Thermal Activation of Semiconductive NiO1+x (0

Abstract

We previously performed the complete removal of volatile organic compounds (VOCs) using thermally excited holes in TiO2 at high temperatures of about 350–500 °C. In this study, we intend to replace TiO2 with greenish NiO1+x (0<x<1) to lower operation temperature and elucidate the operation mechanism on the basis of the optical and electrical properties of NiO1+x. The decomposition of toluene (i.e., a representative VOC) starts at 250 °C and is completed at about 300 °C in pure powder. Furthermore, even honeycomb units coated with powdered NiO1+x exhibit a performance almost equivalent to that of a powdered system. The present performance of NiO1+x is found to exceed that of the previously investigated TiO2, although the specific surface of NiO1+x (1 m2/g) is two orders of magnitude smaller than that of TiO2 (298 m2/g). In parallel, a plausible band scheme for NiO1+x (which is consistent with toluene decomposition) has been proposed on the basis of the presence of Ni vacancies and the temperature dependences of electrical conductivity and Seebeck potential.