Hierarchically mesoporous hematite microspheres and their enhanced formaldehyde-sensing properties

Advanced hematite nanomaterials for newly emerging applications

Because of the combined merits of rich physicochemical properties, abundance, low toxicity, etc., hematite (α-Fe2O3), one of the most chemically stable compounds based on the transition metal element iron, is endowed with multifunctionalities and has steadily been a research hotspot for decades. Very recently, advanced α-Fe2O3 materials have also been developed for applications in some cutting-edge fields. To reflect this trend, the latest progress in developing α-Fe2O3 materials for newly emerging applications is reviewed with a particular focus on the relationship between composition/nanostructure-induced electronic structure modulation and practical performance. Moreover, perspectives on the critical challenges as well as opportunities for future development of diverse functionalities are also discussed. We believe that this timely review will not only stimulate further increasing interest in α-Fe2O3 materials but also provide a profound understanding and insight into the rational design of other materials based on transition metal elements for various applications.

A room-temperature formaldehyde sensor based on hematite for breast cancer diagnosis

Formaldehyde (HCHO) is regarded as one kind of indoor pollutant. Additionally, HCHO serves as a biomarker in the exhaled breath of breast cancer patients. Early warning and management are crucial for the environment and human health. Thus, we have elaborately synthesized hematite (α-Fe₂O₃) employing a facet-engineering hydrothermal strategy using the fine-tuned solvent composition, with special attention to the effect of different exposed surfaces on HCHO detection. The spindle-like α-Fe₂O₃ nanocrystals with the (012) facet exposed exhibited impressively higher response towards HCHO at room temperature than that of the disk-like α-Fe₂O₃ with mainly the (001) facet exposed, partly due to the abundant vacancy oxygen and adsorbed oxygen of high-index facets of α-Fe₂O₃. More importantly, our experimental results coincide with theoretical calculations. Overall, the surface engineering strategy could be extended to a versatile approach for HCHO detection.

Improving the properties of Fe2O3 by a sparking method under a uniform magnetic field for a high-performance humidity sensor

Iron oxide (Fe₂O₃) thin films are promising semiconductors for electronic applications because Fe₂O₃ is an earth-abundant semiconductor with an appropriate band gap. However, many methods for the synthesis of Fe₂O₃ thin films require a corrosive source, complex procedures, and many types of equipment. Here, we report, for the first time, a simple method for Fe₂O₃ deposition using sparking under a uniform magnetic field. The morphology of Fe₂O₃ displayed an agglomeration of particles with a network-like structure. The crystallite size, % Fe content, and optical bandgap of Fe₂O₃ were influenced by changes in the magnitude of the magnetic field. For application in humidity sensors, Fe₂O₃ at a magnetic field of 200 mT demonstrated a sensitivity of 99.81%, response time of 0.33 s, and recovery time of 2.57 s. These results can provide references for new research studies.

Fe₂O₃ deposition by a sparking method under a uniform magnetic field.

Au Nanoparticles Decorated Mesoporous SiO2 -WO3 Hybrid Materials with Improved Pore Connectivity for Ultratrace Ethanol Detection at Low Operating Temperature

Semiconducting metal oxides-based gas sensors with the capability to detect trace gases at low operating temperatures are highly desired in applications such as wearable devices, trace pollutant detection, and exhaled breath analysis, but it still remains a great challenge to realize this goal. Herein, a multi-component co-assembly method in combination with pore engineering strategy is proposed. By using bi-functional (3-mercaptopropyl) trimethoxysilane (MPTMS) that can co-hydrolyze with transition metal salt and meanwhile coordinate with gold precursor during their co-assembly with PEO-b-PS copolymers, ordered mesoporous SiO₂ -WO₃ composites with highly dispersed Au nanoparticles of 5 nm (mesoporous SiO₂ -WO₃ /Au) are straightforward synthesized. This multi-component co-assembly process avoids the aggregation of Au nanoparticles and pore blocking in conventional post-loading method. Furthermore, through controlled etching treatment, a small portion of silica can be removed from the pore wall, resulting in mesoporous SiO₂ -WO₃ /Au with increased specific surface area (129 m²  g^-1 ), significantly improved pore connectivity, and enlarged pore window (>4.3 nm). Thanks to the presence of well-confined Au nanoparticles and ε-WO₃ , the mesoporous SiO₂ -WO₃ /Au based gas sensors exhibit excellent sensing performance toward ethanol with high sensitivity (R_a /R_g = 2-14 to 50-250 ppb) at low operating temperature (150 °C).

Au-Decorated ZnFe2O4 Yolk-Shell Spheres for Trace Sensing of Chlorobenzene

Noble metals supported on metal oxides are promising materials for widely applying on gas sensors because of their enviable physical and chemical properties in enhancing the sensitivity and selectivity. Herein, pristine ZFO yolk-shell spheres composed of ultrathin nanosheets and ultrasmall nanoparticles decorated with nanosized Au particles with a diameter of 1-2 nm are fabricated using the method of solution-phase deposition-precipitation. As a result, the Au@ZFO yolk-shell sphere based sensor exhibits significantly sensing performances for chlorobenzene (CB). In comparison with pristine ZFO, the response (R_air/R_gas= 90.9) of a Au@ZFO based sensor with a low detection limit of 100 ppb increases 4-fold when exposed to 10 ppm chlorobezene at 150 °C. Excitingly, the sensing response for chlorobenzene is the highest among metal oxides semiconductor based sensors. Moreover, the sensors can be further applied in the field of chlorobenzene monitoring, owing to its outstanding selectivity. The results elaborated that the enhanced sensing mechanism is mainly attributed to the effects of electronic sensitization and chemical sensitization, which are induced by the Au nanoparticles on the surface of ZFO yolk-shell spheres. Density functional theory (DFT) calculations further illustrated that the existence of Au nanoparticles exhibits higher adsorption energy and net charge transfer for CB. In addition, the relationship between the sensing performances of pristine ZFO and Au@ZFO yolk-shell spheres for chlorobenzene and the factors of Au loading amount, operating temperature, and humidity was also fully investigated in this work.

Recent advances in amphiphilic block copolymer templated mesoporous metal-based materials: assembly engineering and applications

Mesoporous metal-based materials (MMBMs) have received unprecedented attention in catalysis, sensing, and energy storage and conversion owing to their unique electronic structures, uniform mesopore size and high specific surface area. In the last decade, great progress has been made in the design and application of MMBMs; in particular, many novel assembly engineering methods and strategies based on amphiphilic block copolymers as structure-directing agents have also been developed for the "bottom-up" construction of a variety of MMBMs. Development of MMBMs is therefore of significant importance from both academic and practical points of view. In this review, we provide a systematic elaboration of the molecular assembly methods and strategies for MMBMs, such as tuning the driving force between amphiphilic block copolymers and various precursors (i.e., metal salts, nanoparticles/clusters and polyoxometalates) for pore characteristics and physicochemical properties. The structure-performance relationship of MMBMs (e.g., pore size, surface area, crystallinity and crystal structure) based on various spectroscopy analysis techniques and density functional theory (DFT) calculation is discussed and the influence of the surface/interfacial properties of MMBMs (e.g., active surfaces, heterojunctions, binding sites and acid-base properties) in various applications is also included. The prospect of accurately designing functional mesoporous materials and future research directions in the field of MMBMs is pointed out in this review, and it will open a new avenue for the inorganic-organic assembly in various fields.

Sequential Templating Approach: A Groundbreaking Strategy to Create Hollow Multishelled Structures

Thanks to their distinguished properties such as optimized specific surface area, low density, high loading capacity, and sequential matter transfer and storage, hollow multishelled structures (HoMSs) have attracted great interest from scientists in broad fields, including catalysis, drug delivery, solar cells, supercapacitors, lithium-ion batteries, electromagnetic wave absorption, and sensors. However, traditional synthesis methods such as soft-templating and hierarchical self-assembly methods can hardly realize the controllable synthesis of HoMSs, thus limiting their development and application. Here, the development process of HoMSs is first succinctly reviewed and the shortcomings of the traditional synthesis method are concluded. Subsequently, the sequential templating approach, which shows great generality for the synthesis of HoMSs with controllable composition and geometry configuration and exhibits remarkable effect on the scientific research field, is introduced. The basic material science and chemical reaction mechanism involved in the synthesis and manipulation of HoMSs using the sequential templating approach are then explained in detail. In addition, the effect of the geometric characteristics of HoMSs on their application properties is highlighted. Finally, the current challenges and future research directions of HoMSs are also suggested.

Rational design of yolk–shell nanostructures for photocatalysis

Yolk–shell structures provide an ideal platform for the rational regulation and effective utilization of charge carriers because of their void space and large surface areas. Furthermore, the efficiency of charge behavior in every step can be further improved by many strategies. This review describes the synthesis of yolk–shell structures and their effect for the enhancement of heterogeneous photocatalysis.

Volatile Organic Compound Gas-Sensing Properties of Bimodal Porous α-Fe2O3 with Ultrahigh Sensitivity and Fast Response

Porous solid with multimodal pore size distribution provides plenty of advantages including large specific surface area and superior mass transportation to achieve high gas-sensing performances. In this study, α-Fe₂O₃ nanoparticles with bimodal porous structures were prepared successfully through a nanocasting pathway, adopting the bicontinuous 3D cubic symmetry mesoporous silica KIT-6 as the hard template. Its structure and morphology were characterized by X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, and so on. Furthermore, the gas sensor fabricated from this material exhibited excellent gas-sensing performance to several volatile organic compounds (acetone, ethyl acetate, isopropyl alcohol, n-butanol, ethanol, and methanol), such as ultrahigh sensitivity, rapid response speed (less than 10 s) and recovery time, good reproducibility, as well as stability. These would be associated with the desirable pore structure of the material, facilitating the molecules diffusion toward the entire sensing surface, and providing more active sensing sites for analytical gas.

Ordered mesoporous NiFe2O4 with ultrathin framework for low-ppb toluene sensing

Highly sensitive and selective detection against specific target gases, especially at low-ppb (part per billion) level, remain a great number of challenges in gas sensor applications. In this paper, we first present an ordered mesoporous NiFe₂O₄ for highly sensitive and selective detection against low-ppb toluene. A series of mesoporous NiFe₂O₄ materials were synthesized by templating from mesoporous silica KIT-6 and its framework thickness was reduced from 8.5 to 5 nm by varying the pore size of KIT-6 from 9.4 to 5.6 nm, accompanied with the increase of the specific surface area from 134 to 216 m² g^-1. The ordered mesoporous NiFe₂O₄ with both ultrathin framework of 5 nm and large specific surface area of up to 216 m² g^-1 exhibits a highest response (R_gas/R_air - 1 = 77.3) toward 1,000 ppb toluene at 230 °C and is nearly 7.3 and 76.7 times higher than those for the NiFe₂O₄ replica with thick framework and its bulk counterpart respectively, which also possesses a quite low limit of detection (<2 ppb), and good selectivity.

C-doped ZnO ball-in-ball hollow microspheres for efficient photocatalytic and photoelectrochemical applications

ZnO is an important semiconductor and has been widely used in the field of photocatalysis, solar cell and environmental remediation. Herein, we fabricated C-doped ZnO ball-in-ball hollow microspheres (BHMs) by a facile solvothermal treatment of zinc acetate in ethylene glycol-ethanol mixture. The presence of ethylene glycol (EG) leads to the formation of initial single-layered hollow spheres and then a time-dependent evolution transforms them into uniform BHMs with tunable shell thickness and void space. XPS characterizations reveal that C-dopants are introduced into the lattice of ZnO BHMs, with its concentration increasing with solvothermal time and then becoming saturated in 12h. ZEG-12 (ZnO BHMs with 12-h solvothermal treatment), with an optimal hollow structure and C-doping concentration, performs the best optical absorption capability, efficiency of charge separation and transfer, and mass transfer in reaction media, as proved by SEM, TEM, PL, BET and EIS characterizations. When applied as photocatalyst for organic-pollutant degradation and as photoanode material for PEC water splitting, ZEG-12 exhibits respectively ca. 8.9-fold and 10.5-fold higher activity than pristine ZnO nanoparticles.

Ordered Large-Pore Mesoporous Cr2O3 with Ultrathin Framework for Formaldehyde Sensing

A series of ordered mesoporous chromium oxides (Cr₂O₃) were synthesized by first replicating bicontinuous cubic Ia3d mesoporous silica (KIT-6), then a controlled mesostructural transformation from Ia3d to I4₁32 symmetry during the replication from KIT-6 to Cr₂O₃ was achieved by reducing the pore size and interconnectivities of KIT-6, accompanied with an increase in pore size from 3 to 12 nm and a decrease in framework thickness from 8.6 to 5 nm of the resultant Cr₂O₃ replicas. The gas-sensing behavior of the Cr₂O₃ replicas toward formaldehyde (HCHO) was systematically investigated. Ordered mesoporous Cr₂O₃ with both large accessible pores (12 nm) and an ultrathin framework (5 nm) exhibits the best sensing performance, with a response (R_gas/R_air = 119) toward 9 ppm of HCHO 4.4 times higher than that (R_gas/R_air = 27) of its counterpart with small pores and a thick framework. Moreover, it possesses excellent selectivity for detecting HCHO over other interference gases such as CO, benzene, toluene, p-xylene, NH₃, H₂S, and moisture. The significantly enhanced sensing performance of ordered large-pore mesoporous Cr₂O₃ with ultrathin framework suggests its great potential for the selective detection of HCHO.

Highly Flexible and Porous Nanoparticle-Loaded Films for Dye Removal by Graphene Oxide-Fungus Interaction

Highly flexible and porous films with the ability to load various nanoscale adsorbents are of particular importance in the purification field. Herein, we report the sustainable and large-scale fabrication of a porous and flexible hybrid film based on the graphene oxide/hyphae interaction at a relatively low temperature of 130 °C. Under identical conditions, such films cannot be constructed with solely graphene oxide or hyphae. Moreover, through the addition of nanoscale building blocks [e.g., nanoscale poly(m-phenylenediamine) (PmPD) adsorbents] in the interaction process, the nanoparticles can be in situ loaded into the film. According to FTIR and XPS analyses, the film formation mechanisms mainly involve redox and cross-linking reactions between graphene oxide and fungus hyphae. In a proof-of-concept study, a PmPD nanoparticle-loaded hybrid film was used as a superior key component to build a flow-through adsorption device that displayed a promising adsorption performance toward dye pollutants.

Synthesis of Mesoporous α-Fe2O3 Nanoparticles by Non-ionic Soft Template and Their Applications to Heavy Oil Upgrading

This paper reports the synthetic route of 3-D network shape α-Fe2O3 from aqueous solutions of iron precursor using a non-ionic polymeric soft-template, Pluronic P123. During the synthesis of α-Fe2O3, particle sizes, crystal phases and morphologies were significantly influenced by pH, concentrations of precursor and template. The unique shape of worm-like hematite was obtained only when a starting solution was prepared by a weakly basic pH condition and a very specific composition of constituents. The synthesized nanocrystal at this condition had a narrow pore size distribution and high surface area compared to the bulk α-Fe2O3 or the one synthesized from lower pH conditions. The hydrocracking performance was tested over the synthesized iron oxide catalysts with different morphologies. The worm-like shape of iron oxide showed a superior performance, including overall yield of liquid fuel product and coke formation, over the hydrocracking of heavy petroleum oil.

Coupling Microbial Growth with Nanoparticles: A Universal Strategy To Produce Functional Fungal Hyphae Macrospheres

Macroscale assembly of nanoscale building blocks is an intriguing way to translate the unique characteristics of individual nanoparticles into macroscopic materials. However, the lack of the efficient universal assembly strategy seriously hinders the possibility of macroscale architectures in practical applications. Herein, we develop a general, environment-friendly, and scalable microbial growth method for the construction of macroscopic composite assemblies with excellent mechanical strength by in situ integrating various types of nanoparticles into fungal hyphae (FH) macrospheres. Notably, the size of the FH-based composite spheres and the loading amount of the nanoparticles with different dimensions can be well tuned by controlling the cultivation time and the dosage of nanoparticles, respectively. Interestingly, bifunctional FH-based core-shell macrospheres can also be achieved by programmed assembling two different kinds of nanoparticles in the cultivation process. The produced multifunctional FH-based composite spheres exhibit wide potential applications in magnetic actuation, photothermal therapy, and contaminant adsorption, etc.

Synthesis and applications of porous non-silica metal oxide submicrospheres

A variety of metal oxide particles of spherical morphology from nano to micrometer size have been reviewed with a special emphasis on the appraisal of synthetic strategies and applications in biomedical, environmental and energy-related areas.

Tin-based nanomaterials for electrochemical energy storage

A summary of the synthesis, modification, and electrochemical performance of Sn-based nanomaterials; lithium/sodium ion batteries and supercapacitors are carefully discussed.

Mesoporous Silica Gel-Based Mixed Matrix Membranes for Improving Mass Transfer in Forward Osmosis: Effect of Pore Size of Filler

The efficiency of forward osmosis (FO) process is generally limited by the internal concentration polarization (ICP) of solutes inside its porous substrate. In this study, mesoporous silica gel (SG) with nominal pore size ranging from 4–30 nm was used as fillers to prepare SG-based mixed matrix substrates. The resulting mixed matrix membranes had significantly reduced structural parameter and enhanced membrane water permeability as a result of the improved surface porosity of the substrates. An optimal filler pore size of ~9 nm was observed. This is in direct contrast to the case of thin film nanocomposite membranes, where microporous nanoparticle fillers are loaded to the membrane rejection layer and are designed in such a way that these fillers are able to retain solutes while allowing water to permeate through them. In the current study, the mesoporous fillers are designed as channels to both water and solute molecules. FO performance was enhanced at increasing filler pore size up to 9 nm due to the lower hydraulic resistance of the fillers. Nevertheless, further increasing filler pore size to 30 nm was accompanied with reduced FO efficiency, which can be attributed to the intrusion of polymer dope into the filler pores.

Ordered mesoporous NiO with thin pore walls and its enhanced sensing performance for formaldehyde

A class of formaldehyde (HCHO) gas sensors with a high response were developed based on ordered mesoporous NiO, which were synthesized via the nanocasting route by directly using mesoporous silica as the hard template. A series of mesoporous NiO with different textural parameters such as specific surface area, pore size, pore wall thickness were achieved by selecting mesoporous silica with different pore sizes as templates. The gas sensing properties for formaldehyde (HCHO) of the NiO specimens were examined. The results show that this mesoporous NiO possesses a much higher response to HCHO even at low concentration levels than the bulk NiO, and a larger specific surface area and pore size as well as thinner pore walls would be beneficial for enhancing the sensing properties of NiO.

Enhanced catalytic activity of hierarchically macro-/mesoporous Pt/TiO2 toward room-temperature decomposition of formaldehyde

Hierarchically macro-/mesoporous Pt/TiO₂ exhibits excellent catalytic activity and recyclability toward catalytic decomposition of formaldehyde in air at room temperature.

High-surface-area mesoporous TiO2 microspheres via one-step nanoparticle self-assembly for enhanced lithium-ion storage

Mesoporous TiO2 microspheres assembled from TiO2 nanoparticles with specific surface areas as high as 150 m(2) g(-1) were synthesized via a facile one-step solvothermal reaction of titanium isopropoxide and anhydrous acetone. Aldol condensation of acetone gradually releases structural H2O, which hydrolyzes and condenses titanium isopropoxide, forming TiO2 nanocrystals. Simultaneous growth and aggregation of TiO2 nanocrystals leads to the formation of high-surface-area TiO2 microspheres under solvothermal conditions. After a low-temperature post-synthesis calcination, carbonate could be incorporated into TiO2 as a dopant with the carbon source coming from the organic byproducts during the synthesis. Carbonate doping modifies the electronic structure of TiO2 (e.g., Fermi level, Ef), and thus influences its electrochemical properties. Solid electrolyte interface (SEI) formation, which is not common for titania, could be initiated in carbonate-doped TiO2 due to elevated Ef. After removing carbonate dopants by high-temperature calcination, the mesoporous TiO2 microspheres showed much improved performance in lithium insertion and stability at various current rates, attributed to a synergistic effect of high surface area, large pore size and good anatase crystallinity.

Synthesis of honeycomb-like mesoporous pyrite FeS2 microspheres as efficient counter electrode in quantum dots sensitized solar cells

Honeycomb-like mesoporous pyrite FeS2 microspheres, with diameters of 500-800 nm and pore sizes of 25-30 nm, are synthesized by a simple solvothermal approach. The mesoporous FeS2 microspheres are demonstrated to be an outstanding counter electrode (CE) material in quantum dot sensitized solar cells (QDSSCs) for electrocatalyzing polysulfide electrolyte regeneration. The cell using mesoporous FeS2 microspheres as CE shows 86.6% enhancement in power conversion efficiency (PCE) than the cell using traditional noble Pt CE. Furthermore, it also shows 11.4% enhancement in PCE than the cell using solid FeS2 microspheres as CE, due to the mesoporous structure facilitating better contact with polysulfide electrolyte and fast diffusion of redox couple species in electrolyte.

Nanoflakes-assembled three-dimensional hollow-porous v2 o5 as lithium storage cathodes with high-rate capacity

Three-dimensional (3D) hollow-porous vanadium pentoxide (V2 O5 ) quasi-microspheres are synthesized by a facile solvothermal method followed by annealing at 450 °C in air. The interconnected hollow-porous networks facilitate the kinetics of lithium-ion diffusion and improve the performance of V2 O5 to achieve a high capacity and remarkable rate capability as a cathode material for lithium batteries.

Preparation of hollow core/shell microspheres of hematite and its adsorption ability for samarium

Hollow core/shell hematite microspheres with diameter of ca. 1-2 μm have been successfully achieved by calcining the precursor composite microspheres of pyrite and polyvinylpyrrolidone (PVP) in air. The synthesized products were characterized by a wide range of techniques including powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and Brunauer-Emmett-Teller (BET) gas sorptometry. Temperature- and time-dependent experiments unveil that the precursor pyrite-PVP composite microspheres finally transform into hollow core/shell hematite microspheres in air through a multistep process including the oxidation and sulfation of pyrite, combustion of PVP occluded in the precursor, desulfation, aggregation, and fusion of nanosized hematite as well as mass transportation from the interior to the exterior of the microspheres. The formation of the hollow core/shell microspheres dominantly depends on the calcination temperature under current experimental conditions, and the aggregation of hematite nanocrystals and the core shrinking during the oxidation of pyrite are responsible for the formation of the hollow structures. Moreover, the adsorption ability of the hematite for Sm(III) was also tested. The results exhibit that the hematite microspheres have good adsorption activity for trivalent samarium, and that its adsorption capacity strongly depends on the pH of the solution, and the maximum adsorption capacity for Sm(III) is 14.48 mg/g at neutral pH. As samarium is a typical member of the lanthanide series, our results suggest that the hollow hematite microspheres have potential application in removal of rare earth elements (REEs) entering the water environment.

Nanocasting synthesis of In2O3 with appropriate mesostructured ordering and enhanced gas-sensing property

Ordered mesoporous In2O3 gas-sensing materials with controlled mesostructured morphology and high thermal stability have been successfully synthesized via a nanocasting method in conjunction with the container effect. The mesostructured ordering, as well as the particle size, crystallinity and pore size distribution have been proved to vary in a large range by using the XRD, SAXRD, SEM, TEM, and nitrogen physisorption techniques. The control of the mesostructured morphology was carried out by tuning the transportation rate of indium precursor in template channel resulting from the different escape rate of the decomposed byproducts via the varied container opening and shapes. The particular relation between the mesostructured ordering and gas sensing property of mesoporous In2O3 was examined in detail. It was found that the ordered mesoporous In2O3 with appropriate mesostructured morphology exhibited significantly improved ethanol sensitivity, response and selectivity performances in comparison with the other ordered mesoporous In2O3, which benefits from the large surface area with enough sensing active sites, proper pore distribution for sufficient gas diffusion, and appropriate particle size for effective electron depletion. The resulting sensing behaviors lead to a better understanding of designing and using such mesoporous metal oxides for a number of gas-sensing applications.

High-performance supercapacitor and lithium-ion battery based on 3D hierarchical NH4F-induced nickel cobaltate nanosheet-nanowire cluster arrays as self-supported electrodes

A facile hydrothermal method is developed for large-scale production of three-dimensional (3D) hierarchical porous nickel cobaltate nanowire cluster arrays derived from nanosheet arrays with robust adhesion on Ni foam. Based on the morphology evolution upon reaction time, a possible formation process is proposed. The role of NH4F in formation of the structure has also been investigated based on different NH4F amounts. This unique structure significantly enhances the electroactive surface areas of the NiCo2O4 arrays, leading to better interfacial/chemical distributions at the nanoscale, fast ion and electron transfer and good strain accommodation. Thus, when it is used for supercapacitor testing, a specific capacitance of 1069 F g(-1) at a very high current density of 100 A g(-1) was obtained. Even after more than 10,000 cycles at various large current densities, a capacitance of 2000 F g(-1) at 10 A g(-1) with 93.8% retention can be achieved. It also exhibits a high-power density (26.1 kW kg(-1)) at a discharge current density of 80 A g(-1). When used as an anode material for lithium-ion batteries (LIBs), it presents a high reversible capacity of 976 mA h g(-1) at a rate of 200 mA g(-1) with good cycling stability and rate capability. This array material is rarely used as an anode material. Our results show that this unique 3D hierarchical porous nickel cobaltite is promising for electrochemical energy applications.

C-isolated Ag-C-Co sandwich sphere-nanostructures and their high activity catalysis induced by surface plasmon resonance

Magnetic C-isolated Ag-C-Co sandwich sphere nanostructures have been fabricated through a synchronous growth and assembly process, in which the outer Co sphere-shells assemble around the surface of synchronously grown Ag-C sphere-cores. Raman and UV-vis absorption spectroscopy studies show that the covering of Co shell on Ag-C sphere cores weakens the surface-enhanced Raman scattering (SERS) and surface plasmon resonance (SPR) of Ag-C sphere cores. Owing to its ferromagnetic behaviour, the as-prepared C-isolated Ag-C-Co sandwich nanospheres can be easily separated and recycled by an external magnet field for application. Compared with Ag-Co, C-Co, and Co nanospheres of the same size, the resultant magnetic Ag-C-Co sandwich nanospheres exhibit markedly high catalytic activity toward ammonia borane hydrolytic dehydrogenation at atmospheric pressure and room temperature, which is induced by SPR from C-isolated sandwich structural and electronic synergistic effects.

The visible-light driven photocatalytic destruction of NO(x) using mesoporous TiO2 spheres synthesized via a "water-controlled release process"

Mesoporous anatase TiO2 spheres with tunable sizes ranging from 400 nm to 3 μm were synthesized using an original so-called "water-controlled solvothemal release process". In this method, the well-known esterification reaction between ethanol and acetic acid was creatively employed to generate water gradually during a solvothermal process. Thereafter, the slowly released water molecules functioned as nucleation centers for completing the hydrolysis of titanium tetraisopropoxide to produce homogenous mesoporous TiO2 spheres. In reality, these samples consisted of densely packed nanoparticles that formed spherical secondary particles with interparticle pores. Research has demonstrated that the diameter of the TiO2 spheres can be easily tuned by controlling the concentration of the Ti source in the starting solution. Regardless of their diameter, all of these TiO2 spheres exhibited a high specific surface area (above 150 m(2) g(-1)) originating largely from the contribution of mesopores. On the merits of their porous structure and related high specific surface area, the mesoporous TiO2 spheres showed a higher photocatalytic activity than P25 for the oxidative photo-destruction of NOx gas.

General solution growth of mesoporous NiCo2O4 nanosheets on various conductive substrates as high-performance electrodes for supercapacitors

Mesoporous NiCo(2) O(4) nanosheets can be directly grown on various conductive substrates, such as Ni foam, Ti foil, stainless-steel foil and flexible graphite paper, through a general template-free solution method combined with a simple post annealing treatment. As a highly integrated binder- and conductive-agent-free electrode for supercapacitors, the mesoporous NiCo(2) O(4) nanosheets supported on Ni foam deliver ultrahigh capacitance and excellent high-rate cycling stability.

Monodisperse Fe3O4 and γ-Fe2O3 magnetic mesoporous microspheres as anode materials for lithium-ion batteries

Monodisperse Fe(3)O(4) and γ-Fe(2)O(3) magnetic mesoporous microspheres are prepared via a surfactant-free solvothermal combined with precursor thermal transformation method. The as-prepared Fe(3)O(4) and γ-Fe(2)O(3) magnetic mesoporous microspheres have a relatively high specific surface area of 122.3 and 138.6 m(2)/g, respectively. The Fe(3)O(4) and γ-Fe(2)O(3) magnetic mesoporous microspheres are explored as the anode materials for lithium-ion batteries, and they have a high initial discharge capacity of 1307 and 1453 mA h/g, respectively, and a good reversible performance (450 mA h/g for Fe(3)O(4) and 697 mA h/g for γ-Fe(2)O(3) after 110 cycles) at the current density of 0.2C.

Probing the morphology-device relation of Fe₂O₃ nanostructures towards photovoltaic and sensing applications

A lot of research on nanomaterials has been carried out in recent years. However, there is still a lack of nanostructures that have a combination of superior properties; both efficient electron transport and high surface area. Here, the authors have tried to develop hybrid α-Fe(2)O(3) flower-like morphology which exhibits both superior electron transport and high surface area. Intrigued by the unique properties of Fe(2)O(3) at the nanoscale and its abundance in nature, we have demonstrated a facile template-free solution based synthesis of hybrid α-Fe(2)O(3) comprising nanopetals nucleating radially from a 3D core. Due to its simplicity, the synthesis process can be easily reproduced and scaled up. We carried out in-depth studies on gas sensing and dye-sensitized solar cell (DSSC) device characterization so as to gain an understanding of how surface area and transport properties are affected by variation in morphology. The hybrid α-Fe(2)O(3) nanostructures are studied as potential candidates for gas sensors and for the first time as a working electrode for DSSC.