Flame-Made La2O3-Based Nanocomposite CO2 Sensors as Perspective Part of GHG Monitoring System.

Matvey Andreev,Vadim Platonov,Sergey Generalov,Vladimir Amelichev,Elena Galitskaya,Sergey Polomoshnov,Valeriy Krivetskiy,Marina Rumyantseva,Anastasiya Nikolaeva,Darya Filatova,Oleg Zhdaneev

doi:10.3390/s21217297

Abstract

Continuous monitoring of greenhouse gases with high spatio-temporal resolution has lately become an urgent task because of tightening environmental restrictions. It may be addressed with an economically efficient solution, based on semiconductor metal oxide gas sensors. In the present work, CO2 detection in the relevant concentration range and ambient conditions was successfully effectuated by fine-particulate La2O3-based materials. Flame spray pyrolysis technique was used for the synthesis of sensitive materials, which were studied with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) and low temperature nitrogen adsorption coupled with Brunauer–Emmett–Teller (BET) effective surface area calculation methodology. The obtained materials represent a composite of lanthanum oxide, hydroxide and carbonate phases. The positive correlation has been established between the carbonate content in the as prepared materials and their sensor response towards CO2. Small dimensional planar MEMS micro-hotplates with low energy consumption were used for gas sensor fabrication through inkjet printing. The sensors showed highly selective CO2 detection in the range of 200–6667 ppm in humid air compared with pollutant gases (H2 50 ppm, CH4 100 ppm, NO2 1 ppm, NO 1 ppm, NH3 20 ppm, H2S 1 ppm, SO2 1 ppm), typical for the atmospheric air of urbanized and industrial area.

Highlights

Introduction iationsGlobal climate change is directly correlated with anthropogenic greenhouse gas (GHG)emissions
A similar phenomenon is observed in the case of NO. This gas is a reducing one, its interaction with the sensitive layer at elevated temperatures leads to formation of NO2 molecules, which is mediated by oxygen on the surface of semiconductor oxide [74]
The main difference in the behavior of surface bidentate carbonates and monodentate carbonates is that the former are completely desorbed when CO2 is removed from the atmosphere, and the latter are partially preserved on the surface

Summary

Materials and Methods

Gas sensitive materials were synthesized by the flame-spray pyrolysis (FSP) technique with the use of the setup, described previously [70]. The LEH solution was diluted to 0.2 M with toluene before FSP process This mixture was supplied to the nozzle with 3 mL/min rate and atomized with the oxygen flow at bar pressure drop. The mm diameter pellets of the samples were pressed from the 0.5 mg of studied material finely grinded with 50 mg of KBr. In situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to investigate the solid-gas interactions. The measurements were performed using constant flow air with a pre-assigned concentration of target gas through a gastight polytetrafluoroethylene (PTFE) sensor chamber. The sensor response S = 100% × (RCO2 − Rair )/Rair was calculated as the difference in electrical resistance of the sensitive layer in the presence of target gas admixture (RCO2 ) and in clean air (Rair ), related to the resistance in clean air (Rair )

Materials Morphology and Phase Composition

Gas Sensor Properties

Conclusions