Northwestern University chemists develop a fundamentally new mode of adsorption

Northwestern University Chemists Sir Fraser Stoddart and Omar Farha have made a breakthrough in surface science by introducing a new active mechanism of adsorption. Such adsorption-based phenomena, in which molecules are attracted onto a solid surface, are essential for today’s catalysts, energy storage and environmental remediation.

The new adsorption mechanism, called mechanisorption, results from non-equilibrium pumping to form mechanical bonds between the adsorbent (the surface) and the adsorbate (the molecules).

“The importance of this piece of research lies in the fact that it is the first major fundamental advance in surface chemistry since physisorption and chemisorption — both equilibrium-based phenomena — were the order of the day back in the 1930s,” said Stoddart, who received the 2016 Nobel Prize in Chemistry for his work involving the design and synthesis of molecular machines.

The research illustrates the synergy that results from combining theory with experiment. The molecular contraption was synthetically implemented in Stoddart’s laboratory using rotaxanes — long dumbbell-shaped molecules — terminated on one or both ends with a recognition site for rings surrounded by two groups to provide kinetic barriers between the bulk where the rings are swimming around in solution and polymer chains where the rings are collected one at a time following each redox cycle.

Importantly, these barrier-forming groups can be designed to respond differently to changes in their environment. These pumping cassettes can be incorporated into many types of polymer chains, giving rise to numerous possible applications.

Mechanisorption has important implications for the storage and controlled release of many different molecules. This work focuses on the recruitment of ring molecules to surfaces, but it is anticipated that these rings can be functionalized to bring many different types of molecules at high concentrations to surfaces.

Read more about this study in Northwestern Now.