Synthesis of Stable Aluminum Nanoparticles at Varying Reactant Concentrations and Their Surface-Enhanced Raman Scattering Activity

Aluminum nanoparticles (Al NPs) were synthesized via catalyzed thermal reduction of an aluminum precursor in the presence of a capping ligand. A systematic study was conducted to examine the effect of dilution on nanoparticle synthesis by varying the volume of anhydrous toluene across four dilution factors while maintaining constant molar quantities of the aluminum precursor, catalyst, and ligand. This methodology is relevant for scale-up processes, where more dilute conditions can mitigate nanoparticle reactivity and enhance safety. The resulting Al NPs were characterized with respect to the yield, size distribution, chemical composition (bulk and surface), and morphology. Consistent and favorable yields were observed across all of the dilution conditions. The synthesized Al NPs were further evaluated as low-cost substrates for surface-enhanced Raman spectroscopy (SERS). While Au and Ag nanoparticles are known to exhibit SERS activity in the visible region for chemical warfare agent (CWA) surrogates, little is known about SERS performance in the ultraviolet (UV) region by using metallic substrates. Al NPs, with broadband optical absorption extending from the UV to the near-infrared (NIR), were investigated for this application. Rhodamine 6G (R6G), a standard dye, and dimethyl methylphosphonate (DMMP), a commonly used CWA surrogate, were analyzed by using 248.6 nm UV excitation. The Al NPs exhibited modest SERS activity for both analytes under these conditions. To the best of our knowledge, this is the first report to examine both the synthesis of Al NPs under varying reagent concentrations by changing the solvent volumes and their SERS performance in the UV region for CWA surrogates. Further efforts aimed at reducing particle agglomeration and tailoring surface chemistry are expected to improve sensitivity and enable the development of cost-effective SERS-based sensors for trace CWA detection.