RESUMEN

Constructing heterostructures is an effective way to improve the carrier mobility for metal oxide sensing material, since heterojunctions are usually built only on the surface of the material, the carrier transport efficiency inside the material still needs to be improved. In this paper, BiVO4 nanocrystals (BVO NCs) with an average size of 1 nm generated by pulsed laser irradiation were embedded in situ at the particle boundaries (PBs) of SnO2 nanofibers to form an effective n-n heterojunctions inside the material. After embedding the BVO NCs in the SnO2 samples, the response value for 10 ppm NO was improved to 48.91, which was 2.5 times higher than that of pure SnO2 at near room temperature (50 °C). Meanwhile, the detection limit was lowered to 50 ppb with excellent long term stability. Detailed analysis and theoretical calculations demonstrated that the formation of abundant n-n heterojunctions not only promotes the electron-hole separation and the carrier mobility, but also reduces the conductivity and adsorption energy of the material, which significantly improves its sensing performance. This work demonstrates a new approach to modulate the gas-sensing performance of metal oxide semiconductors by generating heterostructure inside the bulk of the material.

RESUMEN

Organic field-effect transistor (OFET) gas sensors based on conjugated polymer films have recently attracted considerable attention for use in environmental monitoring applications. However, the existing devices are limited by their poor sensing performance for gas analytes. This drawback is attributed to the low charge transport in and the limited charge-analyte interaction of the conjugated polymers. Herein, we demonstrate that the incorporation of graphitic carbon nitride (g-C3N4) into the conjugated polymer matrix can improve the sensing performance of OFET gas sensors. Moreover, the effect of graphitic carbon nitride (g-C3N4) on the gas sensing properties of OFET sensors based on poly(3-hexylthiophene) (P3HT), a conjugated polymer, was systematically investigated by changing the concentration of the g-C3N4 in the P3HT/g-C3N4 composite films. The obtained films were applied in OFET to detect NO gas at room temperature. In terms of the results, first, the P3HT/g-C3N4 composite films containing 10 wt.% g-C3N4 exhibited a maximum charge carrier mobility of ~1.1 × 10-1 cm2 V-1 S-1, which was approximately five times higher than that of pristine P3HT films. The fabricated P3HT/g-C3N4 composite film based OFET sensors presented significantly enhanced NO gas sensing characteristics compared to those of the bare P3HT sensor. In particular, the sensors based on the P3HT/g-C3N4 (90/10) composite films exhibited the best sensing performance relative to that of the bare P3HT sensor when exposed to 10 ppm NO gas: responsivity = 40.6 vs. 18.1%, response time = 129 vs. 142 s, and recovery time = 148 vs. 162 s. These results demonstrate the enormous promise of g-C3N4 as a gas sensing material that can be hybridized with conjugated polymers to efficiently detect gas analytes.

Asunto(s)

RESUMEN

We fabricated a gas sensor with a wide-bandgap ZnGa2O4 (ZGO) epilayer grown on a sapphire substrate by metalorganic chemical vapor deposition. The ZGO presented (111), (222) and (333) phases demonstrated by an X-ray diffraction system. The related material characteristics were also measured by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. This ZGO gas sensor was used to detect nitric oxide (NO) in the parts-per-billion range. In this study, the structure effect on the response of the NO gas sensor was studied by altering the sensor dimensions. Two approaches were adopted to prove the dimension effect on the sensing mechanism. In the first approach, the sensing area of the sensors was kept constant while both channel length (L) and width (W) were varied with designed dimensions (L × W) of 60 × 200, 80 × 150, and 120 ×100 µm2. In the second, the dimensions of the sensing area were altered (60, 40, and 20 µm) with W kept constant. The performance of the sensors was studied with varying gas concentrations in the range of 500 ppb~10 ppm. The sensor with dimensions of 20 × 200 µm2 exhibited a high response of 11.647 in 10 ppm, and 1.05 in 10 ppb for NO gas. The sensor with a longer width and shorter channel length exhibited the best response. The sensing mechanism was provided to explain the above phenomena. Furthermore, the reaction between NO and the sensor surface was simulated by O exposure of the ZGO surface in air and calculated by first principles.

RESUMEN

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.

RESUMEN

Gas sensors based on hybrid materials of graphene oxide/metal oxide semiconductors are an effective way to improve sensor performance. In this paper, we demonstrate a high-performance nitric oxide (NO) gas sensor based on nitrogen-doped reduced graphene oxide/ZnO nanocrystals (N-rGO/ZnO) operating at a low work temperature. ZnO nanocrystals, with an average size of approximately 5 nm, can be uniformly and compactly anchored on the surface of N-rGO using a facile two-step hydrothermal synthesis with an appropriate amount of ammonia as the nitrogen source. The sensor based on the N-rGO/ZnO composite with 0.3 mL of ammonia (N-rGO/ZnO-0.3), in comparison with N-rGO/ZnO with different amounts of ammonia, N-rGO, and rGO/ZnO, exhibited a significantly higher sensitivity (S = Rg/Ra) at the parts per billion (ppb) level for NO gas at 90 °C. The maximum sensitivity at 800 ppb NO was approximately 22, with much faster response and recovery times. In addition, the N-rGO/ZnO-0.3 sensor revealed great stability, a low detection limit of 100 ppb, and an excellent selectivity toward NO versus other gases (NO2, H2, CO, NH3, and CH4), especially at the ppb level. More interestingly, when exposed to oxidizing and reducing gases, unlike conventional semiconductor sensitive materials with resistances that normally change in the opposite direction, only the increase in the resistance is surprisingly and incomprehensibly observed for the N-rGO/ZnO-0.3 sensor. The peculiar sensing behaviors cannot be explained by the conventional theory of the adsorption process, redox reactions on the surfaces, and the well-defined p-n junction between N-rGO and ZnO, originating from the chemical bonding of Zn-C. We propose here for the first time that switchable contribution from dual-conduction paths including the corresponding ZnO channel with the p-n junction and the corresponding N-rGO channel to the sensitivity may exist in the interaction between gases and N-rGO/ZnO-0.3 material. When an oxidizing gas (such as NO) is exposed to the N-rGO/ZnO-0.3 sensor, the contribution from the conductive channel of ZnO nanoparticles and the p-n junction to the sensitivity is dominant. On the contrary, as for a reducing gas (such as H2), the contribution alters to the N-rGO channel as the dominating mode for sensitivity. For gas-sensing behavior of the NGZ-0.1 and NGZ-0.5 sensors, there is only one conduction path from the N-rGO channel for the sensitivity. The model of switchable dual-conduction paths has addressed the mysterious response observed for different gases, which may be utilized to enlighten the understanding of other application problems in nanoscale hybrid materials with a heterogeneous structure.

RESUMEN

Herein, we demonstrate the ultraviolet (UV) light activated high-performance room-temperature NO gas sensor based on nitrogen-doped graphene quantum dots (NGQDs)-decorated TiO2 hybrid structure. TiO2 employed in the form of {001} facets exposed rectangular nanoplate morphology, which is highly reactive for the adsorption of active oxygen species. NGQD layers are grown on TiO2 nanoplates by graphitization of precursors via hydrothermal treatment. The decoration of NGQDs on the TiO2 surface dramatically enhanced the efficiency of gas and carriers exchange, charge carrier separation and transportation, and oxygen vacancies, which eventually improved the sensing performance. At room temperature, the TiO2@NGQDs hybrid structure exhibited a response of 12.0% to 100 ppm NO, which is 4.8 times higher compared to that of pristine TiO2 nanoplates. The response of TiO2@NGQDs hybrid structure is further upgraded by employing the ultraviolet light illumination and manipulating the operating temperature. Under the UV (λ = 365 nm) illumination at room temperature, the hybrid structure response escalated to ∼31.1% for 100 ppm NO. On the other hand, the tailoring of working temperature yielded a response of ∼223% at an optimum operating temperature of 250 °C. The NO gas-sensing mechanism of TiO2@NGQDs nanoplate's hybrid structure sensors under UV illumination and different working temperatures is discussed.

RESUMEN

Fast, sensitive, and precise detection of nitric oxide (NO) is critical to many applications in environmental monitoring and early disease diagnosis via respiratory testing. An effective detection system requires a sensor to detect NO gas at the parts per billion (ppb) level, and this system should possess a high degree of anti-interference selectivity. To achieve these targets, a series of gas sensor thin films based on intrinsic WO3, one-additive-doped WO3 (prepared by doping In2O3 or Nb2O5), and two-additive-doped WO3 (synthesized by doping with In2O3 and Nb2O5) oxides were successfully grown. By analyzing the properties of sensitivity, selectivity, responsiveness, and recovery time of the gas sensors, we found that WO3-1wt%In2O3-1wt%Nb2O5 has overwhelming advantages over intrinsic WO3, WO3-In2O3, and WO3-Nb2O5. A sensing response value of 2.4 was observed for NO concentrations as low as 20 ppb from the WO3-1wt%In2O3-1wt%Nb2O5 sensor. With 100 ppb NO gas, the WO3-1wt%In2O3-1wt%Nb2O5 sensor achieved a high response of 56.1 at 70 °C, which is a state-of-the-art performance for NO detection at low working temperature settings. WO3-1wt%In2O3-1wt%Nb2O5 also yields significantly improved selectivity and stability over intrinsic WO3, WO3-In2O3, and WO3-Nb2O5. Studies on the sensing mechanism show that the grain size, rather than the n-n heterostructure effect, plays a dominant role in the observed results. By decreasing the grain size so that it is close to the thickness of the space-charge layer, the sensing response is enhanced. Although room remains to further improve the sensing properties, the performance of WO3-1wt%In2O3-1wt%Nb2O5 is sufficient for implementation in low-content NO detection devices.

RESUMEN

In this work, the fabrication of single titanium oxide nanodot (ND) resistive sensors for NO gas sensing at room temperature is reported. Two atomic force microscopy nanolithography methods, nanomachining and nano-oxidation, are employed. A single titanium nanowire (NW) is created first along with contact electrodes and a single titanium oxide ND is subsequently produced in the NW. Gas sensing is realized by the photo-activation and the photo-recovery approaches. It is found that a sensor with a smaller ND has better performance than a larger one. A response of 31%, a response time of 91 s, and a recovery time of 184 s have been achieved at a concentration of 10 ppm for a ND with a size of around 80 nm. The present work demonstrates the potential application of single metal oxide NDs for gas sensing with a performance that is comparable with that of metal oxide nanowire gas sensors.