RESUMO
The optical properties of 5wt% Fe3O4-TiO2 thin films were evaluated in detail with the aim of proposing a mechanism for solar photocatalytic processes and highlighting the advantages over the use of bare TiO2. The results showed that the incorporation of 5wt% Fe3O4 enhanced the optical properties by a redshift to a wavelength in the visible range, reducing the anatase/rutile band gap energy from 3.2 eV to 2.8 eV. Photoluminescence studies reveal a superior separation efficiency of photoexcited electron-hole pairs when Fe3O4 nanoparticles (NPs) are present in the photocatalyst. X-ray photoelectron spectroscopy spectra confirm the presence of Fe3O4 and existence of a chemical bonding between TiO2 and Fe3O4 NPs. Moreover, in this study, a mechanism of solar photocatalytic processes involving Fe3O4-TiO2 thin films is proposed and it is supported by experimental results. Finally, solar photocatalytic experiments were carried out, indicating that the effectiveness for the removal of the selected pharmaceutical is considerably improved when the composite material is used as catalyst. Furthermore, it was demonstrated that the photocatalytic activity of the prepared Fe3O4-TiO2 thin films depends on their thickness, achieving the highest pharmaceutical removal yields using the 2 µm thick sample. The stability and reusability of the catalyst was confirmed studying the photocatalytic activity over three cycles.
RESUMO
BACKGROUND: Engineered stone silicosis is an emerging disease in many countries worldwide produced by the inhalation of respirable dust of engineered stone. This silicosis has a high incidence among young workers, with a short latency period and greater aggressiveness than silicosis caused by natural materials. Although the silica content is very high and this is the key factor, it has been postulated that other constituents in engineered stones can influence the aggressiveness of the disease. Different samples of engineered stone countertops (fabricated by workers during the years prior to their diagnoses), as well as seven lung samples from exposed patients, were analyzed by multiple techniques. RESULTS: The different countertops were composed of SiO2 in percentages between 87.9 and 99.6%, with variable relationships of quartz and cristobalite depending on the sample. The most abundant metals were Al, Na, Fe, Ca and Ti. The most frequent volatile organic compounds were styrene, toluene and m-xylene, and among the polycyclic aromatic hydrocarbons, phenanthrene and naphthalene were detected in all samples. Patients were all males, between 26 and 46 years-old (average age: 36) at the moment of the diagnosis. They were exposed to the engineered stone an average time of 14 years. At diagnosis, only one patient had progressive massive fibrosis. After a follow-up period of 8 ± 3 years, four patients presented progressive massive fibrosis. Samples obtained from lung biopsies most frequently showed well or ill-defined nodules, composed of histiocytic cells and fibroblasts without central hyalinization. All tissue samples showed high proportion of Si and Al at the center of the nodules, becoming sparser at the periphery. Al to Si content ratios turned out to be higher than 1 in two of the studied cases. Correlation between Si and Al was very high (r = 0.93). CONCLUSION: Some of the volatile organic compounds, polycyclic aromatic hydrocarbons and metals detected in the studied countertop samples have been described as causative of lung inflammation and respiratory disease. Among inorganic constituents, aluminum has been a relevant component within the silicotic nodule, reaching atomic concentrations even higher than silicon in some cases. Such concentrations, both for silicon and aluminum showed a decreasing tendency from the center of the nodule towards its frontier.
