Thermal Activation of Semiconductive NiO1+x(0<x<1) for Use in Complete Removal of Volatile Organic Compounds

We previously performed the complete removal of volatile organic compounds (VOCs) using thermally excited holes in TiO 2 at high temperatures of about 350–500 °C. In this study, we intend to replace TiO 2 with greenish NiO 1+ x (0< x <1) to lower operation temperature and elucidate the operation mechanism on the basis of the optical and electrical properties of NiO 1+ 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 NiO 1+ x exhibit a performance almost equivalent to that of a powdered system. The present performance of NiO 1+ x is found to exceed that of the previously investigated TiO 2 , although the specific surface of NiO 1+ x (1 m 2 /g) is two orders of magnitude smaller than that of TiO 2 (298 m 2 /g). In parallel, a plausible band scheme for NiO 1+ 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.