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

This study reports an original remarkable effect of fibrous palygorskite clay mineral in the stabilization at the ambient temperature of the metastable hexagonal β-phase of Ag2CO3 along with the stable monoclinic one (m-Ag2CO3) and the refinement of their particles size (≈5–10 nm). These structural and microstructural features likely arise owing to heterogeneous nucleation induced by the surface of palygorskite fibers between CO32– anions in solution and Ag+ exchanged palygorskite (Ag+-Pal) as reactants kept maturing for short periods, which should not exceed 1 h. Besides, the phase composition of Ag2CO3 supported on palygorskite, namely β- and m-structures can be monitored by carrying on appropriate low temperature treatments under CO2 atmosphere coupled with aging during several months in such a way that either pure β or m single-phases as well as biphased mixtures with controlled composition can be obtained. Taking into account experimental results and literature data, a growth mechanism is discussed.