A Highly Sensitive and Room Temperature CNTs/SnO2/CuO Sensor for H2S Gas Sensing Applications

Advancement of metal oxide nanomaterials on agri-food fronts

The application of metal oxide nanomaterials (MOx NMs) in the agrifood industry offers innovative solutions that can facilitate a paradigm shift in a sector that is currently facing challenges in meeting the growing requirements for food production, while safeguarding the environment from the impacts of current agriculture practices. This review comprehensively illustrates recent advancements and applications of MOx for sustainable practices in the food and agricultural industries and environmental preservation. Relevant published data point out that MOx NMs can be tailored for specific properties, enabling advanced design concepts with improved features for various applications in the agrifood industry. Applications include nano-agrochemical formulation, control of food quality through nanosensors, and smart food packaging. Furthermore, recent research suggests MOx's vital role in addressing environmental challenges by removing toxic elements from contaminated soil and water. This mitigates the environmental effects of widespread agrichemical use and creates a more favorable environment for plant growth. The review also discusses potential barriers, particularly regarding MOx toxicity and risk evaluation. Fundamental concerns about possible adverse effects on human health and the environment must be addressed to establish an appropriate regulatory framework for nano metal oxide-based food and agricultural products.

Recent Advances on Metal Oxide Based Sensors for Environmental Gas Pollutants Detection

Optimizing materials and associated structures for detecting various environmental gas pollutant concentrations has been a major challenge in environmental sensing technology. Semiconducting metal oxides (SMOs) fabricated at the nanoscale are a class of sensor technology in which metallic species are functionalized with various dopants to modify their chemiresistivity and crystalline scaffolding properties. Studies focused on recent advances of gas sensors utilizing metal oxide nanostructures with a special emphasis on the structure-surface property relationships of some typical n-type and p-type SMOs for efficient gas detection are presented. Strategies to enhance the gas sensor performances are also discussed. These oxide material sensors have several advantages such as ease of handling, portability, and doped-based SMO sensing detection ability of environmental gas pollutants at low temperatures. SMO sensors have displayed excellent sensitivity, selectivity, and robustness. In addition, the hybrid SMO sensors showed exceptional selectivity to some CWAs when irradiated with visible light while also displaying high reversibility and humidity independence. Results showed that TiO2 surfaces can sense 50 ppm SO2 in the presence of UV light and under operating temperatures of 298-473 K. Hybrid SMO displayed excellent gas sensing response. For example, a CuO-ZnO nanoparticle network of a 4:1 vol.% CuO/ZnO ratio exhibited responses three times greater than pure CuO sensors and six times greater than pure ZnO sensors toward H2S. This review provides a critical discussion of modified gas pollutant sensing capabilities of metal oxide nanoparticles under ambient conditions, focusing on reported results during the past two decades on gas pollutants sensing.

Ultrasensitive Bio-H2S Gas Sensor Based on Cu2O-MWCNT Heterostructures

Developing a respiratory analysis disease diagnosis platform for the H2S biomarker has great significance for the real-time detection of various diseases. However, achieving highly sensitive and rapid detection of H2S gas at the parts per billion level at low temperatures is one of the most critical challenges for developing portable exhaled gas sensors. Herein, Cu2O-multiwalled carbon nanotube (MWCNT) heterostructures with excellent gas sensitivity to H2S at room temperature and a lower temperature were successfully synthesized by a facile two-dimensional (2D) electrodeposition in situ assembly method. The combination of Cu2O and MWCNTs via the principle of optimal conductance growth not only reduced the initial resistance of the material but also provided an ideal interfacial barrier structure. Compared to the response of the pure Cu2O sensor, that of the Cu2O-MWCNT sensor to 1 ppm of H2S increased nearly 800 times at room temperature, and the response time decreased by more than 500 s. In addition to the excellent sensitivity with detection limits as low as 1 ppb, the Cu2O-MWCNT sensor was extremely selective with low-temperature adaptability. The sensor had a response value of 80.6 to 0.1 ppm of H2S at -10 °C, which is difficult to achieve with sensors based on oxygen adsorption/desorption mechanisms. The sensor was used for the detection of real oral exhaled breath, confirming its feasibility as a real-time disease monitoring sensor. The Cu2O-MWCNT heterostructures maximized the advantages of the individual components and laid the experimental foundation for future applications of highly sensitive portable breath analysis platforms for monitoring H2S.

Wearable Nano-Based Gas Sensors for Environmental Monitoring and Encountered Challenges in Optimization

With a rising emphasis on public safety and quality of life, there is an urgent need to ensure optimal air quality, both indoors and outdoors. Detecting toxic gaseous compounds plays a pivotal role in shaping our sustainable future. This review aims to elucidate the advancements in smart wearable (nano)sensors for monitoring harmful gaseous pollutants, such as ammonia (NH3), nitric oxide (NO), nitrous oxide (N2O), nitrogen dioxide (NO2), carbon monoxide (CO), carbon dioxide (CO2), hydrogen sulfide (H2S), sulfur dioxide (SO2), ozone (O3), hydrocarbons (CxHy), and hydrogen fluoride (HF). Differentiating this review from its predecessors, we shed light on the challenges faced in enhancing sensor performance and offer a deep dive into the evolution of sensing materials, wearable substrates, electrodes, and types of sensors. Noteworthy materials for robust detection systems encompass 2D nanostructures, carbon nanomaterials, conducting polymers, nanohybrids, and metal oxide semiconductors. A dedicated section dissects the significance of circuit integration, miniaturization, real-time sensing, repeatability, reusability, power efficiency, gas-sensitive material deposition, selectivity, sensitivity, stability, and response/recovery time, pinpointing gaps in the current knowledge and offering avenues for further research. To conclude, we provide insights and suggestions for the prospective trajectory of smart wearable nanosensors in addressing the extant challenges.

Semiconductor-Type Gas Sensors Based on γ-Fe2O3 Nanoparticles and Its Derivatives in Conjunction with SnO2 and Graphene

The gas sensitivity of semiconductor metal oxides, such as γ-Fe2O3 and SnO2, is investigated together with the synergistic effects in conjunction with grapheme. Nanoparticles of γ-Fe2O3, γ-Fe2O3/SnO2, and γ-Fe2O3/SnO2/RGO, prepared by two-step fabrication, were assembled in gas-sensing devices to assess their sensitivities; response and recovery times for the detection of ethanol, methanol, isopropanol, formaldehyde, H2S, CO, and NO gases at different temperatures but constant concentrations of 100 particles per million (ppm); and H2S, which underwent the dynamic gas sensitivity test in different concentrations. Each sample’s crystallinity and microscopic morphology was investigated with X-ray diffraction and a scanning electron microscope. In comparative gas sensitivity measurements, the ternary composite of γ-Fe2O3/SnO2/RGO was identified as an ideal candidate, as it responds to all four tested liquids in the gas phase as well as H2S with a response value equal to 162.6. Further, only the ternary composite γ-Fe2O3/SnO2/RGO hybrid nanoparticles responded to NO gas with a sensor response value equal to 4.09 in 12 s. However, only the binary composite γ-Fe2O3/SnO2 responded to CO with a corresponding sensitivity of 1.59 units in 7 s.

The Combination of Two-Dimensional Nanomaterials with Metal Oxide Nanoparticles for Gas Sensors: A Review

Metal oxide nanoparticles have been widely utilized for the fabrication of functional gas sensors to determine various flammable, explosive, toxic, and harmful gases due to their advantages of low cost, fast response, and high sensitivity. However, metal oxide-based gas sensors reveal the shortcomings of high operating temperature, high power requirement, and low selectivity, which limited their rapid development in the fabrication of high-performance gas sensors. The combination of metal oxides with two-dimensional (2D) nanomaterials to construct a heterostructure can hybridize the advantages of each other and overcome their respective shortcomings, thereby improving the sensing performance of the fabricated gas sensors. In this review, we present recent advances in the fabrication of metal oxide-, 2D nanomaterials-, as well as 2D material/metal oxide composite-based gas sensors with highly sensitive and selective functions. To achieve this aim, we firstly introduce the working principles of various gas sensors, and then discuss the factors that could affect the sensitivity of gas sensors. After that, a lot of cases on the fabrication of gas sensors by using metal oxides, 2D materials, and 2D material/metal oxide composites are demonstrated. Finally, we summarize the current development and discuss potential research directions in this promising topic. We believe in this work is helpful for the readers in multidiscipline research fields like materials science, nanotechnology, chemical engineering, environmental science, and other related aspects.

Volatile Organic Compounds as Potential Biomarkers for Noninvasive Disease Detection by Nanosensors: A Comprehensive Review

Biomarkers are biological molecules associated with physiological changes of the body and aids in the detecting the onset of disease in patients. There is an urgent need for self-monitoring and early detection of cardiovascular and other health complications. Several blood-based biomarkers have been well established in diagnosis and monitoring the onset of diseases. However, the detection level of biomarkers in bed-side analysis is difficult and complications arise due to the endothelial dysfunction. Currently single volatile organic compounds (VOCs) based sensors are available for the detection of human diseases and no dedicated nanosensor is available for the elderly. Moreover, accuracy of the sensors based on a single analyte is limited. Hence, breath analysis has received enormous attention in healthcare due to its relatively inexpensive, rapid, and noninvasive methods for detecting diseases. This review gives a detailed analysis of how biomarker imprinted nanosensor can be used as a noninvasive method for detecting VOC to health issues early using exhaled breath analysis.

Recent advances in g-C3N4 based gas sensors for the detection of toxic and flammable gases: a review

In recent years, many 2D nanomaterials like graphene, MoS2, phosphorene, and metal oxide nanosheets have been investigated for gas sensing applications due to their excellent properties. Amongst other 2D nanomaterials, graphitic carbon nitride (g-C3N4) has attracted significant attention owing to its simple synthesis process, tunable electronic properties, and exceptional physicochemical properties. Such remarkable properties assert g-C3N4 as a potential candidate for the next-generation high-performance gas sensors employed in the detection of toxic and flammable gases. Although several articles and reviews are available on g-C3N4 for their synthesis, functionalities, and applications for the detection of humidity. Few of them has focused their attention on gas sensing using g-C3N4. Thus, in this review, we have methodically summed up the recent advances in g-C3N4 and its composites-based gas sensor for the detection of toxic and flammable gases. Moreover, we have also incorporated the synthesis strategies and the comprehensive physics of g-C3N4 based gas sensors. Additionally, different approaches are presented for the enhancement of gas sensing/detecting properties of g-C3N4 based gas sensors. Finally, the challenges and future scope of g-C3N4 based gas sensors for real-time monitoring of gases have been discussed.

CuxO Nanostructure-Based Gas Sensors for H2S Detection: An Overview

H2S gas is a toxic and hazardous byproduct of the oil and gas industries. It paralyzes the olfactory nerves, with concentrations above 100 ppm, resulting in loss of smell; prolonged inhalation may even cause death. One of the most important semiconducting metal oxides for the detection of H2S is CuxO (x = 1, 2), which is converted to CuxS upon exposure to H2S, leading to a remarkable modulation in the resistance and appearance of an electrical sensing signal. In this review, various morphologies of CuxO in the pristine form, composites of CuxO with other materials, and decoration/doping of noble metals on CuxO nanostructures for the reliable detection of H2S gas are thoroughly discussed. With an emphasis to the detection mechanism of CuxO-based gas sensors, this review presents findings that are of considerable value as a reference.

Thermal interface material with graphene enhanced sintered copper for high temperature power electronics

Sintered nano-copper is becoming a promising candidate as thermal interface material (TIM) for die attaching in high power electronics. It exhibits much higher thermal conductivity and operating temperature than conventional TIMs based on polymer and solder joints, and higher electromigration resistance and lower cost than sintered nano-silver TIM. However, the performance of existing sintered nano-copper is lower than expected because of high porosity resulted from poor sintering of copper particles with oxide shell. Here we demonstrate a method of improving the thermal conductivity of sintered copper by addition of graphene/Cu-Cu_xO with controllable diameter of ∼163 nm. The measured thermal conductivity of the sintered composite TIM is enhanced by up to 123.5% compared with that of sintered pure copper. It can be understood as a result of the formation of graphene heat transfer network in sintered TIM. In addition, the C-O-Cu bonds formed at the interface between graphene and copper nanoparticles are critical for improving thermal performance as well as electrical and mechanical performance of the TIM. The developed TIM can be widely used in high power electronic packaging especially for high temperature applications, including IGBT, SiC and GaN power devices.

A Review on Advanced Sensing Materials for Agricultural Gas Sensors

This work is a comprehensive review of sensing materials, which interact with several target gases pertinent to agricultural monitoring applications. Sensing materials which interact with carbon dioxide, water vapor (relative humidity), hydrogen sulfide, ethylene and ethanol are the focus of this work. Performance characteristics such as dynamic range, recovery time, operating temperature, long-term stability and method of deposition are discussed to determine the commercial viability of the sensing materials considered in this work. In addition to the sensing materials, deposition methods are considered to obtain the desired sensing material thickness based on the sensor's mechanism of operation. Various material classes including metal oxides, conductive polymers and carbon allotropes are included in this review. By implementing multiple sensing materials to detect a single target analyte, the issue of selectivity due to cross sensitivity can be mitigated. For this reason, where possible, it is desirable to utilize more than one sensing material to monitor a single target gas. Among those considered in this work, it is observed that PEDOT PSS/graphene and TiO2-coated g-C3N4 NS are best suited for CO2 detection, given their wide dynamic range and modest operating temperature. To monitor the presence of ethylene, BMIM-NTf2, SWCNTs and PtTiO2 offer a dynamic range most suitable for the application and require no active heating. Due to the wide dynamic range offered by SiO2/Si nanowires, this material is best suited for the detection of ethanol; a gas artificially introduced to prolong the shelf life of the harvested crop. Finally, among all other sensing materials investigated, it observed that both SWCNTs and CNTs/SnO2/CuO are most suitable for H2S detection in the given application.