Self-Assembly and Raman Spectroscopy of Additive Coated Nanocrystals
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1176-Y06-20
Self-Assembly and Raman Spectroscopy of Additive Coated Nanocrystals
Julien Romann1,2, Virginie Chevallier1,2, Alexandre Merlen1,2 and Jean-Christophe Valmalette1,2* 1 Université du Sud Toulon Var, IM2NP 2 CNRS, IM2NP (UMR 6242) Bâtiment R, BP 20132, F-83957 La Garde Cedex, France
ABSTRACT Copper oxalate 1 µm-sized nanocrystalline assemblies with several shapes (cushions, lenses, drilled cushions, and square rods) have been obtained by aqueous precipitation without additive, with glycerol, with PEG and with HPMC. Respective influences of these additives on the nanocrystals self-assembly are suggested from the obtained particles morphologies to provide a better understanding of this assembly process. Raman spectroscopy is used to highlight fluorescence occurring on the copper oxalate samples synthesized with additives. This additive induced fluorescence is suggested to result from specific interactions between the nanocrystals and the adsorbed additives.
INTRODUCTION Designing nanostructures by simple experimental methods has become a major goal in a scale (from a few nanometers (nm) to a hundred microns (µm)) where conventional means of manipulation are poorly adapted. A promising bottom-up way to design new nanostructures is being explored through copper oxalate (CuOx) which particles morphology can be modified in presence of additives during its aqueous precipitation. A previous work has shown that micronscaled particles shaped as cushions, cubes, square rods and finally thin cylindrical rods can successively be obtained by using hydroxypropylmethylcellulose (HPMC) as an additive and by increasing its concentration.1 The nanostructural feature of these particles was recently confirmed through the observation of nano-holes on their faces as well as single CuOx nanocrystals in the aqueous dispersion, and a self-assembly mechanism of the nanocrystals to supracrystalline assemblies has also been proposed.2 The previously observed effect of some additives on the nanocrystalline CuOx assemblies morphology is not clearly understood yet. The way these additives interact with CuOx nanocrystals during their self-assembly and the resulting modifications in the self-assembly mechanism still has to be precisely determined. The effect of the four additives used in this study on the CuOx assemblies shape is observed by scanning electron microscopy (SEM). In addition, Raman spectroscopy is used in an unusual way to investigate the presence of adsorbed additives on the CuOx assemblies by analyzing Raman scattering and fluorescence emission at the same time.
EXPERIMENTAL DETAILS Copper oxalate (CuC2O4, n.H2O with 0 ≤ n < 1) was precipitated in water using copper nitrate dihydrate (Cu(NO3)2.2H2O) and sodium oxalate (Na2C2O4) aqueous solutions. The precipitation was carried out by adding the two reactant solutions (4x10-2 mol/L of Cu(NO3)2.2H2O and Na2C2O4 respectively) to a CuOx saturated solution (2.22x10-4 mol/L of Cu(NO3)2.2H2O and Na2C2O4). All these solutions were adjusted to pH = 5 using HNO3 and NaOH. The pr
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