Separating selenium species by diffusion in Brazilian bentonite: a mathematical modeling approach.

Bentonite was applied in diffusive studies for selenium, an emerging contaminant. The planar source method was used to determine the apparent and effective diffusion coefficients and assess the mobility of the selenium species. A double Gaussian function described the results. Different diffusion coefficients were associated with different mobilities, and consequently, to the coexistence of two selenium species: selenite and selenate. Apparent diffusion coefficients were higher for selenate, around 10- 10 m2 s- 1, than for selenite, around 10- 12 m2 s- 1. Results from sequential extraction and distribution coefficient justified selenate's greater mobility than selenite. Since the increase in redox potential from 448 to 511 mV may be associated with selenite oxidation in an interconversion process, the diffusion in bentonite demonstrates that applications in geological barriers deserve attention regarding the mobilization of selenium species. Interconversions can mobilize selenium, as reduced species can shift to more oxidized and mobile species, enhancing environmental contamination.

Determination of metal content in industrial powder ink and paint thickness over steel plates using X-Ray Fluorescence.

The Energy Dispersive X-Ray Fluorescence (EDXRF) is a well stablished technique that may be used in quality control of industrial processes. In this study, it was proposed an analysis of a two commercial powder inks widely used in the industry. The goals were to determine the composition of the ink by quantifying its inorganics elements by EDXRF, and check if the amount of toxic elements matches with Restriction of Certain Hazardous Substances (RoHS) and with "Norma Brasileira" (NBR) regulations. Moreover, to build Partial Least Squares Regression (PLSR) models to predict the thickness of the ink layer applied over steel plates using EDXRF data. Evaluating the quantitative results, it was found that some samples presented toxic elements, such as Cr and Pb. The PLSR results ranged from 54 µm to 97 µm with an average relative deviation of 1% compared to the conventional method used for thickness determination (magnetic method). The results show that EDXRF is a reliable alternative technique to determine the metal elements on the powder ink composition. Furthermore, a (PLSR) model can be used to determine the thickness of the ink applied over steel plates.

Characterization of Cu2O/TiO2NTs nanomaterials using EDXRF, XRD and DRS for photocatalytic applications.

TiO2 nanotube arrays (TiO2NTs) were decorated with Cu2O nanoparticles by pulse electrochemical deposition. The Cu2O nanoparticles were uniformly distributed onto TiO2NTs surface and with diameter varying between 50 and 200 nm. The effects of the independent variables on the photocatalytic response were simultaneously assessed by a multivariate statistical design. Energy-Dispersive X-Ray Fluorescence, X-Ray Diffraction, FEG-SEM and Diffuse Reflectance Spectroscopy were employed to Cu2O/TiO2NTs characterization. The Cu2O films obtained on TiO2NTs surface were crystalline. DRS analysis confirmed that the modification of TiO2NTs with Cu2O nanoparticles improved the quantum efficiency of the material. The Cu2O/TiO2NTs photoelectrode shows an intense absorption peak in the visible region decreasing the band gap energy from 3.20eV for TiO2NTs to 2.96 eV for Cu2O/TiO2NTs.