Mesoporous Γ-alumina Research Articles

Nanostructured ZrO2 membranes prepared by liquid-injection chemical vapor deposition

Using the molecular compound Zr(OBut)4 in a liquid-injection chemical vapor deposition process, microporous zirconia membranes were deposited on porous multi-layered alumina substrates consisting of a macroporous α-alumina base covered with a mesoporous γ-alumina layer. The structure of nanocrystalline zirconia (ZrO2), membranes formed by the thermal decomposition of the precursor varied depending on the decomposition temperature and the injection frequency. The deposited zirconia membranes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and atomic force microscopy (AFM). X-ray diffraction analysis patterns of the deposits obtained at 500 and 600°C indicated a mixture of tetragonal and monoclinic ZrO2 phases, whereas the fraction of the monoclinic phase increased at higher substrate temperature and injection frequency. Morphology and surface roughness are strongly dependent on the process parameters. ZrO2 membranes prepared by the liquid-injection chemical vapor deposition had a microporous structure with less than 1nm Kelvin diameter. The liquid-injection chemical vapor deposition is a unique method to prepare microporous membranes in one step without any post-treatment.

Synthesis of ordered mesoporous γ-alumina influenced by the interfacial protector

The mesoporous γ-alumina samples were synthesized by the sol–gel method with P123 as the structure directing agent and different structural organic compounds as the interfacial protectors, such as phenylamine (PA), o-phenylenediamine (OPDA), p-aminobenzoic acid (PABA), benzoic acid (BA) and o-phthalic acid (OPA). The results revealed that the functional group of interfacial protector had great impact on the ordered structure and thermal stability of mesoporous γ-alumina. Among those interfacial protectors, the use of the PABA or OPA could shape the ordered mesoporous structure, which was related to the specific structure of interfacial protector. The possible mechanisms about the formation of the ordered mesoporous alumina have been also explored, which will provide the theoretical guidance for choosing the suitable interfacial protector.

Mesoporous γ-alumina nanoparticles: Synthesis, characterization and dye removal efficiency

Herein we present the textural characterization of nano sized mesoporous γ-alumina obtained by template method using dodecylamine, and its potential application as congo red adsorbent from aqueous solution. The physical characteristics of the material were investigated using FT-IR spectroscopy, N2 adsorption study, XRD (both wide and low angle), SEM, and TEM. Wormhole type pores of width 3–12nm were noticed in the material. Meso alumina was identified as the most efficient solid for the adsorptive removal of congo red, which was attributed to its porous texture, nano size, and abundant surface hydroxyl groups.

A facile rout to synthesis lamellate structure mesoporous alumina using polyethylene glycol 6000 (PEG, molecular weight = 6000) as structure directing agent

In this study, Al2(SO4)3 and NaAlO2 were used as aluminum precursors for preparing lamellate structure mesoporous alumina with crystalline framework walls in the presence of non-ionic surfactant PEG6000. The characterization by SEM, TEM, TG-DSC and FTIR revealed that PEG surfactant induced the formation of the lamellate structure boehmite with relatively lower water content. XRD and SAED results conveyed the formation of well-crystallined mesoporous γ-alumina after the samples were calcined at 600°C for 3h. N2 physisorption showed that the mesoporous alumina prepared in this way displayed very rich porosities with large mesopores, and both the pore volumes and the pore sizes increased with the addition of such surfactant in the precipitation process. The obtained γ-alumina with lamellate morphology exhibited a large surface area of 279m2/g, and the powder has no obvious agglomeration. The improved textural parameters in the samples should be attributed to the formation of lamellate structure nanoparticles.

Sorption of phosphate onto mesoporous γ-alumina studied with in-situ ATR-FTIR spectroscopy

BackgroundDue to the extensive use of phosphates in industry, agriculture and households, the phosphate - γ-alumina interactions are important for understanding its detrimental contribution to eutrophication in lakes and rivers. In situ Fourier transform infrared (FTIR) spectroscopy can provide more detailed information on the adsorbate-adsorbent interaction and the formation of hydrogen bonds.ResultsIn situ ATR-FTIR spectroscopy was used to identify phosphate complexes adsorbed within the three-dimensional network of mesoporous γ-alumina at pH 4.1 and 9.0. The integrated intensity between 850 cm-1 and 1250 cm-1 was used as a relative measure of the amount of adsorbed phosphate. The integrated intensity proved to be about 3 times higher at pH 4.1 as compared with the corresponding intensity at pH 9.0. The adsorption of phosphate at the two pH conditions could be well described by the Langmuir adsorption isotherm at low concentrations and the empirical Freundlich adsorption isotherm for the whole concentration range, viz. 5 – 2000 μM.ConclusionsFrom the band shape of infrared spectra at pH 4.1 and pH 9.0, it was proposed that the symmetry of the inner-sphere surface complex formed between phosphate and γ-alumina was C1 at the lower pH value, whilst the higher value (9.0) implied a surface complex with C2v or C1 symmetry. The difference in adsorbed amount of phosphate at the two pH values was ascribed to the reduced fraction of ≡ AlOH2+ surface sites and the increased fraction of ≡ AlO- sites upon increasing pH from 4 to 9.

Facile strategy for synthesis of mesoporous crystalline γ-alumina by partially hydrolyzing aluminum nitrate solution

The facile synthesis of mesoporous γ-alumina is developed through the partial hydrolysis of Al(NO3)3 aqueous solution with (NH4)2CO3 without organic surfactants. In this synthesis, the stable NH4NO3/Al species (AN/Al) hybrid containing Keggin-Al13 polycations is first prepared, which is the key for the successful formation of mesoporous γ-alumina. XRD, 27Al MAS NMR, TEM, and N2 adsorption and desorption results demonstrate that the as-prepared AN/Al hybrid can be transformed to γ-alumina by treatment at 200 °C and exhibit a wormhole-like mesoporous structure with large surface area up to ∼450 m2 g−1, pore volume of ∼0.3 cm3 g−1 and narrow pore size distribution peaked at ∼3.9 nm after completely removing NH4NO3 at 300 °C. The obtained mesoporous γ-aluminas have high thermal stabilities up to 900 °C and excellent hydrothermal stability. The investigation shows that the synergetic effect of NH4NO3 and Al13 species promotes crystallization of Al species to γ-alumina, which may have a unique mechanism distinct from the mesoporous aluminas reported previously. CO2 adsorption measurements indicate that these mesoporous γ-aluminas have a much higher CO2 adsorption capacity than ordered mesoporous alumina synthesized by the surfactant-templating method and conventional γ-alumina derived from aluminum oxyhydroxides. We believe that this research should be useful for providing new insights into the transformation of transition alumina phases and for synthesizing mesoporous γ-alumina with promising properties for various chemical applications.

A simple hydrothermal route to bimodal mesoporous nanorod γ-alumina with high thermal stability

AbstractIn the presence of polyethylene glycol, bimodal mesoporous nanorod γ-alumina was successfully synthesized via the thermal decomposition of ammonium aluminium carbonate hydroxide precursor which was prepared via hydrothermal processing with inorganic aluminium salt. The alumina exhibits high surface area (494 m2g–1), large porosity (1.1 m3g–1) and a particular double-pore structure after calcination at 500 °C. The smaller pore diameter is concentrated on about 3 nm and the larger one is exhibited in the range of 10 – 38 nm. The scaffold-like aggregation of γ-alumina nanorods endows this novel material with excellent thermal stability. A possible formation mechanism of bimodal mesoporous structure is also proposed in this study.

Synthesis of mesoporous γ-alumina by sol–gel process and its characterization and application for sorption of Pu(IV)

Mesoporous γ-alumina samples were prepared by the sol–gel process from the boehmite sol having different template solutions. Copper doped material was also prepared from sol containing template solution along with copper nitrate. Studies were performed to understand the influence of templates on the morphology of the synthesized samples particularly with respect to specific surface area and porosity. Synthesized samples were used to study sorption of Pu(IV) from nitric acid–oxalic acid solutions. Distribution ratios (D) for Pu(IV) were determined using the γ-alumina samples with an objective to employ these for the recovery of Pu.

Expeditious calcination of inorganic membranes by an instant temperature increment

Rapid thermal treatments potentially allow for a significant reduction in production time of ceramic multilayered membranes, in turn aiding increased industrial application of these membranes and accelerating research on their development. Two methods are proposed for the rapid thermal treatment of thin supported inorganic membrane films. Both methods involve an instant increment in temperature imposed on the membrane. In the first method, the instant temperature step is enforced by placing the membrane in a preheated environment; in the second method, the membrane is placed directly onto a hot plate. The proposed methods can be used for a diverse range of materials. Mesoporous γ-alumina and microporous silica have been selected as model membrane materials. Both rapid heating methods require ∼20 min to yield mesoporous γ-alumina membranes that are comparable to membranes made via conventional calcination (∼1 day). Selective silica membranes have been obtained after 1 h exposure to an environment of 400 or 600 °C, and after 1 h contact with a hot plate of 550 °C (compared to up to 2 days for conventional calcination). The results indicate that, although prevention of contaminations needs continuous attention, both methods proposed for rapid heat treatment can reduce cost and time in ceramic membrane production.

Synthesis of ordered mesoporous γ-Al 2O 3:Eu 3+ with high luminous performance and thermal stability

An efficient and convenient one-step process was developed for synthesizing new effective red luminous materials through ordered mesoporous γ-alumina assembling with Eu 3+. Employing P123 as a structure-directing agent and hydrochloric acid, citric acid as pH adjustor, ordered mesoporous γ-alumina was fabricated by simple sol-gel method. The pore structure was characterized by X-ray diffraction (XRD), N 2 adsorption-desorption isotherms and transmission electron microscopy (TEM). The as-synthesized γ-aluminas had narrow pore-size distribution (5–7 nm), large surface area (246 m 2/g) and high thermal stability (750–1000 °C). The luminous property of materials was characterized by Photoluminescence (PL) spectra. The γ-Al 2O 3:Eu 3+ materials had efficient luminescence, and the emission strength was related to the content of Eu 3+.

Synthesis of organized mesoporous γ-alumina templated with polymer–colloidal complex

Mesoporous γ-Al2O3 materials with high surface area and a narrow pore size distribution were synthesized by facile sol–gel procedure with application of the polymer–colloid complex as a template.

A Mesoporous γ‐Alumina Film with Vertical Mesoporosity: The Unusual Conversion from a Im${\bar 3}$m Mesostructure to Vertically Oriented γ‐Alumina Nanowires

A Mesoporous γ‐Alumina Film with Vertical Mesoporosity: The Unusual Conversion from a <i>Im</i>${\bar 3}$<i>m</i> Mesostructure to Vertically Oriented γ‐Alumina Nanowires

Catalytic conversion of chloromethane to methanol and dimethyl ether over mesoporous γ-alumina

Mesoporous γ-alumina, mp-γ-Al 2O 3, possessing surface area around 385 m 2/g and total pore volume of 2.0 cm 3/g was prepared via template-free sol–gel synthesis. The catalytic activity of the prepared alumina for the conversion of chloromethane to dimethyl ether, DME, in the presence of water or methanol was studied in the temperature range of 170–450 °C employing FTIR spectroscopy. In the absence of water and methanol, the fresh surface of mp-γ-Al 2O 3 showed 100% conversion of chloromethane to DME at temperatures between 250 and 350 °C. However, rapid deactivation of the catalyst resulted in a sharp decrease in the conversion to < 5% within a few minutes of reaction. The catalytic activity was noticeably enhanced by adding water vapor to the gas feed resulting in higher conversions to DME and methanol. The catalytic activity and DME selectivity were further enhanced in the presence of methanol instead of water. In the temperature range of 200–300 °C, complete conversions were obtained at the beginning of reactions before they declined to values between 31 and 45% depending on the reaction temperature. It was proposed that the surface hydroxyl groups are the active sites where chloromethane molecules dissociatively adsorb forming adsorbed methoxy ion intermediates. The adsorption of molecular methanol regenerates the surface hydroxyl groups and enhances the formation of adsorbed methoxy ions on the surface which react further with chloromethane or methanol molecules to produce more DME.

Synthesis of Mesoporous γ-alumina Assisted by Room Temperature Ionic Liquid

Boehmite Sols were used as aluminum precursors for preparing mesoporous alumina with crystalline framework walls in the presence of 1-butyl-3-methyl imidazolium tetrafluoroborate([BMIM][BF4]).The structure of the γ-Al2O3 was examined by N2 physical adsorption,X-ray powder diffraction(XRD),transmission electron microscope(TEM),and solid state 27Al MAS NMR spectra.The results show that alumina with the three-dimensional interconnected scaffold-like channels displays very rich porosities with large mesopores,and the addi-tion of [BMIM][BF4] could improve the pore properties of alumina significantly.

Synthesis of mesoporous alumina using a recyclable methylcellulose template

Mesoporous alumina was synthesized from AlCl 3 and NaAlO 2 using methylcellulose (MC) as the template. The MC could be recycled by exploiting its phase changes with temperature, and 63.48% of the template was recovered after the synthesis. The mesoporous γ-alumina produced was in short-range order, with moderately strong acidity, a narrow pore-size distribution and a median pore diameter of 3.7 nm. The mesoporous alumina was thermally stable up to 650 °C and hydrothermally stable. Mesoporous silica was also successfully synthesized using the MC template. This economical and green synthesis could be applied to prepare other mesoporous or porous materials.

Synthesis of highly ordered mesoporous alumina thin films and their framework crystallization to γ-alumina phase

Here we report the preparation of highly ordered mesoporous alumina films existing both as P6(3)/mmc and Fm-3m mesostructures by using triblock copolymer Pluronic P123 as the structure-directing agent. 2D grazing-incidence small-angle X-ray scattering (GI-SAXS) completely proves the existence of two different mesopore structures (i.e., [001]-oriented P6(3)/mmc and [111]-oriented Fm-3m symmetries). After calcination at 1000 °C, the amorphous alumina framework is successfully converted to γ-alumina crystals. During the crystallization process, large uniaxial shrinkage occurs along the direction perpendicular to the substrate with the retention of horizontal mesoscale periodicity, thereby resulting in formation of partially vertical mesoporosity in the film. Through detailed electron microscopic study, we discuss the formation mechanism for the vertical mesoporosity upon calcination. The obtained mesoporous γ-alumina film shows high thermal stability up to 1000 °C, which is highly useful in wide research areas such as catalyst supports and separators.

Cleaner synthesis of mesoporous alumina from sodium aluminate solution

Mesoporous alumina (MA) has attracted much attention because of its potential industrial applications as catalyst and adsorbent. The synthesis of MA is performed commonly from organic aluminium alkoxide in non-aqueous media such as alcohol, although this process is more expensive than its inorganic synthesis. However, to date, MA inorganic synthesis processes have been environmentally unfriendly and generate large masses of worthless salt by-product. A cleaner process for the synthesis of MA from supersaturated sodium aluminate solution by the neutralization of sodium bicarbonate, using Cetyltrimethyl Ammonium Bromide (CTAB) as a template, is proposed in this research. The sodium carbonate by-product from this process can be readily recycled by carbonation with carbon dioxide to prepare the sodium bicarbonate reagent solution. This novel process can be integrated into the commonly and widely used sintering process in the alumina industry, i.e., part of the sodium carbonate by-product can be used to extract alumina from bauxite to make sodium alumina solution through sintering. The prepared MA was characterized as hydrothermally stable and short-range ordered mesoporous γ-alumina with controllable pore size and qualified modality. The cleaner and economical synthesis of MA from inorganic sources can significantly promote its application in industry.

Catanionic-surfactant templated synthesis of organized mesoporous γ-alumina by double hydrolysis method

Organized mesoporous γ-alumina samples were prepared by cationic-anionic double hydrolysis (CADH) method using the mixture of cationic and anionic surfactants as template. The intermediate aluminum oxyhydroxides were characterized by XRD, SEM, TEM, FT-IR and TG. Boehmite could easily form under the given synthetic conditions, where an increase in the crystallization temperature favored the formation of well-crystallized boehmite. After the calcination, organized mesoporous γ-Al2O3 was obtained by dehydroxylation between AlOOH octahedron structures. After being characterized by N2 adsorption–desorption, the obtained γ-Al2O3 was of excellent textural properties, i.e., large pore volume (0.79 cm3 g−1), and large pore size (12.1 nm) with narrow pore size distribution which can be used as good candidates for catalyst support in the processing of heavy petroleum. In this modified CADH method, the mixture of cationic and anionic surfactants plays a key role in the formation of relatively large mesopore.

CTAB-directed synthesis of mesoporous γ-alumina promoted by hydroxy carboxylate: The interplay of tartrate and CTAB

Mesoporous γ-aluminas are prepared via a facile one-pot hydrothermal method using aluminum sulfate as a precursor, urea as precipitating agents, sodium tartrate and CTAB (cetyltrimethylammonium bromide) as co-templates respectively. Characterizations of the intermediate aluminum oxyhydroxides by IR, XRD, element analysis and TG show that the amounts of CTAB occluded in the as-prepared mesoporous aluminum oxyhydroxides are determined by molar ratio of sodium tartrate to aluminum (ST/Al). Especially, no sodium tartrate is added, no CTAB is occluded in the mesoporous aluminum oxyhydroxides. The structures of obtained mesoporous aluminas are characterized by XRD, nitrogen adsorption analysis, and scanning electron micrographs (SEM). And the surface areas, mesopore volume and the order of meso-structure are enhanced with an increase in ST/Al molar ratio. Sodium citrate and sodium succinate are also used as additives to study the formation mechanism of organized mesoporous aluminas. The formation mechanisms are proposed that tartrate interacts with aluminum and CTAB simultaneously to form an intermediate as the building blocks of the final meso-structured hybrid.

Facile Preparation and Characterizations of Potential Low-Cost Nanostructured Materials for Energy Gas Storage

Mesoporous γ-alumina with relatively high surface area of 400 m2/g and pore size of ca. 3.8 nm were successfully prepared using facile and cost-effective method employing sol-gel route at room temperature and atmospheric pressure in the presence of conventional surfactant and fatty alcohol (palm oil derived) as template. The limited amount of water gradually added during the synthesis was found to control the rapid hydrolysis rate of the alumina precursors resulting in mesoporous formation. The mesoporosity were retained when changing the surfactant to fatty alcohol. In addition, the materials porosity was made up from framework porosity as well as textural porosity given rise from the aggregations of γ-alumina nanoparticulates.