Authors: Li Wang, Jiawei Wan,Yasong Zhao, Nailiang Yang, Dan Wang
Journal: Journal of American Chemical Society
All Figures used in this writing were taken from the article with due permission.
What are facets and why are they important in materials? Imagine a diamond that is not cut evenly. It would not appear shiny and attractive as it could not scatter light in all directions. Nowadays, most of the brilliant cut diamonds are cut to create 57-58 facets.
So, facets are essentially flat surfaces oriented to specific directions in a material. Let’s look along the 3D cartesian
Fig. 1 Various Facets in a cube (also known as Miller planes)
Depending on the distance of 6 facets from the origin (0,0,0) and its orientation, we have (100), (010), (001), (1̅00), (01̅0) and (001̅) – these 6 facets present. (Fig 1)
For materials that are applicable in various reactions, facets are useful handles to control
Researchers have discovered that these oxides are also hollow. Why are these hollow structures look interesting to researchers? Because a hollow material can absorb a high concentration of gases such as carbon dioxide, which is a greenhouse gas, and convert it to other useful chemicals. Therefore, it is desirable for the material to achieve high reactivity of towards a specific chemical (CO2 in this case, also known as a substrate) to convert it to one product instead of a mixture of products (selectivity).
Further experiments showed these Co3O4 are more reactive in reducing CO2 to CO under light irradiation more efficiently compared to oxides where mixed facets are present. To understand this
higher photocatalytic activity, they did impedance spectroscopy which is a routine
Scheme 2. Effect of Synthetic Conditions on Higher Number of Shell
To summarize, this work has shown how to control the growth of a single facet in a material by employing a highly ordered metal-organic framework such as ZIF-67 to increase the desired reactivity, selectivity and longevity of that material.