Gas sensors for oxides synthesis by hydrothermal and microwave hydrothermal methods

so far, gas sensors are playing an increasingly important role in environmental detection, agricultural production, medical treatment and other fields. Semiconductor oxide gas sensors are often used to detect toxic gases because of their low cost, simple manufacture, fast response, good selectivity and high sensitivity. There are many methods to prepare semiconductor oxides, such as hydrothermal synthesis, microwave hydrothermal synthesis and sol-gel synthesis. The advantages of hydrothermal synthesis and microwave hydrothermal synthesis are high economic efficiency and simple operation. The synthesized oxides have many different morphologies, such as zero dimensional, one-dimensional, two-dimensional, three-dimensional and so on. These diff erent morphologies are conducive to gas diff usion and enhance gas sensing performance. Especially the hierarchical structure can greatly improve the gas sensing performance due to its large specifi c surface area, large porosity and high carrier concentration. This paper describes the SMO gas sensor prepared by hydrothermal method and microwave hydrothermal method

A Review on Metal Oxide-Graphene Derivative Nano-Composite Thin Film Gas Sensors

Most of the available commercial solid-state gas/vapor sensors are based on metal oxide semiconductors. Metal oxides (MOs) change their conductivity while exposed to gas or vapors ambient can be utilized as gas or vapor sensing materials. In recent days, graphene has attracted tremendous attention owing to its two-dimensional structure with an extremely high surface to volume ratio, electron mobility, and thermal conductivity. However, intrinsic graphene is relatively inefficient for the adsorption of gas/vapor molecules. In this regard, graphene oxide (GO) and reduced graphene oxide (rGO), which are graphene species functionalized with different oxygen groups that offer a higher amount of adsorption sites improving the sensitivity of the film. Up to now, many research groups across the globe have reported the promising performance towards gas detection using various GO/rGO-metal oxide nanocomposites. This chapter reviews the composites of graphene oxide or reduced graphene oxide and metal oxides in nanoscale dimensions (0-D, 1-D, 2-D, and 3-D) for gas sensing applications considering two specific focus areas, that is, synthesis of nanocomposites and performance assessment for gas/vapor sensing

Gas Sensors Based on Semiconducting Metal Oxide One-Dimensional Nanostructures

This article provides a comprehensive review of recent (2008 and 2009) progress in gas sensors based on semiconducting metal oxide one-dimensional (1D) nanostructures. During last few years, gas sensors based on semiconducting oxide 1D nanostructures have been widely investigated. Additionally, modified or doped oxide nanowires/nanobelts have also been synthesized and used for gas sensor applications. Moreover, novel device structures such as electronic noses and low power consumption self-heated gas sensors have been invented and their gas sensing performance has also been evaluated. Finally, we also point out some challenges for future investigation and practical application

A Review on Preparation of ZnO Nanorods and Their Use in Ethanol Vapors Sensing

The devices of polycrystalline film have small sensitivity that can be overthrown by using high aspect ratio of 1D nanostructures, such as ZnO nanostructures. Sensors based on 1D nanostructures show very quick response time and high sensitivity for their high impact factor. The purpose of this article is to provide a comparison of different methods and the quality of the sensors thus produced. Currently, metal oxide 1D nanoarchitectures like ZnO have great attraction due to their applications in sensors. Metal oxide nanostructures have high aspect ratio, with small consumption of power and low weight, however, keeping excellent chemical and thermal dependability. Different techniques have been adopted to fabricate metal oxide one-dimensional nanostructures like hydrothermal, electro-spinning, sol-gel, ultrasonic irradiation, anodization, solid state chemical reaction, molten-salt, thermal evaporation, carbothermal reduction, aerosol, vapor-phase transport, chemical vapor deposition, RF sputtering, gas-phase-assisted nanocarving, molecular beam epitaxy, dry plasma etching, and UV lithography. The sensitivity depends upon the materials; synthesis technique and morphology of the sensor performance toward a particular gas have different range of success. This article estimates the efficiency of ZnO 1D nanoarchitectures, gas sensors. Finally, in this review, we had mentioned the future directions of investigations in this field

Suspended 1D metal oxide nanostructure-based gas sensor

Department of Materials Science and EngineeringWe developed a novel batch fabrication technology for the ultralow-power-consumption metal oxide gas sensing platform consisting of a suspended glassy carbon heating nanostructure and hierarchical metal oxide nanostructures forests fabricated by the carbon-micro electromechanical systems (carbon-MEMS) and selective nanowire growth process. We have developed a new manufacturing process for suspended glass carbon nanostructures such as single nanowire, nano-mesh and nano-membranes fabricated using carbon-MEMS consisting of the UV-lithography and the polymer pyrolysis processes. We designed a gas sensing platform consisting of suspended glassy carbon heating nanostructures and suspended hierarchical metal oxide nanostructure forests for the sensing part. Glassy carbon structure produced by the carbon-MEMS has many advantages such as high thermal & chemical stabilities, good hardness, and good thermal & electrical characteristics. The electrical conductivity of glassy carbon nanostructures has been increased more than three times by using rapid thermal annealing (RTA) process owing to the inferior heating property of glassy carbon nano-heater in the electrical conductivity. In order to divide the suspended glassy carbon nano-heater and the suspended hierarchical metal oxide nanostructures forests, the insulating layer of HfO2 materials is a high dielectric constant and is deposited uniformly using a atomic layer deposition (ALD) process on a suspended glassy carbon nano-heater. Suspended hierarchical metal oxide nanostructures forests were grown circumferentially on the suspended HfO2/glassy carbon nano-heater using a hydrothermal method consisting of the seed deposition and the growth processes. For selective metal oxide seed layer deposition process, a short-time exposed polymer patterning process was performed using the positive photoresist. After the polymer patterning process, a metal oxide seed layer is deposited using the rf-sputtering system, followed by a metal oxide nanostructure growth process. The distinguishing architecture of a suspended hierarchical metal oxide nanostructures forests/HfO2/glassy carbon nanostructure ensures efficient mass transport to the metal oxide nanostructure detection point of the gas analyte, resulting in highly sensitive gas detection. In the absence of an external heating system, the ultralow-power-consumption gas sensing platform of a suspended hierarchical metal oxide nanostructures forests/HfO2/glassy carbon nanostructure has excellent the gas sensing characteristics.ope

Porous Ceramic Sensors: Hydrocarbon Gas Leaks Detection

According to the American National Standards Institute (ANSI), a sensor is a device which provides a usable output in response to a specified measurement of a physical quantity converted into a signal suitable for processing (e.g., optical, electrical, or mechanical signals). On the other hand, porous ceramic materials play an important role as sensor materials, because by selecting a suitable base ceramic material for the intended use and then adjusting their overall porosity, pore size distribution, and pore shape, they can cover different applications such as liquid-gas filters, insulators, catalytic supports, mixed of gases separators and sensors, among others. In addition, they have controlled permeability, high melting point, high superficial area, high corrosion and wear resistance, low expansion coefficient, tailored electronic properties, etc. Currently, a few niche areas demand sensors for compact electronic device design, e.g., leak inspections for oil and gas dispositive, flammable and/or toxic gas detection in waste storage areas and confined spaces, hydrocarbons and their associated gas detection at low temperatures and high humidity conditions, among others. In this chapter, the advances in porous ceramic production for hydrocarbons and associated gas detection will be presented and discussed

Review—Non-Invasive Monitoring of Human Health by Exhaled Breath Analysis: A Comprehensive Review

Exhaled human breath analysis is a very promisingfield of research work having great potential for diagnosis of diseases in non-invasive way. Breath analysis has attracted huge attention in thefield of medical diagnosis and disease monitoring in the last twodecades. VOCs/gases (Volatile Organic Compounds) in exhaled breath bear thefinger-prints of metabolic and biophysicalprocesses going on in human body. It’s a non-invasive, fast, non-hazardous, cost effective, and point of care process for diseasestate monitoring and environmental exposure assessment in human beings. Some VOCs/gases in exhaled breath are bio-markers ofdifferent diseases and their presence in excess amount is indicative of un-healthiness. Breath analysis has the potential for earlydetection of diseases. However, it is still underused and commercial device is yet not available owing to multiferrious challenges.This review is intended to provide an overview of major biomarkers (VOCs/gases) present in exhaled breath, importance of theiranalysis towards disease monitoring, analytical techniques involved, promising materials for breath analysis etc. Finally, relatedchallenges and limitations along with future scope will be touched upon.will be touched upon

Recent Trends in Electrospinning of Polymer Nanofibers and their Applications as Templates for Metal Oxide Nanofibers Preparation

Scientists have been paying a special attention for the synthesis of one-dimensional (1D) morphologies to attain new phenomena and novel physicochemical characteristics of materials. Furthermore, 1D nanostructures exhibit long axial ratio, which has a great influence on the physical and chemical properties of materials. It is worth mentioning that electrospinning is one of the most common and efficient techniques used for the preparation of 1D polymer composite nanofibers. Using electrospinning, nanofibers were fabricated by electrostatic stretching of polymer viscous solution by applying a high voltage. This chapter discusses the synthesis of metal oxide nanofibers such as tin oxide (SnO2), zinc oxide (ZnO), titanium oxide (TiO2), and nickel oxide (NiO) using electrospinning process of polymer solution containing metal precursors and followed by annealing procedures to eliminate the polymer galleries, which were chosen as a sacrificial template for the preparation of metal oxide nanofibers. SEM, XRD, and XPS are equipped to characterize the electrospun metal oxide nanofibers and the results settle the formation of homogeneously distributed metal oxide nanofibers