Stimulated Adsorption of Humic Acids on Capped Plasmonic Ag Nanoparticles Investigated by Surface-Enhanced Optical Techniques

Abstract

The adsorption of humic substances on Ag nanoparticles (AgNPs) is of crucial environmental importance and determines the toxicity of these NPs and the structure of adsorbed organic matter. In this work, the adsorption of two standard soil and leonardite International Humic Substances Society humic acids was studied on AgNPs of different sizes, shapes (spherical and star-like), and interfacial chemical compositions. Surface-enhanced optical (Raman and fluorescence) spectroscopies were used to follow the specific chemical groups involved in this adsorption. By means of the latter optical techniques, information regarding the binding mechanism and the macromolecular aggregation can be deduced. The influence of the surface chemical composition induced by the different functionalizations of the interfaces of these NPs is highly important regarding the chemical interactions of these complex organic macromolecules. The surface functionalization with positively charged alkyl diamines led to a large increase in the adsorption as well as a strong structural rearrangement of the macromolecule once adsorbed onto the surface.

Effectiveness of Humic Substances and Phenolic Compounds in Regulating Plant-Biological Functionality

“…Surface-enhanced Raman scattering (SERS) that is a vibrational technique that can be applied to obtain characteristic structural information on HS [24]. SERS increases the sensitivity of the Raman signal due to the huge intensification of electric field on the surface of nanostructures made of several specific metals, mainly Ag or Au [25].…”

Vibrational Study (Raman, SERS, and IR) of Plant Gallnut Polyphenols Related to the Fabrication of Iron Gall Inks

“…However, the AgC colloid may show bands of the residual citrate ions used for preparing the colloid, which can overlap the bands of the analyte. The higher activity of AgC NPs to render intense SERS spectra is related to the fact that the citrate residual species, still adsorbed onto the metal surface, and its oxidation products can better interact with the –OH groups of polyphenols through the establishment of H-bonds between –COOH in citrate and the –OH groups in the phenols [ 65 ].…”

Solution NMR methods for structural and thermodynamic investigation of nanoparticle adsorption equilibria

“…SERS has found widespread application in qualitative analysis of ligand–NP interactions, providing important information on the binding mode of ligands on the NP surface. 45,46,48,111,115–137 However, this technique nearly always has to be accompanied by other supporting methods, either theoretical ( i.e. DFT, surface selection rules) 127–131 or experimental ( i.e.…”