The role of oxygen vacancies in the sensing properties of Ni substituted SnO2 microspheres

Crystalline Mesoporous F-Doped Tin Dioxide Nanomaterial Successfully Prepared via a One Pot Synthesis at Room Temperature and Ambient Pressure

We report the successful one pot synthesis of crystalline mesoporous tin dioxide powder doped with fluoride at ambient pressure and temperature. This material possesses a high surface area, narrow pore size distribution, small average crystallite sizes, and good opto-electrical properties. The existence of fluorine increased the opto-electronic activity of tin dioxide by 20 times, and conductivity by 100 times compared with pristine tin dioxide prepared via the same method. The conductivity of SnO2 in air at 25 °C is 5 × 10-5 S/m, whereas that of F-SnO2 is 4.8 × 10-3 S/m. The structures of these materials were characterized with powder X-ray diffraction, N2 sorption analysis, transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and UV-visible spectroscopy. Fluorine occupies the framework of tin dioxide by replacing some of the oxygen atoms. The structure, conductance, and optical properties of these materials are discussed in this paper.

Generation of Oxygen Vacancies in Metal-Organic Framework-Derived One-Dimensional Ni0.4Fe2.6O4 Nanorice Heterojunctions for ppb-Level Diethylamine Gas Sensing

Metal-organic frameworks (MOFs) are ideal sensing materials due to their distinctive morphologies, high surface area, and simple calcination to remove sacrificial MOF scaffolds. Oxygen vacancies (O_vs) can be efficiently generated by the thermal annealing of metal oxides in an inert atmosphere. Herein, MIL-53-based Fe and Fe/Ni-MOFs nanorices (NRs) were first prepared by using a solvothermal method, and then one-dimensional (1D) Fe₂O₃ and Ni_0.4Fe_2.6O₄ NRs were derived from the MOFs after calcination at 350 °C in an air and argon (Ar) atmosphere, respectively. It was found that Ar-annealed Ni_0.4Fe_2.6O₄ NRs have higher O_vs concentrations (82.11%) and smaller NRs (24.3 nm) than air-annealed NRs (65.68% & 31.5 nm). Beneficially, among the synthesized NRs, the Ar-Ni_0.4Fe_2.6O₄ NRs show a higher sensitivity to diethylamine (DEA) (R_a/R_g = 23 @ 5 ppm, 175 °C), low detection limit (R_a/R_g = 1.2 @ 200 ppb), wide dynamic response (R_a/R_g = 93.5@ 30 ppm), high stability (30 days), and faster response/recovery time (4 s/38 s). Moreover, the 1D nanostructure containing heterostructures offers excellent sensing selectivity and a wide detection range from 200 ppb to 30 ppm in the presence of DEA. The outstanding gas sensing behavior can be attributable to synergistic impact, structural advantages, high concentration of O_vs, and the heterojunction interface, which can have profound effects on gas sensor performance. This study provides a unique technique for constructing high-performance gas sensors for ppb-level DEA detection and the formation of O_vs in metal oxides without the need for any additives.

Synthesis, Structural and Sensor Properties of Nanosized Mixed Oxides Based on In2O3 Particles

The paper considers the relationship between the structure and properties of nanostructured conductometric sensors based on binary mixtures of semiconductor oxides designed to detect reducing gases in the environment. The sensor effect in such systems is determined by the chemisorption of molecules on the surface of catalytically active particles and the transfer of chemisorbed products to electron-rich nanoparticles, where these products react with the analyzed gas. In this regard, the role is evaluated of the method of synthesizing the composites, the catalytic activity of metal oxides (CeO₂, SnO₂, ZnO), and the type of conductivity of metal oxides (Co₃O₄, ZrO₂) in the sensor process. The effect of oxygen vacancies present in the composites on the performance characteristics is also considered. Particular attention is paid to the influence of the synthesis procedure for preparing sensitive layers based on CeO₂-In₂O₃ on the structure of the resulting composites, as well as their conductive and sensor properties.

Growth of Graphitic Carbon Nitride-Incorporated ZnO Nanorods on Silicon Pyramidal Substrates for Enhanced Hydrogen Sensing Applications

Monitoring the hydrogen gas (H₂) level is highly important in a wide range of applications. Oxide-carbon hybrids have emerged as a promising material for the fabrication of gas sensors for this purpose. Here, for the first time, graphitic carbon nitride (g-C₃N₄)-doped zinc oxide nanorods (ZNRs) have been grown on silicon (Si) pyramid-shaped surfaces by the facile hydrothermal reaction method. The systematic material analyses have revealed that the g-C₃N₄ nanostructures (NS) have been consistently incorporated into the ZNRs on the pyramidal silicon (Py-Si) surface (g-C₃N₄-ZNRs/Py-Si). The combined properties of the present structure exhibit an excellent sensitivity (∼53%) under H₂ gas exposure, better than that of bare ZNRs (12%). The results revealed that the fine incorporation of g-C₃N₄ into ZNRs on the Py-Si surface improves the H₂ gas sensing properties when compared to that of the planar silicon (Pl-Si) surface. The doping of g-C₃N₄ into ZNRs increases the electrical conductivity through its graphene-like edges (due to the formation of delocalized bonds in g-C₃N₄ during carbon self-doping), as revealed by FESEM images. In addition, the presence of defects in g-C₃N₄ induces the gas adsorption properties of ZnO through its active sites. Moreover, the integration of the 1D structure (g-C₃N₄-ZNRs) into a 3D pyramidal structure opens up new opportunities for low-cost H₂ gas sensing at room temperature. It is an easy way to enhance the gas sensing properties of ZNRs at room temperature, which is desirable for practical H₂ sensor applications.

Saliva-based COVID-19 detection: A rapid antigen test of SARS-CoV-2 nucleocapsid protein using an electrical-double-layer gated field-effect transistor-based biosensing system

Facing the unstopped surges of COVID-19, an insufficient capacity of diagnostic testing jeopardizes the control of disease spread. Due to a centralized setting and a long turnaround, real-time reverse transcription polymerase chain reaction (real-time RT-PCR), the gold standard of viral detection, has fallen short in timely reflecting the epidemic status quo during an urgent outbreak. As such, a rapid screening tool is necessitated to help contain the spread of COVID-19 amid the countries where the vaccine implementations have not been widely deployed. In this work, we propose a saliva-based COVID-19 antigen test using the electrical double layer (EDL)-gated field-effect transistor-based biosensor (BioFET). The detection of SARS-CoV-2 nucleocapsid (N) protein is validated with limits of detection (LoDs) of 0.34 ng/mL (7.44 pM) and 0.14 ng/mL (2.96 pM) in 1× PBS and artificial saliva, respectively. The specificity is inspected with types of antigens, exhibiting low cross-reactivity among MERS-CoV, Influenza A virus, and Influenza B virus. This portable system is embedded with Bluetooth communication and user-friendly interfaces that are fully compatible with digital health, feasibly leading to an on-site turnaround, an effective management, and a proactive response taken by medical providers and frontline health workers.

Effect of Composition and Structure of Metal Oxide Composites Nanostructured on Their Conductive and Sensory Properties

Abstract

The relationship between the structure and properties of nanoscale conductometric sensors based on binary mixtures of metal oxides in the detection of reducing gases in the environment is considered. The sensory effect in such systems is determined by the chemisorption of oxygen molecules and the detected gas on the surface of metal oxide catalytically active particles, the transfer of the reaction products to electron-rich nanoparticles, and subsequent reactions. Particular attention is paid to the doping of nanoparticles of the sensitive layer. In particular, the effect of doping on the concentration of oxygen vacancies, the activity of oxygen centers, and the adsorption properties of nanoparticles is discussed. In addition, the role of heterogeneous contacts is analyzed.

Mesoporous polycrystalline SnO2 framework synthesized by direct soft templating method for highly selective detection of NO2

SnO2 is one of the most studied oxide materials for gas sensing applications. Investigations have shown that SnO2 is sensitive to a wide range of gaseous compounds. However, its lack of selectivity remains an issue. Here, a mesoporous polycrystalline SnO2 framework was successfully synthesized using a soft templating method at ambient temperature and pressure. The prepared materials were characterized using x-ray diffraction analysis, high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy, N2 sorption tests, and x-ray photoelectron spectroscopy. Gas sensing analyses were performed on two batches of the material calcined at 400 °C and 500 °C. The resultant materials were highly conductive at relatively low operating temperatures. The thermal annealing and operating temperatures of the materials had significant effects on their gas sensing response and selectivity. The structure calcined at 400 °C showed a very selective response of 407 to 1 ppm NO2. The superior sensing performance of the obtained mesoporous SnO2 framework is attributed to its small crystal size of 4-5 nm-less than double the thickness of the critical electron depletion layer-as well as its high surface area of 89 m2 g-1 and high pore volume of 0.12 cm3 g-1.