Correlation between the Dynamics of Nanoconfined Water and the Local Chemical Environment in Calcium Silicate Hydrate Nanominerals

Abstract

Calcium silicate hydrates are members of a large family of minerals with layered structures containing pendant CaOH and SiOH groups that interact with confined water molecules. To rationalize the impact of the local chemical environment on the dynamics of water, SiOH‐ and CaOH‐rich model nanocrystals were synthesized by using the continuous supercritical hydrothermal method and then systematically studied by a combination of spectroscopic techniques. In our comprehensive analysis, the ultrafast relaxation dynamics of hanging hydroxy groups can be univocally assigned to CaOH or SiOH environments, and the local chemical environment largely affects the H‐bond network of the solvation water. Interestingly, the ordered “ice‐like” solvation water found in the SiOH‐rich environments is converted to a disordered “liquid‐like” distribution in the CaOH‐rich environment. This refined picture of the dynamics of confined water and hydroxy groups in calcium silicate hydrates can also be applied to other water‐containing materials, with a significant impact in many fields of materials science.

Geoinspired syntheses of materials and nanomaterials

“…122 A significant effort has been made recently for the development of an innovative hydrothermal supercritical flow synthesis to expand the synthetic CSH mineral production towards industrial requirements. [123][124][125] In 2017, Diez-Garcia et al reported the first supercritical hydrothermal flow synthesis of two calcium silicate hydrate minerals, namely xonotlite and tobermorite. 123,124 Then, Musumeci et al optimized the process to improve the purity, crystallinity, and quantity of the produced materials.…”

“…123,124 Then, Musumeci et al optimized the process to improve the purity, crystallinity, and quantity of the produced materials. 125,126 Natural xonotlite is commonly found near the contact between igneous rocks and calcium bearing rocks. 127 Xonotlite is usually described using the ideal stoichiometric formula Ca 6 Si 6 O 17 (OH) 2 .…”

“…124 Two precursor solutions were prepared by dissolving separately stoichiometric amounts of calcium nitrate tetrahydrate and sodium metasilicate nonahydrate in water. Supercritical conditions, 400 1C at 25 MPa, delivered high crystallinity xonotlite in only 7 s. 125,126 The lab-scale set-up yielded a continuous production of about 2.9 g h À1 . 126 Under these conditions (Fig.…”

“…12D and E). 123,125,126 XRD, TEM, solid-state nuclear magnetic resonance spectroscopy (SSNMR), Raman spectroscopy and High Pressure X-Ray Diffraction (HP-XRD) showed that the crystallinity was increased under supercritical conditions compared to conventional hydrothermal synthesis. 126 The overall morphological and structural features of the SHFS product were much more comparable to natural specimens than other synthetic samples less crystallized.…”

“…In particular, these model minerals improved our knowledge of the relationship between the dynamics of nanoconfined water and surface chemistry in these materials. 125 Musumeci et al investigated this relationship by using tobermorite as a model of the effect of the Si-OH environment on water dynamics, and xonotlite as a mineral archetype to examine the additional contribution of the Ca-OH chemical environment. The hydrogen bond network of the minerals was investigated through a combination of 1 H SSNMR, Raman spectroscopy and Fourier-transform infrared (FTIR) spectroscopy, and then exhaustive broadband dielectric spectroscopy measurements were carried out.…”