Ultrathin In2O3 Nanosheets with Uniform Mesopores for Highly Sensitive Nitric Oxide Detection

High-Performance Self-Powered Photoelectrochemical Ultraviolet Photodetectors Based on an In2O3 Nanocube Film

Ultraviolet photodetectors (UV PDs) have attracted significant attention due to their wide range of applications, such as underwater communication, biological analysis, and early fire warning systems. Indium oxide (In2O3) is a candidate for developing high-performance photoelectrochemical (PEC)-type UV PDs owing to its high UV absorption and good stability. However, the self-powered photoresponse of the previously reported In2O3-based PEC UV PDs is unsatisfactory. In this work, high-performance self-powered PEC UV PDs were constructed by using an In2O3 nanocube film (NCF) as a photoanode. In2O3 NCF photoanodes were synthesized on FTO by using hydrothermal methods with a calcining process. The influence of the electrolyte concentration, bias potential, and irradiation light on the photoresponse properties was systematically studied. In2O3 NCF PEC UV PDs exhibit outstanding self-powered photoresponses to 365 nm UV light with a high responsivity of 44.43 mA/W and fast response speed (20/30 ms) under zero bias potential, these results are superior to those of previously reported In2O3-based PEC UV PDs. The improved self-powered photoresponse is attributed to the higher photogenerated carrier separation efficiency and faster charge transport of the in-situ grown In2O3 NCF. In addition, these PDs exhibit excellent multicycle stability, maintaining the photocurrent at 98.69% of the initial value after 700 optical switching cycles. Therefore, our results prove the great promise of In2O3 in self-powered PEC UV PDs.

Facile preparation of Au-loaded mesoporous In2O3 nanoparticles with improved ethanol sensing performance

The in situ monitoring of toxic volatile organic compound gases using metal oxide-based gas sensors is still challenging. Herein, mesoporous In2O3 nanoparticles, assembled using smaller nanoparticles, were synthesized via a facile solvothermal method and used to load Au nanoparticles to prepare mesoporous Au/In2O3 for ethanol detection. The obtained In2O3 and Au/In2O3 were meticulously analysed by XRD, SEM, BET, TEM and XPS techniques. It was revealed that Au nanoparticles were uniformly distributed on mesoporous In2O3 nanoparticles. Notably, the obtained mesoporous 1% Au/In2O3 is highly sensitive to ethanol gas at an optimal working temperature of 180 °C, showing a response of 55 to 50 ppm of ethanol, which is considerably higher compared to that of In2O3 nanoparticles. The significantly enhanced sensitivity results from the electronic and chemical sensitization effects of Au nanoparticles. Moreover, the mesoporous Au/In2O3 nanoparticles also showed eminent selectivity, short response/recovery time, low detection limit, good linear relationship, superb repeatability, and wonderful long-term stability, suggesting that Au/In2O3 nanoparticles have great potential application for in situ monitoring of ethanol gas.

Surface-Modified In2O3 for High-Throughput Screening of Volatile Gas Sensors in Diesel and Gasoline

In this paper, with the help of the method of composite materials science, parallel synthesis and high-throughput screening were used to prepare gas sensors with different molar ratios of rare earths and precious metals modified In₂O₃, which could be used to monitor and warn the early leakage of gasoline and diesel. Through high-throughput screening, it is found that the effect of rare earth metal modification on gas sensitivity improvement is better than other metals, especially 0.5 mol% Gd modified In₂O₃ (Gd_0.5In) gas sensor has a high response to 100 ppm gasoline (R_a/R_g = 6.1) and diesel (R_a/R_g = 5) volatiles at 250 °C. Compared with the existing literature, the sensor has low detection concentration and suitable stability. This is mainly due to the alteration of surface chemisorption oxygen caused by the catalysis and modification of rare earth itself.

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.

Ultrathin In2 O3 Nanosheets toward High Responsivity and Rejection Ratio Visible-Blind UV Photodetection

Photoelectrochemical-type visible-blind ultraviolet photodetectors (PEC VBUV PDs) have gained ever-growing attention due to their simple fabrication processes, uncomplicated packaging technology, and high sensitivity. However, it is still challenging to achieve high-performance PEC VBUV PDs based on a single material with good spectral selectivity. Here, it is demonstrated that individual ultrathin indium oxide (In₂ O₃ ) nanosheets (NSs) are suitable for designing high-performance PEC VBUV PDs with high responsivity and UV/visible rejection ratio for the first time. In₂ O₃ NSs PEC PDs show excellent UV photodetection capability with an ultrahigh photoresponsivity of 172.36 mA W^-1 and a high specific detectivity of 4.43 × 10¹¹ Jones under 254 nm irradiation, which originates from the smaller charge transfer resistance (R_ct ) at the In₂ O₃ NSs/electrolyte interface. The light absorption of In₂ O₃ NSs takes a blueshift due to the quantum confinement effect, granting good spectral selectivity for visible-blind detection. The UV/visible rejection ratio of In₂ O₃ NSs PEC PDs is 1567, which is 30 times higher than that of In₂ O₃ nanoparticles (NPs) and exceeds all recently reported PEC VBUV PDs. Moreover, In₂ O₃ NSs PEC PDs show good stability and good underwater imaging capability. The results verify that ultrathin In₂ O₃ NSs have potential in underwater optoelectronic devices.

Recent Progress of Carbon Dots for Air Pollutants Detection and Photocatalytic Removal: Synthesis, Modifications, and Applications

Rapid industrialization has inevitably led to serious air pollution problems, thus it is urgent to develop detection and treatment technologies for qualitative and quantitative analysis and efficient removal of harmful pollutants. Notably, the employment of functional nanomaterials, in sensing and photocatalytic technologies, is promising to achieve efficient in situ detection and removal of gaseous pollutants. Among them, carbon dots (CDs) have shown significant potential due to their superior properties, such as controllable structures, easy surface modification, adjustable energy band, and excellent electron-transfer capacities. Moreover, their environmentally friendly preparation and efficient capture of solar energy provide a green option for sustainably addressing environmental problems. Here, recent advances in the rational design of CDs-based sensors and photocatalysts are highlighted. An overview of their applications in air pollutants detection and photocatalytic removal is presented, especially the diverse sensing and photocatalytic mechanisms of CDs are discussed. Finally, the challenges and perspectives are also provided, emphasizing the importance of synthetic mechanism investigation and rational design of structures.

Edge-enriched MoS2 nanosheets modified porous nanosheet-assembled hierarchical In2O3 microflowers for room temperature detection of NO2 with ultrahigh sensitivity and selectivity

Nitrogen dioxide (NO₂) is one of the most hazardous toxic pollutants to human health and the environment. However, deficiencies of low sensitivity and poor selectivity at room temperature (RT) restrain the application of NO₂ sensors. Herein, the edge-enriched MoS₂ nanosheets modified porous nanosheets-assembled three-dimensional (3D) In₂O₃ microflowers have been synthesized to improve the sensitivity and selectivity of NO₂ detection at RT. The results show that the In₂O₃/MoS₂ composite sensor exhibits a response as high as 343.09-5 ppm NO₂, which is 309 and 72.5 times higher than the sensors based on the pristine MoS₂ and In₂O₃. The composite sensor also shows short recovery time (37 s), excellent repeatability and long-term stability. Furthermore, the response of the In₂O₃/MoS₂ sensor to NO₂ is at least 30 times higher than that of other gases, proving the ultrahigh selectivity of the sensor. The outstanding sensing performance of the In₂O₃/MoS₂ sensor can be attributed to the synergistic effect and abundant active sites originating from the p-n heterojunction, exposed edge structures and the designed 2D/3D hybrid structure. The strategy proposed herein is expected to provide a useful reference for the development of high-performance RT NO₂ sensors.

The Combination of Two-Dimensional Nanomaterials with Metal Oxide Nanoparticles for Gas Sensors: A Review

Metal oxide nanoparticles have been widely utilized for the fabrication of functional gas sensors to determine various flammable, explosive, toxic, and harmful gases due to their advantages of low cost, fast response, and high sensitivity. However, metal oxide-based gas sensors reveal the shortcomings of high operating temperature, high power requirement, and low selectivity, which limited their rapid development in the fabrication of high-performance gas sensors. The combination of metal oxides with two-dimensional (2D) nanomaterials to construct a heterostructure can hybridize the advantages of each other and overcome their respective shortcomings, thereby improving the sensing performance of the fabricated gas sensors. In this review, we present recent advances in the fabrication of metal oxide-, 2D nanomaterials-, as well as 2D material/metal oxide composite-based gas sensors with highly sensitive and selective functions. To achieve this aim, we firstly introduce the working principles of various gas sensors, and then discuss the factors that could affect the sensitivity of gas sensors. After that, a lot of cases on the fabrication of gas sensors by using metal oxides, 2D materials, and 2D material/metal oxide composites are demonstrated. Finally, we summarize the current development and discuss potential research directions in this promising topic. We believe in this work is helpful for the readers in multidiscipline research fields like materials science, nanotechnology, chemical engineering, environmental science, and other related aspects.

Electrospun Bi-doped SnO2 porous nanosheets for highly sensitive nitric oxide detection

The real-time monitoring of NO in the low-concentration range from the ppb- to ppm-level is of great importance in the field of healthcare; however, accomplishing this is still challenging owing to the technical issues regarding highly efficient and selective sensing materials. In this study, we demonstrate the highly sensitive and selective detection of NO by Bi-doped SnO₂ two-dimensional ultrathin nanosheets with porous structures, fabricated using a facile one-step electrospinning method. It was found that the SnO₂ with 0.75 mol% Bi exhibits the highest sensitivity of 217-10 ppm of NO at a relatively low temperature of 75 °C. Further, a low detection limit of 50 ppb; high selectivity; and good stability have also been achieved. Further detailed analysis indicates that the promising sensing properties can be attributed to the ultrathin nanosheet structure, which has a high surface area and abundant pores. These results indicate that 2D metal-oxide ultrathin nanosheets achieve superior gas-sensing performance, and Bi-doped SnO₂ is a potential material for use in the real-time and low-power detection of NO.

In situtailoring the morphology of In(OH)3nanostructures via surfactants during anodization and their transformation into In2O3nanoparticles

The present work reports the effect of various surfactants on the morphology of In(OH)₃nanostructures prepared via anodization. In-sheets were anodized in an environmentally benign electrolyte containing a small quantity of CTAB, CTAC, and PDDA surfactants at room temperature. The produced nanostructures were characterized using XRD, HRTEM, SAED, and EDAX. The morphology of indium hydroxide (In(OH)₃) nanostructures was successfully tailoredin situwith the help of surfactants in 1 M KCl aqueous electrolyte. XRD results confirmed the formation of In(OH)₃and indium oxyhydroxide (InOOH) nanostructures in the pristine form which were transformed into single-phase cubic In₂O₃nanoparticles (NPs) after calcination. HRTEM analyses showed that the morphology and size of the In(OH)₃nanostructures can be tuned to form nanorods, nanosheets and nanostrips using different surfactants. The results revealed that CTAC and PDDA surfactants have a profound effect on the morphology of In(OH)₃nanostructure compared to CTAB due to the higher concentration of Cl^-ion. The possible mechanism of surfactants effect on the morphology is proposed. Furthermore, annealing converted the In(OH)₃nanostructures into spherical In₂O₃NPs with uniform and homogeneous size. We anticipate that the morphology of other metal-oxides nanostructure can be tuned using this simple, facile and rapid technique. In₂O₃NPs prepared without and with CTAB surfactant were further explored for the non-enzymatic detection of hydrogen peroxide (H₂O₂). Electrochemical measurements showed enhanced electrocatalytic performance with fast electron transfer (∼2s) between the redox centers of H₂O₂and electrode surface. The In₂O₃NPs prepared using CTAB/Au electrode exhibited about 4-fold increase in sensitivity compared to the bare Au electrode. The biosensor also demonstrated good reproducibility, higher selectivity, and increased shelf life.

Olivine-type cadmium germanate: a new sensing semiconductor for the detection of formaldehyde at the ppb level

In this study, for the first time, olivine-structured Cd2GeO4 was identified as an excellent formaldehyde sensing material, with a low detection limit of 60 ppb.

Negatively-Doped Single-Walled Carbon Nanotubes Decorated with Carbon Dots for Highly Selective NO2 Detection

In this study, we demonstrated a highly selective chemiresistive-type NO₂ gas sensor using facilely prepared carbon dot (CD)-decorated single-walled carbon nanotubes (SWCNTs). The CD-decorated SWCNT suspension was characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV-visible spectroscopy, and then spread onto an SiO₂/Si substrate by a simple and cost-effective spray-printing method. Interestingly, the resistance of our sensor increased upon exposure to NO₂ gas, which was contrary to findings previously reported for SWCNT-based NO₂ gas sensors. This is because SWCNTs are strongly doped by the electron-rich CDs to change the polarity from p-type to n-type. In addition, the CDs to SWCNTs ratio in the active suspension was critical in determining the response values of gas sensors; here, the 2:1 device showed the highest value of 42.0% in a sensing test using 4.5 ppm NO₂ gas. Furthermore, the sensor selectively responded to NO₂ gas (response ~15%), and to other gases very faintly (NO, response ~1%) or not at all (CO, C₆H₆, and C₇H₈). We propose a reasonable mechanism of the CD-decorated SWCNT-based sensor for NO₂ sensing, and expect that our results can be combined with those of other researches to improve various device performances, as well as for NO₂ sensor applications.

Thiourea-assistant growth of In2O3 porous pompon assembled from 2D nanosheets for enhanced ethanol sensing performance

The flower-like porous In₂O₃ pompon assembled from two-dimensional (2D) nanosheets was synthesized through a simple thiourea-assistant hydrothermal method following the annealed process. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images manifest that the In₂O₃ pompon possesses a clear porous structure with a nanosheet thickness of about 37.5 nm. Further, we compare the performance of intermediate products (In₂S₃, In₂S₃/In₂O₃) and In₂O₃ nanostructures as ethanol detection gas sensors. The fabrication of In₂O₃-based sensors exhibits enhanced ethanol sensing performance than that of In₂S₃/In₂O₃-based and In₂S₃-based sensors, which is mainly attributed to more chemical oxygen and oxygen vacancies on the material surface. The In₂O₃-based sensors for ethanol detection revealed a wide linear range from 2 ppm to 100 ppm, meanwhile the corresponding detection limits (LOD) as low as ~0.4 ppm at 260 °C. And the In₂O₃-based sensors also exhibit superior repeatability and reliable selectivity. The simple fabrication strategy of 2D nanosheets-assembled flower-like In₂O₃ porous pompon may facilitate other ethanol gas sensors production and other 2D metal oxide semiconductor materials-based sensors preparation.

Current Trends in Nanomaterials for Metal Oxide-Based Conductometric Gas Sensors: Advantages and Limitations. Part 1: 1D and 2D Nanostructures

This article discusses the main uses of 1D and 2D nanomaterials in the development of conductometric gas sensors based on metal oxides. It is shown that, along with the advantages of these materials, which can improve the parameters of gas sensors, there are a number of disadvantages that significantly limit their use in the development of devices designed for the sensor market.

Surface enhanced Raman spectroscopic studies on the adsorption behaviour of nitric oxide on a Ru covered Au nanoparticle film

Nitric oxide (NO) is very interesting because of its effects on air pollution and especially biological systems. The adsorption behavior of NO molecules has fundamental importance with great technical challenges due to complex processes and species identification. Herein, the NO adsorption behavior on a Ru surface has been investigated using well-designed surface enhanced Raman spectroscopy (SERS) substrates. A Au nanoparticle monolayer film on ITO was employed as the electrode and Ru layers were electrochemically deposited. The internal SERS effect from the Au nanoparticles with high sensitivity and the metallic surfaces of Ru with practical application were integrated into a composite Au/Ru substrate. The molecular adsorption and dissociation of NO were observed simultaneously by SERS. A competitive relationship between adsorption and dissociation was observed at higher NO pressure, and the 3-fold and 2-fold bridge and top adsorption configurations appeared on the surface and were associated with different ν_NO vibrational frequencies. The results indicated that 3-fold bridge sites are preferred for dissociation over other structures. The dissociation of NO produced adsorbed atomic nitrogen and oxygen species to form Ru–N and Ru–O bonds, respectively. The dissociation process, especially for linear NO, was site dependent and blocked at higher pressure or coverage. Due to the change in adsorption energy and coverage, a conversion of the adsorption configuration from bridge to top was observed in the initial stage of NO adsorption, and this was followed by a mixture of bridge and top configurations of NO and dissociated species. A two-step dissociation mechanism and the steps of NO adsorption were proposed. The present study suggested that the SERS technique with appropriate attractive metal overlayers provided a significant and possibly even a valuable approach to explore adsorption behavior and kinetics at gas–solid interfaces.

A SERS borrowing strategy with well-designed substrates has been developed to monitor the adsorption and dissociation of NO at Au/Ru surfaces.

SnS2/SnS p-n heterojunctions with an accumulation layer for ultrasensitive room-temperature NO2 detection

The unique features of SnS₂ make it a sensitive material ideal for preparing high-performance nitrogen dioxide (NO₂) gas sensors. However, sensors based on pristine tin disulfide (SnS₂) fail to work at room temperature (RT) owing to their poor intrinsic conductivity and weak adsorptivity toward the target gas, thereby impeding their wide application. Herein, an ultrasensitive and fully recoverable room-temperature NO₂ gas sensor based on SnS₂/SnS p-n heterojunctions with an accumulation layer was fabricated. The amounts of SnS₂/SnS heterojunctions can be effectively controlled by tuning the ratios of tin and sulfur precursors in the easy one-step solvothermal synthesis. Compared with pristine SnS₂, the conductivity of SnS₂/SnS heterostructures improved considerably. Such improvement was caused by the electron transfer from p-type SnS to n-type SnS₂ because the Fermi level of SnS was higher than that of SnS₂. The sensing response of optimized SnS₂/SnS toward 4 ppm NO₂ was 660% at room temperature, which was higher than most reported sensitivity values of other two-dimensional (2D) materials at room temperature. The superior sensing response of SnS₂/SnS heterostructures was attributed to the enhanced electron transport and the increased adsorption sites caused by the SnS₂/SnS p-n heterojunctions. Moreover, the SnS₂/SnS sensor showed good selectivity and long-term stability. These achievements of SnS₂/SnS heterostructured sensors make them highly desirable for practical applications.

ZIF-67-Derived 3D Hollow Mesoporous Crystalline Co3 O4 Wrapped by 2D g-C3 N4 Nanosheets for Photocatalytic Removal of Nitric Oxide

ZIF-67-derived 3D hollow mesoporous crystalline Co₃ O₄ wrapped by 2D graphitic carbon nitride (g-C₃ N₄ ) nanosheets are prepared by low temperature annealing, and are used for the photocatalytic oxidation of nitric oxide (NO) at a concentration of 600 ppb. The p-n heterojunction between Co₃ O₄ and g-C₃ N₄ forms a spatial conductive network frame and results in a broad visible light response range. The hollow mesoporous structure of Co₃ O₄ contributes to the circulation and adsorption of NO, and the large specific surface area exposes abundant active sites for the reaction of active species. A maximum NO degradation efficiency of 57% is achieved by adjusting the mass of the Co₃ O₄ precursor. Cycling tests and X-ray diffraction indicate the high stability and recyclability of the composite, making it promising in environmental purification applications.

Mechanistic Understanding of Cu-CHA Catalyst as Sensor for Direct NH3-SCR Monitoring: The Role of Cu Mobility

The concept to utilize a catalyst directly as a sensor is fundamentally and technically attractive for a number of catalytic applications, in particular, for the catalytic abatement of automotive emission. Here, we explore the potential of microporous copper-exchanged chabazite (Cu-CHA, including Cu-SSZ-13 and Cu-SAPO-34) zeolite catalysts, which are used commercially in the selective catalytic reduction of automotive nitrogen oxide emission by NH₃ (NH₃-SCR), as impedance sensor elements to monitor directly the NH₃-SCR process. The NH₃-SCR sensing behavior of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts at typical reaction temperatures (i.e., 200 and 350 °C) was evaluated according to the change of ionic conductivity and was mechanistically investigated by complex impedance-based in situ modulus spectroscopy. Short-range (local) movement of Cu ions within the zeolite structure was found to determine largely the NH₃-SCR sensing behavior of both catalysts. Formation of NH₃-solvated, highly mobile Cu^I species showed a predominant influence on the ionic conductivity of both catalysts and, consequently, hindered NH₃-SCR sensing at 200 °C. Density functional theory calculations over a model Cu-SAPO-34 system revealed that Cu^II reduction to Cu^I by coadsorbed NH₃ and NO weakened significantly the coordination of the Cu site to the CHA framework, enabling high mobility of Cu^I species that influences substantially the NH₃-SCR sensing. The in situ spectroscopic and theoretical investigations not only unveil the mechanisms of Cu-CHA catalyst as sensor elements for direct NH₃-SCR monitoring but also allow us to get insights into the speciation of active Cu sites in NH₃-SCR under different reaction conditions with varied temperatures and gas compositions.

Tailoring energy level and surface basicity of metal oxide semiconductors by rare-earth incorporation for high-performance formaldehyde detection

The elevated Fermi level and increased surface basicity of 5Y-In₂O₃ led to the improvement of response and selectivity towards formaldehyde.

Improved Room Temperature NO2 Sensing Performance of Organic Field-Effect Transistor by Directly Blending a Hole-Transporting/Electron-Blocking Polymer into the Active Layer

Over the past decades, organic field-effect transistor (OFET) gas sensors have maintained a rapid development. However, the majority of OFET gas sensors show insufficient detection capability towards oxidizing gases such as nitrogen oxide, compared with the inorganic counterpart. In this paper, a new strategy of OFET nitrogen dioxide (NO₂) gas sensor, consisting of poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(9-vinylcarbazole) (PVK) blend, is reported. Depending on the gate voltage, this sensor can operate in two modes at room temperature. Of the two modes exposed to NO₂ for 5 min, when the gate voltage is 0 V, the highest NO₂ responsivity of this OFET is >20 000% for 30 ppm (≈700% for 600 ppb) with the 1:1 P3HT/PVK blend, it is ≈40 times greater than that with the pure P3HT. The limit of detection of ≈300 ppb is achieved, and there is still room for improvement. While in the condition of -40 V, the response increases by 15 times than that with the pure P3HT. This is the first attempt to improve the OFET sensing performance using PVK, which usually functions as a hole-transport layer in the light- emitting device. The enhancement of sensing performance is attributed to the aggregation-controlling and hole-transporting/electron-blocking effect of PVK. This work demonstrates that the hole-transport material can be applied to improve the NO₂ sensor with simple solution process, which expands the material choice of OFET gas sensors.

Ultrafine Pt NPs-Decorated SnO2/α-Fe2O3 Hollow Nanospheres with Highly Enhanced Sensing Performances for Styrene

Styrene, a chronic toxic gas, is of great harm to human health. It is urgently required to develop a portable, efficient, and inexpensive method to detect this toxic gas. Chemiresistive gas sensor based on semiconductor metal-oxides is considered as one of the best candidate suited to above features, while its sensitivity and selectivity are not enough high for the applications. Herein, the ultrafine Pt NPs embellished SnO₂/α-Fe₂O₃ hollow nanoheterojunctions were achieved by in-situ reduction and subsequent calcination treatment. Particularly, such yielding products exhibited excellent styrene sensing performances with a detection limit of 50 ppb and extremely fast response/recovery time (3/15 s, respectively). More importantly, this SnO₂/α-Fe₂O₃/Pt sensing platform revealed improved styrene selectivity against other malodorous gases. Additionally, the significant enhancement for styrene sensing response was also obtained compared to other two sensors (pristine SnO₂ and SnO₂/α-Fe₂O₃, respectively). Further studies demonstrated that such enhanced performances possibly be owing to the "catalytic sensitization" effect driven by Pt NPs and "electronic sensitization" effect triggered through the formation of Schottky junction as well as n-n nanoheterojunction. Based on these sensing features, it is probably great promising in the detection of styrene gas in the future.

Zinc oxide-black phosphorus composites for ultrasensitive nitrogen dioxide sensing

Multi-layer black phosphorus (m-BP) has been successfully incorporated in zinc oxide (ZnO) hollow spheres, thus forming hetero-structured ZnO-BP composites; a study performed on their properties reveals that the BP environmental stability can be significantly enhanced by the introduction of ZnO, and the sensors based on ZnO-BP composites exhibit high response, fast response behavior, outstanding selectivity, and ultralow detection limit of 1 ppb towards NO₂ gas molecules. The ultrasensitive sensing performance is suggested to be due to the large surface area, excellent carrier mobility, and enhanced charge transfer of ZnO-BP in the presence of BP. Moreover, the mechanism of NO₂ sensing with ZnO-BP is confirmed by the calculations obtained from the first-principle studies.

Density Gradient Strategy for Preparation of Broken In2O3 Microtubes with Remarkably Selective Detection of Triethylamine Vapor

Tubule-like structured metal oxides, combined with macroscale pores onto their surfaces, can fast facilitate gas-accessible diffusion into the sensing channels, thus leading a promoted utilization ratio of sensing layers. However, it generally remains a challenge for developing a reliable approach to prepare them. Herein, this contribution describes a density gradient strategy for obtaining broken In₂O₃ microtubes from the In₂O₃ products prepared using a chemical conversion method. These In₂O₃ microtubes hold a diameter about 1.5 μm with many broken regions and massive ultrafine nanopores onto their surfaces. When employed as a sensing element for detection of triethylamine (TEA) vapor, these broken In₂O₃ microtubes exhibited a significant response toward TEA at 1-100 ppm and the lowest detected concentration can reach 0.1 ppm. In addition, an excellent selectivity of the sensor to TEA was also displayed, though upon exposure of other interfering vapors, including ammonia, methanol, ethanol, isopropanol, acetone, toluene, and hydrogen. Such promoted sensing performances toward TEA were ascribed to the broken configuration (superior gas permeability and high utilization ratio), one-dimensional configuration with less agglomerations, and low bond energy for C-N in a TEA molecule.

Hierarchical SnS2/SnO2 nanoheterojunctions with increased active-sites and charge transfer for ultrasensitive NO2 detection

SnS2 nanosheets with unique properties are excellent candidate materials for fabricating high-performance NO2 gas sensors. However, serious restacking and aggregation during sensor fabrication have greatly impacted the sensing response. In this study, flower-like hierarchical SnS2 was prepared by a simple microwave method and partially thermally oxidized to form hierarchical SnS2/SnO2 nanocomposites to further improve the sensing performance at low operating temperature. The fabricated SnS2/SnO2 sensor exhibited ultrahigh response (resistance ratio = 51.1) toward 1 ppm NO2 at 100 °C, roughly 10.2 times higher than that of pure SnS2 nanoflowers. The excellent and enhanced NO2 sensing performances of hierarchical SnS2/SnO2 nanocomposites were attributed to the novel hierarchical structure of SnS2 and the nanoheterojunction between SnS2 and the ultrafine SnO2 nanoparticles. The SnS2/SnO2 sensors also exhibited excellent selectivity and reliable repeatability. The simple fabrication of high performance sensing materials may facilitate the large-scale production of NO2 gas sensors.

One-Step Synthesis of Co-Doped In2O3 Nanorods for High Response of Formaldehyde Sensor at Low Temperature

Uniform and monodisperse Co-doped In₂O₃ nanorods were fabricated by a facile and environmentally friendly hydrothermal strategy that combined the subsequent annealing process, and their morphology, structure, and formaldehyde (HCHO) gas sensing performance were investigated systematically. Both pure and Co-doped In₂O₃ nanorods had a high specific surface area, which could offer abundant reaction sites to gas molecular diffusion and improve the response of the gas sensor. Results revealed that the In₂O₃/1%Co nanorods exhibited a higher response of 23.2 for 10 ppm of HCHO than that of the pure In₂O₃ nanorods by 4.5 times at 130 °C. More importantly, the In₂O₃/1%Co nanorods also presented outstanding selectivity and long-term stability. The superior gas sensing properties were mainly attributed to the incorporation of Co, which suggested the important role of the amount of oxygen vacancies and adsorbed oxygen in enhancing HCHO sensing performance of In₂O₃ sensors.

The Morphologies of the Semiconductor Oxides and Their Gas-Sensing Properties

Semiconductor oxide chemoresistive gas sensors are widely used for detecting deleterious gases due to low cost, simple preparation, rapid response and high sensitivity. The performance of gas sensor is greatly affected by the morphology of the semiconductor oxide. There are many semiconductor oxide morphologies, including zero-dimensional, one-dimensional, two-dimensional and three-dimensional ones. The semiconductor oxides with different morphologies significantly enhance the gas-sensing performance. Among the various morphologies, hollow nanostructures and core-shell nanostructures are always the focus of research in the field of gas sensors due to their distinctive structural characteristics and superior performance. Herein the morphologies of semiconductor oxides and their gas-sensing properties are reviewed. This review also proposes a potential strategy for the enhancement of gas-sensing performance in the future.

The effect of the phase structure on physicochemical properties of TMO materials: a case of spinel to bunsenite

It is worthwhile to comprehensively investigate the relationship between different phase structures and physicochemical properties of TMO materials.