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Published on: May 29, 2018
The charge of solid-liquid interfaces measured by x-ray standing waves and streaming current
Martin Brücher1, Alex von Bohlen, Peter Jacob
1Leibniz-Institut für Analytische Wissenschaften - ISAS e.V. Bunsen-Kirchhoff-Str. 11, 44139 Dortmund, Germany.
Summary
X-ray standing waves precisely measured ion distributions and Debye lengths at charged interfaces. This technique quantified surface charge and detected pH-dependent ion behavior in aqueous solutions.
Area of Science:
- Physical Chemistry
- Surface Science
- Electrochemistry
Background:
- Understanding ion behavior at charged interfaces is crucial for various chemical and electrochemical processes.
- X-ray standing waves (XSW) offer a powerful, non-invasive method for probing interfacial structures at the nanoscale.
Purpose of the Study:
- To measure ion distributions and Debye lengths at charged solid-liquid interfaces using XSW.
- To investigate the influence of pH and surface functionalization on ion adsorption and repulsion.
- To quantify surface charge by correlating XSW measurements with streaming current data.
Main Methods:
- Utilized high-energy synchrotron radiation (17.48 keV) to generate X-ray standing waves within a thin water film on a silicon wafer.
- Employed aqueous solutions containing bromide (Br) and rubidium (Rb) ions, with surface charge controlled via titration across a pH range of 2.2-9.
- Measured the XSW pattern to determine ion distribution and Debye lengths, complemented by streaming current measurements for surface charge quantification.
Main Results:
- Successfully measured ion distributions and Debye lengths, revealing values between 1-4 nm.
- Observed pH-dependent transitions from ion attraction to repulsion on functionalized wafers, identifying the isoelectric point.
- Quantified the surface charge of the sample through combined XSW and streaming current analysis.
Conclusions:
- XSW is an effective technique for characterizing ion distributions and interfacial properties at charged solid-liquid interfaces.
- The study provides quantitative data on Debye lengths and surface charge, enhancing our understanding of electrochemical interfaces.
- Demonstrated the ability to detect specific ion interactions and surface charge characteristics as a function of pH and surface modification.
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