ZIF-derived oxygen vacancy-rich CoO for constructing an efficient Z-scheme heterojunction to boost photocatalytic water splitting.

With ZIF-67 as the precursor, oxygen vacancy-rich CoO nanoparticles were derived and anchored on the surface of 2D polyimide (PI) to construct a Z-scheme hybrid heterojunction (20ZP) through a simultaneous solvothermal crystallization and polymerization strategy. XRD, XPS and EPR confirmed that both Co(III) and oxygen vacancies are formed during the low temperature conversion of ZIF-67 to CoO nanoparticles that in turn accelerate the polymerization of PI. Synchronous crystallization makes the interfacial architecture intermetal and compact, inducing a strong interfacial electronic interaction between CoO nanoparticles and PI. UV-vis DRS spectra and transient photocurrent response demonstrate that the incorporation of CoO on polyimide not only extends the light absorption in the visible range, but also enhances the charge transfer rate. EIS, TRPL techniques and DFT calculations have confirmed that the photoinduced interfacial charge transfer pathway of this hybrid heterojunction characterized the Z-scheme in which the photoinduced electrons transfer from the conduction band of CoO to the valence band of PI, significantly inhibiting the recombination of electrons and holes within PI. More importantly, the oxygen vacancies located below the conductor band of CoO can deepen the band bending, improve the charge separation efficiency and accelerate electron transfer between CoO and PI. This Z-scheme hybrid heterojunction structure can not only maintain the high reducing capacity of photoinduced electrons on the conductor band of PI, but also enhance the oxidative capacity of the heterojunction composite material, thus promoting the overall progress of the photocatalytic hydrogen release reaction.