Composite Sr2TiO4/SrTiO3(La,Cr) heterojunction based photocatalyst for hydrogen production under visible light irradiation

Abstract

A composite Sr₂TiO₄/SrTiO₃(La,Cr) heterojunction photocatalyst has been prepared by a simple in situ polymerized complex method. Upon Pt cocatalyst loading, this catalyst shows higher photocatalytic activity towards hydrogen production than individual SrTiO₃(La,Cr) and Sr₂TiO₄(La,Cr) in the presence of methanol sacrificial reagent. Microscopic morphology studies show that well defined heterojunctions are formed by matching the lattice fringes of SrTiO₃(La,Cr) and Sr₂TiO₄(La,Cr), and Pt was preferentially loaded on the surface of the Sr₂TiO₄(La,Cr) component in the composite Sr₂TiO₄/SrTiO₃(La,Cr) photocatalyst. XPS and EPR analyses show that the composite photocatalyst also has the lowest amount of Cr⁶⁺ electron trapping sites. Band structure analysis by combining absorption spectroscopy and Mott–Schottky plots shows that, in the composite photocatalyst, the photogenerated electrons and holes tend to migrate from SrTiO₃(La,Cr) to Sr₂TiO₄(La,Cr) and from Sr₂TiO₄(La,Cr) to SrTiO₃(La,Cr), respectively. This kind of band structure can facilitate charge transfer and separation driven by the minor potential difference between the two components, which is further confirmed by the observation of long lived electrons in the time resolved FT-IR spectroscopic study. It is concluded that the superior photocatalytic activity of the composite heterojunction photocatalyst is due to efficient charge transfer and separation by well defined heterojunctions formed between SrTiO₃(La,Cr) and Sr₂TiO₄(La,Cr), preferential loading of Pt nanoparticles on the Sr₂TiO₄(La,Cr) component, and the lowest amount of Cr⁶⁺ in the composite photocatalyst. The tailored design and synthesis of the composite heterojunction structure is a promising approach for the improvement of the photocatalytic activity of a photocatalyst.