Study On The Catalytic Ozonation Efficiency And Mechanism Of Fe-MOFs For The Degradation Of Organic Pollutants From Dyeing&Finishing Wastewater

As a vital link of the entire textile eco-system,Dyeing&Finishing(D&F)guarantees the high quality and value of textile products.However,the D&F industry is facing severe issues of extensive water consumption,uncountable wastewater discharge,and strict regulations recently.These problems may pose a negative impact on the sustainable development of the D&F industry.The advanced treatment of D&F wastewater by the catalytic ozonation technique(COT)provides a promising solution to overcome these challenges.However,the current catalysts for COT suffer from the weak mass transferability,unsatisfactory catalysis capacity,poor stability,difficult separation behavior,and heavy metal pollution.As a result,the engineering application of COT is mainly limited.Therefore,it is significantly essential to explore novel green catalysts with high-performance and stability for the efficient catalytic ozonation process(COP).As inspired by the unique structures and characteristics of the iron-based metal-organic frameworks(Fe-MOFs),the catalytic efficiency and mechanism of Fe-MOFs applying for the COP were first explored.Second,according to the relation of coordinatively unsaturated sites(CUSs)within Fe-MOFs and surface Lewis acid sites(LASs)as well as the semiconductor property of Fe-MOFs,two novel strategies to strongly enhance the catalytic ozonation performance of Fe-MOFs by manipulating the molecular structures of Fe-MOFs or introducing the external energy field(e.g.,UV light)were developed.Finally,in order to address the potential issues of the unstable loading and difficult separation of powder Fe-MOFs in the engineering applications,the MOFs monoliths(noted as MOFiths)was fabricated via a proposed method by integrating with melamine foam(MF)as carrier and PVDF as film former.The fabricated MOFiths could stable load powder Fe-MOFs,and showed easy separation property and high-efficient performance for the robust COP.The main contents and results are summarized as follows:(1)Study on the COP efficiency and mechanism of typical Fe-MOFsFe-MOFs with unique surface properties as new platforms for the efficient catalytic ozonation were explored.The catalytic performances of Fe-MOFs for the degradation of organic pollutants from D&F wastewater was highly ascribed to their plentiful porosities and abundant LASs.Mechanism studies revealed that the LASs in Fe-MOFs were the active sites for the ozone decomposition.The ozone molecule could be catalytically decomposed into ·OHads,·O2-and 1O2 for the degradation of RhB in the Fe-MOFs/COP system.As a result,the kinetic rate constant and TOC removal of the Fe-MOFs/COP system were almost 13 and 4 times that of ozonation alone.By the combination of characterization techniques and density functional theory calculations,the intrinsic structure of LASs was confirmed as the coordinatively(i.e.,tetrahedrally)unsaturated iron centers(CUICs).The catalytic ozonation performance of Fe-MOFs was eventually governed by the content of CUICs,which provided a new insight for designing more efficient catalysts.On the view of molecular structure,the CUICs could be recognized as ligand missing defects within Fe-MOFs.(2)Study on enhanced COP performance and mechanism of Ce doping strategy.According to the relationship between CUICs and LASs found in the first section,a simple strategy to improve the Lewis acidity of Fe-MOFs was proposed.The enhanced COP performance and mechanism of Ce doping method were systematically investigated via the degradation of organic pollutants from D&F wastewater.The results turned out that the content of ligand missing defects of Fe-MOFs could be adjusted by the Ce doping ratio,which could tune the Lewis acidities of Fe-MOFs for improving activity purpose.When the doping ratio reached to 0.20,Ce-doping MIL-88A(Fe)(denoted as MIL-88A(Fe0.80Ce0.20))exhibited the largest Lewis acidity and excellent enhanced catalytic performance.The rate constant(0.190 min-1)and TOC removal(66%)of MIL-88A(Fe0.80Ce0.20)for salicylic acid degradation were about 2 and 1 times higher than that of parent MIL-88A(Fe),respectively.This was mainly because that the increased LASs after Ce doping could serve as additional active sites to promote ozone molecules decomposition into more·OHads and 1O2.(3)Study on enhanced COP performance and mechanism of UV light coupling strategy.Taking the unique advantages of the semiconductor property of Fe-MOFs and the strong electron capture ability of ozone,we developed an another enhanced strategy for COP by introducing the UV light into the catalytic system,called photocatalytic ozonation.The enhanced COP performance and mechanism of this method was systematically investigated via the degradation of organic pollutants from D&F wastewater.The results turned out that the rate constant(0.1632 min-1),TOC removal(75.4%)and EE/O(27.38 kWh m-3 order-1)value of photocatalytic ozonation for 4-NP degradation were 1.94,2.0,and 0.51 times that of catalytic ozonation,and 11.4,4.3,and 0.44 times that of photocatalysis,respectively.The chemical behavior of the ozone molecule was determined to be the key factor for the synergistic enhancement of this method.On the one hand,the ozone molecule could be catalyzed into ·OH,·O2-,and 1O2 for the mineralization of organic pollutants via the LASs of MIL-88A(Fe).On the other hand,the ozone molecule could capture the photogenerated electrons in the conductor band to mitigate the carrier recombination and facilitate the separation and utilization of carriers to produce more ROS.(4)Study on preparation and application of separable and ultrastable MOFs monoliths.In order to make Fe-MOFs easily separated and ultrastable loaded,a simple and effective method to stable load powder Fe-MOFs to fabricate MOFs monoliths(noted as MOFiths)with easy separation and high-efficient performance for the robust COP via integrating with MF and PVDF was proposed.The results turned out that by comparison to other MOFs/MF composites fabricated from conventional methods,the MOFiths displayed more ultrahigh loading stability when encountering mechanical destructions(i.e.,squeezing,stirring,centrifugation,and ultrasonication)and solvent corrosions,which had the better potential for long-term engineering applications.Notably,the rate constant and TOC removal of the COP for 4-NP degradation by a MOFith catalyst(i.e.,53(Fe)-MOFith20)barely suffered delays at 6th recycle.Therefore,the MOFith catalyst showed fantastic properties of easy separation,high activity,and outstanding catalysis stability.In conclusion,this study first demonstrated the highly efficient catalytic ozonation performance of Fe-MOFs,which highly related to the key role of ligand missing defects within Ee=MOFs.Subsequently,by manipulating.the molecule structures of Fe-MOFs or introducing UV light,two novel strategies including Ce doping and UV light coupling were developed to substantially enhance the catalytic ozonation performance of Fe-MOFs.Finally,with the help of PVDF as a film former and MF as a carrier,a simple and effective method that fabricates ultrastable MOFiths was proposed to realize the application of Fe-MOFs with easy separation and high-efficient performance for the robust COP.This study can provide deep insights and guidelines that control the design and engineering application of high-efficient ozonation catalysts for the advanced treatment of D&F wastewater.