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.     

Sol–Gel Assisted Preparation of Chromia–Silica Catalysts for Non-Oxidative Dehydrogenation of Propane

Preparation of continuous silica gel in the presence of dissolved Cr(NO₃)₃ leads to a hard high surface area (710 m²/g) microporous xerogel. Formation of the gel in the pore structure of mesoporous Pore-Expanded MCM-41 (PE-MCM-41) and macroporous commercial Cab–O–Sil silica results in retention of the mesoporous structure in the case of PE-MCM-41, and the formation of a powder with a broad pore size distribution in the case of Cab–O–Sil silica. Comparison of the catalytic activities in non-oxidative dehydrogenation of propane revealed a linear correlation of the initial conversion with the surface area for all three samples. The sample prepared from PE-MCM-41 through a sol–gel assisted procedure was the most active, particularly with respect to the catalysts prepared by simple wet impregnation with chromium nitrate.     

Morphologies of Sol–Gel Derived Thin Films of ZnO Using Different Precursor Materials and their Nanostructures

We have shown that the morphological features of the sol–gel derived thin films of ZnO depend strongly on the choice of the precursor materials. In particular, we have used zinc nitrate and zinc acetate as the precursor materials. While the films using zinc acetate showed a smoother topography, those prepared by using zinc nitrate exhibited dendritic character. Both types of films were found to be crystalline in nature. The crystallite dimensions were confined to the nanoscale. The crystallite size of the nanograins in the zinc nitrate derived films has been found to be smaller than the films grown by using zinc acetate as the precursor material. Selected area electron diffraction patterns in the case of both the precursor material has shown the presence of different rings corresponding to different planes of hexagonal ZnO crystal structure. The results have been discussed in terms of the fundamental considerations and basic chemistry governing the growth kinetics of these sol–gel derived ZnO films with both the precursor materials.

Co/SiO2 Sol–Gel Catalysts for Fischer–Tropsch Synthesis

Six catalysts with a different cobalt content were prepared following the sol–gel method. The samples were tested by the Fischer–Tropsch synthesis performed both at low and high temperature and pressure. All the catalytic performances are well correlated with the characterization results which highlighted the good metal distribution and the presence of a large amount of metallic cobalt (but not the whole) on the surface of both 10 and 30% Co catalysts. As a result, high CO conversions were observed with a particular sensitivity to the reaction pressure and also the limitation of the produced hydrocarbons fraction to C₆ or C₉ at low or high pressure, respectively.     

Sol–Gel and Thermally Evaporated Nanostructured Thin ZnO Films for Photocatalytic Degradation of Trichlorophenol

In the present work, thermal evaporation and sol–gel coating techniques were applied to fabricate nanostructured thin ZnO films. The phase structure and surface morphology of the obtained films were investigated by X-ray diffractometer (XRD) and scanning electron microscope (SEM), respectively. The topography and 2D profile of the thin ZnO films prepared by both techniques were studied by optical profiler. The results revealed that the thermally evaporated thin film has a comparatively smoother surface of hexagonal wurtzite structure with grain size 12 nm and 51 m²/g. On the other hand, sol–gel films exhibited rough surface with a strong preferred orientation of 25 nm grain size and 27 m²/g surface area. Following deposition process, the obtained films were applied for the photodegradation of 2,4,6-trichlorophenol (TCP) in water in presence of UV irradiation. The concentrations of TCP and its intermediates produced in the solution during the photodegradation were determined by high performance liquid chromatography (HPLC) at defined irradiation times. Complete decay of TCP and its intermediates was observed after 60 min when the thermal evaporated photocatalyst was applied. However, by operating sol–gel catalyst, the concentration of intermediates initially increased and then remained constant with irradiation time. Although the degradation of TCP followed first-order kinetic for both catalysts, higher photocatalytic activity was exhibited by the thermally evaporated ZnO thin film in comparison with sol–gel one.     

Preparation of Thermally Stable Mesostructured Nano-sized TiO2 Particles by Modified Sol–Gel Method Using Ionic Liquid

The mesoporous anatase form of TiO₂ was prepared by modified sol–gel method using ionic liquid as a template agent. The prepared nanosize TiO₂ particle was characterized by N₂-physisorption, XRD, TEM, and SEM. The physical properties of prepared TiO₂ particles were compared with that prepared by conventional sol–gel method without template. It has been proved that the anatase phase prepared by modified sol–gel process using ionic liquid was preserved well even if the TiO₂ samples were treated at high temperatures up to 800 °C while those prepared by conventional sol–gel method were transformed from anatase to rutile phase gradually during calcinations at 600 °C. Moreover, there was no phase transition in the sample obtained by sol–gel method with ionic liquid in spite of prolonged calcination for 60 h at 600 °C. However, in case of those samples prepared by conventional sol–gel method, the portion of rutile form was continuously increased with the increase in the calcination period.     

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.     

Sol–Gel Pd Exhaust Catalysts and Hydrocarbon Speciation

Sol–gel Pd/alumina promoted by oxygen-storing CeO₂ or CeO₂–Tb₄O₇ catalysts has higher hydrocarbon oxidation activity than commercial three-way catalysts. It is active in hydrocarbon (and CO) oxidation even under net reducing conditions albeit over short periods of time. This observation is relevant to cold start conditions. Cryo-focussing GCMS and pulse RGA experiments suggest that mechanistically interesting by-product hydrocarbon species evolve from the catalysts under just these conditions, even when the fuel is LPG in type. Further catalyst developments and analytical refinements are likely to go hand in hand as the mode of operation of these environmental catalysts is better understood from their by-product fingerprint.     

A Sol–Gel Derived CuOx/Al2O3–ZrO2 Catalyst for the Selective Reduction of NO by Propane in the Presence of Excess Oxygen

Copper catalysts supported on alumina-doped zirconia were prepared by sol–gel processing followed by supercritical drying or aging in the mother solution at 100°C. After drying and calcination, the catalyst supports were impregnated with a copper(II) nitrate aqueous solution by the incipient wetness method to achieve a Cu loading of about 2%. The samples showed 90% NO conversion at 350–400°C. The catalytic performance of these systems appears to be determined by the degree of clustering of copper cations as probed by FTIR spectroscopy of adsorbed CO.     

Electrochemical Sensor for Detection of Trichlorfon Based on Molecularly Imprinted Sol–Gel Films Modified Glassy Carbon Electrode

Thin films of molecularly imprinted sol–gel polymer with specific binding sites for trichlorfon were prepared, fixed on glassy carbon electrodes and used as recognition material. The binding characteristic of the imprinted films to trichlorfon was evaluated by equilibrium binding experiments; and, the morphology was studied by scanning electronic microscope. A novel electrochemical sensor for determination of trichlorfon was developed based on the reaction between trichlorfon and the molecularly imprinted sol–gel film, which was a modified glassy carbon electrode. The sensor displayed excellent selectivity and high sensitivity. The linear response range of the sensor was 10⁻⁸ –10⁻⁶ g mL⁻¹, and the limit of detection was 2.8 × 10⁻⁹ g mL⁻¹. The relative standard deviation for the determination of 10⁻⁷ g mL⁻¹ trichlorfon was 3.5%. The sensor was applied to the determination of trichlorfon in vegetables with satisfactory results.     

Sol–gel incorporation of silica nanofillers for tuning the anti-corrosion protection of acrylate-based coatings

The aim of the present work is to synthesize through sol–gel approach new hybrid polymeric nanocomposites to be used as coating materials. An acrylic-based polymer was prepared by free-radical copolymerization of two monomers widely used for coatings, namely 2-ethylhexylacrylate (EHA) and glycidyl methacrylate (GMA) bearing epoxy moieties, in which silica nanoparticles were incorporated by in situ acid hydrolysis and subsequent condensation of tetraethoxysilane (TEOS). Glycidoxypropyl trimethoxysilane (GPTS) was used as coupling agent to fine-tune the compatibility between organic and inorganic phases. The morphology, mechanical properties and corrosion resistance of thin films applied on aluminum alloys were optimized by varying the content of silica nanoparticles whose properties were strongly affected by the TEOS/GPTS ratios. Performances of the obtained hybrid materials were scrutinized by atomic force microscopy (AFM), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and electrochemical impedance spectroscopy (EIS). Thus it was evidenced that an optimum amount of silica nanoparticles with a precise morphology and composition in term of TEOS/GPTS ratio is needed to maintain good coating barrier properties. Outstanding anti-corrosion protection was reached by using optimized hybrid films.     

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.     

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).

     

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.     

Sol–gel derived hybrid materials as heterogeneous catalysts for the epoxidation of olefins

CH₃ReO₃ has been heterogenized inside the porous system of hybrid silica matrixes via the sol–gel method using 1,4-bis(triethoxysilyl)benzene as a co-condensation agent and 4-((3-triethoxysilyl)propylamino)pyridine hydrochloride as a hydrolysable ligand. The resulting solids are stable and recyclable epoxidation catalysts.     

Effect of Processing Conditions on Adhesion Performance of a Sol–Gel Reinforced Epoxy/Aluminum Interface

The Boeing sol–gel process (Boegel-EPII) is a surface preparation method for metallic substrates for adhesive bonding and painting applications. This paper describes an investigation into the effect of processing conditions on adhesion strength and durability of a sol–gel reinforced, rubber toughened epoxy/aluminum joint. Using an asymmetric double cantilever beam (ADCB) wedge test, the adhesion performance of the sol–gel reinforced epoxy/aluminum joint in a humid environment was measured as a function of sol–gel processing conditions. The sol–gel drying time, concentration and drying humidity all have an effect on adhesion performance. Prolonged drying led to a decrease in fracture energies. The critical and threshold fracture energies show different trends as sol–gel concentration varies, and better adhesion performance was observed for sol–gel dried at higher humidity compared to lower humidity. The failure modes and mechanisms were studied by XPS and SEM. Analysis of locus of failure revealed that the observed trends for adhesion performance can be explained in terms of interdiffusion of the sol–gel film and epoxy. The diffusion of the epoxy into the sol–gel layer is hypothesized to strongly depend on the degree of condensation of the sol–gel film and is directly affected by the sol–gel processing conditions.     

Textured YBCO-Film Formation by Sol–Gel Process and Post Annealing

Thick YBCO-films were prepared on single crystalline SrTiO₃(001) and LaAlO₃(001) substrates by the dip-coating process starting with Y-, Ba- and Cu-acetylacetonates. When a characteristic temperature during transformation of the precursor into YBa₂Cu₃O_x is exceeded a strong biaxial texture with FWHM = 1·2° for 1 μm thick fims results. When the O₂ partial pressure of the annealing atmosphere is lowered the characteristic temperature decreases and films with increased current density (j_c) are obtained. The values of J_c achieved for films deposited onto SrTiO₃(001) at 77 K in self field are as high as 50·000 A cm⁻² with T_cs of 90K.     

Sol–Gel Pd Exhaust Catalysts and N2O Production

Al₂O₃, CeO₂–Al₂O₃, CeO₂–Tb₄O₇–Al₂O₃ and ZrO₂–Al₂O₃ supported Pd samples have been prepared by sol–gel methods. Extents and mechanisms of N₂O production in CO–NO and CO–NO–O₂ reactions on these have been considered. This occurs most selectively under oxidising (lean-burn) conditions or in the presence of CeO₂ and CeO₂–Tb₄O₇ promoters near the CO–NO light off temperature. Over Pd/ZrO₂–Al₂O₃ the CO–NO reaction at 573 K has CO and NO conversions that are second order with respect to p _CO and p _NO. Over this catalyst NO conversion is faster than that of CO until O_2(g) is added, causing CO conversion and N₂O production at 573 K to rise simultaneously. CeO₂ or CeO₂–Tb₄O₇ incorporation into a Pd/Al₂O₃ catalyst enhances N₂O production near the CO–NO light-off temperature in the absence of added O₂ without CO conversion being raised. There is current attention on pollution control opportunities through lean-burn conditions, Pd catalysts and oxygen storage capacity enhancement. The present work suggests that their role in N₂O production may need to be better understood and controlled. For the moment N₂O formation provides a window on mechanisms of TWC operation.     

Spectrophotometric Study of Interaction with Water of Barley Seeds after Their Colloid Treatment in Silica Sols with γ-Fe2O3 Nanopowders

Glass Physics and Chemistry - It is shown that the deposition of silica sol shells on the surface of barley seeds based on hydrolyzed tetraethoxysilane with the addition of γ-Fe2O3 (maghemite)...