Ordered Mesoporous Tin Oxide Semiconductors with Large Pores and Crystallized Walls for High-Performance Gas Sensing

n-n type In2O3@-WO3 heterojunction nanowires: enhanced NO2 gas sensing characteristics for environmental monitoring

Solvothermal synthesis of 1D n-In2O3@n-WO3 heterojunction nanowires (HNWs) and their NO2 gas sensing characteristics are reported. The n-In2O3@n-WO3 HNWs have been well-characterised using XRD, Raman spectroscopy, XPS, SEM and HRTEM analyses. The NO2 sensing performance of n-In2O3@n-WO3 HNWs showed superior performance compared with pristine WO3 NWs. Due to the distinctive configuration of WO3-In2O3 heterojunctions, the n-In2O3@n-WO3 HNWs demonstrated remarkable sensitivity reaching 182% in response towards 500 ppb of NO2 gas at operating temperature of 200°C which is nearly 3.5 times greater than the response observed with pristine WO3 (50%). Moreover, the n-In2O3@n-WO3 HNWs also exhibited fast response (8-13 s)/recovery (54-62 s) time characteristics. A plausible sensing mechanism has been discussed. The enhancement in sensor characteristics shows that n-In2O3@n-WO3 HNWs could serve as a promising material for high-performance NO2 gas sensors for real-time environmental monitoring applications. This work could provide new understandings of the sensing mechanism of n-In2O3@n-WO3-based heterojunction nanowires, which can be applied to the design of novel n-n type MOS heterojunction materials for the application of low-temperature real-time high-performance NO2 sensors.

Achieving Room-Temperature ppb-Level H2S Detection in a Au-SnO2 Sensor with Low Voltage Enhancement Effect

Although semiconductor metal oxide-based sensors are promising for gas sensing, low-power and room temperature operation (24 ± 1 °C) remains desirable for practical applications particularly considering the request of energy saving or net zero emission. In this study, we demonstrate a Au/SnO2-based ultrasensitive H2S gas sensor with a limit of detection (LOD) of 2 ppb, operating at very low voltages (0.05 to 0.5 V) at room temperature. The Au/SnO2-based sensor showed approximately 7 times higher response (the ratio of change in the current to initial current) of ∼270% and 4 times faster recovery (126 s) compared to the pure SnO2-based sensor when exposed to 500 ppb H2S gas concentration at 0.5 V operating voltage at relative humidity (RH) 17.5 ± 2.5%. The enhancement can be attributed to the catalytic characteristics of AuNPs, increasing the number of adsorbed oxygen species on sensing material surfaces. Additionally, AuNPs aid in forming flower-petal-like Au/SnO2 nanostructures, offering a larger surface area and more active sites for H2S sensing. Moreover, at low voltage (<1 V), the localized dipoles at the Au/SnO2 interface may further enhance the absorption of polar oxygen molecules and hence promote the reaction between H2S and oxygen species. This low-power, ultrasensitive H2S sensor outperforms high-powered alternatives, making it ideal for environmental, food safety, and healthcare applications.

Maillard Reaction Inspired Microexplosion toward Fast Synthesis of Two-Dimensional Mesoporous Tin Oxides for Efficient Chemiresistive Gas Sensing

Two-dimensional (2D) mesoporous transition metal oxides are highly desired in various applications, but their fast and low-cost synthesis remains a great challenge. Herein, a Maillard reaction inspired microexplosion approach is applied to rapidly synthesize ultrathin 2D mesoporous tin oxide (mSnO2). During the microexplosion between granular ammonia nitrate with melanoidin at high temperature, the organic species can be carbonized and expanded rapidly due to the instantaneous release of gases, thus producing ultrathin carbonaceous templates with rich functional groups to effectively anchor SnO2 nanoparticles on the surface. The subsequent removal of carbonaceous templates via calcination in air results in the formation of 2D mSnO2 due to the confinement effect of the templates. Pd nanoparticles are controllably deposited on the surface of 2D mSnO2 via in situ reduction, forming ultrathin 2D Pd/mSnO2 nanocomposites with thicknesses of 6-8 nm. Owing to the unique 2D mesoporous structure with rich oxygen defects and highly exposed metal-metal oxide interfaces, 2D Pd/mSnO2 exhibits excellent sensing performance toward acetone with high sensitivity, a short response time, and good selectivity under low working temperature (100 °C). This fast and convenient microexplosion synthesis strategy opens up the possibility of constructing 2D porous functional materials for various applications including high-performance gas sensors.

Oxygen vacancy induced interaction between Pt and TiO2 to improve the oxygen reduction performance

In proton exchange membrane fuel cells (PEMFCS), a Pt-based catalyst has been plagued by activity and durability, making it difficult to implement in large-scale commercial applications. In this paper, a composite material formed by titanium dioxide and carbon black containing oxygen vacancies (TiO2(OV)-C) was used as a functional support to successfully load Pt nanoparticles (NPS). The introduction of oxygen vacancies induces the formation of a connection between Pt and TiO2, which not only strengthens the fixation of Pt by the composite support but also optimizes the local charge density of Pt. Compared with Pt/C (0.842 V) and Pt/TiO2-C (0.841 V), the half-wave potential (E1/2) of Pt/TiO2(OV)-C (0.862 V) is increased by 20 mV and 21 mV, respectively. After a long-term durability test, the E1/2 of Pt/TiO2(OV)-C is only attenuated by 5 mV. In addition, the mass activity (MA) and specific activity (SA) decreased from 183.4 mA mg-1 and 0.565 mA cm-2 to 144.4 mA mg-1 and 0.483 mA cm-2 at 0.85 V, only decreasing by 21% and 17 %, showing good stability. X-ray photoelectron spectroscopies (XPS) and density functional theory (DFT) calculations show that the interaction between Pt and TiO2 reduces the d-band center of Pt, thereby improving the desorption of intermediates *OH, which in turn promotes the activity of alkaline ORR. This study not only shows that OV plays a key role in the process of inducing interaction, but also deeply studies the influence of this interaction on the active site Pt, which provides more choices for the design of excellent multiphase catalysts.

Synergistic Effect of Electron Scattering and Space Charge Transfer Enabled Unprecedented Room Temperature NO2 Sensing Response of SnO2

Metal oxide gas sensors have long faced the challenge of low response and poor selectivity, especially at room temperature (RT). Herein, a synergistic effect of electron scattering and space charge transfer is proposed to comprehensively improve gas sensing performance of n-type metal oxides toward oxidizing NO2 (electron acceptor) at RT. To this end, the porous SnO2 nanoparticles (NPs) assembled from grains of about 4 nm with rich oxygen vacancies are developed through an acetylacetone-assisted solvent evaporation approach combined with precise N2 and air calcinations. The results show that the as-fabricated porous SnO2 NPs sensor exhibits an unprecedented NO2 -sensing performance, including outstanding response (Rg /Ra  = 772.33 @ 5 ppm), fast recovery (<2 s), an extremely low detection limit (10 ppb), and exceptional selectivity (response ratio >30) at RT. Theoretical calculation and experimental tests confirm that the excellent NO2 sensing performance is mainly attributed to the unique synergistic effect of electron scattering and space charge transfer. This work proposes a useful strategy for developing high-performance RT NO2 sensors using metal oxides, and provides an in-depth understanding for the basic characteristics of the synergistic effect on gas sensing, paving the way for efficient and low power consumption gas detection at RT.

Recent advancement in quantum dot-based materials for energy storage applications: a review

The need for energy storage and conversion is growing as a result of the worsening consequences of climate change and the depletion of fossil fuels. Energy conversion and storage requirements are rising as a result of environmental problems including global warming and the depletion of fossil fuels. The key to resolving the energy crisis is anticipated to be the quick growth of sustainable energy sources including solar energy, wind energy, and hydrogen energy. In this review, we have focused on discussing various quantum dots (QDs) and polymers or nanocomposites used for SCs and have provided examples of each type's performance. Effective QD use has really led to increased performance efficiency in SCs. The use of quantum dots in energy storage devices, batteries, and various quantum dots synthesis have all been emphasized in a number of great literature articles. In this review, we have homed in on the electrode materials based on quantum dots and their composites for storage and quantum dot based flexible devices that have been published up to this point.

SnO2 mesoporous nanoparticle-based gas sensor for highly sensitive and low concentration formaldehyde detection

Indoor air quality detection, especially formaldehyde (HCHO) detection, is of great importance in practical application. A key limitation of promoting gas-sensing devices is the lack of sensing materials with high sensing sensitivity and selectivity. In this study, SnO₂ mesoporous nanoparticles are fabricated by a facile hydrothermal route with a subsequent acid etching process. The prepared samples show high response toward HCHO (133.5, 222.8 for 100 ppm and 200 ppm HCHO, respectively) and short response/recovery time (15/22 s at 10 ppm). The excellent HCHO sensing performance benefits from the comprehensive regulation of the depletion region width, surface area and rich porosity, which is effective for the promotion of surface adsorption and catalyst activity. It is expected that the excellent sensing properties are promising for practical HCHO gas detection.

Functionalization of Mesoporous Semiconductor Metal Oxides for Gas Sensing: Recent Advances and Emerging Challenges

With the emerging of the Internet of Things, chemiresistive gas sensors have been extensively applied in industrial production, food safety, medical diagnosis, and environment detection, etc. Considerable efforts have been devoted to improving the gas-sensing performance through tailoring the structure, functions, defects and electrical conductivity of sensitive materials. Among the numerous sensitive materials, mesoporous semiconductor metal oxides possess unparalleled properties, including tunable pore size, high specific surface area, abundant metal-oxygen bonds, and rapid mass transfer/diffusion behavior (Knudsen diffusion), which have been regarded as the most potential sensitive materials. Herein, the synthesis strategies for mesoporous metal oxides are overviewed, the classical functionalization techniques of sensitive materials are also systemically summarized as a highlight, including construction of mesoporous structure, regulation of micro-nano structure (i.e., heterojunctions), noble metal sensitization (e.g., Au, Pt, Ag, Pd) and heteroatomic doping (e.g., C, N, Si, S). In addition, the structure-function relationship of sensitive materials has been discussed at molecular-atomic level, especially for the chemical sensitization effect, elucidating the interface adsorption/catalytic mechanism. Moreover, the challenges and perspectives are proposed, which will open a new door for the development of intelligent gas sensor in various applications.

Modeling Interfacial Interaction between Gas Molecules and Semiconductor Metal Oxides: A New View Angle on Gas Sensing

With the development of internet of things and artificial intelligence electronics, metal oxide semiconductor (MOS)-based sensing materials have attracted increasing attention from both fundamental research and practical applications. MOS materials possess intrinsic physicochemical properties, tunable compositions, and electronic structure, and are particularly suitable for integration and miniaturization in developing chemiresistive gas sensors. During sensing processes, the dynamic gas-solid interface interactions play crucial roles in improving sensors' performance, and most studies emphasize the gas-MOS chemical reactions. Herein, from a new view angle focusing more on physical gas-solid interactions during gas sensing, basic theory overview and latest progress for the dynamic process of gas molecules including adsorption, desorption, and diffusion, are systematically summarized and elucidated. The unique electronic sensing mechanisms are also discussed from various aspects including molecular interaction models, gas diffusion mechanism, and interfacial reaction behaviors, where structure-activity relationship and diffusion behavior are overviewed in detail. Especially, the surface adsorption-desorption dynamics are discussed and evaluated, and their potential effects on sensing performance are elucidated from the gas-solid interfacial regulation perspective. Finally, the prospect for further research directions in improving gas dynamic processes in MOS gas sensors is discussed, aiming to supplement the approaches for the development of high-performance MOS gas sensors.

Enhanced Response for Foodborne Pathogens Detection by Au Nanoparticles Decorated ZnO Nanosheets Gas Sensor

Listeria monocytogenes is a hazardous foodborne pathogen that is able to cause acute meningitis, encephalitis, and sepsis to humans. The efficient detection of 3-hydroxy-2-butanone, which has been verified as a biomarker for the exhalation of Listeria monocytogenes, can feasibly evaluate whether the bacteria are contained in food. Herein, we developed an outstanding 3-hydroxy-2-butanone gas sensor based on the microelectromechanical systems using Au/ZnO NS as a sensing material. In this work, ZnO nanosheets were synthesized by a hydrothermal reaction, and Au nanoparticles (~5.5 nm) were prepared via an oleylamine reduction method. Then, an ultrasonic treatment was carried out to modified Au nanoparticles onto ZnO nanosheets. The XRD, BET, TEM, and XPS were used to characterize their morphology, microstructure, catalytic structure, specific surface area, and chemical composition. The response of the 1.0% Au/ZnO NS sensors vs. 25 ppm 3-hydroxy-2-butanone was up to 174.04 at 230 °C. Moreover, these sensors presented fast response/recovery time (6 s/7 s), great selectivity, and an outstanding limit of detection (lower than 0.5 ppm). This work is full of promise for developing a nondestructive, rapid and practical sensor, which would improve Listeria monocytogenes evaluation in foods.

Sensing beyond Senses: An Overview of Outstanding Strides in Architecting Nanopolymer-Enabled Sensors for Biomedical Applications

Nano-enabled sensing is an expanding interdisciplinary field of emerging science with dynamic multifunctional detecting capabilities, equipped with a wide range of multi-faceted nanomaterial having diverse dimensions and composition. They have proven to be highly robust, sensitive, and useful diagnostic tools ranging from advanced industrial processes to ordinary consumer products. As no single nanomaterial has proved to be unparalleled, recent years has witnessed a large number of nanomaterial-based sensing strategies for rapid detection and quantification of processes and substances with a high degree of reliability. Nano-furnished platforms, because of easy fabrication methods and chemical versatility, can serve as ideal sensing means through different transduction mechanisms. This article, through a unified experimental-theoretical approach, uses literature of recent years to introduce, evaluate, and analyze significant developments in the area of nanotechnology-aided sensors incorporating the various classes of nanomaterial. Addressing the broad interests, the work also summarizes the sensing mechanisms using schematic illustrations, attempts to integrate the performance of different categories of nanomaterials in the design of sensors, knowledge gaps, regulatory aspects, future research directions, and challenges of implementing such techniques in standalone devices. In view of a dependency of analysis and testing on sustained growth of sensor-supported platforms, this article inspires the scientific community for more attention in this field.

Ultra-sensitive H2S sensor based on sunflower-like In-doped ZnO with enriched oxygen vacancies

In–ZnO with oxygen vacancies exhibits a higher sensing response and a shorter recovery time for H2S compared to ZnO.

Interfacial Assembly and Applications of Functional Mesoporous Materials

Functional mesoporous materials have gained tremendous attention due to their distinctive properties and potential applications. In recent decades, the self-assembly of micelles and framework precursors into mesostructures on the liquid-solid, liquid-liquid, and gas-liquid interface has been explored in the construction of functional mesoporous materials with diverse compositions, morphologies, mesostructures, and pore sizes. Compared with the one-phase solution synthetic approach, the introduction of a two-phase interface in the synthetic system changes self-assembly behaviors between micelles and framework species, leading to the possibility for the on-demand fabrication of unique mesoporous architectures. In addition, controlling the interfacial tension is critical to manipulate the self-assembly process for precise synthesis. In particular, recent breakthroughs based on the concept of the "monomicelles" assembly mechanism are very promising and interesting for the synthesis of functional mesoporous materials with the precise control. In this review, we highlight the synthetic strategies, principles, and interface engineering at the macroscale, microscale, and nanoscale for oriented interfacial assembly of functional mesoporous materials over the past 10 years. The potential applications in various fields, including adsorption, separation, sensors, catalysis, energy storage, solar cells, and biomedicine, are discussed. Finally, we also propose the remaining challenges, possible directions, and opportunities in this field for the future outlook.

Designing hierarchical porosity in tin oxide monoliths and their application as a solid acid catalyst

Hierarchically porous tin oxide monoliths were prepared through a sol–gel accompanied by phase separation for application as a solid acid catalyst.

Hydrangea-like mesoporous WO3 nanoflowers with crystalline framework for 3-hydroxy-2-butanone sensing

In this study, a simple and efficient strategy for the construction of hydrangea-like mesoporous WO₃ nanoflowers templated using diblock copolymer PS₁₁₉-PtBA₁₂₉ was developed. The nanoflower shows good gas sensing properties, especially for 3-hydroxy-2-butanone (3H-2B), which is the signature metabolite of Listeria monocytogenes (L. monocytogenes). Therefore, the gas sensing of 3H-2B by hydrangea-like mesoporous WO₃ nanoflowers can be used to detect L. monocytogenes. In the case of 25 ppm 3H-2B as target gas, the response (R_a/R_g) of the hydrangea-like mesoporous WO₃ nanoflowers at 205 °C is 152, where R_a and R_g are the resistances of the sensing device in air and target gas, respectively, and the response and recovery times at 25 ppm are 25 s and 146 s, respectively. Schematic illustration of the formation of hydrangea-like mesoporous WO₃ nanoflowers and its gas sensing implication.

Boosting the performance of NO2 gas sensors based on n-n type mesoporous ZnO@In2O3 heterojunction nanowires: in situ conducting probe atomic force microscopic elucidation of room temperature local electron transport

Herein, n-n type one dimensional ZnO@In₂O₃ heterojunction nanowires have been developed and their local electron transport properties during trace-level NO₂ gas sensing process have been probed at room-temperature using conducting probe atomic microscopy. Solvothermally synthesized 1D ZnO@In₂O₃ heterojunction nanowires have been characterized by various spectroscopic and microscopic techniques, which revealed the mesoporous structure indicating their enhanced sensing properties. The dangling bonds and fraction of metal ions to oxygen ions existing on the exposed crystal facets of the heterojunction nanowires have been visualized by employing crystallographic simulations with TEM analysis, which aided in forecasting the nature of surface adsorption of NO₂ gas species. In situ electrical characteristics and Scanning Spreading Resistance Microscopic (SSRM) imaging of single ZnO@In₂O₃ heterojunction nanowires revealed the local charge transport properties in n-n type ZnO@In₂O₃ heterojunction nanowires. Moreover, the ZnO@In₂O₃ heterojunction nanowires based sensor exhibited excellent sensitivity (S = 274%), a fast response (4-6 s) and high selectivity towards trace-level concentration (500 ppb) of NO₂ gas under ambient conditions with low power consumption. Spatially resolved surface potential (SP) variations in ZnO@In₂O₃ heterojunction nanowires have been visualized using in situ Scanning Kelvin Probe Force Microscopy (SKPM) under NO₂ gas environment at room temperature, which was further correlated with its energy band structure. The work functions of the material evaluated by SKPM reveal considerable changes in the energy band structure owing to the local electron transport between ZnO and In₂O₃ at the heterojunctions upon exposure to NO₂ gas indicating the charge carrier recombination. A plausible mechanism has been proposed based on the experimental evidences. The results suggest that new insights into complex sensing mechanisms deduced from the present investigation on n-n type MOS based heterojunction nanowires under ambient conditions can pave the way for the novel design and development of affordable and superior real-time gas sensors.

Gas Sensor Detecting 3-Hydroxy-2-butanone Biomarkers: Boosted Response via Decorating Pd Nanoparticles onto the {010} Facets of BiVO4 Decahedrons

The newly emerged gas sensing detection of 3-hydroxy-2-butanone (3H-2B) biomarker is deemed as an effective avenue to indirectly monitor Listeria monocytogenes (LM). However, 3H-2B sensing materials requiring critically high sensitivity and selectivity, and ppb-level detection limit, remain challenging. Here, we report the advanced gas sensors built with bismuth vanadate microdecahedron (BiVO₄ MDCD) {010} facets selectively decorated with Pd nanoparticles (Pd NPs, Pd-{010}BiVO₄ MDCDs) for boosted detection of the 3H-2B biomarker. Meanwhile, BiVO₄ MDCDs with overall facets are randomly deposited with Pd NPs (Pd-BiVO₄ MDCDs). Comparatively, Pd-{010}BiVO₄ MDCD sensors show 1 order of magnitude higher response toward the 3H-2B biomarker at 200 °C. Further, Pd-{010}BiVO₄ MDCD sensors enable to detect as low as 0.2 ppm 3H-2B and show best selectivity and stability, and fastest response and recovery. Density functional theory calculations reveal a lower adsorption energy of 3H-2B onto Pd-{010}BiVO₄ MDCDs than those of pristine and Pd-BiVO₄ MDCDs. The extraordinary Pd-{010}BiVO₄ sensing performance is ascribed to the Pd NP-assisted synergetic effect of the preferential adsorption of 3H-2B target molecules, accumulated sensing agent of ionic oxygen species, and concentrated catalysts on the {010} facets. This strategy offers rapid and noninvasive detection of LMs and is thus of great potential in the upcoming Internet of Things.

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.

Controllable synthesis of an intercalated SnS2/aEG structure for enhanced NO2 gas sensing performance at room temperature

An intercalated SnS₂/aEG structure with abundant heterojunctions for enhanced NO₂ gas sensing performance at room temperature.

Self-assembly of block copolymers towards mesoporous materials for energy storage and conversion systems

This paper reviews the progress in the field of block copolymer-templated mesoporous materials, including synthetic methods, morphological and pore size control and their potential applications in energy storage and conversion devices.

Synthesis and characterization of lignosulfonate/amino-functionalized SBA-15 nanocomposites for the adsorption of methylene blue from wastewater

The synthesis, characterization, and methylene blue (MB) adsorption study of a new lignosulfonate/amino-functionalized SBA-15 nanocomposite are described.

Gas sensing mechanisms of metal oxide semiconductors: a focus review

In recent years, gas sensors have been increasingly used in industrial production and daily life. Metal oxide semiconductor gas sensing materials are favoured for their outstanding physical and chemical properties, low cost and simple preparation methods. However, the gas sensing mechanisms of metal oxide semiconductors have not been considered by researchers, resulting in omissions and errors in the interpretation of gas sensing mechanisms in many articles. This review organizes and introduces several common gas sensing mechanisms of metal oxide semiconductors in detail and classifies them into two categories. The scope and relationship of these mechanisms are clarified. In addition, this review selects four strategies for enhancing the gas sensing properties of metal oxide semiconductors and analyses the gas sensing mechanisms to highlight the importance of the gas sensing mechanism. Finally, some perspectives for future investigations on the gas sensing mechanisms of metal oxide semiconductors are discussed as well.

Sn13-Oxo Clusters with an Open Hollow Structural Motif and Decorated by Different Functional Ligands

The first open hollow Sn₁₃-oxo cluster family has been successfully prepared and characterized. These Sn₁₃ clusters contain a {Sn₇} moiety that is similar to the basic structure unit of rutile SnO₂. Interestingly, the Sn₁₃ clusters show labile coordination sites on the edge, which could be functionalized by different ligands. With the different decorated types of functionalized ligands, the open hollow Sn₁₃ clusters present different structural details and framework diameters. The presented results provide a new open hollow structural motif of tin-oxo clusters and also a good platform for their ligand functionalization.

Rational Synthesis and Gas Sensing Performance of Ordered Mesoporous Semiconducting WO3/NiO Composites

Semiconducting metal oxides have attracted increasing attention in various fields due to their intrinsic properties. In this study, a facile solvent evaporation-induced multicomponent co-assembly approach coupled with a carbon-supported crystallization strategy is employed to controllably synthesize crystalline mesoporous nickel oxide-doped tungsten oxides in an acidic THF/H₂O solution with poly(ethylene oxide)-b-polystyrene diblock copolymers (PEO-b-PS) as the structure-directing agent, tungsten(VI) chlorides as WO₃ precursors, and Ni(AcAc)₂ as the NiO precursor. The obtained materials possess a face-centered cubic mesoporous structure, large pore size (∼30 nm), high surface area (30-50 m² g^-1), large pore volume (0.15-0.19 cm³ g^-1), and ultralarge pore windows (12-16 nm) connecting adjacent mesopores, and the mesoporous WO₃ framework was decorated by ultrafine NiO nanocrystals. Due to their well-connected porous structure and high surface areas with rich WO₃-NiO interfaces, the composite materials exhibit superior gas sensing performance with an ultrafast response (∼4 s), high sensitivity (R_a/R_g = 58 ± 5.1), and selectivity to 50 ppm H₂S at a relatively low working temperature (250 °C). The chemical mechanism study reveals complicated surface reactions of WO₃/NiO-based gas sensors, and SO₂, WS₂, and NiS intermediates were found to be generated during the gas sensing process.

Biomolecule-Assisted Synthesis of Hierarchical Multilayered Boehmite and Alumina Nanosheets for Enhanced Molybdenum Adsorption

The effective utilization of various biomolecules for creating a series of mesoporous boehmite (γ-AlOOH) and gamma-alumina (γ-Al₂ O₃ ) nanosheets with unique hierarchical multilayered structures is demonstrated. The nature and concentration of the biomolecules strongly influence the degree of the crystallinity, the morphology, and the textural properties of the resulting γ-AlOOH and γ-Al₂ O₃ nanosheets, allowing for easy tuning. The hierarchical γ-AlOOH and γ-Al₂ O₃ multilayered nanosheets synthesized by using biomolecules exhibit enhanced crystallinity, improved particle separation, and well-defined multilayered structures compared to those obtained without biomolecules. More impressively, these γ-AlOOH and γ-Al₂ O₃ nanosheets possess high surface areas up to 425 and 371 m²  g^-1 , respectively, due to their mesoporous nature and hierarchical multilayered structure. When employed for molybdenum adsorption toward medical radioisotope production, the hierarchical γ-Al₂ O₃ multilayered nanosheets exhibit Mo adsorption capacities of 33.1-40.8 mg g^-1 . The Mo adsorption performance of these materials is influenced by the synergistic combination of the crystallinity, the surface area, and the pore volume. It is expected that the proposed biomolecule-assisted strategy may be expanded for the creation of other 3D mesoporous oxides in the future.

sp2-Hybridized Carbon-Containing Block Copolymer Templated Synthesis of Mesoporous Semiconducting Metal Oxides with Excellent Gas Sensing Property

In recent years, rational design of ordered mesoporous metal oxides, especially metal oxide semiconductors with adjustable pore architecture and framework compositions, has aroused extensive research interest owing to their unique electronic structures, long-range ordered porous framework, uniform mesopore size, and high specific surface area. Research on mesoporous materials has been booming in the past 30 years, and many synthesis methods have been developed, such as templating methods based on amphiphilic copolymers as soft templates or mesoporous carbon/silica as hard templates, respectively. Soft-templating synthesis has been considered as one of the most efficient and flexible methods in designing ordered mesoporous materials through the controllable interfacial induced coassembly process. However, most commercial amphiphilic copolymers, such as poly(ethylene oxide)- b-poly(propylene oxide) based Pluronic-type ones, suffer the drawback of poor thermal stability, because they are too easy to be decomposed even in inert atmosphere. Therefore, they are difficult to support the structures of mesoporous metal oxides under high calcination temperatures (>400 °C). To solve this challenge, we designed new amphiphilic block copolymers with high content of sp²-hybridized carbon in the hydrophobic segments that were relatively stable and could be in situ converted into residual carbon to support the mesoporous structure, via living free radical polymerization. We developed a variety of novel synthesis methods based on sp²-hybridized carbon-containing block copolymer, such as ligand-assisted assembly and resol-assisted assembly strategies, achieving a controllable and versatile synthesis of mesoporous semiconducting metal oxides with excellent gas sensing performance. In this Account, we first outline the features of sp²-hybridized carbon-containing block copolymers synthesized via living free radical polymerization, particularly their pyrolysis behavior in converting into residual carbon. Combining the solvent evaporation induced coassembly and the carbon-supported crystallization strategies, we realized the rational design of various ordered mesoporous semiconducting metal oxides (e.g., WO₃, SnO₂, Co₃O₄, In₂O₃, TiO₂, ZnO) and the regulation of their architectural features. To overcome the fast hydrolysis rate of metal precursors and weak interaction between block copolymers and metal precursors, we developed efficient ligand-assisted (e.g., acetylacetone and acetic acid) coassembly and resol-assisted coassembly methods to retard hydrolysis behavior and enhance the interaction via hydrogen bonds, covalent bonds, electrostatic interactions, etc. We also highlight the applications of these ordered mesoporous semiconducting metal oxides of both n-type and p-type in gas sensing fields, and they show tremendous sensing performance due to their abundant active sites on electron depletion layer and rapid gas diffusion via accessible pore channels. Finally, on the basis of the classic surface-electron depletion layer model, we elucidated in depth the surface catalytic reactions between the target gas molecules and the activated species (e.g., the adsorbed oxygen species) in the surface of mesoporous metal oxides during sensing process. These newly developed soft-templating synthesis methods that rely on sp²-hybridized carbon-containing block copolymers will open a new avenue for the design and application of ordered mesoporous semiconducting metal oxides in various fields.

Red Phosphorus: An Elementary Semiconductor for Room-Temperature NO2 Gas Sensing

Black and blue phosphorus (both allotropes of elementary phosphorus) have recently been widely explored as an active material for electronic devices, and their potential in gas sensing applications has been demonstrated. On the other hand, amorphous red phosphorus (a-RP), a much cheaper and readily available phosphorus allotrope, has seldom been investigated as an electronic material, and its gas sensing properties have never been studied. In this work we have investigated these properties of a-RP by combining experimental characterizations with theoretical calculations. We found that a-RP exhibited an amphoteric character for detecting both commonly regarded reducing and oxidizing gas molecules, featuring a negative correlation between the electrical resistance of a-RP and the gas concentration. Interestingly, the a-RP based sensors appear to be particularly suitable for room-temperature NO₂ detection, exhibiting excellent sensitivity and selectivity, as well as fast temporal response and recovery. A unique sensing feature of a-RP toward NO₂ was identified, which is associated with the expansion of P-P bonds upon NO₂ chemisorption. Based on density functional theory calculations we proposed a physiochemical model to elaborate the synergistic effects of the P-P bond expansion and Langmuir isotherm adsorption on the electronic properties and gas sensing processes of a-RP.

Effect of Surfactants on the Microstructures of Hierarchical SnO2 Blooming Nanoflowers and their Gas-Sensing Properties

Hierarchical SnO₂ blooming nanoflowers were successfully fabricated via a simple yet facile hydrothermal method with the help of different surfactants. Here we focus on exploring the promotion effects of surfactants on the self-assembly of 2D SnO₂ nanosheets into 3D SnO₂ flower-like structures as well as their gas-sensing performances. The polyporous flower-like SnO₂ sensor exhibits excellent gas-sensing performances to ethanol and H₂S gas due to high porosity when polyvinyl pyrrolidone is added into the precursor solution as a surfactant. The response/recovery times were about 5 s/8 s for 100 ppm ethanol and 4 s/20 s for 100 ppm H₂S, respectively. Especially, the maximum response value of H₂S is estimated to be 368 at 180 °C, which is one or two orders of magnitude higher than that of other test gases in this study. That indicates that the sensor fabricated with the help of polyvinyl pyrrolidone has good selectivity to H₂S.

Amphiphilic Block Copolymers Directed Interface Coassembly to Construct Multifunctional Microspheres with Magnetic Core and Monolayer Mesoporous Aluminosilicate Shell

Core-shell magnetic porous microspheres have wide applications in drug delivery, catalysis and bioseparation, and so on. However, it is great challenge to controllably synthesize magnetic porous microspheres with uniform well-aligned accessible large mesopores (>10 nm) which are highly desired for applications involving immobilization or adsorption of large guest molecules or nanoobjects. In this study, a facile and general amphiphilic block copolymer directed interfacial coassembly strategy is developed to synthesize core-shell magnetic mesoporous microspheres with a monolayer of mesoporous shell of different composition (FDUcs-17D), such as core-shell magnetic mesoporous aluminosilicate (CS-MMAS), silica (CS-MMS), and zirconia-silica (CS-MMZS), open and large pores by employing polystyrene-block-poly (4-vinylpyridine) (PS-b-P4VP) as an interface structure directing agent and aluminum acetylacetonate (Al(acac)₃ ), zirconium acetylacetonate, and tetraethyl orthosilicate as shell precursors. The obtained CS-MMAS microspheres possess magnetic core, perpendicular mesopores (20-32 nm) in the shell, high surface area (244.7 m² g^-1 ), and abundant acid sites (0.44 mmol g^-1 ), and as a result, they exhibit superior performance in removal of organophosphorus pesticides (fenthion) with a fast adsorption dynamics and high adsorption capacity. CS-MMAS microspheres loaded with Au nanoparticles (≈3.5 nm) behavior as a highly active heterogeneous nanocatalyst for N-alkylation reaction for producing N-phenylbenzylamine with a selectivity and yields of over 90% and good magnetic recyclability.

Synthesis of Pd-loaded mesoporous SnO2 hollow spheres for highly sensitive and stable methane gas sensors

This work reports a simple, rapid, effective and reliable CH₄ sensor based on Pd-loaded SnO₂ hollow spheres with high surface area and porosity, which is of great importance to gas sensing performance.