Recovery Time Of Sensor Research Articles

Development of Reduce Graphene Oxide (rGO)/ Polypyrrole Composite towards Potential Application of CO2 Gas Sensor

Ppy and Ppy/rGO composites were synthesized using a one-step in-situ oxidation polymerization process. The synthesis involves incorporating reduced graphene oxide (rGO) into the Ppy matrix to improve its sensing properties. Composites were characterized using XRD and FTIR. Response time and the recovery time of sensors were estimated by the static response. The response time of pure Ppy substrate is found to be more than that of Ppy/rGO 10%. Recovery time of Ppy is more as compared to shorter recovery time of Ppy/rGO 10 % i.e 54s. As the recovery time of Ppy/rGO is very less, the active layer can be used as a potential CO2 sensor for carbon dioxide gas sensing and monitoring. Thus, study demonstrates the potential of using Ppy/rGO composites in practical gas-sensing devices, especially for detecting CO2. The enhanced performance attributed to the rGO doping makes it a valuable approach for improving sensor technologies.

Preliminary mechanistic insights into the detection of ethanol vapour using MnO2 NRs-CNPs-poly-4-(vinylpyridine) based solid-state sensor operating at room temperature.

Semiconductor metal oxide gas sensors are widely used to detect ethanol vapours, commonly used in industrial productions, road safety detection, and solvent production; however, they operate at extremely high temperatures. In this work, we present manganese dioxide nanorods (MnO2 NRs) prepared via hydrothermal synthetic route, carbon soot (CNPs) prepared via pyrolysis of lighthouse candle, and poly-4-vinylpyridine (P4VP) composite for the detection of ethanol vapour at room temperature. MnO2, CNPs, P4VP, and MnO2 NRs-CNPs-P4VP composite were characterised using scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. Five sensors were prepared, namely, sensor 1 (MnO2 -NRs), sensor 2 (CNPs), sensor 3 (CNPs-P4VP composite of a mass ratio of 1:3), sensor 4 (MnO2 NRs-CNPs-P4VP composite of a mass ratio 1:1:3), and sensor 5 (MnO2 NRs-CNPs-P4VP composite of a mass ratio 2:1:3). All the five sensors were used detect to 2-propanol, acetone, ethanol, methanol, and mesitylene vapours at room temperature, but among all the tested sensors, sensor 4 was highly sensitive to ethanol vapour and less sensitive to 2-propanol, methanol, acetone, and mesitylene vapours. The response and recovery time of sensor 4 towards ethanol vapour at 20.4ppm were 82seconds and 74seconds, respectively. The limit of detection on ethanol vapour using sensor 4 was 789ppb. During detection, the ethanol vapour undergoes total deep oxidation on the surface of sensor 4.

Application of partially zwitterionic poly(ionic liquid)s in humidity sensors.

Polyelectrolytes have shown promise as sensitive material for high-performance humidity sensors in recent years. How to obtain fast recovery and high sensitivity polyelectrolyte humidity sensors is a great challenge. A kind of poly(ionic liquid)s (PILs) humidity sensors modified by zwitterionic polymers (partially zwitterionic PILs, named PZPILs) were prepared in this work. The PZPILs can transform between PILs and zwitterionic polymers in different humidity sensitive processes. In the adsorption process of water molecules, characteristics of PZPILs are similar to those of PILs. When desorbing water molecules, the characteristics of PZPILs trend to those of sulfobetaine (SB) type zwitterionic polymers. This design endowed the humidity sensors high response and fast response/recovery characteristics. The optimized PZPILs sensor shows high response (4862.8) in a wide relative humidity (RH) range of 11%-95%, with short response/recovery time (1.0s/15.0s) and small humidity hysteresis about 0.6% RH. The PZPILs shortened the recovery time of the PILs humidity sensors (from 143.4s to 15.0s), and improved the response (from 1980.8 to 4862.8).

Fabrication of hydrogen gas sensor using sputtered palladium-copper composite on tapered optical fiber

Abstract In this study, we fabricated a hydrogen (H2) gas sensor based on tapered optical fiber using sputtering method. Also, as the first attempt, we explored how palladium (Pd) and palladium-copper (Pd-Cu) coatings, deposited using the sputtering method (RF and DC), affect tapered optical fibers as H2 gas sensors (ranging from 1 to 8% H2). It investigates changes in sensor output power, response and recovery times, and the influence of fiber tapering angle on output power. The investigation reveals that two main factors, including permeability and elasto-optic effect significantly impact the results. At H2 concentrations of 1 to 3%, permeability predominantly affects Pd sensors, yielding better output power changes and sensitivity than Pd-Cu tapered optical fiber sensors. Conversely, at higher H2 concentrations (4 to 8%), the dominant factors appear to be permeability as well as elasto-optic effect. These characteristics have a greater influence in the Pd-Cu layer at higher H2 concentration, resulting in smoother slope in response to H2. Due to higher permeability, Pd sensors reach saturation faster, while Pd-Cu sensors exhibit more linear changes with increasing H2 levels and do not saturate like Pd sensors very fast. Moreover, the study shows that a larger tapering angle can enhance the output power of Pd-Cu tapered optical fiber sensors.

Oxygen-defect rich SnO2-based homogenous composites for fast response and recovery hydrogen sensor

As a kind of green energy, hydrogen (H2) has been widely concerned and applied by people. One of the biggest challenges for sensing applications is the quick detection of hydrogen leaks or their release in various conditions, particularly in large electric vehicle batteries. This study successfully constructed a quick response and recovery hydrogen sensor based on the In2O3-SnO2 heterojunction. The response and recovery time of the In2O3-SnO2 hydrogen sensor is 1.1/1.9 s to 50 ppm H2. This is reduced to 11.0 %/9.5 % compared to the SnO2 hydrogen sensor. This sensor's remarkable gas detecting properties are mainly attributed to the In2O3-SnO2 heterojunction creation, crystal structure modification, and increased specific surface area (92.9 m2/g). Homogenous In2O3-SnO2 nanocomposites contain more oxygen defects, which is the primary factor enhancing the sensor's ability to detect gases. Firstly, indium ions are incorporated in the lattice of SnO2 results in lattice distortion and enhances the presence of oxygen deficiency in the composites, which plays a pivotal role in achieving rapid response and recovery of the sensor. Secondly, In2O3-SnO2 heterostructures promote rapid adsorption of oxygen molecules and target gases by facilitating effective electron mobility on their surface. The quicker response and recovery times of hydrogen sensors based on In2O3-SnO2 heterojunctions are observed. This innovative approach to creating fast-responding gas sensors highlights the promise of heterojunction-based hydrogen sensors for real-time H2 monitoring and opens up new research directions.

Fiber optic relative humidity and temperature sensor with the cascaded Vernier effect based on the C-shaped cavity structure.

The water-absorbent sensing film, coated on the surface of traditional optical fiber humidity sensors, often suffers from detachment issues. In this paper, we present what we believe to be a new fiber-optic cascaded Fabry-Perot interferometer sensor for detecting relative humidity (RH) and temperature, without the need for sophisticated instrumentation. The sensing structure comprises two sections of single-mode optical fibers and a C-shaped cavity between them. The C-shaped cavity is created by grinding the side of a hollow-core fiber with fiber optic abrasive paper. The Vernier effect arises from the cascaded interaction between the C-shaped cavity filled with ultraviolet optical glue (NOA61) and the subsequent single-mode fiber pigtail. The sensor exhibits a high RH sensitivity of 0.248 nm/%RH (35-95%RH) and an RH resolution of up to 0.08%RH. It also has high-temperature sensitivities of -1.091 nm/°C (25 - 65°C). Furthermore, simultaneous measurement of RH and temperature is achieved by establishing a dual parameter matrix, and the sensor's response time and recovery time for RH and temperature are within 300s. Therefore, this work provides a simple and cost-effective manufacturing process and the proposed RH and temperature sensor features a compact size, strong environmental adaptability, and significant potential for practical applications.

A room-temperature ammonia gas sensor based on the h-MoO3@Graphene composite film with fast response time

The release of ammonia (NH3) in industry or daily life is harmful to human health. A gas sensor was developed using h-MoO3 nanorods and graphene film to detect and eliminate this. The h-MoO3 nanorods were first synthesized by chemical bath deposition using ammonium molybdate tetrahydrate (NH4)6Mo7O24•4H2O and HNO3 and then deposited on the graphene film transferred to SiO2/Si substrate by electrochemical bubbling method. Subsequently, gas-sensitive h-MoO3@Graphene composite films were prepared and analyzed using Raman, XRD, SEM, and UV–vis. The gas sensor's performance was evaluated to detect NH3 at a room temperature concentration range of 1–60 ppm. Compared with graphene, the conductivity of the composite film with 10 mg/ml h-MoO3 nanorods was increased by 40 % and the sensitivity increased by 10 times. The sensor h-MoO3@G-10 showed the best sensing performance to 1 ppm NH3. Sensor sensitivity, response and recovery time are 1.1 %, 46.8 s and 17.8 s.

Silver nanowires@TiO2 core-shell for room-temperature 1000 ppm NH3 gas sensors

This study employs a simple liquid-phase deposition method to grow TiO2 onto nanoscale silver wires, with a diameter of 90 nm and a length of 15∼20 μm. This core-shell structure possesses a high specific surface area, which enhances the gas reaction surface. Measurements can be conducted at room temperature. The main mechanism relies on the conductive properties of silver to transmit electrons, while Schottky barriers between Ag and TiO2 further accelerate oxygen ionization and surface redox reactions. This structure may contribute to enhancing the response value, response time, and recovery time of gas sensors.

Exploring the diverse performance of nickel and cobalt spinel ferrite nanoparticles in hazardous pollutant removal and gas sensing performance.

A simple sol-gel combustion process was employed for the creation of MFe2O4 (M=Ni, Co) nanoparticles. The synthesized nanoparticles, acting as both photocatalysts and gas sensors, were analyzed using various analytical techniques. MFe2O4 (M=Ni, Co) material improved the degradation of methylene blue (MB) under UV-light irradiation, serving as an enhanced electron transport medium. UV-vis studies demonstrated that NiFe2O4 achieved a 60% degradation, while CoFe2O4 nanostructure exhibited a 76% degradation efficacy in the MB dye removal process. Furthermore, MFe2O4 (M=Ni, Co) demonstrated chemosensitive-type sensor capabilities at ambient temperature. The sensor response and recovery times for CoFe2O4 at a concentration of 100ppm were 15 and 20, respectively. Overall, the synthesis of MFe2O4 (M=Ni, Co) holds the potential to significantly improve the photocatalytic and gas sensing properties, particularly enhancing the performance of CoFe2O4. The observed enhancements make honey MFe2O4 (M=Ni, Co) a preferable choice for environmental remediation applications.

ZnO/TiO2 hetero-structured nanosheets for effectively detecting formaldehyde at room temperature

In this study, ZnO/TiO2 nanosheets were synthesized using a hydrothermal method followed by annealing. The resulting hierarchical ZnO–TiO2 heterostructures exhibited improved gas-sensing performance compared with pure ZnO. We demonstrated that tuning the ratio of Zn to Ti components in the heterostructure allowed us to adjust the sensor stability, with the best- performing sample having a Zn:Ti ratio of 2:1. A notable reduction was observed in both the sensor response and recovery times, down to 22 and 17 s, respectively, by utilizing nanosheet- structured ZnO/TiO2 heterojunctions. To gain insight into the interaction between the sensing materials and formaldehyde (HCHO) molecules, we performed first-principles calculations to examine the density of states, charge transfer, and energy of adsorption. Our approach to constructing heterogeneous structures contributes to overcoming the low desorption efficiency and slow response-recovery time of pure ZnO for gas-sensing applications.

Room temperature acetone gas sensing performance of ZnS-NiO nanocomposite sensor enhanced by UV activation for diabetes detection

Metal oxide semiconductors are popular in gas sensor applications.Current metal oxide-based acetone sensors struggle to deliver ppb-level acetone sensing at low temperatures for biological use. This study synthesizes 4mol% ZnS combined with NiO for acetone sensing. Nanoparticles were studied using FE-SEM, XPS, XRD, and UV-Vis spectroscopy. Mixed ZnS and NiO resulted in rapid gas channel movement and n-p heterojunction development, which increased acetone sensitivity. ZnS-NiO showed a gas sensing response of 163% for 20 ppm acetone at room temperature under UV irradiation, which is 2.3 times higher than pristine NiO (70% at 180 ∘C). ZnS improves sensor selectivity. Heterojunction sensor reaction and recovery times were 20 and 14 seconds, respectively. The composite sensor detection limit was 0.1 ppm. The increased sensitivity validates the n-p heterojunction. The sensor’s higher response values and lower detection limit point to breath analyzer applications such as diabetes detection.

Low hysteresis, high sensitivity, fast response, and recovery time of humidity sensor based on Schiff bases material

Low hysteresis, high sensitivity, fast response, and recovery time of humidity sensor based on Schiff bases material

A film composed of PEDOT:PSS/PVA as a sensitive medium for pH sensor in optical fiber

In this work, a pH sensitive transducer element attached to a multimode optical fiber section is proposed. The sensitive element is a PEDOT:PSS/PVA composite film that exhibited sensitivity at low pH values in the range of 1–7 pH. The addition of PVA was important for the adhesion process to the optical fiber surface. The morphology of the PEDOT:PSS polymers allowed characterization at pH stimuli that were based on the optical power transmission generated from the interaction of the light propagating in the optical fiber core and the optical fiber section coated with the sensitive film. A sensitivity of −0.05 dB/pH and a linear fit R2 of 0.93 was obtained, the response time was 3 s, while the sensor recovery time was 50 s maintaining stability higher than 10 min.

Interconnected SnO2 nanoflakes decorated WO3 composites as wearable and ultrafast sensors for real-time wireless sleep quality tracking and breath disorder detection

Monitoring human breath is critical for determining human well-being. Most reported humidity sensors are unsuitable for breath monitoring because of their long response and recovery time, poor stability, and high operating temperature. To address these challenges, robust tungsten oxide (WO3) and tin oxide (SnO2) composite sensors were fabricated, and their humidity-sensing properties were investigated. The SnO2/WO3 composites were optimized by altering the SnO2 fraction to achieve high humidity sensitivity. The SnO2/WO3 composite exhibited superior sensing performance (88) than pristine WO3 and SnO2 under 97 % relative humidity. The sensor demonstrated good linearity while altering humidity from 15 % to 97 %, with an R2 = 0.9729. The sensor's rapid response (0.6 s) and recovery (0.6 s) time allow for breath rate monitoring and breath disorder detection. The wearable sensor demonstrated multifunctional human breath detections such as varied breath rates (5–60 breaths per minute), nose blocking for separate nostrils, wireless sleep quality tracking for more than 7 h continuously, and sleep apnea-hypopnea detection via a smartphone. The capabilities of the humidity sensor allow for robust application in sleep quality, sleep apnea, and hypopnea detection.

Optical fiber gas sensor with multi-parameter sensing and environmental anti-interference performance

Formic acid finds widespread applications in numerous fields, including the petrochemicals production, rubber industry, and leather tanning process, in which the operational environments are complex and diverse. The corresponding industrial systems are often intricate and highly integrated. Indeed, formic acid gas is insidious and poses a hazard to both operating personnel and industrial equipment. The existing detection technologies for formic acid gas suffer from inherent technical limitations, making it challenging to effectively shield against industrial interference in complex environments while accurately conveying information. Furthermore, the simultaneous transmission of essential environmental data alongside formic acid gas concentration remains a formidable challenge, which is crucial for facilitating the integration and simplification of industrial system. In response to the aforementioned challenges, this research firstly employs an optical fiber structure (SNS: single mode fiber-no-core fiber-single mode fiber) with natural resistance to electromagnetic interference as the substrate. Subsequently, considering the characteristics of spectral variations and the response mechanism of formic acid gas, and addressing the issue of humidity interference of the current-stage sensors based on sensitive material, the chitosan and chitosan@PDMS are chosen as sensitive membranes. Finally, a correction formula was introduced to address the temperature and humidity coupling issue of the sensor, resulting in the successful development of two formic acid gas sensors. The chitosan-based sensor has a detection sensitivity of up to 7.7 pm/ppm, whose dual parameter detection performance for temperature and formic acid gas has been experimentally demonstrated. It can also correct the humidity-induced detection error in real-time by the correction formula. The chitosan@PDMS-based sensor was fabricated by plating a hydrophobic and breathable PDMS membrane on the surface of the chitosan-based sensor. In addition to maintaining the performance compared to the original sensor (response and recovery time was increased), the latter sensor can effectively resist the humidity interference from the environment. Furthermore, the new capability has been complemented for the simultaneous detection of temperature and humidity. That is, it realizes the dual parametric detection for formic acid gas and humidity, meanwhile providing the compensation ability for temperature change. The proposed sensors have the outstanding sensitivity, selectivity, immunity, and safety. This research not only effectively resolves the interference problem in formic acid gas detection, but also provides a new idea for equipment simplification and information integration in complex industrial systems.

Rapid and Efficient NO2 Sensing Performance of TeO2 Nanowires.

Gas sensors play a pivotal role in environmental monitoring, with NO2 sensors standing out due to their exceptional selectivity and sensitivity. Yet, a prevalent challenge remains: the prolonged recovery time of many sensors, often spanning hundreds of seconds, compromises efficiency and undermines the precision of continuous detection. This paper introduces an efficient NO2 sensor using TeO2 nanowires, offering significantly reduced recovery times. The TeO2 nanowires, prepared through a straightforward thermal oxidation process, exhibit a unique yet smooth surface. The structural characterizations confirm the formation of pure-phase TeO2 after the anneal oxidation. TeO2 nanowires are extremely sensitive to NO2 gas, and the maximum response (defined as the ratio of resistance in the air to that under the target gas) to NO2 (10 ppm) is 1.559. In addition, TeO2 nanowire-based sensors can return to the initial state in about 6-7 s at 100 °C. The high sensitivity can be attributed to the length-diameter rate, which adsorbs more NO2 to facilitate the electron transfer. The fast recovery is due to the smooth surface without pores on TeO2 nanowires, which may release NO2 quickly after stopping the gas supply. The present approach for sensing TeO2 nanowires can be extended to other sensor systems as an efficient, accurate, and low-priced tactic to enhance sensor performance.

SILAR-Deposited CuO Nanostructured Films Doped with Zinc and Sodium for Improved CO2 Gas Detection.

Gas sensing is of significant importance in a wide range of disciplines, including industrial safety and environmental monitoring. In this work, a low-cost SILAR (Successive Ionic Layer Adsorption and Reaction) technique was employed to fabricate pure CuO, Zn-doped CuO, and Na-doped CuO nanotextured films to efficiently detect CO2 gas. The structures, morphologies, chemical composition, and optical properties of all films are characterized using different tools. All films exhibit a crystalline monoclinic phase (tenorite) structure. The average crystallite size of pure CuO was 83.5 nm, whereas the values for CuO/Zn and CuO/Na were 73.15 nm and 63.08 nm, respectively. Subsequently, the gas-sensing capabilities of these films were evaluated for the detection of CO2 in terms of sensor response, selectivity, recovery time, response time, and limits of detection and quantification. The CuO/Na film offered the most pronounced sensitivity towards CO2 gas, as evidenced by a sensor response of 12.8% at room temperature and a low limit of detection (LoD) of 2.36 SCCM. The response of this sensor increased to 64.5% as the operating temperature increased to 150 °C. This study thus revealed a brand-new CuO/Na nanostructured film as a highly effective and economically viable sensor for the detection of CO2.

Effect of Eu3+ and Sc3+ on the structure, microstructure and humidity sensing properties of copper ferrites for sensor applications

In this investigation, we studied the effect of rare lanthanides on the structure, microstructure, and humidity sensing characteristics of CuEuxScyFe(2-x)O4 ceramics with the following x = y values: 0.00, 0.01, 0.02, and 0.03. The preparation of the samples was accomplished through the utilization of the solution combustion method. The X-ray diffraction (XRD) patterns show the main cubic spinel crystal structure with the space group Fd3‾m with an additional second Fe2O3 phase. The estimated average spinel crystallite size varied from 25 to 10 nm across doping. The microstructure studied by scanning electron microscopy (SEM) proved the porous nature of CuEuxScyFe(2-x)O4 with agglomerated particles. The resistance and the humidity sensing responses become more evident for higher concentrations of Eu–Sc. As demonstrated by the hysteresis curves, the desorption process proceeds somewhat slower than the adsorption process. As recorded, the sensor response and recovery times were each clocked at 39 and 40 s, respectively.

Fast Nitrogen Dioxide Sensing with Ultralow‐Power Nanotube Gas Sensors

AbstractThe study reports fast, ultralow‐power operation of carbon nanotube‐based nitrogen dioxide (NO2) sensors enabled by nanotube self‐heating and transient sensing. The self‐heating effect in the nanotube channel significantly accelerates the desorption of gas molecules, reducing the sensor recovery time to a minute. As gas molecules re‐adsorb on the nanotube after cooling, the initial rate of the sensor transient is used to determine NO2 concentration within a few minutes. To accelerate and optimize the operation of the sensor, the study considered temperature profiles along the self‐heated carbon nanotube, their effect on different sensing regions, and a physical model‐based fit. As a result, the nanotube‐based NO2 sensor demonstrates recovery and readout times below 5 min and an extrapolated limit of detection below 10 ppb. The peak power consumption of this operation mode is below 6 µW. The combination of fast readout, fast recovery, low limit of detection, and ultralow power consumption demonstrated in this work shows strong promise of carbon nanotube‐based NO2 sensors in mobile or Internet‐of‐Things (IoT) applications.

Influence of DC Magnetron Sputtering Power on Structural, Topography, and Gas Sensor Properties of Nb2O5/Si Thin Films.

This study focuses on synthesizing Niobium pentoxide (Nb2O5) thin films on silicon wafers and quartz substrates using DC reactive magnetron sputtering for NO2 gas sensors. The films undergo annealing in ambient air at 800 °C for 1 hr. Various characterization techniques, including X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), Hall effect measurements, and sensitivity measurements, are employed to evaluate the structural, morphological, electrical, and sensing properties of the Nb2O5 thin films. XRD analysis confirms the polycrystalline nature and hexagonal crystal structure of Nb2O5. The optical band gap values of the Nb2O5 thin films demonstrate a decrease from 4.74 to 3.73 eV as the sputtering power is increased from 25 to 75 W. AFM images illustrate a progressive increase in particle size ranging from (41.86) to (45.56) nm, with varying sputtering power between 25 and 75 W. Additionally, EDS analysis validates the rise in Nb content, increasing from 12.2 at. % to 20.1 at. %, corresponding to the increase in sputtering power. Hall effect measurements show that all films exhibit n-type charge carriers, and increasing sputtering power leads to decreased carrier concentration and enhanced mobility. The gas sensor's sensitivity, response, and recovery time were evaluated at various operating temperatures. The NO2 sensor exhibited an optimal sensitivity of 28.6% at 200 °C when the sputtering power was set to 50 W.