The lack of knowledge of how nickel crystallizes in a solid has hindered its prospective application in new nanomaterials and as a low-cost catalyst in chemical reactions that take place in many industrial processes.
However, researchers have now been able to observe this crystallization of the two structural forms of nickel on an atomic scale using liquid-phase electron microscopy. Image credit: Nano Research.
Researchers have now used liquid-phase electron microscopy to observe this crystallization of the two structural forms of nickel on an atomic scale.
On May 13, 2022, a report was published explaining its findings in the journal Nano Research.
Catalysts are materials that accelerate the rate of chemical reactions and are necessary for the creation of a wide range of industrial goods. However, one of the obstacles they face in a variety of applications, especially in energy technologies, is that many of them are precious metals.
Platinum, for example, costs hundreds of dollars per ounce and is used as a catalyst to speed up processes to such an extent that a variety of clean fuel sources are a practical reality.
Nickel, on the other hand, is one of the most abundant metals in the earth’s crust, costing only a few cents per ounce. Nickel is also quite stable in a wide range of conditions. As a result of their wide range of catalytic applications, nickel-based catalysts have recently attracted much attention in research.
Catalysts containing precious metals, on the other hand, increase the reaction rate more than nickel.
Various strategies have been devised to increase the catalytic capacity of nickel and use nickel as a component of new nanomaterials, but to advance further, researchers need to better understand some of the most fundamental characteristics of formation and structure. of nickel.
They investigate nickel crystals in their tiny form, at the beginning of their formation (or nucleation) from a liquid, to conduct this research. Any crystal particle with at least one side measuring less than 100 nm is called a nanocrystal (one billionth of a meter).
Nickel nanocrystals can be found in two forms of crystal lattice: cubic and hexagonal, often known as “hexagonal-packed” or hcp. The mechanism behind the formation of these two lattice structures, the crystallization process, has remained largely unexplained.
To gain a complete understanding of the crystallization process, direct real-time monitoring of the nucleation pathways of hcp nickel nanocrystals at the atomic level is required.
Other researchers have used liquid-phase electron microscopy to study the crystallization pathways of silver and gold nanocrystals in real time, showing the nucleation processes in various steps of crystal formation of these elements.
In contrast to a traditional microscope, electron microscopy uses a beam of electrons to illuminate an object of interest instead of photons. Because the wavelength of an electron is much shorter than that of the photons that make up visible light, it is possible to investigate incredibly small things.
The procedure is the same in liquid phase electron microscopy, but allows the study of liquid samples. Liquid phase electron microscopy has proven to be a useful method for monitoring the nucleation and development of nanocrystals, as the goal is to see how solid crystals form from a liquid.
In principle, Ni nanocrystals could crystallize in fcc or hcp phases. Normally, the formation of the new phase of nanocrystals depends on the adsorption energy of the surfactant and the surface energy of the exposed facets. Some researchers had previously used this technique to investigate the formation of the cubic structural form of nickel nanocrystals in a homogeneous growth solution of Ni (II) containing Ni-amine-acetate complexes.
Junyu Zhang, co-author of the study and researcher, Instrumental Analysis Center, Huaqiao University
Zhang added: “And now, in this work, both the TEM study of liquid cells in situ and the theoretical calculations identified the non-classical characteristics of the crystallization of hcp Ni in N, N-Dimethylformamide solution. (DMF) at a high dose rate of the electron beam. ”
The researchers prepared a liquid solution with more nickel than could be dissolved (a “supersaturated solution”) so that any excess would precipitate naturally as a solid (i.e., by crystallization). They then used a liquid-phase electron microscope to see the nucleation in real time.
They have specifically reported the direct and real-time visualization of the dynamic processes of amorphous phase-mediated crystallization of faceted Ni hcp nanoparticles (10) or hcp Ni (0001) in a homogeneous solution by spinodal, solidification, and atomic decomposition. scale crystallization under high electron beam dose rates.
They also used layer-by-layer growth to examine the development of the facets of Ni nanocrystals. Eventually, the brittle Ni disintegrated into solution.
Researchers hope that a better understanding of the fundamental processes of nickel crystal formation at the lower scale will help them create better systems and catalysts for hcp-nickel materials in the future.
Magazine reference:
Zhang, J, et al. (2022) Atomic mechanisms of closed hexagonal Ni nanocrystallization revealed by electron transmission microscopy of liquid cells in situ. Nano Research doi: 10.1007 / s12274-022-4475-3.
Source: