Synthesis of Co3+ Doped TiO2 by Co-precipitation Route and Its Gas Sensing Properties

Roussin Lontio Fomekong,Bilge Saruhan

doi:10.3389/fmats.2019.00252

Abstract

Abstract Undoped and Co-doped TiO2 nanoparticles were synthesized by a facile co-precipitation method and calcined at 700°C. The phase identification carried out by XRD measurements and Raman spectroscopy analysis of calcined powders reveals the formation of mainly anatase phase for undoped TiO2, and 0.5 mol % Co-doped TiO2 whereas rutile phase for 1 mol % Co-doped TiO2. The sensors prepared with these powders deposited on interdigital (IDE) sensor platforms were tested toward NO2 and H2 sensing properties at 600 °C. As the undoped and 0.5 % Co-doped TiO2 reveal n-type behavior, 1 % Co-doped TiO2 shows p-type semi-conductive behavior. 1 % Co-doped TiO2 exhibits good sensing performance toward NO2 while the undoped TiO2 powder yields the best sensor performance toward H2 at 600°C. This indicates that the crystal structure of TiO2 sensing material must be adjusted depending on the nature of target gas. The results indicate that the main factor influencing high temperature gas sensor performance of nanoparticulate TiO2 is either the alteration of its electronic structure or the type of polymorphs.

Highlights

NOx gas sensors are gaining importance in automotive exhausts and combustion systems
The undoped and the 0.5 Co-doped TiO2 samples showed pure TiO2 consisted of its two polymorphs; anatase and rutile phases
The amount of rutile phase was found to be slightly higher in 0.5 Co-doped TiO2 than the undoped one

Summary

INTRODUCTION

NOx gas sensors are gaining importance in automotive exhausts and combustion systems. Semiconducting metal oxides are ideally used as gas sensing materials in resistive sensors due to their numerous benefits such as reasonably high sensitivity, easy fabrication processes and low cost (Dey, 2018). Some previous studies in our team show how the Al and Cr-addition alters the electron conductivity of TiO2 from n- to p-type leading to effective gas sensing materials. This paper reports, to the best of our knowledge for the first time, the effect of Co3+doping on the high temperature gas sensing behavior of TiO2. The cobalt acetate and titanium iso-propoxide solutions were adjusted to obtain 0.5 and 1 mol.% of cobalt in TiO2 and were labeled as 0.5 Co-doped TiO2 and 1 Codoped TiO2, respectively These solutions were mixed to each other and stirred for 5 min. The sensor response for n-type semiconductors is defined by (Rgas/Rair – 1) × 100 and (Rair/Rgas – 1) × 100 for oxidizing and reducing gases, respectively, while for p-type semiconductor, (Rgas/Rair – 1) × 100 and (Rair/Rgas – 1) × 100 for reducing and oxidizing gases, respectively

RESULTS AND DISCUSSIONS

CONCLUSION

DATA AVAILABILITY STATEMENT