Controllable synthesis of recyclable core-shell γ-Fe2O3@SnO2 hollow nanoparticles with enhanced photocatalytic and gas sensing properties

The role of tin species in doped iron (III) oxide for photocatalytic degradation of methyl orange dye under UV light

Iron (III) oxide, a stable semiconductor with versatile applications, was synthesized alongside Sn-doped Fe₂O₃ (Sn-Fe₂O₃) using the sol-gel technique. Characterization via X-ray diffraction, field-emission scanning electron microscopy, and UV-visible spectroscopy confirmed the presence of α- and γ-Fe2O3 phases in the synthesized powders. Incorporation of the dopant reduced the initial band gap energy of Fe₂O₃ (2.2 eV) by approximately 0.1 eV. To evaluate photocatalytic performance, Fe₂O₃ and Sn-Fe₂O₃ were tested for decolorization efficiency of a methyl orange solution. Results revealed the 5 wt% Sn-doped catalyst as optimal, achieving complete degradation of methyl orange within 120 min under simulated solar light. The addition of small amounts of Sn effectively reduced the Fe₂O₃ band gap and significantly enhanced photocatalytic performance. Investigation of pH and dye concentration impact on photocatalytic degradation revealed superior activity under acidic conditions compared to alkaline. Furthermore, maintaining a moderate concentration of methyl orange (10 ppm) ensured optimum photocatalytic activity.

Incorporating N Atoms into SnO₂ Nanostructure as an Approach to Enhance Gas Sensing Property for Acetone

The development of high-performance acetone gas sensor is of great significance for environmental protection and personal safety. SnO₂ has been intensively applied in chemical sensing areas, because of its low cost, high mobility of electrons, and good chemical stability. Herein, we incorporated nitrogen atoms into the SnO₂ nanostructure by simple solvothermal and subsequent calcination to improve gas sensing property for acetone. The crystallization, morphology, element composition, and microstructure of as-prepared products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Electron paramagnetic resonance (EPR), Raman spectroscopy, UV–visible diffuse reflectance spectroscopy (UV–vis DRS), and the Brunauer–Emmett–Teller (BET) method. It has been found that N-incorporating resulted in decreased crystallite size, reduced band-gap width, increased surface oxygen vacancies, enlarged surface area, and narrowed pore size distribution. When evaluated as gas sensor, nitrogen-incorporated SnO₂ nanostructure exhibited excellent sensitivity for acetone gas at the optimal operating temperature of 300 °C with high sensor response (R_air/R_gas − 1 = 357) and low limit of detection (7 ppb). The nitrogen-incorporated SnO₂ gas sensor shows a good selectivity to acetone in the interfering gases of benzene, toluene, ethylbenzene, hydrogen, and methane. Furthermore, the possible gas-sensing mechanism of N-incorporated SnO₂ toward acetone has been carefully discussed.

Corn-like, recoverable γ-Fe2O3@SiO2@TiO2 photocatalyst induced by magnetic dipole interactions

Corn-like, γ-Fe2O3@SiO2@TiO2 core/shell heterostructures were synthesized by a modified solvothermal reduction combined with a sol-gel method. SiO2 shells were first deposited on monodisperse Fe3O4 microspheres by a sol-gel method. Fe3O4@SiO2@TiO2 corn-like heterostructures were then obtained by sequential TiO2 coating, during which the magnetic dipolar interactions induced the anisotropic self-assembly process. After annealing at 350 °C, the crystalized TiO2 enhanced photocatalytic activity, while Fe3O4 was converted to γ-Fe2O3. The corn-like γ-Fe2O3@SiO2@TiO2 photocatalyst can be recycled and reused by magnet extraction. Despite the photocatalytic activity decreased with each cycle, it can be completely recovered by moderate heating at 200 °C.

Designed synthesis and surface engineering strategies of magnetic iron oxide nanoparticles for biomedical applications

Iron oxide nanoparticles (NPs) hold great promise for future biomedical applications because of their magnetic properties as well as other intrinsic properties such as low toxicity, colloidal stability, and surface engineering capability. Numerous related studies on iron oxide NPs have been conducted. Recent progress in nanochemistry has enabled fine control over the size, crystallinity, uniformity, and surface properties of iron oxide NPs. This review examines various synthetic approaches and surface engineering strategies for preparing naked and functional iron oxide NPs with different physicochemical properties. Growing interest in designed and surface-engineered iron oxide NPs with multifunctionalities was explored in in vitro/in vivo biomedical applications, focusing on their combined roles in bioseparation, as a biosensor, targeted-drug delivery, MR contrast agents, and magnetic fluid hyperthermia. This review outlines the limitations of extant surface engineering strategies and several developing strategies that may overcome these limitations. This study also details the promising future directions of this active research field.

Hierarchical growth of ZnFe2O4 for sensing applications

Selective sensing of toxic heavy metals Hg(ii) and environmentally hazardous acetone vapour using mesoporous ZnFe₂O₄ NFs, synthesized from our laboratory developed modified hydrothermal technique.

Ag-doped nano magnetic γ-Fe2O3@DA core–shell hollow spheres: an efficient and recoverable heterogeneous catalyst for A3 and KA2 coupling reactions and [3 + 2] cycloaddition

An effective protocol for the fabrication of Ag-doped nano magnetic γ-Fe₂O₃@DA core–shell hollow spheres (h-Fe₂O₃@DA/Ag) by a simple hydrothermal method is demonstrated without any templates in the reaction system.

Hierarchical Assembly of α-Fe₂O₃ Nanosheets on SnO2₂Hollow Nanospheres with Enhanced Ethanol Sensing Properties

We present the preparation of a hierarchical nanoheterostructure consisting of inner SnO2 hollow spheres (SHS) surrounded by an outer α-Fe2O3 nanosheet (FNS). Deposition of the FNS on the SHS outer surface was achieved by a facile microwave hydrothermal reaction to generate a double-shell SHS@FNS nanostructure. Such a composite with novel heterostructure acted as a sensing material for gas sensors. Significantly, the hierarchical composites exhibit excellent sensing performance toward ethanol, which is superior to the single component (SHS), mainly because of the synergistic effect and heterojunction.

Fabrication of SnO2-SnO nanocomposites with p-n heterojunctions for the low-temperature sensing of NO2 gas

In this report, the fabrication of a novel SnO2-SnO nanostructure with p-n heterojunctions has been achieved through a facile one-pot and low-cost hydrothermal process. The structure and properties of the nanocomposite were analyzed with X-ray techniques and electron microscopy. HRTEM characterization showed that the p-n heterojunctions were formed with small n-type SnO2 nanocrystals dispersed on the surface of large p-type SnO crystals. Compared to the single SnO2-based material, a gas sensor fabricated from the SnO2-SnO composite exhibited an enhanced sensing performance for NO2 gas detection, with a limit of detection and sensitivity of 0.1 ppm and 0.26 ppm(-1), respectively, at a relatively low operating temperature (50 °C). Moreover, the p-n heterojunctions exhibited high sensing selectivity for NO2. Such a high sensing sensitivity and a low operating temperature make the SnO2-SnO p-n nanomaterial a promising gas sensor for practical NO2 gas detection. The improved sensing response characteristics of the hybrid material could be attributed to the p-n junctions formed through the in situ growth of SnO2 nanocrystals on SnO nanoplates. The present study is helpful for the design of novel gas sensing materials and the development of NO2 gas sensors.

Recent progress on magnetic iron oxide nanoparticles: synthesis, surface functional strategies and biomedical applications

This review focuses on the recent development and various strategies in the preparation, microstructure, and magnetic properties of bare and surface functionalized iron oxide nanoparticles (IONPs); their corresponding biological application was also discussed. In order to implement the practical in vivo or in vitro applications, the IONPs must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of IONPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The new functionalized strategies, problems and major challenges, along with the current directions for the synthesis, surface functionalization and bioapplication of IONPs, are considered. Finally, some future trends and the prospects in these research areas are also discussed.

Morphology-modulation of SnO2 hierarchical architectures by Zn doping for glycol gas sensing and photocatalytic applications

The morphology of SnO2 nanospheres was transformed into ultrathin nanosheets assembled architectures after Zn doping by one-step hydrothermal route. The as-prepared samples were characterized in detail by various analytical techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen adsorption-desorption technique. The Zn-doped SnO2 nanostructures proved to be the efficient gas sensing materials for a series of flammable and explosive gases detection, and photocatalysts for the degradation of methyl orange (MO) under UV irradiation. It was observed that both of the undoped and Zn-doped SnO2 after calcination exhibited tremendous gas sensing performance toward glycol. The response (S = Ra/Rg) of Zn-doped SnO2 can reach to 90 when the glycol concentration is 100 ppm, which is about 2 times and 3 times higher than that of undoped SnO2 sensor with and without calcinations, respectively. The result of photocatalytic activities demonstrated that MO dye was almost completely degraded (~92%) by Zn-doped SnO2 in 150 min, which is higher than that of others (MO without photocatalyst was 23%, undoped SnO2 without and with calcination were 55% and 75%, respectively).

Recent progress in magnetic iron oxide-semiconductor composite nanomaterials as promising photocatalysts

Photocatalytic degradation of toxic organic pollutants is a challenging tasks in ecological and environmental protection. Recent research shows that the magnetic iron oxide-semiconductor composite photocatalytic system can effectively break through the bottleneck of single-component semiconductor oxides with low activity under visible light and the challenging recycling of the photocatalyst from the final products. With high reactivity in visible light, magnetic iron oxide-semiconductors can be exploited as an important magnetic recovery photocatalyst (MRP) with a bright future. On this regard, various composite structures, the charge-transfer mechanism and outstanding properties of magnetic iron oxide-semiconductor composite nanomaterials are sketched. The latest synthesis methods and recent progress in the photocatalytic applications of magnetic iron oxide-semiconductor composite nanomaterials are reviewed. The problems and challenges still need to be resolved and development strategies are discussed.

Designing of YVO4 supported β-AgI nano-photocatalyst with improved stability

The proposed schematic diagram of electron transfer in AgI–YVO₄ for the photodegradation of Rh-B under simulated solar light irradiation.

Tube-like α-Fe2O3@Ag/AgCl heterostructure: controllable synthesis and enhanced plasmonic photocatalytic activity

Plasmonic photocatalysts coupled with semiconductors are one of the most popular combinations in environmental remediation applications.

Bio-templated fabrication of hierarchically porous WO3 microspheres from lotus pollens for NO gas sensing at low temperatures

Lotus pollen was used as a template to prepare WO₃ microspheres. The porous structure of the microspheres is ideal for gas sensing. The microsphere-based sensor has high sensitivity (S = 46.2) to 100 ppm NO gas with fast response and recovery speed 62 s/223 s) at 200 °C.

Cyanogel-derived formation of 3 D nanoporous SnO2-MxOy (M=Ni, Fe, Co) hybrid networks for high-performance lithium storage

Three-dimensional (3 D) nanoporous SnO2 -Mx Oy (M=Fe, Co, Ni, Cu, etc.) hybrid networks possess unique compositional and structural features that are beneficial to lithium storage and are thus anticipated to meet the performance requirements of advanced lithium-ion batteries for transportation and stationary energy storage. Herein, a facile, scalable, and versatile cyanogel-derived method for the construction of 3 D nanoporous SnO2 -Mx Oy hybrid networks was developed for the first time. The formation of 3 D nanoporous SnO2 -NiO, SnO2 -α-Fe2 O3 , and SnO2 -NiO-Co3 O4 hybrid networks was illustrated by using Sn-M cyanogels as precursors. Moreover, the anodic performance of the 3 D nanoporous SnO2 -NiO hybrid network was examined to demonstrate proof of concept. After coating with polypyrrole-derived carbon, the SnO2 -NiO@C hybrid network exhibited superior lithium-storage capabilities in terms of specific capacity, cycling stability, and rate capability.

Tube-like ternary α-Fe2O3@SnO2@Cu2O sandwich heterostructures: synthesis and enhanced photocatalytic properties

Heterogeneous photocatalysis is of great interest for environmental remediation applications. However, fast recombination of photogenerated electron-hole pair and a low utilization rate of sunlight hinder the commercialization of currently available semiconductor photocatalysts. In this regard, we developed a unique ternary single core-double shell heterostructure that consists of α-Fe2O3@SnO2@Cu2O. This heterostructure exhibits a tube-like morphology possessing broad spectral response for the sunlight due to the combination of narrow bandgap and wide bandgap semiconductors forming a p-n heterojunction. To fabricate such a short nanotube (SNT), we used an anion-assisted hydrothermal route for deposition of α-Fe2O3, a seed-mediated deposition strategy for SnO2, and finally an aging process to deposit a Cu2O layer to complete the tube-like ternary α-Fe2O3@SnO2@Cu2O single core-double shell heterostructures. The morphology, composition, and photocatalytic properties of those ternary core-shell-shell heterostructures were characterized by various analytical techniques. These ternary heterostructures exhibited enhanced photocatalytic properties on the photodegradation of the organic dye of Rhodamine B (RhB) under simulated sunlight irradiation. The origin of enhanced photocatalytic activity is due to the synergistic effect of broad spectral response by combining narrow bandgap and wide bandgap semiconductors and, hence, an efficient charge separation of photogenerated electron-hole pairs facilitated through the p-n heterojunction. Furthermore, our unique structure provides an insight on the fabrication and controlled preparation of multilayer heterostructural photocatalysts that have intriguing properties.

Enhanced ethanol gas sensing properties of SnO₂-core/ZnO-shell nanostructures

An inexpensive single-step carbon-assisted thermal evaporation method for the growth of SnO2-core/ZnO-shell nanostructures is described, and the ethanol sensing properties are presented. The structure and phases of the grown nanostructures are investigated by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. XRD analysis indicates that the core-shell nanostructures have good crystallinity. At a lower growth duration of 15 min, only SnO2 nanowires with a rectangular cross-section are observed, while the ZnO shell is observed when the growth time is increased to 30 min. Core-shell hierarchical nanostructures are present for a growth time exceeding 60 min. The growth mechanism for SnO2-core/ZnO-shell nanowires and hierarchical nanostructures are also discussed. The sensitivity of the synthesized SnO2-core/ZnO-shell nanostructures towards ethanol sensing is investigated. Results show that the SnO2-core/ZnO-shell nanostructures deposited at 90 min exhibit enhanced sensitivity to ethanol. The sensitivity of SnO2-core/ZnO-shell nanostructures towards 20 ppm ethanol gas at 400 °C is about ~5-times that of SnO2 nanowires. This improvement in ethanol gas response is attributed to high active sensing sites and the synergistic effect of the encapsulation of SnO2 by ZnO nanostructures.

Template and silica interlayer tailorable synthesis of spindle-like multilayer α-Fe2O3/Ag/SnO2 ternary hybrid architectures and their enhanced photocatalytic activity

Our study reports a novel iron oxide/noble metal/semiconductor ternary multilayer hybrid structure that was synthesized through template synthesis and layer-by-layer deposition. Three different morphologies of α-Fe2O3/Ag/SiO2/SnO2 hybrid architectures were obtained with different thicknesses of the SiO2 interlayer which was introduced for tailoring and controlling the coupling of noble metal Ag nanoparticles (NPs) with the SnO2 semiconductor. The resulting samples were characterized in terms of morphology, composition, and optical property by various analytical techniques. The as-obtained α-Fe2O3/Ag/SiO2/SnO2 nanocomposites exhibit enhanced visible light or UV photocatalytic abilities, remarkably superior to commercial pure SnO2 products, bare α-Fe2O3 seeds, and α-Fe2O3/SnO2 nanocomposites. Moreover, the sample of α-Fe2O3/Ag/SiO2/SnO2 also exhibits good chemical stability and recyclability because it has higher photocatalytic activity even after eight cycles. The origin of enhanced photocatalytic activity on the multilayer core-shell α-Fe2O3/Ag/SiO2/SnO2 nanocomposites was primarily ascribed to the coupling between noble metal Ag and the two semiconductors Fe2O3 and SnO2, which are proven to be applied in recyclable photocatalysis.

Template-free synthesis of Cu2O–Co3O4 core–shell composites and their application in gas sensing

Cu₂O–Co₃O₄ core–shell composites were prepared via a hydrothermal method.