Inhibition of charge recombination of NiTiO3 photocatalyst by the combination of Mo-doped impurity state and Z-scheme charge transfer

Abstract

Ilmenite (NiTiO3) semiconductor and metal-free graphitic carbon nitride (g-C3N4) have attracted great attention as photocatalysts because of their visible-light-driven activity. Despite the benefits of visible-light-driven photocatalysis, the utilizations of both semiconductors are limited by their high recombination rates. In this study, molybdenum (Mo)-doped NiTiO3/g-C3N4 composite photocatalysts are introduced as a novel Z-scheme photocatalyst that can efficiently inhibit electron–hole recombination via charge transfer from Mo-doped NiTiO3 to the g-C3N4 phase. The doping of Mo into the NiTiO3 lattice structure not only generates more oxygen vacancies but also promotes the linkage between Ti in NiTiO3 and N in g-C3N4 in the composite photocatalysts. The novel combination of g-C3N4 and Mo-doped NiTiO3 as a composite photocatalyst synergistically affects the photocatalytic degradation of methylene blue under visible-light irradiation through Z-scheme photocatalysis where photogenerated electron–hole pairs are efficiently separated. Thus, the apparent kinetic rate constant of the composite photocatalysts for the removal of methylene blue (MB) under visible-light irradiation is increased by a factor of 6.5 compared with that of pristine NiTiO3. The photoluminescence and electrochemical impedance spectra strongly indicate that the recombination in the composite photocatalysts is efficiently inhibited by the Mo doping as well as by the coupling with g-C3N4.