Effects of Ag Additive in Low Temperature CO Detection with In₂O₃ Based Gas Sensors.

Daniil Naberezhnyi,Nikolay Khmelevsky,Marina Rumyantseva,Alexander Gaskov,Alexander Baranchikov,Joke Hadermann,Elizaveta Konstantinova,Anatoly Aksenenko,Maria Batuk,Darya Filatova

doi:10.3390/nano8100801

Abstract

Nanocomposites In2O3/Ag obtained by ultraviolet (UV) photoreduction and impregnation methods were studied as materials for CO sensors operating in the temperature range 25–250 °C. Nanocrystalline In2O3 and In2O3/Ag nanocomposites were characterized by X-ray diffraction (XRD), single-point Brunauer-Emmet-Teller (BET) method, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping. The active surface sites were investigated using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy and thermo-programmed reduction with hydrogen (TPR-H2) method. Sensor measurements in the presence of 15 ppm CO demonstrated that UV treatment leads to a complete loss of In2O3 sensor sensitivity, while In2O3/Ag-UV nanocomposite synthesized by UV photoreduction demonstrates an increased sensor signal to CO at T < 200 °C. The observed high sensor response of the In2O3/Ag-UV nanocomposite at room temperature may be due to the realization of an additional mechanism of CO oxidation with participation of surface hydroxyl groups associated via hydrogen bonds.

Highlights

Most of the materials for semiconductor gas sensors are nanocomposites in which noble metal nanoparticles are distributed in a semiconductor oxide matrix [1,2,3,4,5,6]
In2O3/Ag nanocomposites were synthesized by UV photoreduction and impregnation methods
Both modification with silver and UV treatment lead to an increase in the concentration of surface hydroxyl groups compared with unmodified In2O3

Summary

Introduction

Most of the materials for semiconductor gas sensors are nanocomposites in which noble metal nanoparticles are distributed in a semiconductor oxide matrix [1,2,3,4,5,6]. In the case of In2O3-UV, the partial replacement of chemisorbed oxygen with surface hydroxyl groups leads to a slight decrease in hydrogen consumption in the low-temperature region in accordance with reactions (3) and (4), respectively: O2(ads) + 2H2 = 2H2O (3). Formation of more active atomic form of chemisorbed oxygen should facilitate the oxidation of carbon monoxide leading to the increase in sensor response It was shown in [48] that supported catalysts containing partially oxidized silver particles possess high catalytic activity in low-temperature oxidation of CO due to the presence of active centers Ag+ and Agδ+, which ensure the adsorption of CO with the formation of carbonyls Ag+-CO or Agδ+-CO that weaken the C–O bond. In addition to the renewal of surface hydroxyl groups capable of oxidizing carbon monoxide again, process (6) will lead to an increase in conductivity, which adds to the increase in the sensor signal

Materials and Methods

Conclusions