溶胶-凝胶法制备不对称氧化铝膜

以异丙醇铝为原料,过量的水、醇溶剂的存在有利于异丙醇铝水解．适宜的水铝比H₂O／Al^3＋为100：1;醇铝比ROH／Al^3＋为5：1;酸胶溶剂的浓度H^＋／Al^3＋为0．07：1．溶胶的雾化快速胶凝法,大大缩短了凝胶干燥的时间,采用这种方法能容易地制备膜厚均匀、且无龟裂的无机氧化铝膜．适宜的溶胶浓度为0．5～1．4mol AlOOH／L溶胶,喷雾距离＜200mm,膜厚与溶胶浓度、喷雾时间成正比,与喷雾距离的平方成反比．用γ-AlOOH溶胶对基质膜作进一步的修饰制备不对称氧化铝膜时,勃母石溶胶的初始晶粒的大小决定着氧化铝膜的孔径,勃母石溶胶的胶体粒子的直径决定着形成的不对称膜的稳定性．勃母石溶胶的胶体粒子的平均直径与支撑体基质膜表面的最可见孔径相当时,喷涂于基质膜表面的溶胶快速胶凝后,能形成无裂纹和针孔的均匀凝胶膜．以表面最可几孔径为0．1μm的氧化铝膜为基质膜,雾化溶胶胶粒平均直径为100nm左右的勃母石溶胶,喷涂于基质膜表面,快速胶凝后于400℃焙烧形成的支撑γ-Al₂O₃膜孔径为3nm．     

Potential of fusion technique in production of mesoporous zeolite A powder from poor kaolin through modification by boehmite: Effect of clay mineralogy on particle morphology

The aim of present study is to investigate the modification of poor kaolin by boehmite to produce zeolite A via fusion techniques. The processed kaolins containing considerable content of quartz, as a major impurity, were employed, and alkalinity, boehmite content, fusion temperature, and ageing time were changed to achieve zeolite A. Regardless of the starting material composition, the sodium hydroxide/kaolin ratio should be fixed in the range of 2.00–2.33 to delete quartz. Boehmite was added to material mixtures for compensating aluminum deficit followed by thermal treatment at 700, and 800 °C. The presence of boehmite in the precursors is very crucial for the formation of zeolite A. The maximum relative crystallinity was obtained by control of the boehmite/kaolin ratio at the level of 0.26. The zeolite A produced from clay containing illite + kaolinite + pyrophyllite indicated the semi-cubic particles with rounded edges, and lower surface area, 17.5 m².g^?1 while the application of kaolinite-rich clay resulted in the mesoporous product with an average pore size of 8 nm, and larger surface area of about 59.6 m².g^?1.     

Nano-porous hydrosodalite fabrication via hydrothermal modification of processed kaolin by boehmite: Aluminum source effect on physico-chemical characteristics of product

The nano-porous hydrosodalite was produced from a poor kaolin containing quartz, as major impurity, via the hydrothermal modification with boehmite and sodium aluminate. The physico-chemical characteristics of products were evaluated by XRD, SEM and BET techniques. The obtained results indicated that the direct reaction between poor metakaolin and sodium hydroxide leads to the zeolite compound formation in which the partially crystallized hydrosodalite and remained quartz were embedded in amorphous phase. Different trends were observed in crystallinity of produced materials with aluminum source content revealed the predominantly crystalline structure for hydrosodalite fabricated via use of sodium aluminate. There is an inverse relationship between the boehmite content and crystallinity whilst the increase in the sodium aluminate content led to production of a well-crystalline hydrosodalite. Although, the dense cabbage-like particle structure was successfully created by hydrothermal reaction between metakaolin and sodium aluminate, NaAlO₂/MK: 0.36, and the nano-porous hydrosodalite can be fabricated at limited content of boehmite, AlOOH/MK: 0.20. Moreover, the hydrothermal reaction in the presence of boehmite causes the generation of nano-porous structure with average pore size of 8.0 nm, accompanied with negligible co-crystallization of cancrinite. This change in porous structure could be useful in engineering applications like water and wastewater treatments.     

Printable and flexible macroporous organosilica film with high protein adsorption capacity

An approach for creating a flexible and macroporous silsesquioxane film using phase separation method is described. The porous film was prepared by a simple coating method where sol-gel solution containing polyacrylic acid (PAA) and 1,6-bis(trimethoxysilyl)hexane in water was applied on boehmite silica coated polymethylmethacrylate (PMMA) film. After drying, the water soluble PAA template was removed by washing the film with water revealing the porous film. With certain ratios of PAA and water, fully co-continuous pore system with open surface was obtained. Porous films with 3-4 μm thickness were found to be highly flexible. The biocompatibility of the porous film was tested by immobilizing a high affinity biotin-binding chimeric avidin (ChiAVD(I117Y)) into the porous matrix The porous film was found to adsorb higher amounts of functional chimeric avidin compared to the pure PMMA film or a boehmite silica coated PMMA film.     

Template-free solvothermal synthesis of hierarchical boehmite hollow microspheres with strong affinity toward organic pollutants in water

Three-dimensional hierarchical boehmite hollow microspheres with a very high yield at low cost were successfully synthesized via a one-pot template-free solvothermal route using aluminum chloride hexahydrate as precursor in a mixed ethanol–water solution with assistance of trisodium citrate. The as-synthesized products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption/desorption techniques. The results show that Cl⁻ and addition amount of trisodium citrate have significant effect on the morphologies of the resultant products, and 6–8 mmol of trisodium citrate is optimal for the synthesis of boehmite hollow microspheres assembled from randomly interconnecting and aligned nanorods with solvothermal time no less than 15 h. A synergistic mediation mechanism of citrate ions and Cl⁻ to form boehmite hollow spheres via self-assembly morphology evolution was proposed based on the experimental results. Interestingly, the typical boehmite hollow microspheres with a surface area of 102 m² g⁻¹, pore volume of 0.37 cm3 g⁻¹, and the average pore size of 14.6 nm show superb adsorption properties for Congo red with maximum capacity of 114.7 mg g⁻¹ which is higher than that of a commercial boehmite. This simple synthetic route is a very promising way for the design and synthesis of new functional hierarchical nanostructured materials with desired adsorptive properties.     

Boehmite nanopetals self assembled to form rosette-like nanostructures

Rosette-like boehmite nanostructures were prepared successfully via a simple hydrothermal process. The obtained material was characterized with X-ray powder diffractometry (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Using Scherrer formula, the average crystallite size of the obtained boehmite rosettes was measured to be about 8 nm. It was shown that boehmite nanopetals with average width of about 41 nm determined by TEM, were formed during the hydrothermal process and then self assembled due to weak hydrogen bonds to fabricate boehmite rosettes. The specific surface area of the obtained rosette-like nanostructures was calculated through BET N₂-adsorption technique to be about 143.08 m²/g.     

Control of micropore size distribution in alumina by the hydrothermal treatment of an alkoxide derived-alcogel

Alumina precursors were prepared by hydrothermal treatment of an alkoxide derivedalcogel. By selection of appropriate hydrothermal conditions aluminas with a variety of pore distributions were obtained, and the pore radius can be easily controlled from 5.0 to 23.5 nm. The hydrothermal conditions were found to strongly affect pore size distribution: (i) elevating the hydrothermal temperature and increasing the time increased the particle size of boehmite, resulting in the above average pore radius of the aluminas; (ii) the alumina obtained from HT-270-10 had an average pore radius of approximately 20 nm and 1 ml g^–1 pore volume, which were maintained until 1000°C. After heating at 1200°C for 5 h, their values were 17.9 nm and 0.45 ml g^–1, respectively; (iii) the hydrothermal treatment with ethanol gave boehmites with a large particle size and aluminas with a sharp pore distribution and small pore radius. These results were explained by differences in the three-dimensional structures formed by the hydrothermal treatments.     

勃姆石纳米片增强锂离子电池隔膜性能研究

采用勃姆石涂覆改性聚烯烃隔膜可以提升锂离子电池的隔膜热稳定性和电解液润湿性。本工作通过简单的水热法合成了平均粒径约为150 nm的勃姆石纳米片, 并采用刮涂法涂覆在聚乙烯(Polyethylene, PE)隔膜表面。该涂覆隔膜的孔隙率达到46.6%、吸液率为138.9%、离子电导率为0.47 mS/cm和锂离子迁移数为0.42, 使得该隔膜组装的锂离子电池具有较好的循环稳定性, 在1C(1C=150 mA/g)的电流密度下循环100次后仍能保留93.7%的放电比容量。同时, 勃姆石纳米片涂覆的隔膜的孔结构分布均匀, 优化了锂离子传输通量, 抑制了锂枝晶。     

Application of surface behaviour diagrams to the study of hydration of phosphoric acid-anodized aluminium

The hydration of aluminium surfaces prepared for adhesive bonding by anodization in phosphoric acid has been studied using surface behaviour diagrams. These surface behaviour diagrams, which are similar to phase diagrams for equilibrium bulk phases, trace the evolution of the aluminium adherend surface composition, obtained by X-ray photoelectron spectroscopy, during the hydration process. When supplemented with high-resolution scanning electron micrographs and Auger depth profiles, the surface behaviour diagrams show that hydration proceeds in three steps. The first step is reversible and consists of the adsorption of water by the monolayer of AlPO₄ initially present on the surface. It involves no change in the oxide morphology. The second, which appears to be rate-controlling, involves the slow dissolution of the phosphate followed by rapid hydration of the exposed alumina to the oxyhydroxide, boehmite. During this stage, extensive morphological changes occur as the boehmite fills the pore cells and bridges the whiskers of the original surface. The third step consists of the nucleation and growth of the trihydroxide, bayerite, on top of the boehmite. Using these results as examples, we propose the surface behaviour diagram approach as a new tool for the study of surface reactions in general.     

The preparation and characterization of alumina membranes with ultra-fine pores

Alumina films less than 20m thick are prepared by a process in which a boehmite sol is successively gelled, dried and calcined. The resulting structure has the unique property that only ultra-fine pores with a narrow pore size distribution are present within large crack-free layers. The microstructure can be influenced by the sintering temperature and the acid concentration of the precursor sol. The minimum modal pore size which has been obtained is 2.5 nm. A consistent model of the microstructure of the membranes and an explanation of its uniformity are presented.     

Self-repairing poly(phenylenesulfide) coatings in hydrothermal environments at 200 °C

Usefulness of hydraulic calcium aluminate (CA) fillers, containing monocalcium aluminate (CaO.Al₂O₃) and calcium bialuminate (CaO.2Al₂O₃) reactants as the major phases, in healing and repairing micro-sized cracks generated on the surfaces of poly(phenylenesulfide) (PPS) coating was evaluated by exposing the cleaved coatings to a simulated geothermal environment. CA fillers with a grain size of <40 μm were incorporated into the PPS coatings. The cleaved PPS coatings containing fillers then were exposed for up to 20 days in a 200 °C CO₂-laden brine. The decalcification–hydration reactions of the CaO.Al₂O₃ and CaO.2Al₂O₃ reactants disclosed in the cracks led to the rapid growth of boehmite crystals, while the crystalline calcite phase formed by the carbonation of these reactants was leached out of cracks because of the formation of water-soluble calcium bicarbonate. During exposure for 24 h, the block-like boehmite crystals, ∼4 μm in size, densely filled and sealed the open cracks; this was reflected in an increase in pore resistance to two orders of its magnitude compared with that of cleaved coatings without fillers. Extending the exposure time to 20 days resulted in no change in pore resistance, suggesting that the sealing of the cracks by boehmite crystals played an essential role in reconstituting and restoring the function of the failed coatings as corrosion-preventing barrier. Therefore, CA-filled PPS coatings are able to self-heal and -repair cracks generated on the surfaces of coating films in hydrothermal environments.     

Synthesis and characterization of Al2O3 catalyst carriers by sol-gel

The sol-gel method has been used to synthesize alumina powder with high surface area from boehmite. The characteristics of the final powder product have been systematically studied in light of the preparation method and starting materials by fractional factorial design. The results show that the type of precursor and pH of the precursor sol are the most important parameters for the textural properties of the calcined alumina powder. When the calcination temperature is increased the type of precursor loses its significance, while the pH still has decisive importance after calcination at 1000°C, on pore volume and surface area. There is also a significant combined effect of several parameters on the surface area and the pore volume. The electrophoretic mobility, agglomerate size and size distribution have been determined as a function of the pH for one type of boehmite sol. The relation between characteristics of the precursor and powder properties is clearly emphasized.     

Hydrothermal crystallization of boehmite from freshly precipitated aluminium hydroxide

Hydrothermal crystallization of boehmite from freshly precipitated aluminium hydroxide was monitored using X-ray powder diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. Crystallite sizes and interplanar spacings for boehmite samples were determined. Changes in the crystallinity of boehmite influenced the corresponding FT-IR spectra. The maximum specific area for boehmite powder was 246 m² g⁻¹, as measured by the Brunauer–Emmet–Teller (BET) method. With an increase of the crystallinity of boehmite, the specific area decreased and for the best crystalline sample, was 91 m² g⁻¹. All boehmite samples contained particles of colloidal dimensions. For the best crystalline boehmite sample, hexagonal-like plates were observed and some of them were elongated.     

Preparation of porous boehmite nanosolid and its composite fluorescent materials by a novel hydrothermal hot-press method

Boehmite (AlO(OH)) porous nanosolid has been successfully prepared by a novel hydrothermal hot-press (HHP) method, using Al₂O₃ nanoparticles as the starting material. Furthermore, a new organic fluorescent material (E,E)-4-{2-[P′-(N,N-di-n-butylamino)stilben-p-yl]vinyl}pyridine (DBASVP) was assembled into the pores of the boehmite porous nanosolid, thus a DBASVP/boehmite porous nanocomposite was obtained. Because of the interaction between DBASVP molecules and the surface of boehmite porous nanosolid, a red-shift of the fluorescent peak was observed in boehmite/DBASVP composite by comparing with that of DBASVP.     

水热处理和尿素改性对三水铝石微观结构的影响

以尿素为改性剂,用水热处理方法对三水铝石进行了改性处理。结果表明,尿素的加入量和水热处理时间对产物微观结构有显著的影响,当尿素与三水铝石的摩尔比小于6∶1时,水热处理24 h的产物为片状薄水铝石;当摩尔比超过8∶1时,产物为板条组装的球形碱式碳酸铝铵.纯相碱式碳酸铝铵的形成与水热处理的时间有关,随处理时间的延长,氢氧化铝经历了由三水铝石到薄水铝石与碱式碳酸铝铵混相结构再到纯相碱式碳酸铝铵的演变过程,期间发生由块体到片状再到片组装块体的微观形貌变化,最后演变为板条组装球形结构。     

Nanoparticles assembly of boehmite nanofibers without a surfactant

Self-assembly of aluminum hydrate particles into larger boehmite (γ-AlOOH) nanofibers was illustrated by a facile hydrothermal method without using any surfactants. The size and morphology of boehmite nanofibers could be controlled by adjusting the pH value of the reaction mixture. The resulting products were characterized by XRD (X-ray diffraction), FTIR (Fourier transform infrared spectra), SEM (scanning electron microscopy), and TEM (transmission electron microscopy). The specific surface area and pore-size distribution of the obtained product as determined by gas-sorption measurements show that the boehmite nanofibers possess high-surface area and porosity properties. A possible formation mechanism of nanofibers via a nanoparticle assembly procedure is proposed based on the experiments under the different conditions.     

Sol-gel synthesis of alumina,titania and mixed alumina/titania in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulphonyl) amide

In this paper we report on the synthesis of alumina, titania and mixed alumina–titania in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulphonyl) amide [Py_1,4]TFSA via sol-gel methods using aluminium isopropoxide and titanium isopropoxide as precursors. Our results show that the as-synthesized alumina is mainly mesoporous boehmite with an average pore diameter of 3.8 nm. The obtained boehmite is subject to a phase transformation into γ-Al₂O₃ and δ-Al₂O₃ after calcinations at 800 and 1,000 °C, respectively. The as-synthesized TiO₂ shows amorphous behaviour and calcination at 400 °C yields anatase which undergoes a further transformation to rutile at 800 °C. The as-prepared alumina–titania powders are amorphous and transformed to rutile and α-Al₂O₃ after calcination at 1,000 °C TiO₂. The obtained alumina–titania has a higher surface area than those of alumina or titania. The surface area of the as-synthesized alumina–titania was found to exceed 486 m² g⁻¹, whereas the surface areas of the as-synthesized boehmite and titania were around 100 m² g⁻¹, respectively.     

Preparation and characterization of Au/CeO2–Al2O3 monoliths

Porous CeO₂–Al₂O₃ monoliths with hierarchical pore structure were prepared by mixing boehmite particles with solutions containing different amounts of cerium chloride and aluminum nitrate. The monoliths were functionalized with gold nanoparticles using the incipient wetness method. The resulting materials were characterized by X-ray diffraction, nitrogen sorption, mercury porosimetry, UV–vis spectroscopy and transmission electron microscopy. The catalysts were tested in liquid phase glucose oxidation, comparing continuously stirred batch reactor and continuous-flow fix-bed reactor setups.     

Effects of the hydrogen content on the development of anodic aluminum oxide film on pure aluminum

In this study, high purity aluminum (Al) samples containing different levels of hydrogen were used as a base metal for anodization. To ensure constant current densities during the experiments, the voltage-time (V-t) curves were recorded. The differential ΔV/Δt curves were plotted and the energy consumed during different steps of anodization was calculated. Experimental observations show that differences in the hydrogen content affected the amount of energy consumed. The process was divided into three steps.When the voltage response at the end of step 2 exceeded 25 V, the energy consumed in steps 2 + 3 reached or exceeded 7.4 J/cm², and the pore channels branched or merged, creating a spike in the ΔV/Δt curves in step 3. A combination of the effects of the high voltage response at the end of step 2 and the high hydrogen content in the Al samples led to the formation of an anodic aluminum oxide (AAO) film in the sulfuric acid solution, which produced crystallized boehmite. This study proposes a unique tool for understanding certain special anodic behaviors of pure Al, wherein the branching or merging of pore channels and the partial crystallization of the AAO film can be ascertained by looking at the irregularities in the ΔV/Δt curves obtained in step 3.     

Formation characteristics of an aluminum hydroxide fiber by a hydrolysis of aluminum nano powder

Formation of aluminum hydroxide by a hydrolytic reaction of nano aluminum powder synthesized by a pulsed wire evaporation (PWE) method has been studied. The type and morphology of the hydroxides were investigated with various initial pH and temperatures. The nano fibrous boehmite (AlOOH) was formed predominantly over 40°C of the hydrolytic temperature, while the bayerite (Al(OH)₃) was formed predominantly below 30°C with a faceted crystalline structure. As a result, the boehmite showed a much larger specific surface area (SSA) than that of bayerite. The highest SSA of the boehmite was found about 409 m²/g.