In
recent years, there has been increasing interest in developing cost-efficient,
fast, and user-friendly <sup>17</sup>O enrichment protocols to help understand
the structure and reactivity of materials using <sup>17</sup>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 <sup>17</sup>O-compositions were measured at
different milling times using LG-SIMS. High-resolution <sup>17</sup>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 <sup>17</sup>O polarization and indirect <sup>17</sup>O{<sup>1</sup>H}
CP excitation, agreed with selective<sup> </sup>labeling of the surface.
Information on the distribution of Si-OH environments at the surface was
obtained from 2D <sup>1</sup>H-<sup>17</sup>O D-HMQC correlations. Finally, the
surface-labeled silica was reacted with titania and using <sup>17</sup>O DNP,
their common interface was probed and Si-O-Ti bonds identified.