Highly efficient photocatalysts by pyrolyzing a Zn–Ti heterometallic metal–organic framework

Abstract

A series of carbon composite materials containing metal oxides (ZnO and/or TiO_x) were synthesized by pyrolyzing a Zn–Ti heterometallic metal–organic framework (MOF) as the precursor. The photocatalytic activities of these composites were evaluated by the photodegradation of methylene blue (MB) in aqueous solutions. The chemical composition and porosity of the prepared composites can be facilely tuned by varying the pyrolysis temperature. The sample being pyrolyzed at 1000 °C exhibited a dramatically increased surface area due to the carbothermal reduction of Zn²⁺ into metallic Zn followed by vaporization as an extra pore-forming mechanism. Because Zn and Ti are adjacent in the heterometallic secondary building units (SBUs) of the MOF precursor, the catalytically active TiO_x sites generated during pyrolysis would remain in the pores and channels formed by Zn vaporization and were readily accessible to MB, leading to a huge increase of photocatalytic activity. Our work reveals a novel mechanism to generate porosity in photocatalysts facilitating the access of substrates to catalytically active sites which can be readily applied to other MOFs containing low boiling point metals.