Pt activated SnO2 nanoparticle clusters were synthesized by a simple solvothermal method. The structure, morphology, chemical state and specific surface area were analyzed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2-sorption studies, respectively. The SnO2 nanoparticle cluster matrix consists of tens of thousands of SnO2 nanoparticles with an ultra-small grain size estimated to be 3.0 nm. And there are abundant random-packed wormhole-like pores, caused by the inter-connection of the SnO2 nanoparticles, throughout each cluster. The platinum element is present in two forms including metal (Pt) and tetravalent metal oxide (PtO2) in the Pt activated SnO2 nanoparticle clusters. The as-synthesized pure and Pt activated SnO2 nanoparticle clusters were used to fabricate gas sensor devices. It was found that the gas response toward 500 ppm of ammonia was improved from 6.48 to 203.44 through the activation by Pt. And the results indicate that the sensor based on Pt activated SnO2 not only has ultrahigh sensitivity but also possesses good response–recovery properties, linear dependence, repeatability, selectivity and long-term stability, demonstrating the potential to use Pt activated SnO2 nanoparticle clusters as ammonia gas sensors. At the same time, the formation mechanisms of the unique nanoparticle clusters and highly enhanced sensitivity are also discussed.

Nanoparticle cluster gas sensor: Pt activated SnO2 nanoparticles for NH3 detection with ultrahigh sensitivity.

This paper reports metal oxide (MOx)-decorated graphene-based sensor array combining with back-propagation (BP) neural network toward the detection of indoor air pollutant exposure. Tin dioxide (SnO 2 ) nanospheres and copper oxide (CuO) nanoflowers-decorated graphene were used as candidates for formaldehyde and ammonia gas sensing, respectively. The as-synthesized sensing materials were characterized in terms of their nanostructural, morphological and compositional features by SEM, Raman spectra, and XRD. The sensor array was fabricated via one-step hydrothermal route and layer-by-layer (LbL) self-assembly technique on the substrate with interdigital microelectrodes. The sensing properties of MOx/graphene composite toward the mixture gas of ammonia and formaldehyde, such as dynamic response, sensitivity, response/recovery time, and stability, were investigated at room temperature. And furthermore, this work successfully achieved the recognition and quantitative prediction of components in the gas mixture of formaldehyde and ammonia through the combination of MOx/graphene-based sensor array and neural network-based signal processing technologies.

Quantitative detection of formaldehyde and ammonia gas via metal oxide-modified graphene-based sensor array combining with neural network model

High sensitivity ammonia gas sensor based on Ag/ZnO composite (SZO) nanostructures and their structural, optical, morphological and gas sensing properties were investigated. Field- emission scanning electron microscopy and high- resolution transmission electron microscopy revealed that pure ZnO flower-like nanorods transformed into nanoellipsoids upon adding of silver (Ag). Scanning transmission electron microscopy (STEM) analysis showed clear flower-like morphology of Ag/ZnO composite. STEM-mapping measurement showed that Zn, Ag and O were homogeneously distributed. The ammonia gas sensing analysis revealed that the Ag/ZnO (6 wt%) showed higher gas response compared with other content of Ag wt%. Ag/ZnO (6 wt%) exhibited the highest response of 29.5 when exposed to 100 ppm ammonia gas. Interestingly, Ag/ZnO (6 wt%) possessed good response and recovery property of 13 and 20 s at low concentration of ammonia at 10 ppm, respectively. The mechanism of gas sensing and enhanced gas response of pure ZnO and Ag/ZnO composite was discussed.

Sensitivity enhancement of ammonia gas sensor based on Ag/ZnO flower and nanoellipsoids at low temperature

Recently, there is an increasing interest in ammonia sensing and detection for a wide range of applications, including food, automotive, chemical, environmental, and medical sectors. A major challenge is to obtain selective, sensitive and environmentally stable sensing polymer/chemical materials that can meet the stringent performance requirements of these application areas. Among various polymer-based sensing materials, polyaniline has emerged as a preferred choice owing to its cost-effectiveness, facile preparation steps, and superior sensing performance towards ammonia. In this review, advances in polyaniline based ammonia detection sensors are summarized, with a special focus on progresses in polyaniline modification techniques to achieve enhanced sensing performance. These techniques utilize interfacial and high dilution syntheses, multifunctional dopants, template synthesis, self-oxidizing template synthesis, etc. , methods. Most up-to-date developments in combining polyaniline with other ammonia sensing materials, including polyaniline nanocomposites with metal oxides, graphene, carbon nanotubes and other carbon nanomaterials, are included. These novel nanocomposites have special capabilities of forming p - n nanojunctions or electron interphase interactions for superior detection sensitivity and selectivity. In addition, existing challenges toward understanding, reproducing, and optimizing the design of polyaniline based ammonia sensors are discussed.

A review on advances in application of polyaniline for ammonia detection

It remains a challenge to find a suitable gas sensing material that shows a high response and shows selectivity towards various gases simultaneously. Here, we report a mixed metal oxide WO3-SnO2 nanostructured material synthesized in situ by a simple, single-step, one-pot hydrothermal method at 200 °C in 12 h, and demonstrate its superior sensing behavior towards volatile organic compounds (VOCs) such as ammonia, ethanol and acetone. SnO2 nanoparticles with controlled size and density were uniformly grown on WO3 nanoplates by varying the tin precursor. The density of the SnO2 nanoparticles on the WO3 nanoplates plays a crucial role in the VOC selectivity. The responses of the present mixed metal oxides are found to be much higher than the previously reported results based on single/mixed oxides and noble metal-doped oxides. In addition, the VOC selectivity is found to be highly temperature-dependent, with optimum performance obtained at 200 °C, 300 °C and 350 °C for ammonia, ethanol and acetone, respectively. The present results on the cost-effective noble metal-free WO3-SnO2 sensor could find potential application in human breath analysis by non-invasive detection.

Hierarchical nanostructured WO3-SnO2 for selective sensing of volatile organic compounds.

In this communication, the fabrication of NH3 gas sensor based on SnO2 thin films modified with metallic clusters (MCs) has been reported. Amongst all the MCs (Pt, Pd, Cr, Au, Cu and In), the integration of Pt MCs of thickness ∼8 nm and 200 μm diameter onto surface of SnO2 thin film exhibit a high sensing response (∼25.7) with a fast response time (∼1 s) towards 450 ppm NH3 at an operating temperature of 230 °C. Pt MCs activate the spill over mechanism for NH3 gas molecules and enhance its interaction with uncovered SnO2 surface. The structural and surface morphology of SnO2 film have been studied and a correlation between the high degree of response behaviour of sensor and highly nanoporous active sensing element is identified. Sensor operation was also tested and showed a good selectivity towards ammonia over acetone, LPG, methane, TCE, NOx, IPA, chloroform and CO2. The Pt/SnO2 sensor was tested for repeated cycles and no significant deterioration in the sensing response was observed and sensor was found to be completely reversible operation for a long span of time. The simple and low-cost sensor structure shows the promising results for the practical realization in NH3 sensing.

Metal clusters activated SnO2 thin film for low level detection of NH3 gas

Custom designed metal anchored SnO2 sensor for H2 detection

In the present work an effort has been made to synthesize nanocrystalline composites (NCC) of Zinc oxide and Tin oxide (ZSO) using chemical route for efficient sensing of NO2 gas at lower operating temperature. The structural, microstructural and optical information have been revealed by X-ray diffraction (XRD), Atomic force microscopy (AFM) and UV-Visible spectroscopy respectively. Sensor structure showed a better sensing response (S ~ 6.64×10 2 ) at a relatively low operating temperature of 70 °C for 20 ppm NO2 gas with an average response time of about 2 min. The sensing response characteristics for NO2 gas has been compared with corresponding results obtained for pure SnO2 and ZnO thin film based sensor structure. Copyright © 2013 VBRI press.

Low Temperature Sensing Of NO2 Gas Using SnO2-ZnO Nanocomposite Sensor

Dodecyl benzene sulfonic acid (DBSA) doped polyaniline (PANI) has been synthesized by ex-situ doping inemeraldine base (EB). The optical and functional properties of as synthesized DBSA doped PANI (PANI-DBSA) have been studied by UV-Visible and FTIR spectroscopy, respectively. A chemo-resistive gas sensorwas prepared using spin coated PANI-DBSA thin ﬁlm for quantitative detection of ammonia (NH 3 ) under ambi-ent conditions (27 C, 50% RH). The sensing characteristics of fabricated sensor were recorded using thedynamic resistance measurement, that revealed high sensitivity in relative response (∼4.5), response time(∼55 sec) and rapid recovery (∼100 sec). The PANI-DBSA thin ﬁlm sensor shows good linearity ( R =0.996)and repeatability over a wide concentration range of NH 3 from 5 to 250 ppm.KEYWORDS: Conducting Polymers, Polyaniline, Dodecyl Benzene Sulfonic Acid (DBSA), Ammonia. 1. INTRODUCTION Ammonia (NH 3 ) is widely used in the production of fer-tilizer, chemicals, refrigeration systems, medical diagno-sis system, material processing and its global productionexceeds from 100 million tons per annum. Its long-termexposure of about 8 hours and inhalation to higher con-centrations≥5000ppmcancauseserioushealthhazards.

Highly Sensitive Chemo-Resistive Ammonia Sensor Based on Dodecyl Benzene Sulfonic Acid Doped Polyaniline Thin Film

The pure and cadmium doped zinc oxide (Cd–ZnO) thick films were deposited on glass substrates by screen printing method from their nanopowders, followed by sintering at 550 °C to obtain desired stoichiometry and better adherence of films. The structural, morphological, optical and electrical properties of the samples were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) with UV–visible spectroscopy, Fourier transform infrared spectroscopy, photoluminescence (PL) and two probe techniques. XRD patterns confirm hexagonal wurtzite structure with single phase of all the samples and SEM micrographs reveal granular grains and porosity in films. The incorporation of cadmium in ZnO lattice is confirmed by IR transmission and Raman spectrum. The E2 (high) phonon and multiphoton modes are observed at 433 and 1136 cm−1 respectively in Raman spectra. The recombination of free and neutral bound excitons near band edge emission are observed in PL spectra. UV–visible measurement confirms the direct band gap that decrease from 3.27 to 3.18 eV and resistivity measurement shows semiconducting nature of the films with decreasing activation energy from 0.31 to 0.26 eV respectively on increasing Cd2+ content due to increase in lattice parameters on doping bigger Cd2+ ions at Zn sites in ZnO.

Md. Shahabuddin

Papers

Metal clusters activated SnO2 thin film for low level detection of NH3 gas

Custom designed metal anchored SnO2 sensor for H2 detection

Low Temperature Sensing Of NO2 Gas Using SnO2-ZnO Nanocomposite Sensor

Highly Sensitive Chemo-Resistive Ammonia Sensor Based on Dodecyl Benzene Sulfonic Acid Doped Polyaniline Thin Film

Novel composites of Zn1−xCdxO (x = 0, 0.05, 0.1) thick films for optoelectronic device application