Reactivity and Chemical Sintering of Carey Lea Silver Nanoparticles.

Sergey Vorobyev,Alexander Romanchenko,Yuri Mikhlin,Elena Vishnyakova,Maxim Likhatski,Ivan Nemtsev

doi:10.3390/nano9111525

Abstract

Carey Lea silver hydrosol is a rare example of very concentrated colloidal solutions produced with citrate as only protective ligands, and prospective for a wide range of applications, whose properties have been insufficiently studied up to now. Herein, the reactivity of the immobilized silver nanoparticles toward oxidation, sulfidation, and sintering upon their interaction with hydrogen peroxide, sulfide ions, and chlorocomplexes of Au(III), Pd(II), and Pt(IV) was investigated using SEM and X-ray photoelectron spectroscopy (XPS). The reactions decreased the number of carboxylic groups of the citrate-derived capping and promoted coalescence of 7 nm Ag NPs into about 40 nm ones, excluding the interaction with hydrogen peroxide. The increased nanoparticles form loose submicrometer aggregates in the case of sulfide treatment, raspberry-like micrometer porous particles in the media containing Pd(II) chloride, and densely sintered particles in the reaction with inert H2PtCl6 complexes, probably via the formation of surface Ag-Pt alloys. The exposure of Ag NPs to HAuCl4 solution produced compact Ag films along with nanocrystals of Au metal and minor Ag and AgCl. The results are promising for chemical ambient temperature sintering and rendering silver-based nanomaterials, for example, for flexible electronics, catalysis, and other applications.

Highlights

Silver nanoparticles (Ag NPs) attract considerable attention from a wide range of fields such as catalysis, printed electronics, optics, biomedicine, and so forth, with the wet chemical synthesis is the main route for their manufacturing [1,2,3]
The citrate-assisted synthesis of silver nanoparticles is hampered by a low rate of reaction, which proceeds at elevated temperature or requires of an additional reductant [5]
It is generally assumed that the properties of the Ag NPs are due to adsorbed citrate anions [8,9,10], it was recently demonstrated [14] that surface ligands are not citrate but the products of partial oxidation and decarboxylationof citrate, different on particles of distinct morphology

Summary

Introduction

Silver nanoparticles (Ag NPs) attract considerable attention from a wide range of fields such as catalysis, printed electronics, optics, biomedicine, and so forth, with the wet chemical synthesis is the main route for their manufacturing [1,2,3]. The very high-concentration Ag NPs sols are used as inks in the production of printed circuits and thin films with enhanced electric and thermal conductivity [3] and can provide large-scale synthesis of nanoparticles for other applications. In 1889, Carey Lea [6] has proposed a synthetic protocol involving silver nitrate, sodium citrate, and ferrous sulfate as reducing agent and yielding a stable, highly concentrated silver hydrosol at room temperature. The origin of the enhanced colloidal stability of the Carey Lea hydrosol is still unclear, since the studies devoted to these silver colloids and related immobilized particles are not numerous [7,8,9,10,11,12,13] and conducted with diluted sols. It is generally assumed that the properties of the Ag NPs are due to adsorbed citrate anions [8,9,10], it was recently demonstrated [14] that surface ligands are not citrate but the products of partial oxidation and decarboxylationof citrate, different on particles of distinct morphology

Objectives

Methods

Results