Fe 3 O 4 nanoparticles were synthesized and functionalized with (3-aminopropyl) trimethoxysilane (APTMS) and chitosan, forming Fe 3 O 4 -NH 2 and Fe 3 O 4 -NH 2 -chitosan nanoparticles. The Fe 3 O 4 nanoparticles were synthesized by a co-precipitation method and functionalization was performed in further stages. The nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential, and transmission electron microscopy (TEM). The results of XRD showed that magnetite did not experience an oxidation reaction. The functionalization of the surface of Fe 3 O 4 nanoparticles was confirmed by FTIR and zeta potential measurements. The TEM results showed a thin layer around Fe 3 O 4 nanoparticles due to the functionalization with the APTMS. The later functionalization by chitosan contributed to the agglomeration of nanoparticles. Functionalization provided the nanoparticles better colloidal stability mainly for a pH below 7 and this improvement was related to the protection and new functional groups from the APTMS and chitosan.

The surface of Fe 3 O 4 nanoparticles is very reactive and can oxidize to γ-Fe 2 O 3 (maghemite) and α-Fe 2 O 3 (hematite) structures. Based on this, the oxidation process of Fe 3 O 4 nanoparticles must be prevented, and one of the strategies is surface functionalization with organic or inorganic molecules. Thus, this study analyzed the thermal behavior of Fe 3 O 4 and Fe 3 O 4 -EDTA nanoparticles using X-ray diffraction (XRD), simultaneous thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC). Results showed that γ-Fe 2 O 3 was obtained as an intermediate in Fe 3 O 4 and Fe 3 O 4 -EDTA decomposition, as confirmed by TG-DTA and DSC curves. Moreover, Fe 3 O 4 -EDTA exhibited a temperature peak (T p = 573.5°C) of phase transformation (γ-Fe 2 O 3 → α-Fe 2 O 3 ) higher than that of Fe 3 O 4 (T p = 533.0°C), confirming that EDTA molecules stabilized the nanoparticles efficiently. The kinetic behavior of samples changed, and the activation energy for functionalized samples decreased.

This study investigated the synthesis, characterization of ZnO nanostructures using different precipitating agents in the photodegradation of rhodamine B (Rh B) using scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared (FTIR) and UV/Vis spectroscopy and zeta potential measurements. The results indicated the dependence of morphology on calcination temperature and the precipitating agent. The colloidal stability of these nanomaterials is affected with the morphology changed. The photocatalytic results showed that ZnO nanostructures synthesized with NH4OH (98.98%) were more efficient in the degradation of Rh B than ZnO nanostructures synthesized with NaOH (62.68%). This is related to ZnO (NH4OH) nanoparticles should present a higher density of electronic defects than ZnO (NaOH), producing energy levels between the band gaps. These results are potentially associated with a combination of optical and geometric factors that create other paths for the generation of electron-hole pairs in the precipitated ZnO nanocatalyst with different alkaline solutions.