Toluene Gas Sensor Research Articles

Polyaniline nanofibers based gas sensor for detection of volatile organic compounds at room temperature

In the present study, toluene gas sensor was developed by depositing the film of polyaniline nanofibers (PANI NFs) on silicon substrate. PANI NFs were synthesized by in situ chemical oxidative polymerization method using aniline as monomer. PANI NFs were confirmed by the x-ray Diffraction (XRD), Fourier Infrared Transform Spectroscopy (FTIR), Field - Emission Scanning Electron Microscope (FE-SEM) and High Resolution-Transmission Electron Microscope (HR-TEM). The FE-SEM and HR-TEM were showed that interconnected nanofibers structure of the PANI particles. The diameters of the PANI NFs were measured in range 70–80 nm and length in 400–450 nm. These PANI NFs were explored for the volatile organic compounds (VOCs) sensing such as toluene, ethanol, chloroform, acetone and methanol in the concentration ranging from 50 ppm to 1000 ppm. PANI NFs based sensor was observed to be selective for low concentration of toluene than all VOCs tested. Sensitivity of the PANI NFs sensor found to be 24.5% for 50 ppm for toluene gas. The response and recovery time for toluene (400 ppm) were observed to be 92 s and 120 s, respectively. The PANI NFs sensor was observed to be stable for 45 days.

MOFs-Derived Porous NiFe2O4 Nano-Octahedrons with Hollow Interiors for an Excellent Toluene Gas Sensor.

Toluene is extensively used in many industrial products, which needs to be effectively detected by sensitive gas sensors even at low-ppm-level concentrations. Here, NiFe2O4 nano-octahedrons were calcinated from NiFe-bimetallic metal-organic framework (MOFs) octahedrons synthesized by a facile refluxing method. The co-existence of p-Phthalic acid (PTA) and 3,3-diaminobenzidine (DAB) promotes the formation of smooth NiFe-bimetallic MOFs octahedrons. After subsequent thermal treatment, a big weight loss (about 85%) transformed NiFe2O4 nanoparticles (30 nm) into NiFe2O4 porous nano-octahedrons with hollow interiors. The NiFe2O4 nano-octahedron based sensor exhibited excellent gas sensing properties for toluene with a nice stability, fast response, and recovery time (25 s/40 s to 100 ppm toluene), and a lower detection limitation (1 ppm) at 260 °C. The excellent toluene-sensing properties can not only be derived from the hollow interiors combined with porous nano-octahedrons to favor the diffusion of gas molecules, but also from the efficient catalytic activity of NiFe2O4 nanoparticles.

Toluene- and benzene-selective gas sensors based on Pt- and Pd-functionalized ZnO nanowires in self-heating mode

Selective toluene and benzene gas sensors, based on Pt- and Pd-functionalized ZnO nanowires (NW) in self-heating mode, are presented. The thickness of the initial sputtered metal layer (5 and 10 nm) and annealing temperature (500–750 °C) were varied to optimize the formation of Pt nanoparticles (NPs), whereas the UV irradiation time was optimized to obtain isolated Pd NPs on the surface of crystalline ZnO NWs. After a series of gas sensing studies and optimization of the gas sensors under the self-heating mode, Pt- and Pd-functionalized ZnO NWs showing most sensitive responses to toluene and benzene gases, respectively, and exhibiting sufficient selectivity for these two amongst other reducing gases were obtained. At room temperature, under an applied voltage of 20 V, the maximum response of Pt-functionalized ZnO NWs (initial thickness, 5 nm; annealing temperature, 600 °C) to 50 ppm toluene is 2.86. Moreover, the maximum response of Pd-functionalized ZnO NWs (UV irradiation time, 5 s) to 50 ppm benzene is 2.20. Further, the sensing mechanisms of these sensors are explained. Chemical sensitization by Pd and Pt, as well as the generation of ZnO/Pd and ZnO/Pt heterointerfaces enhanced the sensing performance of these sensors. The selective sensing of toluene and benzene gases by Pt- and Pd-functionalized ZnO NWs, respectively, is explained in terms of the adsorption phenomena. This study opens a pathway to the fabrication of selective toluene and benzene gas sensors with low power consumption operating in the self-heating mode.

One-step synthesis of micro-/mesoporous SnO2 spheres by solvothermal method for toluene gas sensor

Abstract A facile solvothermal synthesis in an ethanol/acetic acid mixture for the fabrication of SnO2 with a controllable hierarchical spherical size and micro-/mesoporosity is presented. SEM, TEM and N2 adsorption/desorption investigation unveiled that the obtained SnO2 spheres exhibited a particle size in the range of 0.6–1.6 μm and a pore size of about 1.4–1.9 nm depending on the volume ratio of acetic acid to ethanol in the reaction mixture, and the spheres were constructed by nanoscale particles. Due to its micro-/mesoporous structure, the SnO2 spheres exhibited large specific surface areas over 100 m2/g. When 10 vol. % of acetic acid at 200 °C for 20 h was used for the reaction, the obtained SnO2 possessed a higher specific surface area of 145 m2/g (SnO2_10). The gas sensing property of SnO2_10 without an additional noble metal co-catalyst exhibited a large toluene sensing response (Ra/Rg) of 20.2 at 400 °C, which was about 6 times higher and acceptable selectivity compared to those of other samples. The study found that the sensing performance in the SnO2 hierarchical spheres was influenced by several factors e.g. particle morphology, pore size and specific surface area rather than only a single parameter. Therefore, a precise control of those influencing parameters may lead to the optimum sensing property. These findings are important for the further development of the micro-/mesoporous metal-based oxide as an alternative successor for toluene gas sensor material.

Toluene Gas Sensing Properties of Pt-Nanoparticle-Decorated Indium Oxide Nanofibers on a Low-Power Consumable Bridge-Type Micro-Platform

Pt-decorated In2O3 nanofibers with tailored size and morphology were synthesized as sensing materials for a highly sensitive toluene gas sensor. The bridge-type micro-platforms, including micro-heaters and micro-electrodes for the integration of In2O3 nanofibers-based sensing materials, were designed to demonstrate the sensing at high temperature with low power consumption. The gas sensing properties of the fabricated toluene gas sensor were systematically investigated by controlling the power of the micro-heater and the concentration of the toluene gas. Additionally, the enhanced sensing properties for various gas concentrations of toluene were investigated for Pt-nanoparticle-decorated In2O3 nanofibers.

Room temperature toluene gas sensor based on TiO2 nanoparticles decorated 3D graphene-carbon nanotube nanostructures

This work presents a highly sensitive room-temperature gas sensor based on 3D titanium dioxide/graphene-carbon nanotube (3D TiO2/G-CNT) fabricated by chemical vapor deposition and sparking methods. Characterizations by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and Transmission electron microscopy confirmed the formation of 3D graphene-carbon nanotube nanostructures decorated with TiO2 nanoparticles. The toluene detection performances of 3D TiO2/G-CNT structures with varying Ti sparking times were investigated in comparison with 3D G-CNT, TiO2-CNT, graphene and CNTs at room temperature. From result, the optimal sparking time of 60 s led to an optimal sensor response of 42%–500 ppm at room temperature. In addition, the optimal 3D TiO2/G-CNT exhibited substantially higher toluene response, sensitivity and selectivity than 3D G-CNT, TiO2-CNT, graphene and CNTs over a low concentration range of 50–500 ppm. The toluene-sensing mechanisms of 3D titanium dioxide/graphene-carbon nanotube nanostructures were proposed based on the formation of Schottky metal-semiconductor junctions between metallic 3D graphene-carbon nanotube structures and n-type semiconducting titanium dioxide nanoparticles due to the adsorption of toluene molecules via low-temperature reducing reactions or direct charge transfer process.

A low temperature, highly sensitive and fast response toluene gas sensor based on In(III)-SnO2 loaded cubic mesoporous graphitic carbon nitride

Abstract Low temperature gas sensors for monitoring low ppm volatile organic compounds (VOCs) in indoor climate have critical advantages in designing portable sensing devices. Herein, a highly sensitive as well as fast response In(III)-SnO2 loaded cubic mesoporous mpg-CN (commonly known as g-C3N4) based toluene gas sensor has been fabricated through template inversion of KIT-6. When exposed to a variety of test VOCs at 200 °C, the In(III)-SnO2/mpg-CN (1% In) showed a highly selective response (Ra/Rg = 61.4) and fast reversible response/recovery (4/2 s) to 50 ppm toluene gas. The sensor was also able to selectively detect 50 ppm (R = 2.4) and 100 ppm (R = 3.6) toluene gas at 90 °C. Compared to mesoporous In(III)-SnO2, the mpg-CN supported In(III)-SnO2 nanocomposite shows ∼2 fold increase in response to toluene gas while reducing the optimized operating temperature by 50 °C. The significant enhancement in sensitivity and lowering down of optimized operating temperature is attributed to the higher surface area, easily accessible mesopore channels of 3D mesoporous cubic structure and suitable heterojunction formation by the semiconducting In(III)-SnO2/mpg-CN nanocomposite. The findings reported in this study shows promising glimpse for designing a novel strategy to the development of ultrasensitive VOCs sensors working at low operating temperature.

Ultrasensitive and low detection limit of toluene gas sensor based on SnO2-decorated NiO nanostructure

Abstract In this work, an ultrasensitive and low detection limit of toluene gas sensor based on SnO 2 -decorated NiO nanostructure synthesized via a simple hydrothermal route was described. The test results demonstrated that the sensor based on SnO 2 -decorated NiO nanostructure showed excellent sensitivity and selectivity toward toluene, giving a high response of 66.2–100 ppm, which was 50 times higher than that of the pure NiO nanospheres (1.3–100 ppm). Additionally, the sensor had surpassingly low detection limit (ppb-level), showing a response of 1.2–10 ppb toluene. Besides, the sensor also exhibited anti-humidity properties in some way, giving an acceptable response (11.1–10 ppm) to toluene at 90% relative humidity. The ultrasensitive characteristics and low detection limit could be explained from the variation of the carrier concentration caused by the change of the thickness of near-surface hole accumulation layer between p-type NiO and n-type SnO 2 . Furthermore, the increase of oxygen adsorption also improved the sensing performance.

Multiwalled carbon nanotubes–zinc oxide nanocomposites as low temperature toluene gas sensor

The performance of nanocomposite MWCNT–ZnO thin films was investigated as toluene gas sensor. The nanocomposites MWCNT–ZnO thin films were synthesized by reflux method with the variation of MWCNT:ZnO ratio on 1:0, 3:1, 1:1, 1:3, and 0:1. Crystallinity and morphology characterization show that the crystal structure was not influenced by the presence of MWCNT, and the presence of MWCNTs could prevent the agglomeration of ZnO nanostructure. The dynamic response curve of nanocomposites MWCNT–ZnO thin films shows two different patterns at low temperature region and high temperature region. At low temperature region, the sensor response decreases as the increasing operating temperature and increasing the concentration of ZnO. On the other hand, at high temperature region, the sensor response increases as the increasing operating temperature and increasing the concentration of ZnO. Moreover, the variation concentration of MWCNT and ZnO can decrease the operating temperature of the sensors. The sensor with the ratio of MWCNT:ZnO at 1:3 show highest sensor response that reaches 17% at 150 °C of operating temperature, while the pure MWCNTs and pure ZnO show no response at that temperature.

Reduced graphene oxide for fiber-optic toluene gas sensing.

A fiber-optic toluene gas sensor based on reduced graphene oxide (rGO) is demonstrated and its sensing property is investigated experimentally and theoretically. The rGO film is deposited on a side polished fiber (SPF), allowing the strong interaction between rGO film and propagating field and making the SPF sensitive to toluene gas. It is found that the sensor has good linearity and reversibility and can work at room temperature with the response and the recovery time of 256 s and the detection limit of 79 ppm. Moreover, a theoretical model for the sensor is established to analyze the sensing mechanism. Theoretical analysis indicates this type of sensor could work in a wide range of toluene gas concentration and shows that a significant rise in its sensitivity can be expected by adjusting the doping level or chemical potential of graphene.

Synthesis and enhanced toluene gas sensing properties of 1-D α-MoO3/Fe2(MoO4)3 heterostructure

One-dimensional (1-D) α-MoO3/Fe2(MoO4)3 heterostructure nanomaterials has been synthesized by a low-cost and environmentally friendly hydrothermal strategy. The structure and morphology of composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). The results revealed that Fe2(MoO4)3 nanoparticles were uniformly coated on the surface of α-MoO3 nanobelts. The α-MoO3/Fe2(MoO4)3 nanocomposite showed enhanced sensing response and selectivity to toluene vapor compared to bare α-MoO3 nanobelts at the optimal operating temperature of 250 °C. The improved performance can be attributed to the unique 1-D belt-like morphology of α-MoO3 support, the improved catalytic properties of Fe2(MoO4)3, and the formation of the heterojunction barrier at the interface of the two phases, which illuminates that α-MoO3/Fe2(MoO4)3 composite is a potential candidate for toluene gas sensors.

Monodisperse ZnFe2O4 nanospheres synthesized by a nonaqueous route for a highly slective low-ppm-level toluene gas sensor

Monodisperse ZnFe2O4 nanospheres were succesuffully synthesized via a nonaqueous route in benzyl alcohol at low temperaure of 200°C. It was found that the ZnFe2O4 is 7–16nm in diameter with a large surface area of 87.40m2/g. The gas sensor based on ZnFe2O4 nanospheres shows a high pontential for detecting low-ppm-level toluene, exhibiting a good linearity ranging from 1 to 100ppm with a high response (100ppm:9.98) and excellent selectivity.

Selective detection of low concentration toluene gas using Pt-decorated carbon nanotubes sensors

We demonstrated the preparation of high-performance toluene (C7H8) gas sensor, by using the Pt-multiwalled carbon nanotubes (MWCNTs) composite materials. We optimized the size of the Pt nanoparticles by controlling the predeposited Pt thickness, for obtaining the highest sensing performances. We have obtained the sensor responses of 3.91 and 5.06, at concentrations of 1 and 5ppm of C7H8 gas, respectively, at 150°C. We discussed the associated sensing mechanisms and proposed the reasons why the Pt-functionalization drastically enhanced the sensing behaviors of the Pt-MWCNTs composite sensors selectively to C7H8 gas.

Fabrication of porous α-Fe2O3nanoshuttles and their application for toluene sensors

1D unique porous α-Fe2O3 nanoshuttles (NSs) were synthesized by a template-/surfactant-free low temperature hydrothermal approach (60 °C, 48 h), followed by a simple annealing process (300 °C, 1 h). The prepared α-Fe2O3 NSs (ca. 40 nm in diameter and 250 nm in length) have a rugged surface and a porous structure with numerous nanopore inlets (about 1–10 nm in diameter). The hydrothermal time dependent experiment demonstrated that the formation of the NSs is a gradual process, which underwent growth, strong, spilt, and re-spilt processes as reaction times were prolonged from 6 to 48 h. The reaction temperature also has a significant influence on the morphology of the α-Fe2O3 products. Increasing reaction temperature to 100 and 120 °C led to the formation of rod-like nanostructures instead of NSs, and a higher reaction temperature of 140 °C produced a large solid sphere-like morphology (700 nm–1 μm in diameter). Gas sensing properties of the porous α-Fe2O3 NSs were investigated for toluene detection. The sensor showed excellent gas sensing performance for toluene with good reproducibility, short response and recovery time (3–8 and 2–4 s, respectively), and high response. Notably, the α-Fe2O3 NS sensor showed a nearly linear response in the range of 10–100 ppm of toluene, indicating the potential for application in ppm-level toluene gas sensors. The present work is expected to provide new insights into the easy and effective development of 1D porous α-Fe2O3 nanostructures.

A Nanopore Structured High Performance Toluene Gas Sensor Made by Nanoimprinting Method

Toluene gas was successfully measured at room temperature using a device microfabricated by a nanoimprinting method. A highly uniform nanoporous thin film was produced with a dense array of titania (TiO2) pores with a diameter of 70∼80 nm using this method. This thin film had a Pd/TiO2 nanoporous/SiO2/Si MIS layered structure with Pd-TiO2 as the catalytic sensing layer. The nanoimprinting method was useful in expanding the TiO2 surface area by about 30%, as confirmed using AFM and SEM imaging. The measured toluene concentrations ranged from 50 ppm to 200 ppm. The toluene was easily detected by changing the Pd/TiO2 interface work function, resulting in a change in the I–V characteristics.

진공여과증착법을 이용한 SWNT-PtOx계 마이크로 톨루엔 가스센서

Toluene() gas sensors were fabricated using loaded with SWNTs by a new deposition method. The nanoparticle powders of SWNTs- composite were deposited on Si wafer substrates by a vacuum filtering deposition method. The fabricated sensors were tested against toluene gas which is a kind of the Volatile Organic Compounds. The composition ratio that exhibited the highest response to toluene gases was SWNTs : $PtO_x\;

Development of a novel hand-held toluene gas sensor: Possible use in the prevention and control of sick building syndrome

A novel hand-held toluene gas sensor has been developed. It can be utilized in the control and prevention of sick building syndrome. The sensor is based on the principle that toluene gas reacts with iodine pentoxide producing a brown coloured product, iodine. Iodine pentoxide is impregnated on a filter which is subsequently exposed to toluene gas for a duration of 30 min. The product is detected by measuring the intensity of reflected light at 460 nm using a photo diode and a light emitting diode housed in a hand-held photometer. The degree of colour change is proportional to the concentration of toluene gas. The relative standard deviation for the response ( n = 3) to colour change was <10.5% proving this method to be reproducible. By using optimized conditions, we were able to detect 0.05 ppm toluene gas, lower than the 0.07 ppm guideline value for indoor toluene concentration set by World Health Organization. The technique is hardly affected by other common indoor gases, except for a possible interference by benzenoid aromatic hydrocarbons. This sensor is simple, specific, highly sensitive and is suitable for field operations.