Synthesis of Mesoporous Ag2O/SnO2 Nanospheres for Selective Sensing of Formaldehyde at a Low Working Temperature

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.

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.

Electrochemical epoxidation enhanced by C2H4 activation and hydroxyl generation at the Ag/SnO2 interface

Direct electrochemical ethylene (C2H4) epoxidation with water (H2O) represents a promising approach for the production of value-added ethylene oxide (EO) in a sustainable way. However, the activity remains limited due to the sluggish activation of C2H4 and the stiff formation of *OH intermediate. This paper describes the design of a Ag/SnO2 electrocatalyst to achieve efficient electrochemical C2H4 epoxidation with a high faradaic efficiency of 39.4% for EO and a high selectivity of 91.5% at 25 mA/cm2 in a membrane electrode assembly. Results of in situ attenuated total reflection infrared spectra characterizations and computational calculations reveal that the Ag/SnO2 interface promotes C2H4 adsorption and activation to obtain *C2H4. Moreover, electrophilic *OH is generated on the catalyst surface through H2O dissociation, which further reacts with *C2H4 to facilitate the formation of *C2H4OH, contributing to the enhanced electrochemical epoxidation activity. This work would provide general guidance for designing catalysts for electrochemical olefin epoxidation through interface engineering.

Universal Gas-Sensitive Detection of Various Lithium-Ion Battery Electrolyte Leakages via Ag@Ag2O-Functionalized SnO2 Nanoflowers with Abundant Oxygen Vacancies

Lithium-ion batteries (LIBs) provide many benefits, but trace electrolyte leakage can cause serious safety risks such as thermal runaway. Although gas sensors offer a potential solution, the complexity of electrolyte solvents in LIBs makes it challenging to develop sensing materials capable of universally detecting multiple solvent molecules. Here, Ag@Ag2O-functionalized SnO2 nanoflowers were synthesized using a self-template pyrolysis strategy for the sensitive detection of both common solvent molecules and widely used electrolytes. These sensors, enhanced by abundant oxygen vacancies introduced by Ag@Ag2O functionalization, exhibit excellent sensitivity, particularly to dimethyl carbonate, with a response of 106-100 ppm, a low detection limit of 11.76 ppb, and rapid response/recovery times (28/55 s) at an operating temperature of 200 °C. The sensor performance was validated by density functional theory calculations, which corroborated the effectiveness of the sensing material. In simulated LIB leakage scenarios, such as puncture and electrolyte injection, the sensors demonstrated quick responses to various common electrolyte compositions, indicating their potential for practical applications. This study highlights an effective method for fabricating composite sensing materials and emphasizes the practical significance of our universal detection approach for practical monitoring of electrolyte leakage in energy storage devices.

Insights into Selective Sensitivity of In2O3-CuO Heterojunction Nanocrystals to CH4 over CO and H2: Experiments and First-Principles Calculations

Metal oxide semiconductor gas sensors have demonstrated exceptional potential in gas detection due to their high sensitivity, rapid response time, and impressive selectivity for identifying various sorts of gases. However, selectively distinguishing CH4 from those of CO and H2 remains a significant challenge. This difficulty primarily stems from the weakly reducing nature of CH4, which results in a low adsorption response and makes it prone to interference from stronger reducing gases in the surroundings. Herein, we synthesized In2O3-xCuO nanocomposites using a hydrothermal method to explore their gas sensing properties toward CH4, CO, and H2. Characterization tests confirmed the successful preparation of In2O3-xCuO nanocomposites with different In:Cu molar ratios and the formation of a p-n heterojunction. The gas sensing test results indicated that the In2O3-2.1CuO nanocomposites calcined at 500 °C and measured at 350 °C displayed a p-type response for CH4 and an n-type response for CO and H2, allowing for accurate differentiation of CH4 from CO and H2. Moreover, the In2O3-2.1CuO sensor also showed excellent stability and reproducibility across all three gases. First-principles calculations revealed distinct changes in the electronic structure of the In2O3-CuO heterojunction upon adsorption of CH4, CO, and H2, a finding that aligns with empirical evidence. The gas selectivity mechanism was effectively explained by variations in the energy band gap, driven by electrical behavior during the adsorption process. This work suggests a promising approach for developing selective gas sensors capable of detecting weakly reducing gases.

Magnetic Field Assisted Enhanced Sensitivity of Nonferromagnetic Materials Boosting the Carrier Transfer: Mechanistic Studies

The performance of semiconductor sensors is determined by reaction kinetics, conductivity, and electron mobility, which are undoubtedly closely related to the electron motion behavior. Therefore, the effective regulation of electronic states is crucial for improving gas sensing properties. Previous methods of enhancing the gas-sensing performance have induced complex material modifications, and the extent of performance improvement is usually very limited. Further optimization of the gas sensing performance requires continuous efforts to advance new technologies. Toward this issue, a novel magnetic field-induced strategy is adopted to boost the carrier transfer efficiency of nonferromagnetic semiconductors. The gas sensing investigation results manifest that the applied magnetic field can effectively enhance the sensitivity and reduce the baseline resistance. The In2O3 NC-2 (In2O3 nanocubes) with an applied magnetic field have a greatly enhanced response of 161.4 toward 100 ppm formaldehyde, which is 2.5 times higher than that without magnetic field. The enhanced gas sensing properties can be mainly attributed to magnetization of reactive materials, which makes the orientation of electronic magnetic moments consistent, thus greatly contributing to reactivity. This work introduces a practical approach to effectively improve gas sensing performance without further morphology optimization, noble metal catalysis, structural modification, and material cladding. The results of this study provide new insights for designing novel gas sensors to improve the gas sensing performance.

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.

Metal-Organic Framework-Derived Au-Doped In2O3 Nanotubes for Monitoring CO at the ppb Level

Achieving selective detection of ppb-level CO is important for air quality testing at industrial sites to ensure personal safety. Noble metal doping enhances charge transfer, which in turn reduces the detection limit of metal oxide gas sensors. In this work, metal-organic framework-derived Au-doped In2O3 nanotubes with high electrical conductivity are synthesized by pyrolysis of the Au-doped metal-organic framework (In-MIL-68) as a template. Gas-sensing experiments reveal that the detection limit of 0.2% Au-doped In2O3 nanotubes (0.2% Au, mass fraction) is as low as 750 ppb. Meanwhile, the sensing material shows a response value of 18.2 to 50 ppm of CO at 240 °C, which is about 2.8 times higher than that of pure In2O3. Meanwhile, the response and recovery times are short (37 s/86 s). The gas-sensing mechanism of CO is uncovered by in situ DRIFTS through the reaction intermediates. In addition, first-principles calculations suggest that Au doping of In2O3 significantly enhances its adsorption energy for CO and improves the electron transfer properties. This study reveals a novel synthesis pathway for Au-doped In2O3 nanotubular structures and their potential application in low concentration CO detection.

Mussel-inspired interface deposition strategy for mesoporous metal-phenolic nanospheres with superior antioxidative, photothermal and antibacterial performance

Metal-phenolic networks (MPNs) have emerged as a versatile and multifunctional platform applied in bioimaging, disease treatment, electrocatalysis, and water purification. The synthesis of MPNs with mesoporous frameworks and ultra-small diameters (<200 nm), crucial for post-modification, cargo loading, and mass transport, remains a formidable challenge. Inspired by mussel chemistry, mesoporous metal-phenolic nanospheres (MMPNs) are facilely prepared by direct deposition of the metal-polyphenol complex on the interface of oil nano-droplets composed of block copolymers/1,3,5-trimethylbenzene followed by a spontaneous template-removal process. Due to the penetrable and stable networks, the oil nano-droplets gradually leak from the networks driven by shear stress during the stirring process. As a result, MMPNs are obtained without additional template removal procedures such as solvent extraction or high-temperature calcination. The materials have a large pore size (∼12.1 nm), uniform spherical morphology with a small particle size (∼99 nm), and a large specific surface area (49.8 m2 g-1). Due to the abundant phenolic hydroxyl groups, the MMPNs show excellent antioxidative property. The MMPNs also have excellent photothermal property, whose photothermal conversion efficiency was 40.9 %. Moreover, the phenolic hydroxyl groups can reduce Ag+ in situ to prepare Ag nanoparticles loaded MMPNs composites, which have excellent inhibition performance of drug-resistant bacteria biofilm.

Synergistic sensitization effects of single-atom gold and cerium dopants on mesoporous SnO2 nanospheres for enhanced volatile sulfur compound sensing

The real-time monitoring of volatile sulfur compounds is indispensable; however, it continues to pose a significant challenge due to issues such as limited performance towards parts-per-billion (ppb)-level gas. Herein, a concept of synergistic sensitization effects involving single-atom gold (Au) and cerium (Ce) dopants is proposed to boost the sensing performance of allyl mercaptan, a common volatile sulfur compound. As a proof-of-concept, a chemiresistive gas sensor based on mesoporous SnO2 nanospheres with single-atom Au decoration and Ce dopant (denoted Au/Ce-SnO2) is successfully synthesized. The synthesis of Au/Ce-SnO2 is achieved through the utilization of a self-template strategy, employing metal-phenolic hybrids as a precursor. The obtained materials exhibit high specific surface area (89.4 m2 g-1), and small particle size (∼86 nm). The gas sensor reveals unprecedented sensitivity (0.097 ppb-1) and ultra-low detection limit (0.74 ppb), surpassing all state-of-the-art allyl mercaptan gas sensors. Furthermore, a wireless gas sensor is constructed for highly selective and real-time monitoring of allyl mercaptan. The decoration of single-atom Au facilitates the adsorption and dissociation of oxygen and target gases. Simultaneously, the Ce dopant enhances the oxidation of allyl mercaptan. The sensing performance is boosted by the mesoporous framework of SnO2, as well as the synergistic sensitization effects resulting from single-atom Au decoration and Ce doping, thereby facilitating its potential application in environmental and health-related domains.

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.

Handheld Crop Pest Sensor Using Binary Catalyst-Loaded Nano-SnO2 Particles for Oxidative Signal Amplification

In agriculture, pest management is a major challenge. Crop releases volatiles in response to the pest; hence, sensing these volatile signals at a very early stage will ease pest management. Here, binary catalyst-loaded SnO2 nanoparticles of <5 nm were synthesized for the repeated capture and oxidation of the signature volatile and its products to amplify the chemoresistive signal to detect concentrations as low as ≈120 ppb. The sensitivity may be due to the presence of the elements in the Sn-Fe-Pt bond evidenced by extended X-ray absorption fine-structure spectroscopy (EXAFS) that captures and oxidize the volatile without escaping. This strong catalyst may oxidize nontarget volatiles and can cause false signals; hence, a molecular sieve filter has been coupled to ensure high selectivity for the detection ofTuta absolutainfestation in tomato. Finally, with the support of a mobile power bank, the optimized sensor has been assembled into a lightweight handheld device.

Rational Integration of SnMOF/SnO2 Hybrid on TiO2 Nanotube Arrays: An Effective Strategy for Accelerating Formaldehyde Sensing Performance at Room Temperature

Formaldehyde is ubiquitously found in the environment, meaning that real-time monitoring of formaldehyde, particularly indoors, can have a significant impact on human health. However, the performance of commercially available interdigital electrode-based sensors is a compromise between active material loading and steric hindrance. In this work, a spaced TiO2 nanotube array (NTA) was exploited as a scaffold and electron collector in a formaldehyde sensor for the first time. A Sn-based metal-organic framework was successfully decorated on the inside and outside of TiO2 nanotube walls by a facile solvothermal decoration strategy. This was followed by regulated calcination, which successfully integrated the preconcentration effect of a porous Sn-based metal-organic framework (SnMOF) structure and highly active SnO2 nanocrystals into the spaced TiO2 NTA to form a Schottky heterojunction-type gas sensor. This SnMOF/SnO2@TiO2 NTA sensor achieved a high room-temperature formaldehyde response (1.7 at 6 ppm) with a fast response (4.0 s) and recovery (2.5 s) times. This work provides a new platform for preparing alternatives to interdigital electrode-based sensors and offers an effective strategy for achieving target preconcentrations for gas sensing processes. The as-prepared SnMOF/SnO2@TiO2 NTA sensor demonstrated excellent sensitivity, stability, reproducibility, flexibility, and convenience, showing excellent potential as a miniaturized device for medical diagnosis, environmental monitoring, and other intelligent sensing systems.

Pattern Recognition with Temperature Regulation: A Single YSZ-Based Mixed Potential Sensor Classifies Multiple Mixtures of Isoprene, n-Propanol, and Acetone

Gas sensors integrated with machine learning algorithms have aroused keen interest in pattern recognition, which ameliorates the drawback of poor selectivity on a sensor. Among various kinds of gas sensors, the yttria-stabilized zirconia (YSZ)-based mixed potential-type sensor possesses advantages of low cost, simple structure, high sensitivity, and superior stability. However, as the number of sensors increases, the increased power consumption and more complicated integration technology may impede their extensive application. Herein, we focus on the development of a single YSZ-based mixed potential sensor from sensing material to machine learning for effective detection and discrimination of unary, binary, and ternary gas mixtures. The sensor that is sensitive to isoprene, n-propanol, and acetone is manufactured with the MgSb2O6 sensing electrode prepared by a simple sol-gel method. Unique response patterns for specific gas mixtures could be generated with temperature regulation. We chose seven algorithm models to be separately trained for discrimination. In order to realize more accurate discrimination, we further discuss the selection of suitable feature parameters and its reasons. With temperature regulation coefficients which are easily available as feature input to model, a single sensor is verified to achieve elevated accuracy rates of 95 and 99% for the discrimination of seven gases (three unary gases, three binary gas mixtures, and one ternary gas mixture) and redefined six gas mixtures. This article provides a potential new approach via a mixed potential sensor instead of a sensor array that could provide a wide application prospect in the field of electronic nose and artificial olfaction.

Synthesis of Mesoporous Lanthanum-Doped SnO2 Spheres for Sensitive and Selective Detection of the Glutaraldehyde Disinfectant

Glutaraldehyde disinfectant has been widely applied in aquaculture, farming, and medical treatment. Excessive concentrations of glutaraldehyde in the environment can lead to serious health hazards. Therefore, it is extremely important to develop high-performance glutaraldehyde sensors with low cost, high sensitivity, rapid response, fabulous selectivity, and low limit of detection. Herein, mesoporous lanthanum (La) doped SnO2 spheres with high specific surface area (52-59 m2 g-1), uniform mesopores (with a pore size concentrated at 5.7 nm), and highly crystalline frameworks are designed to fabricate highly sensitive gas sensors toward gaseous glutaraldehyde. The mesoporous lanthanum-doped SnO2 spheres exhibit excellent glutaraldehyde-sensing performance, including high response (13.5@10 ppm), rapid response time (28 s), and extremely low detection limit of 0.16 ppm. The excellent sensing performance is ascribed to the high specific surface area, high contents of chemisorbed oxygen species, and lanthanum doping. DFT calculations suggest that lanthanum doping in the SnO2 lattice can effectively improve the adsorption energy toward glutaraldehyde compared to pure SnO2 materials. Moreover, the fabricated gas sensors can effectively detect commercial glutaraldehyde disinfectants, indicating a potential application in aquaculture, farming, and medical treatment.

Growth, Characterization, and Application of Vertically Aligned Carbon Nanotubes Using the RF-Magnetron Sputtering Method

The aim of this work is to synthesize and characterize a nanostructured material with improved parameters suitable as a chemiresistive gas sensor sensitive to propylene glycol vapor (PGV). Thus, we demonstrate a simple and cost-effective technology to grow vertically aligned carbon nanotubes (CNTs) and fabricate a PGV sensor based on Fe2O3:ZnO/CNT material using the radio frequency magnetron sputtering method. The presence of vertically aligned carbon nanotubes on the Si(100) substrate was confirmed by scanning electron microscopy and Fourier transform infrared (FTIR), Raman, and energy-dispersive X-ray spectroscopies. The uniform distribution of elements in both CNTs and Fe2O3:ZnO materials was revealed by e-mapped images. The hexagonal shape of the ZnO material in the Fe2O3:ZnO structure and the interplanar spacing in the crystals were clearly visible by transmission electron microscopy images. The gas-sensing behavior of the Fe2O3:ZnO/CNT sensor toward PGV was investigated in the temperature range of 25-300 °C with and without ultraviolet (UV) irradiation. The sensor showed clear and repeatable response/recovery characteristics in the PGV range of 1.5-140 ppm, sufficient linearity of response/concentration dependence, and high selectivity both at 200 and 250 °C without UV radiation. This is a basis for concluding that the synthesized Fe2O3:ZnO/CNT structure is the best candidate for use in PGV sensors, which will allow its further successful application in real-life sensor systems.