title: Surface Characterization of Mechanochemically Modified Exfoliated Halloysite Nanoscrolls.
abstract: Surface modifications fundamentally influence the morphology of kaolinite nanostructures as a function of crystallinity and the presence of contaminants. Besides morphology, the catalytic properties of 1:1-type exfoliated aluminosilicates are also influenced by the presence of defect sites that can be generated in a controlled manner by mechanochemical activation. In this work, we investigated exfoliated halloysite nanoparticles with a quasi-homogeneous, scroll-type secondary structure toward developing structural/functional relationships for composition, atomic structure, and morphology. The surface properties of thin-walled nanoscrolls were studied as a function of mechanochemical activation expressed by the duration of dry-grinding. The surface characterizations were carried out using N2, NH3, and CO2adsorption measurements. The effects of grinding on the nanohalloysite structure were followed using thermoanalytical thermogravimetric/derivative thermogravimetric (TG/DTG) and infrared spectroscopic [Fourier transform infrared/attenuated total reflection (FTIR/ATR)] techniques. Grinding results in partial dehydroxylation with similar changes as those observed for heat treatment above 300 °C. Mechanochemical activation shows a decrease in the dehydroxylation mass loss and the DTG peak temperature, a decrease in the specific surface area and the number of mesopores, an increase in the surface acidity, blue shift of surface hydroxide bands, and a decrease in the intensity of FTIR/ATR bands as a function of the grinding time. The experimental observations were used to guide atomic-scale structural and energetic simulations using realistic molecular cluster models for a nanohalloysite particle. A full potential energy surface description was developed for the mechanochemical activation and/or heating toward nanometahalloysite formation that aids the interpretation of experimental results. The calculated differences upon dehydroxylation show a remarkable agreement with the mass loss values from DTG measurements.
authors.forename: Balázs
authors.identifier: 0000-0001-9788-484X
authors.initials: B
authors.lastname: Zsirka
authors.forename: Attila
authors.initials: A
authors.lastname: Táborosi
authors.forename: Péter
authors.initials: P
authors.lastname: Szabó
authors.affiliation: Department of Chemistry and Biochemistry, Montana State University , P.O. box 173400, Bozeman, Montana 59717, United States.
authors.forename: Róbert K
authors.identifier: 0000-0002-9314-6222
authors.initials: RK
authors.lastname: Szilágyi
authors.forename: Erzsébet
authors.initials: E
authors.lastname: Horváth
authors.forename: Tatjána
authors.initials: T
authors.lastname: Juzsakova
authors.forename: Dávid
authors.initials: D
authors.lastname: Fertig
authors.forename: János
authors.initials: J
authors.lastname: Kristóf