Dramatic visible activity in phenol degradation of TCNQ@TiO2 photocatalyst with core–shell structure

Abstract

TCNQ@TiO2 visible photocatalyst with core–shell structure was synthesized by adsorption methods. The photocatalytic activity was adjusted by the thickness of the shell. After formation of TCNQ@TiO2 core–shell structure, visible light photoactivity can be obtained. The photocatalyst activity of TCNQ@TiO2 was enhanced gradually with the increasing proportion of TCNQ. When the mass fraction of TCNQ reaches 20%, it exhibits the highest visible activity. The apparent rate constant k of TCNQ@TiO2-20% is 0.2583h−1, which is almost 67.9 times as high as that of pure TiO2. Under visible irradiation, the photogenerated holes on the HOMO orbit of TCNQ can be injected into the VB of TiO2, resulting in the oxidation of organic pollutant directly. However, the energy of the holes injected into the VB of TiO2 is not high enough to mineralize phenol completely. Under UV irradiation, the photogenerated electrons on the CB of TiO2 can be injected into the LUMO orbit of TCNQ, which is too low that electrons could not combine with O2 easily, interdicting the formation of superoxide radicals and resulting in the decrease of photoactivity.