Sulfidation And Photocatalytic Properties Of Cobalt-Based Metal-Organic Frameworks (ZIF-67)

The fossil fuels as a major energy supplier have the characteristics of rapid consumption and high pollution,which has prompted the development of environmental-friendly reproducible energy.H₂ with clean and high calorific value is an ideal alternative energy.Its manufacturing technology has been widely concerned,and the photocatalytic hydrolysis of H₂production is considered to be an effective technology that is expected to solve the problems of energy consumption and environmental protection.Cobalt-based metal-organic framework（ZIF-67）as a photocatalyst with large specific surface area,tunable structure,good chemical and thermal stability,has potential application value in the field of photocatalytic H₂ production.Pure ZIF-67 has weak ability to capture light due to wide forbidden band.The light-excited electrons are easy to recombine with holes,which restricts its photocatalytic application and energy needs of industry.Therefore,it is very necessary to improve the light utilization and electron-hole separation efficiency and study the photocatalytic H₂ yielding performance by modification measures.In this study,a series of ZIF-67-based composites were synthesized using ZIF-67 as precursor with different methods of sulfurization modification.And the structure-activity relationship between composition and photocatalytic H₂ production of different photocatalysts was studied.X-ray diffrotometer（XRD）,UV-vis diffuse reflectance spectroscopy（UV-vis DRS）,photoluminescence spectroscopy（PL）and electrochemical tests were applied to reveal the composition,capacity of light-absorption,separation of photoelectrons from holes and possible photocatalytic reaction mechanism of the synthesized materials.The main results achieved are as follows:（1）Binary Co₉S₈/Cd S nanocomposite was synthesized via natural aging and pyrolysis method of ZIF-67 and Cd S,as the cobalt source and sulfur source,respectively,and the different activity of photocatalytic H₂ evolution before and after pyrolysis was studied under simulated visible-light.The properties of pyrolysis samples were markedly higher than those of precursors in the light of experimental results.Especially,the highest H₂ production rate of 1852μmol h^-1g^-1 for ZCC-600 was correlated to an AQE of 0.35%at 420 nm.It is found that the enhanced photocatalytic ability of the composite photocatalyst Co₉S₈/Cd S was mainly attributed to the strong interaction between Co₉S₈ and Cd S and the formation of Co₉S₈ nanoparticles,which induced the separation of electrons and holes in Co₉S₈ and provided more sites for redox reaction.（2）The bimetallic organic framework Ni-ZIF-67 was introduced on the basis of pure ZIF-67.The Ni S/Co₃S₄/Zn Cd S heterojunction photocatalysts were synthesized by chemical vapor deposition and ultrasonic methods.The optimal synthesis scheme was clarified by optimizing the experimental parameters such as material ratio,synthesis temperatures and addition amount of Ni S/Co₃S₄.Scanning electron microscopy（SEM）,transmission electron microscopy（TEM/HRTEM）and X-ray photoelectron spectroscopy（XPS）were used to confirm the successful synthesis of the Ni S/Co₃S₄/Zn Cd S photocatalyst.And the photoelectrochemical test analysis showed that Ni S/Co₃S₄/Zn Cd S had higher transfer and separation efficiency of charge.The outstanding H₂ production rate of 98600μmol h^-1 g^-1 for final synthesized NCS/ZCS-20was correlated to an AQE of 9.53%at 420 nm after 4 h of reaction,which was about 3 times stronger than that of pure Zn Cd S,and the performance of photocatalytic H₂ production still remained unchanged after 4 cycling tests.Finally,the photocatalytic reaction mechanism was deeply studied.（3）The ZIF-67-based material/microbial symbiosis system was successfully constructed by coupling the ZIF-67-based material Ni S/Co₃S₄/Zn Cd S catalyst with Shewanella oneidensis MR-1（S.oneidensis MR-1）through mild expansion culture.The synergistic action between Ni S/Co₃S₄/Zn Cd S and S.oneidensis MR-1 promoted the transfer and separation of charge.The photocatalytic performance of the nanomaterial/microbial symbiosis system was analyzed by experiments of photocatalytic H₂ production,which reached up to 17408.93μmol h^-1 g^-1 and was nearly 20 times that of S.oneidensis MR-1 after the addition of NiS/Co₃S₄/ZnCdS.