Jayakumar Karthikeyan

• Karthikeyan, Jayakumar; Fjellvåg, Helmer; Vistad, Ørnulv Bjørnsson; Knudsen, Kenneth & Sjåstad, Anja Olafsen (2016). Quantification and key factors in delamination of (Mg1-yNiy)1-xAlx(OH3)x·mH2O. Applied Clay Science. ISSN 0169-1317. 124-125, p. 102–110. doi: 10.1016/j.clay.2016.02.001. Show summary

  Dispersions of delaminated layered double hydroxides (LDH) contain nanosheets of interest for single particle studies and for preparation of different types of clay mineral-clay mineral or clay mineral–polymer nanocomposites and coatings. Reproducible methods were currently benchmarked, key parameters influencing the degree of delamination were identified, and prerequisites for achieving high yield delamination routes evaluated. Inert synthesis, screening by turbidity measurements and gravimetric quantification allowed identification of how various parameters influence delamination. For (Mg1 − yNiy)1 − xAlx(OH)2(NO3)x·mH2O preparative parameters as hydrothermal treatment, drying conditions and pH during synthesis have significant impact on delamination abilities. Poorly delaminating Ni0.75Al0.25(OH)2(NO3)0.25·mH2O LDH is by adequate hydrothermal treatment converted to a material that undergoes almost complete delamination. The adopted procedures allow systematic studies on how preparative parameters as well as more chemical parameters such as interlayer chemistry and cationic composition in the brucite like layers interacts with solvent properties. Improved insight into parameters controlling delamination properties open up for routes on large scale manufacturing of clay mineral-clay mineral nanocomposites requested for novel types of catalysts. Particles, dispersions and nanosheets were characterized by ICP-OES, CN-analysis, turbidity, XRD, TEM, SAXS, AFM and XPS measurements.

• Karthikeyan, Jayakumar; Song, Haiyan; Olsbye, Unni; Fjellvåg, Helmer & Sjåstad, Anja Olafsen (2015). Supported Nickel Based Catalysts, Ni/Mg(Al)O, for Natural Gas Conversion, Prepared via Delamination and Restacking of MgAl- and NiAl-Nanosheets. Topics in catalysis. ISSN 1022-5528. 58(14-17), p. 877–886. doi: 10.1007/s11244-015-0454-1.
• Sjåstad, Anja Olafsen; Andersen, Niels Højmark; Vajeeston, Ponniah; Karthikeyan, Jayakumar; Arstad, Bjørnar & Karlsson, Arne [Show all 7 contributors for this article] (2015). On the Thermal Stability and Structures of Layered Double Hydroxides Mg1-xAlx(OH)2(NO3)x·mH2O (0.18 ≤ x ≤ 0.38). European Journal of Inorganic Chemistry (EurJIC). ISSN 1434-1948. 2015(10), p. 1775–1788. doi: 10.1002/ejic.201403232. Show summary

  Nitrate-based layered double hydroxides, Mg1–xAlx(OH)2(NO3)x·mH2O, have been investigated to settle issues relating to stability towards humidity, dehydration and staging, nitrate group orientation, Al migration and crystal structure. Raman and IR spectroscopy together with modelling methods proved that flat-lying water and nitrate become tilted towards [001] at higher nitrate concentrations, accompanied by expansion along the c-axis. The distribution of the molecular tilts is greatest for x = 0.25, which explains the extraordinary broad diffraction peaks. The unit cell volume was modified for all samples when subjected to moist air, most strongly for x = 0.25. On heating, in situ synchrotron diffraction data showed continuous changes along the c-axis during dehydration of samples with x = 0.20 and 0.33. For x = 0.25, an intermediate phase appeared. Dehydroxylation was initiated at the OH groups bonded to the cations MgAl2, Mg2Al and Mg3 (in said order), whereas complete nitrate loss occurred at higher temperatures for higher Al contents. Some aluminium simultaneously moved to tetrahedral sites, which, according to 1H–27Al CP NMR spectroscopy, lack protons in their near neighbourhood. In contrast, octahedral aluminium remains surrounded by protons during decomposition. For the metastable oxide product, neutron diffraction indicated that 2/3 of aluminium reside in tetrahedral interstices. This oxide is defective, probably mimicking wüstite rather than a regular rock salt structure.

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• Karthikeyan, Jayakumar; Fjellvåg, Helmer & Sjåstad, Anja Olafsen (2016). Properties and delamination of layered double hydroxides a systematic study. Universitetet i Oslo.

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