NiO Decorated Ti/TiO2 Nanotube Arrays (TiO2NT)/TiO2/g-C3N4 Step-Scheme Heterostructure Thin Film Photocatalyst with Enhanced Photocatalytic Activity for Water Splitting

Abstract A new strategy to enhance the photocatalytic properties of graphitic carbon nitride is reported via constructing an effective NiO decorated Ti/TiO 2 NT/TiO 2 /g-C 3 N 4 S-scheme heterostructure photocatalyst thin film (Ti/TiO 2 NT/TiO 2 /g-C 3 N 4 /NiO). This thin film photocatalyst can separate hydrogen gas and oxygen gas into different sides of the Ti substrate. Owing to the synergistic effect of the NiO as co-catalyst and the formation of Step-scheme (S-scheme) heterojunction between g-C 3 N 4 and TiO 2 , the electrons and holes were successfully separated to their opposing active centers, which is beneficial to inhibiting the recombination of the charge carriers. The gas evolution rate of Ti/TiO 2 NT/TiO 2 /g-C 3 N 4 /NiO is 7.97 μmol h −1  cm −2 under the irradiation of high-pressure mercury lamp, which was 3 and 1.3 times as high as that of the Ti/TiO 2 NT/g-C 3 N 4 and Ti/TiO 2 NT/TiO 2 /g-C 3 N 4 , respectively. Firstly, benefiting from the well-matched band structure, a direct S-scheme Ti/TiO 2 NT/g-C 3 N 4 heterojunction thin film is constructed easily driven by the built-in electric field across the Ti/TiO 2 NT/g-C 3 N 4 interface. Furthermore, the introduction of the TiO 2 layer on the TiO 2 NT will broaden light absorption range and increase the heterojunction area, which in turn conduces to effective charge separation. In addition, NiO as a co-catalyst cannot only accelerate the charge separation but also provide plentiful catalytic sites and decompose H 2 O 2 produced by g-C 3 N 4 . The thin film photocatalysts can be recycled again, which is different from traditional powdered photocatalysts. This work constructs a NiO decorated Ti/TiO 2 NT/TiO 2 /g-C 3 N 4 S-scheme heterostructure photocatalyst thin film, and provides a new insight to promote photocatalytic activity of g-C 3 N 4 under the synergetic impact of S-scheme heterostructure and NiO co-catalyst. Graphic Abstract A novel NiO decorated Ti/TiO 2 NT/TiO 2 /g-C 3 N 4 S-scheme heterostructure photocatalyst thin film was fabricated to enhance photocatalytic activity for water splitting.