Effect of pH on Au Nanorods in Ag Ion-Assisted Seed-Mediated Growth

Au nanorods (NRs) with different aspect ratios were synthesized using a silver ion-assisted seed-mediated growth method through controlling the pH of solutions using hydrochloric acid to adjust the pH values of solutions. The Au NRs with longitudinal absorption peak range from 713 nm to 916 nm were fabricated by adjusting the concentrations of silver nitrate, hydrochloric acid, and cetyltrimethy-lammonium bromide in the growth solution. It was found that silver ions and hydrochloricacid were used together to systematically tune the shape and size of Au NRs. H⁺ ions other than Cl^- ions play important role to govern the growth of Au NRs. Au NRs with a large aspect ratio and high yield can be synthesized in a relative high silver nitrate concentration and a low pH value. In optimal conditions, the Au NRs reveal an average diameter of 10 nm and length of 60 nm. Namely, the Au NRs became slender at a lower pH value and higher concentration of the AgNO₃ in the growth solution.