Ice cubes melt to make single atom metals
Trapping a reagent in an ice cube and letting it slowly melt in a solution of another reagent is the simplest way to make isolated transition metal atoms, researchers in China have discovered.Certain reactions – like the one between silver nitrate and sodium chloride – produce insoluble solids that precipitate. Often, this process is undesirable as it creates large and irregular clumps of solids. Nanoparticles, for example, have different properties depending on their size, and when it comes to metal catalysts, smaller particles are often more efficient.
‘Usually, we have two bottles, one is solution A, the other solution B, and we mix the two solutions by stirring,’ says Hui Wu from Tsinghua University, who led the study together with Binghui Ge from the Chinese Academy of Sciences and Li-Min Liu from Beihang University. However, this creates high local concentrations of one reagent and can cause uncontrolled precipitation. A workaround is to add one solution to the other drop by drop. Still, each droplet contains huge numbers of molecules.‘I did some brainstorming with my students in a group meeting to see if we could come up with new ways to do solution chemistry,’ says Wu. What they thought up is as simple as it is effective: freeze one of the solutions in water and drop the ice cube into the other solution, which is kept at just above 0°C. Reagent release from the ice cube is so slow that formation of nuclei – tiny particles that can aggregate and grow in uncontrolled manner – is suppressed, which allowed the team to make single metal atoms.