Copper Organic Framework-based Photocatalysts For Hydrogen Evolution And Dye Degradation

Photocatalytic H₂production technology is a promising method to solve the current energy shortage and environmental pollution problems.However,the current semiconductor photocatalytic materials generally have several problems including the narrow light response range,easy recombination of photogenerated electron holes,low H₂ production efficiency,complicated preparation process,and high cost.Cu-based semiconductor materials are widely used as photocatalytic materials due to their abundant reserves,economical benefits,and good light absorption properties.In this thesis,Cu-I-bpy（bpy=4,4’-bipyridine）as a Cu-based metal-organic framework（Cu-MOFs）can be controllably synthesized and modified.Then,as-modified Cu-MOFs were further studied the performance and mechanism of photocatalytic H₂ production and dye degradation,respectively.The main research contents are as follows:（1）In the first part of this thesis,three single-anion-containing Cu-X-bpy（X=Cl,Br or I）and three mixed-anion-containing secondary structural units（SBUs）in novel Cu-X-bpy（X=Cl/Br,Cl/I or Br/I）were successfully synthesized by one-pot method.To determine the chemical and structural information,several techniques have been adopted and analysized for above as-modified Cu-MOFs by single crystal X-ray diffraction,powder X-ray diffraction,Fourier transform infrared spectroscopy and Raman spectroscopy,extended X-ray absorption fine structure spectroscopy,energy dispersive X-ray spectroscopy,organic element analysis and inductively coupled plasma.In order to systematically investigate the photocatalytic H₂production efficiency of Cu-X-bpy（X=Cl/Br,Cl/I or Br/I）,the photocatalytic activity was assessed by comparison of the corresponding single anion Cu-X-bpy（X=Cl,Br,I）.It found that the H₂production efficiency can be tuned from 2.79 mmol/gh（Cu-I-bpy）to10.04 mmol/gh（Cu-Cl/I-bpy）.Additionally,the theoretical calculations demonstrated that the water dissociation energy and hydrogen adsorption energy of Cu₂X₂ units could be affected by changing the anionμ-X^-in SBUs,which was the main reason for the huge differences in photocatalytic H₂ production performance while there are minor differences in light absorption,charge separation and transfer efficiency in Cu-X-bpy（X=Cl/Br,Cl/I Or Br/I）.Cu-MOFs with mixed anion SBUs have been synthesized for the first time and systematically investigated the effect of anion composition on the photocatalytic performance of Cu-MOFs.The results show that the composition of anions in SBUs has a great influence on the catalytic activity of Cu-MOFs,which provides a new idea for the design of Cu-MOFs catalysts and other related catalytic materials in the application of water splitting.（2）The combination of photocatalytic H₂ production and dye degradation is a promising and challenging technology in wastewater treatment and renewable energy production.In the second part of this thesis,a direct Z-type heterogeneity catalyst（Ce O₂/Cu-I-bpy）was designed and constructed by in situ modification of Ce O₂ nanoparticles on Cu-I-bpy.The chemical and structural information were characterized by powder X-ray diffraction spectroscopy,X-ray photoelectron spectroscopy,Raman spectroscopy,ultraviolet diffuse reflectance spectroscopy,field emission scanning electron microscopy and field emission transmission electron microscopy.Taking Rhodamine B as a model pollutant,the Ce O₂/Cu-I-bpy composite simultaneously achieved the photodegradation of Rh B and H₂ evolution without any co-catalysts.The H₂ production efficiency was detected by gas chromatography（GC）while the degradation performance was characterized by UV spectrophotometer.It was found that using Ce O₂/Cu-I-bpy composites as photocatalysts,the results of dye degradation and H₂evolution were significantly better than the corresponding pristine Ce O₂and Cu-I-bpy,respectively.Specifically,the H₂ evolution efficiency of Ce O₂/Cu-I-bpy was 6.9 times as large as that of pristine Cu-I-bpy.Similarly,the degradation efficiency was 2.5 times higher that of pristine Ce O₂.The photocatalytic mechanism of Ce O₂/Cu-I-bpy was investigated by active species trapping,electron paramagnetic resonance and charge-transfer tracing experiments.It confirmed that Ce O₂/Cu-I-bpy possessed a direct Z-type charge-transfer mechanism.This work demonstrates the possibility of converting wastewater into energy using a photocatalytic system.