Mechanistic Study of the Electrodeposition of Nanoporous Self-Assembled ZnO/Eosin Y Hybrid Thin Films: Effect of Eosin Concentration
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- 作者：Auré ; lie Goux ; Thierry Pauporté ; Tsukasa Yoshida ; Daniel Lincot
- 刊名：Langmuir
- 出版年：2006
- 出版时间：December 5, 2006
- 年：2006
- 卷：22
- 期：25
- 页码：10545 - 10553
- 全文大小：256K
- 年卷期：v.22,no.25(December 5, 2006)
- ISSN：1520-5827
文摘
ZnO films prepared by one-step electrodeposition in the presence of dissolved eosin molecules present an internalnanoporous hybrid structure resulting from self-assembling processes occurring in solution between ZnO and eosincomponents. This study aims to better understand the underlying growth mechanism, which is still unexplained. Thefilms were deposited by cathodic electrodeposition from an oxygen-saturated aqueous zinc chloride solution. Theeffects of the addition of 10 to 100 
mol·L-1 eosin Y, as a sodium salt, on the growth rate and film properties, weresystematically studied while all other parameters remained constant (concentrations of zinc salt and supporting electrolyte,applied potential of -1.4 V versus the mercurous sulfate electrode (MSE), temperature of 70 
C, rotating disk electrodeat 300 rotations per min, and a glass-coated tin oxide electrode). It is shown that the addition of eosin provokes theformation of a nanoporous "cauliflower" structure whose nodule size and composition depend on the eosin concentrationin the bath. The growth rate of the hybrid films increases markedly with the eosin concentration. The ZnO and eosincontents of the films are determined for each concentration by chemical analysis. Comparing with thickness determinations,it is shown that the total porosity increases up to 60-65% in volume fraction toward an eosin concentration of 100mol·L-1. The empty pore volume fraction increases up to about 30% at an eosin concentration of about 20 mol·L-1and then decreases. These correlations have been precisely established for the first time. It is shown that the globalcomposition is fixed by the relative rate of deposition for zinc oxide, which is constant, and for the relative rate ofeosin inclusion, which is proportional to the concentration in solution. This is explained on the basis of different stepsin the growth mechanism, in particular, a diffusion effect limitation for both oxygen and eosin. This variation explainspart of the increase in the growth rate. Another contribution is related by the structural effect on the nanoscale leadingto the formation of the interpenetrated porous network. Competition between empty and eosin-filled parts of the porenetwork is evidenced. The formation of the porous network structure could be governed by a diffusion-limited aggregationmechanism. The system may represent a reference case of competing reactions in the electrochemical self-assemblyof hybrid nanostructures.
mol·L-1 eosin Y, as a sodium salt, on the growth rate and film properties, weresystematically studied while all other parameters remained constant (concentrations of zinc salt and supporting electrolyte,applied potential of -1.4 V versus the mercurous sulfate electrode (MSE), temperature of 70 C, rotating disk electrodeat 300 rotations per min, and a glass-coated tin oxide electrode). It is shown that the addition of eosin provokes theformation of a nanoporous "cauliflower" structure whose nodule size and composition depend on the eosin concentrationin the bath. The growth rate of the hybrid films increases markedly with the eosin concentration. The ZnO and eosincontents of the films are determined for each concentration by chemical analysis. Comparing with thickness determinations,it is shown that the total porosity increases up to 60-65% in volume fraction toward an eosin concentration of 100mol·L-1. The empty pore volume fraction increases up to about 30% at an eosin concentration of about 20 mol·L-1and then decreases. These correlations have been precisely established for the first time. It is shown that the globalcomposition is fixed by the relative rate of deposition for zinc oxide, which is constant, and for the relative rate ofeosin inclusion, which is proportional to the concentration in solution. This is explained on the basis of different stepsin the growth mechanism, in particular, a diffusion effect limitation for both oxygen and eosin. This variation explainspart of the increase in the growth rate. Another contribution is related by the structural effect on the nanoscale leadingto the formation of the interpenetrated porous network. Competition between empty and eosin-filled parts of the porenetwork is evidenced. The formation of the porous network structure could be governed by a diffusion-limited aggregationmechanism. The system may represent a reference case of competing reactions in the electrochemical self-assemblyof hybrid nanostructures.