A Study of the Influence of Percentage of Copper on the Structural and Optical Properties of Au-Cu Nanoparticle

Here we present our experimental results in synthesizing Au-Cu nano-particles with tunable localized surface plasmon resonance frequency through wet-chemical at temperature room. The reaction is performed in the presence of ascorbic acid as a reducing agent and polyvinyl pyrrolidone as capping agent via four different procedures: (1) mixture of 90% HAuCl4 and 10% CuSO4.5H2O precursors, (2) mixture of 75% HAuCl4 and 25% CuSO4.5H2O precursors, (3) mixture of 50% HAuCl4 and 50% CuSO4.5H2O precursors (4) mixture of 25% HAuCl4 and 75% CuSO4.5H2O precursors. Effect of different percentages of Cu on Au nanoparticles has been analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM with EDAX analysis), DRS UV-Vis, and Fourier transform IR spectra (FTIR) analysis. X-ray diffraction (XRD) analysis revealed that the nanoparticles are of cubic structure without an impure phase. The successful doping of the Cu into the Au host was evident by XRD line shiftings. The increasing percentage of copper leads to the decreasing grain size. With the increase of Cu2+ to Au3+ ratio in the Cu2+/Au3+ mixed solution (> 50% Cu), XRD lines show no shifting. The average crystal sizes of the particles at room temperature were less than 9.9 nm. The surface plasmon resonance peak shifts from 380 to 340 nm, party due to the change in particle size. SEM images show a spherical shape and the size of nanoparticles becomes smaller with increasing the percentage of copper. Moreover, in the molar ratio of Cu2+/Au3+ = 75/25 (>50% Cu), mixture of spherical and trigonal nanoparticles were prepared. Fourier transform infrared spectroscopy (FT-IR) showed the coordination and conjugation nanoparticles with N and O atoms of C-N and C=O bonds.