Gas sensitivity and sensing mechanism studies on Au-doped TiO₂ nanotube arrays for detecting SF₆ decomposed components

Experimental Studies on TiO2 NT with Metal Dopants through Co-Precipitation, Sol-Gel, Hydrothermal Scheme and Corresponding Computational Molecular Evaluations

In the last decade, TiO₂ nanotubes have attracted the attention of the scientific community and industry due to their exceptional photocatalytic properties, opening a wide range of additional applications in the fields of renewable energy, sensors, supercapacitors, and the pharmaceutical industry. However, their use is limited because their band gap is tied to the visible light spectrum. Therefore, it is essential to dope them with metals to extend their physicochemical advantages. In this review, we provide a brief overview of the preparation of metal-doped TiO₂ nanotubes. We address hydrothermal and alteration methods that have been used to study the effects of different metal dopants on the structural, morphological, and optoelectrical properties of anatase and rutile nanotubes. The progress of DFT studies on the metal doping of TiO₂ nanoparticles is discussed. In addition, the traditional models and their confirmation of the results of the experiment with TiO₂ nanotubes are reviewed, as well as the use of TNT in various applications and the future prospects for its development in other fields. We focus on the comprehensive analysis and practical significance of the development of TiO₂ hybrid materials and the need for a better understanding of the structural-chemical properties of anatase TiO₂ nanotubes with metal doping for ion storage devices such as batteries.

Pd-Decorated WTe2 Monolayer as a Favorable Sensing Material toward SF6 Decomposed Species: A DFT Study

Based on density functional theory, this work first investigates the Pd-decorating property on the pristine WTe₂ monolayer and then simulates the adsorption performance of a Pd-decorated WTe₂ (Pd-WTe₂) monolayer on SO₂ and SOF₂ molecules, in order to explore its sensing potential for SF₆ decomposed species. It is found that the Pd atom can be stably anchored on the top of the W atom of the WTe₂ monolayer with a binding energy of -2.43 eV. The Pd-WTe₂ monolayer performs chemisorption on SO₂ and SOF₂, with adsorption energies of -1.36 and -1.17 eV, respectively. The analyses of the band structure and density of states reveal the deformed electronic property of the WTe₂ monolayer by Pd-decoration, as well as that of the Pd-WTe₂ monolayer by gas adsorption. The bandgap of the Pd-Wte₂ monolayer is increased by 1.6% in the SO₂ system and is decreased by -3.9% in the SOF₂ system, accounting for the sensing response of 42.0 and -56.7% for the detection of two gases. Moreover, the changed work function (WF) in two gas systems in comparison with that of the pristine Pd-WTe₂ monolayer suggests its potential as a WF-based gas sensor for sensing two gases as well. This paper uncovers the gas sensing potential of the Pd-WTe₂ monolayer to evaluate the operation status of SF₆ insulation devices, which also illustrates the strong potential of WTe₂-based materials for gas sensing applications in some other fields.

Theoretical Study of Adsorption Behavior of Dimethylamine and Ammonia on Al- and Ga-Doped BN Monolayer Surfaces Based on DFT

Endogenous volatile organic compounds (VOCs) can reflect human health status and be used for clinical diagnosis and health monitoring. Dimethylamine and ammonia are the signature VOC gases of nephropathy. In order to find a potential gas sensitivity material for the detection of both signature VOC gases of nephropathy, this paper investigated the adsorption properties of dimethylamine and ammonia on Al- and Ga-doped BN monolayers based on density functional theory. Through analyzing the adsorption energy, adsorption distance, charge transfer, density of states, and HOMO/LUMO, the results indicated that the adsorption effect of Al- and Ga-doped BN monolayers to dimethylamine and ammonia is probably good, and these nanomaterials have the potential to be applied for nephropathy monitoring and clinical diagnosis.

TiO2 Gas Sensors Combining Experimental and DFT Calculations: A Review

Gas sensors play an irreplaceable role in industry and life. Different types of gas sensors, including metal-oxide sensors, are developed for different scenarios. Titanium dioxide is widely used in dyes, photocatalysis, and other fields by virtue of its nontoxic and nonhazardous properties, and excellent performance. Additionally, researchers are continuously exploring applications in other fields, such as gas sensors and batteries. The preparation methods include deposition, magnetron sputtering, and electrostatic spinning. As researchers continue to study sensors with the help of modern computers, microcosm simulations have been implemented, opening up new possibilities for research. The combination of simulation and calculation will help us to better grasp the reaction mechanisms, improve the design of gas sensor materials, and better respond to different gas environments. In this paper, the experimental and computational aspects of TiO2 are reviewed, and the future research directions are described.

Nanostructured Metal Oxide Semiconductors towards Greenhouse Gas Detection

Climate change and global warming are two huge current threats due to continuous anthropogenic emissions of greenhouse gases (GHGs) in the Earth’s atmosphere. Accurate measurements and reliable quantifications of GHG emissions in air are thus of primary importance to the study of climate change and for taking mitigation actions. Therefore, the detection of GHGs should be the first step when trying to reduce their concentration in the environment. Throughout recent decades, nanostructured metal oxide semiconductors have been found to be reliable and accurate for the detection of many different toxic gases in air. Thus, the aim of this article is to present a comprehensive review of the development of various metal oxide semiconductors, as well as to discuss their strong and weak points for GHG detection.

InP3 Monolayer as a Promising 2D Sensing Material in SF6 Insulation Devices

In this letter, we perform a first-principles study on the adsorption performance of the InP3 monolayer upon three SF6 decomposed species, including SO2, SOF2, and SO2F2, to investigate its potential as a resistance-type, optical or field-effect transistor gas sensor. Results indicate that the InP3 monolayer exhibits strong chemisorption upon SO2 but weak physisorption upon SO2F2. The most admirable adsorption behavior is upon SOF2, which provides a favorable sensing response (-19.4%) and recovery property (10.4 s) at room temperature as a resistance-type gas sensor. A high response of 180.7% upon SO2 and a poor one of -1.9% upon SO2F2 are also identified, which reveals the feasibility of the InP3 monolayer as a resistance-type sensor for SO2 detection with recycle use via a heating technique to clean the surface. Moreover, the InP3 monolayer is a promising optical sensor for SO2 detection due to the obvious changes in adsorption peaks within the range of ultraviolet and is a desirable field-effect transistor sensor for selective and sensitive detection of SO2 and SOF2 given the evident changes of Q T and E g under the applied electric field.

First-Principles Calculations for Adsorption of HF, COF2, and CS2 on Pt-Doped Single-Walled Carbon Nanotubes

HF, CS₂, and COF₂ are three important decomposition components of the SF₆ gas insulation medium. In this paper, the gas sensitivity of Pt doped on (8, 0) single-walled carbon nanotube (SWCNT) to HF, CS₂, and COF₂ is investigated based on density functional theory. The binding energy, charge transfer, density of states, and frontier molecular orbital theory are discussed. It is found that all processes of HF, CS₂, and COF₂ adsorbed on Pt-SWCNT are exothermic. Pt-SWCNT donated 0.182 electrons to CS₂ molecules during the interaction process but acts as an electron acceptor during adsorption of HF and COF₂ on it. After comprehensive consideration of binding energy and charge transfer, the response of Pt- SWCNT to CS₂ may be the best, and those to HF and COF₂ are almost the same. In addition, after the adsorption of the three kinds of gases on Pt-SWCNT, the order of the conductivity of the Pt-SWCNT material is CS₂ > COF₂ ≈ HF via frontier molecular orbital theory analysis. The Pt-SWCNT material is probably more suitable as a gas sensor for the detection of CS₂ in the application of gas-insulated equipment.

SF6 decomposed gas sensing performance of van der Waals layered cobalt oxyhydroxide: insights from a computational study

The detection of SF₆ decomposition products plays a significant part in identifying and assessing the electric discharge faults in SF₆ insulation equipment. We performed dispersion corrected density functional theory calculations to study the adsorption performance of CoOOH upon SO₂, SF₄, SOF₂, CF₄, and SO₂F₂ toxic gases, to investigate their potential application as a gas sensor. The results clearly show a weak force between the CoOOH sheet, and the molecular gas with moderate adsorption strength enhances the desorption processes. According to Löwdin charge population analysis, electrons transfer from the molecular gas to the CoOOH surface, where the molecular gas behaves like an electron donor. The lower bandgap energy of the adsorption systems compared with pristine CoOOH significantly increases its electrical conductivity and gas sensing performance. The higher charge transfer and adsorption energy of the SOF₂ adsorption system compared with the other four molecular gas is due to orbital hybridization around the Fermi energy. The theoretical computed adsorption energy with ultrahigh sensitivity and fast recovery time suggests that SF₆ decomposed gases reusability is achieved with CoOOH as a resistance-type gas sensor.

Room temperature monitoring of SF6decomposition byproduct SO2F2based on TiO2/NiSO4composite nanofibers

Sulfuryl fluoride (SO₂F₂) is one of the ideal decomposition components of sulfur hexafluoride (SF₆), which is widely used as an insulating and arc extinguishing medium in gas-insulated switchgear. To detect the decomposition component of SF₆at room temperature, the use of SO₂F₂is still a challenge. In this work, we have successfully fabricated TiO₂nanofibers and nickel sulfate (NiSO₄NPs) via simple electrospun and hydrothermal methods, followed by calcination process to improve the sensing performance. Metal oxide semiconductor materials (MOSs) are widely used in gas sensing applications due to their superior performance and fast recovery speed. Although the performance of our TiO₂/NiSO₄composite nanofiber sensor decreases at higher temperatures, it shows an excellent response to target gasses at room temperature. Ni-decoration on the outer surface of the nanofibers could maximize the sensing response of 100 ppm SO₂F₂by up to 189% at room temperature, showing that the TiO₂/NiSO₄composite nanofibers are 2.5 times superior to the pure TiO₂nanofiber sensors. Thus, the approach for this novel composite nanofiber-based material is promising for the fabrication of superior gas sensors for decomposition of SF₆.

Multicomponent SF6 decomposition product sensing with a gas-sensing microchip

A difficult issue restricting the development of gas sensors is multicomponent recognition. Herein, a gas-sensing (GS) microchip loaded with three gas-sensitive materials was fabricated via a micromachining technique. Then, a portable gas detection system was built to collect the signals of the chip under various decomposition products of sulfur hexafluoride (SF₆). Through a stacked denoising autoencoder (SDAE), a total of five high-level features could be extracted from the original signals. Combined with machine learning algorithms, the accurate classification of 47 simulants was realized, and 5-fold cross-validation proved the reliability. To investigate the generalization ability, 30 sets of examinations for testing unknown gases were performed. The results indicated that SDAE-based models exhibit better generalization performance than PCA-based models, regardless of the magnitude of noise. In addition, hypothesis testing was introduced to check the significant differences of various models, and the bagging-based back propagation neural network with SDAE exhibits superior performance at 95% confidence.

Platinum-Doped Anatase (101) Surface as Promising Gas-Sensor Materials for HF, CS2, and COF2: A Density Functional Theory Study

In order to find promising sensor materials for HF, CS₂, and COF₂ detection to realize the online internal insulation defect diagnosis of a SF₆ gas electrical device, the gas sensing property, binding energy, adsorption distance, charge transfer, and density of states distribution, of Pt-doped anatase TiO₂ (101) surfaces on HF, CS₂, and COF₂ gas molecules was calculated and analyzed in this paper based on the density functional theory. The work suggested that the Pt-TiO₂ surface has a nice gas sensing upon CS₂ and COF₂ because of the increase of the conductivity of the Pt-TiO₂ surface and the suitable adsorption parameter after CS₂ and COF₂ adsorbing on it. However, this material is not suitable as a gas sensor for HF gas. All of the works provide theoretical adsorption information of Pt-TiO₂ as a gas sensor material for HF, CS₂, and COF₂ detection.

Adsorption Property of CS2 and COF2 on Nitrogen-Doped Anatase TiO2(101) Surfaces: A DFT Study

SF6 has been utilized widely as an electrical insulation medium because of its excellent arc extinguishing performance and insulation characteristics. In this paper, the adsorption property of two kinds of key SF6 carbon-containing decomposition components (CS2 and COF2) on nitrogen-doped anatase TiO2(101) (N-TiO2) surfaces was simulated and analyzed based on density functional theory. The results demonstrated that N-TiO2 shows good gas sensitivity toward CS2 with the increase of conductivity but is insensitive toward COF2. In addition, the gas-sensing property of CS2 on N-TiO2 is stronger than that of COF2. This work provides the theoretical information on such a gas-sensitive material for key SF6 carbon-containing decomposition components, supporting its utilization as a chemical sensor applied in condition monitoring and defect diagnosis in SF6 gas-insulated equipment based on decomposition component analysis.

Multivariate Evaluation Method for Screening Optimum Gas-Sensitive Materials for Detecting SF6 Decomposition Products

In previous studies, the selection of optimal gas-sensing materials for detecting target gases mainly relied on their response value, but other indices, such as the recovery capability of materials, have usually been overlooked. Here, we propose a new method for evaluating sensor effectiveness that includes a broader range of performance indices. In this study, four gas sensors based on metal-oxide semiconductors (WO₃, CeO₂, In₂O₃, and SnO₂) were used as examples, and their performance in the detection of four decomposition products of sulfur hexafluoride (SF₆) was investigated. After gas-sensing experiments, values for working temperature, response value, and recovery capability were obtained. A multivariate evaluation method of mixing principal component analysis, information entropy, and variation coefficient was developed to calculate the weights of various indices, and the sensors' optimal working temperatures could be identified quantitatively. Using five variables (working temperature, response value, recovery capability, fluctuation rate, and detection limit), we continued to apply this multivariate evaluation method to calculate the weights and acquire comprehensive scores for the four sensors. Finally, these scores were used to identify the optimal materials for detecting SF₆ decomposition products. This procedure has the potential for selecting the best sensors for other gases.

IoT-Enabled Gas Sensors: Technologies, Applications, and Opportunities

Ambient gas detection and measurement had become essential in diverse fields and applications, from preventing accidents, avoiding equipment malfunction, to air pollution warnings and granting the correct gas mixture to patients in hospitals. Gas leakage can reach large proportions, affecting entire neighborhoods or even cities, causing enormous environmental impacts. This paper elaborates on a deep review of the state of the art on gas-sensing technologies, analyzing the opportunities and main characteristics of the transducers, as well as towards their integration through the Internet of Things (IoT) paradigm. This should ease the information collecting and sharing processes, granting better experiences to users, and avoiding major losses and expenses. The most promising wireless-based solutions for ambient gas monitoring are analyzed and discussed, open research topics are identified, and lessons learned are shared to conclude the study.

Porous TiO₂-Based Gas Sensors for Cyber Chemical Systems to Provide Security and Medical Diagnosis

Gas sensors play an important role in our life, providing control and security of technical processes, environment, transportation and healthcare. Consequently, the development of high performance gas sensor devices is the subject of intense research. TiO₂, with its excellent physical and chemical properties, is a very attractive material for the fabrication of chemical sensors. Meanwhile, the emerging technologies are focused on the fabrication of more flexible and smart systems for precise monitoring and diagnosis in real-time. The proposed cyber chemical systems in this paper are based on the integration of cyber elements with the chemical sensor devices. These systems may have a crucial effect on the environmental and industrial safety, control of carriage of dangerous goods and medicine. This review highlights the recent developments on fabrication of porous TiO₂-based chemical gas sensors for their application in cyber chemical system showing the convenience and feasibility of such a model to provide the security and to perform the diagnostics. The most of reports have demonstrated that the fabrication of doped, mixed and composite structures based on porous TiO₂ may drastically improve its sensing performance. In addition, each component has its unique effect on the sensing properties of material.

Synthesis, Characterization and Enhanced Sensing Properties of a NiO/ZnO p-n Junctions Sensor for the SF₆ Decomposition Byproducts SO₂, SO₂F₂, and SOF₂

The detection of partial discharge and analysis of the composition and content of sulfur hexafluoride SF₆ gas components are important to evaluate the operating state and insulation level of gas-insulated switchgear (GIS) equipment. This paper reported a novel sensing material made of pure ZnO and NiO-decorated ZnO nanoflowers which were synthesized by a facile and environment friendly hydrothermal process for the detection of SF₆ decomposition byproducts. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the structural and morphological properties of the prepared gas-sensitive materials. Planar-type chemical gas sensors were fabricated and their gas sensing performances toward the SF₆ decomposition byproducts SO₂, SO₂F₂, and SOF₂ were systemically investigated. Interestingly, the sensing behaviors of the fabricated ZnO nanoflowers-based sensor to SO₂, SO₂F₂, and SOF₂ gases can be obviously enhanced in terms of lower optimal operating temperature, higher gas response and shorter response-recovery time by introducing NiO. Finally, a possible gas sensing mechanism for the formation of the p–n junctions between NiO and ZnO is proposed to explain the enhanced gas response. All results demonstrate a promising approach to fabricate high-performance gas sensors to detect SF₆ decomposition byproducts.

Continuous microfluidic synthesis of colloidal ultrasmall gold nanoparticles:in situstudy of the early reaction stages and application for catalysis

The formation of gold nanoparticles in the first 2–20 ms of the reaction was studiedin situwith XAS using microfluidics.

Investigation of Gas-Sensing Property of Acid-Deposited Polyaniline Thin-Film Sensors for Detecting H₂S and SO₂

Latent insulation defects introduced in manufacturing process of gas-insulated switchgears can lead to partial discharge during long-time operation, even to insulation fault if partial discharge develops further. Monitoring of decomposed components of SF₆, insulating medium of gas-insulated switchgear, is a feasible method of early-warning to avoid the occurrence of sudden fault. Polyaniline thin-film with protonic acid deposited possesses wide application prospects in the gas-sensing field. Polyaniline thin-film sensors with only sulfosalicylic acid deposited and with both hydrochloric acid and sulfosalicylic acid deposited were prepared by chemical oxidative polymerization method. Gas-sensing experiment was carried out to test properties of new sensors when exposed to H₂S and SO₂, two decomposed products of SF₆ under discharge. The gas-sensing properties of these two sensors were compared with that of a hydrochloric acid deposited sensor. Results show that the hydrochloric acid and sulfosalicylic acid deposited polyaniline thin-film sensor shows the most outstanding sensitivity and selectivity to H₂S and SO₂ when concentration of gases range from 10 to 100 μL/L, with sensitivity changing linearly with concentration of gases. The sensor also possesses excellent long-time and thermal stability. This research lays the foundation for preparing practical gas-sensing devices to detect H₂S and SO₂ in gas-insulated switchgears at room temperature.

Low-temperature liquid phase reduced TiO2 nanotube arrays: synergy of morphology manipulation and oxygen vacancy doping for enhancement of field emission

The partially reduced TiO(2) nanotube arrays (TNAs) are prepared via an uncomplicated and low-cost liquid phase reduction strategy using NaBH(4) as the reducing agent. By controlling and adjusting the reduction temperatures from 30 to 90 °C, the reduction treatment can not only change their surface morphology but also introduce oxygen vacancies into them, resulting in an optimized morphology, elevated Fermi-level, reduced effective work function and improved conductivity of the TNAs. Meanwhile, the thermal and long-term stability of oxygen vacancy are also investigated, indicating that the oxygen vacancies retain long-term stability from room temperature up to 150 °C. More interesting, partially reduced TNAs show drastically enhanced field emission (FE) performances including substantially decreased turn-on field from 18.86 to 1.53 V μm(-1), a high current density of 4.00 mA cm(-2) at 4.52 V μm(-1), and an excellent FE stability and repeatability. These very promising results are attributed to the combination of the optimized morphology and introduced oxygen vacancies, which can increase FE sites, reduce effective work function and increase conductivity.