Isaías Juárez-Ramírez

Photodegradation of indigo carmine and methylene blue dyes in aqueous solution by SiC–TiO2 catalysts prepared by sol–gel

Indigo carmine and methylene blue dyes in aqueous solution were photodegraded using SiC-TiO(2) catalysts prepared by sol-gel method. After thermal treatment at 450°C, SiC-TiO(2) catalysts prepared in this work showed the presence of SiC and TiO(2) anatase phase. Those compounds showed specific surface area values around 22-25 m(2)g(-1), and energy band gap values close to 3.05 eV. In comparison with TiO(2) (P25), SiC-TiO(2) catalysts showed the highest activity for indigo carmine and methylene blue degradation, but this activity cannot be attributed to the properties above mentioned. Therefore, photocatalytic performance is due to the synergy effect between SiC and TiO(2) particles caused by the sol-gel method used to prepare the SiC-TiO(2) catalysts. TiO(2) nanoparticles are well dispersed onto SiC surface allowing the transfer of electronic charges between SiC and TiO(2) semiconductors, which avoid the fast recombination of the electron-hole pair during the photocatalytic process.

Methylene blue degradation by NaTaO3 sol-gel doped with Sm and La.

In this work, NaTaO(3) compounds doped with 1M% of La and Sm, were prepared by the sol-gel (SG) method and solid state (SS) reaction; and tested as photocatalysts on the degradation of methylene blue (MB) under UV light. The structural characterization by X-ray powder diffraction revealed that the crystallization of the NaTaO(3) phase prepared by the sol-gel method started at 600 degrees C, reaching maximum crystallization at 800 degrees C. It was determined that the presence of Sm and La retard the crystallization of the NaTaO(3) phase. On the other hand, the compounds synthesized in this work showed particle sizes in the nanometric scale, as it was observed by scanning electron microscopy (SEM). The specific surface area of the compounds synthesized by the sol-gel method, showed values 4 times higher than those obtained by the solid state reaction, favoring their functional and photocatalytic performance in the methylene blue degradation. In addition, the best photocatalytic performance was shown by the NaTaO(3) doped with Sm and heated at 600 degrees C, having a half-life time of 65 min.

Sm2FeTaO7 Photocatalyst for Degradation of Indigo Carmine Dye under Solar Light Irradiation

This paper is focused to study Sm2FeTaO7 pyrochlore-type compound as solar photocatalyst for the degradation of indigo carmine dye in aqueous solution. Sm2FeTaO7 was synthesized by using conventional solid state reaction and sol-gel method. X-ray diffraction results indicated that Sm2FeTaO7 exhibit a monoclinic crystal structure. By scanning electron microscopy analysis, it was observed that sol-gel material presents particle size of around 150 nm. The specific surface area and energy bandgap values were 12 m2 g−1 and 2.0 eV, respectively. The photocatalytic results showed that indigo carmine molecule can be degraded under solar light irradiation using the synthesized materials, sol-gel photocatalyst was 8 times more active than solid state. On the other hand, when Sm2FeTaO7 was impregnated with CuO as cocatalyst the photocatalytic activity was increased because CuO acts as electron trap decreasing electron-hole pair recombination rates.

Sol-Gel Preparation of Bi2InTaO7 and its Photocatalytic Behavior for Organic Compounds Degradation

In this work it was carried out the synthesis of Bi2InTaO7 pyrochlore-type structure compound by the sol-gel method. By X-Ray powder diffraction the sol-gel compound calcined at 600°C showed the pyrochlore-type structure phase and by scanning electron microscopy its morphology revealed the presence of particles with size lower than 1 micron. Its chemical elemental composition was determined by EDS analysis. Results of SBET area and Eg values of this compound suggested higher properties than those obtained by the compound prepared by solid state reaction. Bi2InTaO7 sol-gel was used as active photocatalyst on the degradation reaction of organic compounds such as Alizarin Red S, and Red and Green Tide, under UV-light. Half time life results showed that Bi2InTaO7 sol-gel compound could be a good candidate for the degradation of organic compounds because after few minutes showed high efficiency on the degradation reaction of Alizarin Red S (t1/2 = 30 min), and Green Tide inactivation (t1/2 = 17 min).

Structure Sensitivity of Sol-Gel Alkali Tantalates, ATaO3 (A= Li, Na and K): Acetone Gas Phase Condensation

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.

Development of Porous Material with High Young’s Modulus and Low Thermal Expansion Coefficient in SiC-Vitrified Bonding Material-LiAlSiO4 System

Machines for manufacturing large scale flat displays are enlarging as the size of glasses increases. This work develops porous materials with a low thermal expansion coefficient and a high Young’s modulus. SiC and LiAlSiO4 were used for a positive and a negative thermal expansion materials, respectively. Compositions of powders for porous materials were determined to obtain a desirable Young’s modulus and thermal expansion coefficient by using SiC-VBM-LiAlSiO4 phase diagram at 20 % of porosity. The empirical values of Young’s modulus and a thermal expansion coefficient are close to the theoretical values by using the diagram. Fabricated porous material had high enough Young’s modulus of 87 GPa, and low enough thermal expansion coefficient of 2 x 10-6 K-1 at temperatures ranging from -17 °C to 190 °C with 22 % of porosity.

Fabrication of low thermal expansion SiC/ZrW2O8 porous ceramics

Low or zero thermal expansion porous ceramics are required for several applications. In this work near zero thermal expansion porous ceramics were fabricated by using SiC and ZrW2O8 as positive and negative thermal expansion materials, respectively, bonded by soda lime glass. The mixture of SiC, ZrW2O8 and soda lime glass was sintered by Pulsed Electric Current Sintering (PECS, or sometimes called Spark Plasma Sintering, SPS) at 700 °C. Sintered samples with ZrW2O8 particle size smaller than 25 μm have high thermal expansion coefficient, because ZrW2O8 has the reaction with soda lime glass to form Na2ZrW3O12 during sintering process. The reaction between soda lime glass and ZrW2O8 is reduced by increasing particle size of ZrW2O8. Sintered sample with ZrW2O8 particle size 45-90 μm shows near zero thermal expansion.

Use of Fly Ash as Bonding Material on Low Thermal Expansion Porous Materials

In this work it was determined the effect of fly ash (FA) as bonding material during the fabrication of low thermal expansion porous materials. SiC, fly ash, Vitrified Bonding Material (VBM), and LiAlSiO4 powders were used as raw materials. Porous materials were sintered at 850°C and 950°C after manual milling and mechanical milling in a planetary ball milling at 800 RPM. SEM micrographs showed the presence of porous materials, and it was observed that fly ash particles did not melt at 850°C. However if sintering temperature increases at 950°C, FA starts to melt and it is forming bridges between SiC particles. Thermal expansion values were around 3.0x10-6 K-1. According to these results, it seems that it is possible to have a favorable synergy between FA and VBM to fabricate SiC porous materials with low thermal expansion values.

Comparison of Porous Ceramic Materials with Low Thermal Expansion Coefficient Prepared with SiC and Black-Al2O3

Porous ceramic materials with low thermal expansion (LTE) at room temperature were prepared by heating a mixture of SiC or black-Al2O3, vitrified bonding material (VBM) and LiAlSiO4 at temperatures from 850°C to 1100°C. The mixture was prepared in adequate proportions to obtain a material with LTE according to previous works made in our laboratory. It was observed that a change in temperature provoked the formation of a new phase, LiAlSi3O8, which appears above 900°C. The presence of this new phase did not affect the thermal expansion value, keeping LTE at room temperature. All compounds showed around 40% of porosity, and Young’s modulus values of 30 GPa using black-Al2O3 or SiC. X-ray diffraction analysis (XRD) revealed that above 900°C the phase LiAlSi3O8 starts to appear as a consequence of the melting of VBM, which is reacting with the raw materials. SEM micrographs showed the presence of SiC or black-Al2O3 grains joined by VBM, which is acting as a bridge between them.