Nicholas M. Bedford

Polymer‐derived ceramics (PDCs) are becoming an alluring class of materials that can incorporate the ceramic chemistries found in ultra‐high‐temperature ceramics, such as Ti, Zr, and Hf carbides. The use of polymeric materials intrinsically enables processing techniques with a higher degree of complexity in a more straightforward fashion, such as three‐dimensional printing. In this contribution, a series of click‐derived preceramic polymers (PCPs) was synthesized using azide‐modified metallocene monomers and an alkynyl‐modified aromatic monomer, with Ti, Zr, and/or Hf serving as the metals of interest. PDCs were generated via pyrolysis at 800, 1100, and 1500°C and thoroughly examined using a range of synchrotron‐based scattering and spectroscopy techniques to better couple atomic‐scale structure back to precursor chemistry and pyrolysis conditions. Reverse Monte Carlo (RMC) simulations were implemented to model synchrotron datasets for the extraction of structural metrics, such as local coordination numbers (CNs) and bond angle distributions. Heterogeneous RMC approaches were also used to better reflect the multi‐phase structure found in these materials. In addition to examining single metal PDCs, the click chemistry approach implemented here enables the ready inclusion of different metallocene monomers, wherein TiZrHf PDCs were synthesized and further examined to determine the structural evolution of these materials. Overall, our work showcases a pathway for accessing atomic‐scale structure in these emergent materials, providing the ability to assess structure‐property relationships for future materials development.

The platinum‐ruthenium (PtRu) system is highly active for hydrogen evolution reaction (HER) in alkaline media with both Pt and Ru playing active roles in the water dissociation step that generates adsorbed hydrogen atoms. Precise control of the arrangement of Pt atoms on Ru nanoparticles can maximize the Pt‐Ru sites for water dissociation and Pt‐Pt sites for hydrogen production and can considerably improve HER catalytic performance. By directing the growth and distribution of Pt on Ru hourglass nanoparticles, the arrangement of Pt on Ru is controlled into forming Pt islands, small Pt clusters, and strings of a few Pt atoms. Calculations show that the unique atomic string arrangements of Pt on Ru is the thermodynamically favorable configuration. Additionally, these strings have a favorable combination of Pt‐Ru and Pt‐Pt sites, making the Pt‐string on Ru the most active catalyst with a more than fivefold increase in turnover frequency for alkaline HER compared to the Pt‐island on Ru catalyst. The results show how controlling the Pt atomic arrangement on Ru nanoparticle surfaces for the tuning of Pt‐Pt and Pt‐Ru neighboring sites can direct toward a more efficient HER mechanism and thereby significantly enhancing HER performance.

Silicon oxycarbide (SiOC) is a versatile ceramic material with tunable microstructure and compositions that can be modulated through precursor chemistry and processing conditions. Though there are several noteworthy uses of SiOC across a range of application spaces, the difficulties in elucidating the short- to medium-range order within these materials have limited the maturation of strategies to precisely control SiC _x O_4-x compositions for user-tailored applications. In this contribution, we implement a range of synchrotron scattering and spectroscopy methods coupled with stochastic modeling techniques to elucidate changes in local chemistry and structure associated with the pyrolysis of a commercially available SiOC polymer precursor. Stochastic modeling approaches provide valuable insights into decoupling local Si-O and Si-C environments while confirming predominate heterogeneous phases in materials. Using pyrolysis temperatures between 250 to 800 °C results in a heterogeneous material predominately composed of SiOC and amorphous SiO₂ domains. At 1100 °C, redistribution of Si-C pairs in the SiOC network and Si-O from the SiO₂ domains create a more ordered SiOC phase with local cubic SiC-like ordering. In addition, residual carbon leads to a detectable carbon phases at 1100 °C that persist at higher temperatures. These efforts address the difficulties of obtaining atomic-scale insights into the local structure and nanoscale heterogeneities in SiOC, providing pathways toward establishing structure-property relationships for future materials development.

Glyphosate (N‐phosphonomethyl glycine, GPh) is an industrial herbicide used worldwide in modern agricultural practices. With the growing concerns regarding cumulative environmental and health effects, pathways for catalytic GPh degradation to benign products are becoming a pressing societal need. This report demonstrates that Zr‐based metal–organic framework (MOF‐808) with different crystal sizes and designed defect sites can be employed as an efficient heterogeneous catalyst for the complete degradation of GPh at room temperature. Importantly, the degradation mechanism produces N‐formyl glycine and hydroxymethyl‐phosphonate, which are largely innocuous chemicals, especially when compared to more common GPh degradation products. Nanocrystalline MOF‐808 (nMOF‐808) exhibits enhanced reactivity than larger MOF‐808 crystals, attributed to the higher coordination of hydroxyl and water molecules to the secondary building units (SBU) as determined using a range of X‐ray absorption spectroscopy (XAS) techniques. These studies indicate that the crystal size‐dependency in GPh degradation is related to structural modifications on coordinative unsaturated Zr site that promote the fast exchange of weakly bonded ligands. Taken together, this study demonstrates that GPh degradation can be optimized through ligand field tuning in MOFs, which can help improve overall reactivity while also pushing the reaction toward desirable, nontoxic products.

Minor actinide (MA) selective materials that are resistant to radiation are necessary to enable separation of MAs from lanthanides in nuclear wastes. Zirconium(IV) phosphonates (ZrPs) are a class of amorphous coordination polymers with promising applications as a solid-phase sorbent for MA-lanthanide separations. In this study, a zirconium phosphonate sorbent (ZrPTP) that intramolecularly incorporates the MA-selective 2,6-bis(1,2,3-triazol-4-yl)pyridine (PTP) ligand was synthesised and evaluated for radiation tolerance with high energy electron irradiation to doses of 2 MGy. The MA sorption selectivity of ZrPTP before and after irradiation was compared using Am and Eu. ZrPTP demonstrated maintained selectivity for Am over Eu even after a 2 MGy dose. Synchrotron radiation characterisation techniques and solid-state NMR were employed to accurately assess the average local structure before and after irradiation, where minor amounts of Zr–O bonds, aliphatic C–H bonds, and triazole groups were broken, showcasing excellent radiation stability for doses up to 2 MGy. Our results demonstrate the importance of chemistry in ZrP coordination polymers maintaining not only selective separation properties, but also maintaining radiation stability as well.