Effect of Plant-Extract Liquid Media on the Plasmonic and Morphological Properties of Au and Au/Ag Nanoparticles Synthesized by Pulsed Laser Ablation in Liquids

Objectives Gold nanoparticles (Au NPs) and gold/silver bimetallic nanoparticles (Au/Ag BNPs) were synthesized via pulsed laser ablation in liquid (PLAL) process in distilled water, along with, for the first time, in the Haloxylon persicum and Tamarix plant extracts. Material and Methods Plant extracts play an important role in modifying the characteristics of NPs, including morphology, optical properties, and colloidal stability. Haloxylon persicum and Tamarix plant extracts were used as a liquid medium for the ablation of Au NPs and Au/Ag BNPs in the PLAL technique. Results Analysis of the UV-Vis spectra reveals a red shift of the surface plasmon resonance (SPR) band between 500 and 550 nm in Au NPs due to tuning of the dielectric environment, capping with phytochemicals, and plasmonic coupling between NPs. For the Au/Ag BNPs, there are two absorption bands: one at 390-450 nm, and another between 500 and 550 nm. Transmission electron microscopy (TEM) shows that the mean size of Au NPs decreases from about 35 nm in distilled water to 8–13 nm in extracts, while the mean size of Au/Ag bimetallic NPs increases from 9 nm to 10–23 nm with primarily spherical morphology. It is noteworthy that the overall red shift of the plasmon peaks is due to the predominance of the effects of the medium dielectric constant and particle coupling over the decrease in NP size, which normally causes a blue shift. The photoluminescence spectrum exhibits excitation-dependent and double emission, resulting from the presence of surface states and NP-environment interaction. Conclusion Zeta potential and conductivity studies indicate that plant extracts enhanced stability by passivating the NP surface using organic capping.