Zinc ferrite based gas sensors: A review

Flammable, explosive and toxic gases, such as hydrogen, hydrogen sulfide and volatile organic compounds vapor, are major threats to the ecological environment safety and human health. Among the available technologies, gas sensing is a vital component, and has been widely studied in literature for early detection and warning. As a metal oxide semiconductor, zinc ferrite (ZnFe2O4) represents a kind of promising gas sensing material with a spinel structure, which also shows a fine gas sensing performance to reducing gases. Due to its great potentials and widespread applications, this article is intended to provide a review on the latest development in zinc ferrite based gas sensors. We first discuss the general gas sensing mechanism of ZnFe2O4 sensor. This is followed by a review of the recent progress about zinc ferrite based gas sensors from several aspects: different micro-morphology, element doping and heterostructure materials. In the end, we propose that combining ZnFe2O4 which provides unique microstructure (such as the multi-layer porous shells hollow structure), with the semiconductors such as graphene, which provide excellent physical properties. It is expected that the mentioned composites contribute to improving selectivity, long-term stability, and other sensing performance of sensors at room or low temperature

Breakthroughs in the Design of Novel Carbon-Based Metal Oxides Nanocomposites for VOCs Gas Sensing

Nowadays, the detection of volatile organic compounds (VOCs) at trace levels (down to ppb) is feasible by exploiting ultra-sensitive and highly selective chemoresistors, especially in the field of medical diagnosis. By coupling metal oxide semiconductors (MOS e.g., SnO2, ZnO, WO3, CuO, TiO2 and Fe2O3) with innovative carbon-based materials (graphene, graphene oxide, reduced graphene oxide, single-wall and multi-wall carbon nanotubes), outstanding performances in terms of sensitivity, selectivity, limits of detection, response and recovery times towards specific gaseous targets (such as ethanol, acetone, formaldehyde and aromatic compounds) can be easily achieved. Notably, carbonaceous species, highly interconnected to MOS nanoparticles, enhance the sensor responses by (i) increasing the surface area and the pore content, (ii) favoring the electron migration, the transfer efficiency (spillover effect) and gas diffusion rate, (iii) promoting the active sites concomitantly limiting the nanopowders agglomeration; and (iv) forming nano-heterojunctions. Herein, the aim of the present review is to highlight the above-mentioned hybrid features in order to engineer novel flexible, miniaturized and low working temperature sensors, able to detect specific VOC biomarkers of a human's disease

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

Multilayer Thin Films

This book, "Multilayer Thin Films-Versatile Applications for Materials Engineering", includes thirteen chapters related to the preparations, characterizations, and applications in the modern research of materials engineering. The evaluation of nanomaterials in the form of different shapes, sizes, and volumes needed for utilization in different kinds of gadgets and devices. Since the recently developed two-dimensional carbon materials are proving to be immensely important for new configurations in the miniature scale in the modern technology, it is imperative to innovate various atomic and molecular arrangements for the modifications of structural properties. Of late, graphene and graphene-related derivatives have been proven as the most versatile two-dimensional nanomaterials with superb mechanical, electrical, electronic, optical, and magnetic properties. To understand the in-depth technology, an effort has been made to explain the basics of nano dimensional materials. The importance of nano particles in various aspects of nano technology is clearly indicated. There is more than one chapter describing the use of nanomaterials as sensors. In this volume, an effort has been made to clarify the use of such materials from non-conductor to highly conducting species. It is expected that this book will be useful to the postgraduate and research students as this is a multidisciplinary subject

NEW FLEXIBLE POLYVINYLIDENE FLUORIDE NANOCOMPOSITES FOR FUTURE APPLICATIONS

In this work, we report novel flexible polyvinylidene fluoride (PVDF) hybrid pressure sensors with good mechanical properties. Hybrid combinations of reduced graphene oxide (rGO) with different nano metal oxides -titanium nanolayer (TNL), iron oxide (FeO), and zinc oxide (ZnO)- in PVDF matrix were prepared by solution casting method. In addition to the pressure sensing and vapor sensing properties, the thermal, mechanical, electrical, and dielectric characteristics of the materials are studied. PVDF/rGO (2.5 wt.%)-TNL (2.5 wt.%) hybrid composite showed 2 and 3.6 times enhancement, respectively in tensile strength and Young’s modulus compared to the neat PVDF. The dielectric constant for PVDF/rGO-TNL at 100 Hz was 3.6 times higher than neat PVDF. In pressure sensing, the additives in the matrix increased the sensitivity by 333.46% at 5 kPa and 200.7% at 10.7 kPa and 246.7% at 17.6 kPa compared to PVDF/TNL (5 wt.%). The hybrid composite also exhibited good sensing ability towards the vapors of acetone, tetrahydrofuran (THF), and dimethylformamide (DMF) respectively 1.8, 2.5 and 2 times higher than PVDF/TNL. PVDF/rGO (2.5 wt.%)-FeO (2.5 wt.%) hybrid composite showed 1.3 and 13.8 times enhancement in tensile strength and Young’s modulus respectively, compared to neat PVDF. The dielectric constant at 100 Hz was 1.87 times higher than the pure polymer. In pressure sensing, the sensitivity increased by 41% at 5 kPa, 24.8% at 10.7 kPa and 30.3% at 17.6 kPa compared to PVDF/FeO (5 wt.%). PVDF/rGO-FeO also exhibited good vapor sensing towards acetone, THF, and DMF respectively 1.2, 1.24 and 1.4 times higher than the PVDF/FeO. For PVDF/rGO (2.5 wt.%)-ZnO (2.5 wt.%) hybrid composite, the enhancement in tensile strength and Young’s modulus was 1.98 and 14 times respectively higher than the PVDF. Its dielectric constant at 100 Hz was 1.6 times higher compared to PVDF. In pressure sensing, the sensitivity increased by 167.6% at 5 kPa, 657% at 10.7 kPa and 1066.6% at 17.6 kPa compared to PVDF/ZnO (5 wt.%). PVDF/rGO-ZnO also exhibited good vapor sensing towards acetone, THF, and DMF respectively 1.76, 2.6 and 1.89 times higher than PVDF/ZnO. It was found that PVDF/rGO-FeO possesses the best performance to detect Acetone asn PVDF/rGO-ZnO to detect THF. PVDF/rGO-ZnO and PVDF/rGO-FeO showed the same performance to detect DMF, thus suggesting the future fabrication of electronic nose or e-nose to distinguish polar and non-polar solvents with these polymer nanocomposites.QNRF for providing some financial support through the research grant NPRP 6-282-2-119

Multilayer Thin Films

This book, "Multilayer Thin Films-Versatile Applications for Materials Engineering", includes thirteen chapters related to the preparations, characterizations, and applications in the modern research of materials engineering. The evaluation of nanomaterials in the form of different shapes, sizes, and volumes needed for utilization in different kinds of gadgets and devices. Since the recently developed two-dimensional carbon materials are proving to be immensely important for new configurations in the miniature scale in the modern technology, it is imperative to innovate various atomic and molecular arrangements for the modifications of structural properties

Exploring SnxTi1-xO2 Solid Solutions Grown onto Graphene Oxide (GO) as Selective Toluene Gas Sensors

The major drawback of oxide-based sensors is the lack of selectivity. In this context, SnxTi1- xO2/graphene oxide (GO)-based materials were synthesized via a simple hydrothermal route, varying the titanium content in the tin dioxide matrix. Then, toluene and acetone gas sensing performances of the as-prepared sensors were systematically investigated. Specifically, by using 32:1 SnO2/GO and 32:1 TiO2/GO, a greater selectivity towards acetone analyte, also at room temperature, was obtained even at ppb level. However, solid solutions possessing a higher content of tin relative to titanium (as 32:1 Sn0.55Ti0.45O2/GO) exhibited higher selectivity towards bigger and non-polar molecules (such as toluene) at 350 \ub0C, rather than acetone. A deep experimental investigation of structural (XRPD and Raman), morphological (SEM, TEM, BET surface area and pores volume) and surface (XPS analyses) properties allowed us to give a feasible explanation of the different selectivity. Moreover, by exploiting the UV light, the lowest operating temperature to obtain a significant and reliable signal was 250 \ub0C, keeping the greater selectivity to the toluene analyte. Hence, the feasibility of tuning the chemical selectivity by engineering the relative amount of SnO2 and TiO2 is a promising feature that may guide the future development of miniaturized chemoresistors

Multilayer Thin Films

This book, "Multilayer Thin Films-Versatile Applications for Materials Engineering", includes thirteen chapters related to the preparations, characterizations, and applications in the modern research of materials engineering. The evaluation of nanomaterials in the form of different shapes, sizes, and volumes needed for utilization in different kinds of gadgets and devices. Since the recently developed two-dimensional carbon materials are proving to be immensely important for new configurations in the miniature scale in the modern technology, it is imperative to innovate various atomic and molecular arrangements for the modifications of structural properties

An electrochemical outlook upon the gaseous ethanol sensing by graphene oxide-SnO2 hybrid materials

Breakthroughs in the synthesis of hybrid materials have led to the development of a plethora of chemiresistors that could operate at lower and lower temperatures. Herein, we report the fabrication of novel composite ma- terials (SnO2-GO 4:1, 8:1 and 16:1) based on graphene oxide (GO) sheets decorated with tin dioxide nano- particles, through a controlled chemical growth. We succeeded in obtaining widely spaced isles of the metal oxide on the carbonaceous material, thus enhancing the electron transfer process (i.e. favored convergent dif- fusion, as investigated through cyclic voltammetric analysis), which plays a pivotal role for the final sensing behavior. Indeed, only with SnO2-GO 16:1 sample, superior responses towards gaseous ethanol were observed both at 150 \ub0C and at RT (by exploiting the UV light), with respect to pristine SnO2 and mechanically prepared SnO2(16)@GO material. Particularly, an improvement of the sensitivity (down to 10 ppb), response and recovery times (about of 60\u201370 s) was assessed. Besides, all the powders were finely characterized on structural (XRPD, FTIR and Raman spectroscopies), surface (active surface area, pores volume, XPS), morphological (SEM, TEM) and electrochemical (cyclic voltammetries) points of view, confirming the effective growth of SnO2 nano- particles on the GO sheets

Semiconductor Gas Sensors: Materials, Technology, Design, and Application

This paper presents an overview of semiconductor materials used in gas sensors, their technology, design, and application. Semiconductor materials include metal oxides, conducting polymers, carbon nanotubes, and 2D materials. Metal oxides are most often the first choice due to their ease of fabrication, low cost, high sensitivity, and stability. Some of their disadvantages are low selectivity and high operating temperature. Conducting polymers have the advantage of a low operating temperature and can detect many organic vapors. They are flexible but affected by humidity. Carbon nanotubes are chemically and mechanically stable and are sensitive towards NO and NH3, but need dopants or modifications to sense other gases. Graphene, transition metal chalcogenides, boron nitride, transition metal carbides/nitrides, metal organic frameworks, and metal oxide nanosheets as 2D materials represent gas-sensing materials of the future, especially in medical devices, such as breath sensing. This overview covers the most used semiconducting materials in gas sensing, their synthesis methods and morphology, especially oxide nanostructures, heterostructures, and 2D materials, as well as sensor technology and design, application in advance electronic circuits and systems, and research challenges from the perspective of emerging technologies. © 2020 by the authors. Licensee MDPI, Basel, Switzerland