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

Enhancement of Hydrogen-Sensing Properties of Pd-Modified WO3 Nanocubes via Tannic Acid-Assisted Surface Functionalization

The growing use of hydrogen as a clean energy source demands the development of efficient and reliable sensors to ensure safety. Traditional metal-oxide-semiconductors, particularly WO3, face challenges such as limited sensitivity, high operating temperatures, and slow response times. The present study explores the enhancement of hydrogen-sensing properties through the modification of WO3 with Pd nanoparticles utilizing tannic acid (TA)-assisted surface functionalization. Due to its branched molecular structure and inherent phenolic characteristics, TA plays a significant role as a mediator in facilitating the adsorption of Pd onto the surface of WO3. Furthermore, TA effectively prevents the agglomeration of Pd, a result of the unique growth patterns of TA observed during high-temperature pyrolysis. Optimal content of Pd and TA is 0.10 atom % and 0.25 g, respectively. The gas sensor of 0.25 g TA@WO3-0.10 atom % Pd exhibits remarkable sensitivity with a response value of 456, alongside a rapid response time of 1 s at 200 °C toward 500 ppm hydrogen. Additionally, the gas sensor demonstrates excellent stability and reproducibility over multiple cycles. The enhanced performance is attributed to the synergistic effect of the formation of oxygen vacancies increasing active sites, the uniform dispersion of Pd nanoparticles facilitated by TA, and the catalytic activity of Pd accelerating hydrogen adsorption and reaction kinetics. This research highlights the potential of ecofriendly materials to enhance hydrogen sensor performance for safety monitoring.

Rapid and Selective Detection of Trace Hydrogen by Mesoporous SnO2 Anchored with Au-Pd Dual-Atom Sensitizers

Due to weak interactions between hydrogen molecules and sensing materials as well as slow H2 oxidation kinetics, traditional semiconductor metal oxides (SMOs) have limited capability for selective and rapid hydrogen sensing. We propose an innovative strategy to enhance gas-sensing performance by modifying SMOs with atomically dispersed dual noble-metal sensitizers, differing from conventional single-atom or nanoparticle sensitizers. This sensor shows fast response time (1 s), strong resistance to CO, NO, H2S, and SO2 interference, and an ultralow detection limit (70 ppb) toward hydrogen, surpassing single noble-metal modified hydrogen sensors. The excellent sensing performance can be attributed to the synergistic sensitization of atomically dispersed Au/Pd dual catalysts with complementary gas activation properties. The hand-held hydrogen detector, featuring a fast response (<1 s), demonstrates robust early warning capability for H2 leakage. This work introduces an atomically dispersed dual noble-metal sensitization strategy for superior hydrogen sensing, paving the way for hydrogen safety.

Reduced graphene oxide/ZnO nanocomposites: one-step solid-state preparation for room temperature photo-sensing and photoelectrical gas sensing capabilities

Detecting triethylamine (TEA), which is a highly active industrial chemical, is crucial in today's globalized world with increasing air pollution. In this work, we propose reduced graphene oxide (rGO)/ZnO nanocomposites for efficient TEA detection under ultraviolet (UV) light activation at room temperature. rGO@ZnO nanocomposites with different rGO weight percentages (1, 2.5, 5, and 10 wt%) were synthesized through a scalable, one-step solid-state method and characterized using various physicochemical techniques. Among the samples, the 2.5wt% rGO@ZnO nanocomposite (2.5%G@ZnO) exhibited the highest photo-response after UV light irradiation, indicating its superior carrier concentration generation under UV light. TEA sensing studies were carried out under UV light using sensors based on pristine ZnO nanopowder and the 2.5%G@ZnO nanocomposite. The 2.5%G@ZnO sensor demonstrated a significantly enhanced TEA sensing response (35%) compared with pristine ZnO, and it exhibited a lower detection limit of 15.6 ppm at room temperature. The sensing mechanism was explained using the depletion layer model, accompanied by scanning Kelvin probe analysis, which highlighted the role of UV light activation in improving sensor performance. These findings underscore the potential of UV-activated rGO/ZnO nanocomposite sensors for sensitive and efficient TEA detection.

Resonant Coupling Effect by Metal Nanoparticles Modification: An Effective Strategy for High Sensitization of MOS-Based Chemiresistive Gas Sensors

Metal nanoparticle surface modification is a simple and efficient method to realize highly sensitive detection for chemiresistive gas sensors. Although a few theoretical explanations for the complicated matching relationship in the sensing system constructed from the modified metal, semiconductor material, and target gas have been proposed, there are no corresponding specific evaluation parameters based on the metal sensitization mechanism, which are crucial for the guidance of high-performance sensing materials design. Herein, taking MnO2-based chemiresistive gas sensors as examples, the improvement effect of the metal nanoparticles modification on the gas-sensing properties of MnO2-based chemiresistive sensors toward HCHO and NH3 is investigated. Combined with the first-principle calculations based on density functional theory (DFT), a novel resonant coupling model based on the impurity energy levels, originating from charge transfer between target gas and metal, is first proposed to reveal the sensitization mechanism that the coupling strength between metal and target gas determines the carrier concentration of MOS. Coupling strength is closely positive correlated with the response, which provides an effective parameter to semiquantitatively describe the sensitization effect of metal nanoparticles on target gas. Our work establishes a model that clarifies the matching correlation in the sensing system and excavates new road to further comprehend the metal sensitization mechanism, which will provide an effective theoretical guide for the design of high-performance gas-sensing materials.

Recent Advances in Functionalizing Metal Oxide Semiconductors for Highly Sensitive Gas Sensors

Metal oxide semiconductors (MOSs) have emerged as pivotal materials for gas sensing technologies due to their inherent advantages, including cost-effectiveness, simplicity in synthesis, and easy fabrication of sensing nanodevices. These characteristics have made MOSs widely applicable in industrial, environmental, and biological monitoring. While MOSs offer intrinsic gas-sensing properties, their limited active site density and function diversity restrict sensitivity and selectivity, especially in complex gaseous environments. To overcome these limitations, extensive research efforts have been devoted to functionalizing MOSs through strategies such as heterojunction construction, noble metal nanoparticle loading (e.g., Au, Pt, Ag, Pd), and heteroatom doping (e.g., Si, Cr). Furthermore, composite materials have emerged as an effective approach to enhance MOSs-based gas sensors by integrating carbon-based materials or polymers to leverage synergistic interactions. These modifications expand the applicability of MOSs sensors for detecting volatile organic compounds, toxic gases, and flammable gases. This review systematically examines the synthesis strategies and performance enhancements achieved through MOSs functionalization and composite material integration, emphasizing structure-property relationships, interfacial charge transfer dynamics, and adsorption mechanisms. Finally, the challenges and future directions for the rational design of next-generation MOSs-based gas sensors are outlined, providing critical insights for advancing intelligent gas sensing technologies.

Stepwise Self-Assembly of Multisegment Mesoporous Silica Nanobamboos for Enhanced Thermal Insulation

Imitating the multinodal structures of plants and arthropods, precisely engineered multisegment nanostructures demonstrate enhanced synergistic properties and exceptional functionalities that surpass those of individual components. Utilizing micelle assemblies for constructing segments allows for precise structural control but requires management of interactions and assembly from molecular to mesoscopic levels, posing a significant challenge. In this paper, we present a stepwise self-assembly strategy to fabricate multisegment mesoporous silica (mSiO2) nanobamboos. The nanobamboos are characterized by 16-25 shuttle-shaped mesoporous segments connected end-to-end in line, forming the main chains with an overall length of approximately 0.7-1.0 μm. Each individual segment is composed of 10-13 parallel layers, with an average layer thickness of ∼2.5 nm. The formation of this multisegment mesoporous nanobamboos, as proven by in situ testing, is initiated by the formation of shuttle-shaped segments from small bilayer micelle units, which then further assemble to form the nanobamboo. This stepwise self-assembly can be regulated from a kinetic perspective, thereby obtaining multisegment mesoporous nanostructures with varying lengths and branched morphologies. Due to multiple segments along with multilayer mesostructures, the nanobamboos can significantly restrict gas flow, resulting in a very low thermal conductivity (∼41.67 mW·m-1·K-1). By blending the multisegment mSiO2 nanobamboos with cellulose nanofibers, mechanically stable, lightweight, and porous aerogels with an ultralow thermal conductivity (∼19.85 mW·m-1·K-1) can be obtained, verifying their potential in thermal insulation devices. The fabrication of this multisegment mesoporous nanobamboos enhances our understanding of micro-to-nanoscale assembling, establishing a foundation for precise control of complex structures.

Wafer-Scale Integration of Metal Oxide Nanocrystals on Gas Sensor Chips via Direct Lithographic Patterning

Nanomaterial-based gas sensors are essential due to their high sensitivity and scalability, enabling efficient gas detection across diverse applications. However, a key challenge hindering their practical applications is the variation in sensing performance between devices. Addressing this requires careful consideration of the relationship between on-chip sensing materials and miniaturized devices. As feature sizes reduce to the microscale, accurately and uniformly positioning sensing nanomaterials onto specific regions of the device electrodes becomes increasingly difficult. This challenge arises from the incompatibility between the bottom-up nanomaterial synthesis methods and the top-down lithography-based fabrication processes. Herein, we introduce a cleanroom-compatible fabrication workflow for chemiresistive gas sensors employing direct lithographic patterning of metal oxide nanocrystals. Gas sensors located across different regions of a 4 in. wafer exhibit highly consistent gas-sensing performances, highlighting the potential of this approach, which integrates the strengths of both top-down and bottom-up approaches. This approach opens new opportunities for integrating a wide range of bottom-up synthesized functional nanomaterials into diverse types of chemical sensors.

Selective Design of Mesoporous Bi2Se3 Films with Orthorhombic and Rhombohedral Crystals

Materials with the same chemical composition can exhibit distinct properties depending on their crystal phases. Here, the synthesis of two types of mesoporous Bi2Se3 films at different reduction potentials is reported and their application in electrochemical glucose sensing. Mesoporous Bi2Se3 is synthesized by incorporating block copolymer micelle assemblies into the deposition solution and applying a reduction potential. To characterize the crystal phases accurately, Bi2Se3 films are heat-treated at 200 °C for 1 h in a nitrogen atmosphere. The results reveal that the Bi2Se3 films synthesized under different conditions exhibit clearly distinct phases: rhombohedral (R-Bi2Se3) and orthorhombic (O-Bi2Se3). The R-Bi2Se3-8 nm, featuring 8 nm pores and synthesized at a more negative reduction potential, outperforms its nonporous counterpart, achieving a glucose sensing sensitivity of 0.143 µA cm-2 µM-1 and a detection limit of 6.2 µM at pH 7.4 in 0.1 M phosphate-buffered saline solution. In contrast, the O-Bi2Se3, prepared at a relatively positive potential, exhibits no glucose-sensing activity. The inactivity of O-Bi2Se3 for glucose oxidation is likely due to the energetically unfavorable intermediates, as predicted by density functional theory calculations. These findings underscore the critical role of crystal phase control in porous nanomaterials and pave the way for developing innovative porous systems.

Rapid and Sensitive Detection of 2-Ethylhexanol Vapor Utilizing Mesoporous Neodymium-Doped Indium Oxide for Real-Time Monitoring of Overheated Electrical Cables

Rapid and sensitive detection of 2-ethylhexanol vapor, a critical indicator of overheating in electrical cables, is essential for the early warning of potential electrical fires. However, traditional chemiresistive gas sensors are inadequate for real-time detection of 2-ethylhexanol owing to its chemical stability. Herein, a chemiresistive gas sensor based on mesoporous Nd-doped In2O3 is designed for rapid detection of ppb-level 2-ethylhexanol vapor. The sensor exhibits a high response (22.8@1 ppm), excellent sensitivity (4.7 ppm-1), a short response time (29 s), and a low detection limit (760 ppb). After Nd doping, the response of the mesoporous Nd-doped In2O3 sensor is approximately 20 folds higher than that of the In2O3 sensor. Furthermore, a wireless sensing device has been developed to enable real-time monitoring of cable overheating. The outstanding sensing performance can be attributed to neodymium doping within the mesoporous framework, which enhances the accessibility of active sites on the interface of sensing materials, increases the concentration of surface-adsorbed oxygen at the gas-solid interface, and improves the adsorption capacity for 2-ethylhexanol. This work showcases an efficient semiconductor metal oxide gas sensor capable of rapidly and sensitively detecting parts per billion levels of 2-ethylhexanol induced by the overheating of electrical cables, demonstrating significant potential for early warning of electrical fires.

Commodity Thermoplastic Elastomer-Enabled Templated Synthesis of Large-Pore Ordered Mesoporous Materials

Fabrication of ordered mesoporous materials (OMMs) has predominantly relied on templating-based methods. However, these methods are constrained by several limitations, especially the limited pore sizes attainable with commercially available surfactants used as structure-directing agents. To unlock the full potential of the OMMs, it is essential to develop synthetic strategies that facilitate the production of large-pore OMMs using scalable processes and cost-effective precursors. This work demonstrates the use of thermoplastic elastomer (TPE)-derived carbon replicas for synthesizing ordered mesoporous silica (OMS) and metal oxides (OMMOs) via precursor infiltration and template removal. The nanostructural evolution of the resulting inorganic materials was systematically investigated. Specifically, using tetraethyl orthosilicate (TEOS) as a silica precursor, this method can produce an OMS with relatively large pores. To establish the generalizability of this process, the fabrication approach was extended to other commercially available TPEs with varied chemical compositions and molecular weights while consistently resulting in ordered structures. Additionally, this synthetic strategy can be successfully applied to the production of OMMOs, including tin and titanium oxide matrix chemistries, yielding pore sizes of 16.0 and 19.2 nm, respectively. By developing a general method and using low-cost precursors, this work presents a scalable approach for fabricating large-pore OMMs with tunable pore textures and matrix chemistries.

Atomic Ru Species Driven SnO2-Based Sensor for Highly Sensitive and Selective Detection of H2S in the ppb-Level

Timely and accurate detection of H2S is crucial for preventing serious health issues in both humans and livestock upon exposure. However, metal-oxide-based H2S sensors often suffer from mediocre sensitivity, poor selectivity, or long response/recovery time. Here, an atomic Ru species-driven SnO2-based sensor is fabricated to realize highly sensitive and selective detection of H2S at the parts per billion level as low as 100 ppb. The sensor shows a high sensing response (Rair/Rgas = 310.1) and an ultrafast response time (less than 1 s) to 20 ppm H2S at an operating temperature of 160 °C. Operando SR-FTIR spectroscopic characterizations and DFT calculations prove that the superior sensing properties can be mainly attributed to the driven effect of atomic Ru species on the formation of surface-adsorbed oxygen species on the surface of SnO2, which provides more active sites and enhances the sensing performance of SnO2 for H2S. Furthermore, a lab-made wireless portable H2S monitoring system is developed to rapidly detect the H2S for early warning, suggesting the potential application of the fabricated H2S sensor and monitoring system. This work provides a novel approach for fabricating a highly sensitive and selective gas sensor driven by atomic metal species loaded on metal-oxide semiconductors.

Research Progress on Chemiresistive Carbon Monoxide Sensors

The development of high-performance carbon monoxide (CO) sensors is essential for protecting human health, ensuring industrial safety, and maintaining environmental well-being. Among various types of sensors, chemiresistive sensors exhibit considerable promise for real-time applications due to their operational capabilities. To achieve high performances of chemiresistive sensors, this review emphasizes various enhancement strategies, encompassing the refinement of sensing materials, the augmentation of sensor structures, and the optimization of gas recognition algorithms. Specifically, the modification techniques of sensing materials, which include the construction of heterostructures, the decoration with noble metals, surface functionalization, hetero-element-doping, and morphology engineering, are delved into comprehensively. This review provides insights into the rational design of cost-effective CO sensors.

Organic-inorganic hybrid covalent superlattice for temperature-compensated ratiometric gas sensing

Room-temperature chemiresistive sensors are valued for their low power consumption, ease of operation, and real-time monitoring capabilities, making them highly advantageous for various applications. However, the challenge of inaccurate detection due to variations in operating temperature is a significant hurdle for their practical use. To address this, we develop a ratiometric-gas sensing method that leverages the exceptional photoelectric and chemiresistive gas sensing sensitivity of organic-inorganic hybrid superlattice materials AgBDT (BDT = 1,4-benzenedithiol). This approach can effectively detect nitrogen dioxide molecules, with a detection limit of 3.06 ppb. Crucially, the ratiometric-gas sensing technique offers robust diminution to temperature interference, with the coefficient of variation value dropping from 21.81% to 7.81% within the temperature range of 25 to 65 °C, which significantly enhances the stability and reliability of the device. This method would be capable of not only the detecting of gases but also providing rapid, accurate analysis in real conditions.

Hydrogen-Bonded Organic Framework Nanosheets with Rich Free Oxygen Atoms for NO2 Sensing

Hydrogen-bonded organic frameworks (HOFs) are under fast development in broad applications but have not been well explored for chemiresistive gas sensing yet primarily due to insufficient active sites. Herein, a new porphyrin-based HOF-199 is constructed by OH···O hydrogen bonds featuring layered networks and rich free oxygen (O) atoms, which is further exfoliated into few-layer nonosheets with more dangling O sites through an ultrasound-assisted liquid exfoliation method (namely L-HOF-199). Benefiting from rich electron-donor sites, L-HOF-199 demonstrates exceptional NO2 sensing properties under ambient conditions, achieving a remarkable 3.25-fold improvement in sensitivity (152% toward 5 ppm of NO2) and a faster response speed (52 s), relative to HOF-199. This work provides a promising platform for the rational design of advanced gas sensors via functional HOF chemistry.

IGZO-Based Electronic Device Application: Advancements in Gas Sensor, Logic Circuit, Biosensor, Neuromorphic Device, and Photodetector Technologies

Metal oxide semiconductors, such as indium gallium zinc oxide (IGZO), have attracted significant attention from researchers in the fields of liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs) for decades. This interest is driven by their high electron mobility of over ~10 cm2/V·s and excellent transmittance of more than ~80%. Amorphous IGZO (a-IGZO) offers additional advantages, including compatibility with various processes and flexibility making it suitable for applications in flexible and wearable devices. Furthermore, IGZO-based thin-film transistors (TFTs) exhibit high uniformity and high-speed switching behavior, resulting in low power consumption due to their low leakage current. These advantages position IGZO not only as a key material in display technologies but also as a candidate for various next-generation electronic devices. This review paper provides a comprehensive overview of IGZO-based electronics, including applications in gas sensors, biosensors, and photosensors. Additionally, it emphasizes the potential of IGZO for implementing logic gates. Finally, the paper discusses IGZO-based neuromorphic devices and their promise in overcoming the limitations of the conventional von Neumann computing architecture.

Porous and Homogeneous Nanoheterojunction-Accumulating PdO@ZnO Structure for Exhaled Breath Ammonia Sensing

The functional gas sensor device plays a pivotal role in intelligent medical treatment, among which metal oxide semiconductors are widely studied because of their inexpensiveness and ease of fabrication. However, the metal oxide sensors present a significant challenge in detecting NH3 at ppm levels within complex exhaled gases. Herein, the ZnO/PdO-x series were prepared by in situ loading palladium particles and calcining using nano-ZIF-8 as a precursor, which not only provided more transport path for ammonia adsorption but also achieved homogeneous nanoheterojunction accumulation structure. The tailor-made ZnO/PdO-2 sensor exhibits the optimum gas sensitivity, with a response value of 5.56 for 100 ppm of NH3 at 160 °C and a lower detection limit of 0.75 ppm. Particularly, it has a clear quantitative response to the actual exhaled gas of liver and kidney patients. By elucidating the intrinsic link between the in situ loading of MOF templates and the sensing mechanism, it is expected to broaden the rational design of metal-oxide sensors and thus provide an effective method for clinical detection.

Gas-Sensing Properties of Co9S8 Films Toward Formaldehyde, Ethanol, and Hydrogen Sulfide

The chemiresistive gas-sensing properties of pristine Co9S8 film are little known despite its potential as a promising gas sensor material due to its intrinsic characteristics. In this study, a pristine polycrystalline Co9S8 film (approximately 440 nm in thickness) is fabricated by depositing a Co3O4 film followed by sulfidation to investigate its gas-sensing properties. The prepared Co9S8 film sensor is found to exhibit high responsiveness towards formaldehyde (HCHO), ethanol (C2H5OH), and hydrogen sulfide (H2S) at operating temperatures of 300 °C and 400 °C, with strong concentration dependence. On the other hand, the sensor shows very low or no responsiveness towards hydrogen (H2), acetone (CH3COCH3), and nitrogen dioxide (NO2). These results enhance our understanding of the intrinsic gas-sensing properties of Co9S8, aiding in the design and fabrication of high-performance chemiresistive gas sensors based on Co9S8.

Metal-Organic Frameworks (MOFs): Classification, Synthesis, Modification, and Biomedical Applications

Metal-organic frameworks (MOFs) are a new variety of solid crystalline porous functional materials. As an extension of inorganic porous materials, it has made important progress in preparation and application. MOFs are widely used in various fields such as gas adsorption storage, drug delivery, sensing, and biological imaging due to their high specific surface area, porosity, adjustable pore size, abundant active sites, and functional modification by introducing groups. In this paper, the types of MOFs are classified, and the synthesis methods and functional modification mechanisms of MOFs materials are summarized. Finally, the application prospects and challenges of metal-organic framework materials in the biomedical field are discussed, hoping to promote their application in multidisciplinary fields.

Nitrogen-Doped Indium Oxide Electrochemical Sensor for Stable and Selective NO2 Detection

Efficient gas sensors are critical for environmental monitoring and industrial safety. While metal oxide semiconductor (MOS) sensors are cost-effective, they struggle with poor selectivity, high operating temperatures, and limited stability. Electrochemical sensors, though selective and energy-efficient, face high costs, and stability issues due to precious metal catalysts like platinum on carbon (Pt/C). Herein, a novel, cost-effective electrochemical sensor using nitrogen-doped indium oxide In2O3- xN2 x /3Vx /3 (0.01≤x≤0.14), synthesized with varying nitriding times is presented. The optimized In2O3 N-40 min sensor demonstrates a remarkable response current of 771 nA to 10 ppm nitrogen dioxide (NO2) at ambient temperature, with outstanding long-term stability (over 30 days) and rapid response/recovery times (5/16 s). Compared to Pt/C sensors, it shows 84% and 67% reductions in response and recovery times, respectively, and maintains 98% performance after a month, versus 68% for Pt/C. This cost-effective sensor presents a promising alternative for electrochemical gas sensing, eliminating the need for precious metal catalysts.

Theoretical study of adsorption of gas (CO, CO2, NH3) by metal (Au, Ag, Cu)-doped single-layer WS2

CONTEXT

The adsorptions of gas (CO, CO2, NH3) by metal (Au, Ag, Cu)-doped single layer WS2 are studied by density functional theory. The doping of metal atoms makes WS2 behave as n-type semiconductors. The final adsorption sites for CO, CO2, and NH3 are close to the atomic sites of the doped metal. The adsorptions of CO and NH3 gases on Cu/WS2, Ag/WS2, and Au/WS2 are dominated by chemisorption. The doped metal atoms enhance the hybridization of the substrate with the gas molecular orbitals, which contributes to the charge transfer and enhances the adsorption of the gas with the material surface. The adsorptions of CO and NH3 on Cu/WS2 and Ag/WS2 allow favorable desorption in a short time after heating. The single-layer Cu/WS2 is proved to have the potential to be used as a reliable recyclable sensor for CO. This work provides a theoretical basis for developing high-performance WS2-based gas sensors.

METHODS

In this paper, the adsorption energy, electronic structure, charge transfer, and recovery time of CO, CO2, and NH3 in the doped system have been investigated based on the CASTEP code of density functional theory. The exchange correlation function used is the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA). The TS (Tkatchenko-Scheffler) dispersion correction method was used to involve the effects of van der Waals interaction on the adsorption energies for all adsorption system. The ultrasoft pseudopotentials are chosen and the plane-wave cut-off energies are set to 500 eV. The k-point mesh generated by the Monkhorst package scheme is used to perform the numerical integration of the Brillouin zone and 5 × 5 × 1 k-point grid is used. The tolerances of total energy convergence, maximum ionic force, ionic displacement, and stress component are 1.0 × 10-5 eV/atom, 0.03 eV/Å, 0.001 Å, and 0.05 GPa, respectively.

A Straightforward Solvent-Pair-Enabled Multicomponent Coassembly Approach toward Noble-Metal-Nanoparticle-Decorated Mesoporous Tungsten Oxide for Trace Ammonia Sensing

The straightforward synthesis of noble-metal-nanoparticle-decorated ordered mesoporous transition metal oxides remains a great challenge due to the difficulty of balancing the interactions between precursors and templates. Herein, a solvent-pair-enabled multicomponent coassembly (SPEMC) strategy is developed for straightforward synthesis of noble-metal-nanoparticle-decorated nitrogen-doped ordered mesoporous tungsten oxide (abbreviated as NM/N-mWO3, NM = Pt, Rh, Pd). The amphiphilic poly(ethylene oxide)-block-polystyrene (PEO-b-PS) copolymers coassemble with ammonium metatungstate (AMT) clusters and different kinds of hydrophilic noble metal precursors without phase separation. SPEMC synthesis requires no direct interaction between PEO-b-PS and AMT, thus the assembly equilibriums between noble metal precursors and PEO-b-PS can be readily controlled. The obtained NM/N-mWO3 nanocomposites possess ordered mesopores, abundant oxygen vacancies, and metal-metal oxide interfaces. As a result, the Pt/N-mWO3 sensors exhibit superior ammonia sensing performances with high sensitivity, an ultralow limit of detection (51.2 ppb), good selectivity, and long-term stability. Spectroscopic analysis reveals that ammonia is oxidized stepwise to NO, NO2 -, and NO3 - during the sensing process. Moreover, a portable wireless module based on Pt/N-mWO3 sensor can recognize ppm-level concentration of ammonia, which lays a solid foundation for its application in various fields.

A Stimulus-Responsive Ternary Heterojunction Boosting Oxidative Stress, Cuproptosis for Melanoma Therapy

Cuproptosis, a recently discovered copper-dependent cell death, presents significant potential for the development of copper-based nanoparticles to induce cuproptosis in cancer therapy. Herein, a unique ternary heterojunction, denoted as HACT, composed of core-shell Au@Cu2O nanocubes with surface-deposited Titanium Dioxide quantum dots and modified with hyaluronic acid is introduced. Compared to core-shell AC NCs, the TiO2/Au@Cu2O exhibits improved energy structure optimization, successfully separating electron-hole pairs for redox use. This optimization results in a more rapid generation of singlet oxygen and hydroxyl radicals triggering oxidative stress under ultrasound radiation. Furthermore, the HACT NCs initiate cuproptosis by Fenton-like reaction and acidic environment, leading to the sequential release of cupric and cuprous ions. This accumulation of copper induces the aggregation of lipoylated proteins and reduces iron-sulfur proteins, ultimately initiating cuproptosis. More importantly, HACT NCs show a tendency to selectively target cancer cells, thereby granting them a degree of biosecurity. This report introduces a ternary heterojunction capable of triggering both cuproptosis and oxidative stress-related combination therapy in a stimulus-responsive manner. It can energize efforts to develop effective melanoma treatment strategies using Cu-based nanoparticles through rational design.

Single-Atom Au-Functionalized Mesoporous SnO2 Nanospheres for Ultrasensitive Detection of Listeria monocytogenes Biomarker at Low Temperatures

Semiconductor metal oxide gas sensors have been proven to be capable of detecting Listeria monocytogenes, one kind of foodborne bacteria, through monitoring the characteristic gaseous metabolic product 3-hydroxy-2-butanone. However, the detection still faces challenges because the sensors need to work at high temperatures and output limited gas sensing performance. The present study focuses on the design of single-atom Au-functionalized mesoporous SnO2 nanospheres for the sensitive detection of ppb-level 3-hydroxy-2-butanone at low temperatures (50 °C). The fabricated sensors exhibit high sensitivity (291.5 ppm-1), excellent selectivity, short response time (10 s), and ultralow detection limit (10 ppb). The gas sensors exhibit exceptional efficacy in distinguishing L. monocytogenes from other bacterial strains (e.g., Escherichia coli). Additionally, wireless detection of 3-hydroxy-2-butanone vapor is successfully achieved through microelectromechanical systems sensors, enabling real-time monitoring of the biomarker 3-hydroxy-2-butanone. The superior sensing performance is ascribed to the mesoporous framework with accessible active Au-O-Sn sites in the uniform sensing layer consisting of single-atom Au-modified mesoporous SnO2 nanospheres, and such a feature facilitates the gas diffusion, adsorption, and catalytic conversion of 3-hydroxy-2-butanone molecules in the sensing layer, resulting in excellent sensing signal output at relatively low temperature that is favorable for developing low-energy-consumption gas sensors.

An electrochemical H2S sensor based on the screen printing Fe@Pt/C/PTFE sensing electrode

A novel electrochemical gas sensor for sensitive detection of H2S at room temperature is constructed based on the Fe@Pt/C composite material. The core-shell structured Fe@Pt catalyst was synthesized by a two-step reduction method and physically dispersed in Vulcan XC-72 carbon powders. The core-shell structure increases the effective catalytic surface area of Pt while significantly reducing the usage of the noble metal Pt, leading to improved catalytic performance and decreased production costs. Additionally, the mature screen-printing process is used to coat the catalyst film. A waterproof and breathable PTFE film was used as the substrate and the parameters in the screen printing process were also optimized to achieve the best gas sensing performance of the electrode film. Through the detection of hydrogen sulfide (H2S) with different concentrations, it is found that the sensor strictly shows linear correlation in the range of 1-20 ppm, R2 = 0.99974. Notably, the sensor exhibits high sensitivity (658.45 nA ppm-1) and a low detection limit of 0.33 ppm. Moreover, the consistency and stability of the sensor are satisfactory. The constructed gas sensor is expected to be well applied to industrial H2S detection.

Enhance Ethanol Sensing Performance of Fe-Doped Tetragonal SnO2 Films on Glass Substrate with a Proposed Mathematical Model for Diffusion in Porous Media

This research enhances ethanol sensing with Fe-doped tetragonal SnO2 films on glass, improving gas sensor reliability and sensitivity. The primary objective was to improve the sensitivity and operational efficiency of SnO2 sensors through Fe doping. The SnO2 sensors were synthesized using a flexible and adaptable method that allows for precise doping control, with energy-dispersive X-ray spectroscopy (EDX) confirming homogeneous Fe distribution within the SnO2 matrix. A morphological analysis showed a surface structure ideal for gas sensing. The results demonstrated significant improvement in ethanol response (1 to 20 ppm) and lower temperatures compared to undoped SnO2 sensors. The Fe-doped sensors exhibited higher sensitivity, enabling the detection of low ethanol concentrations and showing rapid response and recovery times. These findings suggest that Fe doping enhances the interaction between ethanol molecules and the sensor surface, improving performance. A mathematical model based on diffusion in porous media was employed to further analyze and optimize sensor performance. The model considers the diffusion of ethanol molecules through the porous SnO2 matrix, considering factors such as surface morphology and doping concentration. Additionally, the choice of electrode material plays a crucial role in extending the sensor's lifespan, highlighting the importance of material selection in sensor design.

Construction of semiconductor nanocomposites for room-temperature gas sensors

Gas sensors are essential for ensuring public safety and improving quality of life. Room-temperature gas sensors are notable for their potential economic benefits and low energy consumption, and their expected integration with wearable electronics, making them a focal point of contemporary research. Advances in nanomaterials and low-dimensional semiconductors have significantly contributed to the enhancement of room-temperature gas sensors. These advancements have focused on improving sensitivity, selectivity, and response/recovery times, with nanocomposites offering distinct advantages. The discussion here focuses on the use of semiconductor nanocomposites for gas sensing at room temperature, and provides a review of the latest synthesis techniques for these materials. This involves the precise adjustment of chemical compositions, microstructures, and morphologies. In addition, the design principles and potential functional mechanisms are examined. This is crucial for deepening the understanding and enhancing the operational capabilities of sensors. We also highlight the challenges faced in scaling up the production of nanocomposite materials. Looking ahead, semiconductor nanocomposites are expected to drive innovation in gas sensor technology due to their carefully crafted design and construction, paving the way for their extensive use in various sectors.

Sensitive detection of H2S based on Ce doped ZnCo2O4 hollow microspheres at low working temperature

In order to develop a highly efficient H2S gas sensor at low working temperature, in this work, a kind of novel Ce-doped ZnCo2O4 hollow microspheres (Ce/ZnCo2O4 HMSs) were successfully synthesized using a template-free one-pot method, showing a sensitive response toward H2S. The microstructure and morphology of the material were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The gas-sensing performance of the composite was investigated, showing that the ZnCo2O4 doped with 6 mol% Ce had the highest response to 20 ppm H2S at a low operating temperature of 160 °C with a response value of 67.42, which was about 2 times higher than that of original ZnCo2O4. The prepared Ce/ZnCo2O4 HMS sensor in response to H2S exhibited a linear range of 0.1-200 ppm with a low detection limit of 0.1 ppm under the conditions of ambient humidity of 45% and ambient temperature of 20 °C. Meanwhile, it also possessed good selectivity, repeatability and reproducibility. The response value of the sensor decreased by 5.32% after 7 months of continuous monitoring of H2S in an atmospheric environment of a pig farm, indicating that the sensor had a long-term stability and continuous service life with important application prospects.

Scalable Optical Nose Realized with a Chemiresistively Modulated Light-Emitter Array

Biological olfaction relies on a large number of receptors that function as sensors to detect gaseous molecules. It is challenging to realize artificial olfactory systems that contain similarly large numbers of sensory materials. It is shown that combinatorial materials processing with vapor deposition can be used to fabricate large arrays of distinct chemiresistive sensing materials. By combining these with light-emitting diodes, an array of chemiresistively-modulated light-emitting diodes, or ChemLEDs, that permit a simultaneous optical read-out in response to an analyte is obtained. The optical nose uses a common voltage source and ground for all sensing elements and thus eliminates the need for complex wiring of individual sensors. This optical nose contains one hundred ChemLEDs and generates unique light patterns in response to gases and their mixtures. Optical pattern recognition methods enable the quantitative prediction of the corresponding concentrations and compositions, thereby paving the way for massively parallel artificial olfactory systems. ChemLEDs open the possibility to explore demanding gas sensing applications, including in environmental, food quality monitoring, and potentially diagnostic settings.

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.

Wireless Gas Sensor Based on the Mesoporous ZnO-SnO2 Heterostructure Enables Ultrasensitive and Rapid Detection of 3-Methylbutyraldehyde

Achieving ultrasensitive and rapid detection of 3-methylbutyraldehyde is crucial for monitoring chemical intermediate leakage in pharmaceutical and chemical industries as well as diagnosing ventilator-associated pneumonia by monitoring exhaled gas. However, developing a sensitive and rapid method for detecting 3-methylbutyraldehyde poses challenges. Herein, a wireless chemiresistive gas sensor based on a mesoporous ZnO-SnO2 heterostructure is fabricated to enable the ultrasensitive and rapid detection of 3-methylbutyraldehyde for the first time. The mesoporous ZnO-SnO2 heterostructure exhibits a uniform spherical shape (∼79 nm in diameter), a high specific surface area (54.8 m2 g-1), a small crystal size (∼4 nm), and a large pore size (6.7 nm). The gas sensor demonstrates high response (18.98@20 ppm), short response/recovery times (13/13 s), and a low detection limit (0.48 ppm) toward 3-methylbutyraldehyde. Furthermore, a real-time monitoring system is developed utilizing microelectromechanical systems gas sensors. The modification of amorphous ZnO on the mesoporous SnO2 pore wall can effectively increase the chemisorbed oxygen content and the thickness of the electron depletion layer at the gas-solid interface, which facilitates the interface redox reaction and enhances the sensing performance. This work presents an initial example of semiconductor metal oxide gas sensors for efficient detection of 3-methylbutyraldehyde that holds great potential for ensuring safety during chemical production and disease diagnosis.

Regulating electron transfer and orbital interaction within metalloporphyrin-MOFs for highly sensitive NO2 sensing

The understanding of electron transfer pathways and orbital interactions between analytes and adsorption sites in gas-sensitive studies, especially at the atomic level, is currently limited. Herein, we have designed eight isoreticular catechol-metalloporphyrin scaffolds, FeTCP-M and InTCP-M (TCP = 5,10,15,20-tetrakis-catechol-porphyrin, M = Fe, Co, Ni and Zn) with adjustable charge transfer schemes in the coordination microenvironment and precise tuning of orbital interactions between analytes and adsorption sites, which can be used as models for exploring the influence of these factors on gas sensing. Our experimental findings indicate that the sensitivity and selectivity can be modulated using the type of metals in the metal-catechol chains (which regulate the electron transfer routes) and the metalloporphyrin rings (which fine-tune the orbital interactions between analytes and adsorption sites). Among the isostructures, InTCP-Co demonstrates the highest response and selectivity to NO2 under visible light irradiation, which could be attributed to the more favorable transfer pathway of charge carriers in the coordination microenvironment under visible light illumination, as well as the better electron spin state compatibility, higher orbital overlap and orbital symmetry matching between the N-2s2pz hybrid orbital of NO2 and the Co-3dz2 orbital of InTCP-Co.

WO3 Nanoplates Decorated with Au and SnO2 Nanoparticles for Real-Time Detection of Foodborne Pathogens

Nowadays, metal oxide semiconductor gas sensors have diverse applications ranging from human health to smart agriculture with the development of Internet of Things (IoT) technologies. However, high operating temperatures and an unsatisfactory detection capability (high sensitivity, fast response/recovery speed, etc.) hinder their integration into the IoT. Herein, a ternary heterostructure was prepared by decorating WO3 nanoplates with Au and SnO2 nanoparticles through a facial photochemical deposition method. This was employed as a sensing material for 3-hydroxy-2-butanone (3H-2B), a biomarker of Listeria monocytogenes. These Au/SnO2-WO3 nanoplate-based sensors exhibited an excellent response (Ra/Rg = 662) to 25 ppm 3H-2B, which was 24 times higher than that of pure WO3 nanoplates at 140 °C. Moreover, the 3H-2B sensor showed an ultrafast response and recovery speed to 25 ppm 3H-2B as well as high selectivity. These excellent sensing performances could be attributed to the rich Au/SnO2-WO3 active interfaces and the excellent transport of carriers in nanoplates. Furthermore, a wireless portable gas sensor equipped with the Au/SnO2-WO3 nanoplates was assembled, which was tested using 3H-2B with known concentrations to study the possibilities of real-time gas monitoring in food quality and safety.

Bottom-Up Construction of Mesoporous Cerium-Doped Titania with Stably Dispersed Pt Nanocluster for Efficient Hydrogen Evolution

Hydrogen generation is one of the crucial technologies to realize sustainable energy development, and the design of advanced catalysts with efficient interfacial sites and fast mass transfer is significant for hydrogen evolution. Herein, an in situ coassembly strategy was proposed to engineer a cerium-doped ordered mesoporous titanium oxide (mpCe/TiO2), of which the abundant oxygen vacancies (Ov) and highly exposed active pore walls contribute to good stability of ultrasmall Pt nanoclusters (NCs, ∼ 1.0 nm in diameter) anchored in the uniform mesopores (ca. 20 nm). Consequently, the tailored mpCe/TiO2 with 0.5 mol % Ce-doping-supported Pt NCs (Pt-mpCe/TiO2-0.5) exhibits superior H2 evolution performance toward the water-gas shift reaction with a 0.73 molH2·s-1·molPt-1 H2 evolution rate at 200 °C, which is almost 6-fold higher than the Pt-mpTiO2 (0.13 molH2·s-1·molPt-1 H2). Density functional theory calculations confirm that the structure of Ce-doped TiO2 with Ce coordinated to six O atoms by substituting Ti atoms is thermodynamically favorable without the deformation of Ti-O bonds. The Ov generated by the six O atom-coordinated Ce doping is highly active for H2O dissociation with an energy barrier of 2.18 eV, which is obviously lower than the 2.37 eV for the control TiO2. In comparison with TiO2, the resultant Ce/TiO2 support acts as a superior electron acceptor for Pt NCs and causes electron deficiency at the Pt/support interface with a 0.17 eV downshift of the Pt d-band center, showing extremely obvious electronic metal-support interaction (EMSI). As a result, abundant and hyperactive Ti3+-Ov(-Ce3+)-Ptδ+ interfacial sites are formed to significantly promote the generation of CO2 and H2 evolution. In addition, the stronger EMSI between Pt NCs and mpCe/TiO2-0.5 than that between Pt and mpTiO2 contributes to the superior self-enhanced catalytic performance during the cyclic test, where the CO conversion at 200 °C increases from 72% for the fresh catalyst to 99% for the used one. These findings reveal the subtle relationship between the mesoporous metal oxide-metal composite catalysts with unique chemical microenvironments and their catalytic performance, which is expected to inspire the design of efficient heterogeneous catalysts.

Structure-Function Relationship of Highly Reactive CuOx Clusters on Co3 O4 for Selective Formaldehyde Sensing at Low Temperatures

Designing reactive surface clusters at the nanoscale on metal-oxide supports enables selective molecular interactions in low-temperature catalysis and chemical sensing. Yet, finding effective material combinations and identifying the reactive site remains challenging and an obstacle for rational catalyst/sensor design. Here, the low-temperature oxidation of formaldehyde with CuOx clusters on Co3 O4 nanoparticles is demonstrated yielding an excellent sensor for this critical air pollutant. When fabricated by flame-aerosol technology, such CuOx clusters are finely dispersed, while some Cu ions are incorporated into the Co3 O4 lattice enhancing thermal stability. Importantly, infrared spectroscopy of adsorbed CO, near edge X-ray absorption fine structure spectroscopy and temperature-programmed reduction in H2 identified Cu+ and Cu2+ species in these clusters as active sites. Remarkably, the Cu+ surface concentration correlated with the apparent activation energy of formaldehyde oxidation (Spearman's coefficient ρ = 0.89) and sensor response (0.96), rendering it a performance descriptor. At optimal composition, such sensors detected even the lowest formaldehyde levels of 3 parts-per-billion (ppb) at 75°C, superior to state-of-the-art sensors. Also, selectivity to other aldehydes, ketones, alcohols, and inorganic compounds, robustness to humidity and stable performance over 4 weeks are achieved, rendering such sensors promising as gas detectors in health monitoring, air and food quality control.

Cobalt group transition metals (TM: Co, Rh, Ir) coordination of S-doped porphyrins (TM_S@PPR) as sensors for molecular SO2 gas adsorption: a DFT and QTAIM study

CONTEXT

The intricate challenges posed by SO2 gas underscore the imperative for meticulous monitoring and detection due to its adverse effects on health, the environment, and equipment integrity. Hence, this research endeavors to delve deeply into the intricate realm of transition-metals functionalized sulfur-doped porphyrins (S@PPR) surfaces through a comprehensive computational study. The electronic properties revealed that upon adsorption, Ir_S@PPR surface reflects the least energy gap of 0.109 eV at the O-site of adsorptions, indicating an increase in electrical conductivity which is a better adsorption trait. Owing to the negative adsorption energy observed, the adsorption behavior is described as chemisorption, with the greatest adsorption energy of - 10.306 eV for Ir_S@PPR surface at the S-site of adsorption. Based on the mechanistic attributes, iridium-functionalized S@PPR surface is a promising detecting material towards the sensing of SO2 gas. This report will provide useful insight for experimental researchers in selecting and engineering materials to be used as detectors for SO2 gas pollutant.

METHOD

All theoretical investigations were carried out using density functional theory (DFT), calculated at PW6B95-D3/GenECP/Def2svp/LanL2DZ computational method.

Adjusting surface coverage of Pt nanocatalyst decoration for selectivity control in CMOS-integrated SnO2 thin film gas sensors

Smart gas-sensor devices are of crucial importance for emerging consumer electronics and Internet-of-Things (IoT) applications, in particular for indoor and outdoor air quality monitoring (e.g., CO2 levels) or for detecting pollutants harmful for human health. Chemoresistive nanosensors based on metal-oxide semiconductors are among the most promising technologies due to their high sensitivity and suitability for scalable low-cost fabrication of miniaturised devices. However, poor selectivity between different target analytes restrains this technology from broader applicability. This is commonly addressed by chemical functionalisation of the sensor surface via catalytic nanoparticles. Yet, while the latter led to significant advances in gas selectivity, nanocatalyst decoration with precise size and coverage control remains challenging. Here, we present CMOS-integrated gas sensors based on tin oxide (SnO2) films deposited by spray pyrolysis technology, which were functionalised with platinum (Pt) nanocatalysts. We deposited size-selected Pt nanoparticles (narrow size distribution around 3 nm) by magnetron-sputtering inert-gas condensation, a technique which enables straightforward surface coverage control. The resulting impact on SnO2 sensor properties for CO and volatile organic compound (VOC) detection via functionalisation was investigated. We identified an upper threshold for nanoparticle deposition time above which increased surface coverage did not result in further CO or VOC sensitivity enhancement. Most importantly, we demonstrate a method to adjust the selectivity between these target gases by simply adjusting the Pt nanoparticle deposition time. Using a simple computational model for nanocatalyst coverage resulting from random gas-phase deposition, we support our findings and discuss the effects of nanoparticle coalescence as well as inter-particle distances on sensor functionalisation.

Recent Progress on Functionalized Graphene Quantum Dots and Their Nanocomposites for Enhanced Gas Sensing Applications

Gas-sensing technology has witnessed significant advancements that have been driven by the emergence of graphene quantum dots (GQDs) and their tailored nanocomposites. This comprehensive review surveys the recent progress made in the construction methods and applications of functionalized GQDs and GQD-based nanocomposites for gas sensing. The gas-sensing mechanisms, based on the Fermi-level control and charge carrier depletion layer theory, are briefly explained through the formation of heterojunctions and the adsorption/desorption principle. Furthermore, this review explores the enhancements achieved through the incorporation of GQDs into nanocomposites with diverse matrices, including polymers, metal oxides, and 2D materials. We also provide an overview of the key progress in various hazardous gas sensing applications using functionalized GQDs and GQD-based nanocomposites, focusing on key detection parameters such as sensitivity, selectivity, stability, response and recovery time, repeatability, and limit of detection (LOD). According to the most recent data, the normally reported values for the LOD of various toxic gases using GQD-based sensors are in the range of 1-10 ppm. Remarkably, some GQD-based sensors exhibit extremely low detection limits, such as N-GQDs/SnO2 (0.01 ppb for formaldehyde) and GQD@SnO2 (0.10 ppb for NO2). This review provides an up-to-date perspective on the evolving landscape of functionalized GQDs and their nanocomposites as pivotal components in the development of advanced gas sensors.

Recent Advances of Graphene Quantum Dots in Chemiresistive Gas Sensors

Graphene quantum dots (GQDs), as 0D graphene nanomaterials, have aroused increasing interest in chemiresistive gas sensors owing to their remarkable physicochemical properties and tunable electronic structures. Research on GQDs has been booming over the past decades, and a number of excellent review articles have been provided on various other sensing principles of GQDs, such as fluorescence-based ion-sensing, bio-sensing, bio-imaging, and electrochemical, photoelectrochemical, and electrochemiluminescence sensing, and therapeutic, energy and catalysis applications. However, so far, there is no single review article on the application of GQDs in the field of chemiresistive gas sensing. This is our primary inspiration for writing this review, with a focus on the chemiresistive gas sensors reported using GQD-based composites. In this review, the various synthesized strategies of GQDs and its composites, gas sensing enhancement mechanisms, and the resulting sensing characteristics are presented. Finally, the current challenges and future prospects of GQDs in the abovementioned application filed have been discussed for the more rational design of advanced GQDs-based gas-sensing materials and innovative gas sensors with novel functionalities.

Enhanced Sensing Performance of SnX Ti1-X O2 -TiX Sn1-X O2 Core-Shell Heterostructure via Increasing the Density of Unsaturated Sn and Ti Atoms

The strategy of combining different semiconductor materials is adjudged an effective approach to improve the sensing performances of semiconductor materials. However, the specific synergistic mechanism for the excellent gas-sensitive performances of composite materials has not been elucidated. Herein, a facile solvothermal method is employed to synthesize SnX Ti1-X O2 -TiX Sn1-X O2 core-shell heterostructures using SnCl4 •5H2 O and tetrabutyl titanate (TBOT) as raw materials. When the molar ratio of SnCl4 •5H2 O/TBOT is 1.8/3.0, the afforded composite exhibited the highest gas sensing performances compared with other composites prepared with other molar ratios. The enhanced sensing performance is attributed to the simultaneous incorporation of Sn and Ti ions into each other's lattice, leading to an increase in the density of unsaturated Sn and Ti atoms on the surface. Ultimately, more oxygen vacancies are formed by the unsaturated Sn and Ti atoms, which benefits electron capture and the redox reaction of adsorbed gases. Thus, the concept of increased unsaturated metal atoms and oxygen vacancy resulting from the doping of different metal ions into each other's lattice has deepened the understanding of gas sensing and the catalytic reaction mechanisms. The lattice synergy of different metals provides a pathway for the design of advanced gas-sensing materials and catalysts.

Integrated Smart Gas Tracking Device with Artificially Tailored Selectivity for Real-Time Monitoring Food Freshness

The real-time monitoring of food freshness in refrigerators is of significant importance in detecting potential food spoiling and preventing serious health issues. One method that is commonly reported and has received substantial attention is the discrimination of food freshness via the tracking of volatile molecules. Nevertheless, the ambient environment of low temperature (normally below 4 °C) and high humidity (90% R.H.), as well as poor selectivity in sensing gas species remain the challenge. In this research, an integrated smart gas-tracking device is designed and fabricated. By applying pump voltage on the yttria-stabilized zirconia (YSZ) membrane, the oxygen concentration in the testing chamber can be manually tailored. Due to the working principle of the sensor following the mixed potential behavior, distinct differences in sensitivity and selectivity are observed for the sensor that operated at different oxygen concentrations. Typically, the sensor gives satisfactory selectivity to H2S, NH3, and C2H5OH at the oxygen concentrations of 10%, 30%, and 40%, respectively. In addition, an acceptable response/recovery rate (within 24 s) is also confirmed. Finally, a refrigerator prototype that includes the smart gas sensor is built, and satisfactory performance in discriminating food freshness status of fresh or semi-fresh is verified for the proposed refrigerator prototype. In conclusion, these aforementioned promising results suggest that the proposed integrated smart gas sensor could be a potential candidate for alarming food spoilage.

Pt-Pd Nanoalloys Functionalized Mesoporous SnO2 Spheres: Tailored Synthesis, Sensing Mechanism, and Device Integration

Methane (CH4 ), as the vital energy resource and industrial chemicals, is highly flammable and explosive for concentrations above the explosive limit, triggering potential risks to personal and production safety. Therefore, exploiting smart gas sensors for real-time monitoring of CH4 becomes extremely important. Herein, the Pt-Pd nanoalloy functionalized mesoporous SnO2 microspheres (Pt-Pd/SnO2 ) were synthesized, which show uniform diameter (≈500 nm), high surface area (40.9-56.5 m2 g-1 ), and large mesopore size (8.8-15.8 nm). The highly dispersed Pt-Pd nanoalloys are confined in the mesopores of SnO2 , causing the generation ofoxygen defects and increasing the carrier concentration of sensitive materials. The representative Pt1 -Pd4 /SnO2 exhibits superior CH4 sensing performance with ultrahigh response (Ra /Rg = 21.33 to 3000 ppm), fast response/recovery speed (4/9 s), as well as outstanding stability. Spectroscopic analyses imply that such an excellent CH4 sensing process involves the fast conversion of CH4 into formic acid and CO intermediates, and finally into CO2 . Density functional theory (DFT) calculations reveal that the attractive covalent bonding interaction and rapid electron transfer between the Pt-Pd nanoalloys and SnO2 support, dramatically promote the orbital hybridization of Pd4 sites and adsorbed CH4 molecules, enhancing the catalytic activation of CH4 over the sensing layer.

Alkaloid Precipitant Reaction Inspired Controllable Synthesis of Mesoporous Tungsten Oxide Spheres for Biomarker Sensing

Highly porous sensitive materials with well-defined structures and morphologies are extremely desirable for developing high-performance chemiresistive gas sensors. Herein, inspired by the classical alkaloid precipitant reaction, a robust and reliable active mesoporous nitrogen polymer sphere-directed synthesis method was demonstrated for the controllable construction of heteroatom-doped mesoporous tungsten oxide spheres. In the typical synthesis, P-doped mesoporous WO3 monodisperse spheres with radially oriented channels (P-mWO3-R) were obtained with a diameter of ∼180 nm, high specific surface area, and crystalline skeleton. The in situ-introduced P atoms could effectively adjust the coordination environment of W atoms (Wδ+-Ov), giving rise to dramatically enhanced active surface-adsorbed oxygen species and unusual metastable ε-WO3 crystallites. The P-mWO3-R spheres were applied for the sensing of 3-hydroxy-2-butanone (3H2B), a biomarker of foodborne pathogenic bacteria Listeria monocytogenes (LM). The sensor exhibited high sensitivity (Ra/Rg = 29 to 3 ppm), fast response dynamics (26/7 s), outstanding selectivity, and good long-term stability. Furthermore, the device was integrated into a wireless sensing module to realize remote real-time and precise detection of LM in practical applications, making it possible to evaluate food quality using gas sensors conveniently.

Recent Progress in Spinel Ferrite (MFe2O4) Chemiresistive Based Gas Sensors

Gas-sensing technology has gained significant attention in recent years due to the increasing concern for environmental safety and human health caused by reactive gases. In particular, spinel ferrite (MFe2O4), a metal oxide semiconductor with a spinel structure, has emerged as a promising material for gas-sensing applications. This review article aims to provide an overview of the latest developments in spinel-ferrite-based gas sensors. It begins by discussing the gas-sensing mechanism of spinel ferrite sensors, which involves the interaction between the target gas molecules and the surface of the sensor material. The unique properties of spinel ferrite, such as its high surface area, tunable bandgap, and excellent stability, contribute to its gas-sensing capabilities. The article then delves into recent advancements in gas sensors based on spinel ferrite, focusing on various aspects such as microstructures, element doping, and heterostructure materials. The microstructure of spinel ferrite can be tailored to enhance the gas-sensing performance by controlling factors such as the grain size, porosity, and surface area. Element doping, such as incorporating transition metal ions, can further enhance the gas-sensing properties by modifying the electronic structure and surface chemistry of the sensor material. Additionally, the integration of spinel ferrite with other semiconductors in heterostructure configurations has shown potential for improving the selectivity and overall sensing performance. Furthermore, the article suggests that the combination of spinel ferrite and semiconductors can enhance the selectivity, stability, and sensing performance of gas sensors at room or low temperatures. This is particularly important for practical applications where real-time and accurate gas detection is crucial. In conclusion, this review highlights the potential of spinel-ferrite-based gas sensors and provides insights into the latest advancements in this field. The combination of spinel ferrite with other materials and the optimization of sensor parameters offer opportunities for the development of highly efficient and reliable gas-sensing devices for early detection and warning systems.

Enhanced Acetone-Sensing Properties of Pt-Decorated In2O3 Hollow Microspheres Derived from Pt-Embedded Template

Pt-decorated In2O3 hollow microspheres were prepared using a template and reflux method. The size of the prepared carbon templates was adjusted from 200 nm to 1.3 μm by introducing chloroplatinic acid during the hydrothermal process. At the same time, Pt nanoparticles inside the carbon layer were protected from oxidation and agglomeration. Also, the folds created on the surface of the hollow sphere during shrinkage led to a substantial increase in specific surface area. The response of the In2O3-based sensor toward acetone was significantly enhanced by the addition of Pt decoration. This improvement can be attributed to the increased availability of active sites for the target gas and the consequential alteration of the energy band structure. In addition, high response sensitivity, rapid dynamic processes, long-term reliability, and selectivity have all been achieved. The detectable limit is less than 1 ppm, which might satisfy the 1.8 ppm threshold value in the exhaled breath of patients with diabetes. Consequently, the proposed sensor has great sensitivity and can detect low-concentration of acetone, making it an ideal choice for applications such as monitoring daily dietary intake, managing diabetes, and inspecting industrial production processes.

Polymerization-Induced Aggregation Approach toward Uniform Pd Nanoparticle-Decorated Mesoporous SiO2/WO3 Microspheres for Hydrogen Sensing

Hydrogen as an important clean energy source with a high energy density has attracted extensive attention in fuel cell vehicles and industrial production. However, considering its flammable and explosive property, gas sensors are desperately desired to efficiently monitor H₂ concentration in practical applications. Herein, a facile polymerization-induced aggregation strategy was proposed to synthesize uniform Si-doped mesoporous WO₃ (Si-mWO₃) microspheres with tunable sizes. The polymerization of the melamine-formaldehyde resin prepolymer (MF prepolymer) in the presence of silicotungstic acid hydrate (abbreviated as H₄SiW) leads to uniform MF/H₄SiW hybrid microspheres, which can be converted into Si-mWO₃ microspheres through a simple thermal decomposition treatment process. In addition, benefiting from the pore confinement effect, monodispersed Pd-decorated Si-mWO₃ microspheres (Pd/Si-mWO₃) were subsequently synthesized and applied as sensitive materials for the sensing and detection of hydrogen. Owing to the oxygen spillover effect of Pd nanoparticles, Pd/Si-mWO₃ enables adsorption of more oxygen anions than pure mWO₃. These Pd nanoparticles dispersed on the surface of Si-mWO₃ accelerated the dissociation of hydrogen and promoted charge transfer between Pd nanoparticles and WO₃ crystal particles, which enhanced the sensing sensitivity toward H₂. As a result, the gas sensor based on Pd/Si-mWO₃ microspheres exhibited excellent selectivity and sensitivity (R_air/R_gas = 33.5) to 50 ppm H₂ at a relatively low operating temperature (210 °C), which was 30 times higher than that of the pure Si-mWO₃ sensor. To develop intelligent sensors, a portable sensor module based on Pd/Si-mWO₃ in combination with wireless Bluetooth connection was designed, which achieved real-time monitoring of H₂ concentration, opening up the possibility for use as intelligent H₂ sensors.