Controllable Synthesis Of MOFs-based Heterojunction Photocatalysts And The Removal Of Typical Antibiotics In Aqueous Solution

Nowadays,a large number of antibiotics and their metabolites have entered in natural water bodies due to improper handling,causing serious environmental problems and potentially adverse effects on public health.Therefore,how to effectively remove antibiotics in water bodies has become a concern in the environmental field.Recently,some research progress in the field of materials has provided new research space for pollution control,especially the development of water treatment technology.One of the developments is the application of new materials combined with photocatalysis theory to water pollution control technology.In view of the excellent properties of metal-organic framework materials such as high specific surface area,functionalization,multiple active sites,and semiconductor-like behavior,it has certain application potential in the field of photocatalytic degradation of pollutants.However,peer studies have shown that metal-organic framework material with wide band gap has a narrow light absorption range,resulting in a lower photocurrent density.Besides,the photo-generated carriers are easy to recombine,which inhibits the catalytic activity of the metal-organic framework material.In response to the above problems,this project is based on metal organic-framework materials,and its controllable construction in terms of optimizing chemical composition,improving heterojunction interface contact,adjusting energy band structure,morphology through one-step solvothermal method and semi-sacrificial template method.A series of new metal-organic framework materials-based heterojunction photocatalytic materials were fabricated.In addition,a metal-organic framework material-based heterojunction activated hydrogen peroxide system was constructed to further strengthen its rapid removal of antibiotics in water.The main research contents are as follows:（1）The separation and transfer efficiency of photogenerated hole electrons in metal-organic frame materials is low.Hence,the Ti₃C₂-modulated NH₂-MIL-125-based nanohybrids with dual-heterojunctions was synthetized by a one-step solvothermal strategy for enhanced photocatalysis activity.The Ti₃C₂nanosheets played a significant role in determining the morphology,constituent and photoelectricity property of NH₂-MIL-125-based nanohybrids.Under visible light irradiation（λ>420 nm）,the optimized NH₂-MIL-125（Ti）（TiO₂）/Ti₃C₂ nanohybrids exhibited 11.5 times higher tetracycline hydrochloride（TC-HCl）degradation efficiency（82.80%）than that of the pristine NH₂-MIL-125（Ti）.The improved photocatalytic activities were dominantly ascribed to the dual-heterojunction in NH₂-MIL-125（Ti）（TiO₂）/Ti₃C₂,which not only enhanced the carrier density,but also remarkably accelerated the interfacial charge separation,as well as transfer.The·OH and h⁺were the major reactive species in photocatalytic activities.Additionally,the TC-HCl degradation pathway was proposed by liquid chromatography-mass spectrometry and the transport pathway of carriers in this system was speculated.The construction of MIL-125-NH₂（TiO₂）/Ti₃C₂nanohybrid provides a promising hybridization idea on MOFs-based composites with controllable adjustment and property optimization for addressing issues on the environment.（Chapter 3）（2）In heterojunction photocatalysts,incompact contact interface and inappropriate band alignment in the heterointerface of two materials increase interfacial recombination,lowering the degradation efficiency.Hence,a facile semi-sacrificial strategy was proposed to construct metal-organic frame-based heterojunction photocatalysts with close contact interfaces.At first,cubic Cu₂O acted as a metal source.A series of Cu₂O@HKUST-1 materials was fabricated by oriented growth of HKUST-1 around cubic Cu₂O（Cu₂O@HKUST-1）.In particular,the core-shell Cu₂O@HKUST-1 with close contact interfaces was obtained through adjusting the feedstock ratio.The optimized Cu₂O@HKUST-1 heterostructures exhibited enhanced tetracycline hydrochloride（TC-HCl）removal rate of 93.40%within 60 min under visible light irradiation.Obviously,mechanism exploration revealed that the the core-shell structure with compact interfacial contact and an ideal type-Ⅱ band alignment in Cu₂O@HKUST-1 were beneficial to interfacial charge separation and transfer.Meanwhile,HKUST-1shell protected Cu₂O core from the photocorrosion well,assuring the robust stability of photocatalyst during the photocatalytic process.To explore the relationship between crystalline structure and activity of heterojunctions,on the basis of the above research,three types of Cu₂O@HKUST-1 composite photocatalysts were compared by using Cu₂O（exposed to（100）crystal face）,Cu₂O（exposed to（111）crystal face and（100）crystal face）,Cu₂O（exposed to（111）crystal face）and Cu₂O（exposed to（111）crystal face）as growth templates to contrast three types of Cu₂O@HKUST-1.Characterization results showed that the growth of HKUST-1 was different on different Cu₂O crystal planes,and was more favorable on（111）crystal plane than on（100）crystal plane in Cu₂O.Under visible light irradiation,the degradation rates of the cubic Cu₂O@HKUST-1,the truncated octahedral Cu₂O@HKUST-1 and the octahedral Cu₂O@HKUST-1to tetracycline hydrochloride（TC-HCl）were 95.35%,78.81%and 66.58%,respectively in 60 min.The band structure analysis results confirmed that a Type Ⅰ heterojunction formed in octahedral Cu₂O and HKUST-1,and the photogenerated carriers were gathered on the octahedral Cu₂O,leading to the recombination of photogenerated carriers.This result was consistent with the photoelectric characterization results of poor photogenerated carrier sepa ration performance in octahedral Cu₂O@HKUST-1.At the same time,the staggered energy band structure between cubic Cu₂O,truncated octahedral Cu₂O and HKUST-1 formed Type Ⅱ heterojunction,which was favorable for the separation and transfer of photogenerated carriers.The position of the valence band of cubic Cu₂O was more positive than that of truncated octahedral Cu₂O.So the oxidation capacity of photogenous holes was stronger in cubic Cu₂O,which was conducive to the degradation of TC-HCl.This work is oriented to the environmental application and provides a facile method towards creating efficient and stable metal-organic frame-based photocatalyst for organic pollutant removal.（Chapter 4 and 5）（3）The experimental results in the first three chapters show that although the heterogeneous photocatalytic system can achieve a high removal efficiency of TC-HCl,its degradation rate needs to be further improved.Based on this,a novel series of 2D/2D FeNi-layered double hydroxide/bimetal-organic frameworks nanosheets（FeNi-LDH/BMNSs-x）photocatalyst was successfully fabricated via a facile semi-sacrificial template strategy.The flower-like FeNi-LDH NSs acted not only as a template but also as a self-sacrificed metal source to form FeNi-BMNSs by confined ligand coordination.By controlling the number of organic ligands,incomplete conversion occurred after catching the abundant metal cations neighboring to the surface of FeNi-LDH NSs by organic linkers,obtaining the in-situ formed heterojunction.The optimized FeNi-LDH/BMNSs+H₂O₂+Vis system showed excellent tetracycline hydrochloride（TC-HCl）removal rate of 82.12%in 15 min and 95.76%in 60 min.Besides,the high TC-HCl degradation rates（above 80%）were obtained in a wide pH range.The TC-HCl removal rate of 82.12%and total organic carbon removal rate of48.98%was remained after four cycles.Mechansim exploration identified the fast catalysis process were ascribed to the synergetic effect between 2D/2D heterojunctions and Lewis acid sites with mixed-valence（Fe（Ⅲ）/Ni（Ⅱ））in FeNi-LDH/BMNSs.As a result,the catalysis of H₂O₂ and the reduction of O₂was accelerated by the continuous generation of Fe（Ⅱ）and available photogenerated electrons,respectively,producing abundant active radicals including·OH and·O₂^-.Finally,this photo-Fenton system exhibited high removal rate to oxycycline,levofloxacin,norfloxacin and doxycycline.The findings provide a new idea towards creating low dimensional metal-organic framework nanocomposites with excellent catalytic performance.（Chapter 6）...