In-situ X-ray powder diffraction is a powerful tool in studies of dynamic structural transformations and microtextural changes in crystalline materials. By means of a high intensity synchrotron source and a special designed in-situ cell even fast chemical reactions and transformations involving crystalline materials can be monitored. In this work we have followed structural changes of anionic clays in-situ during ion exchange.
Layered double hydroxides (LDH) comprise a group of materials with the general composition [M(II)_1-xM(III)_x(OH)₂](A^n-)_x/n · mH₂O where M(II) and M(III) are di- and trivalent metal ions and A^n- is the counter anion. LDHs have among other things been used as catalysts, catalyst supports, absorbents, and anion exchangers. The LDH structure can be described as a stacking of alternating positively charged metal hydroxide layers (brucite-type) and layers of negatively charged counter anions and water. The anion may be e.g. CO₃^2-, NO₃^-, OH^-, Cl^-, SO₄^2- or a combination of these.
Structural and microtextural changes during anion exchange in cobalt-aluminum layered double hydroxides were studied using in-situ X-ray powder diffraction (e.g. acid-enhanced ion exchange of carbonate LDH and subsequent back-exchange was studied). The ion exchange process is a one or two phase transformation depending of the composition of the initial LDH and the ion-exchange environment. Rietveld refinements of selected layered double hydroxides reveal structural changes as the ion exchange progresses.

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1. Growth of 3D core-shell nanostructures by ALD