A DFT Study on the Interaction Mechanisms and Adsorption-Induced Raman Spectral Changes of Tire-Derived Contaminants...

The growth of the global transportation sector has driven sustained increases in tire demand, and tire wear releases emerging particulate pollutants such as 6PPD and its ozone-oxidation product, 6PPD-Q. Both compounds are highly toxic, environmentally persistent, and widely distributed in aquatic systems, posing severe risks to ecological integrity and human health. Current understanding of the intrinsic interfacial interactions and electronic coupling mechanisms between these tire-derived pollutants and noble-metal sensing substrates remains incomplete, which severely limits the rational design of related sensing materials and calls for systematic theoretical investigation. In this work, we present a density functional theory (DFT)-based theoretical study that systematically examines the interaction mechanisms between 6PPD/6PPD-Q and Au16 nanoclusters and the intrinsic rules governing adsorption-induced changes in Raman spectra, with emphasis on the charge-transfer-driven chemical enhancement (CM) component of Raman scattering. First, we used a suite of theoretical toolsfrontier molecular orbitals (FMO), molecular electrostatic potential (MEP), interaction region indicator (IRI), independent gradient model based on Hirshfeld partition (IGMH), and quantum theory of atoms in molecules (QTAIM)to clarify the thermodynamic stability and the microscopic interaction mechanisms that govern adsorption of 6PPD/6PPD-Q on Au16 nanoclusters. Second, computed UV-visible and Raman spectra reveal an intrinsic link between interfacial adsorption and spectral response: the UV-visible spectra undergo pronounced redshifts upon adsorption, and the Raman signals of the pollutants' characteristic functional groups are substantially enhanced and display distinct frequency shifts. These results clarify the intrinsic electronic coupling and charge-transfer behavior at the 6PPD/6PPD-Q@Au16 interface and establish a quantitative structure-property relationship linking interfacial adsorption to Raman spectral changes. The study provides systematic theoretical insight and benchmark computational data for understanding molecule-noble metal nanocluster interactions and lays a theoretical foundation for the rational design of sensing substrates for tire-derived environmental pollutants.