Abstract
AbstractThe front cover artwork is provided by the groups of Prof. Werner Kunz (University of Regensburg, Germany) and Prof. Juan Manuel García‐Ruiz (Laboratorio de Estudios Cristalográficos, CSIC‐UGR, Spain) as well as Dr. Matthias Kellermeier (BASF SE, Germany). The image shows silica gardens, a peculiar form of tubular precipitates that grow spontaneously in purely inorganic environments. In addition to their striking morphologies, these self‐assembled structures sustain drastic chemical gradients that drive a cascade of coupled diffusion and precipitation processes, which were studied by complementary synchrotron‐based techniques in the present work.Read the full text of the article at 10.1002/cphc.201600748.
Highlights
Precipitation of multivalent metal cations from silica-rich solutions at high pH results in the spontaneous formation of intriguing tubular structures with plantlike morphologies.[1,2,3]. These so-called silica gardens arise from the coupling of chemical reaction with osmotic and buoyancy forces,[4] and were shown to consist of a mixed metaloxide/silica(te) membrane[5,6,7,8,9,10] that separates two solutions with fundamentally different compositions.[11]
Despite their purely inorganic nature, silica gardens mimic biogenic matter and have recurrently been the subject of discussions around the origin of life.[3,12,13]. This notion was recently refueled by the discovery of the existence of considerable electrochemical potential differences across such tubular precipitates during the early stages of evolution,[11,14] which could successfully be employed as a source of energy.[15]
Apart from that, related structures are known to occur in geological environments[16] and industrial settings,[17] and the formed membrane materials have been scrutinized with respect to their properties for application as, for example, catalysts[18,19] and reactors.[20]
Summary
Precipitation of multivalent metal cations from silica-rich solutions at high pH results in the spontaneous formation of intriguing tubular structures with plantlike morphologies.[1,2,3] These so-called silica gardens arise from the coupling of chemical reaction with osmotic and buoyancy forces,[4] and were shown to consist of a mixed metal (hydr)oxide/silica(te) membrane (the wall of the tubes)[5,6,7,8,9,10] that separates two solutions with fundamentally different compositions.[11]. In previous studies,[11,21] we have developed a procedure to grow single macroscopic silica-garden tubes with well-defined dimensions and an open end on top (Figure 1), which for the first time allowed for straightforward sampling and in situ analysis of the two solutions separated by the formed inorganic membrane. In this way, it was possible to monitor changes in pH and the concentrations of the various ionic species present in the system as a function of time. The resulting data provided detailed information on the dynamic behavior of silica gar-
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