Gas Sensors Research Articles

Investigating the adsorption performance of agricultural greenhouses hazardous gases on Rh doped HfX2 (X=S, Se) monolayers through DFT for potential gas sensor applications

This study uses density functional theory to study the adsorption performance of agricultural greenhouses hazardous gases on Rh doped HfX2 (X=S, Se) monolayers. After multiple geometric optimizations, the most stable adsorption configuration was found. The results indicate that the adsorption energy of Rh doped HfX2 monolayers is very stable for adsorbing small molecule gases. The change in the total density of states of the adsorption system reveals the transfer and recombination of electrons during the adsorption process, and the partial density of states helps to understand the interactions between bonding atoms. Molecular orbital analysis shows that LUMO is mainly concentrated near Hf atoms, while HOMO is mainly concentrated near X atoms, Rh atom, and gases. By calculating the work function, the interaction strength and electron transfer mechanism between the adsorbent and the metal surface are revealed. In addition, the recovery time indicates that HfX2 and Rh-HfSe2 are excellent adsorbents for these four gases at room temperature, but when HfS2 operates at 473 K, it will be an efficient and excellent gas sensor for the four gases. Thus, Rh-HfS2 can be a feasible resistance sensing material for Cl2 and SO2. This DFT results provide a theoretical basis for potential gas sensor applications of Rh doped HfX2 (X=S, Se) monolayers, leading to the design and development of more efficient greenhouse gas identification sensor devices.

Controlling Oxygen Vacancy Content by Varying Calcination Temperature to Enhance the Gas Sensing Performance of BiVO4 Material

Compared to gas sensors based on single metal oxide, gas sensors based on binary metal oxide semiconductors (MOS) offer a rich variety of structural types and hold great potential for excellent selectivity. Inspired by this, we synthesized BiVO4 powder through a stepwise reaction combining calcination with hydrothermal bath and investigated the influence of different calcination temperatures on its gas sensitivity performance. Our study revealed that BiVO4-600 exhibited optimal TEA gas sensing behavior at 225 °C, showing high response values (Ra/Rg = 43.4) and fast response/recovery times (15 s/52 s). Additionally, the sensor displayed high stability, repeatability, and exceptional selectivity. Preliminary research indicates that calcination temperature induces changes in the oxygen vacancy content of BiVO4, thus affecting its sensing performance.

Customizable Colorimetric Sensor Array via a High-Throughput Robot for Mitigation of Humidity Interference in Gas Sensing.

One challenge for gas sensors is humidity interference, as dynamic humidity conditions can cause unpredictable fluctuations in the response signal to analytes, increasing quantitative detection errors. Here, we introduce a concept: Select humidity sensors from a pool to compensate for the humidity signal for each gas sensor. In contrast to traditional methods that extremely suppress the humidity response, the sensor pool allows for more accurate gas quantification across a broader range of application scenarios by supplying customized, high-dimensional humidity response data as extrinsic compensation. As a proof-of-concept, mitigation of humidity interference in colorimetric gas quantification was achieved in three steps. First, across a ten-dimensional variable space, an algorithm-driven high-throughput experimental robot discovered multiple local optimum regions where colorimetric humidity sensing formulations exhibited high evaluations on sensitivity, reversibility, response time, and color change extent for 10-90% relative humidity (RH) in room temperature (25 °C). Second, from the local optimum regions, 91 sensing formulations with diverse variables were selected to construct a parent colorimetric humidity sensor array as the sensor pool for humidity signal compensation. Third, the quasi-optimal sensor subarrays were identified as customized humidity signal compensation solutions for different gas sensing scenarios across an approximately full dynamic range of humidity (10-90% RH) using an ingenious combination optimization strategy, and two accurate quantitative detections were attained: one with a mean absolute percentage error (MAPE) reduction from 4.4 to 0.75% and the other from 5.48 to 1.37%. Moreover, the parent sensor array's excellent humidity selectivity was validated against 10 gases. This work demonstrates the feasibility and superiority of robot-assisted construction of a customizable parent colorimetric sensor array to mitigate humidity interference in gas quantification.

Determination of the sensing properties of the fluorescence-based sensor for atmospheric NO2 gas

Air pollution in urban areas poses a serious threat to human health and therefore the studies about the development of low cost and sensitive sensors to monitor the air quality with high spatial and low temporal resolution continue to be an extensive area in literature. In this study, oxime modified poly(4-(1-pyrenyl) styrene) (P(PySt)-NOX) probes were synthesized to use as a sensor to detect NO2 gas in ambient air. The structural characterization results showed that the probe was successfully synthesized. The sensitivity, selectivity, repeatability, and aging tests were performed during the study, and it was observed that P(PySt)-NOX loaded sensor is sensitive to NO2 for concentrations below 200ppb. The selectivity measurements were performed against O3 and SO2 which are common interfering gases in ambient air, and it was shown that the sensor is selective to NO2. Additionally, according to the aging tests performed in laboratory for 23 days, it was observed that the sensor is stable in this time interval. The studies showed the sensor synthesized and designed in this study is suitable for NO2 concentration measurements in ambient air where the concentration levels of NO2 is below 100 ppb.

Cation-oxygen dual-defective ACu3Ti4O12 (A = Sr, Ba) perovskites enable high-performance humidity sensors for human-body related moisture monitoring

ACu3Ti4O12 (A = Sr, Ba) double perovskites are attractive dielectric materials, yet they have not been reported in the field of gas and humidity sensors. In this work, SrCu3Ti4O12 (SCTO) and BaCu3Ti4O12 (BCTO) powders were synthesized by a facile modified solid-phase sintering method with characteristic of abundant cation-oxygen dual-defects (oxygen vacancy, metal deficiencies of Cu+ and Ti3+). For the first time, SCTO and BCTO are explored as humidity sensing materials, while the SCTO sensor holds a response value of four orders of magnitude (Sr = 2.8 × 104), which is over a thousand times higher than that of BCTO (Sr = 25). In addition, the SCTO sensor is featured in fast response (7 s), reliable linearity (R2 = 0.97), small hysteresis (ΔHmax = 0.8%) and good repeatability in a wide relative humidity (RH) range (11%–97%). The boosted humidity sensing performance enables the SCTO sensor to possess great potential in human-body related moisture monitoring of breath and finger detection. Finally, the complex impedance analysis reveals different majority carriers of SCTO (H+) and BCTO (H3O+) under high RH range. The enhanced humidity sensing performance of SCTO can be attributed to the synergistic effects of richer dual-defects and larger ion potential. This work provides an excellent humidity sensing material of SCTO, and furthermore, gives new insights on defect sensitization strategy of perovskites for high-performance electronic sensory devices.

Synthesis, characterization, and gas-sensing application of Cd0.5Zn0.5NdxFe2–xO4 nanoparticles

Fabrication of Cd0.5Zn0.5NdxFe2–xO4 nanoparticles, with x = 0.00, 0.01, 0.02, 0.04, 0.06, and 0.08, has been carried out using a wet chemical co-precipitation method. The effect of the rare earth Nd3+ doping on the prepared ferrites was structurally investigated using x-ray diffraction (XRD) along with Rietveld refinement. The results indicate great crystallinity in the FCC Fd3m spinel structure of Cd0.5Zn0.5NdxFe2–xO4 nanoparticles. The lattice parameter increases with the increase of doping concentration from 8.5378 until 8.5432 Å and the crystallite size obtained using Debye-Sherrer, Williamson–Hall, Size-strain plot (SSP), and Halder-Wagner (H-W) methods, decreases until the solubility limit of the materials is at x = 0.04. By using transmission electron microscopy (TEM), the morphological analysis reveals the spherical shape of the samples with minor agglomeration with the aid of using a Polyvinylpyrrolidone (PVP) capping agent. The grain size ranges from 14.37 to 15.24 nm. Raman spectroscopy verifies the incorporation of Nd3+ in the octahedral sites and the decrease in particle size. The elemental composition was verified using x-ray photoelectron spectroscopy (XPS). The magnetic properties were studied using a vibrating sample magnetometer (VSM) and it shows superparamagnetic behavior with a decrease in the saturation magnetization from 2.207 to 1.918 emu g−1 and an increase in coercivity from 7.194 to 14.397 G. The prepared materials were tested as liquefied petroleum gas (LPG) sensors by studying their sensitivity, selectivity, optimum working temperature, response, and recovery times. Nd3+ doping shows a great increase in LPG sensing sensitivity 4 to 20 times than the pure samples. The doping concentration also decreases the response and recovery times.

Study on the acetone adsorption mechanism of In2O3/SnO2 heterocomposite fibers

A heterocomposite structure offers significant advantages for enhancing the gas sensing performance of metal oxide-based sensors. In this study, In2O3/SnO2 heterocomposite fibers were fabricated by electrospinning. In2O3/SnO2 heterocomposite fibers show excellent gas sensing performance for acetone. The response of the In2O3/SnO2 sensor is 9.3–100 ppm acetone, markedly outperforming sensors made solely of SnO2 or In2O3. To clarify the improved mechanism, the adsorption behavior of In2O3/SnO2 for acetone was studied based on Density Functional Theory (DFT). The adsorption energy of In2O3/SnO2 for acetone at the optimal adsorption site is 0.89 |eV|, which is 0.18 |eV| and 0.04 |eV| higher than that of SnO2 and In2O3, respectively. Additionally, the electron transfer numbers of acetone to In2O3/SnO2 are also 0.08|e| and 0.05|e| greater than those of SnO2 and In2O3, respectively. The n-n heterojunction of In2O3/SnO2 alters the material's barrier, significantly enhancing carrier concentration and electron transfer. This n-n heterojunction is key to the improved gas sensing performance of the In2O3/SnO2 sensor for acetone. Therefore, In2O3/SnO2 heterocomposite fibers have great application potential in the field of gas sensors.

Hydrothermal synthesis of NdFeO3 nanoparticles and their high gas-sensitive properties

N-butanol, a volatile organic compound prevalent in numerous industrial processes, poses significant risks to human health and the environment if not properly monitored. Consequently, the development of high-sensitivity n-butanol sensors is imperative. For this reason, NdFeO3 nanoparticles were successfully synthesized by hydrothermal method and used for the detection of n-butanol. They were fully analyzed using characterization techniques such as XRD, BET, EDX, SEM, TEM and XPS. The test results revealed that the prepared samples exhibited a granular structure with an average diameter of approximately 65 nm. The specific surface area measured 15.415 m2/g, and the pore size was determined to be 16.638 nm. The NdFeO3 sensor responds up to 441 for 100 ppm n-butanol at 260°C, response and recovery times were 33 s and 7 s respectively. The response value of the NdFeO3 sensor is still 4.3 for 1 ppm n-butanol with a minimum detection limit of 0.024 ppm. Simultaneously, the NdFeO3 sensor has excellent selectivity, stability and moisture resistance. These good sensing properties indicate that this work provides a possible strategy for developing an economical and repeatable high performance gas sensor for the detection of n-butanol.

Does a large response suffice?: Thermally stable and low noise Si-doped IZO thin-film transistor-type gas sensors

Does a large response suffice?: Thermally stable and low noise Si-doped IZO thin-film transistor-type gas sensors

Theoretical investigation of 4d noble metal (Ru, Rh or Pd) single atom structures influencing surface oxygen behavior on SnO2(1 1 0)

Surface oxygen species play a key role in determining the chemi-resistive gas sensing performance of SnO2. Through surface modification, the type of oxygen species at different working temperatures can be modulated, leading to changes in carrier concentration and surface activity. Single atom structures (SAS) hold enormous potential in the gas sensing domain; however, the impact of different SAS on surface oxygen species on SnO2 remains unclear, resulting in inconsistent improvements in sensing properties. This study conducted a theoretical investigation of different 4d noble metal SAS (Ru, Rh, and Pd) modified SnO2(110) surface, encompassing both electronic and chemical sensitization. All three SAS, when substituting Sn5c, can inject holes and create a thicker depletion layer to varying degrees. Ru and Rh SAS can accelerate the decomposition of adsorbed O2 and O3. More importantly, Ru and Rh can hinder the combination of adsorbed O* species with adjacent two-coordinated lattice oxygen (O2c), enhancing the chemical stability of O*, which plays a decisive role in detecting reducing gases, with Ru exhibiting a better effect. This theoretical work not only enhances methods and mechanisms for adjusting surface oxygen species and improving the sensing performance of SnO2-based gas sensors, but also provides useful guidance for screening and designing SAS in experimental procedures on different semiconductor metal oxide surfaces.

Flexible room temperature gas sensor based on α-Fe2O3/Ti3C2Tx MXene composites for ppb-level H2S detection

Ti3C2Tx MXene have attracted enormous attention in portable, wearable electronics areas due to its excellent flexible, electrical conductivity and outstanding physical and chemical properties. Here, 2D α-Fe2O3/Ti3C2Tx MXene composites were synthesized by in-suit growth of α-Fe2O3 on the surface of Ti3C2Tx MXene and between the layers of Ti3C2Tx MXene by solvothermal and annealing methods. Compared with pure α-Fe2O3, the optimal α-Fe2O3/Ti3C2Tx MXene composites exhibited excellent gas sensitive performance (100 ppm can reach 20.27) and a theoretical ultra-low limit-of-detection of 10.19 ppb to H2S gas at room temperature (25 ○C). The combination of α-Fe2O3 and Ti3C2Tx lead to the layer spacing of Ti3C2Tx MXene are further enlarged which is more favorable for H2S gas adsorption. And the excellent performance is maintained even under bending conditions. This work provides a new idea for MOS/Ti3C2Tx MXene in the field of flexible room temperature sensors.

An ethanol gas sensor based on floating gate carbon-based FETs with humidity resistance

An ethanol gas sensor based on floating gate carbon-based FETs with humidity resistance

Room temperature detection of n-butanol Ce-doped MOF:ZnO sensor under UV activation

Being one of toxic and flammable volatile organic compounds (VOC), n-butanol has brought about many potential health risks, there is an urgent demand for highly sensitive detection techniques to monitor its concentration in occupational environments and the air. In this paper, Ce-doped MOF:ZnO sensors under UV activation for room-temperature detection of n-butanol were synthesized by the co-precipitation method and systemically characterized by XRD, SEM, HRTEM, and XPS. The sensitive performances were evaluated by the use of a WS-30A gas sensor measurement system. The results showed that Ce doping has significantly enhanced the sensitivity of the MOF:ZnO sensors, and the response value of the 0.08 % Ce-doped ZnO sensor has achieved to 397.30, which was 9.32 times higher than that of the pristine MOF:ZnO. And the response and recovery times were 17 and 117 s respectively, demonstrating a speedy detection capability. In addition, the sensor gained excellent stability and reproducibility with special selectivity for n-butanol. The comprehensive achievements of this research would be promising to promote the development of volatile organic compound detection technology and beneficial to the well application in the fields of environmental monitoring, industrial safety, and public health.

High sensitivity and ultra-low detection limit of violet phosphorus-based formaldehyde gas sensor by ultrasonic-assisted laser ablation

Formaldehyde (HCHO) pollution has emerged as a progressively critical environmental concern, with the detection of formaldehyde at trace levels being an indispensable requirement. Violet phosphorus (VP) nanoplates, recognized as innovative two-dimensional materials, are promising candidates for gas sensing due to their rich active sites and substantial specific surface area. This work pioneered the use of ultrasonic-assisted laser ablation in the synthesis of VP nanoplates. The as-produced VP nanoplates had the lateral dimension of 6.5 μm and the thickness of 2–6 nm (1–5 layers), which was strongly influenced by the ablation techniques employed and the processing parameters. The VP nanoplates demonstrated excellent sensitivity towards formaldehyde: gauge factor is 7.23 × 109; and resistance response is 144.6 % for detecting 20 ppb of formaldehyde. The detection limit is only 3 ppb. This work employed experiments and calculations to study the sensing mechanism. The binding energy between VP/G and HCHO is −1.276 eV, demonstrating the strong chemical adsorption. This paper provided a novel approach to fabricate VP nanoplates with superior formaldehyde sensitivity and ultra-low detection limitation, thereby showcasing significant potential for applications in detecting of air pollution.

Toluene sensing properties of YSZ-based gas sensors attached with Au-based electrodes prepared by a drop-coating method

Toluene sensing properties of YSZ-based gas sensors attached with Au-based electrodes prepared by a drop-coating method

One step synthesis of Rh embedded hollow spherical WO₃ composite for enhanced acetone sensing: A promising approach for non-invasive diabetes monitoring

This study investigated the enhancement of WO₃/Rh composite gas sensors for improved acetone detection. WO₃/Rh composite samples (WO₃/Rh-1, WO₃/Rh-2, WO₃/Rh-3) were synthesized via spray pyrolysis, and materials were studied using XRD, SEM, and TEM. These analyses confirmed successful introduction of Rh nanoparticles and indicated favorable alterations in structure and morphology. Gas sensing tests with varying acetone concentrations (0.1–4 PPM, balanced with simulated exhaled gas with RH% of ∼30 %) demonstrated that Rh introduction significantly improved sensitivity and selectivity. Notably, WO₃/Rh-3 exhibited the highest performance, with enhanced response times and selectivity critical for diabetes monitoring. These results highlight the potential of WO₃/Rh sensors in medical diagnostics, offering a promising approach for the early detection of diabetes through breath analysis.

First principle investigation on gas sensing properties of MoS2/ZnO heterojunction

MoS2/ZnO heterojunction is theoretically constructed based on density functional theory (DFT). The adsorption and electrical properties of MoS2/ZnO heterojunction after adsorbing six toxic gas molecules (CO, NO, NO2, SO2, H2S and NH3) are investigated, including adsorption energy, energy gap, density of states, charge density difference, planar-average charge density, total charge density, work function and recovery time. The results suggest that the adsorption energy of MoS2/ZnO for six gas molecules are significantly increased compared with intrinsic MoS2. Especially, the adsorption energy of the heterojunction for NO2, SO2, H2S and NH3 reach to −0.88, −0.98, −0.79 and −1.08 eV, respectively, indicating that the adsorption behavior is changed from physisorption to chemisorption. In addition, after adsorption of gas molecules (CO, NO, NO2, SO2, H2S and NH3), the energy gap of MoS2/ZnO is decreased to 0.793, 0.964, 0.834, 0.864, 0.804 and 0.770 eV, respectively, which indicates that the conductivity of MoS2/ZnO is improved. The adsorption distance (D) is also decreased after adsorption gases, especially for H2S gas molecule (0.797 Å). In addition, the work function (WF) of adsorption system is decreased and the charge transfer is increased. These results indicate that the interaction between MoS2/ZnO and gas molecules is stronger than that of intrinsic MoS2. Therefore, MoS2/ZnO has potential application for gas sensor to detect toxic gas molecules.

Uniform Temperature Control for MEMS Gas Sensors Under Mismatch Conditions

Uniform Temperature Control for MEMS Gas Sensors Under Mismatch Conditions

Role of graphene substrate in the formation of MoS2-based nanoparticles with improved sensitivity to NO2 gas

MoS2 coatings were formed on surface-oxidized silicon, chemical vapor deposition (CVD)-grown graphene, and reduced fluorinated graphene (rFG) from ammonium tetrathiomolybdate. The samples were annealed under ultra-high vacuum conditions at a temperature of 1000 °C. Analysis of X-ray photoelectron and X-ray absorption spectra revealed a bonding between MoS2 and the supporting material that was particularly strong for CVD-graphene. Uniform covering of the flat graphene surface with MoS2 nanoparticles and numerous contacts between them promoted the removal of sulfur and the formation of exposed molybdenum edges. A cracked MoS2 coating consisting of dense domains was formed on the wrinkled rFG surface. The study of samples as NO2 gas sensors revealed the best performance of MoS2/CVD-graphene. The sensor detected NO2 in air below 50 ppb at room temperature, had good response and recovery, operated in humid air, and demonstrated excellent NO2 selectivity. The other two sensors gave signals at elevated temperatures. The advantage of MoS2/CVD-graphene is due to improved electron transport in the hybrid, accessibility of small MoS2 nanoparticles to the analyte, and passivation of high-energy molybdenum sites by oxygen, which improves NO2 desorption.

Ni-MoTe2 as a gas-sensitive material for sevoflurane exposure detection: A fluorinated anesthetic agent

Sevoflurane (C4H3F7O) is a fast-acting anesthetic with low side effects and is widely used in surgery for adults and children. However, small amounts of sevoflurane gas may leak from the breathing apparatus during surgery, which can pose a serious health risk to healthcare workers. In this regard, a study on monitoring of accidental leakage of sevoflurane by different gas-sensitive materials is carried out in this paper. The modified structures of Ni, Pt and Ag on the MoTe2 surface are built. The stabilities of Ni-MoTe2, Pt-MoTe2 and Ag-MoTe2 are investigated by adsorption configurations, Independent Gradient Model based on Hirshfeld partition (IGMH), Electronic Location Function (ELF) and Density of States (DOS). The adsorption properties of three gas-sensitive materials on sevoflurane are subsequently investigated. The gas-sensitive materials with excellent performance are selected combining sensitivity and recovery time. The results show that Ni and Pt can be stably doped on the surface of MoTe2 with forming chemical bonds. The adsorption of Ni-MoTe2 on sevoflurane is chemisorption with the adsorption energy of −0.811 eV. The DOS and IGMH results also indicate that the force of Ni-MoTe2 on sevoflurane is mainly the attraction caused by chemical bonding. Meanwhile, the sensitivity of Ni-MoTe2 for sevoflurane is between 56.26 % and 50.84 %, and the recovery time is between 35.21 s and 0.01157 s, which can meet the requirements of the gas sensor. As a result, Ni-MoTe2 can be used as a gas-sensitive sensor to detect the concentration of sevoflurane in the environment.