Cation Redistribution along the Spiral of Ni‐Doped Phyllosilicate Nanoscrolls: Energy Modelling and STEM/EDS Study

Abstract

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.

Thermal behavior of Mg−Ni‐phyllosilicate nanoscrolls and performance of the resulting composites in hexene‐1 and acetone hydrogenation

“…In this case the all dependencies of size parameters upon nominal Ni content (relied on mass contribution of particles) demonstrated a maximum at x =0.5. This maximum could be related to chemical composition features revealed in previous works, [7h,25] such as growth of conical nanoscrolls and redistribution of Mg and Ni cations along the nanoscroll's spiral. This feature can be possible because of the nanotubular phyllosilicate crystal growth, in addition to conventional crystal growth processes, is guided by a strain energy [1a,b,26] .…”

“…Temperature of the shoulder was approximately equal to that of the sample with x =1, while the main peak's temperature shifted from 635 °C ( x =0) to 649 °C ( x =0.33) and 637 °C ( x =0.5). We attributed this splitting to the effect of cations redistribution along the nanoscroll's spiral as mentioned elsewhere [7h] . The Ni‐rich shell of the nanoscroll could dehydroxylate at lower temperature (585–587 °C) thus serving as a sacrificial layer against heat action.…”

“…Relatively low bulk concentration of Ni cations in the sample with x=0.67 decreased an amount of nucleation acts per time unit. In addition, in case of several cations (Mg and Ni) constitute the nanoscroll structure, they can be distributed inhomogeneously [7h] among the layers of different curvature in order to minimize the strain energy of the whole nanoscroll. Thus, nucleation and growth of Ni nanoparticles in that case stretched in time giving a chance for some particles to grow and yielding a broad size distribution (Figure 9.a, 600 °C).…”

Copper Phyllosilicates-Derived Catalysts in the Production of Alcohols from Hydrogenation of Carboxylates, Carboxylic Acids, Carbonates, Formyls, and CO2: A Review

“…For example, chrysocolla (Cu2Si2O5(OH)2) is a lamellar structure consisted of layers of SiO4 tetrahedra sandwiched between discontinuous layers of CuO6 octahedra [40]; kaolinite is an 1:1 aluminum phyllosilicates while pyrophyllite is 2:1 [41]; chrysotile is made of 1:1 magnesium phyllosilicates (Mg3Si2O5(OH)4) [37]. The difference between the radius of tetrahedrally coordinated Si and octahedrally coordinated cation can bend the layer-structured phyllosilicates [37,42], resulting in distorted morphologies such as rolling of paper sheets into a tube. Compared to conventional catalysts (metal impregnated on SiO2), the high surface area of laminar structured phyllosilicate allows metal atoms to be finely dispersed.…”

The ''rolling up'' effect of platinum layer obtained on nickel surface by interaction with solution of H2PtCl6 and its electrocatalytic properties in hydrogen evolution reaction during water electrolysis in alkaline medium

“…For example, novel metamaterials were obtained using this approach [1] and new types of 3D devices with small form factors [2][3][4]. There are also known works devoted to the synthesis and research of nanoscrolls of hydrosilicates of metals [5][6][7][8], as well as microtube of a number of oxides [9,10], fluorides [11] and sulfides of metals [12]. As shown by the authors of these works, the reason for this rolling up is mechanical forces that arise inside planar structures due to density or composition gradients.…”