Abstract
Morphology-controlled strontianite nanostructures have attracted interest in various fields, such as electrocatalyst and photocatalysts. Basic additives in aqueous strontium solutions is commonly used in controlling strontianite nanostructures. Here, we show that trace water also serves an important role in forming and structuring vertically oriented strontianite nanorod arrays on strontium compounds. Using in situ Raman spectroscopy, we monitored the structural evolution from hydrated strontium to strontianite nanorods, demonstrating the epitaxial growth by vapor–liquid–solid mechanism. Water molecules cause not only the exsolution of Sr liquid droplets on the surface but also the uptake of airborne CO2 followed by its ionization to CO32−. The existence of intermediate SrHO+–OCO22− phase indicates the interaction of CO32− with SrOH+ in Sr(OH)x(H2O)y cluster to orient strontianite crystals. X-ray diffraction simulation and transmission electron microscopy identify the preferred-orientation plane of the 1D nanostructures as the (002) plane, i.e., the growth along the c-axis. The anisotropic growth habit is found to be affected by the kinetics of carbonation. This study paves the way for designing and developing 1D architecture of alkaline earth metal carbonates by a simple method without external additives at room temperature.
Highlights
Morphology-controlled strontianite nanostructures have attracted interest in various fields, such as electrocatalyst and photocatalysts
We have studied water-mediated Sr-precipitate and growth of strontianite nanorod arrays on the surface of strontium compounds in ambient conditions
The segregated Sr(OH)2·8H2O subsequently converts to SrCO3 in ambient air, which interestingly has nanorod morphology
Summary
Morphology-controlled strontianite nanostructures have attracted interest in various fields, such as electrocatalyst and photocatalysts. We show that trace water serves an important role in forming and structuring vertically oriented strontianite nanorod arrays on strontium compounds. Strontium is an alkaline earth metal that has two electrons in the outer valence shell It has a very low electronegativity (1.0), tending to be readily ionized as Sr2+ to react with oxygen and H2O in air[1]. The morphology control of S rCO3 has attracted considerable interest as providing the opportunity to explore and develop novel properties: e.g., urchin-like SrCO3 particles showed enhanced specific capacitance[26], and vertically-oriented S rCO3 nanorods exhibited photoluminescence (PL) quenching over the full solar spectrum r ange[27]. Our recent work showed that the continuous Sr segregation induced by H2O absorption leads to the formation of SrCO3 (Supplementary Fig. S1 online), especially with nanorod morphology[16]. For further design and development of onedimensional (1D) architectures of S rCO3, the growth mechanism of SrCO3 nanorods needs to be understood
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