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

Direct Z-scheme composite is an ideal system for photocatalytic H-2 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 H-2 evolution performance. The maximum photocatalytic H-2 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.