Drying Controlled Synthesis of Catalytic Metal Nanocrystals Within 2D-Material Nanoconfinements

Abstract

The synthesis of low-dimensional metal nanocrystals with precise atom-to-nanoscale structure control is crucial for modulating their physicochemical properties. Traditional synthetic routes encounter challenges due to isotropic metallic bonding, which leads to limited control over metal nanostructures. Herein, a versatile approach is developed using various 2D material (2DM) nanoconfinements to produce a wide range of metal nanocrystals with controllable morphologies. Utilizing graphene oxide (GO) and Ti₃C₂T_x MXene nanosheets, thin multilayer films are assembled through vacuum filtration and are crosslinked with tetraammineplatinum(II) nitrate (TPtN), followed by in situ thermal reduction. By controlling the concentration of TPtN solution, precise loadings of platinum (Pt) are attained while preserving the nanoconfinement integrity. Two water removal techniques, air-drying and freeze-drying, are investigated to assess their impacts on resultant morphologies of Pt nanocrystals. Transmission electron microscopy and molecular dynamics simulations demonstrate high-aspect-ratio Pt nanosheets on MXene substrates and few-atom Pt nanoclusters on GO substrates. A decrease in size distribution is observed upon the use of freeze-drying. In the semihydrogenation reaction of phenylacetylene, freeze-dried Pt–MXene heterostructures achieve a high turnover frequency of 2.93 s⁻¹. This comprehensive study highlights the potential of utilizing 2DM nanoconfinement to synthesize metal nanostructures for catalysts and beyond.