#nanoporosity

Liquid crystals in nanopores produce a surprisingly large negative pressure

Negative pressure governs not only the Universe or the quantum vacuum. This phenomenon, although of a different nature, appears also in liquid crystals confined in nanopores. At the Institute of Nuclear Physics of the Polish Academy of Sciences in Cracow, a method has been presented that for the first time makes it possible to estimate the amount of negative pressure in spatially limited liquid crystal systems.

At first glance, negative pressure appears to be an exotic phenomenon. In fact, it is common in nature, and what's more, occurs on many scales. On the scale of the universe, the cosmological constant is responsible for accelerating the expansion of spacetime. In the world of plants, attracting intermolecular forces guarantee the flow of water to the treetops of all trees taller than ten metres. On the quantum scale, the pressure of virtual particles of a false vacuum leads to the creation of an attractive force, appearing, for example, between two parallel metal plates (the famous Casimir effect).

"The fact that a negative pressure appears in liquid crystals confined in nanopores was already known. However, it was not known how to measure this pressure. Although we also cannot do this directly, we have proposed a method that allows this pressure to be reliably estimated," says Dr. Tomasz Rozwadowski from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Cracow, the first author of a publication in the Journal of Molecular Liquids.

X-ray analysis of carbon nanostructures helps material design

Optimized nanoporous carbons can serve as electrodes for fast electron and ion transport or improve the performance of energy storage and conversion devices. Thus the tunability of the size, shape, and distribution of pores is highly required. The team at the HZB Institute for Soft Matter and Functional Materials collaborated with a group at the University of Tartu, Estonia, to inquire the nanoarchitecture, inner surface, size, form and distribution of nanopores in dependence of the synthesis conditions.

Colleagues in Estonia produced a series of nanoporous carbons by reacting a powder of molybdenum carbide (Mo2C) with gaseous chlorine at 600, 700, 800, 900, and 1000 degrees Celsius. Depending on the synthesis conditions chosen, the nanoporous carbon exhibit different properties such as surface area, porosity, electronic and ionic conductivity, hydrophilicity and electrocatalytic activity.

Surface structures were analysed by transmission electron microscopy at the HZB. The interior surface area of nanocarbon materials is usually investigated by adsorption of gas. However, this method is not only comparatively inaccurate, it also contains no information about the shape and size of the pores. For deeper insights, Dr. Eneli Härk and her colleagues at HZB worked with small-angle X-ray scattering, a technique permitting to obtain information on various structural features on the nanometer scale including the mean pore size.

Materials that open in the heat of the moment

Kyoto University researchers have designed a temperature-controllable, copper-based material for sieving or storing gases. The principle used to design the material, described in the journal Science, could act as a blueprint for developing nanoporous materials with a wide variety of energy, medical and environmental applications.

The porous nanomaterials that are currently used for gas separation and storage are not tuneable because their pores are persistent and rigid. Susumu Kitagawa, Nobuhiko Hosono, and their colleagues of Kyoto University's Institute for Integrated Cell-Material Sciences (iCeMS) wanted to find a way to dynamically change pore sizes in this type of material.

They designed a porous coordination polymer that was formed of copper atoms linked by butterfly-shaped ligands made from isophthalic acid and phenothiazine-5,5-dioxide. The resultant material was composed of tiny nanocages, each with eight protruding channels. At very low temperatures, the channels connecting the nanocages were so narrow that they were effectively closed. As the temperature increased, the channels progressively widened, allowing gas molecules to move between the cages.

Taming defects in nanoporous materials to put them to a good use

The word "defect" universally evokes some negative, undesirable feature, but researchers at the Energy Safety Research Institute (ESRI) at Swansea University have a different opinion: in the realm of nanoporous materials, defects can be put to a good use, if one knows how to tame them.

Metal Organic Frameworks

A team led by Dr. Marco Taddei, Marie Sklodowska-Curie Actions Fellow at Swansea University, is investigating how the properties of metal-organic frameworks, a class of materials resembling microscopic sponges, can be adjusted by taking advantage of their defects to make them better at capturing CO2.

Dr. Taddei said: "Metal-organic frameworks, or MOFs, are extremely interesting materials because they are full of empty space that can be used to trap and contain gases. In addition, their structure can be manipulated at the atomic level to make them selective to certain gases, in our case CO2."

New nanoporous metal foams uses sunlight to clean up water

A researcher from the University of Bath is leading the way in creating a new, more efficient way for the water industry to safely remove micropollutants from water without increasing their carbon footprint.

Professor Davide Mattia from the University of Bath's Department of Chemical Engineering has been awarded a five-year EPSRC (Engineering and Physical Sciences Research Council) Established Career Fellowship in Water Engineering, to develop novel photocatalytic nanoporous anodic metal foams – a sponge-like substance—which will use sunlight to safely remove micropollutants from water.

One of the biggest public health and environmental challenges

Micropollutants – found in toxic chemicals such as drugs, hormones and pesticides—represent today one of the biggest public health and environmental challenges in the UK as well as other countries. Present in wastewater at very low concentrations, micropollutants slowly accumulate in the soil and in ground water, upsetting the ecological balance and eventually finding their way into the human food supply chain, with a potential to cause severe adverse long-term health effects.

New, simplified technique makes light metallic nanofoam: Potential use in hydrogen storage

A simple method for manufacturing extremely low-density palladium nanofoams could help advance hydrogen storage technologies, reports a new study from the University of California, Davis.

A nanofoam is what it sounds like -- a foamy version of some material, filled with very small pores. First introduced about 20 years ago, metallic nanofoams have potential for diverse applications. The porous structures are strong and lightweight -- like their natural counterparts of bone and cork. Palladium and certain other metal nanofoams can also rapidly store and release hydrogen, making them an ideal candidate for hydrogen fuel cells.

But before cars can start fueling up via nanofoam, using metallic foams on an industrial scale must overcome challenges including demanding manufacturing conditions, contamination and poor crystallinity, said senior author Kai Liu, professor of physics in the UC Davis College of Letters and Science. It is also difficult to achieve extremely lightweight foams without compromising their stability, Liu noted.

New technique produces tunable, nanoporous materials

Nanostructures with unique properties

A collaborative group of researchers including Petr Kral, professor of chemistry at the University of Illinois at Chicago, describe a new technique for creating novel nanoporous materials with unique properties that can be used to filter molecules or light. They describe their research in the journal Science.

Nanoparticles are tiny particles made up of a central solid core to which molecules called ligands are often attached. Nanoparticles can self-assemble into lattice-like formations that have unique optical, magnetic, electronic and catalytic properties.

Experimentalists led by Rafal Klajn, professor of chemistry at the Weizmann Institute of Science in Israel and corresponding author on the paper, produced thin lattice structures made up of two kinds of nanoparticles: one with a magnetite core and another with a gold core.

In order to form these thin, lattice-like structures, nanoparticles self-assembled within a layer of drying solvent floating on another liquid in which the particles are insoluble.

Just squeeze in—researchers discover when spaces are tight, nature loosens its laws

It turns out that when they're in a hurry and space is limited, ions, like people, will find a way to cram in—even if that means defying nature's norms. Recently published research from an international team of scientists, including Drexel University's Yury Gogotsi, PhD, shows that the charged particles will actually forgo their "opposites attract" behavior, called Coulombic ordering, when confined in the tiny pores of a nanomaterial. This discovery could be a pivotal development for energy storage, water treatment and alternative energy production technologies, which all involve ions packing into nanoporous materials.

In their paper, which was recently published in the journal Nature Materials, the researchers explain how Coulombic ordering in liquid salts starts to break down when ions are confined in small spaces—specifically carbon pores less than a nanometer in diameter. And the narrower the pore, the less the ions adhere to Coulombic ordering.

"This is the first time breaking of the Coulombic ordering in subnanometer pores has been convincingly demonstrated," said Gogotsi, an author of the paper, who is the Distinguished University and Bach professor in Drexel's College of Engineering. "The breaking of symmetry principals, like Coulombic ordering, plays an essential role in nature. But many of these processes occur without us understanding them and knowing their mechanisms. Science can reveal those hidden processes. And if we understand them, we can eventually develop better technology by working at the same nanometer and subnanometer scales that nature does."