Effect of the nature of anions of aluminum salts used to synthesize a precursor of the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> ceramics on the stabilization of the tetragonal modification of zirconium dioxide

Samples of a precursor for an aluminum oxide ceramics reinforced with zirconium oxide were synthesized by hydrolysis of various aluminum salts in the presence of a ZrO₂ sol under conditions of urea decomposition at 90°C and pH < 4 maintained, with hydrolysis products deposited onto the surface of ZrO₂ sol particles. It was found that the nature of a salt anion affects the interaction of hydrolysis products of the aluminum cation with the surface of ZrO₂ sol particles. The structure of products formed in thermal treatment of samples of a precursor for Al₂O₃-ZrO₂ (T = 1250°C) was characterized by X-ray phase analysis and scanning electron microscopy. The phase transition temperatures of the oxides Al₂O₃ and ZrO₂ contained in the precursor were estimated using the results of thermal analysis of the samples in the temperature range 20–1300°C.     

Preparation of highly active and reusable heterogeneous Al2O3–Pd catalysts by the sol–gel method using bayberry tannin as stabilizer

A novel heterogeneous Al₂O₃–Pd catalyst has been prepared by the sol–gel method; bayberry tannin (BT) was used as stabilizer to prevent the migration and aggregation of Pd species during calcination. According to N₂ adsorption/desorption determination, Al₂O₃–Pd has a mesoporous structure and its specific area is as high as 336.5 m²/g. Transmission electron microscopy observation indicated that the size of the Pd particles was greatly reduced by the presence of BT. On the basis of X-ray photoelectron spectra analysis, it was found that the most of Pd nanoparticles were dispersed in the pores, implying that BT can prevent migration of Pd particles from the pores to the outer surface of Al₂O₃ during calcination. For comparison, Al₂O₃–Pd^* was prepared by the sol–gel method but without use of BT. In the hydrogenation of acrylic acid, Al₂O₃–Pd had high catalytic activity and excellent reusability compared with commercial and traditionally prepared heterogeneous Pd catalysts. The turnover number of Al₂O₃–Pd is as high as 11,328.0 mol/mol after recycling seven times, which is much higher than that of a commercial Pd–C catalyst (8048.0 mol/mol).     

Synthesis of a precursor for an alumina ceramic reinforced by zirconium dioxide from inorganic compounds in the presence of urea

Samples of a precursor for an alumina ceramic reinforced by zirconium dioxide were synthesized. The samples have a uniform structure and are characterized by high ratios of the tetragonal and monoclinic modifications of ZrO₂, tlm, after a thermal treatment (1250°C). The structure of samples in the system Al₂O₃-ZrO₂ is formed under conditions favorable for deposition of products of hydrolysis of Al(III) ions on the surface of ZrO₂ sol particles in decomposition of urea. The coating of ZrO₂ sol particles by products of hydrolysis of Al(III) salts was confirmed by electrophoresis. The size distribution of particles of the in?dividual ZrO₂ sol was determined by small-angle X-ray scattering. The structure of the products formed in thermal treatment of samples of mixed oxides Al₂O₃-ZrO₂ was characterized by X-ray phase analysis and scanning electron microscopy. The porosity and specific surface area of a thermally treated sample was determined by measuring nitrogen absorption isotherms.     

Preparation of superhydrophobic PET fabric from Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> hybrid: geometrical approach to create high contact angle surface from low contact angle materials

In this work we prepare high contact Poly Ethylene Terephthalate (PET) fabric surface from low contact angle materials. Superhydrophobic PET fabric is prepared by coating the fabric with hybrid Al₂O₃–SiO₂ sol. In this case, the high contact angle Al₂O₃–SiO₂ hybrid is created from low contact angle Al₂O₃ and SiO₂ precursors. PET treated with hybrid Al₂O₃–SiO₂ exhibit Water Contact Angle (WCA) as 150°, while PET treated with individual Al₂O₃ sol or SiO₂ sol exhibits lower WCA, (Al₂O₃ WCA = 137°; SiO₂ WCA = 141°). FESEM and AFM investigations show that the hybrid Al₂O₃–SiO₂ sol and individual Al₂O₃ or SiO₂ sol imparted different roughness geometry on the PET fabric surface. We observe surface structure of fish fin-like, particle-like and hybrid fin-particle for treated PET fabric with; Al₂O₃, SiO₂ and hybrid Al₂O₃–SiO₂ sol, under FESEM and AFM observations.AFM observations show the evolution of roughness (Ra) dimension of different surface structures with the order of: SiO₂ < Al₂O₃ < Al₂O₃–SiO₂ (Ra = 31, 63 and 273 nm). We believe that the disparity of the surface geometries lead into different surface WCA. FTIR spectra of Hybrid Al₂O₃–SiO₂ shows additional peak at 902, 850, 557, and 408 cm⁻¹ which can be ascribed to the hybridization structure.     

溶胶-凝胶法合成硅溶胶包覆型均分散纳米β分子筛

在系统考察铝源、反应体系硅铝比、钠离子、反应温度等对分子筛粒度影响的基础上,优化合成条件合成出了粒径为100 nm左右的β分子筛。利用XRD和TEM对所合成样品进行了表征。采用溶胶凝胶法研究了硅溶胶包覆的均分散纳米β分子筛复合材料的合成,结果表明合成产物为纳米β分子筛均匀分散于硅溶胶基质中的微孔-介孔双孔复合材料。     

Highly transparent silica monoliths embedded with high concentration oxide nanoparticles

Silica monoliths embedded with high concentration of γ-Fe₂O₃ or TiO₂ nanoparticles were prepared by a sol–gel procedure designed according to the inherent properties of oxide colloids. In the first step, highly dispersible oxide nanoparticles were produced using an in situ modification sol–gel strategy. Then, these particles were re-dispersed in silicon alkoxide-containing solution to form a stable colloidal solution. The hydrolysis and condensation reactions of alkoxide were catalyzed by an organic base (morpholine). Due to the large molecule size of morpholine, the electric double layer on the surface of colloidal particles was not compressed by the ionized morpholine molecules. The colloidal solution thus remained stable during the gelation process. Through this procedure, oxide nanoparticles could be immobilized homogeneously in the pores of a silica matrix, forming highly transparent and crack-free monoliths.     

Synthesis of sub-micro-sized solid alpha alumina fibers with smooth surfaces by sol–gel method

Alumina sol containing nano-meter sized Al₂O₃ particles were synthesized using aluminum sec-butoxide and nitric acid as precursor and peptizing agent, respectively. Polyvinylpyrrolidone (PVP) was added to prevent particle growth and adjust sol viscosity. PVP/alumina hybrid fibers were drawn from the sol with a viscosity value in the range of 2,500–3,000 mPa.s. By guided through a temperature gradient tube furnace at a rate of 4 m/min, the wet PVP/alumina hybrid fibers were sufficiently dried. Sub-micro-sized pure alpha alumina fibers were obtained by sintering the dry hybrid fibers at 1,000 °C for 3 h. The organic matters were decomposed within a wide temperature range from 150 to 800 °C allowing the nano Al₂O₃ particles to gradually get together and form solid alumina fibers with smooth surfaces.     

Adsorption of colloidal trivalent iron on alumina

The adsorption of colloidal trivalent iron on neutral, acid and basic Al₂O₃ from aqueous solution as a function of pH has been studied. The dependence of sorption of pH is characterized by a maximum, whose position depends on the nature of colloidal particles and surface properties of the sorbents. Adsorption isotherms for the given range of sorbent loading can be expressed by the Langmuir adsorption equation.     

"一步法"合成多级孔SAPO-34分子筛

以TPOAC和硅溶胶为硅源,合成了多级孔SAPO-34分子筛,总比表面积达到649 m²·g^-1。详细考察了TPOAC和硅溶胶的配比对多级孔SAPO-34外比表面的影响,通过XRD、BET、SEM、NH₃-TPD等对其结构进行表征,结果表明多级孔SAPO-34的外比表面积可调变,晶体外观有较多缺陷位置,弱酸量减少,强酸位有变弱的趋势。在TPOAC与硅溶胶的投料比为3:2,晶化时间为10 d,投料比为n_Al2O3:n_P2O5:n_Si:n_TEAOH:n_H2O=1:0.9:0.5:2:60时,合成的多级孔SAPO-34的外比表面积达到最大,为100 m²·g^-1。     

Role of ammonium ions on the stability of TiO2 sol

In this paper, the role of the trace ammonium ions on the stability of TiO₂ sol prepared by peroxo titanic acid (PTA) sol was investigated. The results showed that the removal of ammonium ions in PTA sol is beneficial to reduce agglomeration and increase the negative charge on the surface of TiO₂ colloidal particles, contributing to the higher stability and longer storage time of the TiO₂ sol. It was also approved by the increase of interaction energy calculated by classical DLVO theory. In addition, the photocatalytic performance of TiO₂ sol was improved due to the decrease of aggregation of TiO₂ colloidal particles.     

Interaction between metallic gold and support and its influence on catalysis

The interaction between gold particles and support in Au/TiO₂ and Au/Al₂O₃ catalysts prepared by immobilizing colloidal gold on the support was evidenced by X-ray photoelectron spectroscopy. The reducibility of the support is more responsible than the interaction between the nanogold particles and support for the activity of catalysts.     

Effect of sol-gel preparation method on particle morphology in pure and nanocomposite PZT thin films

Double-scale composite lead zirconate titanate Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films of 360 nm thickness were prepared by a modified composite sol-gel method. PZT films were deposited from both the pure sol and the composite suspension on Pt/Al₂O₃ substrates by the spin-coating method and were sintered at 650°C. The composite suspension formed after ultrasonic mixing of the PZT nanopowder and PZT sol at the powder/sol mass concentration 0.5 g mL⁻¹. PZT nanopowder (≈ 40–70 nm) was prepared using the conventional sol-gel method and calcination at 500°C. Pure PZT sol was prepared by a modified sol-gel method using a propan-1-ol/propane-1,2-diol mixture as a stabilizing solution. X-ray diffraction (XRD) analysis indicated that the thin films possess a single perovskite phase after their sintering at 650°C. The results of scanning electron microscope (SEM), energy-dispersive X-ray (EDX), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analyses confirmed that the roughness of double-scale composite PZT films (≈ 17 nm) was significantly lower than that of PZT films prepared from pure sol (≈ 40 nm). The composite film consisted of nanosized PZT powder uniformly dispersed in the PZT matrix. In the surface micrograph of the film derived from sol, large round perovskite particles (≈ 100 nm) composed of small spherical individual nanoparticles (≈ 60 nm) were observed. The composite PZT film had a higher crystallinity degree and smoother surface morphology with necklace clusters of nanopowder particles in the sol-gel matrix compared to the pure PZT film. Microstructure of the composite PZT film can be characterized by a bimodal particle size distribution containing spherical perovskite particles from added PZT nanopowder and round perovskite particles from the sol-matrix, (≈ 30–50 nm and ≈ 100–120 nm), respectively. Effect of the PZT film preparation method on the morphology of pure and composite PZT thin films deposited on Pt/Al₂O₃ substrates was evaluated.     

Preparation, morphology and properties of nano-sized Al2O3/polyimide hybrid films

Nano-sized Al₂O₃/polyimide (PI) hybrid films based on 4,4′-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) were prepared by incorporation with different content of nano-sized Al₂O₃ via in situ polymerization. The TEM and SEM micrographs indicated that the Al₂O₃ particles were homogenously dispersed in the polyimide matrix by means of the ultrasonic treatment and the addition of coupling agent. The mechanical properties and thermal stability of the pure PI film can be improved by adequate addition of Al₂O₃. The PI hybrid film was strengthened and toughened simultaneously by the introduction of the well-dispersed Al₂O₃ particles. The PI hybrid films showed improved electrical aging performance as compared with pure PI film. Especially, the PI hybrid films with 10 wt.% of Al₂O₃ content exhibited obviously enhanced electrical aging performance with the time to failure of 3.4 times longer than that of pure PI film. The improved electrical aging performance of the hybrid film was attributed to the nano-sized Al₂O₃ particles highly dispersed in the hybrid film, which confirmed by the investigation of the morphology and the surface composition of PI hybrid film before and after electrical aging.     

A Novel Method for Preparing Nano‐ and Microcomposite Al2O3‐ZrO2 Ceramic Coatings

Nano‐ and microcomposite Al₂O₃‐ZrO₂ coatings were deposited on various substrates in a sol‐gel ceramic paint by a supercentrifugal force and a gradual sintering process. Fine metal oxide powders were dispersed in a sol‐gel solution by superpower ball milling so as to form a uniform stable ceramic paint. High‐resolution microscopy (FE‐SEM) was used to characterize the coating, indicating that the coating is composed of composite particle clusters with an average diameter of ～1 µm. The clusters consisted of larger particles with an average diameter of ～0.5 µm in center and smaller particles of ～100 nm surrounding the larger ones. The coating was relatively dense and increasingly dense toward the substrate surface.     

Preparation of compact Al2O3 film on metal for oxidation resistance by polyvinylpyrrolidone

Oxidation resistance of metal at high temperature can be improved by an environmentally friendly solution deposition approach. Stable precursor solution with high oxide concentration, favorable viscosity and low surface tension was prepared using aluminum sec-butoxide (ASB) and polyvinylpyrrolidone (PVP) as starting raw materials. Alumina sol-gel films were deposited onto metal by spin-coating followed by heat treatment. When PVP was added according to an amount of 50 mg/mL into a sol with an ASB/H₂O molar ratio of 1:35, the as-obtained sol exhibited favorable gelation time and viscosity. The surface tension of the alumina sol with PVP was examined to be lower by 32% than the sol (ASB:H₂O = 1:100) without PVP. TG-DTA analyses show the densification of the alumina gel film with PVP was progressed within a wide temperature range from 200 to 650 °C. Crack-free Al₂O₃ film with a thickness up to 1.5 μm was successfully produced on metallic substrate by three spin-coating cycles. SEM and XRD analyses revealed the gel film transformed into compact α-Al₂O₃ material after calcined at 1,000 °C for 0.5 h. The weight gained by the samples during firing at 1,000 °C indicated that the Al₂O₃ coating film could reduce the rate of oxidation by ∼81%. The hardness of the Al₂O₃ film coated metal was higher by 260% than the uncoated metal that was calcined at 1,000 °C for 0.5 h. It was confirmed by adhesion test that both the alumina/PVP hybrid film and the as-produced α-Al₂O₃ coating film had strong adhesion.     

Controlled synthesis of graphene oxide/alumina nanocomposites using a new dry sol–gel method of synthesis

The present paper gives new insight into the problem of controlling the morphology of reduced graphene oxide/alumina (RGO/Al₂O₃) nanocomposites. The dry and simplified sol–gel methods of RGO/Al₂O₃ nanocomposite synthesis were compared and the influence of six key synthesis parameters on the morphology of the resulting nanocomposite powders was investigated to optimize the morphology of RGO/Al₂O₃ nanocomposites in terms of reducing the undesired agglomeration of RGO/Al₂O₃ nanocomposite flakes to a significant minority and obtaining the uniform coverage of RGO surface with Al₂O₃ nanoparticles. Our investigations indicate that, despite the high excess of Al₂O₃ used (95 wt%), the lowest RGO/Al₂O₃ flake agglomeration and the formation of a uniform layer composed of Al₂O₃ nanoparticles with the average size of 58 nm occurred only when 5 wt% of graphene oxide was used as a substrate for the deposition of Al₂O₃ nanoparticles together with triethyl aluminium as an Al₂O₃ precursor and dry hexane as the reaction environment. The resulting organic precursor was thermally decomposed at 280 °C for 3 h in air atmosphere (R4 reaction pathway). This was confirmed by the high BET-specific surface area (242.4 m²/g) and the high open porosity (0.7 cm³/g) of the obtained RGO(5 wt%)/Al₂O₃ nanocomposite. This is also the first study with a detailed discussion of the reactions expected to occur during the synthesis of an RGO/Al₂O₃ nanocomposite.     

Synthesis of Nano‐Sized TiO2 Colloidal Sol and Its Optical Properties

Nano‐sized TiO₂ sol was prepared through a wet synthesis process. The synthesis procedure involved hydrolysis of TiCl₄, acid treatment, and a SiO₂ surface‐modifying process. Before surface modification, the TiO₂ suspension was treated with acid to remove Na ions, soluble TiO_2, and other impurities. The acid treatment of a TiO₂ suspension at a higher temperature was proved to be useful for effective SiO₂ modification. The colloidal sol provided high transparency in visible light as well as excellent UV‐shielding properties. Surface modification of TiO₂ particles with SiO₂ greatly improved both the dispersing stability in neutral pH and the photostability of TiO₂ colloidal sol.     

Efficient conversion of fructose to 5‐hydroxymethylfurfural by functionalized γ‐Al2O3 beads

Millimeter size γ‐Al₂O₃ beads were prepared by alginate assisted sol–gel method and grafting organic groups with propyl sulfonic acid and alkyl groups as functionalized γ‐Al₂O₃ bead catalysts for fructose dehydration to 5‐hydroxymethylfurfural (5‐HMF). Experiment results showed that the porous structure of γ‐Al₂O₃ beads was favorable to the loading and dispersion of active components, and had an obvious effect on the properties of the catalyst. The lower calcination temperature of γ‐Al₂O₃ beads increased the specific surface area, the hydrophobicity and the activity of catalysts. Competition between the reaction of alkyl groups and ‐SH groups with surface hydroxyl during the preparation process of the catalyst influenced greatly the acid site densities, hydrophobic properties and activity of the catalyst. With an increase in the alkyl group chain, the hydrophobicity of catalysts increased obviously and the activity of the catalyst was enhanced. The most hydrophobic catalyst C₁₆‐SO₃H‐γ‐Al₂O₃–650°C exhibited the highest yield of 5‐HMF (84%) under the following reaction conditions: reaction medium of dimethylsulfoxide/H₂O (V/V, 4:1), catalyst amount of 30 mg, temperature of 110°C and reaction time of 4 hr.     

Hydrogen production via CO2-reforming of methane over Cu and Co doped Ni/Al2O3 nanocatalyst: impregnation versus sol–gel method and effect of process conditions and promoter

In this study, Cu and Co doped Ni/Al₂O₃ nanocatalyst was synthesized via impregnation and sol–gel methods. The physiochemical properties of nanocatalyst were characterized by XRD, field emission scanning electron microscopy (FESEM), particle size distribution, BET, fourier transform infrared spectroscopy (FTIR), TG–DTA and energy dispersive X-ray (EDX) analysis. The samples were employed for CO₂-reforming of methane in atmospheric pressure, temperature range from 550 to 850 °C, under various mixture of CH₄/CO₂ and different gas hourly space velocity. XRD patterns besides indicating the decline of the peaks intensity in sol–gel method, proved the potential of this procedure in diminishing the crystal size and preventing the NiAl₂O₄ spinel formation. Moreover, high surface area might derive of smaller particle size and uniform morphology of sol–gel prepared ones, confirmed by FESEM and BET analysis. TG–DTG analysis as well supported the higher surface area for sol–gel made ones, represented the proper calcination temperature (approximately 600 °C). Also, presence of the active phases and elemental composition of nanocatalysts determine via EDX analysis. Promoting the basicity and the adsorption rate of CO₂, is attributed to the higher amount of OH groups for sol–gel prepared samples, proved by FTIR. Ni–Co/Al₂O₃ due to the synergetic effect of sol–gel method and cobalt addition depicted excellent characterization such as higher surface area, smaller particle size, supplying more stable support and enhanced morphology. Therefore, this nanocatalyst represented the best products yield (H₂ = 98.21 and CO = 95.64), H₂/CO close to unit (0.92–1.05) and stable conversion during 1,440 min stability test. So, Ni–Co/Al₂O₃ among all of the prepared nanocatalysts demonstrated the best catalytic performance and presented it as a highly efficient catalyst for dry reforming of methane. Despite of the stable yield of Ni–Cu/Al₂O₃, it depicted the lower catalytic activity and H₂/CO ratio than the unprompted nanocatalysts.     

Effect of synthesis parameters on the particle size, composition and colloid stability of polypyrrole–silica nanocomposite particles

 The effect of varying the oxidant, monomer and silica sol concentrations, silica sol diameter, polymerization temperature, stirring rate and oxidant type, on the particle size, polypyrrole content and conductivity of the resulting polypyrrole– silica colloidal nanocomposites has been studied. Surprisingly, nanocomposite formation appears to be relatively insensitive to most of the above synthesis parameters. One synthesis parameter which does have a significant and reproducible effect is the stirring rate: smaller, more monodisperse nanocomposite particles are obtained from rapidly stirred reaction solutions. However, this effect is only observed for the (NH₄)₂S₂O₈ oxidant. An alternative oxidant, H₂O₂/Fe³⁺, was found to give nanocomposites of similar particle size, polypyrrole content and conductivity to those obtained using the (NH₄)₂S₂O₈ oxidant. The colloid stability of these polypyrrole–silica nanocomposite particles depends on their silica content. The colloid stability of a silica-rich nanocomposite prepared using the (NH₄)₂S₂O₈ oxidant in the presence of electrolyte was comparable to that of a silica sol, whereas a polypyrrole-rich nanocomposite prepared using FeCl₃ had markedly poorer colloid stability under these conditions. These observations are consistent with a charge stabilization mechanism for these nanocomposite particles. Received: 5 March 1998 Accepted: 27 April 1998