Nanocrystalline Iron Oxide Aerogels as Mesoporous Magnetic Architectures

3D microprinting of inorganic porous materials by chemical linking-induced solidification of nanocrystals

Three-dimensional (3D) microprinting is considered a next-generation manufacturing process for the production of microscale components; however, the narrow range of suitable materials, which include mainly polymers, is a critical issue that limits the application of this process to functional inorganic materials. Herein, we develop a generalised microscale 3D printing method for the production of purely inorganic nanocrystal-based porous materials. Our process is designed to solidify all-inorganic nanocrystals via immediate dispersibility control and surface linking-induced interconnection in the nonsolvent linker bath and thereby creates multibranched gel networks. The process works with various inorganic materials, including metals, semiconductors, magnets, oxides, and multi-materials, not requiring organic binders or stereolithographic equipment. Filaments with a diameter of sub-10 μm are printed into designed complex 3D microarchitectures, which exhibit full nanocrystal functionality and high specific surface areas as well as hierarchical porous structures. This approach provides the platform technology for designing functional inorganics-based porous materials.

Microwave-Assisted Synthesis of Iron-Based Aerogels with Tailored Textural and Morphological Properties

Iron aerogels have been synthesized by microwave heating for the first time. Therefore, it is essential to optimize this synthesis process to evaluate the possibility of obtaining nanometric materials with tailored properties and fitting them to the needs of different applications. Herein, the effect of the ratio between reagents and the time of synthesis on the final textural, morphological, and structural properties has been evaluated. The micro-meso-macroporosity of the samples can be tailored by modifying the ratio between reagents, whereas the time of synthesis has only a slight effect on the microporosity. Both the proportion between reagents and the time of synthesis are essential to controlling the nanometric morphology, making it possible to obtain either cluster- or flake-type structures. Regarding the chemical and structural composition, the samples are mainly composed of iron(II) and iron(III) oxides. However, the percentage of iron(II) can be modulated by changing the ratio between reagents, which implies that it is possible to obtain materials from highly magnetic materials to materials without magnetic properties. This control over the properties of iron aerogels opens a new line of opportunities for the use of this type of material in several fields of applications such as electrochemistry, electrocatalysis, and electrical and electronic engineering.

Crystalline Magnetic Gels and Aerogels Combining Large Surface Areas and Magnetic Moments

The production of materials that simultaneously combine large surface areas and high crystallinities is a major challenge. Conventional sol-gel chemistry strategies to produce high-surface-area gels and aerogels generally result in amorphous or poorly crystalline materials. To attain proper crystallinities, materials are exposed to relatively high annealing temperatures that result in significant surface losses. This is a particularly limiting issue in the production of high-surface-area magnetic aerogels owing to the strong relationship between crystallinity and magnetic moment. To overcome this limitation, we demonstrate here the gelation of preformed magnetic crystalline nanodomains to produce magnetic aerogels with high surface area, crystallinity, and magnetic moment. To exemplify this strategy, we use colloidal maghemite nanocrystals as gel building blocks and an epoxide group as the gelation agent. After drying from supercritical CO₂, aerogels show surface areas close to 200 m² g^-1 and a well-defined maghemite crystal structure that provides saturation magnetizations close to 60 emu g^-1. For comparison, the gelation of hydrated iron chloride with propylene oxide provides amorphous iron oxide gels with slightly larger surface areas, 225 m² g^-1, but very low magnetization, below 2 emu g^-1. Thermal treatment at 400 °C is necessary to crystallize the material, which results in a surface area loss down to 87 m² g^-1, well below the values obtained from the nanocrystal building blocks.

Magnetic nanofluids (Ferrofluids): Recent advances, applications, challenges, and future directions

Impelled by the need to find solutions to new challenges of modern technologies new materials with unique properties are being explored. Among various new materials that emerged over the decades, magnetic fluids exhibiting interesting physiochemical properties (optical, thermal, magnetic, rheological, apparent density, etc.) under a magnetic stimulus have been at the forefront of research. In the initial phase, there has been a fervent scientific curiosity to understand the field-induced intriguing properties of such fluids but later a plethora of technological applications emerged. Magnetic nanofluid, popularly known as ferrofluid, is a colloidal suspension of fine magnetic nanoparticles, has been at the forefront of research because of its magnetically tunable physicochemical properties and applications. Due to their stimuli-responsive behaviour, they have been finding more applications in biology and other engineering disciplines in recent years. Therefore, a critical review of this topic highlighting the necessary background, the potential of this material for emerging technologies, and the latest developments is warranted. This review also provides a summary of various applications, along with the key challenges and future research directions. The first part of the review addresses the different types of magnetic fluids, the genesis of magnetic fluids, their synthesis methodologies, properties, and stabilization techniques are discussed in detail. The second part of the review highlights the applications of magnetic nanofluids and nanoemulsions (as model systems) in probing order-disorder transitions, scattering, diffraction, magnetically reconfigurable internal structures, molecular interaction, and weak forces between colloidal particles, conformational changes of macromolecules at interfaces and polymer-surfactant complexation at the oil-water interface. The last part of the review summarizes the interesting applications of magnetic fluids such as heat transfer, sensors (temperature, pH, urea detection, cations, defect detection sensors), tunable optical filters, removal of dyes, dynamic seals, magnetic hyperthermia-based cancer therapy and other biomedical applications. The applications of magnetic nanofluids in diverse disciplines are growing day by day, yet there are challenges in their practical adaptation as field-worthy or packaged products. This review provides a pedagogical description of magnetic fluids, with the necessary background, key concepts, physics, experimental protocols, design of experiments, challenges and future directions.

The roles of metal species supported on Fe3O4 aerogel for photoassisted 4-nitrophenol reduction and benzoic acid oxidation

Metal-supported Fe₃O₄ aerogel is employed for photoassisted 4-NP reduction and benzoic acid oxidation.

Mechanism of Heterogeneous Fenton Reaction Kinetics Enhancement under Nanoscale Spatial Confinement

Nanoscale catalysts that can enable Fenton-like chemistry and produce reactive radicals from hydrogen peroxide activation have been extensively studied in order to overcome the limitations of homogeneous Fenton processes. Despite several advantageous features, limitation in mass transfer of short-lived radical species is an inherent drawback of the heterogeneous system. Here, we present a mechanistic foundation for the way spatial confinement of Fenton chemistry at the nanoscale can significantly enhance the kinetics of radical-mediated oxidation reactions-pollutant degradation in particular. We synthesized a series of Fe₃O₄-functionalized nanoreactors with precise pore dimensions, based on an anodized aluminum oxide template, to enable quantitative analysis of nanoconfinement effects. Combined with computational simulation of spatial distribution of radicals, we found that hydroxyl radical concentration was strongly dependent on the distance from the surface of Fenton catalysts. This distance dependency significantly influences the gross reaction kinetics and accounts for the observed nanoconfinement effects. We further found that a length scale below 25 nm is critical to avoid the limitation of short-lived species diffusion and achieve kinetics that are orders of magnitude faster than those obtained in a batch suspension of heterogeneous catalysts. These findings suggest a new strategy to develop an innovative heterogeneous catalytic system with the most effective use of hydroxyl radicals in oxidation treatment scenarios.

Ultralight magnetic aerogels from Janus emulsions

Magnetite containing aerogels were synthesized by freeze-drying olive oil/silicone oil-based Janus emulsion gels containing gelatin and sodium carboxymethylcellulose (NaCMC). The magnetite nanoparticles dispersed in olive oil are processed into the gel and remain in the macroporous aerogel after removing the oil components. The coexistence of macropores from the Janus droplets and mesopores from freeze-drying of the hydrogels in combination with the magnetic properties offer a special hierarchical pore structure, which is of relevance for smart supercapacitors, biosensors, and spilled oil sorption and separation. The morphology of the final structure was investigated in dependence on initial compositions. More hydrophobic aerogels with magnetic responsiveness were synthesized by bisacrylamide-crosslinking of the hydrogel. The crosslinked aerogels can be successfully used in magnetically responsive clean up experiments of the cationic dye methylene blue.

Magnetite containing aerogels were synthesized by freeze-drying olive oil/silicone oil-based Janus emulsion gels containing gelatin and sodium carboxymethylcellulose (NaCMC).

Strong metal–support interactions between palladium nanoclusters and hematite toward enhanced acetylene dicarbonylation at low temperature

A four-fold increase in palladium-based acetylene dicarbonylation activity was obtained at low temperature due to the strong metal–support interaction between Pd and the earth-abundant α-Fe₂O₃ material.

Versatile Aerogels for Sensors

Aerogels are unique solid-state materials composed of interconnected 3D solid networks and a large number of air-filled pores. They extend the structural characteristics as well as physicochemical properties of nanoscale building blocks to macroscale, and integrate typical characteristics of aerogels, such as high porosity, large surface area, and low density, with specific properties of the various constituents. These features endow aerogels with high sensitivity, high selectivity, and fast response and recovery for sensing materials in sensors such as gas sensors, biosensors and strain and pressure sensors, among others. Considerable research efforts in recent years have been devoted to the development of aerogel-based sensors and encouraging accomplishments have been achieved. Herein, groundbreaking advances in the preparation, classification, and physicochemical properties of aerogels and their sensing applications are presented. Moreover, the current challenges and some perspectives for the development of high-performance aerogel-based sensors are summarized.

Electrospun γ-Fe2O3 nanofibers as bioelectrochemical sensors for simultaneous determination of small biomolecules

Nanofibers of α-Fe₂O₃ and γ-Fe₂O₃ have been obtained after the controlled calcination of precursor nanofibers synthesized by electrospinning. α-Fe₂O₃ nanofibers showed an irregular toruloid structure due to the decomposition of poly (4-vinyl) pyridine in air while γ-Fe₂O₃ nanoparticles decorated nanofibers were observed after the calcination under N₂ atmosphere. Electrochemical measurements showed that different electrochemical behaviors were observed on the glassy carbon electrodes modified by α-Fe₂O₃ and γ-Fe₂O₃ nanofibers. The electrode modified by γ-Fe₂O₃ nanofibers exhibited high electrocatalytic activities toward oxidation of dopamine, uric acid and ascorbic acid while α-Fe₂O₃ nanofibers cannot. Furthermore, the γ-Fe₂O₃ modified electrode can realize the selective detection of biomolecules in ternary electrolyte solutions. The synthesis of nanofibers of α-Fe₂O₃ and γ-Fe₂O₃ and their electrochemical sensing properties relationship have been discussed and analyzed based on the experimental results.

Polymerization-Induced Colloid Assembly Route to Iron Oxide-Based Mesoporous Microspheres for Gas Sensing and Fenton Catalysis

Iron oxide materials have wide applications due to their special physicochemical properties; however, it is a great challenge to synthesize mesoporous iron oxide-based microspheres conveniently and controllably with high surface area, large pore volume, and interconnected porous structures. Herein, mesoporous α-Fe₂O₃-based microspheres with high porosity are synthesized via a facile polymerization induced colloid assembly method through polymerization of urea-formaldehyde resin (UF resin) and its simultaneously cooperative assembly with Fe(OH)₃ colloids in an aqueous solution, followed by subsequent thermal treatment. Remarkably, by controlling the cross-linking degree of UF, pure mesoporous α-Fe₂O₃ and α-Fe₂O₃/carbon hybrid microspheres can be synthesized controllably, respectively. They exhibit a uniform spherical morphology with a particle size of around 1.0 μm, well-interconnected mesopores (24.5 and 8.9 nm, respectively), and surface area of 54.4 m²/g (pure mFe₂O₃ microspheres) and 144.7 m²/g (hybrids), respectively. As a result, mesoporous pure α-Fe₂O₃ microspheres exhibited excellent H₂S sensing performance with a good selectivity, high response to low concentration H₂S at 100 °C, and quick response (4 s)/recovery (5 s) dynamics owing to the high surface area, open mesopores, and crystalline structure of the n-type α-Fe₂O₃ semiconductor. Moreover, mesoporous α-Fe₂O₃/carbon hybrid microspheres were used as a novel Fenton-like catalyst for the decomposition of methylene blue in a mild condition and exhibit quick degradation rate, high removal efficiency (∼93% within 35 min), and stable recycling performance owing to the synergetic effect of a high surface area and the carbon-protected α-Fe₂O₃.

Micelle-assisted electrodeposition of highly mesoporous Fe-Pt nodular films with soft magnetic and electrocatalytic properties

Mesoporous Fe-Pt nodular films (with a regular spatial arrangement of sub-15 nm pores) are grown onto evaporated Au, Cu and Al conductive layers by micelle-assisted electrodeposition from metal chloride salts in the presence of Pluronic P123 tri-block copolymer dissolved in the aqueous electrolytic bath. This synthetic approach constitutes a simple, one-step, versatile procedure to grow multifunctional mesoporous layers appealing for diverse applications that take advantage of materials with an ultra-high surface area-to-volume ratio. The films exhibit tuneable composition with relative Fe/Pt weight ratios, disregarding oxygen, varying from 4/96 to 52/48. All the mesoporous alloys show a soft magnetic behaviour with tuneable saturation magnetization and coercivity values (the latter ranging from ca. 5 Oe to 40 Oe). In addition, the Au/Fe-Pt deposits (even the ones with higher Fe content) exhibit good performance towards hydrogen evolution reaction in both alkaline and acidic media due to the inherent mesoporosity, with excellent stability after running 50 cycles. The interest of alloying Fe with Pt is thus two-fold: (i) to confer magnetic properties to the mesoporous alloys and (ii) to reduce the amount of the costly noble metal in the electrocatalyst in an environmentally sustainable manner.

A pure magnetite hydrogel: synthesis, properties and possible applications

A magnetite-only hydrogel was prepared for the first time by weak base mediated gelation of stable magnetite hydrosols at room temperature. The hydrogel consists of 10 nm magnetite nanoparticles linked by interparticle Fe-O-Fe bonds and has the appearance of a dark-brown viscous thixotropic material. The water content in the hydrogel could be up to 93.6% by mass while volume fraction reaches 99%. The material shows excellent biocompatibility and minor cytotoxic effects at concentrations up to 207 μg mL^-1. The gel shows excellent sorption capacity for heavy metal adsorption such as chrome and lead ions, which is 225% more than the adsorption capacity of magnetite nanoparticles. Due to thixotropic nature, the gel demonstrates mechanical stimuli-responsive release behavior with up to 98% release triggered by ultrasound irradiation. The material shows superparamagnetic behavior with a coercivity of 65 emu g^-1 at 6000 Oe. The magnetite gels prepared could be used for the production of magnetite aerogels, magnetic drug delivery systems with controlled release and highly efficient sorbents for hydrometallurgy.

Self-Assembly-Directed Aerogel and Membrane Formation from a Magnetic Composite: An Approach to Developing Multifunctional Materials

Herein, we report the preparation of an aerogel and a membrane from a magnetic composite material by tuning the self-assembly at the molecular level. The gel exhibits an excellent oil absorption property, and the membrane shows a remarkable autonomous self-healing property. The composite is formed from an organosilicon-modified poly(amidoamine) (PAMAM) dendrimer, which is linked with iron oxide nanoparticles and poly(vinyl alcohol). Upon the addition of a cross-linker (formaldehyde), the system undergoes a fast self-assembly and gelation process. The aerogel, obtained after drying of the hydrogel, was modified with 1- bromohexadecane at room temperature and utilized for the removal of oil from water with 22.9 g/g absorption capacity. Intriguingly, the same system forms a membrane with 97% autonomous self-healing ability, in the absence of the cross-linker. The membrane was used to remove the salt content from water with an efficiency of 85%. The control experiments suggest that the presence of the magnetic material (iron oxide) plays a key role in the formation of both the aerogel and membrane.

Synthesis of aerogels: from molecular routes to 3-dimensional nanoparticle assembly

Colloidal nanocrystals are extensively used as building blocks in nanoscience, and amazing results have been achieved in assembling them into ordered, close-packed structures. But in spite of great efforts, the size of these structures is typically restricted to a few micrometers, and it is very hard to extend them into the macroscopic world. In comparison, aerogels are macroscopic materials, highly porous, disordered, ultralight and with immense surface areas. With these distinctive characteristics, they are entirely contrary to common nanoparticle assemblies such as superlattices or nanocrystal solids, and therefore cover a different range of applications. While aerogels are traditionally synthesized by molecular routes based on aqueous sol-gel chemistry, in the last few years the gelation of nanoparticle dispersions became a viable alternative to improve the crystallinity and to widen the structural, morphological and compositional complexity of aerogels. In this Review, the different approaches to inorganic non-siliceous and non-carbon aerogels are addressed. We start our discussion with wet chemical routes involving molecular precursors, followed by processing methods using nanoparticles as building blocks. A unique feature of many of these routes is the fact that a macroscopic, often monolithic body is produced by pure self-assembly of nanosized colloids without the need for any templates.

Three-Dimensional Assembly of Yttrium Oxide Nanosheets into Luminescent Aerogel Monoliths with Outstanding Adsorption Properties

The preparation of macroscopic materials from two-dimensional nanostructures represents a great challenge. Restacking and random aggregation to dense structures during processing prevents the preservation of the two-dimensional morphology of the nanobuilding blocks in the final body. Here we present a facile solution route to ultrathin, crystalline Y2O3 nanosheets, which can be assembled into a 3D network by a simple centrifugation-induced gelation method. The wet gels are converted into aerogel monoliths of macroscopic dimensions via supercritical drying. The as-prepared, fully crystalline Y2O3 aerogels show high surface areas of up to 445 m(2)/g and a very low density of 0.15 g/cm(3), which is only 3% of the bulk density of Y2O3. By doping and co-doping the Y2O3 nanosheets with Eu(3+) and Tb(3+), we successfully fabricated luminescent aerogel monoliths with tunable color emissions from red to green under UV excitation. Moreover, the as-prepared gels and aerogels exhibit excellent adsorption capacities for organic dyes in water without losing their structural integrity. For methyl blue we measured an unmatched adsorption capacity of 8080 mg/g. Finally, the deposition of gold nanoparticles on the nanosheets gave access to Y2O3-Au nanocomposite aerogels, proving that this approach may be used for the synthesis of catalytically active materials. The broad range of properties including low density, high porosity, and large surface area in combination with tunable photoluminescence makes these Y2O3 aerogels a truly multifunctional material with potential applications in optoelectronics, wastewater treatment, and catalysis.

Manganese Oxide Nanoarchitectures as Broad-Spectrum Sorbents for Toxic Gases

We demonstrate that sol-gel-derived manganese oxide (MnOx) nanoarchitectures exhibit broad-spectrum filtration activity for three chemically diverse toxic gases: NH3, SO2, and H2S. Manganese oxides are synthesized via the reaction of NaMnO4 and fumaric acid to form monolithic gels of disordered, mixed-valent Na-MnOx; incorporated Na(+) is readily exchanged for H(+) by subsequent acid rinsing to form a more crystalline H-MnOx phase. For both Na-MnOx and H-MnOx forms, controlled pore-fluid removal yields either densified, yet still mesoporous, xerogels or low-density aerogels (prepared by drying from supercritical CO2). The performance of these MnOx nanoarchitectures as filtration media is assessed using dynamic-challenge microbreakthrough protocols. We observe technologically relevant sorption capacities under both dry conditions and wet (80% relative humidity) for each of the three toxic industrial chemicals investigated. The Na-MnOx xerogels and aerogels provide optimal performance with the aerogel exhibiting maximum sorption capacities of 39, 200, and 680 mg g(-1) for NH3, SO2, and H2S, respectively. Postbreakthrough characterization using X-ray photoelectron spectroscopy (XPS) and diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) confirms that NH3 is captured and partially protonated within the MnOx structure, while SO2 undergoes oxidation by the redox-active oxide to form adsorbed sulfate at the MnOx surface. Hydrogen sulfide is also oxidized to form a combination of sulfate and sulfur/polysulfide products, concomitant with a decrease in the average Mn oxidation state from 3.43 to 2.94 and generation of a MnOOH phase.

Ultrathermostable, Magnetic-Driven, and Superhydrophobic Quartz Fibers for Water Remediation

A quartz fiber based 3D monolithic materials was fabricated, which combines ultrahigh thermostability, remote controllability, mechanical flexibility, high water/oil selectivity, high processing capacity, and regeneration ability. This material exhibited great potential in water remediation, such as large absorption capacity (50- to 172-fold weight gain) toward oil standing in front of all magnetic sorbents and remarkable oil/water separation performance.

A facile strategy for synthesis of spinel ferrite nano-granules and their potential applications

A number of spinel ferrite nano-granules were synthesized in DMF through a calcination process under air.

Binary Crystallized Supramolecular Aerogels Derived from Host-Guest Inclusion Complexes

Aerogels with low density and high porosity show outstanding properties such as large surface area and low thermal and acoustic conductivity. However, great challenges remain to convert hydrophilic polymer based hydrogels to corresponding aerogels. Here, we report a structurally new type of aerogels, supramolecular aerogels (SMAs), derived from supramolecular hydrogels formed by self-assembling of poly(ethylene glycol) and α-/γ-cyclodextrin. The SMAs posses a characteristic binary crystallized nanosheet structure due to their supramolecular cross-linking nature, and their specific surface areas and nanosheet structures are tunable. Furthermore, we demonstrated application of the aerogels as solid-solid phase change materials with tunable latent heat, reversible melting-crystallization cycle while keeping the microstructure of the SMAs unchanged.

Coat Protein-Dependent Behavior of Poly(ethylene glycol) Tails in Iron Oxide Core Virus-like Nanoparticles

Here we explore the formation of virus-like nanoparticles (VNPs) utilizing 22-24 nm iron oxide nanoparticles (NPs) as cores and proteins derived from viral capsids of brome mosaic virus (BMV) or hepatitis B virus (HBV) as shells. To accomplish that, hydrophobic FeO/Fe3O4 NPs prepared by thermal decomposition of iron oleate were coated with poly(maleic acid-alt-octadecene) modified with poly(ethylene glycol) (PEG) tails of different lengths and grafting densities. MRI studies show high r2/r1 relaxivity ratios of these NPs that are practically independent of the polymer coating type. The versatility and flexibility of the viral capsid protein are on display as they readily form shells that exceed their native size. The location of the long PEG tails upon shell formation was investigated by electron microscopy and small-angle X-ray scattering. PEG tails were located differently in the BMV and HBV VNPs, with the BMV VNPs preferentially entrapping the tails in the interior and the HBV VNPs allowing the tails to extend through the capsid, which highlights the differences between intersubunit interactions in these two icosahedral viruses. The robustness of the assembly reaction and the protruding PEG tails, potentially useful in modulating the immune response, make the systems introduced here a promising platform for biomedical applications.

Iron oxyhydroxide aerogels and xerogels by controlled hydrolysis of FeCl3·6H2O in organic solvents: stages of formation

Transient species appear in early stages of hydrolysis of iron in organic media with simultaneous progress of gel formation.

Magnetic studies of mesoporous nanostructured iron oxide materials synthesized by one-step soft-templating

A combined magnetization and ⁵⁷Fe spin-echo nuclear magnetic resonance (NMR) study has been carried out on mesoporous nanostructured materials consisting of the magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃) phases.

Hybrid wood materials with magnetic anisotropy dictated by the hierarchical cell structure

Anisotropic and hierarchical structures are bound in nature and highly desired in engineered materials, due to their outstanding functions and performance. Mimicking such natural features with synthetic materials and methods has been a highly active area of research in the last decades. Unlike these methods, we use the native biomaterial wood, with its intrinsic anisotropy and hierarchy as a directional scaffold for the incorporation of magnetic nanoparticles inside the wood material. Nanocrystalline iron oxide particles were synthesized in situ via coprecipitation of ferric and ferrous ions within the interconnected pore network of bulk wood. Imaging with low-vacuum and cryogenic electron microscopy as well as spectral Raman mapping revealed layered nanosize particles firmly attached to the inner surface of the wood cell walls. The mineralogy of iron oxide was identified by XRD powder diffraction and Raman spectroscopy as a mixture of the spinel phases magnetite and maghemite. The intrinsic structural architecture of native wood entails a three-dimensional assembly of the colloidal iron oxide which results in direction-dependent magnetic features of the wood-mineral hybrid material. This superinduced magnetic anisotropy, as quantified by direction-dependent magnetic hysteresis loops and low-field susceptibility tensors, allows for directional lift, drag, alignment, (re)orientation, and actuation, and opens up novel applications of the natural resource wood.

Ordered mesoporous ferrosilicate materials with highly dispersed iron oxide nanoparticles and investigation of their unique magnetic properties

Ordered mesoporous ferrosilicate materials with highly dispersed iron oxide nanoparticles are directly synthesized through a hydrothermal approach under acidic conditions.

Formation of three-dimensional ordered hierarchically porous metal oxides via a hybridized epoxide assisted/colloidal crystal templating approach

Three-dimensionally ordered hierarchically porous alumina, iron(III) oxide, yttria, and nickel oxide have been prepared through the hybridization of colloidal crystal-templating and a modified sol-gel method. Simply, highly ordered arrays of poly(methyl methacrylate) (PMMA) were infiltrated with a precursor solution of metal salt and epoxide. Calcination after solidification of the material removed the polymer template while forming the inverse replicas, simultaneously. These hierarchical structures possessing macropore windows and mesopore walls were characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and N2 adsorption/desorption techniques to probe the structural integrity. It was revealed by PXRD that the prepared 3D frameworks were single-phase polycrystalline structures with grain sizes between 5 and 27 nm. The thermal stability as studied by TGA illustrates expected weight losses and full decomposition of the PMMA template. SEM reveals the bimodal, hierarchical macroporous frameworks with well-defined macropore windows and mesoporous walls. Gas sorption measurements of the ordered materials display surface areas as high as 93 m(2) g(-1), and average mesopore diameter up to 33 nm. Due to the versatility of this method, we expect these materials will be ideal candidates for applications in catalysis, adsorption, and separations. Furthermore, the implementation of this technology for production of three-dimensionally ordered macroporous materials can improve the cost and efficiency of metal oxide frameworks (MOFs) due to its high versatility and amenability to numerous systems.

Bifunctional graphene/γ-Fe₂O₃ hybrid aerogels with double nanocrystalline networks for enzyme immobilization

Highly porous hosting materials with conducting (favorable to electron transfer) and magnetic (favorable to product separation) bicontinuous networks should possess great potentials for immobilization of various enzymes in the field of biocatalytic engineering, but the synthesis of such materials is still a great challenge. Herein, bifunctional graphene/γ-Fe2 O3 hybrid aerogels with quite low density (30-65 mg cm(-3) ), large specific surface area (270-414 m(2) g(-1) ), high electrical conductivity (0.5-5 × 10(-2) S m(-1) ), and superior saturation magnetization (23-54 emu g(-1) ) are fabricated. Single networks of either graphene aerogels or γ-Fe2 O3 aerogels are obtained by etching of the hybrid aerogels with acid solution or calcining of the hybrid aerogels in air, indicative of the double networks of the as-synthesized graphene/γ-Fe2 O3 hybrid aerogels for the first time. The resulting bifunctional aerogels are used to immobilize β-glucuronidase for biocatalytic transformation of glycyrrhizin into glycyrrhetinic acid monoglucuronide or glycyrrhetinic acid, with high biocatalytic activity and definite repeatability.

Something from nothing: enhancing electrochemical charge storage with cation vacancies

The performance of electrochemical energy storage devices (e.g., batteries and electrochemical capacitors) is largely determined by the physicochemical properties of the active electrode materials, such as the thermodynamic potential associated with the charge-storage reaction, ion-storage capacity, and long-term electrochemical stability. In the case of mixed ion/electron-conducting metal oxides that undergo cation-insertion reactions, the presence of cation vacancies in the lattice structure can enhance one or more of these technical parameters without resorting to a drastic change in material composition. Examples of this enhancement include the charge-storage properties of certain cation-deficient oxides such as γ-MnO2 and γ-Fe2O3 relative to their defect-free analogues. The optimal cation-vacancy fraction is both material- and application-dependent because cation vacancies enhance some materials properties at the expense of others, potentially affecting electronic conductivity or thermal stability. Although the advantages of structural cation vacancies have been known since at least the mid-1980s, only a handful of research groups have purposefully integrated cation vacancies into active electrode materials to enhance device performance. Three protocols are available for the incorporation of cation vacancies into transition metal oxides to improve performance in both aqueous and nonaqueous energy storage. Through a processing approach, researchers induce point defects in conventional oxides using traditional solid-state-ionics techniques that treat the oxide under appropriate atmospheric conditions with a driving force such as temperature. In a synthetic approach, substitutional doping of a highly oxidized cation into a metal-oxide framework can significantly increase cation-vacancy content and corresponding charge-storage capacity. In a scaling approach, electrode materials that are expressed in morphologies with high surface areas, such as aerogels, contain more defects because the increased fraction of surface sites favors the formation of cation vacancies. In this Account, we review studies of cation-deficient electrode materials from the literature and our laboratory, focusing on transition metal oxides and the impact cation vacancies have on electrochemical performance. We also discuss the challenges and limitations of these defective structures and their promise as battery materials.

Two-in-one strategy for effective enrichment of phosphopeptides using magnetic mesoporous γ-Fe₂O₃ nanocrystal clusters

Designed with a two-in-one strategy, the magnetic mesoporous γ-Fe(2)O(3) nanocrystal clusters (m-γ-Fe(2)O(3)) have been successfully prepared for integrating the functions of effective enrichment and quick separation of phosphopeptides into a single architecture. First, the mesoporous Fe(3)O(4) nanocrystal clusters (mFe(3)O(4)) were synthesized by solvothermal reaction and then were subjected to calcination in air to form m-γ-Fe(2)O(3). The obtained m-γ-Fe(2)O(3) have spherical morphology with uniform particle size of about 200 nm and mesoporous structure with the pore diameter of about 9.7 nm; the surface area is as large as 117.8 m(2)/g, and the pore volume is 0.34 cm(3)/g. The m-γ-Fe(2)O(3) possessed very high magnetic responsiveness (Ms = 78.8 emu/g, magnetic separation time from solution is less than 5 s) and were used for the selective enrichment of phosphopeptides for the first time. The experimental results demonstrated that the m-γ-Fe(2)O(3) possessed high selectivity for phosphopeptides at a low molar ratio of phosphopeptides/nonphosphopeptides (1:100), high sensitivity (the detection limit was at the fmol level), high enrichment recovery (as high as 89.4%), and excellent speed (the enrichment can be completed in 10 min). Moreover, this material is also quite effective for enrichment of phosphopeptides from the real sample (drinking milk), showing great potential in the practical application.

Lithium titanate aerogel for advanced lithium-ion batteries

This work details the synthesis and characterization of a novel lithium titanate aerogel as an anode material for lithium ion batteries. Excessive loss of lithium during supercritical drying can be overcome by increasing the lithium precursor concentration during synthesis. Chronopotentiometry shows the aerogel to have a capacity about 80 % of theoretical at a symmetric C/3 rate, which is comparable to a commercial product. Cyclic voltammetry reveals a batt-cap behavior for the high-surface area aerogel, implying the potential for improved rate capability if electrical conductivity can be maintained.

Self-assembly and embedding of nanoparticles by in situ reduced graphene for preparation of a 3D graphene/nanoparticle aerogel

A 3D graphene architecture can be prepared via an in situ self-assembly of graphene prepared by a mild chemical reduction. Fe(3) O(4) nanoparticles are homogeneously dispersed into graphene oxide (GO) aqueous suspension and a 3D magnetic graphene/Fe(3) O(4) aerogel is prepared during the reduction of GO to graphene. This provides a general method to prepare 3D graphene/nanoparticle composites for a wide range of applications including catalysis and energy conversion.

Two steps bulk-surface functionalization of nanoporous alumina by methyl and vinyl-silane adsorption. Evidence for oxide surface highly reactive sites creation

Functionalization of a novel nanoporous monolithic alumina synthesized from amalgam is investigated. The structure is studied by X-ray diffraction, BET, MEB and IR spectroscopy, before and after chemical functionalization by trimethylethoxy silane adsorption and annealing at high temperature. These treatments retain both monolith microstructure and nanostructure while strongly improving material mechanical properties. Allyldimethoxysilane and alcohol adsorption on the annealed samples, proves that highly reactive sites are available for further polymer grafting, as demonstrated by a significant shift of allyldimethoxysilane ν(SiH) to 2,215 cm(-1) and adsorbed acetate formation. Simple quantum computations on model systems support this conclusion. Chemical processes reported in this paper, allow a nanostructured alumina monoliths functionalization to optimize ceramics-polymer bonds, and to tune new hybrid biomaterial properties.

Controlled synthesis of mesoporous hematite nanostructures and their application as electrochemical capacitor electrodes

In this work, iron oxalate (FeC₂O₄·2H₂O) with different morphologies was synthesized through a simple solution-based direct precipitation process. Three samples with distinct morphologies, i.e., microrods with a parallelogram-like cross-section, nanorods, and multi-layered nanosheets, could be obtained in a selective manner. We found that the shapes of the iron oxalate could be controlled just through simply altering the solvents used. The one-dimensional (1D) characteristic of the infinite linear chains and the selective interaction between solvents and various crystallographic planes of FeC₂O₄·2H₂O played an important role in the formation of FeC₂O₄·2H₂O with different morphologies. Phase-pure hematite (α-Fe₂O₃) had be obtained by annealing these as-prepared FeC₂O₄·2H₂O precursors without significant alterations in morphology. The as-obtained mesoporous α-Fe₂O₃ products had high specific surface areas with narrow pore size distribution. The electrochemical properties of the α-Fe₂O₃ electrodes were investigated using cyclic voltammetry (CV) and galvanostatic charge-discharge measurements by a three electrode system. The electrochemical experiments revealed that they showed a structure-dependence in their specific capacitances. The mesoporous multi-layered nanosheets exhibited a significant structurally induced enhancement of capacity properties associated with their novel structure characteristic in addition to the high specific surface area. They can present the highest specific capacitance value (116.25 F g⁻¹) and excellent long cycle life within the voltage window from - 0.6 to 0 V. This method can be easily controlled and is expected to be extended to produce other functional materials with controlled structure.