Catalysts are used to accelarate reactions, reduce their energy cost, and selectively produce desired products. Many nanomaterials are catalytic, and some are commercially used for this purpose. Still, much remains unknown about their properties, and especially about the performance of hybrid organic-inorganic materials. We bring clarity to this field.
In our first study, we wanted to understand and quantify the impact organic coatings have on the catalytic activity of gold nanoparticles (NPs). The literature in this field suffered from a crucial limitation – since nanoparticles (NPs) require coatings (ligands) to be stable in solution, studies were only able to compare one coating to another. We wanted to determine the absolute impact of a coating, compared to uncoated, bare, NPs. To do so, we immobilized gold NPs on glass surfaces, using a high-temperature annealing process to stabilize them while removing organic coatings. We measured the catalytic activity of such immobilized NPs; while we coated others with organic ligands and evaluated their performance. In this way, we were able to quantify the impact a variety of commonly used ligands have on activity, and demonstrated the slow process of ligand removal in some reaction conditions (Langer and Kedem, J. Phys. Chem. C, 2022, 126, 13705–13713).
We then took this study one step further – previously, all of the ligands we tested inhibited the catalytic activity. Can a coating increase it? Turns out, yes! A thin (<1 nm) coating of a cationic polymer, PAH, actually doubles (or more) the catalytic activity for anionic reactants. We demonstrated the effect for a transfer hydrogenation reaction, where the activation energy was lowered by half for the coated catalyst. The enhancement effect is also present for an oxidation reaction, so it seems it will be widely applicable. This study is the first time such an enhancement is conclusively proven, and we are exicted to see how we can further build on these findings (Langer, LeGrand and Kedem, ACS Appl. Mater. Interfaces 2023, 15, 29160–29169).