Crystalline nanotubes of gamma-AlOOH and gamma-Al2O3: hydrothermal synthesis, formation mechanism and catalytic performance

From metal nanowires to ultrathin crystalline ALD nanotubes: process development and mechanism revealed by in situ TEM heating experiments

The creation of hollow nanomaterials based on metal oxides has become an important research topic, as they show potential in a broad range of technical applications. However, the controlled synthesis of long and at the same time thin nanotubes is still challenging. Here we present a universal approach to create ultrathin aluminum oxide nanotubes with a length/diameter ratio of >1200 and minimum wall thickness of ≤4 nm. We use a facile process based on defined heat treatment of specific core-shell nanowires. The metal nanowires act as a template, which is thermally removed during heat treatment until an empty tube is created. The core-shell nanowires are produced by Physical Vapour Deposition (PVD) with a subsequent coating via Atomic Layer Deposition (ALD). The custom-built PVD-ALD system enables a direct sample transfer without breaking the vacuum, which allows determining the effect of a native oxide layer on the metal-ALD bonding. In combination with correlative ex situ observations, in situ Transmission Electron Microscopy (TEM) heating experiments unravel the dynamical processes going on at small scales. Based on the microscopic analysis, the energetics of the core material is analyzed, giving insights about heat induced effects as well as the phase transition from the amorphous to the crystalline state.

Newly engineered alumina quantum dot-based nanofluid in enhanced oil recovery at reservoir conditions

In this work, a newly engineered alumina quantum dot-based nanofluid (α-AQDs; D ~ 4 nm; amorphous solid) and one commercial alumina nanoparticle-based nanofluid (γ-ANPs; D ~ 20 nm; crystalline type) with the capability of strong colloidal dispersion at reservoir conditions, such as, high salinity, divalent ions (Ca²⁺) and high temperature was compared. The main goal of this research was to study the crude oil displacement mechanisms of alumina suspensions as a function of variety in size and particle morphology in aged carbonate rocks. The strong interaction potential between the particles was achieved by the citric acid and a special composition of a carboxylate-sulfonate-based polyelectrolyte polymer as an effective dispersant compound on the surface, leading to a negative particle charges and an additional steric and electrostatic repulsion. Wettability alteration upon exposure to fluids using the contact angle and the Amott cell were performed on saturated carbonate plug samples and rock slices. While, dynamic core displacements were conducted to test the water/nanofluid/oil flow and nanoparticle retention behavior thorough typical pore throats underground the reservoir conditions. The stability results revealed that PE-polymer was able to create a long-term colloidal fluid during 30 days. It was found that mass concentration of nanofluid increased with decreasing in particle size. The optimal amount of particles in aqueous solution was obtained 0.05 wt% for ANPs, increased up to 0.1 wt% for AQDs. Analysis of experiments showed that wettability alteration was the main mechanism during nanofluid injection. Laboratory core-flooding data proved that the enhanced oil recovery due to a less concentration state by ANPs was consistent with AQDs at higher concentrations. In addition, permeability-impairment-behavior study was discussed in terms of possible mineral scale deposition and alumina release on the rock surface. Results showed that a large extent of permeability damage caused by mineral scale (55-59%). Alumina quantum dot-based nanofluids were found a minimum impairment (2-4%) and a significant reduction of ~ 10% in permeability was observed for ANPs-based nanofluid.

Enhanced phosphate removal with fine activated alumina synthesized from a sodium aluminate solution: performance and mechanism

Fine activated alumina (FAA) acting as an adsorbent for phosphate was synthesized from an industrial sodium aluminate solution based on phase evolution from Al(OH)₃ and NH₄Al(OH)₂CO₃. This material was obtained in the form of γ-Al₂O₃ with an open mesoporous structure and a specific surface area of 648.02 m² g⁻¹. The phosphate adsorption capacity of the FAA gradually increased with increases in phosphate concentration or contact time. The maximum adsorption capacity was 261.66 mg g⁻¹ when phosphate was present as H₂PO₄⁻ at a pH of 5.0. A removal efficiency of over 96% was achieved in a 50 mg L⁻¹ phosphate solution. The adsorption of phosphate anions could be explained using non-linear Langmuir or Freundlich isotherm models and a pseudo-second-order kinetic model. Tetra-coordinate AlO₄ sites acting as Lewis acids resulted in some chemisorption, while (O)_nAl(OH)₂⁺ (n = 4, 5, 6) Brønsted acid groups generated by the protonation of AlO₄ or AlO₆ sites in the FAA led to physisorption. Analyses of aluminum-oxygen coordination units using Fourier transform infrared and X-ray photoelectron spectroscopy demonstrated that physisorption was predominant. Minimal chemisorption was also verified by the significant desorption rate observed in dilute NaOH solutions and the high performance of the regenerated FAA. The high specific surface area, many open mesopores and numerous highly active tetra-coordinate AlO₄ sites on the FAA all synergistically contributed to its exceptional adsorption capacity.

A fine activated alumina with high specific surface area was prepared by phase evolution from sodium aluminate solution, Al(OH)₃ and NH₄Al(OH)₂CO₃. The maximum adsorption capacity was 261.66 mg g⁻¹ and the regenerated material exhibited high performance phosphate removal.

Morphology dependent effect of γ-Al2O3 for ethanol dehydration: nanorods and nanosheets

γ-Al2O3 nanorods gave the improved selectivity of C2H4 in ethanol dehydration due to the selective exposure of {100} facets.

Template-free method for the synthesis of high-pore-volume γ-Al2O3 nanofibers in a membrane dispersion microreactor

Mesoporous γ-Al₂O₃ nanofibers with high pore volume and uniform pore size distributions were successfully synthesized via a template-free method in a membrane dispersion microreactor followed by calcination. The effects of crystal temperature, pH values, continuous phase concentration and washing solvent on the γ-Al₂O₃ nanofibers were carefully studied. The results showed that the as-obtained γ-Al₂O₃ nanofibers showed a length of 40-60 nm and a width of 3.2-3.4 nm, which were attributed to the high microscopic mixing rate in the membrane dispersion microreactor. Moreover, the precursors of γ-Al₂O₃ nanofibers treated with deionized water and mixed deionized water/alcohol solution had high pore volumes, reaching to 1.60 ml g^-1 and 2.00 ml g^-1, respectively. Furthermore, the adsorption performance of γ-Al₂O₃ nanofibers with high pore volumes was also investigated. These fibers showed an excellent adsorption capacity of 1323.68 mg g^-1 for the removal of Congo red from aqueous solution, thereby indicating their potential for applications in adsorption and other related areas.

Liquid Phase Hydrogenation of Pharmaceutical Interest Nitroarenes over Gold-Supported Alumina Nanowires Catalysts

In this work, Au nanoparticles, supported in Al₂O₃ nanowires (ANW) modified with (3-aminopropyl)trimethoxysilane were synthetized, for their use as catalysts in the hydrogenation reaction of 4-(2-fluoro-4-nitrophenyl)-morpholine and 4-(4-nitrophenyl)morpholin-3-one. ANW was obtained by hydrothermal techniques and the metal was incorporated by the reduction of the precursor with NaBH₄ posterior to superficial modification. The catalysts were prepared at different metal loadings and were characterized by different techniques. The characterization revealed structured materials in the form of nanowires and a successful superficial modification. All catalysts show that Au is in a reduced state and the shape of the nanoparticles is spherical, with high metal dispersion and size distributions from 3.7 to 4.6 nm. The different systems supported in modified-ANW were active and selective in the hydrogenation reaction of both substrates, finding for all catalytic systems a selectivity of almost 100% to the aromatic amine. Catalytic data showed pseudo first-order kinetics with respect to the substrate for all experimental conditions used in this work. The solvent plays an important role in the activity and selectivity of the catalyst, where the highest efficiency and operational stability was achieved when ethanol was used as the solvent.

Constructing Amino-Functionalized Flower-like Metal-Organic Framework Nanofibers in Sulfonated Poly(ether sulfone) Proton Exchange Membrane for Simultaneously Enhancing Interface Compatibility and Proton Conduction

A novel flower-like MIL-53(Al)-NH₂ nanofiber (MNF) was successfully constructed, in which the electro-blown spinning Al₂O₃ nanofibers were introduced as Al precursors to coordinate with ligand in hydrothermal reaction for the formation of MOFs nanofibers. By incorporating the functional and consecutive MNFs fillers in sulfonated poly(ether sulfone) (SPES) matrix, high-performance MNFs@SPES hybrid membranes were obtained. Specifically, the peak stress strength could be strengthened to 33.42 MPa and the proton conductivity was remarkably improved to 0.201 S cm^-1 as MNFs content increased to 5 wt %, achieving a simultaneous improvement on proton conduction and membrane stability. The highly promoted performance could be ascribed to the synergy advantages of unique structure and amino modification of MNFs: (1) The flower-like nanofiber structure of MNFs with high surface area could be beneficial to construct long-range and compatible interfaces between MNFs and SPES matrix, leading to sufficient continuous proton pathways as well as strengthened stability for the hybrid membrane. (2) The hydrophilic MNFs rendered the hybrid membrane with sufficient water retention for proton transfer via Vehicle mechanism. (3) Functional -NH₂ groups of MNFs and -SO₃H groups of SPES were consecutively and tightly bonded via acid-base electrostatic interactions, which further accelerated the proton conduction via Grotthuss hopping mechanism and effectively suppressed the methanol penetration in the meanwhile for the MNFs@SPES hybrid membranes.

Al atomistic surface modulation on colloidal gradient quantum dots for high-brightness and stable light-emitting devices

Quantum-dot (QD) light-emitting devices (QLEDs) have been attracting considerable attention owing to the unique properties of process, which can control the emission wavelength by controlling the particle size, narrow emission bandwidth, and high brightness. Although there have been rapid advances in terms of luminance and efficiency improvements, the long-term device stability is limited by the low chemical stability and photostability of the QDs against moisture and air. In this study, we report a simple method, which can for enhance the long-term stability of QLEDs against oxidation by inserting Al into the shells of CdSe/ZnS QDs. The Al coated on the ZnS shell of QDs act as a protective layer with Al₂O₃ owing to photo-oxidation, which can prevents the photodegradation of QD with prolonged irradiation and stabilize the device during a long-term operation. The QLEDs fabricated using CdSe/ZnS/Al QDs exhibited a maximum luminance of 57,580 cd/m² and current efficiency of 5.8 cd/A, which are significantly more than 1.6 times greater than that of CdSe/ZnS QDs. Moreover, the lifetimes of the CdSe/ZnS/Al-QD-based QLEDs were significantly improved owing to the self-passivation at the QD surfaces.

Facile Preparation of Hydrophobic Aluminum Oxide Film via Sol-Gel Method

Hydrophobic aluminum oxide films (AOFs) are widely used in anti-oxidation and anti-corrosion applications. In preparing AOFs, complex and high temperature conditions are usually necessary. Here, we report aluminum nanowire structures with hydrophobic properties, prepared using a facile sol-gel method by magnetic stirrer and hydrothermal reaction. The electromagnetic force work has great influence on the structure of AOFs. The surface morphology and compositions of the AOFs were analyzed by scanning electron microscope (SEM), energy dispersive X-ray spec-trometers (EDS), X-ray diffraction (XRD), 3M peeling test, and X-ray photoelectron spectroscopy (XPS). With the increase of water content in hydrothermal reaction, the hydrophobicity of AOFs proportional increased. Adding 10 ml deionized water leads to the formation of the upper nanowires and the lower nanohole with 129.3° water contact angle. Meanwhile, the AOF provide a good substrate for electroless deposition (ELD) of copper (Cu) to achieve a simple fabrication of metal conductor.

Hybrid functionalized chitosan-Al2O3@SiO2 composite for enhanced Cr(VI) adsorption

In this study, we prepared a novel hybrid functionalized chitosan-Al₂O₃@SiO₂ composite (FCAS) for removing hexavalent chromium [Cr(VI)] from aqueous system. Spectroscopic studies like Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and energy dispersive spectroscope (EDS) were characterized. The effects such as dosage of adsorbent, pH, contact time and initial Cr(VI) concentration were evaluated. It has been illustrated that a wide acidic condition in the pH range of 2-6 was conducive to Cr(VI) adsorption and only 10 min was required to reach about 80% adsorption. Also, the adsorption properties of prepared adsorbent such as kinetics, thermodynamics and isotherms were comprehensively studied. Additionally, the adsorption capacity barely declined even after five cycles. Studies found that FCAS with characteristics of high performance of adsorption rate and capacity and better reusability would be a potential adsorbent for wastewater treatment.

Enhanced Immune Adjuvant Activity of Aluminum Oxyhydroxide Nanorods through Cationic Surface Functionalization

Aluminum-salt-based vaccine adjuvants are prevailingly used in FDA-approved vaccines for the prevention of infectious diseases for over eighty years. Despite their safe applications, the mechanisms regarding how the material characteristics affect the interactions at nano-bio interface and immunogenicity remain unclear. Recently, studies have indicated that the activation of NLRP3 inflammasome plays a critical role in inducing adjuvant effects that are controlled by the inherent shape and hydroxyl contents of aluminum oxyhydroxide (AlOOH) nanoparticles; however, the detailed relationship between surface properties and adjuvant effects for these materials remains unknown. Thus, we engineered AlOOH nanorods (ALNRs) with controlled surface functionalization and charge to assess their effects on the activation of NLRP3 inflammasome in vitro and the potentiation of immunogenicity in vivo. It is demonstrated that NH₂-functionalized ALNRs exhibited higher levels of cellular uptake, lysosomal damage, oxidative stress, and NLRP3 inflammasome activation than pristine and SO₃H-functionalized ALNRs in cells. This structure-activity relationship also correlates with the adjuvant activity of the material using ovalbumin (OVA) in a mouse vaccination model. This study demonstrates that surface functionalization of ALNRs is critical for rational design of aluminum-based adjuvants to boost antigen-specific immune responses for more effective and long-lasting vaccination.

Synthesis and characterization of hierarchical γ-AlOOH and γ-Al2O3 microspheres with high adsorption performance for organic dyes

A segmented heating process with CTAB as a surfactant and pore forming agent has been successfully developed to synthesize hierarchical γ-AlOOH and γ-Al₂O₃ microspheres with ultra-excellent adsorption performance for Congo red.

Synthesis of nanostructured γ-AlOOH and its accelerating behavior on the thermal decomposition of AP

The hydrothermal treatment of γ-AlOOH agglomerates was introduced to synthesize nanostructured γ-AlOOH.

Rational synthesis of Ni nanoparticle-embedded porous graphitic carbon nanosheets with enhanced lithium storage properties

Carbon-based materials have recently received increased attention as very promising anode materials for rechargeable lithium-ion batteries (LIBs) because of their non-toxicity, low cost, and excellent performances. Nanostructure engineering has been demonstrated as an effective approach to improve the electrochemical performance of electrode materials. Here, we present a facile and scalable synthesis of two-dimensional (2D) porous graphitic carbon nanosheets embedded by numerous homogeneously dispersed Ni nanoparticles. With both structural and compositional advantages, the as-synthesized nanohybrid manifests a very stable high reversible capacity of 740 mA h g(-1) after 100 cycles at a current density of 100 mA g(-1), and also excellent rate capability and cycling stability. We believe that the synthetic strategy outlined here can be extended to other rationally designed anode materials with high performances in LIBs.

Superparamagnetic Fe3 O4 @SiO2 core-shell composite nanoparticles for the mixed hemimicelle solid-phase extraction of benzodiazepines from hair and wastewater samples before high-performance liquid chromatography analysis

Magnetic Fe3 O4 /SiO2 composite core-shell nanoparticles were synthesized, characterized, and applied for the surfactant-assisted solid-phase extraction of five benzodiazepines diazepam, oxazepam, clonazepam, alprazolam, and midazolam, from human hair and wastewater samples before high-performance liquid chromatography with diode array detection. The nanocomposite was synthesized in two steps. First, Fe3 O4 nanoparticles were prepared by the chemical co-precipitation method of Fe(III) and Fe(II) as reaction substrates and NH3 /H2 O as precipitant. Second, the surface of Fe3 O4 nanoparticles was modified with shell silica by Stober method using tetraethylorthosilicate. The Fe3 O4 /SiO2 composite were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and vibrating sample magnetometry. To enhance their adsorptive tendency toward benzodiazepines, cetyltrimethylammonium bromide was added, which was adsorbed on the surface of the Fe3 O4 /SiO2 nanoparticles and formed mixed hemimicelles. The main parameters affecting the efficiency of the method were thoroughly investigated. Under optimum conditions, the calibration curves were linear in the range of 0.10-15 μgmL(-1) . The relative standard deviations ranged from 2.73 to 7.07%. The correlation coefficients varied from 0.9930 to 0.9996.

General Method for the Synthesis of Ultrastable Core/Shell Quantum Dots by Aluminum Doping

Semiconductor quantum dots (QDs) have attracted extensive attention in various applications because of their unique optical and electronic properties. However, long-term photostability remains a challenge for their practical application. Here, we present a simple method to enhance the photostability of QDs against oxidation by doping aluminum into the shell of core/shell QDs. We demonstrate that Al in the coating shell can be oxidized to Al2O3, which can serve as a self-passivation layer on the surface of the core/shell QDs and effectively stop further photodegradation during long-term light irradiation. The prepared CdSe/CdS:Al QDs survived 24 h without significant degradation when they were subjected to intense illumination under LED light (450 nm, 0.35 W/cm(2)), whereas conventional CdSe/CdS QDs were bleached within 3 h.

Self-assembled synthesis of urchin-like AlOOH microspheres with large surface area for removal of pollutants

Urchin-like AlOOH microspheres synthesized by a chemical induced solvothermal method revealed high efficiency for the removal of Congo red pollutant.

Rapid scavenging of methylene blue dye from a liquid phase by adsorption on alumina nanoparticles

The adsorption behavior of methylene blue on as-synthesized alumina nanoparticles has been investigated.

Growth and characterization of ceria thin films and Ce-doped γ-Al2O3 nanowires using sol-gel techniques

γ-Al(2)O(3) is a well known catalyst support. The addition of Ce to γ-Al(2)O(3) is known to beneficially retard the phase transformation of γ-Al(2)O(3) to α-Al(2)O(3) and stabilize the γ-pore structure. In this work, Ce-doped γ-Al(2)O(3) nanowires have been prepared by a novel method employing an anodic aluminium oxide (AAO) template in a 0.01 M cerium nitrate solution, assisted by urea hydrolysis. Calcination at 500 °C for 6 h resulted in the crystallization of the Ce-doped AlOOH gel to form Ce-doped γ-Al(2)O(3) nanowires. Ce(3+) ions within the nanowires were present at a concentration of < 1 at.%. On the template surface, a nanocrystalline CeO(2) thin film was deposited with a cubic fluorite structure and a crystallite size of 6-7 nm. Characterization of the nanowires and thin films was performed using scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, x-ray photoelectron spectroscopy and x-ray diffraction. The nanowire formation mechanism and urea hydrolysis kinetics are discussed in terms of the pH evolution during the reaction. The Ce-doped γ-Al(2)O(3) nanowires are likely to find useful applications in catalysis and this novel method can be exploited further for doping alumina nanowires with other rare earth elements.