Nanostructured copper oxides and phosphates from a new solid-state route

Correlation between structure, chromaticity, and dielectric properties of calcium copper pyrophosphates, Ca2-xCuxP2O7

The solid-state reaction was employed to synthesize Ca_2−xCu_xP₂O₇ by varying the mole ratio between Ca and Cu. The structure and crystallography of the pyrophosphate compounds were identified and confirmed by using X-ray diffraction (XRD). The Rietveld refinement method and the extended X-ray absorption fine structure (EXAFS) least-squares fitting technique were also applied to refine the sample crystal structure. The single phases of the obtained Ca₂P₂O₇, CaCuP₂O₇, and Cu₂P₂O₇ samples and the mixing phases of the obtained Ca_1.5Cu_0.5P₂O₇ and Ca_0.5Cu_1.5P₂O₇ samples were identified, and then only a single phase of the samples was subjected to structural and dielectrical analyses. The structural results exhibit the tetragonal crystal system with the P4₁ space group for β-Ca₂P₂O₇, the monoclinic crystal system with the P2₁/c space group for CaCuP₂O₇, and the C2/c space group for α-Cu₂P₂O₇. The dielectric constant (ε_r) of the single metal pyrophosphates (Ca₂P₂O₇ and Cu₂P₂O₇) was higher than that of binary metal pyrophosphates (CaCuP₂O₇). The image sensor result of the Cu₂P₂O₇ sample (x = 2.00) illustrated a yellowish-green color, while other compounds (x = 0.50−1.50) presented color tones that changed from blue-green to bluish-green. Raman and Fourier transform infrared (FTIR) spectrophotometers were employed to characterize and confirm the vibrational characteristics of the P₂O₇⁴⁻ group, which contains the O–P–O radical ([PO₂]^-) and the P–O–P bride ([OPO]^-) and approximate M–O stretching modes. Furthermore, this work reports for the first time that the change in the crystal structure of Ca_2−xCu_xP₂O₇ (i.e., bond angle of P−O−P in P₂O₇⁴⁻ and distortion phenomena in the M−O₆ octahedral site) are cause the correlation between the structure, chromaticity, and dielectric properties of calcium copper pyrophosphates, Ca_2−xCu_xP₂O₇.

Solid-State Preparation of Metal and Metal Oxides Nanostructures and Their Application in Environmental Remediation

Nanomaterials have attracted much attention over the last decades due to their very different properties compared to those of bulk equivalents, such as a large surface-to-volume ratio, the size-dependent optical, physical, and magnetic properties. A number of solution fabrication methods have been developed for the synthesis of metal and metal oxides nanoparticles, but few solid-state methods have been reported. The application of nanostructured materials to electronic solid-state devices or to high-temperature technology requires, however, adequate solid-state methods for obtaining nanostructured materials. In this review, we discuss some of the main current methods of obtaining nanomaterials in solid state, and also we summarize the obtaining of nanomaterials using a new general method in solid state. This new solid-state method to prepare metals and metallic oxides nanostructures start with the preparation of the macromolecular complexes chitosan·Xn and PS-co-4-PVP·MXn as precursors (X = anion accompanying the cationic metal, n = is the subscript, which indicates the number of anions in the formula of the metal salt and PS-co-4-PVP = poly(styrene-co-4-vinylpyridine)). Then, the solid-state pyrolysis under air and at 800 °C affords nanoparticles of M°, M_xO_y depending on the nature of the metal. Metallic nanoparticles are obtained for noble metals such as Au, while the respective metal oxide is obtained for transition, representative, and lanthanide metals. Size and morphology depend on the nature of the polymer as well as on the spacing of the metals within the polymeric chain. Noticeably in the case of TiO₂, anatase or rutile phases can be tuned by the nature of the Ti salts coordinated in the macromolecular polymer. A mechanism for the formation of nanoparticles is outlined on the basis of TG/DSC data. Some applications such as photocatalytic degradation of methylene by different metal oxides obtained by the presented solid-state method are also described. A brief review of the main solid-state methods to prepare nanoparticles is also outlined in the introduction. Some challenges to further development of these materials and methods are finally discussed.

Insights of the formation mechanism of nanostructured titanium oxide polymorphs from different macromolecular metal-complex precursors

The insight into the mechanism of the unprecedented formation of pure anatase TiO2 from the macromolecular (Chitosan)•(TiOSO4)n precursor has been investigated using micro Raman spectroscopy, Scanning Electron Microscopy (SEM) and thermogravimetric/differential thermal analysis (TGA/DTA). The formation of a graphitic film was observed upon annealing of the macromolecular precursor, reaching a maximum at about 500 °C due to decomposition of the polymeric chain of the Chitosan and (PS-co-4-PVP) polymers. The proposed mechanism is the nucleation and growth of TiO2 nanoparticles over this graphitic substrate. SEM and Raman measurements confirm the formation of TiO2 anatase around 400 °C. The observation of an exothermic peak around 260 °C in the TGA/DTA measurements confirms the decomposition of carbon chains to form graphite. Another exothermic peak around 560 °C corresponds to the loss of additional carbonaceous residues.

Synthesis and magnetic properties of nanostructured metallic Co, Mn and Ni oxide materials obtained from solid-state metal-macromolecular complex precursors

Reaction of chitosan with metallic salts gives nanostructured Mn₂O₃, Co₃O₄ and NiO. Graphitic carbon is formed over the nanostructured oxides.

Solvent-less method for efficient photocatalytic α-Fe2O3 nanoparticles using macromolecular polymeric precursors

Efficient photocatalytic degradation of persistent cationic dye pollutants under visible light is possible with Fe₂O₃ nanoparticles formed by solvent-less synthesis using macromolecular precursor design.