Regulation of the rutile/anatase TiO2 heterophase interface by Ni12P5 to improve photocatalytic hydrogen evolution

Abstract

Anatase/rutile TiO₂ heterophase junction composites have been documented to have much higher photocatalytic activity than single phase TiO₂ (nude anatase or nude rutile) for various chemical reactions, including hydrogen production from methanol–water solution and pollution degradation. Further improving the photocatalytic performance of heterophase junction photocatalysts is a subject worth studying in both theory and practice. Based on the concept of junction interface regulation and our previous findings, we embedded Ni₁₂P₅ nanoparticles at the interface between anatase (A) and rutile (R) TiO₂ by a multi-step preparation method to obtain an A/Ni₁₂P₅/R composite with a sandwich-like structure. It was found that loading Ni₁₂P₅ on the outside surface of anatase TiO₂ (Ni₁₂P₅/A), rutile TiO₂ (Ni₁₂P₅/R), P25 TiO₂ (Ni₁₂P₅/P25), and A/R composite (Ni₁₂P₅/A/R) leads to a decrease in the photocatalytic activity; however, interestingly, the A/Ni₁₂P₅/R sample showed higher photocatalytic activity than the other samples of loaded or unloaded Ni₁₂P₅, although the loaded Ni₁₂P₅ in the latter case is inaccessible to the reactant molecules. This abnormal phenomenon can be attributed to two main reasons. (i) Ni₁₂P₅ as a metal-like material has a higher work function than anatase and rutile, which leads to the formation of Schottky junctions at the interface between the two intimately contacted phases. (ii) When Ni₁₂P₅ is located on the outside surface, the Schottky junction is unfavorable for the transfer of photogenerated electrons from TiO₂ to Ni₁₂P₅. However, when Ni₁₂P₅ is sandwiched between A and R, the formation of a reverse tandem Schottky junction can facilitate the directed transfer of photogenerated electrons from R phase to A phase. This work again verifies that photocatalytic activity can be regulated and controlled by introducing metal and metal-like particles within the junction of a metal/semiconductor interface or even on a semiconductor/semiconductor interface. Our findings not only provide a novel usage of Ni₁₂P₅ as a co-photocatalyst but also deepens the understanding of the Schottky effect on the photocatalytic process.