## 3 Results and Discussion
The only exception is the Cu nanoflowers, constituted of metallic Cu\({}^{0}\) according to X-ray diffraction and X-ray spectroscopy measurements [43], obtained by a wet chemical process using CuI(acac)\({}_{2}\)], acac = acetylacetonate as the reagent, oleyl amine both as the solvent and reducing agent, and cetyltrimethylammonium bromide as the capping agent. We extrapolated that the main driving force used to obtain the Cu nano-roses from red onion peels is the high temperature applied during the annealing process performed in the inert nitrogen atmosphere. This produced both the expulsion of copper from its original organic molecules and the prevention of the oxidation onset to finally give rise to these particular Cu nanostructures. One cannot, however, exclude that the presence of elemental carbon may catalyze the Cu\({}^{0}\) nano-rose formation. In this respect, experiments are in progress to elucidate the actual mechanism of the formation of this new kind of Cu agglomeration, addressing both the physical and chemical aspects involved. This is a crucial point to clarify considering that both our results and those of [43] demonstrate that it is possible to obtain Cu\({}^{0}\) crystalline structures that are stable in air. In the past, Ag structures have been obtained from the reaction of silver nitrate and ascorbic acid in an acidic aqueous solution of polynaphthalene [44]. Such structures are composed of metallic Ag\({}^{0}\) nanoparticles of about 10 nm in diameter linearly ordered inside a filamentous polymer sheath with a mesometric morphological structure in the flower form of about 10 microns in diameter, having meso-petals of a lancoolate shape. This constitutes an example where the Ag nanoparticles are kept chemically inert by a polymeric protective sheath that surrounds them. On the contrary, in the case of our copper nano-roses, as also reported in [43], the structures are self-protected against any oxidation or sulfurization, coming from air or from the precursors of the pyrolyzed carbon nanostructures. To validate this result, the ED-XRD spectrum was collected on the carbon nanostructures as a function of the quantum momentum scattering parameter. In Figure 4, we can easily observe the presence of four peaks, two of which are assigned to the (002) and (101) reflections of the graphitic form of carbon indexed according to ICCD card number 00-001-0640 and corresponding to interplanar spacings with d = 3.380 A and d = 2.020 A, respectively; the other two are attributed to the (111) and (200) diffraction peaks of metallic copper [ICCD card number 00-001-1241] and are due to the interplanar spacings with d = 2.080 A and d = 1.810 A, respectively [21; 24; 25; 43]. It is worth noting that the (110), (002), (-111), (111), and (200) diffraction peaks from CuO, which are expected in the region between 2.1 and 2.9 A\({}^{-1}\)[21; 24; 25], are completely absent in Figure 4, confirming the EDS results. Indeed, the most intense reflection of CuO, (-111) at 20 = 35.744\({}^{\circ}\) (ICDD Reference code: 00-001-1117), would have been located at q = 2.50 A\({}^{-1}\), and is clearly absent. Furthermore, the presence of crystalline CuS (ICDD Reference code: 00-07-0876) is also excluded: the main (103) reflection peak should have been located at q = 2.23 A\({}^{-1}\)[45] and is missing in our pattern. Finally, Figure 5 displays the Raman spectrum from the C nanostructures. Two main peaks labelled D and G, located at 1386 and 1587 cm\({}^{-1}\), are related to the E\({}_{\text{2g}}\) in the plane vibrational mode of the hexagon atoms in the honeycomb C graphitic arrangement and to the defects peak [46; 47; 48]. The G-mode peak is found at 1587 cm\({}^{-1}\). Such a value, slightly blue-shifted with respect to highly crystalline graphite (G-mode at about 1580 cm\({}^{-1}\)) [46; 47; 48], can be attributed to the nanometric-sized C-particles. This agrees with [46; 47; 48], where a frequency shift of about 15 cm\({}^{-1}\) towards higher wavenumbers was found in some samples with extremely small graphite crystal sizes [46].