A Study of the Adsorption Behavior of Malathion with Silver Nanosubstrates by Raman Spectroscopy and Density Functional Theory

In this paper, the chemical adsorption behavior of malathion on silver nanosubstrates is studied by surface-enhanced Raman scattering technology (SERS) and density functional theory (DFT). Based on the concepts of density functional theory (DFT) and hard-soft acid-base (HSAB) theory, the interaction between malathion and Ag was discussed by combining SERS. Four adsorption conformations were confirmed by constructing a model of the malathion-Ag₂₀ complex and evaluating its binding energy, affinity energy, and Boltzmann distribution ratio. Using the HSAB principle, front-line molecular orbitals and the global reactivity descriptor confirmed the charge transfer effect between malathion and Ag. The attribution of SERS peak vibrations at different binding sites of malathion and its complexes was studied, and the reasons for the eigenfrequency shift, broadening, and selectivity enhancement were analyzed, and the comparison between the experimental data and the calculated results showed good agreement. Based on the surface selection rules, it can be inferred that malathion is chemically adsorbed perpendicularly on a silver nanosubstrate by the S2═P3 group. The results of this study provide theoretical support for exploring the chemical enhancement mechanism between malathion and AgNPs and developing a new malathion SERS sensor.