Construction of Molecularly Dispersed Polyoxometalate-Alumina Hybrid Hollow Nanoflowers via Water-Induced Kirkendall Effect

Hybrid nanomaterials with controllable structures and diverting components have attracted significant interest in the functional materials field. Here, we develop a solvent evaporation-induced self-assembly (EISA) strategy to synthesize nanosheet-assembled phosphomolybdic acid (H3PMo)-alumina hybrid hollow spheres. The resulting nanoflowers display a high surface area (up to 697 m2 g-1), adjustable diameter, high chemical/thermal stability, and especially molecularly dispersed H3PMo species. By employing various microscopic and spectroscopic techniques, the formation mechanism is elucidated, revealing the simultaneous control of the morphology by heteropoly acids and water through the water-induced Kirkendall effect. The versatility of the synthesis method is demonstrated by varying surfactants, heteropoly acids, and metal oxide precursors for the facile synthesis of hybrid metal oxides. Spherical hybrid alumina serves as an attractive support material for constructing metal-acid bifunctional catalysts owing to its advantageous surface area, acidity, and mesoporous microenvironment. Pt-loaded hollow flowers exhibit excellent catalytic performance and exceptional stability in the hydrodeoxygenation of vanillin with recyclability for up to 10 cycles. This research presents an innovative strategy for the controllable synthesis of hybrid metal oxide nanospheres and hollow nanoflowers, providing a multifunctional platform for diverse applications.

Advances in morphology-controlled alumina and its supported Pd catalysts: synthesis and applications

Alumina materials, as one of the cornerstones of the modern chemical industry, possess physical and chemical properties that include excellent mechanical strength and structure stability, which also make them highly suitable as catalyst supports. Alumina-supported Pd-based catalysts with the advantages of exceptional catalytic performance, flexible regulated surface metal/acid sites, and good regeneration ability have been widely used in many traditional chemical industry fields and have also shown great application prospects in emerging fields. This review aims to provide an overview of the recent advances in alumina and its supported Pd-based catalysts. Specifically, the synthesis strategies, morphology transformation mechanisms, and structural properties of alumina with various morphologies are comprehensively summarized and discussed in-depth. Then, the preparation approaches of Pd/Al2O3 catalysts (impregnation, precipitation, and other emerging methods), as well as the metal-support interactions (MSIs), are revisited. Moreover, Some promising applications have been chosen as representative reactions in fine chemicals, environmental purification, and sustainable development fields to highlight the universal functionality of the alumina-supported Pd-based catalysts. The role of the Pd species, alumina support, promoters, and metal-support interactions in the enhancement of catalytic performance are also discussed. Finally, some challenges and upcoming opportunities in the academic and industrial application of the alumina and its supported Pd-based are presented and put forward.

Confining copper nanoclusters on exfoliation-free 2D boehmite nanosheets: Fabrication of ultra-sensitive sensing platform for α-glucosidase activity monitoring and natural anti-diabetes drug screening

α-Glucosidase (α-Glu) and its inhibitors play critical roles in diabetes therapy. Herein, a simple and ultra-sensitive fluorescence sensing approach was fabricated for α-Glu activity monitoring and natural inhibitor screening by electrostatically confining negatively charged glutathione-capped copper nanoclusters (GSH-CuNCs) on exfoliation-free and positively charged 2D boehmite (Boe) nanosheets. Boe significantly improved the fluorescence emission/stability of GSH-CuNCs and simultaneously led to an obvious blue-shift of the excitation peak of CuNCs from 365 nm to 330 nm. As a result, the fluorescence emission of Boe@GSH-CuNCs was efficiently quenched by 4-nitrophenyl-α-D-glucopyranoside (PNPG) with a maximum absorbance peak (λ_max) at 310 nm via inner filter effect, and sequentially recovered by α-Glu through the hydrolysis of PNPG to p-nitrophenol (λ_max = 410 nm). Accordingly, an ultra-sensitive fluorescence assay for the determination of α-Glu activity was proposed by using Boe@GSH-CuNCs as fluorescence probes. The detection limit of 0.43 U/L was achieved, which was lower than most of other α-Glu activity assays. Furthermore, this method was capable of screening α-Glu inhibitors originated from actinomycetes, peanut, sophora flower, celery, and orange as potential anti-diabetes drugs. Taken together, this work provided a promising strategy for clinical treatment of diabetes and discovery of anti-diabetes drugs.

Effects of pH and ions on the morphological evolution of boehmite prepared by hydrothermal treatment of ultrafine Bayer gibbsite

Boehmite morphology depended on the pH and ions of the solution by hydrothermal treatment of gibbsite owing to the difference in nucleation and growth of boehmite from Al³⁺, Al(OH)₄⁻ or the Al(OH)₄⁻Na⁺ ion pair.

Inception of molybdate as a "pore forming additive" to enhance the bifunctional electrocatalytic activity of nickel and cobalt based mixed hydroxides for overall water splitting

Development of low-cost transition metal based electrocatalysts on inexpensive substrates for overall water splitting is essential to meet the future energy storage demand. In this article, we have synthesized a molybdate incorporated nickel cobalt hydroxide material on Cu mesh with nickel : cobalt : molybdenum in a 13.25 : 21.42 : 1 ratio and the electrode has shown excellent bifunctional electrocatalytic activity as it demonstrates overpotentials as low as 290 mV and 125 mV to reach 10 mA cm-2geo for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively (after both iR and capacitance correction). Control studies with fourteen other nickel-cobalt based hydroxides and rigorous post-catalytic analysis suggested that though molybdate was not the active catalytic centre, it played a pivotal role in enhancing the activity of the material as - (i) it significantly improved the surface area and porosity of the as-synthesized material and (ii) owing to its continuous etching during electrochemical testing, it was found to increase the accessibility of electrochemically active catalytic sites lying in the bulk. Thus, molybdate acts as a "pore forming additive" during both synthesis and electrochemical treatment. Furthermore, the combination of nickel and molybdate helped in the formation of a 2D-sheet like morphology which in turn improves accessibility to catalytically active centres. In addition, the Cu mesh substrate notably lowers the charge transfer resistance. To the best of our knowledge, this is the first ever report of molybdate as a "pore forming additive" and will enthuse the designing of electrocatalytic materials with enhanced performance based on this strategy.

Morphology-controlled synthesis of boehmite with enhanced efficiency for the removal of aqueous Cr(VI) and nitrates

Boehmite with different morphologies was synthesized using a simple hydrothermal method for the removal of Cr(VI) and nitrates from polluted water. When the pH of the hydrothermal system was changed, the final crystallization products had morphologies of one-dimensional rods or two-dimensional sheets with different sizes. The boehmites were characterized and used for the adsorption of aqueous Cr(VI) and nitrates. Their bulk structure and surface properties significantly changed with the corresponding morphology, which prominently affected their adsorption capacity. Boehmite with a 2D small sheet-like structure showed the highest adsorption capacity (64.7 mg g^-1). Moreover, the small sheet-like boehmite showed a remarkable adsorption capacity towards nitrates (74.5-378.5 mg g^-1) and maintained a high selectivity to Cr(VI) in the presence of competing anions such as NO₃ ^-, [Formula: see text] and Cl^-. The isotherms for Cr(VI) sorption could be better explained using the Langmuir model, indicating a monolayer adsorption of the Cr species, while the isotherms for nitrate sorption followed the Freundlich model, suggesting a multilayer adsorption. The active adsorption sites of boehmite were found to be the Lewis acid sites and surface hydroxyl groups according to the outcomes of the analysis using a series of characterization methods such as IR, Raman and x-ray photoelectron spectra. The unique structure of boehmite is beneficial to adsorb anion containments while maintaining a high selectivity to Cr(VI) species. Because of the multiple Lewis or Brönsted acid sites in boehmite, the Cr(VI) was reduced to less toxic Cr(III) species and immobilized on the surface of boehmite. In consideration of the low-cost and good regeneration capacity, the small sheet-like boehmite would be useful for the removal of anions present in polluted water.

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.

Crumpled Aluminum Hydroxide Nanostructures as a Microenvironment Dysregulation Agent for Cancer Treatment

Owing to their unique physicochemical properties, nanomaterials have become a focus of multidisciplinary research efforts including investigations of their interactions with tumor cells and stromal compartment of tumor microenvironment (TME) toward the development of next-generation anticancer therapies. Here, we report that agglomerates of radially assembled Al hydroxide crumpled nanosheets exhibit anticancer activity due to their selective adsorption properties and positive charge. This effect was demonstrated in vitro by decreased proliferation and viability of tumor cells, and further confirmed in two murine cancer models. Moreover, Al hydroxide nanosheets almost completely inhibited the growth of murine melanoma in vivo in combination with a minimally effective dose of doxorubicin. Our direct molecular dynamics simulation demonstrated that Al hydroxide nanosheets can cause significant ion imbalance in the living cell perimembranous space through the selective adsorption of extracellular anionic species. This approach to TME dysregulation could lay the foundation for development of novel anticancer therapy strategies.

Template-Free Fabrication of Mesoporous Alumina Nanospheres Using Post-Synthesis Water-Ethanol Treatment of Monodispersed Aluminium Glycerate Nanospheres for Molybdenum Adsorption

This work reports the template-free fabrication of mesoporous Al₂ O₃ nanospheres with greatly enhanced textural characteristics through a newly developed post-synthesis "water-ethanol" treatment of aluminium glycerate nanospheres followed by high temperature calcination. The proposed "water-ethanol" treatment is highly advantageous as the resulting mesoporous Al₂ O₃ nanospheres exhibit 2-4 times higher surface area (up to 251 m² g^-1 ), narrower pore size distribution, and significantly lower crystallization temperature than those obtained without any post-synthesis treatment. To demonstrate the generality of the proposed strategy, a nearly identical post-synthesis "water treatment" method is successfully used to prepare mesoporous monometallic (e.g., manganese oxide (MnO₂ )) and bimetallic oxide (e.g., CuCo₂ O₄ and MnCo₂ O₄ ) nanospheres assembled of nanosheets or nanoplates with highly enhanced textural characteristics from the corresponding monometallic and bimetallic glycerate nanospheres, respectively. When evaluated as molybdenum (Mo) adsorbents for potential use in molybdenum-99/technetium-99m (⁹⁹ Mo/^99m Tc) generators, the treated mesoporous Al₂ O₃ nanospheres display higher molybdenum adsorption performance than non-treated Al₂ O₃ nanospheres and commercial Al₂ O₃ , thereby suggesting the effectiveness of the proposed strategy for improving the functional performance of oxide materials. It is expected that the proposed method can be utilized to prepare other mesoporous metal oxides with enhanced textural characteristics and functional performance.

Nanocavity-in-Multiple Nanogap Plasmonic Coupling Effects from Vertical Sandwich-Like Au@Al2O3@Au Arrays for Surface-Enhanced Raman Scattering

The development of ideal three-dimensional (3D) tailorable surface-enhanced Raman scattering (SERS) substrates with the properties of timesaving, large area, high throughput, single or few molecules detection, reproducibility, reusable ability, and high density of "hot spots" has been the mainstream challenge and the robust task. Here, we construct perpendicular sandwich-like Au@Al₂O₃@Au hybrid nanosheets (PSHNs) on the Al foil as a 3D flexible substrate for SERS. The design of 3D PSHNs incorporates several advantageous aspects for SERS to enhance the performance of plasmonic diamers via bifunctions of vertical Al₂O₃ nanosheets (NSs) including the nanoscaffold and nanobaffle plate effects. As a nanoscaffold, it increases the space utilization of Au-Au diamers, whereas as a nanobaffle, it forms densely homogeneous Au@Al₂O₃@Au nanojunctions by sub-4 nm thickness of Al₂O₃ NSs as the dielectric isolated layer for the double-sided exposure of slitlike surface plasmon resonance. The optimized PSHN substrate exhibits a fascinating SERS sensitivity with an experimental enhancement factor of 10¹² and is able to detect rhodamine B at an extremely low concentration up to the limit of single or few molecules (10^-18 M), as well as can be recycled without the loss of SERS enhancement via the simple impregnation process. These advantages will greatly facilitate the wider use of SERS in many fields.

Insights into the polymorphic transformation mechanism of aluminum hydroxide during carbonation of potassium aluminate solution

Polymorphic transformation from bayerite to gibbsite is discussed kinetically and structurally. Possibility of crossovers in Al(OH)₃ polymorphs stability is investigated for the first time.

Effects of various morphologies on the optical and electrical properties of boehmite nanostructures

This work reports the variations in the fluorescence and ultra-high dielectric properties of various boehmite nano-structures.

Hierarchically porous, and Cu- and Zn-containing γ-AlOOH mesostrands as adjuvants for cancer immunotherapy

Alum is the only licensed adjuvant by Food and Drug Administration of USA used in many human vaccines and has excellent safety record in clinical applications. However, alum hardly induces T helper 1 (Th1) immune responses that are required for anti-tumor immunity. In the present study, we fabricated hierarchical copper- and zinc- buds dressing γ-AlOOH mesostrands (Cu- and Zn-AMSs) with randomly wrinkled morphology, mesoscale void- or cave-like pockets, high-exposed surface coverage sites, and positive charge streams in saline. We confirmed that Cu- and Zn-AMSs promoted intracellular uptake of model cancer antigen (ovalbumin, OVA) by THP-1-differentiated macrophage-like cells in vitro. Moreover, Cu- and Zn-AMSs enhanced maturation and cytokine release of bone marrow dendritic cells in vitro. In vivo study demonstrated that Cu- and Zn-AMSs markedly induced anti-tumor-immunity and enhanced CD₄⁺ and CD₈⁺ T cell populations in splenocytes of mice. These findings demonstrated that hierarchical copper- and zinc- buds dressing γ-AlOOH mesostrands, which are oriented in randomly wrinkled matrice, are suitable platforms as novel adjuvants for cancer immunotherapy.

A series of five-coordinated copper coordination polymers for efficient degradation of organic dyes under visible light irradiation

Five-coordinated copper(ii) coordination polymers 1–5 are highly efficient and universal photocatalysts for the degradation of the organic dyes methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) under visible light irradiation.

The solvothermal synthesis of γ-AlOOH nanoflakes and their compression behaviors under high pressures

The compression behaviors of γ-AlOOH nanoflakes were investigated via in situ high pressure synchrotron radiation angle dispersive X-ray diffraction techniques.

Synthesis of core-shell AlOOH hollow nanospheres by reacting Al nanoparticles with water

A novel route for the synthesis of boehmite nanospheres with a hollow core and the shell composed of highly crumpled AlOOH nanosheets by oxidizing Al nanopowder in pure water under mild processing conditions is described. The stepwise events of Al transformation into boehmite are followed by monitoring the pH in the reaction medium. A mechanism of formation of hollow AlOOH nanospheres with a well-defined shape and crystallinity is proposed which includes the hydration of the Al oxide passivation layer, local corrosion of metallic Al accompanied by hydrogen evolution, the rupture of the protective layer, the dissolution of Al from the particle interior and the deposition of AlOOH nanosheets on the outer surface. In contrast to previously reported methods of boehmite nanoparticle synthesis, the proposed method is simple, and environmentally friendly and allows the generation of hydrogen gas as a by-product. Due to their high surface area and high, slit-shaped nanoporosity, the synthesized AlOOH nanostructures hold promise for the development of more effective catalysts, adsorbents, vaccines and drug carriers.