Papers by Author: Lorena L. Garza-Tovar

Abstract: Perovskite-type compounds such as alkali tantalates, ATaO3 (A = Li, Na and K), prepared by the sol-gel method are reported as heterogeneous basic catalysts for the acetone aldol condensation. It has been proposed that the activity order and the selectivity patterns (LiTaO3 > > KTaO3 > NaTaO3) depend on the octahedral arrangements of the TaO6 tantalates.

Abstract: A kaolin obtained from a region near to San Luis Potosí (México) was characterized by X-ray powder diffraction (DRX), optical microscopy (OM), scanning electron microscopy (SEM), X-ray fluorescence (XRF), thermal analysis (DTA/TGA), and chemical analysis. Mineralogical and morphological characteristics of the mineral are presented. The kaolin sample was formed mainly by kaolinite, but other minor phases were also detected such as quartz, cristobalite, trydimite, and dolomite. For iron lixiviation process, concentrate HCl was employed. The high content of volcanic glass detected, evidenced by optical microscopy, revealed an incomplete kaolinization process of the raw material. In agreement with these results, X-ray fluorescence analysis showed high- SiO2 and low-Al2O3 content in the sample as is expected on weakly kaolinized materials.

Abstract: The catalytic photodegradation of Rhodamine B with UV irradiation over NaMO3 (M= Ta and Nb) doped with Y2O3, La2O3, Nd2O3 and Sm2O3 has been studied in our laboratories. All catalysts were characterized by different techniques such as X-ray powder diffraction (XRD) and thermal analysis (DTA/TGA). Surface characterization of the solids was carried out from adsorption isotherms and infrared spectroscopy (FTIR). The band gap energy (Eg) of materials ranged from 4.1 to 2.9 eV. For comparative purpose the materials studied as catalysts were also synthesized by classical solid state reaction.

Abstract: Ceramic compound with the formula BaLi2Ti6O14 was prepared by sol-gel method at basic conditions, using ammonium hydroxide as hydrolysis catalyst. Some portions of gel sample obtained were heat treated at 200, 400, 600, and 800°C. Samples were characterized by X-ray diffraction (XRD), thermal analysis (DTA-TGA), UV-Vis and FTIR. Crystalline phase was formed when a sample was treated at 800°C for 6h. This material has been previously synthesized by solid state reaction using temperatures as high as 900-1150°C for 2 to 10 days. The crystal structure of BaLi2Ti6O14 is similar to that corresponding strontium containing phase, SrLi2Ti6O14, which has been reported as catalyst for oxidative dehydrogenation of lower alkanes.

Abstract: The photocatalytic activity of samples of the new ceramic semiconductor, Na2ZrTi5O13 sol-gel, was studied using two different reactions, the decomposition (oxidation) of methylene blue and reduction-oxidation of Pb (II) from aqueous solutions at room temperature. We synthesised Na2Ti5ZrO13, which is isostructural to the family of compounds with general formula AnMTimO13, (A = Li, Na, K; M = Zr). These materials present a zig zag arrangement forming rectangular tunnels in their structure. The synthesis of this compound was achieved by sol-gel technique using metalic alcoxides at two different pH, 3 and 9. The fresh gels were heat treated at 200°C, 400°C, 600°C and 800°C. The reaction products were characterized by X-ray diffraction (XRD), thermal analysis (DTA, TGA) and infrared spectroscopy (FTIR). The band gap energy (Eg) of each sample prepared was calculated from the UV-Vis absorption spectra. . The values of Eg obtained ranged from 3.5 to 3.2 eV. The best activity found for the methylene blue degradation was performed by the Na2ZrTi5O13 sol-gel pH 9, treated at 800oC (99%). We assumed that the photocatalytic activity is favored when the structure was already formed. Lead photocatalysed reactions using Na2ZrTi5O13 sol-gel pH 9, treated at 600 oC showed a higher eficiency (98%) than that obtained by TiO2 (degussa) (85%).