Synthesis And Modification Of Cobalt Based Photocatalysts Derived From ZIF-67

To achieve the objective of"carbon peaking and carbon neutrality"and address the challenges of the energy crisis and environmental pollution,it is imperative to explore and utilize new clean energy sources such as solar and tidal energy.Among these,solar energy is a sustainable and abundant source.And semiconductor photocatalysis is a promising green technology that can utilize solar energy and convert it into chemical energy.However,traditional semiconductor materials often suffer from the recombination of photogenerated charge carriers,which results in low photocatalytic activity.Ion doping or heterojunction construction of semiconductor photocatalytic materials to improve the separation and migration efficiency of photogenerated carriers is one of the current research hotspots.This paper focuses on cobalt-based semiconductors derived from metal organic framework materials（ZIF-67）,and cobalt titanate/graphite carbon nitride（CoTiO₃/g-C₃N₄）heterojunction and gadolinium doped cobalt sulfide（Gd-CoS）photocatalyst were constructed.The relationship between the catalytic activity of the samples and their microstructure and photoelectric properties was investigated.The main research findings are summarized as follows:（1）A series of CoTiO₃/g-C₃N₄photocatalysts（CTO/CN-X,X=1,2,3,4 and X representing photocatalysts with different mass percentages of ZIF-67@TiO₂precursors）were synthesized by the in-situ calcination method using ZIF-67@TiO₂core-shell structure and melamine as precursors.The research showed that CTO/CN-2 with 1 wt%ZIF-67@TiO₂precursor exhibited excellent methyl orange degradation activity under visible light（>420 nm）irradiation and maintained good photocatalytic activity after three cycles.The degradation process fallowed first-order kinetics with a kinetic constant of 0.99082 h^-1,which is 38.1 and6.1 times that of g-C₃N₄and CoTiO₃,respectively.According to research,the interaction of hydroxyl groups on the surface of TiO₂and melamine can result in hydrogen bonds that help to build CoTiO₃/g-C₃N₄heterojunctions.The in-situ-grown CoTiO₃particles are uniformly anchored to the surface of g-C₃N₄nanosheets after calcination,which also increases the system’s capacity to absorb light.In addition,the mechanism of photocatalytic activity enhancement of the composite photocatalyst was clarified by photoelectrochemical analysis,ESR testing.According to studies,the CoTiO₃and g-C₃N₄charge transfer pathway follows the S-scheme transfer pathway,retaining the strong redox ability of electrons and holes.（2）Gd-CoS photocatalyst was prepared by introducing the rare earth element gadolinium（Gd）through a one-step solvothermal method using small-sized ZIF-67 as a precursor and the amount of doped elements was optimized.Using sodium sulfide and sodium sulfite as sacrificial agents,the results demonstrated that Gd-CoS with various doping levels displayed photocatalytic activity for water splitting to produce hydrogen under full spectrum illumination（wavelength range of 350-780 nm）at a temperature of 303.15 K.The Gd-CoS-2（GCS-2）sample with 1 wt%Gd doping has the best hydrogen production activity(2916.7μmol·g^-1·h^-1),which is better than pure CoS(893.1μmol·g^-1·h^-1).SEM,TEM,XPS and other characterization analyses and and photoelectric tests were used to investigate the enhancement mechanism of Gd-CoS（GCS-2）photocatalytic performance.The small-sized ZIF-67 precursor makes Gd-CoS nanoparticles smaller in size and larger in specific surface area,which is conducive to the separation and migration of photogenerated electron-hole pairs.Gd doping provides more active sites for the reaction,which can improve the photoelectric performance and hydrogen production efficiency of CoS materials.