Silver-loaded silica/H-ZSM-5 nanocomposite as a sensitive SERS substrate for the detection of sulfur-containing compounds in diesel fuel

Detection of sulfur-containing compounds in petroleum products is considered an important subject of research for both academia and industry. However, the utilization of surface-enhanced Raman scattering (SERS) spectroscopic methods in that direction has not been well explored. The fluorescence interference and the complexity of the constituents of oil samples represent a challenge to implement spectroanalytical SERS protocols for the characterization of sulfur contaminants. In this study, a combined nanocomposite of silver-loaded silica and H-ZSM-5 (Si/Al₂ = 150) material was employed to identify different concentrations of dibenzothiophene (DBT) in commercial diesel fuel. While silver nanoparticles enhanced Raman signals associated with the DBT molecules, zeolitic materials helped in reducing the fluorescence background, and hence being able to approach a low detection level. The DBT in diesel samples could be successfully traced up to 10⁻⁷ M of concentration by interpreting the SERS peak at 1611 cm⁻¹ which is associated with the aromatic CC stretching vibration. Full characterization of the nanocomposite substrate before and after its components being combined have been performed using FT-IR, Raman, powder-XRD, BET-N₂ sorption, ICP-OES, and SEM techniques. In addition, a meaningful vibrational assignment of the SERS spectrum of DBT has been established on the basis of literature and the density-functional theory (DFT) calculation.