Nanohíbridos de porfirinas e nanoestruturas de Nb2O5 e TiO2: preparo, avaliação do papel do agente de acoplamento APTES e estudo fotocatalítico

Abstract

Titanium dioxide (TiO2) and niobium pentoxide (Nb2O5) are semiconductor metal oxides that stand out in heterogeneous photocatalytic studies, which are environmental purification technologies commonly used in the contaminants’ degradation using visible or ultraviolet (UV) light. However, the application of these materials is limited by the use of UV radiation due to their wide observed band gap (3.0-3.5eV). Therefore, strategies such as photosensitization of these oxides with dyes, like porphyrins, can be adopted to expand the absorption region of these semiconductors for visible light. This work aimed to obtain hybrids of H2T4SPP@TiO2 and H2T4SPP@Nb2O5, in which H2T4SPP is a porphyrin. They could be able to absorb energy in the visible light region through the strategy of using 3-aminopropyltriethoxysilane (APTES) as a molecular bridge. Their application in the degradation of rhodamine B dye under UV and visible light was also studied. The experimental stages of this work consisted of (I) obtaining the starting materials (commercial P25, TiO2 produced by CTNano/UFMG and Nb2O5); (II) surface activation with NaOH; (III) surface functionalization with APTES; (IV) immobilization of the H2T4SPP4- porphyrin to the functionalized nanomaterial; (V) photocatalytic tests under UVC and visible light. The quantification of available terminal amino groups from APTES and the quantification of porphyrin immobilized to metal oxides were carried out, respectively, using the Kaiser test and loading calculation. Surface functionalization with APTES was confirmed through Infrared (IR), Thermogravimetry, and Raman techniques; the IR was essential for identifying organosilane due to the presence of bands referring to Ti-O-Si, Nb-O-Si, and Si-O-Si bonds. The formation of APTES multilayers was identified by transmission electron microscopy images, demonstrating the occurrence of vertical polymerization. The immobilization of porphyrin to functionalized oxides was evidenced by loading and by the diffuse reflectance technique (DRS), in which it was possible to observe the presence of the Soret (418 nm) and Q bands of the porphyrin in the absorption spectra of the obtained hybrids. The H2T4SPP@TiO2 and H2T4SPP@P25 hybrids were photoactivated in UV or visible light, demonstrating the possible formation of a type II heterojunction. In contrast, the H2T4SPP@Nb2O5 hybrid did not lead to the photodegradation of RhB in UVC or visible light, only the occurrence of photolysis processes being distributed, which may have occurred due to the APTES multilayers formed on the oxide surface; it may prevent the light absorption by the semiconductor in UVC region and the electron transfer under visible light.