Nanomaterials

Most important catalytic reactions in nature occur under nano-confined conditions. In living organisms, compartmentalisation within cells and organelles drives catalysis of naturally occurring reactions. All well-known industrial heterogeneous catalytic systems pale in comparison with those in nature with regard to their efficiency and selectivity. Hence, fundamental understanding of how catalysts are affected by a confining environment could provide some remarkable new insights and scientific discoveries [‘Confined catalysis under two-dimensional materials’ by Li, Xiao, Qiang and Bao, PNAS, Vol 114, 5930-5934, June 6, 2017]. The interactions brought about by confinement are complex and their coupling makes interpretation and first principles study difficult. In our current work (funded by the Army Research Office) we intend to apply new experimental techniques for in operando analysis of the state of the catalyst, adsorbates and products.

We are currently looking at linked graphene oxide based systems where the catalyst is intercalated between the sheets or scrolls of the 2D materials for direct conversion of CO 2 to ethane and/or ethylene. Future work involves using hexagonal Boron Nitride as a confining vessel and look at other reactions which are important for mitigating the impact of climate change.

A parallel effort is the study of photothermal reactions using nanoparticles like silver for catalytic conversion. Hematite (α-Fe2O3), the most thermodynamically stable form of iron oxides, is a highly effective catalyst for the complete oxidation of methane with excellent stable performance below 500 °C in both nano and bulk forms, a low light-off temperature of 230 °C, and 100% selectivity to CO2. Our research has demonstrated that modification of hematite with silver nanoparticles has promising applications for conversion of methane to useful products such as methanol. 

In conjunction with our work on confined catalysis, our group began investigating the role of strain in modifying properties of 2D materials like Graphene. 

As a method for investigating the “induced pressure” generated when linking systems of graphene oxide (GO), the strain in linked GO can be measured by observing changes in the G-band of the Raman signature. We demonstrated that strain is generated and maintained after transient pressurization of linked GO systems intercalated with catalytic NP. For more information, see Aislinn’s poster presentation at the 2023 Fall Meeting of the American Chemical Society.  

We have also begun investigating the role of strain in 2D hexagonal Boron Nitride (hBN)  on patterned substrates as a method for generating entangled fields of Quantum Emitters.  Aislinn is investigating the role of layer-thickness of hBN in the strain environments of the patterned material, measuring changes in the photoluminescence signature and intensity. For more information,  see Aislinn’s oral presentation from the 2023 Fall ACS meeting. 

Realizing room temperature superconductivity (Tc) remains an elusive target for condensed matter physicists and materials scientists. This has enormous implications both for applications as well as fundamental understanding of the mechanism of superconductivity. Since Ashcroft’s prediction of high Tc more than 50 years ago [1] hydrogen based compounds have dominated the search for room temperature superconductors. Elemental hydrogen remains a major challenge because of the extremely high pressures of the order of 500 GPa. These include hydrogen sulfide based based systems, hydrogen based metallic alloys [2] as well as clathrate based super hydrides like LaH10 . 

Our current work uses 2D Graphene oxide sheets with well separated spacing as the confining system where various elements can be intercalated [See Nikita’s paper on linked GO]. Similarly metallic nanoparticles, e.x. cobalt,iron, nickel and platinum (some of systems we work with) can have a profound influence on the magnetic properties of a linked graphene oxide system. The impact of incorporating Co nanoparticles on the magnetic properties of a linked GO system under pressure (from 5 to 15 GPa) has been demonstrated. After quenching to ambient pressure, these samples showed ferromagnetic behaviors, demonstrating phase changes created by transient high pressure in the GPa range can be locked in. The figure below shows the hysteresis a function of temperature after the sample was pressurized to 25 GPa in multi anvil Kwai type cell in the Geology Department at Yale and the magnetic measurements were performed by our collaborators at the Naval Research Laboratory in Washington DC.

Atmospheric pressure plasma (APP) are also called non-thermal plasmas. Plasmas are multi component systems (e.g., there are neutrals , excited species and both positive and negatively charged molecules), and at atmospheric pressure (e.g., APP) they are a highly non-equilibrium systems. The concentration of active species can exceed those of ‘near-equilibrium’ systems by many orders of magnitude at the same gas temperature. In particular, the low gas temperature means that while the electrons are at high temperatures, the atoms, molecules and ions of the plasma are typically close to room temperature. We currently have 3 machines installed covering a range of operating conditions and pressure parameters.