A study by a team of University of Oklahoma researchers has been featured in Cell Reports Physical Science, an open-access journal highlighting cutting-edge research in the physical sciences.
“We want to mimic nature’s enzymes and learn more about what we can create synthetically. Our findings could have far-reaching implications in the production of industrial chemicals,” said the project’s co-investigator, Daniel Resasco, Ph.D., a professor in the School of Chemical, Biological and Materials Engineering, Gallogly College of Engineering.
During thermal treatments, the boron species undergo a process called exsolution, where they separate from the bulk phase and accumulate on the catalyst’s surface. This enrichment leads to the formation of acidic species, which boost the activity and selectivity of carbonyl bond hydrogenation by three and two times, respectively.
Resasco explains the significance of the team’s findings. “The role of water in selective hydrogenation has long been a subject of interest. Our study provides new insights into the underlying mechanisms and uncovers a synergistic effect between boron species and water, ultimately leading to enhanced stability and selectivity of the catalysts,” he said.
Associate professor Bin Wang, Ph.D., is a co-investigator on the project and says the study highlights the importance of finding the right balance between catalyst support and desired chemical outcomes. “This research opens new possibilities for developing more efficient and selective catalytic processes in the production of industrial chemicals,” Wang said.
Resasco credits Li Gengnan, Ph.D., for the project’s scientific thinking. Gengnan served as a post-doctorate fellow at OU before joining the Center for Functional Nanomaterials at Brookhaven National Laboratory, one of five Nanoscale Science Research Centers created by the Department of Energy.
“As the search for sustainable and efficient chemical processes continues, we hope to pave the way for transformative advancements in catalysis, driving us closer to a greener and more resourceful future,” Resasco said.
More information: Gengnan Li et al, Cooperative roles of water and metal-support interfaces in the selective hydrogenation of cinnamaldehyde over cobalt boride catalysts, Cell Reports Physical Science (2023). DOI: 10.1016/j.xcrp.2023.101367
Using SLAC’s ultrafast “electron camera,” scientists have directly imaged a photochemical “transition state” as it happened. Credit: Greg Stewart/SLAC National Accelerator Laboratory
Using a high-speed “electron camera” at the Department of Energy’s SLAC National Accelerator Laboratory and cutting-edge quantum simulations, scientists have directly imaged a photochemical “transition state,” a specific configuration of a molecule’s atoms determining the chemical outcome, during a ring-opening reaction in the molecule α-terpinene. This is the first time that scientists have precisely tracked molecular structure through a photochemical ring-opening reaction, triggered when light energy is absorbed by a substance’s molecules.
The results, published in Nature Communications, could further our understanding of similar reactions with vital roles in chemistry, such as the production of vitamin D in our bodies.
Transition states generally occur in chemical reactions which are triggered not by light but by heat. They are like a point of no return for molecules involved in a chemical reaction: As the molecules gain the energy needed to fuel the reaction, they rearrange themselves into a fleeting configuration before they complete their transformation into new molecules.
“Transition states really tell you a lot about how and why reactions happen,” said co-author and SLAC scientist Thomas Wolf. “The investigation of similar critical configurations in photochemical reactions could lead to a better understanding of reactions with key roles in chemistry and biology. It’s important that we can now look at some specific characteristics of such reactions using our diffraction techniques.”
Until now, no method existed that was sensitive enough to capture these fleeting states, which last for only millionths of a billionth of second. At MeV-UED, SLAC’s instrument for ultrafast electron diffraction, the researchers sent an electron beam with high energy, measured in millions of electronvolts (MeV), through a gas to precisely measure distances between the atoms within the molecules in the gas. Taking snapshots of these distances at different intervals after an initial laser flash allows scientists to create a stop-motion movie of the light-induced atomic rearrangements in the molecules.
“These reactions are important for understanding the quantum mechanics underpinning photochemistry,” said SLAC scientist and co-author Yusong Liu. “Comparing our experimental results with quantum simulations of the reaction allows us to get a highly accurate picture of how molecules behave and benchmark the predictive power of theoretical and computational methods.”
In a previous study of a related reaction, MeV-UED allowed the team to capture the coordinated dance between electrons and nuclei. The results provided the first direct confirmation of a half-century-old set of rules about the final product’s stereochemistry, or the three-dimensional arrangement of its atoms.
In the present experiment, the researchers discovered that some parts of the atomic rearrangements happen earlier than other parts, which provides an explanation for why the specific stereochemistry is created by the reaction.
“I recently looked back on some old presentations I did in college about these types of reactions and the famous set of rules that predict the outcomes. But these rules don’t actually explain why and how reactions happen.” Wolf said. “And now I’m coming back to that and can start answering these questions and that makes it incredibly exciting for me.”
Another big motivation for doing these experiments, Wolf said, is that the same reaction also happens in biological processes such as the biosynthesis of vitamin D in human skin. The researchers plan to conduct follow-up studies further exploring this connection.
More information: Y. Liu et al, Rehybridization dynamics into the pericyclic minimum of an electrocyclic reaction imaged in real-time, Nature Communications (2023). DOI: 10.1038/s41467-023-38513-6
Disinfectant powder is stirred in bacteria-contaminated water (upper left). The mixture is exposed to sunlight, which rapidly kills all the bacteria (upper right). A magnet collects the metallic powder after disinfection (lower right). The powder is then reloaded into another beaker of contaminated water, and the disinfection process is repeated (lower left). Credit: Tong Wu
At least 2 billion people worldwide routinely drink water contaminated with disease-causing microbes.
Now Stanford University scientists have invented a low-cost, recyclable powder that kills thousands of waterborne bacteria per second when exposed to ordinary sunlight. The discovery of this ultrafast disinfectant could be a significant advance for nearly 30% of the world’s population with no access to safe drinking water, according to the Stanford team. Their results are published in Nature Wateron May 18.
“Waterborne diseases are responsible for 2 million deaths annually, the majority in children under the age of 5,” said study co-lead author Tong Wu, a former postdoctoral scholar of materials science and engineering (MSE) in the Stanford School of Engineering. “We believe that our novel technology will facilitate revolutionary changes in water disinfection and inspire more innovations in this exciting interdisciplinary field.”
Conventional water-treatment technologies include chemicals, which can produce toxic byproducts, and ultraviolet light, which takes a relatively long time to disinfect and requires a source of electricity.
The new disinfectant developed at Stanford is a harmless metallic powder that works by absorbing both UV and high-energy visible light from the sun. The powder consists of nano-sized flakes of aluminum oxide, molybdenum sulfide, copper, and iron oxide.
“We only used a tiny amount of these materials,” said senior author Yi Cui, the Fortinet Founders Professor of MSE and of Energy Science & Engineering in the Stanford Doerr School of Sustainability. “The materials are low cost and fairly abundant. The key innovation is that, when immersed in water, they all function together.”
Fast, nontoxic, and recyclable
After absorbing photons from the sun, the molybdenum sulfide/copper catalyst performs like a semiconductor/metal junction, enabling the photons to dislodge electrons. The freed electrons then react with the surrounding water, generating hydrogen peroxide and hydroxyl radicals—one of the most biologically destructive forms of oxygen. The newly formed chemicals quickly kill the bacteria by seriously damaging their cell membranes.
For the study, the Stanford team used a 200 milliliter [6.8 ounce] beaker of room-temperature water contaminated with about 1 million E. coli bacteria per mL [.03 oz.].
“We stirred the powder into the contaminated water,” said co-lead author Bofei Liu, a former MSE postdoc. “Then we carried out the disinfection test on the Stanford campus in real sunlight, and within 60 seconds, no live bacteria were detected.”
The powdery nanoflakes can move around quickly, make physical contact with a lot of bacteria and kill them fast, he added.
The chemical byproducts generated by sunlight also dissipate quickly.
“The lifetime of hydrogen peroxide and hydroxy radicals is very short,” Cui said. “If they don’t immediately find bacteria to oxidize, the chemicals break down into water and oxygen and are discarded within seconds. So you can drink the water right away.”
The nontoxic powder is also recyclable. Iron oxide enables the nanoflakes to be removed from water with an ordinary magnet. In the study, the researchers used magnetism to collect the same powder 30 times to treat 30 different samples of contaminated water.
“For hikers and backpackers, I could envision carrying a tiny amount of powder and a small magnet,” Cui said. “During the day you put the powder in water, shake it up a little bit under sunlight and within a minute you have drinkable water. You use the magnet to take out the particles for later use.”
The powder might also be useful in wastewater treatment plants that currently use UV lamps to disinfect treated water, he added.
“During the day the plant can use visible sunlight, which would work much faster than UV and would probably save energy,” Cui said. “The nanoflakes are fairly easy to make and can be rapidly scaled up by the ton.”
The study focused on E. coli, which can cause severe gastrointestinal illness and can even be life-threatening. The U.S. Environmental Protection Agency has set the maximum contaminant-level goal for E. coli in drinking water at zero. The Stanford team plans to test the new powder on other waterborne pathogens, including viruses, protozoa, and parasites that also cause serious diseases and death.
Element mapping of GeAPO-180.025, which shows homogeneously distributed Ge species. Credit: Science (2023). DOI: 10.1126/science.adg2491
Researchers have reported a strategy to disentangle the activity-selectivity tradeoff for direct conversion of syngas, a mixture of carbon monoxide and hydrogen, into desirable ethylene, propylene, and butylene. These hydrocarbons are known as light olefins and are the most-used building blocks for plastics.
“Activity and selectivity are two primary indexes of a successful catalyst for chemical reactions. A higher activity means higher efficiency in converting feedstock to products, thereby reducing energy consumption,” said Jiao Feng, an associate professor at the Dalian Institute of Chemical Physics at the Chinese Academy of Sciences in Dalian, China. “Selectivity reflects the percentage of the desired products; for example, ethylene, propylene and butylene in this case, which determines the economy of the technology.”
For almost a century, a process called the Fischer-Tropsch synthesis (FTS) was used for direct syngas conversion with iron or cobalt-based catalysts for synthesis of chemicals. However, selectivity for light olefins remained a challenge. An alternative process, named OXZEO and developed six years ago by the same research team using metal oxide-zeolite catalyst, improved light-olefin selectivity far beyond the theoretical limit of FTS. Despite the significant progress over the years, the activity is still limited by the activity-selectivity tradeoff.
For example, when FTS is used to convert syngas to light olefins, the yield amounts to around 26%. Using traditional silicon containing zeotypes within the OXZEO catalyst concept, the light-olefins yield has so far maxed out at 27%. These limits originate from activity-selectivity tradeoff, a long-standing challenge in catalysis. This can be traced to the catalytic sites for both the target and side reactions, which are usually entangled on technical catalysts.
Now, in a paper published in the journal Science on May, 18, 2023, a team led by Dr. Jiao, Prof. Pan and Prof. Bao has shown that incorporating germanium-substituted aluminophosphates within the OXZEO catalyst concept can disentangle the desired target reaction from the undesired secondary reactions. It enhances the conversion of the intermediates to produce olefins by creating more active sites and in turn generation of intermediates but without degrading the selectivity of light olefins. With this new strategy, researchers simultaneously achieved high CO conversion and light-olefins selectivity and the yield reached an unprecedented 48% under optimized conditions.
To validate the mechanism, researchers also studied silicon-substitute and magnesium-substitute aluminophosphates and tested them in similar scenarios. The active sites of these two zeotypes cannot efficiently shield the side reaction of hydrogenation and oligomerization, thereby the activity-selectivity tradeoff cannot be overcome, despite optimizing the acid site density or reaction conditions.
“Separating the active sites of the two key steps of syngas conversion via OXZEO catalysts, and increasing the active site density and modulating its properties for kinetics of intermediate transport and reactions within the zeotype confined pores provides one effective solution for syngas conversion to light olefins,” said Pan Xiulian, professor at the Dalian Institute of Chemical Physics at the Chinese Academy of Sciences in Dalian, China. “We expect that this can be applicable to analogous bifunctional catalysis in other reactions and will be of interest for further development of zeolite catalysis.”
“If it can be incorporated with green hydrogen energy technology in the future, it will make significant contribution to the goal of carbon neutrality,” said Bao Xinhe, professor at the Dalian Institute of Chemical Physics at the Chinese Academy of Sciences in Dalian and the President of the University of Science and Technology of China.
More information: Feng Jiao et al, Disentangling the activity-selectivity tradeoff in catalytic conversion of syngas to light olefins, Science (2023). DOI: 10.1126/science.adg2491
Sketches of the three hypotheses of the electronic decay mechanism of the photoexcited uracil. The long trajectory hypothesis assumes that the uracil relaxes into minimum energy geometry in the S2 state and then decays to S1 state in several picoseconds. The short trajectory hypothesis assumes that the uracil arrives at S1 in about 70 femtoseconds. The intermediate trajectory hypothesis assumes that part of the uracil evolves to S0 state within about 0.7 picosecond. Credit: Ultrafast Science
The nucleobase molecules carrying the genetic codes are the most important ingredients for life, but they are also very vulnerable. When the ultraviolet component in the sunlight irradiates these molecules, the electrons in the molecules will be excited, and the excited nucleobase molecules may result in irreversible changes or even damages to the DNA and RNA chains, leading to the “sunburn” of organisms at molecular level.
It is widely believed that there is a “sunscreen” mechanism in these nucleobase molecules which can lead to rapid decay into the ground state. The ultrafast decay mechanism for most types of nucleobases has been confirmed. However, the research team of Professor Todd Martinez at Stanford University proposed that there may be a shallow potential barrier for the excited electronic state of uracil (U) nucleobase, which hinders the decay of excited molecules.
This can be understood as a trick reserved by nature to promote biological variation and evolution.
This novel point of view has caused wide controversy and discussion. There are many different kinds of theoretical models about whether there is indeed a hindrance to the decay of excited state uracil. In this article, using ultrashort electron pulses and X-ray free electron lasers, the research led by Professor Zheng Li and Professor Haitan Xu provides a detailed theoretical analysis of an experimental scheme that incorporates multiple signals of ultrafast electron and X-ray diffraction and X-ray spectroscopy, and opens a way to resolve this interesting controversy.
There are currently three hypotheses about the decay time scale of photoexcited uracil nucleobase. In 2007, the group of Todd Martinez proposed that the decay time of photoexcited uracil may be much longer than other nucleobases, reaching more than 1 picosecond, because the shallow potential barrier for the uracil excited state hinders the decay process.
In 2009, the research group of Zhenggang Lan from the Max Planck Institute proposed that the decay of the uracil base would not pass through the potential barrier. This theoretical model predicts short decay time of photoexcited uracil, which is about 70 femtoseconds.
In 2011, the research group of Pavel Hobza from the Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences proposed the intermediate trajectory hypothesis, in which the uracil may have another way of structural relaxation, and the decay time through this path takes about 0.7 ps. Because the predicted potential barrier in the uracil excited state is very shallow, and due to the precision limit of quantum chemical calculations, different theoretical hypotheses give contradictory predictions of electronic decay pathways.
The authors propose an approach which can uniquely identify the electronic decay mechanism of the photoexcited uracil with ultrafast X-ray spectroscopy (XPS), ultrafast X-ray diffraction (UXD), and ultrafast electron diffraction (UED) methods. Incorporating the signatures of multiple probing methods, the authors demonstrate an approach that can identify the geometric and electronic relaxation characteristic time scales of the photoexcited uracil molecule among several candidate models.
The XPS signal provides the toolkit to map out the valence electron density variation in the chosen atomic sites of molecules. X-ray can ionize core electrons of molecules, and the shift of photoelectron energy in XPS in the molecule reflects the strength of electron screening effect of nuclear charge, which maps out the local density of valence electrons at the specific atom. Ultrafast diffraction imaging has been widely used to resolve the molecular structural dynamics.
UED is capable of characterizing the correlation between electrons and can be used to monitor the electronic population transfer dynamics. Compared to UED, UXD can resolve the transient geometric structure with higher temporal precision, which is free of pulse length limitation of UED because of space charge effect of electron bunch compression.
Combining the above signals of multiple experimental results, the characteristic time scales of geometric and electronic relaxation can be obtained, and the decay pathway of photoexcited uracil molecule can be identified.
The authors have performed molecular dynamics simulations following the long trajectory hypothesis, and calculated the ultrafast X-ray spectroscopy and coherent diffraction imaging signals. In the long trajectory hypothesis, the uracil molecule first relaxes into minimum energy geometry in the S2 state and then decays to S1 state.
The structural and electronic transition dynamics during the decay of uracil nucleobases can be reflected by XPS signal. Choosing the carbon K-edge for the X-ray probe, the variation of XPS signal in corresponding energy range is fitted, and two relaxation time scales (about 3.5 ps and 0.2 ps) are obtained.
These two characteristic time scales are related to the molecular structural evolution and electronic state transition dynamics, but the exact determination of the time scales requires combining analysis of coherent diffraction imaging, because the information of structural and electronic evolutions are usually mixed in the XPS signal.
UED is capable of characterizing the mean distance between electrons and can be used to detect the electronic population transfer dynamics. The calculated time-resolved electron diffraction signal based on molecular dynamics trajectories reflects 4.2 ps time scale of electronic state decay obtained by exponential fitting, which confirms that the 3.5 ps characteristic time scale of XPS is related to electronic transition dynamics.
The pair distribution function reflecting the average distance between atoms is obtained by Fourier transformation of UXD signal, which shows that one of the C-C bond lengths in uracil molecule is elongated in about 0.2 ps after photoexcitation followed by relaxation into minimum energy geometry in the excited state.
The time-frequency analysis of UXD signal by continuous wavelet transform reveals the frequencies of the dominant modes, and the 0.2 ps time scale of molecular structure evolution, which is consistent with the characteristic frequencies and 0.2 ps time scale of structural evolution obtained from XPS signal.
It is shown that the characteristic time scales of geometric relaxation and electronic decay of uracil in the long trajectory model can be faithfully retrieved by incorporating time-resolved XPS, UED and UXD analyses.
Incorporating the signatures of multiple probing methods, the authors demonstrate an approach to identify the decay pathway of photoexcited nucleobases among several candidate models. This study demonstrates the synergy of spectroscopic and coherent diffraction imaging with ultrafast time resolution, which can also serve as a general methodological toolkit for investigating electronic and structural dynamics in ultrafast photochemistry.
The research is published in the journal Ultrafast Science.
More information: Xiangxu Mu et al, Identification of the Decay Pathway of Photoexcited Nucleobases, Ultrafast Science (2023). DOI: 10.34133/ultrafastscience.0015
The study includes scientists from Insilico Medicine, Foxconn, Zapata Computing, and University of Toronto. Credit: Insilico Medicine
Insilico Medicine, a clinical stage generative artificial intelligence (AI)-driven drug discovery company, today announced that it combined two rapidly developing technologies, quantum computing and generative AI, to explore lead candidate discovery in drug development and successfully demonstrated the potential advantages of quantum generative adversarial networks in generative chemistry.
The study, published in the Journal of Chemical Information and Modeling, was led by Insilico’s Taiwan and UAE centers which focus on pioneering and constructing breakthrough methods and engines with rapidly developing technologies—including generative AI and quantum computing—to accelerate drug discovery and development.
The research was supported by University of Toronto Acceleration Consortium director Alán Aspuru-Guzik, Ph.D., and scientists from the Hon Hai (Foxconn) Research Institute.
“This international collaboration was a very fun project,” said Alán Aspuru-Guzik, director of the Acceleration Consortium and professor of computer science and chemistry at the University of Toronto. “It sets the stage for further developments in AI as it meets drug discovery. This is a global collaboration where Foxconn, Insilico, Zapata Computing, and University of Toronto are working together.”
Generative Adversarial Networks (GANs) are one of the most successful generative models in drug discovery and design and have shown remarkable results for generating data that mimics a data distribution in different tasks. The classic GAN model consists of a generator and a discriminator. The generator takes random noises as input and tries to imitate the data distribution, and the discriminator tries to distinguish between the fake and real samples. A GAN is trained until the discriminator cannot distinguish the generated data from the real data.
In this paper, researchers explored the quantum advantage in small molecule drug discovery by substituting each part of MolGAN, an implicit GAN for small molecular graphs, with a variational quantum circuit (VQC), step by step, including as the noise generator, generator with the patch method, and quantum discriminator, comparing its performance with the classical counterpart.
The study not only demonstrated that the trained quantum GANs can generate training-set-like molecules by using the VQC as the noise generator, but that the quantum generator outperforms the classical GAN in the drug properties of generated compounds and the goal-directed benchmark.
In addition, the study showed that the quantum discriminator of GAN with only tens of learnable parameters can generate valid molecules and outperforms the classical counterpart with tens of thousands parameters in terms of generated molecule properties and KL-divergence score.
“Quantum computing is recognized as the next technology breakthrough which will make a great impact, and the pharmaceutical industry is believed to be among the first wave of industries benefiting from the advancement,” said Jimmy Yen-Chu Lin, Ph.D., GM of Insilico Medicine Taiwan and corresponding author of the paper. “This paper demonstrates Insilico’s first footprint in quantum computing with AI in molecular generation, underscoring our vision in the field.”
Building on these findings, Insilico scientists plan to integrate the hybrid quantum GAN model into Chemistry42, the Company’s proprietary small molecule generation engine, to further accelerate and improve its AI-driven drug discovery and development process.
Insilico was one of the first to use GANs in de novo molecular design, and published the first paper in this field in 2016. The Company has delivered 11 preclinical candidates by GAN-based generative AI models and its lead program has been validated in Phase I clinical trials.
“I am proud of the positive results our quantum computing team has achieved through their efforts and innovation,” said Alex Zhavoronkov, Ph.D., founder and CEO of Insilico Medicine. “I believe this is the first small step in our journey. We are currently working on a breakthrough experiment with a real quantum computer for chemistry and look forward to sharing Insilico’s best practices with industry and academia.”
More information: Po-Yu Kao et al, Exploring the Advantages of Quantum Generative Adversarial Networks in Generative Chemistry, Journal of Chemical Information and Modeling (2023). DOI: 10.1021/acs.jcim.3c00562
Bismuth is the heaviest of the stable elements – all subsequent elements are radioactive. Credit: Florian Pircher/Pixabay
To be able to exploit the advantages of elements and their molecular compounds in a targeted manner, chemists have to develop a fundamental understanding of their properties. In the case of the element bismuth, a team from the Max Planck Institut für Kohlenforschung has now taken an important step.
Chemists at the Max Planck Institut für Kohlenforschung strive for the rational design of chemical processes that lead to more efficient and sustainable chemistry for academia as well as industry. A fundamental understanding of the properties of elements such as bismuth and their molecular compounds is necessary in order to be able to take advantage of their potential for catalysis.
A team led by Josep Cornellà and Frank Neese, group leader and director at the Max Planck Institut für Kohlenforschung, has now found that there are still some “white spots” in the chemical landscape that need to be tapped. The researchers have now published their work on an intriguing property of new bismuth complexes in the journal Science.
Why bismuth? Research group leader Josep Cornellà’s team has been interested in this particular metal for quite a while. “Bismuth can offer some advantages—compared to other metals. For example, it is more readily available and less toxic than other elements. In addition, special properties of bismuth that other ‘classical’ catalysis candidates do not have could play a role in future reaction designs,” Cornellà explains.
What is it that makes the Mülheim Bismuth molecule so special? Atoms consist of the atomic nucleus as well as an atomic shell formed by electrons. When molecules are synthesized from atoms or fragments, usually pairs of electrons from different atoms come together to for chemical bonds. However, chemists are often interested in situation that deviate from this situation, which is the case when the molecules have unpaired electrons. Such systems tend to be highly reactive and will readily interact with other molecules.
“Normally, molecules with unpaired electrons are always magnetic,” explains Frank Neese. But now the researchers of the Kohlenforschung have developed a molecule containing bismuth that has unpaired electrons and yet, strangely enough, shows no magnetism at all. The solution to this riddle has to do with, among other things, the special position of bismuth in the periodic table of the elements.
Bismuth is the heaviest of the stable elements—all subsequent elements are radioactive. Due to the particularly heavy atomic nucleus, the electrons show a special behavior, which can only be understood with the help of Einstein’s theory of relativity. These properties lead to the initially perplexing experimental finding.
“Our molecule is not really ‘non-magnetic’,” the researchers explain, “but there is no magnetic field on Earth strong enough to detect magnetism in our system.” The fact that the researchers were able to calculate the fascinating properties of this molecule from first principles of physics is due to the quantum chemistry program package ORCA, developed in Mülheim and widely used throughout all chemical disciplines by tens of thousands of chemists worldwide.
With their work, the scientists from Mülheim have added an important point to the “chemical profile” of bismuth. This may be of importance in the future when designing new types of catalysts.
More information: Yue Pang et al, Synthesis and isolation of a triplet bismuthinidene with a quenched magnetic response, Science (2023). DOI: 10.1126/science.adg2833
Advanced electronic devices require high-quality materials such as metal halide phosphors that can effectively convert light into measurable signals. Toxic element-free copper-based iodides such as cesium copper iodide (Cs3Cu2I5: CCI) are particularly promising in this regard.
CCI is an efficient blue light-emitting material that can convert almost all the absorbed energy into detectable light, making them ideal for use in deep-UV photodetectors and γ-ray scintillators for detecting ionizing radiation, such as gamma or X-rays. However, the thin films of CCI do not meet the required quality standards, hindering their performance improvement for advanced stacking applications.
Now, a study published in the Journal of the American Chemical Society has addressed this issue by proposing an innovative method for producing high-quality thin films of Cs3Cu2I5. The study was led by researchers from Tokyo Institute of Technology (Tokyo Tech), including Professor Hideo Hosono as the corresponding author and Specially Appointed Assistant Professor Masatake Tsuji as the first author.
In an earlier experimental finding, the team had discovered that cesium iodide (CsI) and copper iodide (CuI) powders can react even at room temperature to form Cs3Cu2I5. Building on this insight, they deposited thin films of CuI and CsI onto a silica substrate by evaporating them in a vacuum chamber. The two films were then allowed to react at room temperature to form transparent and highly smooth films with a high optical transmittance (T) of 92%.
Interestingly, the researchers found that the order in which the layers were deposited affected the formed crystalline phases. They noticed that the deposition of CsI layer over CuI resulted in the formation of a blue light-emitting thin film of Cs3Cu2I5, which is the equilibrium phase under this thickness ratio condition.
In contrast, depositing CuI over CsI resulted in a yellow light-emitting thin film of CsCu2I3. The formation of these different phases was attributed to an interdiffusion of the Cs and Cu atoms between the two layers. Based on these observations, the researchers found that the formation of each phase could be controlled by simply adjusting the thickness of each film to reach a specific ratio of CsI to CuI.
The researchers thus argued that the interdiffusion process leads to the formation of distinct local structures containing point defects that decay through nonradiative channels upon photoexcitation, resulting in highly efficient emissions.
“We propose that this formation originates from the rapid diffusion of Cu+ and I− ions into CsI crystals along with the formation of I− at the Cs+ site and interstitial Cu+ in the CsI lattice,” explains Prof. Hosono. The photoluminescent properties of Cs3Cu2I5 originate from the unique local structure around the luminescent center, the asymmetric [Cu2I5]3−polyhedron iodocuprate anion, consisting of the edge-shared CuI3 triangle and the CuI4 tetrahedron dimer that is isolated by Cs+ ions.
Using this approach, the researchers were able to fabricate patterned thin films by selectively depositing a CsI layer through a shadow mask. This allowed them to control the deposition of CsI and pattern only the desired area of the substrate.
By carefully adjusting for the thickness of the CuI and CsI layers, they were able to successfully fabricate a film with a central blue light-emitting Cs3Cu2I5 region bordered by a yellow light-emitting CsCu2I3 region. In addition, they demonstrated that the same thin films can be obtained by using solution-processed CuI and patterned CsI thin films for anticipation of future applications.
“Our study explains the mechanism underlying the formation of the rare local structures in Cs3Cu2I5 and its association with photoluminescence in these materials. These results can ultimately pave the way for the development of high-quality thin film devices with ideal optical properties for advanced stacking applications,” concludes Prof. Hosono.
More information: Masatake Tsuji et al, Room-Temperature Solid-State Synthesis of Cs3Cu2I5 Thin Films and Formation Mechanism for Its Unique Local Structure, Journal of the American Chemical Society (2023). DOI: 10.1021/jacs.3c01713
Flinders University chemists have discovered a new way to make ‘green’ polymers from low-cost building blocks with just a small amount of electricity. Credit: Flinders University
Chemistry researchers at Flinders University have ‘struck gold’ by discovering a new way to make ‘green’ polymers from low-cost building blocks with just a small amount of electricity.
The reaction is fast and occurs at room temperature. No hazardous chemical initiators are required—just electricity, with many potential uses including in gold mining and recycling e-waste, an interdisciplinary team reveal in an article just published in the Journal of the American Chemical Society.
While hundreds of millions of tons of plastic is produced every year, with up to half used for single purposes, the Flinders University research group is working on more sustainable options. The power used in production is a contributor to pollution and global warming.
“The use of electricity to produce new materials is an emerging field of research that opens many doors to new chemicals and polymers that can be produced in a more sustainable way,” says co-author Dr. Thomas Nicholls, an expert in using electrochemistry to make valuable molecules.
The process begins by adding an electron to the basic building block or monomer. After ‘electrocuting’ the monomer, it reacts with another building block in a chain reaction which leads to the formation of a polymer.
First-author and Ph.D. candidate Jasmine Pople says, “Our method to electrochemically produce polymers provides new materials that are highly functional and environmentally friendly.”
“The use of electricity to make valuable molecules is expanding rapidly due to its versatility. Additionally, it may generate less waste than traditional chemical syntheses and it can be powered with renewable energy.”
The key polymer made by the team has sulfur-sulfur bonds in its backbone. These sulfur groups can do useful things like bind precious metals such as gold. The team demonstrated that the key polymer could remove 97% of gold from solutions of relevance to mining and e-waste recycling.
The sulfur-sulfur bonds can also be broken and reformed. This interesting property enabled the team to discover conditions to convert the polymer back to its original building block. This is an important advance in recycling.
Typically, when common plastics are recycled, they are simply heated and reshaped into a new product. This process can cause degradation and down-cycling (conversion to a less valuable material), leading to eventual disposal in landfill.
In contrast, the polymers made in the latest research from Flinders University scientists can be chemically converted back into its constituent building blocks in high yield—meaning that building block can be used again to make new polymers.
The team also carried out quantum mechanical calculations to understand the details of how the reaction works. The findings were surprising and fortuitous.
“The polymerization has a clever self-correcting mechanism: whenever the wrong reaction occurs, it reverses until the correct reaction proceeds, ensuring a uniform polymer,” says Research Associate in computational and physical chemistry Dr. Le Nhan Pham
Future applications of this class of materials include environmental remediation, gold mining, and use of the polymer as an anti-microbial agent.
More information: Jasmine M. M. Pople et al, Electrochemical Synthesis of Poly(trisulfides), Journal of the American Chemical Society (2023). DOI: 10.1021/jacs.3c03239
The never-ending demand for carbon-rich fuels to drive the economy keeps adding more and more carbon dioxide (CO2) to the atmosphere. While efforts are being made to reduce CO2 emissions, that alone cannot counter the adverse effects of the gas already present in the atmosphere.
So, scientists have come up with innovative ways to use existing atmospheric CO2 by transforming it into useful chemicals such as formic acid (HCOOH) and methanol. A popular method for carrying out such conversions is to use visible light for driving the photoreduction of CO2 via photocatalysts.
In a recent breakthrough published in Angewandte Chemie, International Edition, a team of researchers led by Prof. Kazuhiko Maeda of Tokyo Institute of Technology developed a tin-based metal–organic framework (MOF) that can enable selective photoreduction of CO2. They reported a novel tin (Sn)-based MOF called KGF-10, with the formula [SnII2(H3ttc)2.MeOH]n (H3ttc: trithiocyanuric acid and MeOH: methanol).
It successfully reduced CO2 into HCOOH in the presence of visible light. “Most high-performance CO2 reduction photocatalysts driven by visible light rely on rare, precious metals as principal components. Furthermore, integrating the functions of light absorption and catalysis into a single molecular unit made up of abundant metals has remained a long-standing challenge. Hence, Sn was the ideal candidate as it can overcome both challenges,” explains Prof. Maeda.
MOFs, which bring the best of both metals and organic materials, are being explored as the more sustainable alternative to conventional rare-earth metal-based photocatalysts. Sn, known for its ability to act as both a catalyst and absorber during a photocatalytic reaction, could be a promising candidate for MOF-based photocatalysts. While MOFs composed of zirconium, iron, and lead have been widely explored, not much is known about Sn-based MOFs.
For synthesizing the Sn-based MOF KGF-10, the researchers used H3ttc, MeOH, and tin chloride as the starting materials and chose 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as the electron donor and the hydrogen source. The prepared KGF-10 was then subjected to several analysis techniques. They revealed that the material showed moderate CO2 adsorption ability, had a bandgap of 2.5 eV, and absorbed visible light wavelengths.
Once aware of the physical and chemical properties of the new material, scientists used it for catalyzing the reduction of CO2 in the presence of visible light. They found that KGF-10 successfully reduced CO2 into formate (HCOO–) with 99% selectivity without needing any additional photosensitizer or catalyst. It also exhibited a record-high apparent quantum yield— the ratio of the number of electrons involved in the reaction to the total number of incident photons—of 9.8% at 400 nm. Furthermore, structural analysis carried out during the reactions revealed that KGF-10 underwent structural changes while facilitating photocatalytic reduction.
This study presented for the first time a tin-based high-performance, precious-metal free, and single-component photocatalyst for visible-light-driven reduction of CO2 to formate. The excellent properties of KGF-10 demonstrated by the team could open new avenues for its application as a photocatalyst in reactions such as solar energy-driven CO2 reduction.
“The results of our study are a testimony to the fact that MOFs can be a platform for creating outstanding photocatalytic functions, usually unattainable with molecular metal complexes, using non-toxic, inexpensive, and Earth-abundant metals,” concludes Prof. Maeda.
More information: Yoshinobu Kamakura et al, Tin(II)‐Based Metal–Organic Frameworks Enabling Efficient, Selective Reduction of CO2 to Formate under Visible Light, Angewandte Chemie International Edition (2023). DOI: 10.1002/anie.202305923
