On the key role of the surface of palygorskite nanofibers in the stabilization of hexagonal metastable β-Ag2CO3 phase in palygorskite-based nanocomposites

Abstract

On the key role of the surface of palygorskite nanofibers in the stabilization of hexagonal metastable β-Ag2CO3 phase in palygorskite-based nanocomposites. (2019) Applied Clay Science, 172. 123-134.

Influence of the crystal structure of Ag2CO3 on the photocatalytic activity under visible light of Ag2CO3-Palygorskite nanocomposite material

“…This structural transformation is entirely reversible only for pure Ag 2 CO 3 while it is not if the β-phase is stabilized as for instance by the surface of palygorskite. Thus, this reversibility was demonstrated for pure Ag 2 CO 3 by in situ XRD as a function of the temperature under CO 2 atmosphere; the formation of β-Ag 2 CO 3 occurring at about 180°C [39] in agreement with other authors [49][50][51][52][53][54]. In this series of in situ XRD patterns, the strongest diffraction peak (1 3 0) of m-Ag 2 CO 3 at 2θ ≈ 33.7°is not shifted by increasing the temperature until it disappears beyond 200°C to form a high temperature phase ( Fig.…”

“…combining both antibacterial and photocatalytic properties. For this purpose, novel supported nanocomposite photocatalysts based on Ag 2 CO 3 in replacement of TiO 2 as active phase and palygorskite clay mineral as support material, were successfully synthesized as described in details in a companion paper [39]. The beneficial effect of the surface of palygorskite fibers has been shown to refine Ag 2 CO 3 particles size and to stabilize its metastable hexagonal β-phase.…”

“…This growth mode would compete with homogenous nucleation taking place in aqueous solution and leading to m-Ag 2 CO 3 NPs, which tends to form nodular and porous agglomerates trapped in tangled fibers. Both growth mechanisms would occur simultaneously [39]. The β-Ag 2 CO 3 was not observed by TEM analyses probably because it is unstable under electronic impact.…”

“…All support materials do not stabilize the β-phase. For instance, using celite [39] or C 3 N 4 [48], Ag 2 CO 3 keeps the monoclinic structure. Also, metastable phases can be stabilized by the nanometric size of the particles produced by the growth mechanism.…”

“…Pure Ag 2 CO 3 was also synthesized according to the protocol 1 using the same conditions as above but without the palygorskite clay mineral. More details on the synthesis of these composite materials is reported in a companion paper [39]. Theses experimental protocols, completed with others after aging are summarized in Table 2.…”