Multifunctional Metal-organic Framework MIL-88A(Fe) For Pollutants Removal From Water: Performance And Mechanism

With the increase in population,industrialization,and urbanization,water pollution caused by heavy metals,emerging contaminants,and oil spills has become a serious worldwide problem.Therefore,researchers have been committed to developing various technologies and materials to remove pollutants from the water environment.Metal-organic frameworks（MOFs）formed by self-assembly of polydentate organic ligands and inorganic metal ions or clusters,have unique structures and attractive properties,such as large specific surface area,rich nanocavities,open pore channels,and unlimited possibilities for post-modification.Therefore,MOFs have become the hot topic of the field of new materials in recent years.Among them,MIL-88A（Fe）,composed of Fe³⁺and fumaric acid,has the characteristics of environmental friendliness and multiple active sites.Its unique properties in the field of environmental remediation,such as catalytic degradation,separation,adsorption,sensors,and antibacterial therapy,have received widespread attention.However,when MIL-88A（Fe）was used alone as a catalyst,its electron-holes are easily compounded,resulting in a decrease in its catalytic activity.In addition,MIL-88A（Fe）powder as adsorbent or catalyst has problems such as easy agglomeration,poor water stability,and poor recoverability,which greatly limits its wide application in industrial production.In response to the above problems,this thesis aims to solve the problem of difficult separation of electron-hole pairs by combining organic semiconductor perylene-3,4,9,10-tetracarboxylic diimide（PDINH）with MIL-88A（Fe）to construct PDINH/MIL-88A（Fe）composite;additionally,the issue of difficult recovery of MIL-88A（Fe）powder was resolved by fixing MIL-88A（Fe）onto a three-dimensional porous polyurethane sponge to create a macrostructure MIL-88A（Fe）@sponge,providing theoretical and technical support for the use of multifunctional MIL-88A（Fe）in water environment remediation.The main contents are as follows:1.PDINH/MIL-88A（Fe）composites（Px My）were fabricated from MIL-88A（Fe）and perylene-3,4,9,10-tetracarboxylic diimide（PDINH）via facile ball-milling strategy.The optimum P25M175 exhibited outstanding degradation performance toward chloroquine phosphate（CQ）by activating peroxydisulfate（PDS）under low power LED visible light.Relevant experiments and characterization confirmed that the synergistic effect of photocatalytic activations of PDS via the direct electron transfer PDS activation over P25M175and indirect electron transfer PDS activation over pristine MIL-88A could produce active species such as sulfate radical(SO₄^·-),hydroxyl radical（HO^·）,superoxide radical(O₂^·-),non-radical singlet oxygen（¹O₂）and holes（h⁺）to achieve CQ degradation efficiently.Based on LC-MS and DFT theoretical calculations,it was determined that the C-N bond in the side chain of CQ is susceptible to cleavage by the attack of reactive species,and the toxicity of the degraded intermediate was evaluated by toxicity analysis software to be lower than that of the original CQ.Also,P25M175 demonstrated good reusability and stability.2.MIL-88A（Fe）was synthesized economically and efficiently using industrial grade reagents and immobilized on a three-dimensional macroporous polyurethane sponge（MIL-88A（Fe）@sponge,MS）.Under LED UV and real solar light irradiation,MS could activate persulfate as an effective heterogeneous catalyst to degrade tetracycline antibiotics（TCs）like tetracycline（TTC）,oxytetracycline（OTC）,and chlortetracycline（CTC）completely by producing reactive oxygen species（ROSs）such as SO₄^·-,O₂^·-,HO^·and ¹O₂.As well,toxicological simulation and antibacterial studies showed that the aquatic toxicity of the TCs intermediates was lower than those of the original TCs.MS was also filled into a fixed-bed reactor to test the possibility of long-term TCs degradation operation in MS/PDS/UVL system.The results showed that the MS/PDS/UVL system could achieve 100%degradation of TCs within 15 days.Meanwhile,to further explore the practical engineering application of MS,the performance of coupled advanced oxidation process and biological degradation of TCs was first investigated by loading biofilm on the surface of MS,and the results showed that the coupled system could still achieve 100%degradation of TCs after continuous operation for 15 days,and the TOC removal rate was maintained above 90%.It was concluded that immobilizing MOFs onto polyurethane sponge can really increase the duration of the emerging MOFs materials,and the macro-porosity.3.MIL-88A（Fe）@sponge（MS）was synthesized by a dip-coating method,which displayed efficient photocatalytic Cr（VI）reduction efficiency under both low power LED UV light and real solar light irradiation.It was observed that MS（0.2 g/L）could remove 100%Cr（VI）（10mg/L）by adding 0.4 mmol/L tartaric acid（TA）without adjusting p H（p H 5.05）within 6.0 min and 3.0 min under UV light and real solar light irradiation,respectively.Besides,the photo-induced e^-,O₂^·-and carboxyl radical(CO₂^·-)were found to play the momentous roles in the MS/TA/UVL/Cr（VI）system by the scavenger experiments and electron spin resonance（ESR）tests.MS was also filled into a fixed-bed reactor to test the possibility of long-term Cr（VI）reduction operation in TA/UVL system.As expected,the results revealed that MS could still maintain 100%activity up to 60 h.4.A durable and efficient hydrophobic/superoleophilic polyurethane sponge material MIL-88A（Fe）@sponge was synthesized by a dip-coating method.With the modification of MIL-88A（Fe）,the polyurethane sponge exhibited better hydrophobicity and lipophilicity,while the adsorption capacities for pump oil,peanut oil,and CCl₄ were 32.13 g/g,34.85 g/g,and34.25 g/g,respectively.Moreover,the hydrophobic surface of MS has excellent chemical resistance and physical stability in strong acid,strong alkaline and high salt environments.In addition,it was found that the structure and morphology of MS were not significantly changed even after 60 adsorption-compression cycles,proving it to be candidate material for oil/water separation.