Alumina Nanosheets Research Articles

Impact of nano-dopants on the mechanical and physical properties of magnesium oxychloride cement composites – Experimental assessment

The importance of the reduction of the World's CO2 emissions due to their non-negligible contribution to climate change is inevitable. As the Portland cement (PC) industry is one of the main contributors to the overall volume of CO2 emissions produced over the World, a sustainable PC substitute must be implemented. Previous scientific studies suggest that magnesium oxychloride cement (MOC) – an eco-friendly binder based on reactive magnesia – could be a suitable alternative. This contribution studies the influence of various nano-dopants on the mechanical and physical properties of MOC-based composites. The nano-dopants introduced to the MOC composite were the following: multi-walled carbon nanotubes, oxidized multi-walled carbon nanotubes, graphene oxide, graphene nanoplatelets, and alumina nanosheets. Ahead of the composite preparation, the nano-dopants were analysed with a wide spectrum of analytical methods to study their composition and microstructure in detail. The used amount of nano-dopant was 1.0 wt%, relative to the cement paste weight. After a curing period of 28 days, the prepared composite samples underwent a comprehensive analysis of their microstructure, phase, and chemical composition, as well as micro- and macrostructural parameters and mechanical properties. Additionally, the research studied the effects of nano-dopants on the hygric properties and water resistance of the MOC composites after 24-h immersion in water. The findings revealed a noteworthy increase in mechanical parameters with the addition of nano-dopants. The highest compressive strength of 85.4 MPa was obtained for the MOC composite enriched with the addition of oxidized multi-walled carbon nanotubes. MOC doped with alumina nanosheets exhibited the highest value in flexural strength (20.99 MPa) and dynamic modulus of elasticity (38.85 GPa) measurements. The resistance of MOC composites to deterioration in water was also improved by all the implemented nano-dopants. The softening coefficient determined for samples immersed in water for 24 h varied from 62.7 to 74.8%. The best resistance to water degradation was obtained for MOC with alumina nanosheets, which showed a softening coefficient value about 23.2% higher than that of the reference sample. Thus, the incorporation of nanomaterials as functional nano-dopants in MOC-based composites shows promising opportunities in the improvement of both mechanical properties and water resistance, contributing to the development of environmentally sustainable building materials.

Porous alumina nanosheet-supported asymmetric platinum clusters for efficient diboration of alkynes.

Precisely designing asymmetrical structures is an effective strategy to optimize the performance of metallic catalysts. Asymmetric Pt clusters were attached to defect-rich porous alumina nanosheets (Pt clu/dp-Al2O3) using a pyrolysis technique coupled with wet impregnation. These Pt-functionalized nanosheets feature a high concentration of active sites, demonstrating remarkable cycling performance and catalytic activity in alkyne diboration. The conversion yield and selectivity can reach up to 97% and 95%, correspondingly.

Asymmetric organic-inorganic bi-functional composite solid-state electrolyte for long stable cycling of high-voltage lithium battery

Poly(ethylene oxide) (PEO)-based solid-state electrolyte is difficult to achieve high voltage and energy density due to low ionic conductivity and narrow electrochemical stabilization window. Therefore, an urgent demand exists to construct a composite solid-state electrolyte that is resistant to both Li dendrite and high-voltage cathode oxidation. Here, we design and prepare an asymmetric bi-functional composite solid-state electrolyte achieving compatibility with Li anode and high-voltage anode to extend the cycle life of batteries. The F-containing hierarchically structured polyamide acids nanofibers towards the cathode side enhance interfacial compatibility with the cathode and provide excellent oxidation resistance. The rigid two-dimensional alumina nanosheets on the anode side further improve the interfacial stability with the Li anode and effectively inhibit the growth of Li dendrites. The synergistic effect of asymmetric organic-inorganic composite solid-state electrolyte is exploited to improve the cycling stability of different cathode (LiFePO4 (LFP) and LiNi0.8Mn0.1Co0.1O2 (NMC811))/Li batteries, greatly broaden the electrochemical stability window (5.3 V) and significantly enhance lithium dendrite inhibition. Based on density functional theory, the introduction of F-containing groups reduces the highest occupied molecular orbitals of the polyamide acids and that there is a strong binding between alumina and both the PEO terminal group and TFSI−. The result suggests that the composite solid-state electrolyte enhances the stability of PEO with the high-voltage cathode and Li anode, and inhibits the movement of anions. Therefore, it is noteworthy that the excellent electrochemical stability of this composite solid-state electrolyte with the NMC811/Li electrodes ensures long cycle of more than 800 cycles.

Alkali ion-promoted palladium subnanoclusters stabilized on porous alumina nanosheets with enhanced catalytic activity for benzene oxidation

Alkali ion-promoted palladium subnanoclusters stabilized on porous alumina nanosheets with enhanced catalytic activity for benzene oxidation

Low-temperature hydrolysis of carbonyl sulfide in blast furnace gas using Al2O3-based catalysts with high oxidation resistance

Water vapor, O2 and various sulfides in blast furnace gases affect the carbonyl sulfide (COS) hydrolysis reaction. In this study, we investigated the hydrolysis and deactivation mechanisms of a series of catalysts that were synthesized by depositing K2O and MoO3 on industrial alumina-based catalysts. Alumina nanosheets were deposited with potassium oxide, in which MoO3 nanoparticles were incorporated resulting in needle-like structures. The modified catalysts had substantially enhanced COS hydrolysis activity at low temperatures. The introduction of K2O and MoO3 significantly increased the number of weakly basic sites on the catalysts and reduced the lattice oxygen content. The catalysts exhibited high oxidation resistance and hydrolysis properties. According to the poisoning mechanism, the deposition of sulfate species tended to reduce weakly basic sites. High-valent Mo easily excited the adsorbed H2O on the catalysts, producing –OH groups that facilitated the COS hydrolysis reaction. This modification facilitates the further investigation of catalysts capable of promoting COS hydrolysis and their application in the manufacturing industry.

Comparisons on thermal and water-resistance of Ru and Pd supported on cobalt-doped alumina nanosheets for catalytic combustion of propane

Cobalt-doped alumina nanosheets were prepared by dynamic hydrothermal method, and then the precious metal Ru or Pd was loaded and investigated for catalytic combustion of propane. Cobalt doping imparted the prominent redox ability to irreducible alumina nanosheets with superior thermal stability and established the strong metal-support interaction and easy activation of gaseous oxygen. Comparative investigation between Ru and Pd supported on Co-doped Al2O3 nanosheets suggested that Ru based catalysts presented a higher activity and water-resistance while the preferable sintering-resistance and oxygen-tolerance were observed on Pd based catalysts. Unexpectedly, the Pd/CoANS-800 catalysts exhibited a re-dispersion of PdOx at high temperature and re-activation for propane oxidation. Ru based catalysts were more tolerant to Cl species from the metal precursor, and the presence of H2O could accelerate the removal of the residual Cl species from the catalyst surface especially Pd based catalysts, which led to the promotion of catalytic activity.

Mesoporous nickel-alumina catalysts derived from MIL-53(Al) metal-organic framework: A new promising path for synthesizing CO2 methanation catalysts

A new synthesis route for the preparation of highly efficient and stable porous Ni-based alumina catalysts for CO2 methanation is presented. It is based on the use of MIL-53(Al), an Al-containing metal-organic framework (MOF) with high surface area, as sacrificial support. A series of Ni-Al2O3 powder samples with Ni loadings ranging from 5 to 20 wt% was thus obtained. Their properties were thoroughly characterized by a set of complementary techniques including N2-sorption, X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), CO2 adsorption, temperature programmed reduction (H2-TPR) and transmission electron microscopy (TEM). After nickel impregnation and thermal assisted organic ligands elimination, the resulting Ni-Al2O3 materials appear as interwoven alumina nanosheets in which Ni cations are intimately mixed forming NiAl2O4 spinel nanophases dispersed within amorphous alumina. This nanosheet morphology is preserved after the reduction of the Ni cations that leads to Ni0-Al2O3 catalysts composed of homogeneously and highly dispersed Ni0 nanoparticles, even at the highest 20 wt% Ni content. As a result, the activity in CO2 methanation, evaluated between 250–450 °C under atmospheric pressure, using a constant gas hourly space velocity of 68,900 h−1 and a molar reactant ratio H2/CO2 of 4, increased proportionally with respect to the Ni loading. On the most active catalyst, the selectivity to CH4 was always excellent (between 96 % and 100 %) and the obtained CH4 yield (∼70 % at 300 °C) was about two times higher than on a commercial Ni-based Al2O3 catalyst containing 25 wt% of Ni. The catalytic performances were also better than those of the already reported porous catalysts Ni/USY, Ni/SBA-15 as well as a Ni-Al2O3 synthesized by a EISA one-pot procedure, tested under the same reaction conditions for comparison. In this work the utilization of MIL-53(Al) as starting material for the synthesis of Ni-Al2O3 catalysts was responsible for a peculiar improvement of the metallic dispersion due to the high surface area of this MOF and of the metal-support interaction likely due to the existence of remaining NiAl2O4 at the metal-support interface after reduction. Sintering and agglomeration (the main cause of deactivation) were therefore limited, thus boosting the catalytic performance (activity, selectivity and stability).

Phosphate-assisted synthesis of ultrathin and thermally stable alumina nanosheets as robust Pd support for catalytic combustion of propane

Two-dimensional γ-Al2O3 nanosheet with rich pentacoordinate Al3+ sites which can nicely stabilize noble metals via strong interactions between metal and support has been focused. However, the synthesis of ultrathin and highly thermal-stable Al2O3 is challenging. Herein, we report an effective approach to synthesize ultrathin Al2O3 nanosheets with regular leaf-like architecture as well as high thermal-stability. A novel intercalation-swelling-exfoliation pathway was proposed to elucidate the formation of ultrathin sheet-like structure and then its morphology/thickness could be further adjusted via a dissolution-growth induced by phosphate. Meanwhile, the presence of phosphate further enhanced thermal stability of Al2O3 nanosheets due to the occupation or depletion of high-reactive sites and surface hydroxy groups. Subsequently, the thermally stable γ-Al2O3 nanosheets with moderate anchoring sites was used as a support of Pd and investigated for catalytic combustion of propane. The Pd/Al2O3 nanosheet exhibited a superior catalytic activity for propane combustion and the complete conversion was below 300 °C, more importantly, the outstanding resistance to high temperature (1000 °C) was observed, which was ascribed to the re-dispersion of Pd particles and the occurrence of strong metal-support interaction (SMSI) at high temperature.

Filter Coatings Based on Combination of Nanomaterials for Steel Melt Filtration

Carbon‐bonded alumina foam filters are coated using special slurries based on graphene oxide (GO), carbon nanotubes (CNTs), and alumina nanosheets. The aim of such filters is to reduce the concentration of nonmetallic inclusions in the steel melt prior to casting into the molds. To assess the purification efficiency of the coated filters, a steel casting simulator is used. After immersion for a short time into steel melts with artificially generated alumina impurities, the filters are analyzed by optical microscopy and scanning electron microscopy. In addition, the population of remaining inclusions in the treated steel is investigated by the means of a special scanning electron microscope. The results show that, compared with a reference melt where no filter is used, the nanocoated filters cause inclusion growth and the formation of new silicate inclusions. The best purification efficiency, regarding only alumina inclusions, is given by the GO–C sample, whereas the combination of GO with alumina nanosheets or CNTs deliver worse performance.

Peony-like Pentahedral Al(III)-Enriched Alumina Nanosheets for the Dehydrogenation of Propane

In this work, a peony-like coordinatively unsaturating pentahedral aluminum(III)-enriched alumina nanosheet (Al2O3-MG) was successfully prepared by a facile glocuse-assisted hydrothermal approach. ...

Biomolecule-Assisted Synthesis of Hierarchical Multilayered Boehmite and Alumina Nanosheets for Enhanced Molybdenum Adsorption.

The effective utilization of various biomolecules for creating a series of mesoporous boehmite (γ-AlOOH) and gamma-alumina (γ-Al2 O3 ) nanosheets with unique hierarchical multilayered structures is demonstrated. The nature and concentration of the biomolecules strongly influence the degree of the crystallinity, the morphology, and the textural properties of the resulting γ-AlOOH and γ-Al2 O3 nanosheets, allowing for easy tuning. The hierarchical γ-AlOOH and γ-Al2 O3 multilayered nanosheets synthesized by using biomolecules exhibit enhanced crystallinity, improved particle separation, and well-defined multilayered structures compared to those obtained without biomolecules. More impressively, these γ-AlOOH and γ-Al2 O3 nanosheets possess high surface areas up to 425 and 371 m2 g-1 , respectively, due to their mesoporous nature and hierarchical multilayered structure. When employed for molybdenum adsorption toward medical radioisotope production, the hierarchical γ-Al2 O3 multilayered nanosheets exhibit Mo adsorption capacities of 33.1-40.8 mg g-1 . The Mo adsorption performance of these materials is influenced by the synergistic combination of the crystallinity, the surface area, and the pore volume. It is expected that the proposed biomolecule-assisted strategy may be expanded for the creation of other 3D mesoporous oxides in the future.

Crown ether induced assembly to γ-Al2O3 nanosheets with rich pentacoordinate Al3+ sites and high ethanol dehydration activity

Two-dimensional (2D) materials have attracted great attention due to their unique physical and chemical properties derived from the dimensionality effect and modulation in their band structure. Herein, an important industrial catalytic material, gamma alumina (γ-Al2O3) with well-defined two-dimensional nanosheet structure was fabricated by a designed crown ether induced assembly approach. The obtained γ-Al2O3 nanosheets with a thickness of ∼4 nm possess high surface area (351 m2/g) and 16% pentacoordinate Al3+ sites which are the main catalytic active sites for ethanol dehydration to ethylene, compared to almost no pentacoordinate Al3+ sites for the commercial γ-Al2O3 nanoparticles. Furtherly, systematical investigation reveals that the crown ether plays the key role in the assembly of nanosheet structure. As a catalyst for ethanol dehydration to ethylene, the obtained alumina nanosheets with easily-accessible surface and more active sites, exhibit a superior catalytic performance to the commercial alumina with a much higher yield at large space velocity.

Wettability phenomena of molten steel in contact with alumina substrates with alumina and alumina-carbon coatings

The effects of the surface roughness, carbon content and the additions of carbon nanotubes (CNT) and alumina nanosheets (ANS) on the wettability of molten steel on Al2O3 substrates with and without Al2O3(-C) coatings were investigated by the sessile drop wetting method, SEM and EDS, etc. At the beginning of the wetting experiment, the contact angle increased with an increasing surface roughness. With a longer wetting time, the interfacial reactions between the coatings and molten steel became more influential on the contact angles. When the coatings contained 30wt% carbon, a new layer presumably consisting of hercynite (FeAl2O4) was formed at the substrate/steel interface stabilizing the contact angles with time. Moreover, compared to the coatings without nano-additives, the additions of CNT and ANS promoted the reactions at lower temperatures and resulted in a faster stabilization of the contact angles. Finally, the interfacial wetting and reaction mechanisms were proposed.

Filter Functionalization with Carbon Nanotubes and Alumina Nanosheets for Advanced Steel Filtration

In order to explore the influence of nano-sized materials on steel filtration, carbon-bonded alumina filters are coated with multi-walled carbon nanotubes and alumina nanosheets. The samples are tested for different times in contact with a steel melt containing endogenous inclusions at 1650 °C. Investigations of the filters after the test reveal the typical layer buildup described in the literature. After 60 s fine endogenous inclusions are found on the top layer. By means of a special automatic SEM, steel samples after the tests are thoroughly analyzed. The population of detected inclusions is classified in terms of size and chemistry. Nano-coated filters show excellent filtration efficiency for 10 s immersion time. Longer times result in worse performance and generation of new silicate inclusions.

Highly permeable twinned alumina nanoparticles for the precoat filtration of fine colloids

Abstract Pretreatment is key to the success of any fine filtration process. Precoat filtration is a common method to reduce fine particulate matter in feed streams. In this study, precoat filters were formed by the deposition of the diatomaceous earth (DE) or twinned alumina nanosheets (TAN) particles on a substrate. The TAN particles were produced via metal salt hydrolysis. The performance of the precoat filters was investigated during the constant-pressure filtration of a bentonite solution. The results showed that the TAN precoat exhibited enhanced flow properties and reduced the turbidity of the filtrate more rapidly than either of the DE precoats. The TAN precoat reached the required turbidity level of ≤0.10 NTU at a flux that was up to 28 times higher than the fluxes obtained by the DE precoats. The superior performance of the TAN precoat was explained by (1) the ability of the TAN precoat to resist compaction during filtration due to the unique twinning of the alumina nanosheets forming the TAN particles, (2) the strong attractive forces between the bentonite and TAN particles based on their opposite surface charges, and (3) the isotropic permeability of the TAN aggregates.

High surface area mesoporous alumina nanosheets and nanorolls from an aluminum based metal organic framework

High surface area mesoporous γ-alumina was prepared from aluminum fumarate metal organic framework (MOF A520)by calcination at 750°C and characterized by Fourier Transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TGA-DTA), BET surface area measurement, scanning electron microcopy (SEM) and transmission electron microscopy (TEM). The XRD pattern of products derived by calcination of MOF A520 at 450, 550 and 650°C showed a very low degree of crystallinity or amorphous materials, and by raising temperature to 750°C a well crystallized mesoporous γ-alumina developed with surface area of 205m2g−1 and narrow pore size distribution. SEM analysis demonstrated that warm-like morphology of the MOF A520 maintained and did not collapse during calcination; it is just shrunk and transferred to γ-alumina. TEM study showed a one dimension fibrous morphology, in which fibers curled and produced scrolls.

The influence of nano scaled additions on the Young's modulus of carbon-bonded alumina at temperatures up to 1450 °C

Within this investigation the combination of the addition of doped silicon and nano additives (multi-walled carbon nanotubes and alumina nanosheets) on the Young's modulus E of carbon-bonded alumina was investigated. The addition of nano particles resulted in an increase of E at room temperature independent of the graphite level. An interaction between the graphite content and the additive effect was found, complicating the analysis of the main effect. At elevated temperature the nano particle addition resulted in remarkably lower E values at Tmax, whereas the effect of doped silicon was an increase of E at Tmax. Furthermore, a correlation between the pore size (d90) and the normalized Young's modulus at the temperature of the former pyrolysis (Ei⟶1000°C) was found. That correlation is a confirmation of the gap opening and closing theory of Franklin and Tucker [1]. Thus, a reduction of the graphite content is possible without reducing the elasticity of the material and its high temperature elasticity by using multi-walled carbon nanotubes and alumina nanosheets as additives.

Optimal aggregate size distribution for the formation of highly efficient nanosheet dynamic membranes

In this work, intrinsically-porous aggregates of nanosheets having mono-, di-, and tri-modal particle size distributions were synthesized to produce densely-packed dynamic membranes. Alumina nanosheets were synthesized in 0, 25, and 50vol% ethanol-water mixtures (Al-0, Al-25, and Al-50, respectively). Using dynamic image analysis, it was determined that the alumina nanosheets twinned to form aggregate superstructures of distinct size distributions at each synthesis condition. The aggregates were intrinsically porous with three-dimensional pore connectivity. Dynamic membranes (DMs) were formed by the deposition of these aggregates on a substrate. The effect of ethanol content in the synthesis mixture on the performance of the DMs was investigated during the constant-pressure filtration of a bentonite solution. The results show that the Al-50 DM had the best performance based on flux and turbidity removal. The Al-50 DM reached the required turbidity level of <0.10 NTU at a flux that was 177% and 12% higher than the fluxes obtained by the Al-0 and Al-25 DMs, respectively. The superior performance of the Al-50 DM was explained by the presence of three aggregate size distributions providing optimal packing in the synthesized material. This reduced interstitial pores and resulted in a packing density of 74.7 –78.5% versus 54.0–54.2% for Al-0.

The structure-directed effect of Al-based metal–organic frameworks on fabrication of alumina by thermal treatment

In this work, the block-shaped Al-based metal–organic frameworks (Al-MOFs) MIL-53 have been synthesized by hydrothermal method. To detect the correlation between the structure of Al-MOFs and the formation of alumina, the ligands are eliminated by thermal treatment. MIL-53 and the calcination products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption and solid-state 27Al nuclear magnetic resonance (27Al NMR). It was found that after calcination, the block-shaped Al-MOFs precursor turns into high-crystallinity mesoporous alumina nanosheets, and the thermal treatment product γ-alumina possesses a dual pore system and a large surface area (146m2/g), with five-fold aluminum. During the thermal treatment process, the structure of MIL-53 and its secondary building units have structure-directed effect in the formation of alumina.

Mesoporous alumina nanosheets and nanorolls derived from topologically identical Al-based MOFs

Two-dimensional alumina nanosheets and one-dimensional nanorolls were formed via the conversion of MIL-53 and DUT-5, respectively.