and has investigated the chemical reactivity of alloy SNPs obtained through the AHM. “We created monometallic, bimetallic, and trimetallic SNPs (containing one, combination of two, and combination of three metals respectively), all composed of coinage metal elements (copper, silver, and gold), and tested each to see how good of a catalyst each of them is,” reports Dr Tsukamoto. 

Unlike corresponding nanoparticles, the SNPs created were found to be stable and more effective. Moreover, SNPs showed a high catalytic performance even under the milder conditions, in direct contrast to conventional catalysts. Monometallic, bimetallic, and trimetallic SNPs demonstrated the formation of different products, and this hybridization or combination of metals seemed to show a higher turnover frequency (TOF). The trimetallic combination “Au4Ag8Cu16” showed the highest TOF because each metal element plays a unique role, and these effects work in concert to contribute to high reaction activity.

Furthermore, SNP selectively created hydroperoxide, which is a high-energy compound that cannot be normally obtained due to instability. Mild reactions without high temperature and pressure realized in SNP catalysts resulted in the stable formation of hydroperoxide by suppressing its decomposition.

When asked about the relevance of these findings, Prof Yamamoto states: “We demonstrate for the first time ever, that olefin hydroperoxygenation can been catalyzed under extremely mild conditions using metal particles in the quantum size range. The reactivity was significantly improved in the alloyed systems especially for the trimetallic combinations, which has not been studied previously.”

The team emphasized that because of the extreme miniaturization of the structures and the hybridization of different elements, the coinage metals acquired a high enough reactivity to catalyze the oxidation even under the mild condition. These findings will prove to be a pioneering key in the discovery of innovative sub-nanomaterials from a wide variety of elements and can solve energy crises and environmental problems in the years to come.

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Engineers and chemists ‘program’ liquid crystalline elastomers to replicate complex twisting action simply with the use of light

The twisting and bending capabilities of the human muscle system enable a varied and dynamic range of motion, from walking and running to reaching and grasping. Replicating something as seemingly simple as waving a hand in a robot, however, requires a complex series of motors, pumps, actuators and algorithms. Researchers at the University of Pittsburgh and Harvard University have recently designed a polymer known as a liquid crystal elastomer (LCE) that can be “programmed” to both twist and bend in the presence of light.

The research, published in the journal Science Advances was developed at Pitt’s Swanson School of Engineering by Anna C. Balazs, Distinguished Professor of Chemical and Petroleum Engineering and John A. Swanson Chair of Engineering; and James T. Waters, postdoctoral associate and the paper’s first author. Other researchers from Harvard University’s Wyss Institute for Biologically Inspired Engineering and the John A. Paulson School of Engineering include Joanna Aizenberg, Michael Aizenberg, Michael Lerch, Shucong Li and Yuxing Yao.

These particular LCEs are achiral: the structure and its mirror image are identical. This is not true for a chiral object, such as a human hand, which is not superimposable with a mirror image of itself. In other words, the right hand cannot be spontaneously converted to a left hand. When the achiral LCE is exposed to light, however, it can controllably and reversibly twist to the right or twist to left, forming both right-handed and left-handed structures.

“The chirality of molecules and materials systems often dictates their properties,” Dr. Balazs explained. “The ability to dynamically and reversibly alter chirality or drive an achiral structure into a chiral one could provide a unique approach for changing the properties of a given system on-the-fly.” To date, however, achieving this level of structural mutability remains a daunting challenge. Hence, these findings are exciting because these LCEs are inherently achiral but can become chiral in the presence of ultraviolet light and revert to achiral when the light is removed.”

The researchers uncovered this distinctive dynamic behavior through their computer modeling of a microscopic LCE post anchored to a surface in air. Molecules (the mesogens) that extend from the LCE backbone are all aligned at 45 degrees (with respect to the surface) by a magnetic field; in addition, the LCEs are cross-linked with a light-sensitive material. “When we simulated shining a light in one direction, the LCE molecules would become disorganized and the entire LCE post twists to the left; shine it in the opposite direction and it twists to the right,” Dr. Waters described. These modeling results were corroborated by the experimental findings from the Harvard group.

Going a step further, the researchers used their validated computer model to design “chimera” LCE posts where the molecules in the top half of the post are aligned in one direction and are aligned in another direction in the bottom half. With the application of light, these chimera structures can simultaneously bend and twist, mimicking the complex motion enabled by the human muscular system.

“This is much like how a puppeteer controls a marionette, but in this instance the light serves as the strings, and we can create dynamic and reversible movements through coupling chemical, optical, and mechanical energy,” Dr. Balazs said. “Being able to understand how to design artificial systems with this complex integration is fundamental to creating adaptive materials that can respond to changes in the environment. Especially in the field of soft robotics, this is essential for building devices that exhibit controllable, dynamic behavior without the need for complex electronic components.”

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