Many chemical reactions that occur in aqueous solution involve colourless species. In order to determine how fast the chemical reaction occurs, Chemists have traditionally tried to "freeze" the reaction at certain points, purify the solution and determine the amounts of unreacted reactants and products produced present at each stage.
Syracuse University Chemists have taken a different route. They are using nanoparticles that react with the byproduct of a reaction. The nanoparticles they used are known as perovskites.
Perovskites are typically composed of metal ions and oxygen. The structure shown below is for a typical perovskite, calcium titanium oxide (CaTiO3):
Each pale-blue titanium atom is surrounded by 6 red oxygen atoms. The darker-blue calcium atom occupies the space between titanium oxide octahedrons.
The perovskites the researchers used were a bit different to the one shown above. Metal ions were surrounded by halide ions rather than oxygen.
At the nanolevel, perovskites are photo-luminescent, that is, they emit light when "excited" by a laser or a lamp. The colour they emit is largely determined by the concentration of their ions in solution., and it is this property which the researchers used to monitor chemical reactions. It is also this property which is being in exploited in research into light emitting diodes (LEDs), lasers, photodetectors and solar cells.
In this study, perovskites were used to monitor an elimination reaction in which haloalkanes react to form alkenes, eliminating halide ions in the process.
At the start of the reaction, the perovskite fluoresces red.
As the reaction proceeds, halide ions are released which are absorbed by the perovskite nanoparticles, and the fluorescence colour changes from red to yellow to green.
When the fluorescence colour is green, the reaction is over.
The image on the right shows a control colour on the left, and on the right, the changing fluorescence colour of the reaction as it proceeds from 0 minutes at the top to 90 minutes at the bottom.
This technology is patent-pending at the University. In the words of Matthew Maye, Associate Professor of Chemistry, "Who knows, maybe in the future, every chemist will use a Syracuse-based perovskite for monitoring their reactions."
Tennyson L. Doane, Kayla L. Ryan, Laxmikant Pathade, Kevin J. Cruz, Huidong Zang, Mircea Cotlet, Mathew M. Maye. Using Perovskite Nanoparticles as Halide Reservoirs in Catalysis and as Spectrochemical Probes of Ions in Solution. ACS Nano, 2016; DOI: 10.1021/acsnano.6b00806
Reaction Rate: http://www.ausetute.com.au/reactrate.html
Ligands and Complex Ions: http://www.ausetute.com.au/ligands.html
Naming Haloalkanes: http://www.ausetute.com.au/namhaloa.html
Naming Alkenes: http://www.ausetute.com.au/namsenes.html
Substitution Reactions of Haloalkanes: http://www.ausetute.com.au/rxreacts.html
Dehydration of Alkanols: http://www.ausetute.com.au/dehydraol.html
Suggested Study Questions:
- Explain the terms "qualitative" and "quantitative".
- Explain the term "reaction rate".
- Explain the term "nanoparticle".
- What property of nano-perovskite is being applied by the researchers in this article, and how does this property differ for bulk perovskite?
- Explain how these perovskites can be used to monitor the reaction qualitatively.
- Explain how you could use these perovskites to monitor the reaction quantitatively.
- Discuss the differences between ethane, ethene (ethylene) and bromoethane.
- Consider ethane and ethene (ethylene), which is likely to be more chemically reactive? Explain your answer.
- Consider ethane and bromoethane. Which is likely to be more chemically reactive? Explain your answer.
- Explain what is meant by the term "elimination reaction" as used in the article above.
- What is the difference between and addition reaction, a substitution reaction and an elimination reaction? Give examples of each type of reaction.
- Write a chemical reaction to represent the elimination of bromide ions from a bromoethane to produce ethene (ethylene).
- Consider the structure of CaTiO3 given in the article. What is the name of the ligand?
- Give the formula for the perovskite in which all the oxygen atoms have been replaced with bromine.
- Could the same perovskite be used to monitor a chemical reaction in which water is eliminated from an alkanol to produce an alkene? Explain your answer.