Uniform decoration of UiO-66-NH2 nanooctahedra on TiO2 electrospun nanofibers for enhancing photocatalytic H2 production based on multi-step interfacial charge transfer

Abstract

Metal–organic framework (MOF) materials have been extensively incorporated with inorganic semiconductor photocatalysts to improve their photocatalytic activity through an efficient charge transfer process across their heterointerface. In this work, octahedral UiO-66-NH₂ MOFs with edge-lengths of 110–330 nm are uniformly decorated on the surface of TiO₂ electrospun nanofibers by a traditional solvothermal method combined with activation pretreatment. Before the solvothermal growth of UiO-66-NH₂, the TiO₂ electrospun nanofibers were activated in NaOH solution to etch the TiO₂ surface for allowing the exposure of lattice oxygen. The exposed lattice oxygen on the TiO₂ surface could interact with the MOF precursor of Zr⁴⁺ ions, thus enabling octahedral UiO-66-NH₂ to grow uniformly on the surface of TiO₂ nanofibers with an intimate Ti–O–Zr hetero-interface. Such an intimate hetero-interface provides an effective channel for boosting the electron transfer between UiO-66-NH₂ and TiO₂ in their heterostructure. Thus, the UiO-66-NH₂/TiO₂(anatase) heterostructures exhibited enhanced photocatalytic activity for H₂ production as compared to either TiO₂(anatase) nanofibers or UiO-66-NH₂ nanooctahedra in the presence of Rhodamine B (RhB) as a sensitizer under visible light irradiation. In particular, the decoration of UiO-66-NH₂ nanooctahedra on anatase/rutile mixed TiO₂ nanofibers could induce further enhancement of the photocatalytic H₂ production. The enhanced photocatalytic activity is attributed to the multi-step continuous interfacial transfer of photoinduced electrons with the way of RhB → UiO-66-NH₂ → TiO₂(anatase) → TiO₂(rutile).