WO3 Nanofiber‐Based Biomarker Detectors Enabled by Protein‐Encapsulated Catalyst Self‐Assembled on Polystyrene Colloid Templates

A novel catalyst functionalization method, based on protein‐encapsulated metallic nanoparticles (NPs) and their self‐assembly on polystyrene (PS) colloid templates, is used to form catalyst‐loaded porous WO₃ nanofibers (NFs). The metallic NPs, composed of Au, Pd, or Pt, are encapsulated within a protein cage, i.e., apoferritin, to form unagglomerated monodispersed particles with diameters of less than 5 nm. The catalytic NPs maintain their nanoscale size, even following high‐temperature heat‐treatment during synthesis, which is attributed to the discrete self‐assembly of NPs on PS colloid templates. In addition, the PS templates generate open pores on the electrospun WO₃ NFs, facilitating gas molecule transport into the sensing layers and promoting active surface reactions. As a result, the Au and Pd NP‐loaded porous WO₃ NFs show superior sensitivity toward hydrogen sulfide, as evidenced by responses (R_air/R_gas) of 11.1 and 43.5 at 350 °C, respectively. These responses represent 1.8‐ and 7.1‐fold improvements compared to that of dense WO₃ NFs (R_air/R_gas = 6.1). Moreover, Pt NP‐loaded porous WO₃ NFs exhibit high acetone sensitivity with response of 28.9. These results demonstrate a novel catalyst loading method, in which small NPs are well‐dispersed within the pores of WO₃ NFs, that is applicable to high sensitivity breath sensors.     

Density-controllable growth of SnO2 nanowire junction-bridging across electrode for low-temperature NO2 gas detection

The junction-bridging structure of metal oxide nanowires (NWs) improves gas-sensing properties. In this study, an on-chip growth method was used to fabricate gas sensors, it easily and effectively controls NW junctions. SnO₂ NWs were synthesized by thermal evaporation at 800 °C with tin powder as the source. The density of the NW junctions was controlled by changing the mass of the source material. A source material with large mass yielded high-density NW junctions. With electrode spacing of 20 μm, NW junctions were formed from the source material of larger than 2 mg. Gas sensing results revealed that the junction sensors exhibited a good response to NO₂ gas at a concentration of 1–10 ppm. The sensors exhibited a good response to NO₂ gas at low temperature of up to 100 °C and short response–recovery time (~20 s). The sensors also had good selectivity to NO₂ gas. The response (R _gas /R _air) to 1 ppm NO₂ was as high as 22 at 100 °C, whereas the cross gas responses (R _air /R _gas) to 10 ppm CO, 10 ppm H₂S, 100 ppm C₂H₅OH, and 100 ppm NH₃ were negligible (1.1–1.3).     

SnO2‐Based Nanomaterials: Synthesis and Application in Lithium‐Ion Batteries

The development of new electrode materials for lithium‐ion batteries (LIBs) has always been a focal area of materials science, as the current technology may not be able to meet the high energy demands for electronic devices with better performance. Among all the metal oxides, tin dioxide (SnO₂) is regarded as a promising candidate to serve as the anode material for LIBs due to its high theoretical capacity. Here, a thorough survey is provided of the synthesis of SnO₂‐based nanomaterials with various structures and chemical compositions, and their application as negative electrodes for LIBs. It covers SnO₂ with different morphologies ranging from 1D nanorods/nanowires/nanotubes, to 2D nanosheets, to 3D hollow nanostructures. Nanocomposites consisting of SnO₂ and different carbonaceous supports, e.g., amorphous carbon, carbon nanotubes, graphene, are also investigated. The use of Sn‐based nanomaterials as the anode material for LIBs will be briefly discussed as well. The aim of this review is to provide an in‐depth and rational understanding such that the electrochemical properties of SnO₂‐based anodes can be effectively enhanced by making proper nanostructures with optimized chemical composition. By focusing on SnO₂, the hope is that such concepts and strategies can be extended to other potential metal oxides, such as titanium dioxide or iron oxides, thus shedding some light on the future development of high‐performance metal‐oxide based negative electrodes for LIBs.     

Development of sensors based on CuO-doped SnO2 hollow spheres for ppb level H2S gas sensing

An effort has been made to develop a new kind of SnO₂–CuO gas sensor which could detect an extremely small amount of H₂S gas at relatively low working temperature. The sensor nanomaterials were prepared from SnO₂ hollow spheres (synthesized by employing carbon microspheres as temples) and Cu precursor by dipping method. The composition and structural characteristics of the as-prepared CuO-doped SnO₂ hollow spheres were studied by X-ray photoelectron spectroscopy, X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. Gas-sensing properties of CuO-doped SnO₂ hollow sphere were also investigated. It was found that the sensor showed good selectivity and high sensitivity to H₂S gas. A ppb level detection limit was obtained with the sensor at the relatively low temperature of 35 °C. Such good performances are probably attributed to the hollow sphere nanostructures. Our results imply that materials with hollow sphere nanostructures are promising candidates for high-performance gas sensors.     

Coralloid SnO2 with hierarchical structure and their application as recoverable gas sensors for the detection of benzaldehyde/acetone

In this paper, we report a solvothermal route to fabricate coralloid hierarchical SnO₂ nanostructures. We obtain the product with different surface morphology at different reaction temperature. The breadth and length of the shot rod on the surface change with the temperature. A possible growth mechanism governing the formation of the nanostructures is discussed. Gas sensors based on the as-prepared SnO₂ nanostructures exhibit high sensitivity, short recovery time, good reproducibility and linear dependence relation to benzaldehyde/acetone, which is significant for exploiting gas-sensing materials in the future.     

A General and Straightforward Route to Noble Metal‐Decorated Mesoporous Transition‐Metal Oxides with Enhanced Gas Sensing Performance

Controllable and efficient synthesis of noble metal/transition‐metal oxide (TMO) composites with tailored nanostructures and precise components is essential for their application. Herein, a general mercaptosilane‐assisted one‐pot coassembly approach is developed to synthesize ordered mesoporous TMOs with agglomerated‐free noble metal nanoparticles, including Au/WO₃, Au/TiO₂, Au/NbO_x, and Pt/WO₃. 3‐mercaptopropyl trimethoxysilane is applied as a bridge agent to cohydrolyze with metal oxide precursors by alkoxysilane moieties and interact with the noble metal source (e.g., HAuCl₄ and H₂PtCl₄) by mercapto (? SH) groups, resulting in coassembly with poly(ethylene oxide)‐b‐polystyrene. The noble metal decorated TMO materials exhibit highly ordered mesoporous structure, large pore size (≈14–20 nm), high specific surface area (61–138 m² g^?1), and highly dispersed noble metal (e.g., Au and Pt) nanoparticles. In the system of Au/WO₃, in situ generated SiO₂ incorporation not only enhances their thermal stability but also induces the formation of ε‐phase WO₃ promoting gas sensing performance. Owning to its specific compositions and structure, the gas sensor based on Au/WO₃ materials possess enhanced ethanol sensing performance with a good response (R_air/R_gas = 36–50 ppm of ethanol), high selectivity, and excellent low‐concentration detection capability (down to 50 ppb) at low working temperature (200 °C).     

Solvent‐Free Synthesis of Uniform MOF Shell‐Derived Carbon Confined SnO2/Co Nanocubes for Highly Reversible Lithium Storage

Tin dioxide (SnO₂) has attracted much attention in lithium‐ion batteries (LIBs) due to its abundant source, low cost, and high theoretical capacity. However, the large volume variation, irreversible conversion reaction limit its further practical application in next‐generation LIBs. Here, a novel solvent‐free approach to construct uniform metal–organic framework (MOF) shell‐derived carbon confined SnO₂/Co (SnO₂/Co@C) nanocubes via a two‐step heat treatment is developed. In particular, MOF‐coated CoSnO₃ hollow nanocubes are for the first time synthesized as the intermediate product by an extremely simple thermal solid‐phase reaction, which is further developed as a general strategy to successfully obtain other uniform MOF‐coated metal oxides. The as‐synthesized SnO₂/Co@C nanocubes, when tested as LIB anodes, exhibit a highly reversible discharge capacity of 800 mAh g^?1 after 100 cycles at 200 mA g^?1 and excellent cycling stability with a retained capacity of 400 mAh g^?1 after 1800 cycles at 5 A g^?1. The experimental analyses demonstrate that these excellent performances are mainly ascribed to the delicate structure and a synergistic effect between Co and SnO₂. This facile synthetic approach will greatly contribute to the development of functional metal oxide‐based and MOF‐assisted nanostructures in many frontier applications.     

Electron field emitters based on multi-walled carbon nanotubes coated with conducting polymer/metal/metal-oxide composites

The present work describes the field emission properties of multi-walled nanotubes (MWNTs)-based conducting polymer/metal-oxide/metal/MWNTs composites (polyaniline (PANI)/SnO₂/Sn/MWNTs). MWNTs were synthesised by chemical vapour deposition technique. SnO₂/Sn/MWNTs were prepared by using chemical reduction followed by calcination. By in situ polymerisation method, surface of SnO₂/Sn/MWNTs were coated with PANI. PANI/SnO₂/Sn/MWNTs field emitters were fabricated over flexible graphitised carbon fabric substrate by spin coating technique. High-resolution transmission electron microscopy and scanning electron microscopy were used to characterise the field emitters. Field emission properties have been studied using an indigenously made facility. The fabricated PANI/SnO₂/Sn/MWNTs field emitters exhibited excellent field emission properties with a turn on field of 1.83 V µm^?1 and a field enhancement factor of 4800.     

Nanofibers Comprising Yolk–Shell Sn@void@SnO/SnO2 and Hollow SnO/SnO2 and SnO2 Nanospheres via the Kirkendall Diffusion Effect and Their Electrochemical Properties

Nanofibers with a unique structure comprising Sn@void@SnO/SnO₂ yolk–shell nanospheres and hollow SnO/SnO₂ and SnO₂ nanospheres are prepared by applying the nanoscale Kirkendall diffusion process in conventional electrospinning process. Under a reducing atmosphere, post‐treatment of tin 2‐ethylhexanoate‐polyvinylpyrrolidone electrospun nanofibers produce carbon nanofibers with embedded spherical Sn nanopowders. The Sn nanopowders are linearly aligned along the carbon nanofiber axis without aggregation of the nanopowders. Under an air atmosphere, oxidation of the Sn–C composite nanofibers produce nanofibers comprising Sn@void@SnO/SnO₂ yolk–shell nanospheres and hollow SnO/SnO₂ and SnO₂ nanospheres, depending on the post‐treatment temperature. The mean sizes of the hollow nanospheres embedded within tin oxide nanofibers post‐treated at 500 °C and 600 °C are 146 and 117 nm, respectively. For the 250th cycle, the discharge capacities of the nanofibers prepared by the nanoscale Kirkendall diffusion process post‐treated at 400 °C, 500 °C, and 600 °C at a high current density of 2 A g^?1 are 663, 630, and 567 mA h g^?1, respectively. The corresponding capacity retentions are 77%, 84%, and 78%, as calculated from the second cycle. The nanofibers prepared by applying the nanoscale Kirkendall diffusion process exhibit superior electrochemical properties compared with those of the porous‐structured SnO₂ nanofibers prepared by the conventional post‐treatment process.     

A Novel Approach to High‐Performance Aliovalent‐Substituted Catalysts—2D Bimetallic MOF‐Derived CeCuOx Microsheets

Mixed transition metal oxides (MTMOs) have enormous potential applications in energy and environment. Their use as catalysts for the treatment of environmental pollution requires further enhancement in activity and stability. This work presents a new synthesis approach that is both convenient and effective in preparing binary metal oxide catalysts (CeCuO_x) with excellent activity by achieving molecular‐level mixing to promote aliovalent substitution. It also allows a single, pure MTMO to be prepared for enhanced stability under reaction by using a bimetallic metal–organic framework (MOF) as the catalyst precursor. This approach also enables the direct manipulation of the shape and form of the MTMO catalyst by controlling the crystallization and growth of the MOF precursor. A 2D CeCuO_x catalyst is investigated for the oxidation reactions of methanol, acetone, toluene, and o‐xylene. The catalyst can catalyze the complete reactions of these molecules into CO₂ at temperatures below 200 °C, representing a significant improvement in performance. Furthermore, the catalyst can tolerate high moisture content without deactivation.     

One-pot synthesis of intestine-like SnO2/TiO2 hollow nanostructures

In the present study the intestine-like binary SnO₂/TiO₂ hollow nanostructures are one-pot synthesized in aqueous phase at room temperature via a colloid seeded deposition process in which the intestine-like hollow SnO₂ spheres and Ti(SO₄)₂ are used as colloid seeds and Ti-source, respectively. The novel core (SnO₂ hollow sphere)-shell (TiO₂) nanostructures possess a large surface area of 122 m²/g (calcined at 350 °C) and a high exposure of TiO₂ surface. The structural change of TiO₂ shell at different temperatures was investigated by means of X-ray diffraction and Raman spectroscopy. It was observed that the rutile TiO₂ could form even at room temperature due to the presence of SnO₂ core and the unique core-shell interaction.     

Redox reaction-assisted growth of ZnO nanowires on SnO2 thin films

ZnO nanowires were grown onto SnO₂ film coated on Si substrate using a vapor transport method. Zn vapor was found to play important roles in reducing SnO₂ and in being oxidized as a ZnO layer. The growth mechanism of ZnO nanowires was revealed to be a two-step process of Zn-SnO₂ redox reaction and Sn catalyzed V-L-S (vapor-liquid-solid) growth; initially, Zn vapor atoms arriving at the SnO₂ surface reduce the SnO₂ to Sn and O atoms and diffuse into the SnO₂ layer to form a ZnO layer. The reduced Sn atoms diffuse out of the SnO₂ layer and are agglomerated to form Sn liquid droplets. Then, the Sn droplets on the surface of ZnO layer serve as a catalyst for the catalytic V-L-S growth of ZnO nanowires.     

Metal Oxide Hollow Nanostructures for Lithium‐ion Batteries

Metal oxide hollow structures have received great attention because of their many promising applications in a wide range of fields. As electrode materials for lithium‐ion batteries (LIBs), metal oxide hollow structures provide high specific capacity, superior rate capability, and improved cycling performance. In this Research News, we summarize the recent research activities in the synthesis of metal oxide hollow nanostructures with controlled shape, size, composition, and structural complexity, as well as their applications in LIBs. By focusing on hollow structures of some binary metal oxides (such as SnO₂, TiO₂, Fe₂O₃, Co₃O₄) and complex metal oxides, we seek to provide some rational understanding on the effect of nanostructure engineering on the electrochemical performance of the active materials. It is thus anticipated that this article will shed some light on the development of advanced electrode materials for next‐generation LIBs.     

静电纺丝法制备CuO/SnO2复合材料及其气敏特性研究

为研究p型材料和n型材料复合时气敏特性的变化,采用静电纺丝法分别制备了CuO、SnO_2以及3种比例混合的CuO/SnO_2复合纳米纤维材料,并通过XRD及SEM对其形貌、微观结构等进行表征.测试了该5种材料对丙酮、甲醛、甲醇、乙醇、甲苯等VOC气体的敏感特性.研究表明,CuO/SnO_2=2∶1的复合材料对丙酮、甲苯和乙醇的的响应值有一定提高;CuO/SnO_2=1∶1的复合材料对丙酮具有很高响应的同时,对乙醇和甲苯的响应产生了一定的抑制作用,从而大大提高了材料的选择性.其机理是:半导体材料复合后,在复合材料的表面会有更多的氧吸附,导致更多的VOC气体在半导体材料表面发生反应,使材料的电阻值变化更加明显,提高了材料的响应值.     

Water-assisted growth and characterization of SnO2 nanobelts

SnO₂ nanobelts have been synthesized by water-assisted growth at 850 °C using high pure Sn powders as the source materials. The as-synthesized products were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy(TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersed X-ray spectroscopy (EDX), infrared spectrum (IR) and room-temperature photoluminescence (PL) spectrum. XRD pattern of the sample is quite in accord with the standard pattern of the tetragonal rutile SnO₂; SEM and TEM images show that the uniform single-crystalline SnO₂ nanobelts are about tens of micrometers in length, 70-100 nm in width and 5-8 nm in thickness, and is smooth in surface. The special IR and PL properties were also detected by IR and PL testing. The growth mechanisms and special properties relative to the SnO₂ nanostructures are discussed.     

Synthesis and selective gas-sensing properties of hierarchically porous intestine-like SnO2 hollow nanostructures

Hierarchically porous intestine-like SnO₂ hollow nanostructures of different dimension were successfully synthesized via a facile, organic template free, H₂O₂-assisted method at room temperature. The morphology as well as texture (congregated solid sphere, intestine-like solid nanostructure, hollow core–shell one, and intestine-like hollow one) of SnO₂ materials can be controlled by varying H₂O₂ concentration and the size of intestine-like hollow SnO₂ can be tuned in the range of 20–120 nm by changing SnSO₄ concentration. The hierarchically porous intestine-like SnO₂ has high specific surface area (142 m² g⁻¹). The gas-sensing behaviors of the intestine-like SnO₂ material to different gas probes such as ethanol, H₂, CO, methane, and butane have been investigated; among them a high selectivity to ethanol was achieved.     

Adjusting the Chemical Bonding of SnO2@CNT Composite for Enhanced Conversion Reaction Kinetics

Carbon nanotubes (CNTs) with excellent electron conductivity are widely used to improve the electrochemical performance of the SnO₂ anode. However, the chemical bonding between SnO₂ and CNTs is not clearly elucidated despite it may affect the lithiation/delithiation behavior greatly. In this work, an SnO₂@CNT composite with Sn? C and Sn? O? C bonds as a linkage bridge is reported and the influence of the Sn? C and Sn? O? C bonds on the lithium storage properties is revealed. It is found that the Sn? C bond can act as an ultrafast electron transfer path, facilitating the reversible conversion reaction between Sn and Li₂O to form SnO₂. Therefore, the SnO₂@CNT composite with more Sn? C bond shows high reversible capacity and nearly half capacity contributes from conversion reaction. It is opposite for the SnO₂@CNT composite with more Sn? O? C bond that the electrons cannot be transferred directly to CNTs, resulting in depressed conversion reaction kinetics. Consequently, this work can provide new insight for exploration and design of metal oxide/carbon composite anode materials in lithium‐ion battery.     

Controlled growth,characterization and thermodynamic behavior of bismuth–tin nanostructures sheathed in carbon nanotubes

We report the controlled synthesis of bismuth–tin (Bi–Sn) nanostructures sheathed in graphitic shells that resemble carbon nanotubes (CNTs). Our approach is based on a simple catalytic chemical vapor deposition over a mixture of Bi₂O₃ and SnO₂ supplied as starting materials. Shape control of the nanostructures strongly relies on the weight ratio of Bi₂O₃ and SnO₂. Sheathed nanoparticles and nanorods are formed at SnO₂ to Bi₂O₃ weight ratios of less than 4:1. They are composed of two separate crystals: rhombohedral Bi and tetragonal Sn₁₉Bi crystals. On the other hand, the sheathed nanowires are formed at SnO₂ to Bi₂O₃ weight ratios above 4:1. The nanowires have only tetragonal Sn₁₉Bi structure with a diameter of approximately 100 nm. Elementary analyses support the core/shell heterostructure of the resulting products. A favorable temperature for the Sn-rich Sn₁₉Bi nanowires is in the range of 700–800 °C, more specifically around 750 °C. Thermodynamic analysis reveals that the CNTs play a significant role in the protection of the Bi–Sn nanostructures during phase transition by temperature change. This simple and reproducible method may be extended to the fabrication of similar binary or ternary nanostructures.     

Hydrothermal synthesis of different 3D SnO2 nanostructures and their gas-sensing properties

Different morphologies of 3D SnO₂ nanostructures, including sphere-like, net-like, and flower-like, have been successfully synthesised via a facile hydrothermal method. The products were characterized by X-ray diffraction and scanning electron microscopy. The possible growth mechanism of different SnO₂ nanostructures was discussed in detail. We found that the citric acid and PEG play significant roles in synthesizing the flower-like and net-like nanostructures. Furthermore, the gas-sensing properties of the samples were investigated towards the reducing ethanol gas. The results indicate that the flower-like and net-like SnO₂ show larger gas sensing properties than sphere-like SnO₂.     

A Robust and Conductive Black Tin Oxide Nanostructure Makes Efficient Lithium‐Ion Batteries Possible

SnO₂‐based lithium‐ion batteries have low cost and high energy density, but their capacity fades rapidly during lithiation/delithiation due to phase aggregation and cracking. These problems can be mitigated by using highly conducting black SnO_2?x , which homogenizes the redox reactions and stabilizes fine, fracture‐resistant Sn precipitates in the Li₂O matrix. Such fine Sn precipitates and their ample contact with Li₂O proliferate the reversible Sn → Li _x Sn → Sn → SnO₂/SnO_2?x cycle during charging/discharging. SnO_2?x electrode has a reversible capacity of 1340 mAh g^?1 and retains 590 mAh g^?1 after 100 cycles. The addition of highly conductive, well‐dispersed reduced graphene oxide further stabilizes and improves its performance, allowing 950 mAh g^?1 remaining after 100 cycles at 0.2 A g^?1 with 700 mAh g^?1 at 2.0 A g^?1. Conductivity‐directed microstructure development may offer a new approach to form advanced electrodes.