No abstract

Here we report on the thermal properties of Mg−Ni‐phyllosilicate nanoscrolls as a promising precursor for production of Ni/silicate composite catalysts. Spontaneous scrolling of the phyllosilicate layer originating from size difference between metal‐oxygen and silica sheets provides high surface area of the catalyst. Metal nanoparticles can be obtained directly from the matrix by H2 reduction. The phyllosilicate structure passed through a number of transformations including partial dehydroxylation with formation of sepiolite‐like phase followed by silicate or oxide crystallization. Temperature ranges of these transitions overlapped with the reduction process sophisticating the H2 consumption profiles. In particular, some amount of Ni2+ got sealed up by the sepiolite structural features, that opened a path for the tuning of Ni0 : Ni2+ ratio of the catalyst. An increase of Ni content in the system yielded a decrease in the metal nanoparticles sizes due to both high intensity of nucleation and type of residual matrix. Ni nanoparticles size distribution and specific surface area of the composite catalysts governed conversion rate of hexene‐1 and acetone hydrogenation. In the view of the turnover frequency MgNi2Si2O5(OH)4 precursors were slightly more preferable than pure Ni3Si2O5(OH)4.

Here, we study the stress‐induced self‐organization of Mg2+ and Ni2+ cations in the crystal structure of multiwalled (Mg1–x,Nix)3Si2O5(OH)4 phyllosilicate nanoscrolls. The phyllosilicate layer strives to compensate size and surface energy difference between the metal oxide and silica sheets by curling. But as soon as the layer grows, the scrolling mechanism becomes a spent force. An energy model proposes secondary compensation of strain: two cations distribute along the nanoscroll spiral in accordance with preferable radii of curvature. To reveal this, we study synthetic (Mg1–x,Nix)3Si2O5(OH)4 nanoscrolls by the scanning transmission electron microscopy/energy‐dispersive X‐ray spectroscopy (STEM/EDS) technique. For a number of scrolls, we have found indeed a change of Ni concentration with increase in distance from the nanoscroll central axis. The concentration gradient, according to our estimates, can reach 50 at.% over 25 nm of the wall thickness.

The past two decades have been marked by an increased interest in the synthesis and the properties of geoinspired hydrosilicate nanoscrolls and nanotubes. The present review considers three main representatives of this group: halloysite, imogolite and chrysotile. These hydrosilicates have the ability of spontaneous curling (scrolling) due to a number of crystal structure features, including the size and chemical composition differences between the sheets, (or the void in the gibbsite sheet and SiO2 tetrahedron, in the case of imogolite). Mineral nanoscrolls and nanotubes consist of the most abundant elements, like magnesium, aluminium and silicon, accompanied by uncontrollable amounts of impurities (other elements and phases), which hinder their high technology applications. The development of a synthetic approach makes it possible to not only to overcome the purity issues, but also to enhance the chemical composition of the nanotubular particles by controllable cation doping. The first part of the review covers some principles of the cation doping approach and proposes joint criteria for the semiquantitative prediction of morphological changes that occur. The second part focuses on some doping-related properties and applications, such as morphological control, uptake and release, magnetic and mechanical properties, and catalysis.

Ni 3 Si 2 O 5 (OH) 4 phyllosilicate nanoscrolls were investigated by two techniques: the bending-based test method of AFM and the indentation method with visual control in STEM. In the first case, the average measured Young's modulus, about 200 GPa, turned out to be significantly higher than in the second one, 40 GPa. The reasons for this discrepancy are analyzed.