Removal Of Cr(Ⅵ) And Organic Pollutants By MOF And Its Derivatives

With the development of industry,more and more environmental pollutants are produced,including organic pollutants and heavy metal ions.Various chemical and physical methods are used to treat these pollutants.As a low-cost and environment-friendly technology,photocatalysis technology has shown great potential,which has attracted more and more attention in recent decades.For photocatalytic technology,the selection of photocatalyst is the key.Metal organic frameworks(MOF)are novel porous materials with high specific surface area,ultra-high porosity,adjustable pore structure and easy functionalization.It can be used in gas storage and separation,energy storage and conversion,metal ion sensing,drug delivery,catalysis and sensing.In this paper,we prepared different MOF and its derivatives complexes,explored the photocatalytic reduction of Cr(VI)and degradation of organic pollutants under visible light irradiation,and explored the different influencing factors as well as the recycling and stability of materials.Finally,we proposed and verified the relevant mechanism.The main research results are as the following:1.BUC-21/Cd0.5Zn0.5S composites were prepared by mechanical ball milling of BUC-21 synthesized by our group and inorganic semiconductor Cd0.5Zn0.5S,and their structures and morphologies were characterized by a series of characterization methods.The photocatalytic reduction of Cr(VI)with different ratio of BUC-21/Cd0.5Zn0.5S was studied,and the influences of various small molecular organic acids as hole traps and foreign ions on the reduction of Cr(VI)with B100C100 were investigated.At the same time,B100C100 was used to degrade different organic dyes(Rhodamine B(RhB),Reactive brilliant red X-3B(X-3B),Congo Red(CR)).In addition,the removal effect of B100C100 on the coexistence system of dye and Cr(VI)was also studied.The results revealed that removal efficiencies of B100C100 for Cr(VI)and dyes were close to 70%.Photoluminescence(PL),electrochemical analysis,active species trapping experiment and electron spin resonance(ESR)provide further evidence for the improvement of photocatalytic activity.In the cycle experiment,after three cycles,the photocatalytic reduction efficiency of B100C100 for Cr(VI)is still more than 90%,indicating that B100C100 has good recovery and stability.Finally,the photocatalytic mechanism of B100CXwas proposed and verified.2.The classical metal-organic framework NH2-UiO-66 and organic semiconductor 3,4,9,10-Perylenetetracarboxylic dianhydride(PTCDA)were used as raw materials,and their structures and morphologies were characterized by a series of tests.The effects of different ratios of NH2-UiO-66/PTCDA on the photocatalytic reduction of Cr(VI)were studied.The optimal ratio of NU100P10 was selected to explore the influencing factors.The effects of different pH,initial concentration,different catalyst dosage,different small molecule organic acids,actual water and real sunlight on the photocatalytic reduction of Cr(VI)were investigated.In addition,the degradation of bisphenol A(BPA)by NU100P10 photocatalysis activated Peroxydisulfate(PDS)was investigated,and BPA could be completely degraded within 60 min.The effects of different pH and PDS dosage on the degradation of BPA were also explored.The results showed that NU100P10 had the best removal efficiency on BPA without adjusting pH,and the optimal dosage of PDS was 2 mM.The introduction of a small amount of PTCDA on the surface of NH2-UiO-66 can broaden the optical absorption range,improve the separation efficiency of photo induced carriers and the photocatalytic performance.After five times of adsorption photocatalytic reduction of Cr(VI),NU100P10 still showed good reduction activity and reusability.Finally,the mechanism of photocatalytic Cr(VI)reduction and degradation of BPA by NU100P10 was proposed and verified by electrochemical experiments,ESR measurements,X-ray photoelectron spectroscopy(XPS)measurements,photodeposition experiments and Density Functional Theory(DFT)calculations.3.ZIF-8 and PTCDA were used as raw materials.Firstly,ZIF-8 was calcined at high temperature to form a porous network derivative ZIF-NC.Then ZIF-NC and PTCDA were compounded by mechanical ball milling.To characterize the structure and morphology of ZiF-NC and PTCDA,a series of characterization methods were conducted.The photocatalytic degradation of norfloxacin(NFX)with different proportion of PTCDA/ZIF-NC was studied.The photocatalytic degradation efficiency of P120Z80 for NFX within 60 min was more than 90%.The effects of pH,PDS dosage and coexisting ions on the NFX degradation of P120Z80 were investigated.After three cycles,the photocatalytic degradation efficiency of P120Z80 for NFX was still more than 70%.The stability of the material was further proved by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR)and Scanning electron microscope(SEM)before and after the cycle.Finally,the mechanism of photocatalytic NFX degradation by PDS was proposed and proved by electrochemical tests,PL test,ESR test and active substance capture experiments.