Exposed Mo atoms induced by micropores enhanced H2S sensing of MoO3 nanoflowers

Recent Advances in Structure Design and Application of Metal Halide Perovskite-Based Gas Sensor

Metal halide perovskites (MHPs) are emerging gas-sensing materials and have attracted considerable attention in gas sensors due to their unique bandgap structure and tunable optoelectronic properties. The past decade has witnessed significant developments in the gas-sensing field; however, their intrinsic structural instability and ambiguous gas-sensing mechanisms hamper their practical applications. Herein, we summarize the recent advances in MHP-based gas sensors. The physicochemical properties of MHPs are discussed at first. The structure design, including dimension design and engineering design, is overviewed as well as their fabrication methods, and we put forward our insights into the gas-sensing mechanism of MHPs. It is believed that enhanced understanding of gas-sensing mechanisms of MHPs are helpful for their application as gas-sensing materials, and structure design can enhance their stability, sensing sensitivity, and selectivity to target gases as gas sensors. Subsequently, the latest developments in MHP-based gas sensors are summarized according to their different application scenarios. Finally, we conclude with the current status and challenges in this field and propose future perspectives.

Sabatier phenomenon in chemoselective gas-sensing reactions induced by Ag cluster coordination

The Sabatier principle in heterogeneous catalysis provides guidance for designing optimal catalysts with the highest activity. We report a new Sabatier phenomenon induced by nanoclusters on different atomic scales in gas-sensitive reactions. We prepared a series of Ag nanocluster catalysts with coordination structures ranging from Ag0 to Ag13 through a surface coordination strategy. When used as catalysts for gas-sensitive reactions, a volcano-type relationship between the coordination number of Ag nanoclusters and gas-sensitive activity emerges, with a summit at a moderate coordination of Ag5. Mechanistic studies show that the efficient adsorption of activated *C2H6O on electron-rich Ag5 clusters is a key factor for the Sabatier phenomenon (adsorption energy from -0.322 eV to -0.663 eV), which leads to highly selective sensing. We found that the catalyst electron-rich surface layer induced by Ag5 clusters serves as a descriptor to explain the structure-activity relationship. Furthermore, due to the well-defined geometric and electronic structures in the Ag5 clusters, the optimized catalyst achieves both maximum activity and selectivity in chemoselective sensing reactions. This study reveals the Sabatier principle and provides insightful guidance for the rational design of more efficient and practical nanocluster catalysts for heterogeneous catalysis.

Metal-Organic-Framework Derived Co-Mo Multimetal Oxide Semiconductors: Selective Trace-Level Hydrogen Sulfide Detection

The development of a highly selective and trace-level gas sensing platform for detecting hydrogen sulfide (H2S) remains a formidable challenge. To solve this problem, Co-Mo multimetal oxide semiconductors are rationally tailored by employing metal organic frameworks (MOFs) as self-sacrificial templates. The MOF-derived Co3O4/β-CoMoO4 based gas sensors displays high sensitivity (Rg/Ra = 22) to 10 ppm of H2S and ultralow limit of detection (10 ppb H2S). The formation of p-p heterojunction and multivalence states of Mo play a crucial role in electron transfer and oxygen adsorption. A sensor array constructed from four Co3O4/β-CoMoO4 materials with different Co/Mo ratios demonstrates a superior selective discrimination of H2S from other VOCs and malodorous gases by principal component analysis (PCA). Besides, a H2S gas sensing and alarming platform was designed for monitoring the environment contaminated with H2S. This finding provides a feasible approach for the discovery of highly efficient gas sensors to monitor environmental H2S concentration.

Heterostructured MoO3 Anchored Defect-Rich NiFe-LDH/NF as a Robust Self-Supporting Electrocatalyst for Overall Water Splitting

The rational design of inexpensive metal electrocatalysts with exciting catalytic activity for overall water splitting (OWS) remains a significant challenge. Heterostructures of NiFe layered double hydroxides (NiFe-LDHs) with abundant oxygen defects and tunable electronic properties have garnered considerable attention. Here, a self-supporting heterostructured catalyst (named MoO3/NiFe-NF) is synthesized via a hydrothermal method to grow NiFe-LDH with oxygen vacancies (OV) in situ on inexpensive nickel foam (NF). Subsequently, MoO3 is anchored and grown on the surface of NiFe-LDH by electrodeposition. The obtained catalysts achieved outstanding oxygen/hydrogen evolution reaction (OER/HER, 212 mV/85 mV@10 mA cm-2) performance in 1 m KOH. Additionally, when MoO3/NiFe-NF is utilized as the cathode and anode in OWS, a current density of 10 mA cm-2 can be obtained as an ultralow battery voltage of 1.43 V, a significantly lower value compared to the commercial electrolyzer incorporating Pt/C and IrO2 electrode materials. Finally, density functional theory (DFT) calculations and advanced spectroscopy technology are conducted to reveal the effects of heterojunctions and OV on the internal electronic structure of the electrical catalysts. Mainly, the present study provides a novel tactic for the rational design of remarkable, low-cost NiFe-LDH electrocatalysts with heterostructures for OWS.

High Response and Selectivity of the SnO2 Nanobox Gas Sensor for Ethyl Methyl Carbonate Leakage Detection in a Lithium-Ion battery

It is well-known that metal-oxide semiconductors (MOS) have significant gas sensing activity and are widely used in harmful gas monitoring in various environments. With the rapid development of new energy vehicles, the monitoring of the gas composition and concentration in LIB has become an effective way to avoid safety problems. However, the study of typical electrolyte solvent detection, such as EMC and DMC detection by the MOS sensor, is still in its infancy. Here, the SnO2 nanoboxes are synthesized by coordination dissolution using cubic Cu2O as the template, and its sensor shows high sensitivity (0.27 to 10 ppb EMC), excellent response (32.46 to 20 ppm EMC), and superior selectivity. Additionally, the sensor possesses fast and clear response to lithium-ion battery (LIB) leakage simulation tests, suggesting that it should be a promising candidate for LIB safety monitors. These sensing performances are attributed to large specific surface area, small grain size, and high size/thickness ratio of nanoboxes. More importantly, DFT calculations confirm the adsorption of EMC on the surface of the SnO2 nanoboxes, and the EMC decomposition processes catalyzed by SnO2 are deduced by in situ FTIR and GC-MS.

A Brief Review of MoO3 and MoO3-Based Materials and Recent Technological Applications in Gas Sensors, Lithium-Ion Batteries, Adsorption, and Photocatalysis

Molybdenum trioxide is an abundant natural, low-cost, and environmentally friendly material that has gained considerable attention from many researchers in a variety of high-impact applications. It is an attractive inorganic oxide that has been widely studied because of its layered structure, which results in intercalation ability through tetrahedral/octahedral holes and extension channels and leads to superior charge transfer. Shape-related properties such as high specific capacities, the presence of exposed active sites on the oxygen-rich structure, and its natural tendency to oxygen vacancy that leads to a high ionic conductivity are also attractive to technological applications. Due to its chemistry with multiple valence states, high thermal and chemical stability, high reduction potential, and electrochemical activity, many studies have focused on the development of molybdenum oxide-based systems in the last few years. Thus, this article aims to briefly review the latest advances in technological applications of MoO3 and MoO3-based materials in gas sensors, lithium-ion batteries, and water pollution treatment using adsorption and photocatalysis techniques, presenting the most relevant and new information on heterostructures, metal doping, and non-stoichiometric MoO3-x.

2D/2D Dy2O3 Nanosheet/MoO3 Nanoflake Heterostructures for Humidity-Independent and Sensitive Ammonia Detection

Chemiresistive ammonia gas (NH3) sensors have been playing a significant role in the fields of environmental protection, food safety monitoring, and air quality evaluation. Nevertheless, balancing the high sensitivity and humidity tolerance remains challenging. Herein, the two-dimensional (2D) heterostructures of molybdenum trioxide (MoO3) nanoflakes decorated with dysprosium oxide (Dy2O3) nanosheets (termed Dy2O3/MoO3) were synthesized via a facile probe-sonication method. With respect to pristine MoO3 counterparts, the optimal Dy2O3/MoO3 sensors possessed a 4.49-fold larger response at a lower temperature (30.52@328.2 °C vs 6.8@369.7 °C toward 10 ppm of NH3), shorter response/recovery times (11.6/2.9 s vs 26.9/43.4 s), 52.6-fold higher sensitivity (17.35/ppm vs 0.33/ppm), and a lower theoretical detection limit (1.02 vs 32.82 ppb). Besides the nice reversibility, wide detection range (0.45-100 ppm) and robust long-term stability, inspiringly, the Dy2O3/MoO3 sensors showed a nearly humidity-independent response. These impressive improvements in the NH3-sensing performance were attributed to numerous heterojunctions to strengthen the carrier concentration modulation and the compensation/protection effect of Dy2O3 to mitigate the humidity effect. Moreover, the Dy2O3/MoO3 sensors showed preliminary application potential in monitoring pork freshness. This work provides a universal methodology for constructing NH3 gas sensors with high sensitivity and good humidity resistance and probably extends the application scenarios of MoO3-based sensors in the Internet of Things in the future.

Stable photodegradation of antibiotics by the functionalized 3D-Bi2MoO6@MoO3/PU composite sponge: High efficiency pathways, optical properties and Z-scheme heterojunction mechanism

The designation and fabrication of heterogeneous photocatalyst with superior redox capability is an important technique for emerging pollutants treatment. In this study, we designed the Z-scheme heterojunction of stable 3D-Bi₂MoO₆@MoO₃/PU, which could not only accelerate the migration and separation in photogenerated carriers, but also stabilize the separation rate of photo-generation carriers. In the Bi₂MoO₆@MoO₃/PU photocatalytic system, 88.89% of oxytetracycline (OTC, 10 mg L^-1) and 78.25%-84.59% of multiple antibiotics (SDZ, NOR, AMX and CFX, 10 mg L^-1) could be decomposed within 20 min under the optimized reaction condition, revealing the superior performance and potential application value. Specifically, the morphology, chemical structure and optical properties detection of Bi₂MoO₆@MoO₃/PU greatly affected the direct Z-scheme electron transferring mode in the p-n type heterojunction. Besides, the ·OH, h⁺, ·O₂^- dominated the photoactivation process through ring-opening, dihydroxylation, deamination, decarbonization and demethylation in OTC decomposition. Expectantly, the stability and universality of Bi₂MoO₆@MoO₃/PU composite photocatalyst would further broaden the practical application and demonstrated that the potential of photocatalytic technique in antibiotics pollutants for wastewater remediation.

Current Trends in Nanomaterials for Metal Oxide-Based Conductometric Gas Sensors: Advantages and Limitations-Part 2: Porous 2D Nanomaterials

This article discusses the features of the synthesis and application of porous two-dimensional nanomaterials in developing conductometric gas sensors based on metal oxides. It is concluded that using porous 2D nanomaterials and 3D structures based on them is a promising approach to improving the parameters of gas sensors, such as sensitivity and the rate of response. The limitations that may arise when using 2D structures in gas sensors intended for the sensor market are considered.

Mesoporous WS2/MoO3 Hybrids for High-Performance Trace Ammonia Detection

Mesoporous WS₂/MoO₃ hybrids were synthesized by a facile two-step and additive-free hydrothermal approach and employed for high-performance trace ammonia gas (NH₃) detection. Compared with single WS₂ and MoO₃ counterparts, WS₂/MoO₃ sensors exhibited an improvement in NH₃-sensing performance at room temperature (22 ± 3 °C). Typically, the optimal WS₂/MoO₃ sensor showed a higher and quicker response of 31.58% within 57 s toward 3 ppm of NH₃, which was 17.7- and 57.4-fold larger than that of pure MoO₃ (1.78% within 251 s) and WS₂ (0.55% within 153 s) ones. Meanwhile, good reversibility, sensitivity, and selectivity, reliable long-term stability, and the lowest detection limit of 9.0 ppb were achieved. These superior properties were probably ascribed to numerous heterojunctions favorable for additional carrier-concentration modulation via the synergetic effect between WS₂ and MoO₃ components and the large specific surface area beneficial for richer sorption sites and faster molecular transfer at room temperature. Such achievements also imply that the designed WS₂/MoO₃ heterostructure nanomaterials have the potential in achieving trace NH₃ recognition catering for the requirements of high sensitivity and low power consumption in future gas sensors.