NT/ A machine learning-based approach to discover nanocomposite films for biodegradable plastic alternatives

Paradigm

Published in

Paradigm

25 min readApr 29, 2024

Nanotechnology & nanomaterials biweekly vol.54, 15th April — 29th April

TL;DR

The accumulation of plastic waste in natural environments is of utmost concern, as it is contributing to the destruction of ecosystems and is causing harm to aquatic life. In recent years, material scientists have thus been trying to identify all-natural alternatives to plastic that could be used to package or manufacture products. Researchers at the University of Maryland, College Park, recently devised a new approach to discover promising biodegradable plastic alternatives. Their proposed method, outlined in a paper published in Nature Nanotechnology, combines state-of-the-art machine learning techniques with molecular science.
Microplastics pose a great threat to human health. These tiny plastic debris can enter our bodies through the water we drink and increase the risk of illnesses. They are also an environmental hazard; found even in remote areas like polar ice caps and deep ocean trenches, they endanger aquatic and terrestrial lifeforms. To combat this emerging pollutant, researchers at the Indian Institute of Science (IISc) have designed a sustainable hydrogel to remove microplastics from water. The material has a unique intertwined polymer network that can bind the contaminants and degrade them using UV light irradiation.
A recent UCLA study demonstrates a new process for screening T cells, part of the body’s natural defenses, for characteristics vital to the success of cell-based treatments. The method filters T cells based on the receptor proteins found on their surface — which enable them to latch onto certain threats — and the type and amount of cell-killing or immune response-triggering molecules that they secrete.
An afterglow luminescent nanoprobe opens up new possibilities for imaging living cells. As a research team reports in the journal Angewandte Chemie International Edition, their new “nanotorch” can continue to luminesce for more than 10 days after a single excitation. This allows the routes taken through the body by microrobots to be tracked in real time. In addition, it can be “recharged” non-invasively with near-infrared (NIR) light in a non-contact manner.
Researchers from the National University of Singapore (NUS) have developed a new design concept for creating next-generation carbon-based quantum materials, in the form of a tiny magnetic nanographene with a unique butterfly shape hosting highly correlated spins. This new design has the potential to accelerate the advancement of quantum materials which are pivotal for the development of sophisticated quantum computing technologies poised to revolutionize information processing and high-density storage capabilities.
New options for making finely structured soft, flexible and expandable materials called hydrogels have been developed by researchers at Tokyo University of Agriculture and Technology (TUAT). Their work extends the emerging field of “kirigami hydrogels,” in which patterns are cut into a thin film allowing it to later swell into complex hydrogel structures.
A study of oxygen molecules interacting with atomically thin layers of materials being developed as new generations of semiconductors could significantly improve control over the fabrication and applications of these two-dimensional (2D) materials.
For years, scientists have been intrigued by how molecules move across surfaces. The process is critical to numerous applications, including catalysis and the manufacturing of nanoscale devices. Now, using neutron spectroscopy experiments performed at Institut Laue-Langevin (ILL) and advanced theoretical models and computer simulations, a team led by Anton Tamtögl from Graz University of Technology has unveiled the unique movement of triphenylphosphine (PPh3) molecules on graphite surfaces, a behavior akin to a nanoscopic moon lander.
In a study published in ACS Omega, researchers from the United States Department of Agriculture (USDA)’s Agricultural Research Service (ARS) revealed the ability of cotton gin waste to synthesize and generate silver nanoparticles in the presence of silver ions.
Understanding water behavior in nanopores is crucial for both science and practical applications. Scientists from the City University of Hong Kong (CityU) have revealed the remarkable behavior of water and ice under high pressure and temperature, and strong confinement.

Nanotech Market

Nanotechnology deals with the ability to see, understand, measure, predict, produce or control matter at the nanoscale (below 100 nanometers). The realm of nanotechnology lies between 0.1 and 100 nanometers, wherein a nanometer is defined as one-thousandth of a micron. As a versatile technology with widespread applications in a wide range of end-use sectors, nanotechnology is currently facing a mixed bag of challenges and opportunities as the COVID-19 pandemic continues to spread across the globe. With the world fighting its biggest public health crisis in history, nanotechnology healthcare applications are storming into the spotlight led by the focus on nano intervention in terms of designing effective ways to identify, diagnose, treat and eliminate the spread of COVID-19 infections. Their role as nanocarriers has the potential to design risk-free and effective immunization strategies. In the post-COVID-19 period, the use of nanotechnology solutions in the production of a multitude of devices & products will continue to grow.

Amid the COVID-19 crisis, the global market for Nanotechnology estimated at US$42.2 Billion in the year 2020, is projected to reach a revised size of US$70.7 Billion by 2026, growing at a CAGR of 9.2% over the analysis period. Nanocomposites, one of the segments analyzed in the report, is projected to record an 8.7% CAGR and reach US$35.4 Billion by the end of the analysis period. After a thorough analysis of the business implications of the pandemic and its induced economic crisis, growth in the Nanomaterials segment is readjusted to a revised 10.1% CAGR for the next 7-year period.

Global nanotechnology market to reach US $126.8 billion by the year 2027. Amid the COVID-19 crisis, the global market for Nanotechnology is estimated at US $54.2 billion in the year 2020 and is projected to reach a revised size of US $126 billion.

Latest News & Research

Machine intelligence-accelerated discovery of all-natural plastic substitutes

by Tianle Chen et al in Nature Nanotechnology

The accumulation of plastic waste in natural environments is of utmost concern, as it is contributing to the destruction of ecosystems and is causing harm to aquatic life. In recent years, material scientists have thus been trying to identify all-natural alternatives to plastic that could be used to package or manufacture products. Researchers at the University of Maryland, College Park, recently devised a new approach to discover promising biodegradable plastic alternatives. Their proposed method, outlined in a paper published in Nature Nanotechnology, combines state-of-the-art machine learning techniques with molecular science.

“My inspiration for this research was sparked by a 2019 visit to Palau in the Western Pacific,” Prof. Po-Yen Chen, co-author of the paper, told Tech Xplore. “The impact of plastic pollution on marine life there — floating plastic films deceiving fish and sea turtles mistaking plastic waste for food — was deeply disturbing. This motivated me to apply my expertise to this environmental issue and led to my focus on finding a solution when setting up my research lab at UMD.”

Conventional and previously employed methods to search for sustainable plastic alternatives are time-consuming and inefficient. In many cases, they also yield poor results, for instance, identifying materials that are biodegradable but do not have the same desirable properties as plastic.

The innovative approach for identifying plastic alternatives introduced in this recent paper relies on a machine learning model developed by Chen.

In addition to being faster than conventional methods of searching for materials, this approach could be more effective in discovering materials that can be realistically employed in manufacturing and industry settings. Chen applied his machine learning technique to the discovery of all-plastic alternatives in close collaboration with his colleagues Teng Li and Liangbing Hu.

“Combining automated robotics, machine learning, and molecular dynamics simulations, we accelerated the development of environmentally friendly, all-natural plastic substitutes that meet essential performance standards,” Chen explained. “Our integrated approach combines automated robotics, machine learning, and active learning loops to expedite the development of biodegradable plastic alternatives.”

First, Chen and his colleagues compiled a comprehensive library of nanocomposite films derived from various natural sources. This was done using an autonomous pipetting robot, which can independently prepare laboratory samples.

Subsequently, the researchers used this sample library to train Chen’s machine learning-based model. During training, the model gradually became more proficient in predicting the properties of materials based on their composition, through a process known as iterative active learning.

“The synergy of robotics and machine learning not only expedites the discovery of natural plastic substitutes but also allows for the targeted design of plastic alternatives with specific properties,” Chen said. “Our approach significantly reduces the time and resources required, compared to the traditional trial-and-error research method.”

This recent study and the approach it introduced could expedite the future search for eco-friendly plastic alternatives. The team’s model could soon be used by teams worldwide to produce all-natural nanocomposites with adjustable and advantageous properties.

“By coupling robotics, machine learning, and simulation tools, we have established a workflow that accelerates the discovery of new functional materials and enables customization for specific applications,” Chen said.
“Our integrated approach lowers the design barrier for a green alternative to petrochemical plastics while remaining environmentally safe. It also provides an open and expandable database focused on green, eco-friendly, and biodegradable functional materials.”

In the future, the innovative approach developed by Chen could help to reduce plastic pollution worldwide, by facilitating the transition of multiple sectors towards more sustainable materials. In their next studies, the researchers plan to continue working to address the environmental issues caused by petrochemical plastics.

For instance, they hope to expand the range of natural materials that manufacturers can choose from. In addition, they will try to broaden the possible applications of materials identified by their model and ensure that these materials can be produced on a large scale.

“We are now working on finding the right biodegradable and sustainable materials for packaging fresh produce after harvest, replacing single-use plastic food packaging, and improving the shelf life of these post-harvest products,” Chen added.
“We are also investigating how to manage the disposal of these biodegradable plastics, including recycling them or converting them into other useful chemicals. These efforts are crucial steps toward making our solutions not only environmentally friendly but also economically viable alternatives to conventional plastics. This work contributes significantly to the worldwide initiative to reduce plastic pollution.”

Polyoxometalate nanocluster-infused triple IPN hydrogels for excellent microplastic removal from contaminated water: detection, photodegradation, and upcycling

by Soumi Dutta et al in Nanoscale

Microplastics pose a great threat to human health. These tiny plastic debris can enter our bodies through the water we drink and increase the risk of illnesses. They are also an environmental hazard; found even in remote areas like polar ice caps and deep ocean trenches, they endanger aquatic and terrestrial lifeforms. To combat this emerging pollutant, researchers at the Indian Institute of Science (IISc) have designed a sustainable hydrogel to remove microplastics from water. The material has a unique intertwined polymer network that can bind the contaminants and degrade them using UV light irradiation. The research is published in the journal Nanoscale.

Scientists have previously tried using filtering membranes to remove microplastics. However, the membranes can become clogged with these tiny particles, rendering them unsustainable. Instead, the IISc team led by Suryasarathi Bose, Professor at the Department of Materials Engineering, decided to turn to 3D hydrogels.

The novel hydrogel developed by the team consists of three different polymer layers — chitosan, polyvinyl alcohol and polyaniline — intertwined together, making an Interpenetrating Polymer Network (IPN) architecture. The team infused this matrix with nanoclusters of a material called copper substitute polyoxometalate (Cu-POM).

These nanoclusters are catalysts that can use UV light to degrade the microplastics. The combination of the polymers and nanoclusters resulted in a strong hydrogel with the ability to adsorb and degrade large amounts of microplastics.

Most microplastics are a product of the incomplete breakdown of household plastics and fibers. To mimic this in the lab, the team crushed food container lids and other daily-use plastic products to create two of the most common microplastics existing in nature: polyvinyl chloride and polypropylene.

“Along with treatment or removal of microplastics, another major problem is detection. Because these are very small particles, you cannot see them with the naked eye,” explains Soumi Dutta, first author of the study and SERB National Post-doctoral fellow at the Department of Materials Engineering.

To solve this problem, the researchers added a fluorescent dye to the microplastics to track how much was being adsorbed and degraded by the hydrogel under different conditions.

“We checked the removal of microplastics at different pH levels of water, different temperatures, and different concentrations of microplastics,” explains Dutta.

The hydrogel was found to be highly efficient — it could remove about 95% and 93% of the two different types of microplastics in water at near-neutral pH (∼6.5). The team also carried out several experiments to test how durable and strong the material was. They found that the combination of the three polymers made it stable under various temperatures.

“We wanted to make a material that is more sustainable and can be used repetitively,” explains Bose.

The hydrogel could last for up to five cycles of microplastic removal without significant loss of efficacy. What’s more, Bose points out, is that once it has outlived its use, the hydrogel can be repurposed into carbon nanomaterials that can remove heavy metals like hexavalent chromium from polluted water.

Moving forward, the researchers plan to work with collaborators to develop a device that can be deployed on a large scale to help clean up microplastics from various water sources.

Defining T cell receptor repertoires using nanovial-based binding and functional screening

by Doyeon Koo et al in Proceedings of the National Academy of Sciences

A recent UCLA study demonstrates a new process for screening T cells, part of the body’s natural defenses, for characteristics vital to the success of cell-based treatments. The method filters T cells based on the receptor proteins found on their surface — which enable them to latch onto certain threats — and the type and amount of cell-killing or immune response-triggering molecules that they secrete.

The researchers discovered three previously unidentified, naturally occurring T-cell receptors that target prostate cancer using their screening method. In validation tests, T-cell receptors associated with the highest levels of secretion were the most likely to elicit a response against cancer cells. Rate of functional T-cell receptors was around tenfold higher than using previous techniques.

Immunotherapy, treatment that harnesses the body’s natural defenses, is an ever-growing subject of research into cancer and other severe illnesses. The potential of engineered T cell-based immunotherapies comes in part from their ability to narrowly target signatures of disease that are “recognized” by genetically engineered receptors. Since 2017, seven therapies deploying immune cells have gained approval from the Food and Drug Administration to treat blood and skin cancers.

The scientists used nanovials, microscopic bowl-shaped hydrogel containers developed at UCLA. Inside, the containers are customized to include specially shaped molecules that enable each to trap one cell plus selected secretions.

The team first evaluated a population of 20 million T cells sourced from one healthy patient’s blood sample. Different groups of nanovials had targets associated with different common viruses. This study validated the ability for nanovials to find T cells, and their receptors, that react to viruses.

A second experiment with a different patient applied the technology to a much more challenging problem: rare prostate cancer targets the scientists had identified in previous studies. Importantly, those molecular targets acted to both capture the T cells and cause them to secrete certain molecules that kill target cells. In other experiments, the nanovials also had molecules allowing each to capture more than one type of immune-activating secretion.

The three never-before-seen receptors for prostate cancer found in this research could ultimately lead to new tumor-fighting immunotherapies. The ability to select T cells that both bind to a disease-related target and secrete plenty of molecules that trigger an immune response — displayed in the study — is expected to provide major advantages for uncovering additional new disease-targeting receptors, developing cellular therapies and translating those therapies to benefit patients. Using standard lab techniques to label and analyze the nanovials and their contents means that more researchers can apply the new technique.

Rechargeable Afterglow Nanotorches for In Vivo Tracing of Cell‐Based Microrobots

by Gongcheng Ma et al in Angewandte Chemie International Edition

An afterglow luminescent nanoprobe opens up new possibilities for imaging living cells. As a research team reports in the journal Angewandte Chemie International Edition, their new “nanotorch” can continue to luminesce for more than 10 days after a single excitation. This allows the routes taken through the body by microrobots to be tracked in real time. In addition, it can be “recharged” non-invasively with near-infrared (NIR) light in a non-contact manner.

Macrophages are important immune cells that “eat” bacteria as well as being involved in the disposal of cancer cells. In addition, they can take up drugs and transport them into cells, including tumor cells. If they take up magnetic nanoparticles, macrophages can be guided by magnet to a target area within the body, such as a tumor. This allows macrophage “microrobots” to reduce the side effects associated with chemotherapy.

It would be useful to be able to track the microrobots over time as they move through the body. Fluorescence imaging techniques have been considered but require constant external irradiation. This causes is a high level of background noise resulting from the autofluorescence of many biomolecules. In addition, the limited penetration depth of the visible and UV light through tissues required into the tissue limits the depth of detection.

One alternative could be the use of probes that can be irradiated before the procedure and produce an afterglow. However, inorganic nanoparticles with long-lasting afterglow harbor the risk that heavy metal ions will leak out; while organic compounds only luminesce for a short time and cannot be repeatedly excited.

A team from the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences (China) collaborating with Koç University (Turkey) has now developed a “rechargeable nanotorch.” It is made of multiple components: nanoparticles of a precursor to a luminescent organic molecule, photosensitizers (a hydrophobic analog of methylene blue), and polyethylene glycol equipped with cell-penetrating peptides.

The photosensitizer absorbs NIR light and excites surrounding oxygen molecules. This highly reactive singlet oxygen then binds to the precursor and forms a dioxetane group, a four-membered ring made of two oxygen and two carbon atoms. This undergoes a rearrangement that releases the desired luminescent molecule and emits excess energy by luminescing. After the initial irradiation, the nanotorches continue to luminesce for ten days.

Once depleted, the nanotorches can be “remotely” recharged and made to luminesce again by external radiation with NIR light, which can penetrate deep into tissues — multiple times. This requires the relative amounts of photosensitizer and luminescent molecule precursor to be selected so that only some of the precursors are activated with each irradiation. This allows for imaging over longer periods of time.

Highly entangled polyradical nanographene with coexisting strong correlation and topological frustration

by Shaotang Song et al in Nature Chemistry

Researchers from the National University of Singapore (NUS) have developed a new design concept for creating next-generation carbon-based quantum materials, in the form of a tiny magnetic nanographene with a unique butterfly-shape hosting highly correlated spins. This new design has the potential to accelerate the advancement of quantum materials which are pivotal for the development of sophisticated quantum computing technologies poised to revolutionize information processing and high density storage capabilities.

The team was led by Associate Professor Lu Jiong from the NUS Department of Chemistry and Institute for Functional Intelligent Materials, together with Professor Wu Jishan who is also from the NUS Department of Chemistry, and international collaborators. The research was published in Nature Chemistry.

Magnetic nanographene, a tiny structure made of graphene molecules, exhibits remarkable magnetic properties due to the behavior of specific electrons in the carbon atoms’ π-orbitals. By precisely designing the arrangement of these carbon atoms at the nanoscale, control over the behavior of these unique electrons can be achieved. This renders nanographene highly promising for creating extremely small magnets and for fabricating fundamental building blocks needed for quantum computers, called quantum bits or qubits.

The unique structure of the butterfly-shaped magnetic graphene developed by the researchers has four rounded triangles resembling butterfly wings, with each of these wings holding an unpaired π-electron responsible for the observed magnetic properties. The structure was achieved through an atomic-precise design of the π-electron network in the nanostructured graphene.

Assoc Prof Lu said, “Magnetic nanographene, a tiny molecule composed of fused benzene rings, holds significant promise as a next-generation quantum material for hosting fascinating quantum spins due to its chemical versatility and long spin coherence time. However, creating multiple highly entangled spins in such systems is a daunting yet essential task for building scalable and complex quantum networks.”

The achievement is a result of close collaboration among synthetic chemists, materials scientists, and physicists, including key contributors Professor Pavel Jelinek and Dr. Libor Vei, from the Czech Academy of Sciences in Prague.

The magnetic properties of nanographene are usually derived from the arrangement of its special electrons, known as π-electrons, or the strength of their interactions. However, it is difficult to make these properties work together to create multiple correlated spins. Nanographene also predominately exhibits a singular magnetic order, where spins align either in the same direction (ferromagnetic) or in opposite directions (antiferromagnetic).

The researchers developed a method to overcome these challenges. Their butterfly-shaped nanographene, with both ferromagnetic and antiferromagnetic properties, is formed by combining four smaller triangles into a rhombus at the center. The nanographene measures approximately 3 nanometers in size.

To produce the “butterfly” nanographene, the researchers initially designed a special molecule precursor via conventional in-solution chemistry. This precursor was then used for the subsequent on-surface synthesis, a new type of solid-phase chemical reaction performed in a vacuum environment. This approach allowed the researchers to precisely control the shape and structure of the nanographene at the atomic level.

An intriguing aspect of the “butterfly” nanographene its four unpaired π-electrons, with spins mainly delocalized in the “wing” regions and entangled together. Using an ultra-cold scanning probe microscope with a nickelocene tip as an atomic-scale spin sensor, the researchers measured the magnetism of the butterfly nanographenes. Additionally, this new technique helps scientists direct probe entangled spins to understand how nanographene’s magnetism works at the atomic scale.

The breakthrough not only tackles existing challenges but opens up new possibilities for precisely controlling the magnetic properties at the smallest scale, leading to exciting advancements in quantum materials research.

“The insights gained from this study pave the way for creating new-generation organic quantum materials with designer quantum spin architectures. Looking ahead, our goal is to measure the spin dynamics and coherence time at the single-molecule level and manipulate these entangled spins coherently. This represents a significant stride towards achieving more powerful information processing and storage capabilities,” said Assoc Prof Lu.

Adaptive plasticity of auxetic Kirigami hydrogel fabricated from anisotropic swelling of cellulose nanofiber film

by Daisuke Nakagawa et al in Science and Technology of Advanced Materials

New options for making finely structured soft, flexible and expandable materials called hydrogels have been developed by researchers at Tokyo University of Agriculture and Technology (TUAT). Their work extends the emerging field of “kirigami hydrogels,” in which patterns are cut into a thin film allowing it to later swell into complex hydrogel structures. The research is published in the journal Science and Technology of Advanced Materials.

Hydrogels have a network of water-attracting (hydrophilic) molecules, allowing their structure to swell substantially when exposed to water that becomes incorporated within the molecular network. Researchers Daisuke Nakagawa and Itsuo Hanasaki worked with an initially dry film composed of nanofibers of cellulose, the natural material that forms much of the structure of plant cell walls.

They used laser processing to cut structures into the film before water was added allowing the film to swell. The particular design of the Kirigami pattern works in such a way that the width increases when stretched in the longitudinal direction, which is called the auxetic property. This auxetic property emerges provided that the thickness grows sufficiently when the original thin film is wet.

“As Kirigami literally means the cut design of papers, it was originally intended for thin sheet structures. On the other hand, our two-dimensional auxetic mechanism manifests when the thickness of the sheet is sufficient, and this three-dimensionality of the hydrogel structure emerges by swelling when it is used. It is convenient to store it in the dry state before use, rather than keeping the same water content level of the hydrogel,” says Hanasaki.
“Furthermore, the auxeticity is maintained during the cyclic loading that causes the adaptive deformation of the hydrogel to reach another structural state. It will be important for the design of intelligent materials.”

Potential applications for the adaptive hydrogels include soft components of robotic technologies, allowing them to respond flexibly when interacting with objects they are manipulating, for example. They might also be incorporated into soft switches and sensor components.

Hydrogels are also being explored for medical applications, including tissue engineering, wound dressings, drug delivery systems and materials that can adapt flexibly to movement and growth. The advance in kirigami hydrogels achieved by the TUAT team significantly extends the options for future hydrogel applications.

“Keeping the designed characteristics while showing adaptivity to the environmental condition is advantageous for the development of multifunctionality,” Hanasaki concludes.

Defect Passivation of 2D Semiconductors by Fixating Chemisorbed Oxygen Molecules via h‐BN Encapsulations

by Jin‐Woo Jung et al in Advanced Science

A study of oxygen molecules interacting with atomically thin layers of materials being developed as new generations of semiconductors could significantly improve control over the fabrication and applications of these two-dimensional (2D) materials. The work, by researchers at Daegu Gyeongbuk Institute of Science and Technology (DGIST), in South Korea, with colleagues elsewhere in South Korea and in Japan, is published in the journal Advanced Science.

The single layer of bonded atoms that comprise 2D materials can have semiconducting properties suitable for making electronic components including transistors on much smaller scales than generally possible. This could move microelectronics down into the nanoelectronics level, building tiny and more efficient circuits, including flexible devices and solar cells.

Some of the most promising 2D materials are transition metal dichalcogenides (TMDs), which have elements from the transition metal groups of the periodic table combined with twice as many chalcogen elements, especially sulfur, selenium and tellurium. The DGIST team and their colleagues worked with monolayer TMD crystals of tungsten and sulfur, with the formula WS2.

They investigated the tendency of oxygen molecules to become adsorbed onto the defect sites of crystals — sulfur vacancies where a sulfur atom is missing from WS2 lattice sites. They explored the interactions between the defects and oxygen molecules with a technique called electron energy loss spectroscopy (EELS).

This uses an electron microscope to fire electrons through the material, then analyzes the patterns of energy loss by the electrons to reveal crucial structural information. The EELS results were combined with insights from optical analysis and theoretical calculations.

The researchers paid particular attention to the ability of adsorbed oxygen molecules to become fixed in place when the WS2 crystals were encapsulated within monolayers of another material — hexagonal boron nitride (h-BN) — above and below the WS2 layer. h-BN is a common ingredient of electronic and photonic devices constructed using 2D TMDs.

Fixing the oxygen molecules in place at the defect sites alters and stabilizes the electronic behavior of the TMDs in a process called passivation. This affects the crystals in subtle ways that will influence their activity in a range of applications.

“Our work provides a new insight into the defect-related phenomena in 2D TMDs, that can trigger revolutionary approaches to control the defect states,” says semiconductor and nanophotonics specialist Prof. Chang-Hee Cho of the DGIST team.
“We now hope to develop new experimental approaches and techniques to control the defect states of the 2D TMDs using h-BN encapsulation,” adds Cho. “This will allow us to move the method towards being ready for full-scale development and eventual commercial uses.”

Molecular motion of a nanoscopic moonlander via translations and rotations of triphenylphosphine on graphite

by Anton Tamtögl et al in Communications Chemistry

For years, scientists have been intrigued by how molecules move across surfaces. The process is critical to numerous applications, including catalysis and the manufacturing of nanoscale devices. Now, using neutron spectroscopy experiments performed at Institut Laue-Langevin (ILL) and advanced theoretical models and computer simulations, a team led by Anton Tamtögl from Graz University of Technology has unveiled the unique movement of triphenylphosphine (PPh3) molecules on graphite surfaces, a behavior akin to a nanoscopic moon lander.

In fact, PPh3 molecules exhibit a remarkable form of motion, rolling and translating in ways that challenge previous understandings. This moon lander-like motion seems to be facilitated by their unique geometry and three-point binding with the surface.

“Delving into the complex world of molecular motion on graphite surfaces has been an exciting journey,” reveals Anton Tamtögl. “Measurements and simulation unveiled a sophisticated motion and ‘dance’ of the molecules, providing us with a deeper understanding of surface dynamics and opening up new horizons for materials science and nanotechnology.”

Triphenylphosphine is an important molecule for the synthesis of organic compounds and nanoparticles with numerous industrial applications. The molecule exhibits a peculiar geometry: PPh3 is pyramidal with a propeller-like arrangement of its three cyclic groups of atoms.

Neutrons offer unique possibilities in the study of materials’ structure and dynamics. In a typical experiment, neutrons scattered off the sample are measured as a function of the change in their direction and energy. Due to their low energy neutrons are an excellent probe for studying low energy excitations such as molecular rotations and diffusion. Neutron spectroscopy measurements were performed at ILL Instruments IN5 (TOF spectrometer) and IN11 (neutron spin-echo spectrometer).

“It’s amazing to see how ILL’s powerful spectrometers allow us to follow the dynamics of these fascinating molecular systems even if the amount of sample is tiny,” says ILL scientist Peter Fouquet. “Neutron beams do not destroy these sensitive samples and allow for a perfect comparison with computer simulations.”

The study shows that PPh3 molecules interact with the graphite surface in a manner that allows them to move with surprisingly low energy barriers. The movement is characterized by rotations and translations (jump-motions) of the molecules. While rotations and intramolecular motion dominate up to about 300 K, the molecules follow an additional translational jump-motion across the surface from 350–500 K.

Understanding the detailed mechanisms of molecular motion at the nanoscale opens up new avenues for the fabrication of advanced materials with tailored properties. Apart from the fundamental interest, the movement of PPh3 and related compounds on graphite surfaces is of great importance for applications.

Unveiling the Hidden Value of Cotton Gin Waste: Natural Synthesis and Hosting of Silver Nanoparticles

by Sunghyun Nam et al in ACS Omega

In a study published in ACS Omega, researchers from the United States Department of Agriculture (USDA)’s Agricultural Research Service (ARS) revealed the ability of cotton gin waste to synthesize and generate silver nanoparticles in the presence of silver ions.

Cotton gin waste, also known as cotton gin trash, is a byproduct of the cotton ginning process and occurs when the cotton fibers are separated from the seed boll. For cotton gin waste, the treasure is its hidden potential to transform silver ions into silver nanoparticles and create a new hybrid material that could be used to add antimicrobial properties to consumer products, like aerogels, packaging, or composites.

Silver nanoparticles are highly sought-after products in the nanotechnology industry because of their antibacterial, antifungal, antiviral, electrical, and optical properties. These nanoparticles have an estimated global production of 500 tons per year and are widely applied to consumer goods such as textiles, coatings, paints, pigments, electronics, optics, and packaging.

“Our method not only lets cotton gin waste act as chemical agents for producing silver nanoparticles, which makes it cost-effective and environmentally friendly but also enables embedding the nanoparticles within the cotton gin waste matrix,” said Sunghyun Nam, research engineer at ARS’s Cotton Chemistry and Utilization Research Unit in New Orleans. “By embedding them in the cotton gin waste, these materials acquire antimicrobial properties.”

Nam said the researchers used a simple heat treatment of cotton gin waste materials in water containing silver ions that produced silver nanoparticles without the need for additional chemical agents.

This finding is significant since making silver nanoparticles usually requires chemical agents which can be costly and pose environmental concerns. Embedding nanoparticles into a material can also be challenging.

Developing nanoparticle embedding technology is not new for Nam and her team. They previously developed washable antimicrobial wipes by using raw cotton fiber that produced silver nanoparticles inside the fiber. The embedded silver nanoparticles can continue to kill harmful bacteria wash after wash.

Large quantities of cotton gin waste are generated annually, and the cotton ginning industry is always seeking new sustainable processes that upcycle crop residue.

“Our research paves the way for new material applications of cotton gin waste that can protect against microbial contamination,” said Nam.

A provisional patent application on the self-embedding silver nanoparticle biomass waste compositions has recently been filed.

Rich proton dynamics and phase behaviours of nanoconfined ices

by Jian Jiang et al in Nature Physics

Understanding water behavior in nanopores is crucial for both science and practical applications. Scientists from City University of Hong Kong (CityU) have revealed the remarkable behavior of water and ice under high pressure and temperature, and strong confinement.

These findings, which defy the normal behavior observed in daily life, hold immense potential for advancing our understanding of water’s unusual properties in extreme environments, such as in the core of distant ice planets. The implications of this major scientific advancement span various fields, including planetary science, energy science, and nanofluidic engineering.

Led by Professor Zeng Xiaocheng, Head and Chair Professor in the Department of Materials Science and Engineering at CityU, the research team employed state-of-the-art computational methods to simulate the properties of water and ice under extreme conditions.

Through machine learning potential, crystal structure searches, path-integral molecular dynamics, and metadynamics, they conducted comprehensive simulations of mono- and bi-layer water under nanoconfinement. These simulations unveiled a range of intriguing phenomena, including two-dimensional (2D) ice-to-water melting, novel ice behavior, water splitting, and proton dynamics in nano ice.

The research team discovered 10 new 2D ice states, each exhibiting unique characteristics. Notably, they identified 2D molecular ice with a symmetric O-H-O configuration, reminiscent of the highest density 3D Ice X found on Earth. Additionally, they observed dynamic, partially ionic ice and several superionic ices. Surprisingly, these 2D ice states could be produced at much lower pressures than their 3D counterparts with similar water density, making them more accessible in laboratory conditions.

Professor Zeng emphasized the significance of these findings, stating that they represent a new frontier in understanding the physics and chemistry of water and ice under extreme conditions, particularly in the core of ice giant planets.

“The potential to create these unique ice- and water-splitting states in the laboratory, including dynamic, partially ionic and superionic ices at lower pressure than previously thought possible, is particularly exciting,” said Professor Zeng.

Exploring the behavior of water and ice under different conditions, especially when nanoconfinement is considered, is a profoundly complex task.

The research team tackled this challenge through an extensive number of simulations of molecular dynamics and path-integral molecular dynamics, generating a vast dataset. Extracting meaningful insights from this enormous amount of data posed a significant data analysis challenge, requiring meticulous exploration.

These findings pave the way for future research into the mysteries of ice giant planets and the fundamental properties of water. The next phase of this research involves experimental validation of the computational predictions and exploration of practical applications.

Professor Zeng expressed enthusiasm about the potential of this research to deepen our understanding of water, ice, and water-splitting in extreme environments, while also opening new frontiers in nanoscience and planetary research.