Evaluation of Stability and Catalytic Activity in Supercritical Water of Zinc Oxide Samples Prepared by the Sol–Gel Method

Journal of Inorganic and Organometallic Polymers and Materials - Nano-and micro-sized ZnO samples were synthesized by the sol–gel method. Physical and thermal stability of ZnO samples were...     

S–N Co-Doped TiO2 Photocatalysts with Visible-Light Activity Prepared by Sol–Gel Method

S–N co-doped anatase nanosized TiO₂ photocatalyst was successfully prepared by simple sol–gel method. The samples were characterized by XRD, XPS, UV–Vis. From the results of UV–Vis, a red shift of the absorption edge was brought out owing to the S and N codoping. XPS and UV–Vis studies revealed that N and S were in situ codoped in the lattice of TiO₂ and the absorbance in visible light region decreased with the calcination temperature increased. The photocatalytic activity was evaluated by the photocatalytic oxidation of penicillin solution under visible light irradiation. The results show that visible-light induced photocatalytic activities of the as-prepared TiO₂ powders were improved by S–N copoing. The high activity of S–N co-doped TiO₂ can be related to the results of the synergetic effects of strong absorption in the UV–Vis region, red shift in adsorption edge.     

An Amalgam of Mg-Doped TiO2 Nanoparticles Prepared by Sol–Gel Method for Effective Antimicrobial and Photocatalytic Activity

In this study, undoped and Magnesium doped TiO₂ nanoparticles (Mg-TiO₂ NPs) are successfully synthesized via a simple sol–gel method cost-effectively. The prepared Mg- TiO₂ NPs is characterized by UV–Vis, FTIR, PL, XRD, FESEM, TEM, and EDAX. UV–Visible Spectroscopy showed that an increase in the optical bandgap concerning the concentration of dopant Mg increases. The bandgap values were found to be 3.57–3.54 eV. FTIR spectra shows that the presence of the characteristic stretching and bending vibrational band of Ti–O bonding at 468 cm^?1 and shifts in vibrational bands were observed for Mg-TiO₂ NPs. PL spectra of Mg- TiO₂ NPs at different concentrations exhibit a strong UV emission band. X-ray diffraction confirmed the formation of the tetragonal anatase phase. The average crystallite size of synthesized samples was found to be 22–19 nm. The average crystallite size of Mg- TiO₂ NPs decreases with increasing the concentration of dopant Mg. The FESEM and TEM analysis confirmed that the spherical morphology for both TiO₂ and Mg-TiO₂ NPs. SAED pattern confirms the crystalline nature of prepared samples. EDAX spectra confirm the presence of Ti, O, and Mg and confirm that Mg²⁺ ions are present in the TiO₂ lattices. The prepared samples were investigated against gram-positive and gram-negative bacteria. The prepared samples exhibit potent antibacterial activity against gram-negative bacteria than the gram-positive bacteria. The prepared samples exhibit significant photocatalytic degradation for Methylene blue (MB).

     

Fabrication and Characterization of Pure and Pb-doped ZnO Thin Films Prepared by Sol–Gel and Dip-coeting Method

In this paper, undoped and Pb-doped ZnO thin films have been prepared by sol gel method and deposited on glass substrate using dip-coating technique. The structural, morphological, and optical properties of the films were investigated as a function of Pb doping. The results of the structural tests showed that these films are of a polycrystalline hexagonal structure with a preferred orientation in the (002) direction. The grain size values of Pb-doped films were lower than that of pure ZnO, but the strain and the dislocation density values inecrease with increase Pb doping ratio. The atomic force microscopy (AFM) images showed that the particle size and Root Mean Square (RMS) of ZnO decrease with increasing Pb doping. The optical band gap values were found to increase from (3.19 to 3.30 eV) and the Urbach energy decrease from (322 to 313 meV). PL spectra exhibit an increased amount of defects with increasing Pb, which leads to a red shift in the UV region.

     

Structure and Electronic States of Zinc-Doped Iron Oxide Nanotubes Prepared by a Surfactant-Assisted Sol–Gel Method

We report the doping of iron oxide nanotubes with zinc, and the characterization of the resulting zinc ferrite nanotubes. Gels were prepared by polycondensing iron nitrate nonahydrate and zinc nitrate hexahydrate on the surface of a self-assembled non-ionic surfactant in 1-propanol at 45 °C. Evaporation of the solvent within the gels at 120 °C led to the formation of tubular structures, as evidenced by transmission electron microscopy. The nanotubes had internal and external diameters of ~2–6 and 4–10 nm, respectively, and were ~50 nm long. X-ray diffraction and X-ray photoelectron spectroscopy indicated that the nanotubes possessed a spinel structure, and had a composition of Zn _x Fe_3?x O₄, with x ranging from 0 to 0.66. Direct band gaps were evaluated from optical absorption spectra, using the Tauc plot method. The band gaps ranged from 2.4 (x = 0) to 2.0 eV (x = 0.27), thus narrowing upon doping with Zn. This was tentatively attributed to a widening of the band width, and the formation of sub-levels at octahedral B sites of the spinel structure.     

Propylene Epoxidation: High-Throughput Screening of Supported Metal Catalysts Combinatorially Prepared by Rapid Sol–Gel Method

The gas phase oxidation of propylene using molecular oxygen was studied on a variety of supported metal catalysts. The most promising PO activity was obtained for Cu supported on high surface area SiO₂ and the multimetallic systems exhibit synergistic effects that increased the desired PO yield by several folds for Ag promoted with Cu on SiO₂ after screening a large number of catalysts by a high throughput testing technique.     

Methane Combustion Over Copper Chromites Catalysts Prepared by the Sol–Gel Process

Abstract  

Methane combustion was performed over a series of copper chromites (CuCr₂O₄) catalysts prepared by the sol–gel process (SG). The results were compared with those obtained over commercial CuCr₂O₄. The samples were characterised by elemental analysis, thermal analysis, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The as-synthesised CuCr₂O₄ sample exhibited higher specific surface area (248 m² g⁻¹) with respect to commercial solids (42 m² g⁻¹). The surface properties were established using XPS. Simultaneously, an increase in the atomic Cr⁶⁺/Cr³⁺ ratio (0.56 for SG catalyst vs. 0.39 for commercial sample) and a decreasing surface copper concentration (8.3%, for SG specimen vs. 17.6% for commercial catalyst) are observed. XPS study revealed also that Cu²⁺/(Cu° + Cu⁺) ratio of copper species remained constant (ca. 5) in both catalysts. Structure transformations of CuCr₂O₄ under reduction-reoxidation conditions showed that the reduction of copper and/or chromium cations from the CuCr₂O₄ and from delafossite (CuCrO₂) structure (CuCr₂O₄↔CuCrO₂ + Cu + Cr₂O₃↔Cu + Cr₂O₃) were different. This has lead to a difference in catalytic properties of the catalysts. Catalytic activity of SG catalysts was superior to that of commercial CuCr₂O₄ tested under the same conditions. Complex hysteresis behaviour for CuCr₂O₄ catalysts ramped over a temperature range of 220–850 °C where the stables active phases were obtained only after the first ramp of heating under reactants. No catalysts deactivation was further observed after several cycles of heating and cooling. The stabilisation of catalytic activity was attributed to the formation of mixed crystalline phases containing both copper and chromium species.     

Tailoring the Microstructure of Sol–Gel Derived Hydroxyapatite/Zirconia Nanocrystalline Composites

In this study, we tailor the microstructure of hydroxyapatite/zirconia nanocrystalline composites by optimizing processing parameters, namely, introducing an atmosphere of water vapor during sintering in order to control the thermal stability of hydroxyapatite, and a modified sol–gel process that yields to an excellent intergranular distribution of zirconia phase dispersed intergranularly within the hydroxyapatite matrix. In terms of mechanical behavior, SEM images of fissure deflection and the presence of monoclinic ZrO₂ content on cracked surface indicate that both toughening mechanisms, stress-induced tetragonal to monoclinic phase transformation and deflection, are active for toughness enhancement.     

The Effect of Yttrium Oxide on the Microstructure and Properties of Ceramics Based on Lanthanum Hexaaluminate Synthesized by the Sol–Gel Method

The effect of a sintering aid, yttrium oxide, on the properties of ceramic materials based on lanthanum hexaaluminate synthesized by a sol–gel method is studied. The synthesis of a sol of ternary oxide composition conducted via hydrolysis of a mixed salt solution leads to the formation of particles with a nucleus – shell-type structure. The synthesis of lanthanum hexaaluminate with the participation of these particles proceeds at 1000 – 1100°C, and the sintering of ceramic at 1400 – 1500°C. Ceramic based on yttrium-containing lanthanum hexaaluminate exhibits improved strength properties.     

Mixed Alcohol Synthesis from Syngas on K–Co–Mo/C Catalyst Prepared by a Sol–Gel Method

A kind of K–Co–Mo/C catalyst with homogenous components distribution and small particle size was prepared by sol–gel method with citric acid as complexant. Its structure and catalytic performance for mixed alcohol synthesis were investigated. By heat treating the dried gel in argon, the decomposition of citric acid resulted in the formations of amorphous carbon and low-valence MoO₂ species. The incorporation of potassium and cobalt increased significantly the alcohol synthesis activity, especially improved the C₂₊OH selectivity. The optimal atomic composition of catalyst was: 0.10 K: 0.50 Co: 1.0 Mo. Comparing with the similar catalysts reported in literatures, the sol–gel derived K–Co–Mo catalyst showed better performance, especially much higher C₂₊OH selectivity for mixed alcohol synthesis. A 150 h reaction test indicated that the catalyst had good stability during the entire experimental period. It suggested that the homogenous components distribution and small particle size enhanced the synergistic effect of promoters and created more active species, leading to a high catalytic performance. The formation of MoO₂ species was also favorable to improve the catalytic activity because the low-valence Mo⁴⁺ was known to be more active in CO hydrogenation.     

Influence of Solvent–Evaporation Effect on the Structure and Properties of PVDF-g-PNIPAAm Membranes

Temperature-sensitive poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide)(PVDF-g-PNIPAAm) copolymer was synthesized and its flat membranes were prepared through phase inversion method with mixture of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF) as solvent in water coagulation bath. The effects of “open time” (solvent–evaporation time) on the structure and performance of membranes were investigated by X-ray photoelectron spectroscopy, field-emission scanning electronic microscopy, contact angle, filtration experiments and static protein adsorption. It was found that the increasing “open time” endowed the membrane with more pores on the surface, higher flux and better hydrophilicity, provided the membrane with lower protein adsorption. Thus, the copolymer membranes showed a good antiprotein fouling.     

Hydrogenation of Succinic Acid to γ-Butyrolactone (GBL) Over Palladium-Alumina Composite Catalyst Prepared by a Single-Step Sol–Gel Method

Abstract  

Mesoporous palladium-alumina (Pd-A) composite catalysts prepared by a single-step sol–gel method were calcined at various temperatures to control palladium surface area and acidity. The Pd-A catalysts were characterized by XRD, BET, N₂ adsorption–desorption isotherm, H₂ chemisorption, ²⁷Al MAS NMR, NH₃-TPD, and HR-TEM analyses. Liquid-phase hydrogenation of succinic acid to γ-butyrolactone (GBL) was carried out over Pd-A catalyst in a batch reactor. The effect of calcination temperature of Pd-A catalyst on the palladium surface area and catalytic performance was investigated. In the hydrogenation of succinic acid, conversion of succinic acid increased with increasing palladium surface area of Pd-A catalyst. Selectivity for GBL depended on the formation of succinic anhydride (an intermediate product formed by acid catalysis) and by-products (formed by hydrogenolysis). Nevertheless, yield for GBL also increased with increasing palladium surface area of Pd-A catalyst. Thus, palladium surface area played an important role in enhancing the catalytic performance of Pd-A catalyst in the hydrogenation of succinic acid to GBL.     

Preparation of Highly Adhesive and Superhydrophobic Epoxy-Based Thin Film by Sol–Gel Process

In this study the preparation of a superhydrophobic epoxy-based thin film with excellent high adhesion properties was carried out by mixing epoxy polymer solution, MTMOS solution, and silica powder. It was found that the adhesion between the film and a substrate could be improved by adding PET fibers to the above solution. The characteristic properties of the as-prepared films were analyzed by contact angle measurements, scanning electron microscopy (SEM) and by atomic force microscopy (AFM). The adhesion between the film and the substrate was estimated by the cross-cut method. The experimental parameters were: the mole fraction of MTMOS, weight fraction of silica powder, weight fraction of PET fibers, and the curing temperature. The result indicated that the contact angle and the sliding angle of the hybrid film were 153° and 4°, respectively, and the adhesion test result was very good (5B degree), while the mole fraction of MTMOS was 0.4, the silica powder concentration was 30 wt%, and the PET fibers concentration was 0.15 wt%, with the curing temperature in the range of 130–180°C.     

Porous Properties of γ-Alumina/Potassium Aluminosilicate Gel Composites Prepared by Selective Leaching and Precipitation Method

Composites of mesoporous -alumina and potassium aluminosilicate (KAS) gel were prepared by selective leaching of calcined kaolinite using KOH solution followed by neutralization of the solution at pH 5.5 with nitric acid. The porous properties of the composites were characterized by N₂ gas adsorption and their microtextures were observed by electron microscope. The resultant composites have specific surface areas of about 290 m²/g, pore sizes of about 1.85 nm in radius and pore volumes of about 0.5 ml/g. The porous properties of the composites are compared with those of -alumina and KAS gel.     

Methods and Approaches of the Sol–Gel Technology for the Surface Modification of Aluminum Oxide Powders

The results of studies, sol–gel synthesis, and the sedimentation stability of complex multicomponent sol–gel systems of the “silica sol modified with Co(NO₃)₂ · 6H₂O, Al(NO₃)₃ · 9H₂O with α-Al₂O₃ or γ-Al₂O₃ as highly dispersed filler” type are generalized. The physical–chemical processes accompanying the formation of modifying layers on the powder oxide particles are examined. The promising prospects of applying α-Al₂O₃ powders modified with a silicate layer of the composition (wt %) 1.2K₂O · 3Al₂O₃ · 3.2CaO · 12.5Na₂O · 28.1B₂O₃ · 52SiO₂ in the fabrication of ceramic materials with improved strength characteristics are demonstrated.