International audienceThe simple reaction of chitosan with metallic salts yields (chitosan) (MLn)(x), MLn = MnCl2, CoCl2, NiCl2, macromolecular complexes which, after a thermal treatment at 800 degrees C under air, give nanostructured Mn2O3, Co3O4 and NiO. The polymer acts as a template in the solid state, which is eliminated after the combustion process. At an intermediate stage, a layered graphitic carbon matrix was observed by HRTEM over the grown metal oxides. A mechanism for the growth of nanostructured oxides is discussed, including Raman studies. The nanostructured Mn2O3, Co3O4 and NiO particles grow over graphite layers and the solid-state role of chitosan is crucial for the formation of this graphite substrate. An antiferromagnetic transition was observed in Co3O4 nanoparticles, with T-N = 38 K, whereas NiO nanoparticles behave as a superparamagnetic material with a blocking temperature above 300 K
Bimetallic Au/Ag nanostructures have been included inside SiO 2 by pyrolysis of the macromolecular complexes Chitosan(MLn/M'Ln) n •SiO 2 and PSP-4-PVP⋅(MLn/M'Ln)n•SiO 2 with MLn = AuCl 3 and M'Ln = Ag(CF 3 SO 3). The structural characterization was performed by XRD (X-ray diffraction of powder) and UV-vis, and the microstructural characterization was done by SEM/ EDS analysis HRTEM. The resulting products from the pyrolytic precursors PSP-4-PVP•(AuCl 3 /AgSO 3 CF 3) n •SiO 2 1:1 (1), PSP-4-PVP•(AuCl 3 /AgSO 3 CF 3) n •SiO 2 1:5 (2) , Chitosan•(AuCl 3 /AgSO 3 CF 3) n •SiO 2 1:1 (3) and Chitosan •(AuCl 3 /AgSO 3 CF 3) n •SiO 2 1:5 (4) were Au/Ag//SiO 2 , Au// SiO 2 and Ag// SiO 2 as well as isolated Au and Ag, depending on the polymeric precursor. The Chitosan polymer precursor induces mainly Ag and Ag/SiO 2 nanostructures, while PSP-4-PVP induces mainly Au/Ag nanostructures. This can be explained by the facility to link Ag + to the NH 2 and OH groups of Chitosan than to the pyridine of PSP-4-PVP. On the contrary, Au +3 exhibits most coordination ability to pyridine groups of PSP-4-PVP than NH 2-and OHgroups of Chitosan. EDS mapping analysis indicates a uniform distribution of the Au/Ag nanostructure inside the SiO 2 matrix. Using reflectance diffuse analysis, the plasmon is consistent with the Au/Ag alloys structure.
Novel bimetallic Au/Ag superstructures have been prepared from solid-state pyrolysis of the macromolecular complexes Chitosan(MLn/M'Ln) n y PSP-4-PVP×( MLn/M'Ln)n with MLn = AuCl 3 and M'Ln = Ag(CF 3 SO 3 ).The characterization was made from XRD (X-ray diffraction of powder), SEM and EDS analysis. Morphologies are influenced by both the nature of the polymer and the metal/polymer, molar ratio of the polymer precursor. EDS analysis suggests a core/shell Au/Ag structure for the materials. A probable mechanism of the formation of these superstructures is discussed. Although separated reports of metallic superstructures of Au or Ag have been recently described, the here reported are the first bimetallic Au/Ag.
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