2024 AIChE Annual Meeting
(86c) Morphology Controlled Synthesis of Catalytic Metal Nanocrystals within 2D Material Nanoconfinements
Authors
Little, J. - Presenter, University of Maryland
Chen, A., University of Maryland
Akash, T., University of Maryland
Park, C. S., University of Maryland
Liu, D., University of Delaware
Das, S., University of Maryland
Woehl, T. J., University of Maryland-College Park
Chen, P. Y., University of Maryland
The synthesis of products within confined nanoscale regions, termed nano-confined synthesis, has led to the pioneering of a new generation of heterostructured materials. Within the Van der Waals (VdW) gaps of 2D nanomaterials (2DM), a variety of products can be formed with confined synthesis generating unique sizes, geometries, crystallinities, and even catalytic activities due to the enforced anisotropic growth. However, there remains a gap in knowledge in how to precisely control the complexation of metal ions and strategically guide the in-plane crystallization/growth of metals. Additionally, there is no control over surface chemistry and interlayer spacing of 2DM hosts. Herein, a noble metal ion-complexed assembly of graphene oxide (GO) and Ti3C2Tx (MXene) nanosheets was developed through vacuum filtration. This fabrication method generated nano-confined films with adjustable noble metal loadings. Tetraammineplatinum(II) nitrate (TPtN) was able to serve as an efficient ionic crosslinker to quickly assemble an array of different loaded films. To understand how different water removal processes influence the redistribution of noble metal ions on 2DM substrates, two different solvent drying processes were evaluated in 2DM VdW gaps 1) Air drying at ambient conditions and 2) Freeze drying at 190 K. The TPtN–2DM multilayers were then thermally reduced to synthesize Pt–2DM heterostructures. Then, Pt particle size and morphology were evaluated using HAADF-STEM imaging for all samples. This uncovered that the Pt morphologies were different on each substrate despite the same reduction conditions showing high aspect ratio sheets on MXene versus small cluster/single Pt atoms dispersed across reduced GO (rGO). To understand the observed Pt morphologies, molecular dynamic (MD) modeling was performed using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) software to confirm the drying influence on TPtN precursor movement between 2DM sheets by determining equilibrium states of TPtN–2DM systems with and without water. Freeze drying the films result in a greater distribution of noble metal ions within 2DM multilayers, while air drying causes highly concentrated regions of noble metal precursors due to capillary effects of water leaving. Additionally, on MXene surfaces the TPtN ions localize on one side of the confinement while on rGO the TPtN distributes on both sides. Lastly, the Pt–2DM heterostructures showed promise towards the hydrogenation of phenylacetylene. Pt–MXene heterostructures demonstrated a very high substrate dependent activity (2617 molPA molPt-1 h-1) with an average styrene selectivity (82.4%) while Pt–rGO demonstrated a lower activity (1070 molPA molPt-1 h-1) but improved styrene selectivity (85%).
