An automated method to determine the band gap energy ( E g ) of pure and mixed powder compounds using diffuse reflectance spectroscopy is presented. This method is based on a five-step algorithm that mimics the judgment made by an expert analyst in identifying the linear segments in Tauc plots and subsequent estimation of the E g value. It is demonstrated that the method to estimate E g by intersecting the straight-line fit of the Tauc segment with the photon energy axis is not appropriate for those samples containing more than one optical absorbing phase because systematic underestimation of the E g value results. The automated method accounts for such cases by introducing a base line function. The robustness of the implemented algorithm was tested using three model systems, ZnO-Al 2 O 3 , ZnO-CoO and ZnO-CdO. The estimated E g 's using the automated method differ in less than 1% than those obtained by its manual counterpart.

A simple, economical, and environmentally friendly method for the production of layered double hydroxides (LDHs) is presented. The synthesis procedure is based on dispersing insoluble metal oxides, adjusting the pH by adding an optimum amount of metal nitrates, and dispersing and aging the product for a short time (6-8 h). The final product does not require washing, opposite to the traditional coprecipitation synthesis procedure. A dissolution-precipitation-recrystallization mechanism is proposed for the formation of LDHs, based on particle size measurements, XRD analyses, radial distribution functions, and 27 Al MAS NMR studies. Solids were characterized by XRD, N 2 physisorption, TGA-DTA, SEM, and TEM, revealing that both LDHs and their calcination products have very similar properties to those prepared by conventional procedures. Pure LDH phase is obtained after 6-8 h; a large, uniform particle size that would usually require prolonged hydrothermal treatments is attained. Surface areas ranged from 32 to 93 m 2 g -1 and from 140 to 230 m 2 g -1 for fresh and calcined samples, respectively. This new method is intended to satisfy the growing demand of LDHs in large-scale applications as catalysts, SO x adsorbents, PVC additives, etc.

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