Letter Cite This: Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/journal/estlcu
The Aromatic Amine pKa Determines the Affinity for Citrate-Coated Gold Nanoparticles: In Situ Observation via Hot Spot-Normalized Surface-Enhanced Raman Spectroscopy Haoran Wei,*,†,‡,§ Qishen Huang,†,‡,§ and Peter J. Vikesland*,†,‡,§ †
Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, Virginia 24060, United States Virginia Tech Sustainable Nanotechnology Center (VTSuN), Virginia Tech Institute for Critical Technology and Applied Science (ICTAS), Blacksburg, Virginia 24060, United States § Center for the Environmental Implications of Nanotechnology (CEINT), Duke University, Durham, North Carolina 27708, United States Environ. Sci. Technol. Lett. Downloaded from pubs.acs.org by UNIV PARIS-SUD on 04/02/19. For personal use only.
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S Supporting Information *
ABSTRACT: The in situ characterization of organic pollutant dynamics on engineered interfaces provides fundamental insights about pollutant fate, transport, and toxicity in aquatic systems. In this study, the association between aromatic amines and citrate-coated gold nanoparticles (cit-AuNPs) under different pH conditions was monitored in situ using hot spot-normalized surface-enhanced Raman spectroscopy (HSNSERS). HSNSERS minimizes the uncertainty of SERS measurements that arises from substrate heterogeneity, laser intensity fluctuation, and laser focusing, and its application enabled quantification of the influence of solution pH on the measured SERS signals. Our results demonstrate that the accumulation of chloroanilines on cit-AuNP surfaces is dictated by solution pH and analyte pKa. At circumneutral pH (≈5.6), only the chloroanilines with relatively high pKa values were readily detected by SERS, while those with low pKa values (
