title: Direct Observation of Ion Pairing at the Liquid/Solid Interfaces by Surface Enhanced Raman Spectroscopy.
abstract: Ion-pairing, the association of oppositely charged ionic species in solution and at liquid/solid interfaces has been proposed as a key factor for a wide range of physicochemical phenomena. However, experimental observations of ion pairing at the ligand/solid interfaces are challenging due to difficulties in differentiating ion species in the electrical double layer from that adsorbed on the solid surfaces. Using surface enhanced Raman spectroscopy in combination with electrolyte washing, we presented herein the first direct experimental evidence of ion pairing, the coadsorption of oppositely charged ionic species onto gold nanoparticles (AuNPs). Ion pairing reduces the electrolyte concentration threshold in inducing AuNP aggregation and enhances the competitiveness of electrolyte over neutral molecules for binding to AuNP surfaces. The methodology and insights provided in this work should be important for understanding electrolyte interfacial interactions with nanoparticles.
authors.affiliation: Department of Chemistry, Mississippi State University , Mississippi State, Mississippi 39762, United States.
authors.forename: Ganganath S
authors.initials: GS
authors.lastname: Perera
authors.affiliation: Department of Chemistry, Mississippi State University , Mississippi State, Mississippi 39762, United States.
authors.forename: Charles B
authors.initials: CB
authors.lastname: Nettles
authors.affiliation: Department of Chemistry, University of Central Florida , Orlando, Florida 32816, United States.
authors.forename: Yadong
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Department of Chemistry, University of Central Florida , Orlando, Florida 32816, United States.
authors.forename: Shengli
authors.initials: S
authors.lastname: Zou
authors.affiliation: Department of Chemistry, Mississippi State University , Mississippi State, Mississippi 39762, United States.
authors.forename: T Keith
authors.initials: TK
authors.lastname: Hollis
authors.affiliation: Department of Chemistry, Mississippi State University , Mississippi State, Mississippi 39762, United States.
authors.forename: Dongmao
authors.initials: D
authors.lastname: Zhang
mesh_terms: D004573:Electrolytes / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D044367:Phase Transition; D013059:Spectrum Analysis, Raman
chemical_list: D004573:Electrolytes; D006046:Gold