Design of ultrasensitive Ag-LaFeO3 methanol gas sensor based on quasi molecular imprinting technology

Engineering an Ultrafast Ambient NO2 Gas Sensor Using Cotton-Modified LaFeO3/MXene Composites

This work presents a room-temperature (RT) NO2 gas sensor based on cotton-modified LaFeO3 (CLFO) combined with MXene. LaFeO3 (LFO), CLFO, and CLFO/MXene composites were synthesized via a hydrothermal method. The fabricated sensor, utilizing MXene/CLFO, exhibits a p-type behavior and fully recoverable sensing capabilities for low concentrations of NO2, achieving a higher response of 14.2 times at 5 ppm. The sensor demonstrates excellent performance with a response time of 2.7 s and a recovery time of 6.2 s, along with notable stability. The sensor's sensitivity is attributed to gas interactions on the material's surface, adsorption energy, and charge-transfer mechanisms. Techniques such as in situ FTIR (Fourier transform infrared) spectroscopy, GC-MS (gas chromatography-mass spectroscopy), and near-ambient pressure X-ray photoelectron spectroscopy were employed to verify gas interactions and their byproducts. Additionally, finite-difference time-domain simulations were used to model the electromagnetic field distribution and provide insight into the interaction between NO2 molecules and the sensor surface at the nanoscale. A prototype wireless IoT (Internet of Things)-based NO2 gas leakage detection system was also developed, showcasing the sensor's practical application. This study offers valuable insight into the development of room-temperature NO2 sensors with a low detection limit.

Precision Methanol Sensing: Integrating Chemical Insights of Optical Sensors for Enhanced Detection

Methanol has become a very important part of many industries, ranging from chemical production and pharmaceuticals to automotive and electronics manufacturing as a result of which methanol usage has spiked in recent years. But this exponential increase asks for precise detection methods as methanol has not only detrimental effects on environment but it is very dangerous to human health even if consumed in a minute amount .This paper will explore the unique physical and chemical properties of methanol which can be exploited to make it a target for different mechanisms such as H-Bonding, induced self-assembly, Internal Charge Transfer (ICT), Aggregation-induced emission (AIE), conformational flexibility, keto-enol tautomerization, adsorption etc. by various small molecule and nano-particles. Informative studies on small molecules involves functionalized pentacenequinone derivatives, luminogens, ligands and fluorescent probes which can be used to detect methanol by change in color or intensity which can be easily detected in real time and is portable. On the other hand, nanoparticle-based probes reveal the use of materials like chitosan/zinc, sulfide composites, Quantum Dots (QDs) hybrids, graphene polyoxides, Ag-LaFeO3 etc. which provides with selective and sensitive methanol optical and conductometric sensing. This paper acknowledges the contributions of various studies and researchers who contributed to advancing the field of methanol sensing, providing a foundation for future developments.

La-Fe-O Perovskite Based Gas Sensors: Recent Advances and Future Challenges

Interest in the importance of gas sensing devices has increased significantly due to their critical function in monitoring the environment and controlling pollution, resulting in an increased market demand. The present review explores perovskite La-Fe-O based gas sensors with a special focus on LaFeO3 and evaluates their sensitivity to a diverse range of practical target gases that need to be monitored. An analysis has been conducted to assess different routes not only of synthesizing LaFeO3 material but also of characterization with the targeted use for their gas sensing abilities. Additionally, a comprehensive analysis has been performed to explore the effect of introducing other elements through doping. In view of the LaFeO3 sensing performance, more common gases like acetone, ethanol, methanol, formaldehyde, NO x , and CO2 have been targeted. In addition, a discussion on uncommon gases such as CO, SO2, TEA, C2H5, C6H6, and others is also made to give a complete picture of LaFeO3-based gas sensors. The summary and conclusion section of the study addresses the primary obstacles in the synthesis process, the variables that restrict the sensing capabilities of LaFeO3, and its commercial fulfillment.

Operando monitoring of a room temperature nanocomposite methanol sensor

The sensing of volatile organic compounds by composites containing metal oxide semiconductors is typically explained via adsorption-desorption and surface electrochemical reactions changing the sensor's resistance. The analysis of molecular processes on chemiresistive gas sensors is often based on indirect evidence, whereas in situ or operando studies monitoring the gas/surface interactions enable a direct insight. Here we report a cross-disciplinary approach employing spectroscopy of working sensors to investigate room temperature methanol detection, contrasting well-characterized nanocomposite (TiO2@rGO-NC) and reduced-graphene oxide (rGO) sensors. Methanol interactions with the sensors were examined by (quasi) operando-DRIFTS and in situ-ATR-FTIR spectroscopy, the first paralleled by simultaneous measurements of resistance. The sensing mechanism was also studied by mass spectroscopy (MS), revealing the surface electrochemical reactions. The operando and in situ spectroscopy techniques demonstrated that the sensing mechanism on the nanocomposite relies on the combined effect of methanol reversible physisorption and irreversible chemisorption, sensor modification over time, and electron/O2 depletion-restoration due to a surface electrochemical reaction forming CO2 and H2O.

Structural, Vibrational, and Magnetic Characterization of Orthoferrite LaFeO3 Ceramic Prepared by Reaction Flash Sintering

LaFeO₃ perovskite ceramics have been prepared via reaction flash technique using Fe₂O₃ and La₂O₃ as precursors. The obtained pellets have been investigated using several techniques. The formation of LaFeO₃ has been clearly confirmed by X-ray diffraction. The scanning electron microscopy micrographs have shown the microporous character of the obtained pellets due to the low temperature and dwell time used in the synthesis process (10 min at 1173 K). The orthorhombic-rhombohedral phase transition has been observed at approximately 1273 K in differential thermal analysis measurements, which also allows us to determine the Néel temperature at 742 K. The fitted Mössbauer spectra exposed the presence of a single sextet ascribed to the Fe⁺³ ions in the tetrahedral site. Finally, magnetic measurements at room temperature indicate the antiferromagnetic character of the sample.

Molecularly imprinted polymers for sensing gaseous volatile organic compounds: opportunities and challenges

Chemical sensors that can detect volatile organic compounds (VOCs) are the subject of extensive research efforts. Among various sensing technologies, molecularly imprinted polymers (MIPs) are regarded as a highly promising option for their detection with many advantageous properties, e.g., specific binding-site for template molecules, high recognition specificity, ease of preparation, and chemical stability. This review covers recent advances in the sensing application of MIPs toward various types of VOCs (e.g., aliphatic and aromatic compounds). Particular emphasis has been placed on multiple approaches to the synthesis of MIP-based VOC sensors in association with their performance and sensing mechanisms. Current challenges and opportunities for new VOC-sensing applications are also discussed based on MIP technology.

Template Imprinting Versus Porogen Imprinting of Small Molecules: A Review of Molecularly Imprinted Polymers in Gas Sensing

The selective sensing of gaseous target molecules is a challenge to analytical chemistry. Selectivity may be achieved in liquids by several different methods, but many of these are not suitable for gas-phase analysis. In this review, we will focus on molecular imprinting and its application in selective binding of volatile organic compounds and atmospheric pollutants in the gas phase. The vast majority of indexed publications describing molecularly imprinted polymers for gas sensors and vapour monitors have been analysed and categorised. Specific attention was then given to sensitivity, selectivity, and the challenges of imprinting these small volatile compounds. A distinction was made between porogen (solvent) imprinting and template imprinting for the discussion of different synthetic techniques, and the suitability of each to different applications. We conclude that porogen imprinting, synthesis in an excess of template, has great potential in gas capture technology and possibly in tandem with more typical template imprinting, but that the latter generally remains preferable for selective and sensitive detection of gaseous molecules. More generally, it is concluded that gas-phase applications of MIPs are an established science, capable of great selectivity and parts-per-trillion sensitivity. Improvements in the fields are likely to emerge by deviating from standards developed for MIP in liquids, but original methodologies generating exceptional results are already present in the literature.

Pt Single Atom-Induced Activation Energy and Adsorption Enhancement for an Ultrasensitive ppb-Level Methanol Gas Sensor

As an important organic chemical raw material, methanol is used in various industries but is harmful to human health. Developing an effective and accurate detection device for methanol is an urgent need. Herein, we demonstrate a novel gas-sensing material with a Pt single atom supported on a porous Ag-LaFeO₃@ZnO core-shell sphere (Ag-LaFeO₃@ZnO-Pt) with a high specific surface area (192.08 m²·g^-1). Based on this, the surface activity of the Ag-LaFeO₃@ZnO-Pt gas sensor is enhanced obviously, which improved the working temperature and detection limit for methanol gas. Consequently, this sensor possesses an ultrahigh sensitivity of 453.02 for 5 ppm methanol gas at a working temperature of 86 °C and maintains a high sensitivity of 21.25 even at a concentration as low as 62 ppb. The sensitivity of Ag-LaFeO₃@ZnO-Pt to methanol gas is increased by 6.69 times compared with the Ag-LaFeO₃@ZnO core-shell sphere (Ag-LaFeO₃@ZnO). Additionally, the minimum detection limit is found to be 3.27 ppb. Detailed theoretical calculations revealed that the unoccupied 5d state of Pt single atoms increases the adsorption and activation energy of methanol and oxygen, which facilities methanol gas-sensing performance. This work will provide a novel strategy to design high-performance gas-sensing materials.

Platinum-Supported Cerium-Doped Indium Oxide for Highly Sensitive Triethylamine Gas Sensing with Good Antihumidity

Triethylamine is extremely harmful to human health, and chronic inhalation can lead to respiratory and hematological diseases and eye lesions. Hence, it is essential to develop a triethylamine gas-sensing technology with high response, selectivity, and stability for use in healthcare and environmental monitoring. In this work, a simple and low-cost sensor based on the Pt- and Ce-modified In₂O₃ hollow structure to selectively detect triethylamine is developed. The experimental results reveal that the sensor based on 1% Pt/Ce₁₂In exhibits excellent triethylamine-sensing performance, including its insusceptibility to water, reduced operating temperature, enhanced response, and superior long-term stability. This work suggests that the enhancement of sensing performance toward triethylamine can be attributed to the high relative contents of O_V and O_C, large specific surface area, catalytic effect, the electronic sensitization of Pt, and the reversible redox cycle properties of Ce. This sensor represents a unique and highly sensitive means to detect triethylamine, which shows great promise for potential applications in food safety inspection and environmental monitoring.

Ultrafast Detection of Low Acetone Concentration Displayed by Au-Loaded LaFeO3 Nanobelts owing to Synergetic Effects of Porous 1D Morphology and Catalytic Activity of Au Nanoparticles

Herein, we report on one-dimensional porous Au-modified LaFeO₃ nanobelts (NBs) with high surface area, which were synthesized through the electrospinning method. The incorporation and coverage of Au nanoparticles (NPs) on the surface of the LaFeO₃ NBs was achieved by adjusting the HAuCl amount in the precursor solution. Successful incorporation of Au NPs was examined by X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The gas-sensing performance of both the pure and Au/LaFeO₃ NB-based sensors was tested toward 2.5-40 ppm of acetone at working temperatures in the range from room temperature to 180 °C. The gas-sensing findings revealed that Au/LaFeO₃ NB-based sensor with the Au concentration of 0.3 wt % displayed improved response of 125-40 ppm of acetone and rapid response and recovery times of 26 and 20 s, respectively, at an optimal working temperature of 100 °C. Furthermore, all sensors demonstrated an excellent response toward acetone and remarkable selectivity against NO₂, NH₃, CH₄, and CO. Hence, the Au/LaFeO₃-NB-based sensor is a promising candidate for sensitive, ultrafast, and selective acetone detections at low concentrations. The gas-sensing mechanism of the Au/LaFeO₃ sensors is explained in consideration of the catalytic activity of the Au NPs, which served as direct adsorption sites for oxygen and acetone.