© Copyright 2020 Marja Elizabeth Mundy Aminophosphines as Precursors for Doped and Phase Pure Metal Phosphide Nanocrystals: Synthesis Beyond P(SiMe3)3 Marja Elizabeth Mundy A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2020 Reading Committee: Brandi M. Cossairt, Chair Daniel R. Gamelin D. Michael Heinekey Program Authorized to Offer Degree: Chemistry University of Washington Abstract Aminophosphines as Precursors for Doped and Phase Pure Metal Phosphide Nanocrystals: Synthesis Beyond P(SiMe3)3 Marja Elizabeth Mundy Chair of the Supervisory Committee: Associate Professor Brandi M. Cossairt Chemistry Colloidal metal phosphide nanocrystals represent attractive synthetic targets for researchers. They exemplify the diversity of emergent properties presented by nanomaterials, as the class encompasses both semiconductors and metals. When quantum confinement is accounted for, nanoscale semiconducting metal phosphides have optical properties that span the visible and NIR range of the spectrum, making them suitable for a wide range of applications. The metallic transition metal phosphides are consistently touted as earth-abundant alternatives for the hydrogen evolution reaction with competitive catalytic activity, particularly in the form of high surface area nanoparticles. Transition metal phosphides are plagued by synthetic challenges. The reactions are either multistep with low yields, require high temperatures and extended reaction times, or produce mixtures of crystalline phases. While high quality syntheses of several semiconducting metal phosphides exist, many are either capable of only producing nanocrystals in one size or rely on incomplete reactions for size tunability. Recent and exciting work synthesizing indium phosphide from aminophosphines demonstrated precursor-dependent size control based on the indium halide. Prior to the work discussed here, this reactivity was only known for indium phosphide. Chapter 2 discusses our efforts broadening the scope of aminophosphine-based nanocrystal synthesis to include II-V materials and transition metal phosphides. After establishing this versatile platform for the synthesis of phase-pure metal phosphides, Chapter 3 highlights research done establishing aminophosphine-derived InP as a substrate for copper doping and spectroscopic analysis of surface treated materials. TABLE OF CONTENTS List of Figures ................................................................................................................................ iii List of Tables ............................................................................................................................... viii Chapter 1. Introduction ................................................................................................................... 1 1.1 Colloidal nanocrystals and their applications ................................................................. 1 1.2 Metal phosphide nanocrystal synthesis ........................................................................... 2 1.3 Precursor-dependent size control in nanocrystal synthesis ............................................. 5 1.4 Cation doping in nanocrystals ......................................................................................... 6 1.5 References ..................................................................................................................... 10 Chapter 2. Aminophosphines as Versatile Precursors for the Synthesis of Metal Phosphide Nanocrystals .................................................................................................................................. 14 2.1 Note regarding collaborator contributions .................................................................... 14 2.2 Introduction ................................................................................................................... 14 2.3 Results and Discussion ................................................................................................. 15 2.3.1 Synthesis and Characterization of II-V materials ..................................................... 16 2.3.2 Synthesis and Characterization of Transition Metal Phosphides .............................. 21 2.3.3 Reactivity for HER and Proton Transfer .................................................................. 27 2.4 Conclusions ................................................................................................................... 30 2.5 Experimental methods .................................................................................................. 30 2.5.1 Synthentic methods and basic sample preparation ................................................... 31 2.5.2 X-ray absorption measurements ............................................................................... 32 i 2.5.3 Electrochemical characterization .............................................................................. 33 2.6 References ..................................................................................................................... 35 Chapter 3. Synthesis and Spectroscopy of Emissive, Surface-Modified, Copper-Doped Indium Phosphide Nanocrystals ................................................................................................................ 38 3.1 Note regarding collaborator contributions .................................................................... 38 3.2 Introduction ................................................................................................................... 38 3.3 Results and Discussion ................................................................................................. 40 3.3.1 Synthesis of Cu+:InP ................................................................................................. 41 3.3.2 Post-synthetic modifications of doped NCs .............................................................. 46 3.3.3 Photophysical characterizations ................................................................................ 53 3.4 Conclusions ................................................................................................................... 56 3.5 Experimental Details ..................................................................................................... 56 3.6 References ..................................................................................................................... 59 Appendix A: Attempts at the synthesis of InPZnE quaternary alloyed nanocrystals ................... 63 ii LIST OF FIGURES Figure 1.1. Model of a binary semiconducting nanocrystal surrounded by long-chain ligands stabilizing the surface. Reprinted from reference 5 with permission.5 ....................... 2 Figure 1.2. Proposed mechanism showing the formation of InP from aminophosphines and indium chloride. Figure modified from reference 17.17 .............................................. 4 Figure 1.3. Highly monodisperse PbS nanocrystals with size dictated by the reactivity of the thiourea. Reprinted with permission from reference 25.25 .......................................... 5 Figure 1.4. General schematics of synthetic approaches to nanocrystal doping with E 33 representing ion exchange within the previously formed lattice. ............................. 8 Figure 2.1. Standard reaction scheme for metal phosphide nanocrystal formation. ......... 16 Figure 2.2. A) TEM image (6.8 ± 0.5 nm), (B) UV-Vis spectrum, and (C) XRD pattern of Cd3P2 nanocrystals prepared at 250 °C from CdCl2 using a 1:3.6 ratio of Cd:P (Cd3P2 reference pattern PDF 01-070-3099 47-1443). D) TEM image of Cd3P2 prepared from CdCl2 at 250 °C using a 1:1.3 ratio of Cd:P (7.5 ± 0.3 nm). .......................................................... 17 Figure 2.3. (A) UV-Vis final traces of materials synthesized from CdX2 precursors. (B) XRD spectra of materials showing two populations of particles including one subset with a crystalline domain size >30 nm, consistent with mild heterogeneity observed in synthesis. TEM images of (C) CdBr2 (5.9 ± 0.7 nm) and (D) CdI2 (5.6 ± 0.5) products showing the expected trend towards smaller nanocrystals as the halide becomes a better leaving group. ................................................................................................................................... 18 Figure 2.4. Synthesis of Zn3P2 from ZnX2 (X = Cl, Br, I) and P(NEt2)3 at 250°C. (a) Representative UV-Vis absorbance spectra of the final products normalized at 400 nm. Inset: TEM of product from ZnCl2 and P(NEt2)3. (b) Air-free powder X-ray diffraction data of the purified products with Zn3P2 reference pattern (PDF 01-071-6507). ............. 20 31 Figure 2.5. 202.4 MHz P NMR of reaction aliquots in C6D6 with a triphenylphosphine internal standard: (A) Zn3P2 synthesis at 250°C. (B) Cd3P2 synthesis at 250°C. .................. 21 Figure 2.6. (A, B) TEM images (A: CoP 7.8 ± 0.7 nm; B: Co2P of various morphologies with widths/diameters of 6.5 ± 0.6 nm) and (C) XRD pattern of CoP and Co2P prepared at 250 iii °C and 200 °C, respectively. CoP (PDF 01-089-2598 29-497) and Co2P (PDF 01-070-8358) reference patterns. The inset in figure (A) shows a zoomed in image of a single CoP nanocrystal with the corresponding FFT. ................................................................. 22 Figure 2.7. Synthesis of cobalt phosphides from CoI2 at 250 °C. Powder X-ray diffraction data of products after different