Lorena L. Garza-Tovar

Synthesis of sol–gel Na2Zr x Ti6−x O13 (0≤x≤1) materials and their performance in photocatalytic degradation of organic dyes

In this work we present the synthesis and characterization of four compositions of the solid solution with the general formula Na2ZrxTi6−xO13 (0≤x≤1) which was prepared by a sol-gel method. The main goal of this work is to evaluate the influence of the incorporation of different amounts of zirconium into the binary phase Na2Ti6O13 on two properties: the textural surface and Eg values. This titanate phase crystallizes in a monoclinic unit cell and is built into an octahedral TiO6 framework forming a rectangular tunnel structure. Additionally, we have compared their photocatalytic performances in degradation of organic dyes under visible light. The heat-treated sol-gel samples were characterized by X-ray powder diffraction, N2 physisorption, thermal analysis, UV and FT-IR spectroscopy. According to the X-ray powder diffraction results, the new ternary tunnel compound Na2ZrTi5O13 was obtained as a single phase at 800°C. The cell parameters for the two end-member phases of that solid solution were refined to confirm that Zr ion was incorporated into the structural framework. This ternary compound had an Eg value of about 2.9 eV. The activity of all heat-treated Na2ZrTi5O13 samples was tested in the photocatalytic degradation of methylene blue and Rhodamine B under visible light. The Na2ZrTi5O13 calcined at 400°C showed the best performance with 95% of photodegradation of methylene blue and a half time t1/2 of 15 min.

Photocatalytic Activity of Doped NaTaO3 and NaNbO3 : (Y, La, Nd, Sm) Sol Gel on Degradation of Rhodamine B by UV Irradiation

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.

Ultrasonic irradiation-assisted synthesis of Bi2S3 nanoparticles in aqueous ionic liquid at ambient condition

In this work, an easy, fast and environmentally friendly method to obtain Bi2S3 nanostructures with sphere-like morphology is introduced. The promising material was successfully synthesized by a sonochemical route in 20% 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtSO4] ionic liquid solution (IL). Morphological studies by electron microscopy (SEM and TEM) show that the use of IL in the synthesis of Bi2S3 favors the formation of nanocrystals non-agglomerated. Micro Raman and energy dispersive X-ray spectroscopy (EDXS) were used to determine the composition and purity of the synthesized material. X-ray powder diffraction (XRD) and selective area electron diffraction (SAED) revealed that ultrasonic radiation accelerated the crystallization of Bi2S3 into orthorhombic bismuthinite structure. The band gap calculated from the diffuse reflectance spectra (DRS) was found to be 1.5eV.

Photocatalytic Behavior of Na2ZrTi5O13 Sol-Gel

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%).

Aluminum doped Na3V2(PO4)2F3 via sol–gel Pechini method as a cathode material for lithium ion batteries

The solid solution series Na3V2-xAlx(PO4)2F3 (where x = 0, 0.02, 0.05, and 0.1) powders have been prepared using the Pechini method to study the effect of aluminum doping on the electrochemical properties of these cathode materials for lithium ion batteries. The structure, composition, and morphology of the compounds were investigated by X-ray diffraction, thermogravimetric and differential analysis, specific surface area, and pore size analysis using Brunauer-Emmett-Teller—Barret-Joyner-Halenda methods, scanning electron microscopy, elemental chemical analysis with induced coupled plasma-optical emission spectroscopy and charge/discharge galvanostatic experiments. X-ray diffraction indicates a tetragonal crystal structure for the Na3V2(PO4)2F3 phase, and all the Al compositions. The materials obtained have a microstructure consisting of nanoparticles (40–100 nm) with an average pore size 20 nm and 30 m2/g surface area. The phase with 0.05 moles of aluminum gave the best result electrochemical charge/discharge capacities of 123 to 101 mAh/g with cell voltage of 4.4 V vs. Li and a capacity retention of 82%, compared to undoped material which gave 128 to 63 mAh/g, and 49% capacity retention. Hence, Al-doped samples showed better electrochemical performance maybe attributable to improved structure stability compared to the undoped material. Those results suggest a promising material for lithium ion batteries.Graphical Abstract

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.

Preparation of Ternary Compound BaLi2Ti6O14 by the Sol-Gel Process

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.

Sol-Gel Synthesis and Photocatalitic Properties of Bi2MNbO7 (M = Al, Fe, In y Sm)

A family of ceramic compounds with general formula of Bi2MNbO7 (M = In, Al, Fe, Sm) were prepared by both processes of sol-gel and solidstate reaction. The resulting fresh gels were subjected to different heat treaments at 200, 400, 600 and 800°C for 4 h. Reaction products were characterized by X-ray diffraction (XRD), thermal analysis (DTA-TGA), specific surface area (using BET method), UV-Vis and FT-IR. Sol-gel technique has many advantages compared to the conventional methods in preparing raw materials and catalysts. Photocatalytic activity of each compound was determined, by testing them in the degradation reaction of methylene blue at room temperature. The decomposition rate was calculated applying the Langmuir-Hinshelwood model. We have found that photocatalytic activity is favored when the structure of each compound has not been formed. According to the t1/2 (half life) and k (kinetic constants) values, samples of Bi2FeNbO7 sol-gel treated at 400°C presented the highest photocatalytic activity. Photodegradation of methylene blue showed that the photocatalysts obtained by the sol-gel method exhibited higher activity than those prepared by solid state reaction and also higer than the well-know TiO2 (Degussa P-25) photocatalyst. At low temperature such as 400°C, crystalline phases were not detected in any of the componds prepared by sol-gel method. INTRODUCTION The past two decades have witnessed a growing interest in advanced oxidation techniqueheterogeneous photocatalysis, for waste water treatment and water purification [1,2]. The photocatalysis process can break down a large variety of organic compounds, especially trace organics, to carbon dioxide, water and mineral ions [3]. Waste waters generated by textile industries are known to contain considerable amounts of non fixed dyes and especially of azo-dyes [4]. The search for new materials with higher activity than that of TiO2 has been one of the most active areas in heterogeneous photocatalysis. [5-7]. However, until now the number of photocatalyst materials has been limited. Regarding dye removal we can mention that it has been investigated the photocatalytic degradation of five various types of dyes (such as methylene blue) in TiO2/UV aqueous suspensions [8]. Recent works reported a new serie of ceramic photocatalysts, Bi2MNbO7 (M = Al 3+ , Ga 3+ , In 3+ ). These compounds were synthesized by solid state reaction with the A2 3+ B2 4+ O7 pyrochlore structure and presented photocatalytic activity for water conversion to H2 and O2 [9,10]. Other members of this family, containing Fe, Sm, La and Pr 3+ also were reported as photocatalytic materiales for water conversion [11]. On the other hand, the method of preparation affect the physicochemical properties of solids and these in turn affect the catalytic activity [12]. In this work we prepared a pyrochlore family both by sol-gel in basic medium and by solid state reaction. The purpose of this study is to investigate the photocatalitic degradation of methylene blue. Materials Science Forum Online: 2005-06-15 ISSN: 1662-9752, Vols. 486-487, pp 85-88 doi:10.4028/www.scientific.net/MSF.486-487.85

Mineralogical Characterization of Villa Reyes México Kaolin for Industrial Applications

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.