Janus Catalysts Direct Nanoparticle Reactivity

Metal oxide nanoparticles decorated with carbon nanotubes can be turned into readily recovered catalysts that function at the interface between oil and water phases. I'm going to set you a challenge. Go and make a cup of tea. Add milk and sugar, and stir well. Now, please get just the sugar back out for me. Difficult, isn't it? The same problem faces chemists who want to make synthetic products more environmentally friendly. Soluble compounds that are used to speed up desired reactions—homogeneous catalysts—can end up in final products, where they pose a nightmare of a separation problem. Ideally, if these catalysts could be completely recovered, they could be recycled and kept out of the products, in which they could be toxic even at trace levels. One general approach to recovering such catalysts is “phase transfer,” which takes advantage of the different solubility of compounds in water versus organic solvents. On page 68 of this issue, Crossley et al. ( 1 ) have converted solid nanoparticles that have solubility in both water and oils into catalysts that can operate in both phases. These catalysts can be recovered even from complex mixtures, such as those that result when biomass products are upgraded into fuels.