title: Seedless synthesis of nanocomposites, optical properties, and effects of additives on their surface resonance plasmon bands.
abstract: The work describes an easy seedless competitive chemical reduction method for the synthesis of Ag@Au/Ag bimetallic nanoparticles by mixing AgNO3, HAuCl4and cysteine. Transmission electron microscope (TEM) images show that the large number of irregular, cross-linking, and aggregated Ag@Au/Ag are formed in a reaction mixture (HAuCl4+AgNO3+cysteine), whereas flower-like nanocomposites are obtained in presence of cetyltrimethylammonium bromide (CTAB), which acted as a shape-directing agent. Optical images reveal that the initially reaction proceeds through formation of purple color, which changes into dark brown color with the reaction time, indicating the formation of Ag@Au/Ag nanocomposites. The Ag+has strong tendency to form complex with cysteine. Firstly, the reduction of Ag+ions to Ag0occurred by the HS group of the cysteine-Ag complex. Secondly, AuCl4-ions adsorbed on the positive surface of Ag0, which undergoes reduction by potential deposition, and leads to the formation of Ag@Au/Ag bimetallic nanoparticles. Inorganic electrolytes (NaCl, NaBr, NaNO3and Na2SO4) have significant impact on the stability and aggregation of Ag@Au/Ag nanocomposites.
authors.affiliation: Department of Chemistry, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21413, Saudi Arabia. Electronic address: zzkhan@kau.edu.sa.
authors.forename: Zoya
authors.initials: Z
authors.lastname: Zaheer
authors.affiliation: Department of Chemistry, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21413, Saudi Arabia.
authors.forename: Elham Shafik
authors.initials: ES
authors.lastname: Aazam
keywords: Au@Ag; Bimetallic; Cysteine; Seedless