Al2O3 Colloidal Nanocrystals with Strong UV Emission

A facile sol–gel procedure has been developed for the synthesis of colloidal alumina nanocrystals. For the first time, optical characterization procedures were employed to study the quantum confinement effects in optical properties of the prepared Al₂O₃ sol. Accordingly, the hyperbolic band model was used to determine the optical band gap of colloidal alumina nanocrystals. X‐Ray diffraction pattern was used to study the crystallographic phase of the dried gel. Morphological characterization was performed using scanning electron microscopy (SEM). Inductively Coupled Plasma (ICP) emission spectroscopy was used to determination purity of the Al₂O₃ powder. High‐resolution TEM showed that the diameter of colloidal nanocrystals is about 10 nm. Photoluminescence spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 68% with 300 nm excitation wavelength. The experimental observations confirm that highly stable alumina sol with strong UV emission was synthesized. The mentioned optical properties have not been reported before.     

Al2O3·2SiO2 powders synthesized via sol–gel as pure raw material in geopolymer preparation

Geopolymers are inorganic aluminosilicates mainly proposed as environmentally friendly building materials, which are obtained by alkali activation of natural minerals, calcined clay (e.g., metakaolin) and other aluminosilicate sources. The wide range of chemical and mineralogical compositions of these raw materials influences several properties of the obtained geopolymers. In the present work, pure Al₂O₃·2SiO₂ powders were synthesized via the sol–gel technique and proposed as pure aluminosilicate sources to prepare alkali activated geopolymers. Samples differing in the ratio between the SiO₂ precursor and the H₂O used in the sol–gel process were prepared, in order to study the effect of water content on the material structure and reactivity. The chemical structure of all the obtained Al₂O₃·2SiO₂ powders were characterized by Fourier transform infrared (FT‐IR) and solid‐state nuclear magnetic resonance (²⁷Al and ²⁹Si MAS NMR) spectroscopies and compared to that of a reference metakaolin. Moreover, material reactivity was evaluated by alkali activation of the samples. After 28 days of ageing, ²⁷Al and ²⁹Si MAS NMR and FT‐IR spectra ascertained the formation of a geopolymeric network in the activated samples. The results showed that lower water content allows obtaining a homogeneous Al‐rich geopolymer similar to that obtained, using metakaolin as raw material.     

The synthesis of colloidal zeolite TPA–silicalite-1

The synthesis of colloidal TPA–silicalite-1 from a clear xTPAOH–yH₂O–TEOS precursor sol, with x=0.01–0.443 and y=20–80, has been studied at 115°C. Both the starting sol and the reaction products at various times were examined by dynamic light scattering (DLS) to determine the size of the colloidal (or sub-colloidal) particles presented. In addition, the pH of the system has been measured. The observations made with the DLS were consistent with the literature results. In essence, uniform particles of colloidal zeolite were formed during the reaction, and their size grew linearly with reaction time. At the same time, sub-colloidal particles smaller than 5 nm were also observed that persisted throughout the process. The measured pH, on the other hand, could be satisfactorily modeled by the equilibrium theory, suggesting that an equilibrium distribution of dissolved silicates was established before the reaction, and a different equilibrium was attended when colloidal zeolites, as well as the co-existing sub-colloidal particles, were observed. The number density of the colloidal particles ρ was found to depend on the 3.4 power of the silica concentration and the ratio x.     

Studies on the synthesis of diacetyl over oxidation zeolite catalysts

Diacetyl (2,3-butanedione) synthesis from methyl ethyl ketone over oxidation zeolites using O₂ as oxidant was studied. Various zeolites with Fe, V and Ti as active sites were employed. VS-1, Ti-NCL, Ti-MCM-41 and FeBEA type materials were synthesized and characterized by BET, FTIR, XRD, pyridine adsorption and template desorption. The detailed study of the effect of reaction temperature, the effect of concentration of oxygen and the addition of water was realized. The most active catalyst was zeolites with V as oxidation center.     

High capacity cation exchanger by hydrothermal zeolitization of coal fly ash

During; hydrothermal treatment in NaOH medium coal fly ash partially transformed to zeolite P and/or hydroxysodalite, while quartz slowly dissolved and mullite remained stable. Residual coal favored the formation of zeolite P. The relative proportion of the two zeolites could be changed by seeding. During fusion of fly ash with NaOH an endothermic reaction at 170–180°C occurred, resulting in formation of an unreported Na aluminosilicate with approximate composition Na₁₅Si₄Al₃0₂₀ and major XIRD reflections at 4.793, 3.828, 3.000, 2.854, 2.578, and 2.524 Å. The product of fusion interacted with water giving aluminosilicate gel, which yielded zeolite P upon hydrothermal treatment at 100°C without aging and zeolite X after aging in water for 12 hours at room temperature. Cation exchange capacity was 420 and 400 meq/ 100 g for zeolite P and zeolite X respectively.     

TiO2 photocatalyst for degradation of organic compounds in water and air supported on highly hydrophobic FAU zeolite: Structural,sorptive, and photocatalytic studies

Preparation of highly hydrophobic FAU zeolite has been achieved by a two-step preparation method that comprises predealumination treatment using concentrated mineral acids and subsequent calcination treatment. The hydrophilic/hydrophobic character of the zeolites was estimated by detailed adsorption measurements using water and toluene molecules as adsorbates, which showed the strict hydrophobic nature of the prepared FAU zeolites. By means of TG, FT-IR, and ²⁹Si MAS NMR analyses, it was concluded that the enhancement in hydrophobicity originates from the healing of silanol defect sites and the formation of a refined silica surface with fewer adsorption sites. Thus-prepared FAU zeolite, with high crystallinity, structural and thermal stability, and hydrophobicity, significantly improved the photocatalytic degradation rates of 2-propanol in water and acetaldehyde in air on TiO₂ when it was used as a catalyst support. A distinct correlation was found between the hydrophobicity of zeolites and photocatalytic activity of the supported TiO₂.     

Composition and microstructure of alkali activated fly ash binder: Effect of the activator

The alkali activation of fly ashes is a chemical process by which the glassy component of these powdered materials is transformed into very well-compacted cement. In the present work the relationship between the mineralogical and microstructural characteristics of alkaline activated fly ash mortars (activated with NaOH, Na₂CO₃ and waterglass solutions) and its mechanical properties has been established. The results of the investigation show that in all cases (whatever the activator used) the main reaction product formed is an alkaline aluminosilicate gel, with low-ordered crystalline structure. This product is responsible for the excellent mechanical-cementitious properties of the activated fly ash. However the microstructure as well as the Si/Al and Na/Al ratios of the aluminosilicate gel change as a function of the activator type used in the system. As a secondary reaction product some zeolites are formed. The nature and composition of these zeolites also depend on the type of activator used.     

Electrochemical characterization of two different framework Ti(IV) species in Ti/Beta zeolites in contact with solvents

Five Ti/Beta zeolites prepared by the conventional hydroxide procedure or by using fluoride as mineralizer have been studied by cyclic voltammetry and pulse voltammetry. Three peak couples (AA′, BB′ and CC′) were recorded. The AA′ peak was due to Ti atoms leached to the solution. Peak BB′ is relatively insensitive to the electrolyte salt, while the reduction potential of CC′ decreases progressively from perchlorate or nitrate to chloride and bromide. This suggests the presence of two framework Ti populations, one less prone to expand its coordination number (proposed to be Ti(OSi≡)₄) and other Ti atoms that coordinate with ligands within the short timescales of the electrochemical measurements (either (≡SiO)₃TiOH or (≡SiO)₂Ti(OH)₂ titanols). This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of anatase nanostructured TiO2 particles at low temperature using ionic liquid for photocatalysis

Anatase nanostructured TiO₂ particles were synthesized at low temperature by a modified sol–gel method using water immiscible room temperature ionic liquid as an effective template. Anatase phase was formed at low temperature (100 °C) by effective aggregation of TiO₂ particles with a self-assembled IL in the sol. The photocatalytic activity of the prepared sample was tested for the degradation of 4-chlorophenol. The TiO₂ particle prepared with ionic liquid showed higher photocatalytic activity than that prepared with the conventional sol–gel method under identical conditions.     

TiO2/ZnO Supported on Sepiolite: Preparation,Structural Characterization,and Photocatalytic Degradation of Flumequine Antibiotic in Aqueous Solution

In this study, TiO₂, ZnO, TiO₂/ZnO (Ti/Zn), and TiO₂/ZnO/Sep (Ti/Zn/Sep) catalysts have been synthesized using sol–gel and chemical precipitation method. Their photocatalytic performances have been compared using Flumequine (FLQ) antibiotic. X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM), N₂-adsorption, and the determination of a zero point charge has been used to characterize the synthesized catalysts. The degradation studies showed that the catalytic efficiency of Ti/Zn/Sep is higher than that for other catalysts. The operational parameters such as pH, initial FLQ concentration, and catalyst dosage were evaluated. UV–vis and high-resolution mass spectroscopy (HRMS) analyses were used to determine the degradation efficiency and products. ZnO played a major role in the FLQ degradation process, and sepiolite contributed to adsorption of FLQ on the catalyst surface enormously. The catalysts exhibited 11%, 23%, 63%, and 85% degradation efficiency for ZnO, TiO₂, Ti/Zn, and Ti/Zn/Sep in the decomposition of FLQ, respectively.     

Nonionic surfactant-stabilized raspberry-like polymer/silica nanoparticles latex with film formability

Raspberry-like P(St-BA)/SiO₂ nanoparticle latexes were prepared via miniemulsion polymerization of styrene (St) and butyl acrylate (BA) in the presence of 20 nm glycerol-modified SiO₂ sol as a Pickering emulsifier and octaphenyl polyoxyethylene (CA-897) as a nonionic surfactant, using 2,2-azobis (isobutyronitrile) (AIBN) as an initiator. 2-(Methacryloyl) ethyltrimethylammonium chloride (MTC) was introduced to act as an auxiliary monomer to enhance the attraction of SiO₂ sol onto latex nanoparticles (NPs) via increasing their electrostatic interaction with negative-charged SiO₂ sol. The average particle sizes of the latex particles can be well controlled from 200 to 360 nm by variation of the SiO₂ sol content as well as soft monomer BA component. The latex NPs displayed a good colloidal stability with excellent resistance to both strong acidic and basic environment. Furthermore, the nanosized latexes exhibited good film formability. The influence of reaction parameters, e.g., the initial silica amount and soft monomer BA content was systematically investigated on the film performances, such as hardness, abrasive resistance, water absorption, gloss. The results indicated that the increase of SiO₂ sol content can contribute to the increase of the film hardness and water absorption ability, while increasing BA component is beneficial to the improvement of the film gloss.     

Preparation and characterization of sulfated zirconia catalysts obtained via various procedures

Sulfated zirconia catalysts were prepared in two ways: (i) using colloidal sol–gel technique, when the peptization of Zr(OH)₄ precipitated with ammonia from a solution of ZrOCl₂ was carried out with H₂SO₄ or with a solution of CH₃COOH and H₂SO₄, respectively, and by (ii) impregnation of Zr(OH)₄. Impregnation was carried out using Zr(OH)₄ as such or using precipitated Zr(OH)₄ previously heated in suspension at 90°C under reflux and strong stirring. Samples obtained following the above procedures were activated by heating in Ar or air at 550°C or 650°C. Sample characterization was carried out using chemical analysis, N₂ adsorption–desorption techniques, titration with propylamine in the presence of Hammet indicators, XRD, Raman spectroscopy, pyridine and CD₃CN-FTIR and XPS. In the samples obtained via colloidal sol–gel technique the amount of retained sulfur was high and mono and polynucleate sulfate species as well as supported H₂SO₄ were found to coexist. In such conditions, both Lewis and Brønsted acid sites were identified and a large dispersion of acid strength was determined. Samples obtained via impregnation contained only a small amount of sulfur compared with those obtained via colloidal sol–gel technique. In this case only mono and dinucleate sulfate species were found, and the acid strength exhibited a rather sharp distribution. It was also found that in that case Lewis acid sites predominate. Activation in air exhibited a positive effect upon the increase of the acidity, irrespective of the preparation variant, its presence “catalyzing” the nucleation of the superficial sulfate groups.     

Comparison of the photovoltaic efficiency on DSSC for nanometer sized TiO2 using a conventional sol–gel and solvothermal methods

When the two types of TiO₂ coatings prepared by sol–gel and solvothermal methods were applied to dye-sensitized solar cell (DSSC) in this study, the energy conversion efficiency of the solvothermal-modified TiO₂ was considerably higher than that on the sol–gel modified TiO₂; approximately 8.51 (solvothermal) and 5.93% (sol–gel) with the N719 dye under 100 mW/cm² of simulated sunlight, respectively. These results are in agreement with an electrostatic force microscopy (EFM) study showing that the electrons were transferred rapidly to the surface of the solvothermal-modified TiO₂ film, compared with that on a sol–gel modified TiO₂ film. Furthermore, FT-IR analysis of the films after N719 dye adsorption showed that the solvothermal-modified TiO₂ had a strong band at 500 cm^?1, which was assigned to metal–O, due to a new Ti–O bond between the O of COO^? and a Ti atom. This peak was considerably weaker in the sol–gel modified TiO₂.     

Refractive materials for interlayer optical contacts with TiO2‐based organic/inorganic hybrids

Organic/inorganic hybrid materials were prepared by synthesizing from titanium tetraisopropoxide (TTIP), diethanolamine (DEOA), and water. Formulating the materials with thermosetting polymers, the composites were designed for refractive optical contacts with heat lamination of a film having >50 μm thickness. Inherent difficulties of TiO₂ and sol‐gel reaction of TTIP, i.e. photocatalytic properties and prompt sol‐gel reaction to form large TiO₂ particle, were avoided by stabilizing Ti with use of DEOA. The reactivity of the sol‐gel reaction and formation of TiO₂ crystal structure were suppressed by DEOA. However, suppression of the photocatalytic properties was not enough and needed a use of anti‐oxidant agent, 2,6‐di‐t‐butyl‐p‐cresol (BHT). The titanium‐based organic/inorganic hybrid materials and its epoxy composites were transparent in visible wavelength region and gave in the range of 1.66 to 1.73 of refractive indices depending on stoichometric parameters of TTIP, water, and DEOA for the hybrid materials. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Nature, Environment and Quantification of Titanium Species in TiSiBEA Zeolites Investigated by XRD, NMR, DR UV–Vis and XPS

Ti _x SiBEA zeolites (x = 1.5, 3.2 and 5.8 Ti wt%) are prepared by a two-step postsynthesis method involving (1) dealumination of TEABEA zeolite by nitric acid leading to nests of SiO–H groups in vacant T-atom sites and (2) incorporation of Ti into SiBEA zeolite by reacting TiCl₄ vapor with those silanol groups. The incorporation of Ti into the SiBEA framework is evidenced by XRD, ²⁹Si MAS NMR, ¹H–²⁹Si CP MAS NMR and ¹H MAS NMR. DR UV–vis and XPS investigations show that, for low Ti content, mainly framework tetrahedral Ti(IV) ions are present in Ti _x SiBEA zeolites. On the basis of XPS data, the quantification of framework tetrahedral Ti(IV) and framework and/or extra-framework octahedral Ti(IV) ions is followed as a function of Ti content.     

Preparation and characterization of the continuous titanium-doped ZrO2 mesoporous fibers with large surface area

The continuous titanium-doped ZrO₂ mesoporous fibers with a large surface area (190 m² g^?1, TZ50-400) have been prepared by the sol–gel method coupled with the chemical template route. In the formation process, the self-induced acid environment of ZrOCl₂·8H₂O in ethanol solution was utilized to avoid a rapid hydrolysis process and the viscous sol precursors were successfully obtained for spinning fibers. X-ray photoelectron spectroscopy and UV–vis diffuse reflectance spectra were used to study the chemical environment of surface Ti(IV) and Zr((IV)) ions. The findings disclose that the partial Ti atoms (less than 30 %) enter into the ZrO₂ lattice and occupy the positions of Zr atoms, while the excess Ti atoms construct the linear Ti–O–Ti chains inside the extra framework, being favorable to prevent the collapse of meso structure.     

Colloidal Sol–Gel Synthesis and Photocatalytic Activity of Nanoparticulate Nb2O5 Sols

A detailed study of a novel synthesis via colloidal sol–gel route for obtaining nanoparticulate Nb₂O₅ was performed. Parameters such as temperature and H⁺:Nb⁵⁺ and Nb⁵⁺:H₂O molar ratios were controlled in order to determine the best conditions of synthesis. Moreover, particle size distribution, zeta potential, structure by X‐ray diffraction, and the photocatalytic activity of the particulate sols were also evaluated. The obtained results indicate that the colloidal sol–gel synthesis is a good alternative for obtaining Nb₂O₅ either as stable nanoparticulate sol or as a nanosized powder. Nb₂O₅ amorphous nanoparticles with an average size of 20 nm were obtained by controlling the synthesis variables. The heat‐treatment process allowed the formation of Nb₂O₅ with orthorhombic structure that transforms at higher temperatures to monoclinic phase. The highest photocatalytic activity was observed under λ = 365 nm, the smallest UV energy used in the experimental tests.     

Synthesis,characterization and performance evaluation of an optimized ceramic membrane with physical separation and photocatalytic degradation capabilities

The main goal of the present study is synthesis, characterization and performance evaluation of an optimized photocatalytic ceramic membrane for wastewater treatment. It consists of three layers including alumina (Al₂O₃) macroporous support, colloidal titania (TiO₂) mesoporous intermediate layer and polymeric TiO₂ mesoporous top layer in order to obtain a pore gradient from the support through the top layer of membrane. The colloidal and polymeric TiO₂ layers were prepared via the sol-gel method and coated using sol dip-coating approach. In order to optimize the membrane, physical separation and photocatalytic degradation capabilities of each colloidal and polymeric layer as a function of time were evaluated using Rhodamine B (RhB) aqueous solution. Thus, optimum coating number of intermediate layer and top layer were determined. Also, the performance of the optimized membrane was investigated via oily wastewater treatment using crude oil and water emulsion. Based on the performance results, two consequence colloidal layers and one polymeric layer were considered as the optimum layer number. Also, RhB photocatalytic degradation was 24.7% and RhB physical separation and permeation flux were 40.4% and 25.7?kg?m^?2 h^?1, respectively. Furthermore, based on the oily wastewater treatment experiments, permeation flux and chemical oxygen demand (COD) rejection at the best-operating conditions (pressure of 5?bar, the temperature of 30?°C and cross flow of 600?l?h^?1) were 29.1?kg?m^?2 h^?1 and 78.4%, respectively. The prepared membrane was found efficient and exhibited high industrial potential due to its multifunctional capability and thus can be employed as an advanced material for wastewater treatment applications.     

Synthesis and ion exchange of zeolites produced from kaolin for separation of oxygen from atmospheric air

Lithium-based zeolites are the most commonly used materials in PSA (pressure swing adsorption) oxygen concentration from atmospheric air. Synthesizing these adsorbents using mineral raw materials adapts to worldwide environmental requests, as only high-purity chemical reactants such as aluminates and silicates are usually used. The present work aims to synthesize and characterize zeolites using kaolin as raw material by studying the influence of the metakaolinization temperature and SiO₂/Al₂O₃ and H₂O/Na₂O molar ratios by experimental design. Ion exchange was used to incorporate lithium into synthesized zeolites. Kaolin was treated thermically and characterized, and zeolites were synthesized by a hydrothermal reaction. After synthesis, ionic exchange of Na⁺ ions by Li⁺ was performed. The results indicated the presence of three main phases, zeolites A, X, and P. Using ANOVA, it was found that the factors that contributed significantly to the formation of zeolite X were the H₂O/Na₂O and SiO₂/Al₂O₃ molar ratios. For zeolite A, the major influence was by the metakaolinization temperature and for zeolite P none of the factors was influential. Zeolites that incorporated higher amounts of lithium showed higher N₂ adsorption potential, indicating that even without pure phases formed, it was possible to obtain similar adsorption efficiency to commercial zeolite.     

One‐Part Geopolymers Based on Thermally Treated Red Mud/NaOH Blends

In this study, one‐part “just add water” geopolymer binders are synthesized through the alkali‐thermal activation of the red mud which is relatively rich in both alumina and calcium. Calcination of the red mud with sodium hydroxide pellets at 800°C leads to decomposition of the original silicate and aluminosilicate phases present in the red mud, which promotes the formation of new compounds with hydraulic character, including a partially ordered peralkaline aluminosilicate phase and the calcium‐rich phases C₃A and α‐C₂S. The hydration of the “one‐part geopolymer” leads to the formation of zeolites and a disordered binder gel as the main reaction products, and the consequent development of compressive strengths of up to 10 MPa after 7 d of curing. These results demonstrate that red mud is an effective precursor to produce one‐part geopolymer binders, via thermal and alkali‐activation processes.