Fabrication And Degradation Properties Of Metal-organic Frameworks And Their Derived Carbon/Cellulose Composites

Advanced oxidation processes based on activated peroxymonosulfate（PMS）have attracted widespread attention in the field of water treatment due to its high reaction mechanism and simple operation process.However,current catalysts for advanced oxidation processes generally face multiple problems such as low efficiency,low utilization,and easy to cause secondary pollution,which greatly limits the application of this technology in water treatment.Thus,the development of highly efficient,environmentally friendly,and highly stable catalytic materials is an important issue to promote this technology.Metal-organic frameworks（MOFs）and their derivatives have been widely studied for activating PMS as catalysts due to their adjustable structure,easy modification,and large specific surface area.On this basis,this thesis aims at the problem of low catalytic activity,easy to agglomerate and difficult to recycle,MOFs are used as precursors,and the internal relationship between oxygen vacancies and the electronic structure of metal sites has been investigated to modify the controllable synthesis of oxygen vacancies.Fe-doping strategy has been developed to optimize metal active sites in Co-MOFs-derived carbon materials.A defective three-dimensional multi-level structure has been innovatively constructed through morphology modification and the degradation performace has been improved.Meanwhile,combined with the regeneration and plasticity of fiber resources from waste textile,the MOFs and their derivatives/cellulose porous composite materials were constructed and applied to the treatment of organic poluutants such as dyes and antibiotics.In addition,MOFs/cellulose composite porous beads with high load,high strength,and high specific surface area were designed,and a small MOFs/cellulose composite beads water treatment circulation system was constructed.The specific research content is as follows:（1）Co-imidazole-MOFs（ZIF-67 and ZIF-9）with different pore diameters were developed as precursors and carbon composite materials（Z-Co₃O₄/C）were derived from MOFs by carbonization and oxidation.The MOFs-derived carbon materials can inherit the high specific surface of the original MOFs.The metal catalytic sites were encapsulated in carbon layers to improve its durability and reduce the loss of catalytic activity.The carbon layer is conducive to the transmission of electrons and can promote the catalytic activation of PMS.By controlling the oxidation time,the controllable generation of oxygen vacancies and the proportion of Co²⁺are adjusted,thereby promoting the electron conversion in the redox reaction and accelerating the degradation process.Regenerated cellulose hydrogels（CA）were prepared by dissolving waste textile fibers,and Z67-Co₃O₄/C-4@CA and Z9-Co₃O₄/C-4@CA composite porous aerogels were constructed by doping method and freeze-drying strategy.The degradation experiments of dyes and antibiotics were conducted to investigate the degradation performance of Z-Co₃O₄/C-4@CA（The methyl blue is completely removed within 60 minutes,and the degradation rate of tetracycline hydrochloride can reach 98.7%within 25 minutes）.Moreover,cycle experiments illustrated that Z-Co₃O₄/C-4@CA possessed excellent stability for the activation of PMS and the composite aerogel can be recycled.（2）Fe was doped into Co-based MOFs to investigate the effect of bimetallic ratio of catalysts on the degradation performance.The precursors of MOFs with different components were obtained by adjusting the doping ratio of Fe,and the bimetallic carbon nanotubes were obtained by carbonization.The studies have shown that proper doping of Fe can regulate the electronic structure of cobalt and the formation of carbon nanotubes.When the ratio of Co and Fe is 4:1,the derived carbon based material Co Fe0.8@NCNT exhibited high specific surface area(329.5 m² g^-1),abundant carbon nanotubes,and fastest electron transfer rate which endowed Co Fe0.8@NCNT with the best degradation efficiency,including degradation efficiency and kinetic constants.The Co Fe0.8@NCNT@CA composite aerogel was constructed by combining Co Fe0.8@NCNT with cellulose hydrogel.The abundant carbon nanotube structure can improve the adhesion of MOFs-derived materials on the cellulose-based matrix,thereby optimizing the mass transfer path and catalytic sites.In addition,Co Fe0.8@NCNT@CA illustrated high degradation efficiency and excellent recyclability.The free radical capture experiments and electron paramagnetic resonance tests showed that superoxide radicals played a key role in the degradation process.（3）To investigate the influence of morphology of the MOFs-based catalysts on the degradation performance,a series of MOF precursors with same structure and adjustable morphology were developed.One-dimensional（1D）,two-dimensional（2D）and three-dimensional（3D）MOFs-derived carbon materials were develpoed through carbonization.Among them,the 3D hierarchical carbon nanoflower（Ni Fe-CNFs）exhibited large specific surface area and rich defect,and the novel structure was benificial to expose more catalytic active sites and accelerate mass transfer.Ni Fe-CNFs presented excellent pollutant degradation efficiency,and its kinetic constant(1.26 min^-1)is 3.5 and 1.1 times higher than that of 1D carbon nanotubes Ni Fe-CNTs and 2D carbon nanosheets Ni Fe-CNSs,respectively.Ni Fe-CNFs and regenerated cellulose were compounded to obtain Ni Fe-CNFs/CA composite aerogel.3D hierarchical nanoflower Ni Fe-CNFs were uniformly attached to the tunnel of the regenerated cellulose porous aerogel.Ni Fe-CNFs/CA exhibited excellent removal rate of pollution and a good recyclability（after three cycles,the removal rate of tetracycline hydrochloride can still maintain 88.9%）.Meanwhile,the composite aerogel can be used in a wide range of p H environment.In addition,free radical capture experiments and electron paramagnetic resonance testsillustrated that sulfate radicals,hydroxyl radicals and superoxide radicals cooperated to promote the degradation process.（4）MIL-100/cellulose porous beads were prepared by phase separation method,freeze-drying,and drying process using water-soluble carboxymethyl cellulose as binder.It was found that the composite beads prepared by heat-drying method（MIL-100@CMC-HD）exihibited a layer-by-layer cross-linked structure,while the composite beads prepared by freeze-drying method（MIL-100@CMC-FD）have a 3D network cross-linked structure.Studies have shown that MIL-100@CMC-HD porous beads have better mechanical strength（22.1 N of strain pressure）,ultra-high MOF loading rate（79 wt%）and a large specific surface area(1277 m² g^-1).A wastewater recycling system based on MIL-100@CMC-HD was constructed,and the impact of beads dosage,PMS amount,and initial concentration of pollutants was throughly explored.MIL-100@CMC-HD can effectively remove more than 95%methylene blue in the circulating system containing PMS,and the composite beads possessed good recyclability.This reaserch may provide new ideas and theoretical basis for the shaping of MOFs powder.In summary,this thesis systematically studied the preparation of MOFs and their derived carbon-based catalysts,the regulation of catalyst sites,and the modification of morphology on the catalytic degradation of organic pollution in water.We successfully developed a variety of highly efficient and stable MOFs/MOFs-based catalysts for activating PMS to degrade dyes and antibiotics.This thesis also clarified the degradation mechanism of MOFs and their derived carbon/cellulose porous composites.Meanwhile,the MOFs and their derivatives/cellulose porous composite materials were constructed,which overcomes the problem of low utilization of powder catalysts,and provides a new idea for the shaping and utilization of MOFs-based materials.