A pH-Induced Size Controlled Deposition of Colloidal Ag Nanoparticles on Alumina Support for Catalytic Application

Abstract

A rational synthetic method of supported metal catalysts has been proposed. Highly dispersed Ag nanoparticles (NPs) with a mean diameter of ca. 10 nm and a narrow size distribution have been prepared in the presence of 3-mercaptopropionic acid (3-MPA) as a protective reagent. The zeta electric potential of the Ag NPs was negatively charged in the region of pH higher than 5 due to the presence of dissociated carboxylate ion (−COO−), which led to the electric repulsion between Ag NPs. On the other hand, the electric charge gradually increased in the region of pH less than 5 owing to the formation of a protonated carboxyl group (−COOH), which induced the hydrogen bonding between Ag NPs. Such pH-triggered assembly dispersion control enables a strong protocol to deposit Ag NPs with different diameters on the positively charged Al2O3 support by electrostatic attraction. The obtained Ag/Al2O3 materials were characterized by means of UV−vis spectra and transmission electron microscopy (TEM), and the catalytic activities were evaluated in the reduction of 4-nitrophenol in water. The reaction rate increased with increasing pH of the prepared colloidal solution, which is correlated with the decreasing size of the Ag NPs. The reduction of 4-nitrophenol is considered as a structure-insensitive reaction, and all surface atoms of the Ag NPs act catalytically as the same active species in this size range by performing calculations on the Ag crystallites.

Anionic Amphiphilic Cyclodextrins Bearing Oleic Grafts for the Stabilization of Ruthenium Nanoparticles Efficient in Aqueous Catalytic Hydrogenation

“…The zeta potential of Ru_OS‐β‐CD NPs was measured and equal to −41 mV. This value was in good agreement with zeta potential values measured for NPs stabilized in the presence of carboxylate functions (between −40 mV and −60 mV) . This value is also in correlation with good stability of the colloidal suspension in the aqueous phase.…”

“…This value was in good agreement with zeta potential values measured for NPs stabilized in the presence of carboxylate functions (between À 40 mV and À 60 mV). [9] This value is also in correlation with good stability of the colloidal suspension in the aqueous phase. As a control, Ru_β-CD NPs have been synthesized from Ru(NO)(NO 3 ) 3 and native β-CD to study the influence of the grafting on the cyclodextrin backbone on the dispersion and the size of the Ru NPs.…”

Design and assembly of ternary Pt/Re/SnO2 NPs by controlling the zeta potential of individual Pt, Re, and SnO2 NPs

“…The mechanism of surface charging is reported in detail in the monograph by Kosmulski ( 2009 ). However, it is well known that electrostatic interactions, besides pH, are strongly influenced by ionic strength and/or use of ligands for nanoparticle stabilization (Mori et al 2009 ).…”

コロイド状および担持ナノ粒子の設計─その合成，構造解析と触媒作用─

“…10 nm stabilized by 3-mercaptopropionic acid (3-MPA) as a colloidal precursor solution 56) . The synthetic strategy is illustrated in Fig.…”