Browsing by Author "Khan, S"

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    Hybrid microstructure of smectite clay gels revealed using neutron and synchrotron X-ray scattering
    (Springer Nature, 2023-11-07) Shoaib, M; Khan, S; Wani, OB; Mata, JP; Krzysko, AJ; Kuzmenko, I; Bluel, M; Fiddes, LF; Roth, EW; Bobicki, ER
    Aqueous suspensions of swelling clays display a nematic sol-gel transition at very low solid concentrations. The underlying microstructure of the gel has remained a point of contention since the time of Irving Langmuir and has been a major obstacle to fully realizing the potential of clays for practical applications. Here, we comprehensively probe the microstructure of a smectite clay suspension using ultra-small angle neutron/X-ray scattering and find that the nematic gel is structurally ordered and contains entities that are at least an order of magnitude larger than the individual particles. Complementary cryo-electron microscopy shows the presence of domains having particle-particle ordering responsible for nematic texture and regions of particle-particle aggregation responsible for gel-like behavior. We find that the smectic clay gels have a hybrid microstructure with co-existing repulsive nematic domains and attractive disordered domains. © 2023 The Author(s). Open Access. This article is licensed under a Creative Commons Attribution 4.0 International License.
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    Iron oxide-palladium core-shell nanospheres for ferromagnetic resonance-based hydrogen gas sensing
    (Elsevier, 2022-02-08) Khan, S; Lawler, NB; Bake, A; Rahman, R; Cortie, DL; Iyer, KS; Martyniuk, M; Kostylev, M
    Interfaces of ferromagnetic transition metals such as Iron, Cobalt, and Nickel with non-magnetic palladium are of interest due to their unique magnetic and spintronic properties. These interfaces enable ferromagnetic resonance (FMR) based sensing of hydrogen gas. In the present work, we synthesized Fe3O4–Pd core-shell nanospheres via a one-pot synthesis method using the thermal decomposition of Fe3+ acetylacetonate in the presence of a reducing agent to produce the Fe3O4 core, followed by the reduction of a Pd2+ precursor to form the pure Pd shell. We found that our in-situ synthesized core-shell nanostructure is magnetically active and shows excellent H2 gas sensing properties. The effect of reversible hydrogen gas absorption on the magnetism of Fe3O4–Pd core-shell nanospheres was investigated. The hydrogen-induced ferromagnetic-resonance (FMR) peak shift amounted to 30% of the peak linewidth for the virgin state of the sample. In addition, in the presence of hydrogen gas, we observed a fully reversible decrease in the FMR peak linewidth by about two times. This was accompanied by a nearly doubling of the FMR peak height. Response and recovery times of about 2 and 50 s, respectively, were extracted from the measurements. All the data was collected using a mix of just 3% hydrogen in a nitrogen carrier gas. © 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd.