Bimetallic Ag_(core)/Au_(shell) and Au_(core)/Ag_(shell) core-shell nanoparticles are synthesized in aqueous phase using simple citrate reduction method with variations for both sets in the reaction conditions during the fabrication of shell structure, i.e., change in salt concentration, temperature (from 25 to 100 °C), and pH for salt solutions (from 2 to 12). The surface plasmon resonance effect, size and morphology, elemental composition, crystalline structure, and crystallite size were observed for these bimetallic core-shell nanoparticles using techniques such as UV-Vis spectroscopy, SEM, EDX, and XRD respectively. The size observed for Ag_(core)/Au_(shell) nanoparticles was 50 ± 6 nm, and Au_(core)/Ag_(shell) nanoparticles was 64 ± 8 nm. Increasing the concentration of salt for Au or Ag shows better coating and increase in shell thickness as observed by surface plasmon resonance (SPR) peaks. At lower temperatures, generally, agglomeration occurs or in case of Au_(core)/Ag_(shell) nanoparticles, formation of Ag₃O₄ occurs; however, at higher temperatures, homogenous small-sized nanoparticles with higher crystallinity are formed. For Ag_(core)/Au_(shell) nanoparticles, at pH 4, best uniformly distributed nanoparticles are formed with higher crystallinity; however for Au_(core)/Ag_(shell) nanoparticles, pH 7 is the optimal pH, where uniformly sized nanoparticles with higher crystalline structure are formed.

Graphical Abstract

使用简单的柠檬酸盐还原法在水相中合成双金属Ag _（核） / Au _（壳）和Au _（核） / Ag _（壳）核-壳纳米粒子，并在水相中合成壳结构过程中两组反应条件的变化，即盐溶液的盐浓度，温度（从25到100°C）和pH值（从2到12）的变化。使用紫外-可见光谱，SEM，EDX和XRD等技术分别观察了这些双金属核壳纳米粒子的表面等离子体共振效应，尺寸和形态，元素组成，晶体结构和微晶尺寸。Ag _（核） / Au _（壳）的尺寸纳米颗粒为50±6 nm，Au _（核） / Ag _（壳）纳米颗粒为64±8 nm。通过表面等离振子共振（SPR）峰观察到，增加Au或Ag的盐浓度会显示出更好的涂层和壳厚度的增加。通常，在较低温度下会发生团聚，或者在Au _（核） / Ag _（壳）纳米粒子的情况下会发生Ag ₃ O _4的形成。然而，在更高的温度下，会形成具有更高结晶度的均质小尺寸纳米颗粒。对于Ag _（核） / Au _（壳）纳米颗粒，在pH 4时，可形成具有较高结晶度的最佳均匀分布纳米颗粒。但是对于金_（核心）/ Ag _（壳）纳米粒子，pH 7是最佳pH，在此形成具有较高晶体结构的大小均一的纳米粒子。

图形概要