Labeling and Probing the Silica Surface Using Mechanochemistry and ¹⁷O NMR Spectroscopy**

Abstract

In recent years, there has been increasing interest in developing cost-efficient, fast, and user-friendly 17 O enrichment protocols to help understand the structure and reactivity of materials using 17 O NMR. Here, we show for the first time how ball milling (BM) can be used to selectively and efficiently enrich the surface of fumed silica, which is widely used at the industrial scale. Short milling times (up to 15 min) allowed modulation of the enrichment level (up to ca. 5%) without significantly changing the nature of the material. High-precision 17 O-compositions were measured at different milling times using LG-SIMS. High-resolution 17 O NMR analyses (including at 35.2 T) allowed clear identification of the signals from siloxane (Si-O-Si) and silanols (Si-OH), while DNP analyses, performed using direct 17 O polarization and indirect 17 O{ 1 H} CP excitation, agreed with selective labeling of the surface. Information on the distribution of Si-OH environments at the surface was obtained from 2D 1 H-17 O D-HMQC correlations. Finally, the surface-labeled silica was reacted with titania and using 17 O DNP, their common interface was probed and Si-O-Ti bonds identified. File list (2) download file view on ChemRxiv manuscript_20210414.pdf (1.36 MiB) download file view on ChemRxiv supporting information_20210414.pdf (2.04 MiB)

First Direct Insight into the Local Environment and Dynamics of Water Molecules in the Whewellite Mineral Phase: Mechanochemical Isotopic Enrichment and High-Resolution 17O and 2H NMR Analyses

“…In this manuscript, we decided to explore if mechanochemistry with mild milling conditions and involving microliter quantities of water could be used to achieve isotopic enrichment of water molecules within the COM structure without affecting the crystallinity of the starting material. Building upon our recent demonstration that mechanochemistry can be a very powerful technique for enriching in 17 O various inorganic materials and organic molecules, − we will demonstrate for the first time that ball-milling methods are also very well suited for the 17 O-labeling or deuteration of hydrated biomimetic minerals like calcium oxalates. Moreover, it will be shown how information on the actual enrichment mechanism of this mechanochemical labeling procedure can be obtained by using two complementary mass spectrometry methods (one bulk and one for the surface) and analyzing the isotopic compositions of COM phases with water molecules enriched in 2 H, 17 O, or 18 O (the latter being prepared for these mechanistic studies).…”

First direct insight into the local environment and dynamics of water molecules in the whewellite mineral phase: mechanochemical isotopic enrichment and high-resolution 17O and 2H NMR analyses

“…91 Here, enriched water was actually used to play the role of both a liquid grinding assistant and a reagent to introduce the isotopic label, in line with our previous work on isotopic labeling using ball-milling. [61][62][63][64][65][66] Three different experimental conditions were compared for the deuteration of COM. The first experiment adopted a very gentle approach: shaking without a milling ball, allowing the reagents to be mixed at the frequency of 25 Hz for 5 minutes (COM-SHAKE-2 H), and without any risk of affecting the crystallinity of the COM starting material.…”

“…In this manuscript, we decided to explore if mechanochemistry with mild milling conditions and involving microliter quantities of water could be used to achieve isotopic enrichment of water molecules within the COM structure, without affecting the crystallinity of the starting material. Building upon our recent demonstration that mechanochemistry can be a very powerful technique for enriching in 17 O various inorganic materials [61][62][63][64] and organic molecules. 63,65,66 Here, we will demonstrate for the first time that ball-milling methods are also very well suited for the 17 O-labeling or deuteration of hydrated biomimetic minerals like hydrated calcium oxalates.…”

First direct insight into the local environment and dynamics of water molecules in the whewellite mineral phase: mechanochemical isotopic enrichment and high-resolution 17O and 2H NMR analyses

“…81 Here, enriched water was actually used to play the role of both a liquid grinding assistant and a reagent to introduce the isotopic label, in line with our previous work on isotopic labeling using ball-milling. [54][55][56][57][58][59] Three different experimental conditions were compared for the deuteration of COM. The first experiment adopted a very gentle approach: shaking without a milling ball, allowing the reagents to be mixed at the frequency of 25 Hz for 5 minutes (COM-SHAKE-2 H), and without any risk of affecting the crystallinity of the COM starting material.…”

“…starting material. Building upon our recent demonstration that mechanochemistry can be a very powerful technique for enriching in 17 O various inorganic materials [54][55][56][57] and organic molecules. 56,58,59 Here, we will demonstrate for the first time that ball-milling methods are also very well suited for the 17 O-labeling or deuteration of hydrated biomimetic minerals like hydrated calcium oxalates.…”