Excellent Gas-sensing Research Articles

MOF-derived Ag0.16/In1.95Pr0.05O3 sensors with ultra-high sensitivity, quick response and excellent selectivity to formaldehyde gas

In1.95Pr0.05O3 microtubes are derived from MIL-68, and then Ag nanoparticles are anchored to synthesize Ag0.16/In1.95Pr0.05O3 microtubes. All results indicate that Pr-doping and Ag-loading greatly affect the gas-sensing performance of In2O3 sensor, which In1.95Pr0.05O3 and Ag0.16/In2O3 sensors both exhibit the response value exceeding 900. While Ag0.16/In1.95Pr0.05O3 sensor exhibits the highest response value of 2438.67 to 10 ppm formaldehyde gas, which is about 20 times higher than that of In2O3 sensor (122.59). Furthermore, Ag0.16/In1.95Pr0.05O3 sensor also displays the lower operating temperature (200 °C), shorter response time (12 s), excellent long-term stability, high selectivity, and anti-humidity for formaldehyde gas. According to DFT methods, the adsorption energies of In2O3, In1.95Pr0.05O3, and Ag0.16/In1.95Pr0.05O3 sensors for formaldehyde are calculated to be −0.47 eV, −0.63 eV, and −0.94 eV, respectively. These highly-improved gas-sensing properties are due to the synergistic effect of Pr-doping and Ag-loading, which includes the increased surface oxygen from Pr-doping, the electronic and chemical sensitization from Ag nanoparticles. The gas-sensing mechanism of Ag0.16/In1.95Pr0.05O3 sensor provides an effective strategy to achieve an excellent gas sensor for formaldehyde gas.

Regulation of receptor function in NiCo2O4-SnO2 heterojunction for H2S detection at room temperature

In recent years, the World Health Organization has increasingly emphasized air quality in production environments, leading to heightened societal demands for monitoring of pollutant gases at room temperature. Traditional semiconductor gas-sensitive materials, such as tin oxide (SnO2), have their gas-sensing performance largely limited by their receptor functions, resulting in common issues like low response and poor recovery at room temperature. Spinel-type bimetallic oxides, such as nickel cobaltate (NiCo2O4), offer a unique solution due to their rich adsorption sites on the surface, which provide distinctive receptor functions for detecting toxic gases at room temperature. Herein, NiCo2O4 is synthesized via a one-step hydrothermal method, with a porous spherical cluster structure, and combined with SnO2 to form a heterojunction. The NiCo2O4-SnO2 heterojunction film gas sensor exhibits excellent gas-sensing performance for H2S at room temperature, including high response, short response time, good repeatability, and selectivity. Additionally, the unique receptor functions of the NiCo2O4 were analyzed through first-principles calculations, revealing a semiconductor p-n conversion phenomenon in the presence of H2S gas. The composite also demonstrates a conversion from p-n heterojunction to n-n homojunction during the sensing process, enhancing its gas-sensing performance. This work not only addresses the receptor function limitations of traditional gas-sensitive semiconductor but also provides a feasible approach for controlling carrier types in semiconductors.

A pH-responsive dual-emission composite for fast detection of BAs and visual monitoring seafood freshness with large luminescence color difference

Sensing biogenic amine (BAs) content is very important for assessing food freshness. To address the limitations such as small color difference values (ΔE) and complex preparation of probes for visualizing the freshness of seafood, a pH-responsive ratiometric fluorescent probe (EnEB) was prepared by Eu(NO3)3, trimeric acid (BTC), and hydrochloric acid norepinephrine (Enr). EnEB emitted blue (446 nm) and red fluorescence (616 nm) originating from Enr and Eu3+, respectively, and exhibiting a fluorescence wavelength difference up to 170 nm. The ratiometric fluorescent signals of EnEB showed a linear correlation with pH in the range of 5.5–8.0. Thus, EnEB can rapidly and precisely detect BAs, such as histamine, tyramine, and spermine, with detection limits and response times of 1.14 μmol/L (3 s), 1.04 μmol/L (8 s), and 0.41 μmol/L (2 s), respectively. Furthermore, an EnEB aerogel was prepared by loading EnEB in a matrix formed by polyvinyl alcohol (PVA) and agarose (AG). EnEB aerogel exhibited excellent acid-base gas-sensing properties. The fluorescence color of EnEB aerogel can change significantly with the deterioration of seafood. When seafood changed from fresh to decayed, the ΔE value of EnEB aerogel was as high as 80.9. Importantly, the results of seafood freshness by naked eye using EnEB aerogel was consistent well with the TVB-N content and the freshness standard stipulated by national food standard, indicating EnEB aerogel can accurately visually and real-time monitor seafood freshness. Furthermore, the strategy for sensing food freshness based on EnEB aerogel also offered multiple color variations to indicate fine freshness levels of seafood. This work provided a convenient, efficient, and accurate approach to assessing the freshness of seafood. Additionally, EnEB also has promising applications in security and anti-counterfeiting.

A novel peony shaped ZnO and its excellent ethanol gas-sensing performance

In order to improve the gas-sensing performance of ZnO, a novel peony shaped ZnO stacked with nanosheets were prepared using hydrothermal method, and the obtained ZnO was characterized and tested for gas sensitivity. The results showed that the particle distribution of the peony shaped ZnO was uniform, with a particle size of about 0.8 μm. The gas-sensing response test results show that the peony shaped ZnO has excellent selectivity to ethanol gas. When the concentration of ethanol gas is 100 ppm, the gas-sensing response of the peony shaped ZnO to ethanol gas reaches 17.4, and the response time and recovery time are 8 s and 12 s, respectively. Even at an ethanol gas concentration of 2 ppm, the gas-sensing response of the peony shaped ZnO to ethanol gas can reach 2.1. Compared to existing literature reports, the peony shaped ZnO prepared in this paper has better gas-sensing performance. This study will provide data support and theoretical reference for the development of high-performance gas sensors.

UV-enhanced Mg:MOF-ZnO sensor for n-butanol gas detection at a lower operating temperature

In this study, a novel UV-enhanced Mg-doped MOF-ZnO sensor was investigated for its efficient detection of n-butanol gas at lower temperatures. The composite samples were prepared by the co-precipitation method with the appropriate component ratio. The structure, morphology, and optical properties of the as-prepared samples were systematically analyzed through XRD, SEM, TEM, BET, XPS, and UV–vis characterizations. The gas-sensitive performances based on the pristine MOF-ZnO and Mg-doped MOF-ZnO sensor series with the doping levels of 1 %, 3 %, 5 %, and 7 % (wt%) were comprehensively evaluated by adopting the gas-sensitive system. Among them, the 3 % Mg:MOF-ZnO sensor has given prominence to the largest specific surface area and highest oxygen vacancy concentration demonstrating the most excellent gas-sensing performance. Furthermore, with the aid of UV excitation, the 3 % Mg:MOF-ZnO sensor had achieved the enhanced response value of 2049 that was 4.44 times higher than that of pristine MOF-ZnO to 100 of ppm n-butanol at a low temperature of 246 °C, additionally presented out the superior reproducibility with speedy response/recovery time (12/22 s), the theoretical detection limit as low as 200 ppb, as well as the excellent long-term stability and selectivity for n-butanol. This study offers a promising strategy for the well-development of high-performance n-butanol sensors.

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.

Structural and Dielectric Properties of Cu<sub>x</sub> Zn<sub>1-x</sub> Fe<sub>2</sub>O<sub>4</sub> (x = 0.2, 0.6, 0.8) Nano Particles

Researchers widely investigate multi-ferrite nanoparticles due to their fascinating magnetic and electrical properties with satisfactory thermal and chemical stabilities. In the present work CuxZn1-xFe2O4(x = 0.2, 0.6, 0.8) were synthesized using the auto combustion method. The spinel structure of the prepared samples was verified using XRD. The compositional dependent dielectric and ac conductivity studies were performed using impedance spectroscopy technique. The dielectric properties, such as complex dielectric constant and impedance, have been studied as a function of frequency. Changes of dielectric loss tangent (tan δ) with the frequency have been studied to get information about the energy dispersed inside the materials. The ac conduction study, as a function of frequency, suggests the hopping conduction mechanism at the higher frequencies. From the complex impedance spectra (Nyquist plots or Cole-Cole plots), On the real axis, we identified a dispersion as opposed to a centered semicircle. This suggests a relaxation type other than Debye. The dielectric dispersion observed at lower frequencies can be explained using Koop’s phenomenological theory. Since many gases are released during mining and the investigated Cu2Fe2O4 is known to be an excellent gas sensor, this study helps to use it effectively in the mining sector.

Selective adsorption and sensing mechanism of ZnFe2O4 (111) surface towards toxic gases:A first-principles study

ZnFe2O4 possesses an excellent gas-sensing performance, but its sensing mechanism towards different toxic gas molecules requires further exploration. In this study, the competitive adsorption and sensing properties of several toxic gases (NO2, NO, SO2, CO, H2S, and NH3) on the ZnFe2O4 (111) surface were investigated using density functional theory (DFT) calculations. The adsorption energy, charge transfer (QT), occupation function, adsorption free energy, charge density difference (CDD), and density of states (DOS) were compared. The results reveal that the ZnFe2O4 (111) surface exhibits obvious adsorption for NH3, H2S, NO2, and H2O, besides the selectivity of NH3 molecule is highest. Strong chemical interactions exist between these harmful gas molecules and the ZnFe2O4 (111) surface. This study offers valuable theoretical insights into the selective adsorption and sensing mechanism, contributing to the development of high-performance gas sensors to detect toxic gases.

Enhanced gas sensing performance of Ag-Doped BiFeO3 microspheres synthesized via flash auto combustion technology

This investigation demonstrates the successful synthesis of well-crystallized pristine and Ag-doped BiFeO3 microspheres using flash auto combustion technology. The effects of Ag doping on the morphology and microstructural characteristics were thoroughly examined through SEM, EDS, and powder X-ray diffraction (XRD) studies. Gas sensing experiments were performed to evaluate the response of the synthesized materials to NO gas. The results revealed a remarkable enhancement in the gas sensing capabilities of 5% wt Ag-doped BiFeO3 compared to pure BiFeO3. Specifically, the gas response towards NO was found to be 2.4 times higher for Ag-doped BiFeO3. This significant improvement can be attributed to the presence of Ag atoms within the lattice structure, which not only increased the density of holes in the material but also created additional gas molecule adsorption sites. Furthermore, the Ag dopant exhibited a catalytic effect, contributing to the excellent gas sensor performance of the material. These findings hold great promise for the development of highly sensitive and efficient gas sensors, particularly in applications where the detection of low concentrations of NO is crucial. The utilization of flash auto combustion technology in the synthesis process offers a viable route for scalable production of advanced gas sensing materials with enhanced performance.

Pt and black phosphorus co-modified flower-like WS2 composites for fast NO2 gas detection at low temperature.

Incomplete recovery, baseline drift, and a long response time have been impeding the practical applications of transition metal dichalcogenide (TMD)-based gas sensors. Here, we report WS2 sensors with significantly improved gas recovery, rapid response, and negligible baseline drift by the incorporation of black phosphorus (BP) as well as the decoration of Pt to detect NO2 for the first time. Compared to bare WS2, the BP-WS2 sensors show higher sensitivity, better repeatability, and more excellent selectivity towards NO2 at the optimal operating temperature of 50 °C. Furthermore, the optimized 30%BP-WS2/Pt sensors exhibit a continuous enhancement in the recovery level and sensitivity with negligible baseline drift. The 30%BP-WS2/Pt sensor also exhibits a shorter response time of 28 s than 49.5 s for its counterpart WS2 sensor towards 32 ppm NO2. The enhanced sensing properties are primarily due to the combined effects of more adsorption sites provided by BP, the spill-over effect of Pt catalysis, and the WS2/BP heterostructure. Therefore, the Pt-decorated 30%BP-WS2 sensor exhibits prominent gas-sensing properties of high gas sensitivity, a low detection limit of 100 ppb, good selectivity, and fast response. Our strategy provides a new route for designing and optimizing TMD-based gas sensors with excellent gas-sensing performance.

Bismuth tungstate nanosheets sensors based on Temkin adsorption model for triethylamine detection

Nanostructured Bi2WO6 and Bi2W2O9 were synthesized using a hydrothermal method. The crystal structure, morphology, and specific surface area were analyzed via X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller and X-ray photoelectron spectroscopy (XPS) analysis, respectively. The characterization results show that Bi2WO6 has a higher specific surface area and a larger pore size than Bi2W2O9, which promote oxygen adsorption and surface reactions. Gas-sensitive tests show that both sensors have a lower detection limit of 2.5 ppm as well as short response and recovery times for detecting triethylamine (TEA). They also have excellent cycling and long-term stability at 180 °C and exhibit excellent gas-sensing performance. The Bi2WO6 sensor has a higher response and sensitivity, as well as better selectivity, than the Bi2W2O9 sensor, which is related to the uniformly layered structure of the former material. We have analyzed the mechanism that enables these sensors to detect TEA and have used the Temkin adsorption model to explain the linear relationship. We find that this model provides an excellent theoretical foundation for fitting the working curve of these semiconductor sensors.

IoT-enabled surface-active Pd-anchored metal oxide chemiresistor for H2S gas detection

The Internet of Things (IoT) has a crucial role in advancing various fields such as Industry 4.0, Big Data, and Machine-to-Machine technologies. All systems continuously gather information on various parameters such as temperature, speed, pressure, health data, environmental conditions, and consumption. Considering this, we've developed a novel fabrication method for H2S gas sensor prototypes. These sensors are based on noble metal-functionalized on metal oxide semiconductor (MOS) chemiresistors. The fabrication process involved growing CuCrO2 sensing thin film on SiO2/Si substrates using the RF sputtering method. Subsequently, Pd nanoparticles, known for their excellent gas-sensing catalyst properties, were functionalized onto the CuCrO2 films using DC sputtering with varying sputtering times of 3, 6, 9, and 12 s. Nanorice morphology boosts gas absorption, capturing more target molecules. A 9 s Pd sputtering time greatly improved H2S sensing over other gases. CuCrO2 film with Pd showed the highest 72.3% response to 50 ppm H2S, detecting down to 0.5 ppm. These results were achieved at the optimal working temperature of 150 °C. After optimizing parameters, we transferred the technology to develop a sensor module for the prototype with IoT integration. The prototype sensor connects to NODEMCU-ESP8266 Wi-Fi, which links to a smartphone through a mobile hotspot.

Preparation and Gas-Sensing Properties of Two-Dimensional Molybdenum Disulfide/One-Dimensional Copper Phthalocyanine Heterojunction

Although 2D MoS2 alone shows excellent gas-sensing performance, it is prone to stacking when used as the sensitive layer, resulting in insufficient contact with the target gas and lower sensitivity. To solve this, a 2D-MoS2/1D-CuPc heterojunction was prepared with different weight ratios of MoS2 nanosheets to CuPc micro-nanowires, and its room-temperature gas-sensing properties were studied. The response of the 2D-MoS2/1D-CuPc heterojunction to a target gas was related to the weight ratio of MoS2 to CuPc. When the weight ratio of MoS2 to CuPc was 20:7 (7-CM), the gas sensitivity of MoS2/CuPc composites was the best. Compared with the pure MoS2 sensor, the responses of 7-CM to 1000 ppm formaldehyde (CH2O), acetone (C3H6O), ethanol (C2H6O), and 98% RH increased by 122.7, 734.6, 1639.8, and 440.5, respectively. The response of the heterojunction toward C2H6O was twice that of C3H6O and 13 times that of CH2O. In addition, the response time of all sensors was less than 60 s, and the recovery time was less than 10 s. These results provide an experimental reference for the development of high-performance MoS2-based gas sensors.

Mixed potential NH3 sensor based on Ag-Doped La2NiO4+δ sensing electrode

Perovskite-type oxides have attracted extensive focus as sensing electrodes (SE) for NH3 sensors due to their excellent gas-sensing and tunability. The mixed-potential sensor was developed using yttrium stabilized zirconia (YSZ) as the solid electrolyte and non-stoichiometric perovskite oxides La2AgxNiO4+δ (x = 0, 0.025, 0.05, 0.1) as the SE. Due to the Ag doping in the SE, the electrochemical activity was enhanced, and the adsorption capacity of NH3 was further improved. Compared with the La2NiO4+δ-SE-based sensor, the Ag doping in SE significantly improved the response value and sensitivity of the sensor, and the sensor based on La2Ag0.05NiO4+δ-SE had the best capabilities. The response to 200 ppm NH3 was 61.2 mV, and the sensitivity was 8.12 mV/decade (5–25 ppm) and 73.77 mV/decade (50–200 ppm) at 500 ℃. The sensor had a strong anti-interference ability to H2, NO2, NO, CO2, CH4, and the O2 concentrations had little effect on the sensing performance.

Performances of Nano-Structured Cu2O Thin Films Electrochemically Deposited on ITO Substrates in Lactate Bath as Liquid Petroleum Gas Sensors

The investigations are focused on structural and surface morphological features and their influence on electrical and wetting characteristics against liquid petroleum gas (LPG) sensing of synthesized nanostructured cuprous oxide (Cu2O) thin films grown by electrochemical deposition (ECD) on indium tin oxide (ITO) glass substrates in lactate bath (pH 10). p-Cu2O films revealed a cubical-tetrahedron nano-scale polycrystalline grain distribution (average grain size: 64.2 nm, inter planer spacing: 0.24 nm) that exhibited dominance in the crystallographic plane (111). LPG sensing evaluations of p-Cu2O/ITO done at 70 °C constant temperature with 100% LPG at 5 cc min−1 flow rate, showed excellent gas sensor response, recovery, and stability over time due to its moderate wetting behavior (average contact angle: ∼86°). AC impedance measurements carried out at room temperature demonstrated an ionic to electronic conduction variation from 100 Hz to 1 MHz, due to adsorption/desorption of LPG molecules (CnH2n+2) and oxygen species on the nano-particles surface. Cu2O/ITO flat band potential was found to be higher than its’ ambient state after exposure to LPG with an increment in acceptor density. Overall, this efficient LPG sensing could be attributed to the interfacial properties of Cu2O thin films and ITO substrates, that provide an optimized fabrication process of nano-structured Cu2O thin films.

ZnO/GaN n-n heterojunction porous nanosheets for ppb-level NO2 gas sensors

The development of NO2 gas sensors with lower operating temperature and good thermal stability is always a challenge to solve. In this work, 2D loose porous ZnO/GaN heterogeneous nanosheets were synthesized by ultrasonic mixing, in which ZnO nanosheets and GaN nanoparticles were prepared by hydrothermal method and solid-state pyrolysis, respectively. BET characterization result showed that the specific surface area of loose porous ZnO nanosheets was 57.24 m2/g, and XPS tests proved that the formation of heterogeneous interface between ZnO and GaN can effectively increase the number of negative oxygen ion species on the surface. Noticeably, 15 mol % ZnO/GaN composites (Ga:Zn) exhibited the highest response of 134.5–2 ppm of NO2 at 125 °C and lower limit of detection of 20 ppb. Furthermore, it showed outstanding selectivity, repeatability and long-term stability. The excellent gas-sensing properties can be attributed to the loose porous structure of ZnO and the formation of n-n heterojunction between ZnO and GaN. The gas-sensing mechanism of ZnO/GaN composites to NO2 was also discussed in detail.

Mesoporous Co3O4/In2O3 nanocomposites for formaldehyde gas sensors: Synthesis from ZIF-67 and gas-sensing behavior

Mesoporous In2O3 nanowires (NWs) were synthesized with nanocasting method, and then Co3O4/In2O3 nanocomposites were prepared through calcining ZIF-67. All results indicate that Co3O4 nanoparticles greatly affect the microstructures and gas-sensing properties of Co3O4/In2O3 sensors. The response to 10 ppm (formaldehyde) HCHO gas exhibits a significant improvement though the loading of Co3O4. The response values soar from 26.16 for In2O3 NWs to 92.94 for 6%Co3O4/In2O3 and up to maximum 113.6 for 8% Co3O4/In2O3, then decreases to 25.76 for 10% Co3O4/In2O3. 8% Co3O4/In2O3 sensor possesses the excellent HCHO gas-sensing performance with the highest response (113.6) and shortest response time of 20 s. The working temperature of Co3O4/In2O3 sensors is 30 °C lower than that of In2O3 sensor due to Co3O4 catalysis. P-n heterojunctions between p-type Co3O4 and n-type In2O3 affect the interfacial carrier distribution, improving the gas-sensing behavior of Co3O4/In2O3 sensors. Furthermore, oxygen vacancies also play a important role to improve the gas-sensing performance of Co3O4/In2O3 sensors.

Nanocomposites of Quasicrystal Nanosheets and MoS2 Nanoflakes for NO2 Gas Sensors

Nitrogen dioxide (NO2) is one of the air pollutant gases that harms the environment, human health, and the world ecosystem. The main source of NO2 emission is the combustion engine, and therefore, it requires a gas-sensing device to monitor the emission. Herein, we report a highly sensitive and selective NO2 sensor by low-cost and scalable fabrication methods using a hybrid nanocomposite of two-dimensional (2D) Al70Co10Fe5Ni10Cu5 quasicrystal (QC) nanosheets and MoS2 nanoflakes. The 2D-QC nanosheets combined with MoS2 nanoflakes form a heterostructure, which improves the gas sensor’s performance. The Al70Co10Fe5Ni10Cu5/MoS2 heterostructure showed an excellent gas-sensing response (ΔR/Ra %) of ∼66%, which is about 2.27 times higher than that of the pristine MoS2 nanoflakes-based sensor for 100 ppm NO2 at 100 °C. In addition, the hybrid nanocomposite gas sensor device also exhibited high selectivity and good sensitivity. The improvement in the gas sensor performance is explained using the density functional theory analysis, which illustrates that the 2D-QC provides a lot of active sites for the adsorption of NO2 molecules, explained using the adsorption energy, charge difference density, and Bader charges analysis. These gas-sensing results emphasize the significance of the integration of the 2D Al70Co10Fe5Ni10Cu5 QC with MoS2 nanoflakes, being useful to the design and development of NO2-based gas-sensing technology and holding great promise in environmental protection.

Pyrochlore cerium stannate (Ce2Sn2O7) for highly sensitive NO2 gas sensing at room temperature

Gas sensing at low temperatures remains a notable challenge at present. Owing to their strong catalytic activity, oxygen defects, and unique size, pyrochlore-based oxides have attracted considerable attention for preparing conductometric gas sensors that are effective at low temperatures. In this study, we prepared a pyrochlore-Ce2Sn2O7 structure using a facile hydrothermal method. The structure, morphology, and surface valance states of the prepared sample were analyzed. Additionally, we investigated the gas-sensing properties, such as the selectivity, response, response and recovery time, repeatability, stability, limit of detection, and influence of relative humidity on the sensing performance for NO2 gas molecules at room temperature (30 ± 2 ℃). The Ce2Sn2O7 exhibited outstanding selectivity for NO2 gas molecules compared with the interfering gas molecules such as N2O, CO, CO2, SO2, NH3,NO and H2S at room temperature (30 ± 2 ℃.). Moreover, the response and recovery time values were 4 s and 52.5 s, respectively, and an outstanding response of 125% was achieved toward 50 ppm NO2 gas molecules. The Ce2Sn2O7 sensor device exhibited excellent repeatability and stability over 90 days. The excellent gas-sensing performance was attributable to the high specific surface area, presence of oxygen vacancies, and surface-adsorbed oxygen molecules.

Room-temperature methane sensors based on ZnO with different exposed facets: A combined experimental and first-principle study

Methane is a flammable and explosive gas, which is difficult to detect at room temperature. In this work, the photo-activation route was explored to realize the monitoring of methane at room temperature, and the strategy of surface morphology engineering was used to boost excellent methane gas-sensing performance. Three types of ZnO structures: rods, plates, and spheres with exposed (001) and (100) crystal facets in different ratios, were obtained using solvothermal methods. Such characteristics of samples were confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption-desorption analyzer. The gas-sensing performances of sensors based on as-prepared materials were tested under UV light and in the dark. The results indicate that sensors exhibit excellent gas-sensing performances toward methane under UV light at room temperature. ZnO spheres showed a much better response of 20.577 toward 5000 ppm methane and a faster response time of 6 s compared to ZnO plates and rods. The enhanced gas sensing properties were ascribed to high-energy exposed facets and unique hollow structures. In addition, density functional theory (DFT) was investigated to support the effect of crystal facets