Architecture of high efficient zinc vacancy mediated Z-scheme photocatalyst from metal-organic frameworks

Direct Z-scheme composite is an ideal system for photocatalytic H2 production, which can efficient separation photo-induced charges and maintain stronger redox ability. Herein, we developed a facile method to fabricate Zn-vacancy mediated direct Z-scheme CdS/ZnS composites derived from CdS/MOF-5 via using Na2S and Na2SO3 aqueous solution as sacrificial agent in the process of photocatalytic reaction. XPS and PL results demonstrated that the metal-organic frameworks (MOF-5) transformed ZnS possesses abundant zinc vacancies, which help to form ohmic contact and broaden light absorption. Upward PL certifies the two-photons absorption behavior of the zinc vacancies ZnS under visible-light irradiation. Benefited from the ohmic contact which is inducted by zinc vacancy defects, the photo-induced electron of ZnS on the zinc vacancy defect level recombine with the holes of CdS in VB though the ohmic contact. As a result, the electrons and holes of CdS in the VB and CB can be efficiently separation and the photocorrosion is effectively suppressed, leading to drastically enhanced photocatalytic H2 evolution performance. The maximum photocatalytic H2 production rate of 11.62 mmol h−1 g−1 is obtained with an apparent quantum efficiency of 11.09% at 470 nm over CdS/MOF-5(25) heterojunction without any noble-metal as cocatalyst in Na2S and Na2SO3 aqueous solution, which is about 89.38 and 31.4 times greater than that of the bare MOF-5 and CdS, respectively. Moreover, S 2p XPS spectra of recyclability testing CdS/MOF-5(25) sample and the time-resolved fluorescence (TRPL) decay further prove the Z-scheme charge transfer and separation mechanism. This work represents a simple strategy to fabricate visible-light responded Zn-vacancy ZnS derived from MOF-5 and highlights the critical role of defects for developing Z-scheme photocatalyst in solar energy conversion.