Benzene Derivatives Molecules Adsorbed On Silver Nanoparticles Surface Behavior Experiment With Density Functional Theory Study

SERS as a molecular detection methods, with advantages of high sensitivity, high fluorescence quenching, becomes a powerful tool for research molecular surface properties and molecular interaction with the substrate surface. Ag colloid has many excellent features. Therefore, the SERS technology with the silver nanoparticles as the SERS-active substrate has been wide applied in many fields.The adsorption behavior of the molecule in the SERS substrate is mainly affected by these two factors, which are the substrate surface properties and molecular surface configuration. In this paper, we will discuss the surface configuration of the molecule itself effect on the adsorption behavior of the molecule. Combination of SERS and DFT plays a very important role in speculation and interpretation of the interaction between the adsorbed molecules and the substrate. Therefore, we select some representative conformation molecules as adsorbed molecules. We will make use of combination of theoretical and experimental to study the adsorption behavior of adsorbed molecules in the surface of silver nanoparticles. The results as follows:1. We measured and obtained normal Raman spectra of PHBA, MHBA and OHBA powder, and the SERS spectra of these three substances in the silver sol. At the same time, we used DFT method to study the stable structure of these three molecules, their NRS spectrum, and the SERS spectrum of them adsorption of silver nanoparticles surface. We also assigned the vibration modes of these molecules by the Gauss View visualization software. According to the theoretical results with experimental values obtained in the silver colloid solution, the adsorption manner of the group isomers of molecules in the silver nanoparticles surface is different. PHBA molecules adsorbed vertically through the carboxyl, MHBA molecules adsorbed vertically or near vertically through the carboxyl and hydroxyl, and OHBA molecules adsorbed obliquely through carboxyl.2. We study normal Raman spectrum of4-Mpy and2-Mpy solid powder, and these two molecules’near-infrared SERS spectrum absorbed in silver substrate. We use DFT theory to study4-Mpy and the2-Mpy molecular geometry, the NRS spectrum and SERS spectrum adsorbed on silver nanoparticles surface. And then we assigned their vibrational spectra by the Gauss View visualization software. Combination of experiments and theoretical calculations, we study the adsorption behavior of these two isomers in the surface of silver nanoparticles. The result showed that4-Mpy molecules adsorbed on the surface of silver nanoparticles vertically or near vertically through the S atom;2-Mpy molecules also adsorbed through the S atom, but the pyridine ring is no longer perpendicular to the substrate, and with a tilt angle.