Extracting structural information of Au colloids at ultra-dilute concentrations: identification of growth during nanoparticle immobilization.

George F Tierney,Martha Briceno De Gutierrez,Donato Decarolis,Alberto Villa,Scott M Rogers,Paul Collier,C Richard A Catlow,Peter P Wells,Nikolaos Dimitratos,Shusaku Hayama,Norli Abdullah

doi:10.1039/c9na00159j

Abstract

Sol-immobilization is increasingly used to achieve supported metal nanoparticles (NPs) with controllable size and shape; it affords a high degree of control of the metal particle size and yields a narrow particle size distribution. Using state-of-the-art beamlines, we demonstrate how X-ray absorption fine structure (XAFS) techniques are now able to provide accurate structural information on nano-sized colloidal Au solutions at μM concentrations. This study demonstrates: (i) the size of Au colloids can be accurately tuned by adjusting the temperature of reduction, (ii) Au concentration, from 50 μM to 1000 μM, has little influence on the average size of colloidal Au NPs in solution and (iii) the immobilization step is responsible for significant growth in Au particle size, which is further exacerbated at increased Au concentrations. The work presented demonstrates that an increased understanding of the primary steps in sol-immobilization allows improved optimization of materials for catalytic applications.

Highlights

IntroductionThe study of supported metal nanoparticles (NPs) is a cornerstone of heterogeneous catalysis; their reduced size, distribution of surface sites, and interaction with metal oxide supports afford enhanced catalytic properties as well as providing effective use of noble metals.[1,2,3,4,5] Within the various routes typically used to produce supported metal NPs, the application of solimmobilization is becoming increasingly popular; it offersThere have been many elegant studies that have assessed the in uence of these parameters, primarily relying upon advanced electron microscopy to provide structural information on the nal supported catalyst.[3,19,20] to understand better the preparation of supported NPs through sol-immobilization, further insights into all steps in the process are needed
Using state-of-the-art beamlines, we demonstrate how X-ray absorption fine structure (XAFS) techniques are able to provide accurate structural information on nano-sized colloidal Au solutions at mM concentrations
This study demonstrates: (i) the size of Au colloids can be accurately tuned by adjusting the temperature of reduction, (ii) Au concentration, from 50 mM to 1000 mM, has little influence on the average size of colloidal Au NPs in solution and (iii) the immobilization step is responsible for significant growth in Au particle size, which is further exacerbated at increased Au concentrations

Summary

Introduction

The study of supported metal nanoparticles (NPs) is a cornerstone of heterogeneous catalysis; their reduced size, distribution of surface sites, and interaction with metal oxide supports afford enhanced catalytic properties as well as providing effective use of noble metals.[1,2,3,4,5] Within the various routes typically used to produce supported metal NPs, the application of solimmobilization is becoming increasingly popular; it offersThere have been many elegant studies that have assessed the in uence of these parameters, primarily relying upon advanced electron microscopy to provide structural information on the nal supported catalyst.[3,19,20] to understand better the preparation of supported NPs through sol-immobilization, further insights into all steps in the process are needed. Au NPs are one of the most intensely studied nano-particulate systems due to the wide range of potential applications, from medicine to catalysis.[21] Recent approaches to study the structural properties of colloidal solutions of Au NPs, have utilised high brilliance X-rays, produced by synchrotron radiation, for small angle X-ray scattering (SAXS) and X-ray absorption ne structure (XAFS) investigations Much work in this area has followed the formation of Au NPs using time-resolved studies;[21,22,23,24,25,26] the intention is to understand the principal steps in the evolution from de ned precursors to NP entities. They have continually increased their sophistication, moving from simple sample environments, such as a large volume cells, towards precision engineered micro uidic reactors[28,29] or acoustic levitation systems.[21]

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