An article recently published in the journal Materials Today explores the potential of synthesizing titanium carbides, phosphides, nitrides, silicides and borides into two-dimensional flakes by subjecting them to tetramethylammonium hydroxide solution.
Study: Bottom-up, scalable synthesis of anatase nanofilament-based two-dimensional titanium carbo-oxide flakes. Image Credit: l i g h t p o e t/Shutterstock.com
A Glimpse into Synthesizing Processes
Two-dimensional materials are only a few atoms thick and are made by stacking and rotating one layer above another in a specific pattern. These materials offer advantages that three-dimensional materials do not, as they can exhibit interesting properties and changes in behavior when subjected to twists in layering.
Other interesting phenomena for two-dimensional materials include quantum size effects and high specific surface areas.
Typically, layered solids, such as clays, graphite, or, more recently, MAX phases, have been the initial point for producing 2D materials. These can be obtained by top-down processes such as exfoliating or etching layered precursors.
True 2D oxide flakes of micron size, on the other hand, have proven challenging to produce. Furthermore, large-scale synthesis of 2D materials from non-layered solids in a single step was regarded to be challenging, if not impossible.
The published research intended to etch MAX phases selectively without the usage of Fluorine, an expensive, critical component in pre-etching MAX phases approaches. Hence, they developed anatase-based 2D titanium carbo-oxides, or TCOs, which have stoichiometries and structures that differ significantly from those manufactured before.
Interesting Properties
The experiment favors a 4-layered construction as opposed to the 6-layered structure, which is too thick. Conductive films were formed of TiC and MAX phases.
The conductivity is not always there, implying that there is an unknown variable at work. Researchers are currently working to uncover this unknown.
The ability to manufacture these flakes from non-layered precursors and produce structurally and chemically identical Filtered Films demonstrated strong evidence for a bottom-up strategy. After ethanol washing, an X-ray diffraction (XRD) pattern of a Ti3AlC2-derived film is indicative of 2D materials.
Peaks with equal angles were produced in all situations. This is critical and cannot be overstated because it shows that precursor chemistry does not affect the final structures created, including their Lorentz Polarization factors.
To further understand the chemistry of the created two-dimensional flakes, a thermogravimetric analysis (TGA) in Argon up to 800 degrees Celsius was performed on selected films. As a result, up to 400 degrees Celsius, water is the only gas exhaled. The first component is most likely weakly bonded interlayer water; the second component is likely hydration water coupled with Li ions and/or dihydroxylation water.
No Li-containing phases develop after washing the films in ethanol alone and heating them in Argon to 800 degrees Celsius.
The authors obtained XRD patterns of the resultant powders after the TGA runs. Two primary phases were detected in every case: a Li-titanate, LT, phase, and rutile or anatase.
Key Findings
To build 2D anatase-based titanium carbo-oxide films constituted of nanofilaments, the team identified a simple, affordable, reasonably high-yield, near ambient, completely scalable, one-pot, bottom-up technique.
Then researchers transformed ten distinct Ti-based precursor powders into 2D flakes that are anatase-based by heating them in TMAH at varying temperatures (25–85 degrees Celsius) for varied periods.
It is important to emphasize that the authors are only presenting these data as proof of concept, proving the materials' 2D nature and potential. However, it is reasonable to suppose that a better comprehension of the findings will considerably improve them.
Given these observations, it is noted that much more study, certainly beyond the scope of this research, is required to fully comprehend the mechanisms involved.
However, it is fair to state that these materials, particularly as Li-S cathodes, have a lot of potential.
Interview: Developing a Universal Route to Controlled Nanocrystal Synthesis.
Reference
Badr, H. O., El-Melegy, T. et al. (2021). Bottom-up, scalable synthesis of anatase nanofilament-based two-dimensional titanium carbo-oxide flakes. Materials Today. Available at: https://www.sciencedirect.com/science/article/pii/S1369702121003813?via%3Dihub
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