Model-independent X-ray imaging of adsorbed cations at the crystal-water interface

We describe an approach to directly image three-dimensional elemental distributions at the crystal-liquid interface with ∼ 1 Å spatial resolution. This method, based on the Fourier synthesis of X-ray standing wave data, is demonstrated by imaging the distribution of Sr²⁺, Zn ²⁺ and Y³⁺ adsorbed to the rutile (110)-water interface with no a priori assumptions. The approach resolves distinct sites and is robust for systems with single or multiple simultaneous adsorption sites. The observed ion distributions reveal unexpected differences in the adsorption sites of these cations that are needed to interpret electrical double-layer phenomena using surface complexation models. Published by Elsevier B.V.