Reduced Graphene Oxide (rGO)-Loaded Metal-Oxide Nanofiber Gas Sensors: An Overview.

Reduced graphene oxide (rGO) is a reduced form of graphene oxide used extensively in gas sensing applications. On the other hand, in its pristine form, graphene has shortages and is generally utilized in combination with other metal oxides to improve gas sensing capabilities. There are different ways of adding rGO to different metal oxides with various morphologies. This study focuses on rGO-loaded metal oxide nanofiber (NF) synthesized using an electrospinning method. Different amounts of rGO were added to the metal oxide precursors, and after electrospinning, the gas response is enhanced through different sensing mechanisms. This review paper discusses rGO-loaded metal oxide NFs gas sensors.

State-of-the-Art Research on Chemiresistive Gas Sensors in Korea: Emphasis on the Achievements of the Research Labs of Professors Hyoun Woo Kim and Sang Sub Kim.

This review presents the results of cutting-edge research on chemiresistive gas sensors in Korea with a focus on the research activities of the laboratories of Professors Sang Sub Kim and Hyoun Woo Kim. The advances in the synthesis techniques and various strategies to enhance the gas-sensing performances of metal-oxide-, sulfide-, and polymer-based nanomaterials are described. In particular, the gas-sensing characteristics of different types of sensors reported in recent years, including core-shell, self-heated, irradiated, flexible, Si-based, glass, and metal-organic framework sensors, have been reviewed. The most crucial achievements include the optimization of shell thickness in core-shell gas sensors, decrease in applied voltage in self-heated gas sensors to less than 5 V, optimization of irradiation dose to achieve the highest response to gases, and the design of selective and highly flexible gas sensors-based WS2 nanosheets. The underlying sensing mechanisms are discussed in detail. In summary, this review provides an overview of the chemiresistive gas-sensing research activities led by the corresponding authors of this manuscript.

V2CTX MXene-based hybrid sensor with high selectivity and ppb-level detection for acetone at room temperature.

High-performance, room temperature-based novel sensing materials are one of the frontier research topics in the gas sensing field, and MXenes, a family of emerging 2D layered materials, has gained widespread attention due to their distinctive properties. In this work, we propose a chemiresistive gas sensor made from V2CTx MXene-derived, urchin-like V2O5 hybrid materials (V2C/V2O5 MXene) for gas sensing applications at room temperature. The as-prepared sensor exhibited high performance when used as the sensing material for acetone detection at room temperature. Furthermore, the V2C/V2O5 MXene-based sensor exhibited a higher response (S% = 11.9%) toward 15 ppm acetone than pristine multilayer V2CTx MXenes (S% = 4.6%). Additionally, the composite sensor demonstrated a low detection level at ppb levels (250 ppb) at room temperature, as well as high selectivity among different interfering gases, fast response-recovery time, good repeatability with minimal amplitude fluctuation, and excellent long-term stability. These improved sensing properties can be attributed to the possible formation of H-bonds in multilayer V2C MXenes, the synergistic effect of the newly formed composite of urchin-like V2C/V2O5 MXene sensor, and high charge carrier transport at the interface of V2O5 and V2C MXene.

Metal-organic frameworks for advanced transducer based gas sensors: review and perspectives.

The development of gas sensing devices to detect environmentally toxic, hazardous, and volatile organic compounds (VOCs) has witnessed a surge of immense interest over the past few decades, motivated mainly by the significant progress in technological advancements in the gas sensing field. A great deal of research has been dedicated to developing robust, cost-effective, and miniaturized gas sensing platforms with high efficiency. Compared to conventional metal-oxide based gas sensing materials, metal-organic frameworks (MOFs) have garnered tremendous attention in a variety of fields, including the gas sensing field, due to their fascinating features such as high adsorption sites for gas molecules, high porosity, tunable morphologies, structural diversities, and ability of room temperature (RT) sensing. This review summarizes the current advancement in various pristine MOF materials and their composites for different electrical transducer-based gas sensing applications. The review begins with a discussion on the overview of gas sensors, the significance of MOFs, and their scope in the gas sensing field. Next, gas sensing applications are divided into four categories based on different advanced transducers: chemiresistive, capacitive, quartz crystal microbalance (QCM), and organic field-effect transistor (OFET) based gas sensors. Their fundamental concepts, gas sensing ability towards various gases, sensing mechanisms, and their advantages and disadvantages are discussed. Finally, this review is concluded with a summary, existing challenges, and future perspectives.

Boosting the sensing properties of resistive-based gas sensors by irradiation techniques: a review.

The ongoing need to detect and monitor hazardous, volatile, and flammable gases has led to the use of gas sensors in several fields to improve safety and health issues. Conductometric type gas sensors, which have considerable advantages over other gas sensors, have thrived in numerous gas sensing fields. The ever-present key challenges and requirements of these sensors are to achieve excellent performance, including high sensitivity, good selectivity, low working temperature, and durability. Therefore, tremendous research effort has focused on improving these properties, and various state-of-the-art techniques have been reported. This review article discusses the recent advances and utilization of various irradiation techniques, including electron-beam, microwave, ion-beam, and gamma-ray irradiation, along with their investigation of the effects on the physicochemical properties of pre-synthesized nanomaterials, sensing performances, and related gas sensing mechanisms. A review of the progress on the effects of different irradiation techniques for boosting the sensing properties can contribute to the evolution of highly reliable sensors to assess the environment and health. For researchers, who work on gas sensors, this paper provides information on the current trends on the advances in the novel state-of-art of irradiated materials and their promising application in the sensitive detection of various toxic and VOCs.

Recent advances in energy-saving chemiresistive gas sensors: A review.

With the tremendous advances in technology, gas-sensing devices are being popularly used in many distinct areas, including indoor environments, industries, aviation, and detectors for various toxic domestic gases and vapors. Even though the most popular type of gas sensor, namely, resistive-based gas sensors, have many advantages over other types of gas sensors, their high working temperatures lead to high energy consumption, thereby limiting their practical applications, especially in mobile and portable devices. As possible ways to deal with the high-power consumption of resistance-based sensors, different strategies such as self-heating, MEMS technology, and room-temperature operation using especial morphologies, have been introduced in recent years. In this review, we discuss different types of energy-saving chemisresitive gas sensors including self-heated gas sensors, MEMS based gas sensors, room temperature operated flexible/wearable sensor and their application in the fields of environmental monitoring. At the end, the review will be concluded by providing a summary, challenges, recent trends, and future perspectives.

Recent progress and perspectives of gas sensors based on vertically oriented ZnO nanomaterials.

Vertically oriented zinc oxide (ZnO) nanomaterials, such as nanorods (NRs), nanowires (NWs), nanotubes (NTs), nanoneedles (NNs), and nanosheets (NSs), are highly ordered architectures that provide remarkable properties for sensors. Furthermore, these nanostructures have fascinating features, including high surface-area-to-volume ratios, high charge carrier concentrations, and many surface-active sites. These features make vertically oriented ZnO nanomaterials exciting candidates for gas sensor fabrication. The development of efficient methods for the production of vertically oriented nanomaterial electrode surfaces has resulted in improved stability, high reproducibility, and gas sensing performance. Moving beyond conventional fabrication processes that include binders and nanomaterial deposition steps has been crucial, as the materials from these processes suffer from poor stability, low reproducibility, and marginal sensing performance. In this feature article, we comprehensively describe vertically oriented ZnO nanomaterials for gas sensing applications. The uses of such nanomaterials for gas sensor fabrication are discussed in the context of ease of growth, stability on an electrode surface, growth reproducibility, and enhancements in device efficiency as a result of their unique and advantageous features. In addition, we summarize applications of gas sensors for a variety of toxic and volatile organic compound (VOC) gases, and we discuss future directions of the vertically oriented ZnO nanomaterials.

Facile synthesis of ZnFe2O4 photocatalysts for decolourization of organic dyes under solar irradiation.

ZnFe2O4 was fabricated by a simple solution-combustion method. The structural, optical and electronic properties are investigated by XRD, TEM, FESEM, UV-vis DRS, PL, FTIR and photocurrent measurements. The photocatalytic activity of the prepared material is studied with regard to the degradation of rhodamine B (Rh B) and Congo red under solar irradiation. The kinetic study showed that the material exhibits zeroth and first order reaction kinetics for the degradation of Rh B and Congo red, respectively. The photocatalytic behaviour of ZnFe2O4 was systematically studied as a function of the activation temperature. ZnFe2O4 prepared at 500 °C showed the highest activity in degrading Rh B and Congo red. The highest activity of ZnFe2O4-500 °C correlates well with the lowest PL intensity, highest photocurrent and lowest particle size.

Facile Approach to Synthesize Au@ZnO Core-Shell Nanoparticles and Their Application for Highly Sensitive and Selective Gas Sensors.

We successfully prepared Au@ZnO core-shell nanoparticles (CSNPs) by a facile low-temperature solution route and studied its gas-sensing properties. The obtained Au@ZnO CSNPs were carefully characterized by X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, and UV-visible spectroscopy. Mostly spherical-shaped Au@ZnO CSNPs were formed by 10-15 nm Au NPs in the center and by 40-45 nm smooth ZnO shell outside. After the heat-treatment process at 500 °C, the crystallinity of ZnO shell was increased without any significant change in morphology of Au@ZnO CSNPs. The gas-sensing test of Au@ZnO CSNPs was examined at 300 °C for various gases including H2 and compared with pure ZnO NPs. The sensor Au@ZnO CSNPs showed the high sensitivity and selectivity to H2 at 300 °C. The response values of Au@ZnO CSNPs and pure ZnO NPs sensors to 100 ppm of H2 at 300 °C were 103.9 and 12.7, respectively. The improved response of Au@ZnO CSNPs was related to the electronic sensitization of Au NPs due to Schottky barrier formation. The high selectivity of Au@ZnO CSNPs sensor toward H2 gas might be due to the chemical as well as catalytic effect of Au NPs.

Effect of Au nanorods on potential barrier modulation in morphologically controlled Au@Cu2O core-shell nanoreactors for gas sensor applications.

In this work, Au@Cu2O core-shell nanoparticles (NPs) were synthesized by simple solution route and applied for CO sensing applications. Au@Cu2O core-shell NPs were formed by the deposition of 30-60 nm Cu2O shell layer on Au nanorods (NRs) having 10-15 nm width and 40-60 nm length. The morphology of Au@Cu2O core-shell NPs was tuned from brick to spherical shape by tuning the pH of the solution. In the absence of Au NRs, cubelike Cu2O NPs having ∼200 nm diameters were formed. The sensor having Au@Cu2O core-shell layer exhibited higher CO sensitivity compared to bare Cu2O NPs layer. Tuning of morphology of Au@Cu2O core-shell NPs from brick to spherical shape significantly lowered the air resistance. Transition from p- to n-type response was observed for all devices below 150 °C. It was demonstrated that performance of sensor depends not only on the electronic sensitization of Au NRs but also on the morphology of the Au@Cu2O core-shell NPs.

Au@Cu2O core-shell nanoparticles as chemiresistors for gas sensor applications: effect of potential barrier modulation on the sensing performance.

Au@Cu2O core-shell nanoparticles (NPs) were synthesized by a solution method at room temperature and applied for gas sensor applications. Transmission electron microscopy (TEM) images showed the formation of Au@Cu2O core-shell NPs, where 12-15 nm Au NPs were covered with 60-30 nm Cu2O shell layers. The surface plasmon resonance (SPR) peak of Au NPs was red-shifted (520-598 nm) after Cu2O shell formation. The response of Au@Cu2O core-shell NPs was higher than that of bare Cu2O NPs to CO at different temperatures and concentrations. Similarly, the response of Au@Cu2O core-shell NPs was higher than that of bare Cu2O NPs for NO2 gas at low temperature. The improved performance of Au@Cu2O core-shell NPs was attributed to the pronounced electronic sensitization, high thermal stability and low screening effect of Au NPs.