{"title":"Trivalent Rare Earth Adsorption at Phosphonic Acid Monolayers.","authors":"Srikanth Nayak, Ahmet Uysal","doi":"10.1002/cphc.202500429","DOIUrl":null,"url":null,"abstract":"<p><p>The increasing need for rare earth separations requires a detailed understanding of trivalent ion behavior at charged aqueous interfaces. Here, neodymium (Nd) adsorption on Langmuir monolayers of octadecylphosphonic acid (ODPA), a single-chain phosphonic acid capable of double deprotonation, at the air/water interface, is investigated. Combining sum frequency generation (SFG) spectroscopy with X-ray fluorescence near total reflection (XFNTR), both the interfacial water ordering and ion density are examined. Under ambient conditions, Nd ions induce enhanced deprotonation of ODPA headgroups, leading to interfacial ion densities as high as 1 Nd per 30 Å<sup>2</sup>. This adsorption behavior arises from a complex interplay between direct electrostatic interactions, ion pairing, and hydration effects, which cannot be fully captured by classical Gouy-Chapman-Stern models. These insights into trivalent ion adsorption mechanisms provide a pathway toward more effective separation processes for rare earth metals.</p>","PeriodicalId":9819,"journal":{"name":"Chemphyschem","volume":" ","pages":"e2500429"},"PeriodicalIF":2.2000,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Chemphyschem","FirstCategoryId":"92","ListUrlMain":"https://doi.org/10.1002/cphc.202500429","RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
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Abstract
The increasing need for rare earth separations requires a detailed understanding of trivalent ion behavior at charged aqueous interfaces. Here, neodymium (Nd) adsorption on Langmuir monolayers of octadecylphosphonic acid (ODPA), a single-chain phosphonic acid capable of double deprotonation, at the air/water interface, is investigated. Combining sum frequency generation (SFG) spectroscopy with X-ray fluorescence near total reflection (XFNTR), both the interfacial water ordering and ion density are examined. Under ambient conditions, Nd ions induce enhanced deprotonation of ODPA headgroups, leading to interfacial ion densities as high as 1 Nd per 30 Å2. This adsorption behavior arises from a complex interplay between direct electrostatic interactions, ion pairing, and hydration effects, which cannot be fully captured by classical Gouy-Chapman-Stern models. These insights into trivalent ion adsorption mechanisms provide a pathway toward more effective separation processes for rare earth metals.
期刊介绍：
ChemPhysChem is one of the leading chemistry/physics interdisciplinary journals (ISI Impact Factor 2018: 3.077) for physical chemistry and chemical physics. It is published on behalf of Chemistry Europe, an association of 16 European chemical societies.
ChemPhysChem is an international source for important primary and critical secondary information across the whole field of physical chemistry and chemical physics. It integrates this wide and flourishing field ranging from Solid State and Soft-Matter Research, Electro- and Photochemistry, Femtochemistry and Nanotechnology, Complex Systems, Single-Molecule Research, Clusters and Colloids, Catalysis and Surface Science, Biophysics and Physical Biochemistry, Atmospheric and Environmental Chemistry, and many more topics. ChemPhysChem is peer-reviewed.
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