A research team from the UniSysCat Cluster of Excellence at TU Berlin has synthesised silicon-based super Lewis acids containing an additional halogen atom for the first time.
These compounds rank among the strongest Lewis acids known to date and can attack highly stable chemical bonds such as the carbon–fluorine linkages in PFAS.
The new compounds are not consumed during the reaction, and instead, can regenerate. Therefore, they act catalytically, which presents a decisive advantage for potential applications in recycling processes and green chemistry.
Why are PFAS bonds so difficult to break down?
The extreme difficulty of breaking down PFAS bonds comes down to a single, incredibly strong chemical bond: the carbon-fluorine (C-F) bond. This bond is one of the strongest in organic chemistry due to fluorine’s high electronegativity, enabling the creation of a very stable and short covalent bond with carbon.
Due to this unique chemical stability, a substantial amount of energy is required to break it. Traditional chemical and biological degradation processes, which can break down many other organic compounds, are simply not powerful enough.
This is why PFAS are known as “forever chemicals,” as they persist in the environment for decades, if not longer, leading to widespread contamination of soil and water. The C-F bond’s strength makes it a key challenge for scientists developing new remediation technologies.
Electron hunger enables PFAS degradation
The stability of PFAS is due to their particularly strong carbon–fluorine bonds, and breaking them requires substances with an exceptionally high affinity for electron pairs.
The newly developed super Lewis acids meet this requirement: the combination of a silicon atom with a halogen atom generates an extreme electron deficiency, enabling the breakdown of PFAS bonds.
The synthesis process is complex, as the substances must be handled under inert conditions to prevent contamination. Neither oxygen nor water can encounter the compounds.
The breakthrough was achieved using protolysis, a method previously applied in carbon chemistry and now adapted for use in silicon chemistry.
Regeneration of Lewis acids provides predictive power
In addition to experimental work, theoretical calculations played a crucial role. Quantum chemical methods allowed the researchers to predict the acidity of the molecules purely from their structure, and these predictions were later verified experimentally using NMR spectroscopy.
According to the team, the new super-Lewis acids hold great promise for tackling PFAS contamination in both environmental and industrial contexts.
Since they regenerate, even small amounts of the acids could suffice to neutralise large volumes of these persistent pollutants.