Tuning electron orbits and reducibility of spinel Co3O4 via defect engineering for enhanced acetone sensing

Defect engineering is an effective method to regulate the electronic structure and chemical properties of functional materials to improve the catalytic, electrochemical and gas-sensitive properties. However, it is still a major challenge to rationally design defects to boost the amounts and activity of reaction sites. Herein, a strategy is proposed for regulating the content of Co2+ (Oh, octahedron) and oxygen vacancies in spinel Co3O4 (Co-LDH-x, x refers to temperature) via calcination of Co layered double hydroxides (Co-LDH). Where Co2+ (Oh) serves electrons in eg orbitals with a high energy state, and rich oxygen vacancies can act as strong Lewis acid sites to generate Lewis acid-base effects with lone pair electrons. Co-LDH-700 shows excellent repeatability, stability and selectivity in acetone sensing, as well as a low detection limit of 80 ppb. The response of the sensor to 100 ppm acetone is 262.3 at 185 °C, with a rapid response rate (9.8 s). In addition, the formation of the acceptor impurity CoCo′ establishes an acceptor level above the top of the valence band, which is beneficial to the formation of thermal-induced electrons. H2-TPR confirms that the increase of Co2+ content improves the reducing capacity and catalytic effect of Co-LDH-700 in the sensing process. This work proposes a method to increase active sites by modulating Co2+ (Oh) eg orbital and rich oxygen vacancies, which provides a new idea for enhancing the activity of sensitive materials.