RESUMO
Thoria was prepared using a solid-state method from the macromolecular precursor Chitosan·Th(NO3)4 (chitosan) and PS-co-4-PVP·Th(NO3)4 (PVP). The morphology and the average size of ThO2 depend of the chitosan and PS-co-4-PVP polymer forming the precursor. Their photoluminescent properties were investigated, finding a dependence of their intensity emission maxima, with the nature of the precursor polymer. The photocatalytic activity of ThO2 toward the degradation of methylene blue was measured for the first time, finding a degradation of about 66% in 300 min. The inclusion of ThO2 into SiO2 and TiO2 was achieved by the solid-state pyrolysis of the macromolecular composites Chitosan·Th(NO3)4//MO2 and PS-co-4-PVP·Th(NO3)4//MO2, MO2 = SiO2 or TiO2. The ThO2 exhibits a homogeneous dispersion inside the silica, showing sizes of about 40 and 50 nm for the chitosan and PVP polymer precursors, respectively. The luminescent properties of the ThO2/SiO2 and ThO2/TiO2 composites were also studied, finding a decrease in intensity when introducing the SiO2 or TiO2 matrices. The photocatalytic behavior to methylene blue degradation of ThO2 and their composites ThO2/SiO2 and ThO2/TiO2 was investigated for the first time, with them in the following order: ThO2 > ThO2/TiO2 > ThO2/SiO2.
RESUMO
The medium effect of the optical and catalytic degradation of methylene blue was studied in the NiO/SiO2, NiO/TiO2, NiO/Al2O3, and NiO/Na4.2Ca2.8(Si6O18) composites, which were prepared by a solid-state method. The new composites were characterized by XRD (X-ray diffraction of powder), SEM/EDS, TEM, and HR-TEM. The size of the NiO nanoparticles obtained from the PSP-4-PVP (polyvinylpyrrolidone) precursors inside the different matrices follow the order of SiO2 > TiO2 > Al2O3. However, NiO nanoparticles obtained from the chitosan precursor does not present an effect on the particle size. It was found that the medium effect of the matrices (SiO2, TiO2, Al2O3, and Na4.2Ca2.8(Si6O18)) on the photocatalytic methylene blue degradation, can be described as a specific interaction of the NiO material acting as a semiconductor with the MxOy materials through a possible p-n junction. The highest catalytic activity was found for the TiO2 and glass composites where a favorable p-n junction was formed. The isolating character of Al2O3 and SiO2 and their non-semiconductor behavior preclude this interaction to form a p-n junction, and thus a lower catalytic activity. NiO/SiO2 and NiO/Na4.2Ca2.8(Si6O18) showed a similar photocatalytic behavior. On the other hand, the effect of the matrix on the optical properties for the NiO/SiO2, NiO/TiO2, NiO/Al2O3, and NiO/Na4.2Ca2.8(Si6O18) composites can be described by the different dielectric constants of the SiO2, TiO2, Al2O3, Na4.2Ca2.8(Si6O18) matrices. The maxima absorption of the composites (λmax) exhibit a direct relationship with the dielectric constants, while their semiconductor bandgap (Eg) present an inverse relationship with the dielectric constants. A direct relationship between λmax and Eg was found from these correlations. The effect of the polymer precursor on the particle size can explain some deviations from this relationship, as the correlation between the particle size and absorption is well known. Finally, the NiO/Na4.2Ca2.8(Si6O18) composite was reported in this work for the first time.
