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Your search keyword '"Andrei, Stefancu"' showing total 3 results
Start Over Author "Andrei, Stefancu" Journal beilstein journal of nanotechnology
3 results on '"Andrei, Stefancu"'

1. The role of Ag+, Ca2+, Pb2+ and Al3+ adions in the SERS turn-on effect of anionic analytes

Author

Stefania D. Iancu, Andrei Stefancu, Vlad Moisoiu, Loredana F. Leopold, and Nicolae Leopold

Subjects
adion-specific adsorption model, cation bridging, raman, surface enhanced raman scattering (sers), Technology, Chemical technology, TP1-1185, Science, Physics, QC1-999
Abstract

In our recent studies we highlighted the role of adsorbed ions (adions) in turning on the surface-enhanced Raman scattering (SERS) effect in a specific mode for anionic and cationic analytes. In this work, we emphasize the role of Ag+, Ca2+, Pb2+ and Al3+ adions in the specific adsorption of anionic analytes such as the citrate capping agent and three organic acids. Our results suggest an adion-specific adsorption mechanism: the adsorption of anionic analytes is facilitated by positively charged adions such as Ag+, Ca2+, Pb2+ or Al3+, which provide adsorption sites specific for the anionic analytes. The turn-on of the SERS effect is explained in the context of the chemical mechanism of SERS. The adions form SERS-active sites on the silver surface enabling a charge transfer between the adsorbate and the silver surface. High-intensity SERS spectra of uric acid, salicylic acid and fumaric acid could be recorded at a concentration of 50 µM only after activation of the colloidal silver nanoparticles by Ca2+, Pb2+ or Al3+ (50 µM). The chemisorption of the three anionic species to the silver surface occurs competitively and is enhanced with the anions of higher affinities to the silver surface as indicated by the SERS spectra of corresponding mixed solutions.

Published
2019
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2. The role of adatoms in chloride-activated colloidal silver nanoparticles for surface-enhanced Raman scattering enhancement

Author

Nicolae Leopold, Andrei Stefancu, Krisztian Herman, István Sz. Tódor, Stefania D. Iancu, Vlad Moisoiu, and Loredana F. Leopold

Subjects
chloride activation, electronic coupling, photoreduction, silver nanoparticles, SERS-active sites, SERS switch-on effect, Technology, Chemical technology, TP1-1185, Science, Physics, QC1-999
Abstract

Chloride-capped silver nanoparticles (Cl-AgNPs) allow for high-intensity surface-enhanced Raman scattering (SERS) spectra of cationic molecules to be obtained (even at nanomolar concentration) and may also play a key role in understanding some fundamental principles behind SERS. In this study, we describe a fast (

Published
2018
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3. The role of adatoms in chloride-activated colloidal silver nanoparticles for surface-enhanced Raman scattering enhancement

Author

Loredana Leopold, Vlad Moisoiu, Stefania D. Iancu, Krisztian Herman, Andrei Stefancu, István Sz. Tódor, and Nicolae Leopold

Subjects
silver nanoparticles, General Physics and Astronomy, Nanoparticle, 02 engineering and technology, 010402 general chemistry, Photochemistry, lcsh:Chemical technology, 01 natural sciences, lcsh:Technology, Full Research Paper, Silver nanoparticle, chloride activation, Metal, Colloid, symbols.namesake, Nanotechnology, Molecule, General Materials Science, lcsh:TP1-1185, Electrical and Electronic Engineering, lcsh:Science, Chemistry, lcsh:T, SERS-active sites, Cationic polymerization, electronic coupling, 021001 nanoscience & nanotechnology, photoreduction, SERS switch-on effect, lcsh:QC1-999, 0104 chemical sciences, Nanoscience, Chemisorption, visual_art, symbols, visual_art.visual_art_medium, lcsh:Q, 0210 nano-technology, Raman spectroscopy, lcsh:Physics
Abstract

Chloride-capped silver nanoparticles (Cl-AgNPs) allow for high-intensity surface-enhanced Raman scattering (SERS) spectra of cationic molecules to be obtained (even at nanomolar concentration) and may also play a key role in understanding some fundamental principles behind SERS. In this study, we describe a fast (− ions chemisorbed onto the metal surface where the chloride concentration in the colloidal solution is 10−2 M. Consequently, the enhanced SERS spectra of cationic dyes (e.g., crystal violet or 9-aminoacridine) demonstrate the advantages of Cl-AgNPs compared to the as-synthesized AgNPs obtained by standard Ag+ reduction with hydroxylamine (hya-AgNPS) or citrate (cit-AgNPs). The results of SERS experiments on anionic and cationic test molecules comparing Cl-AgNPs, hya-AgNPs and cit-AgNPs colloids activated with different amounts of Cl− and/or cations such as Ag+, Mg2+ or Ca2+ can be explained within the understanding of the adatom model – the chemisorption of cationic analytes onto the metal surface is mediated by the Cl− ions, whereas ions like Ag+, Mg2+ or Ca2+ mediate the electronic coupling of anionic species to the silver metal surface. Moreover, the SERS effect is switched on only after the electronic coupling of the adsorbate to the silver surface at SERS-active sites. The experiments presented in this study highlight the SERS-activating role played by ions such as Cl−, Ag+, Mg2+ or Ca2+, which is a process that seems to prevail over the Raman enhancement due to nanoparticle aggregation.

Published
2018

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