Single-Atom Cu Stabilized on Ultrathin WO2.72 Nanowire for Highly Selective and Ultrasensitive ppb-Level Toluene Detection

In Situ Generatable and Recyclable Oxygen Vacancy-Modified Fe2O3-Decorated WO3 Nanowires with Super Stability for ppb-Level H2S Sensing

Detecting hydrogen sulfide (H2S) odor gas in the environment at parts-per-billion-level concentrations is crucial. However, a significant challenge is the rapid deactivation caused by SO42- deposition. To address this issue, we developed a sensing material comprising Fe2O3-decorated WO3 nanowires (FWO) with strong interfacial interaction. During the H2S sensing process, important oxygen vacancies (OVs) are generated in situ and are recyclable on the surface of the Fe2O3 cluster. This sensor achieves a response of 140 (Ra/Rg) toward 50 ppm of H2S at 250 °C, with an experimentally measured detection limit of 1 ppb. It also exhibits remarkable stability, with no significant change observed over a long period of 150 days. Based on a combination of in situ DRIFT and DFT calculations, we have identified that the overactivation of O2 is the key step in the formation of SO42-. This overactivation can be partially modulated by the synergistic effect of Fe2O3 decoration and the in situ generated OVs, regulating the oxidation product to SO2 rather than the toxic SO42-. Furthermore, the continuous generation of OVs compensates for the loss of active sites pertaining to SO42- deposition, thereby contributing to the excellent stability of the sensor. This study underscores the beneficial impact of in situ OV generation in FWO for H2S sensing, offering a dynamic strategy to enhance sensor performance, particularly in terms of stability.

Decorated-Induced Oxygen Vacancy Engineering for Ultra-Low Concentration Nonanal Sensing: A Case Study of La-Decorated Bi2O2CO3

La-decorated Bi2O2CO3 (BCO-La) microspheres are synthesized using a facile wet chemical strategy for sensing low-concentration nonanal (C9H18O) at room temperature. These BCO-La gas sensors are applied to evaluate agricultural product quality, specifically for cooked rice. The sensitivity of the BCO-6La sensor significantly surpassed that of the pure BCO sensor, achieving a response value of 174.6 when detecting 30 ppm nonanal gas. Notably, the BCO-6La sensor demonstrated a faster response time (36 s) when exposed to 18 ppm of nonanal. Additionally, the selectivity toward nonanal gas detection is higher (approximately 4-24 times) compared to interfering gases (1-octanol, geranyl acetone, linalool, hexanal, 2-pentyfuran, and 1-octen-3-ol) during cooked rice quality detection. The gas sensing mechanism and the factors contributing to the enhanced sensing performance of the BCO-La microspheres are demonstrated through in situ FT-IR spectra and DFT analysis while the realistic detection scenario is carried out. In a broader context, the reported sensors here represent a novel platform for the detection and monitoring of gases released by agricultural products during storage.

Materials Containing Single-, Di-, Tri-, and Multi-Metal Atoms Bonded to C, N, S, P, B, and O Species as Advanced Catalysts for Energy, Sensor, and Biomedical Applications

Modifying the coordination or local environments of single-, di-, tri-, and multi-metal atom (SMA/DMA/TMA/MMA)-based materials is one of the best strategies for increasing the catalytic activities, selectivity, and long-term durability of these materials. Advanced sheet materials supported by metal atom-based materials have become a critical topic in the fields of renewable energy conversion systems, storage devices, sensors, and biomedicine owing to the maximum atom utilization efficiency, precisely located metal centers, specific electron configurations, unique reactivity, and precise chemical tunability. Several sheet materials offer excellent support for metal atom-based materials and are attractive for applications in energy, sensors, and medical research, such as in oxygen reduction, oxygen production, hydrogen generation, fuel production, selective chemical detection, and enzymatic reactions. The strong metal-metal and metal-carbon with metal-heteroatom (i.e., N, S, P, B, and O) bonds stabilize and optimize the electronic structures of the metal atoms due to strong interfacial interactions, yielding excellent catalytic activities. These materials provide excellent models for understanding the fundamental problems with multistep chemical reactions. This review summarizes the substrate structure-activity relationship of metal atom-based materials with different active sites based on experimental and theoretical data. Additionally, the new synthesis procedures, physicochemical characterizations, and energy and biomedical applications are discussed. Finally, the remaining challenges in developing efficient SMA/DMA/TMA/MMA-based materials are presented.

Oxygen Vacancy Enabled Electronic Structure Engineering of Pt-WO3 Nanosheets toward Highly Efficient BTEX Sensing

A Pt nanoparticle-immobilized WO3 material is a promising candidate for catalytic reactions, and the surface and electronic structure can strongly affect the performance. However, the effect of the intrinsic oxygen vacancy of WO3 on the d-band structure of Pt and the synergistic effect of Pt and the WO3 matrix on reaction performance are still ambiguous, which greatly hinders the design of advanced materials. Herein, Pt-decorated WO3 nanosheets with different electronic metal-support interactions are successfully prepared by finely tuning the oxygen vacancy structure of WO3 nanosheets. Notably, Pt-modified WO3 nanosheets annealed at 400 °C exhibit excellent benzene series (BTEX) sensing performance (S = 377.33, 365.21, 348.45, and 319.23 for 50 ppm ethylbenzene, benzene, toluene, and xylene, respectively, at 140 °C), fast response and recovery dynamics (10/7 s), excellent reliability (σ = 0.14), and sensing stability (φ = 0.08%). Detailed structural characterization and DFT results reveal that interfacial Ptδ+-Ov-W5+ sites are recognized as the active sites, and the oxygen vacancies of the WO3 matrix can significantly affect the d-band structure of Pt nanoparticles. Notably, Pt/WO3-400 with improved surface oxygen mobility and medium electronic metal-support interaction facilitates the activation and desorption of BTEX, which contributes to the highly efficient BTEX sensing performance. Our work provides a new insight for the design of high-performance surface reaction materials for advanced applications.

Theoretical Validation of Non-Noble Cu Sites Integrated on SnO2 Nanoflowers for Enhanced Gas Sensing of Ethanethiol at Room Temperature

Ethanethiol (EtSH), being highly toxic, flammable, and explosive, poses significant risks to human health and safety and is capable of causing fires and explosions. Room-temperature detection using chemiresistive gas sensors is essential for managing these risks. However, the gas-sensing performance of conventional metal-oxide sensing materials may be limited by their weak interaction with EtSH at room temperature. Herein, SnO2 nanoflowers assembled with non-noble Cu-site-enriched porous nanosheets were designed and prepared by an in situ self-template pyrolysis synthesis strategy to enable highly sensitive and selective room-temperature detection of EtSH. By regulating the number of non-noble Cu sites, these nanoflowers achieved efficient EtSH sensing with a Ra/Rg value of 11.0 at 50 ppb, ensuring high selectivity, reproducibility, and stability at room temperature. Moreover, a comparative analysis of the room-temperature gas-sensing performance of SnO2 nanoflowers with non-noble Fe- or Ni-site-enriched nanosheets highlights the benefits of non-noble Cu sites for EtSH detection. Density functional theory (DFT) analysis reveals that non-noble Cu sites have a unique affinity for EtSH, offering preferential binding over other gases and explaining the outstanding sensing performance of non-noble Cu-site-enriched nanosheet-assembled SnO2 nanoflowers. The structural and interface engineering of the sensing materials presented in this work provides a promising approach for offering efficient and durable gas sensors operable at room temperature.

Multiarray Gas Sensors Using Ternary Combined Ti3C2Tx MXene-Based Nanocomposites

This paper reports chemiresistive multiarray gas sensors through the synthesized ternary nanocomposites, using a one-pot method to integrate two-dimensional MXene (Ti3C2Tx) with Ti-doped WO3 (Ti-WO3/Ti3C2Tx) and Ti3C2Tx with Pd-doped SnO2 (Pd-SnO2/Ti3C2Tx). The gas sensors based on Ti-WO3/Ti3C2Tx and Pd-SnO2/Ti3C2Tx exhibit exceptional sensitivity, particularly in detecting 70% at 1 ppm acetone and 91.1% at 1 ppm of H2S. Notably, our sensors demonstrate a remarkable sensing performance in the low-ppb range for acetone and H2S. Specifically, the Ti-WO3/Ti3C2Tx sensor demonstrates a detection limit of 0.035 ppb for acetone, and the Pd-SnO2/Ti3C2Tx sensor shows 0.116 ppb for H2S. Simultaneous measurements with Ti-WO3/Ti3C2Tx- and Pd-SnO2/Ti3C2Tx-based sensors enable the evaluation of both the concentration and type of unknown target gases, such as acetone or H2S. Furthermore, density functional theory calculations are performed to clarify the role of Ti and Pd doping in enhancing the performance of Ti-WO3/Ti3C2Tx and Pd-SnO2/Ti3C2Tx nanocomposites. Theoretical simulations contribute to a deeper understanding of the doping effects, providing essential insights into the mechanisms underlying the enhanced gas response of the gas sensors. Overall, this work provides valuable insights into the gas-sensing mechanisms and introduces a novel approach for high-performance multiarray gas sensing.

Tailored Polypyrrole Nanofibers as Ion-to-Electron Transduction Membranes for Wearable K+ Sensors

Conductive polymers are recognized as ideal candidates for the development of noninvasive and wearable sensors for real-time monitoring of potassium ions (K+) in sweat to ensure the health of life. However, the low ion-to-electron transduction efficiency and limited active surface area hamper the development of high-performance sensors for low-concentration K+ detection in the sweat. Herein, a wearable K+ sensor is developed by tailoring the nanostructure of polypyrrole (PPy), serving as an ion-to-electron transduction layer, for accurately and stably tracing the K+ fluctuation in human sweat. The PPy nanostructures can be tailored from nanospheres to nanofibers by controlling the supramolecular assembly process during PPy polymerization. Resultantly, the ion-to-electron transduction efficiency (17-fold increase in conductivity) and active surface area (1.3-fold enhancement) are significantly enhanced, accompanied by minimized water layer formation. The optimal PPy nanofibers-based K+ sensor achieved a high sensitivity of 62 mV decade-1, good selectivity, and solid stability. After being integrated with a temperature sensor, the manufactured wearable sensor realized accurate monitoring of K+ fluctuation in the human sweat.

Emerging single-atom catalysts in the detection and purification of contaminated gases

Single atom catalysts (SACs) show exceptional molecular adsorption and electron transfer capabilities owing to their remarkable atomic efficiency and tunable electronic structure, thereby providing promising solutions for diverse important processes including photocatalysis, electrocatalysis, thermal catalysis, etc. Consequently, SACs hold great potential in the detection and degradation of pollutants present in contaminated gases. Over the past few years, SACs have made remarkable achievements in the field of contaminated gas detection and purification. In this review, we first provide a concise introduction to the significance and urgency of gas detection and pollutant purification, followed by a comprehensive overview of the structural feature identification methods for SACs. Subsequently, we systematically summarize the three key properties of SACs for detecting contaminated gases and discuss the research progress made in utilizing SACs to purify polluted gases. Finally, we analyze the enhancement mechanism and advantages of SACs in polluted gas detection and purification, and propose strategies to address challenges and expedite the development of SACs in polluted gas detection and purification.

Stabilizing Single-Atom Pt on Fe2O3 Nanosheets by Constructing Oxygen Vacancies for Ultrafast H2 Sensing

Single-atom catalysts (SACs) hold great promise in highly sensitive and selective gas sensors due to their ultrahigh atomic efficiency and excellent catalytic activity. However, due to the extremely high surface energy of SACs, it is still a huge challenge to synthesize a stable single-atom metal on sensitive materials. Here, we report an atomic layer deposition (ALD) strategy for the elaborate synthesis of single-atom Pt on oxygen vacancy-rich Fe2O3 nanosheets (Pt-Fe2O3-Vo), which displayed ultrafast and sensitive detection to H2, achieving the stability of Pt single atoms. Gas-sensing investigation showed that the Pt-Fe2O3-Vo materials enabled a significantly enhanced response of 26.5-50 ppm of H2, which was 17-fold higher than that of pure Fe2O3, as well as ultrafast response time (2 s), extremely low detection limit (86 ppb), and improved stability. The experimental and density functional theory (DFT) studies revealed that the abundant oxygen vacancy sites of Fe2O3 contributed to stabilizing the Pt atoms via electron transfer. In addition, the stabilized Pt atoms also greatly promote the electron transfer of H2 molecules to Fe2O3, thereby achieving an excellent H2 sensing performance. This work provides a potential strategy for the development of highly selective and stable chemical sensors.

Advances in Synthesis and Applications of Single-Atom Catalysts for Metal Oxide-Based Gas Sensors

As a stable, low-cost, environment-friendly, and gas-sensitive material, semiconductor metal oxides have been widely used for gas sensing. In the past few years, single-atom catalysts (SACs) have gained increasing attention in the field of gas sensing with the advantages of maximized atomic utilization and unique electronic and chemical properties and have successfully been applied to enhance the detection sensitivity and selectivity of metal oxide gas sensors. However, the application of SACs in gas sensors is still in its infancy. Herein, we critically review the recent advances and current status of single-atom catalysts in metal oxide gas sensors, providing some suggestions for the development of this field. The synthesis methods and characterization techniques of SAC-modified metal oxides are summarized. The interactions between SACs and metal oxides are crucial for the stable loading of single-atom catalysts and for improving gas-sensitive performance. Then, the current application progress of various SACs (Au, Pt, Cu, Ni, etc.) in metal oxide gas sensors is introduced. Finally, the challenges and perspectives of SACs in metal oxide gas sensors are presented.

Domain-Limited Sub-Nanometer Co Nanoclusters in Defective Nitrogen Doped Carbon Structures for Non-Invasive Drug Monitoring

In this work, sub-nanometer Co clusters anchored on porous nitrogen-doped carbon (C─N─Co NCs) are successfully prepared by high-temperature annealing and pre-fabricated template strategies for non-invasive sensing of clozapine (CLZ) as an efficient substrate adsorption and electrocatalyst. The introduction of Co sub-nanoclusters (Co NCs) provides enhanced electrochemical performance and better substrate adsorption potential compared to porous and nitrogen-doped carbon structures. Combined with ab initio calculations, it is found that the favorable CLZ catalytic performance with C─N─Co NCs is mainly attributed to possessing a more stable CLZ adsorption structure and lower conversion barriers of CLZ to oxidized state CLZ. An electrochemical sensor for CLZ detection is conceptualized with a wide operating range and high sensitivity, with monitoring capabilities validated in a variety of body fluid environments. Based on the developed CLZ sensing system, the CLZ correlation between blood and saliva and the accuracy of the sensor are investigated by the gold standard method and the rat model of drug administration, paving the way for non-invasive drug monitoring. This work provides new insights into the development of efficient electrocatalysts to enable drug therapy and administration monitoring in personalized healthcare systems.