Preparation Of Fe(?)-MOFs And Its Catalytic Ozonation Mechanism For The Degradation Of Succinonitrile

In recent years,the threat of increasing acrylic wastewater discharge on water ecological environment has become increasingly serious,and the efficient degradation of succinonitrile,one of the main refractory substances in acrylic wastewater,has gradually become a keypoint for the treatment of acrylic wastewater.Metal-organic frameworks?MOFs?have been attracting increasing attention for their huge specific surface area,ultra-high porosity,strong structural stability,and plentiful catalytic sites on the surface.Especially the iron-based metal-organic framework?Fe-MOFs?as one of the important members of MOFs not only have all the characteristics of MOFs,but also are low cost and easy to be prepared,which are ideal properitis of catalysts for heterogeneous catalytic ozonation of refractory substances.In this study,the mechanism of catalytic ozone oxidation was analyzed.MOFs were prepared us iron trichloride?Fe Cl₃.6H₂O?as the iron source,tartaric acid?C₄H₆O₆?and terephthalic acid?C₈H₆O₄?as organic ligands through hydrothermal synthesis,and some MOFs were doped with metal ions such as Al³⁺and Cu²⁺.Also,the catalysts were screened.X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FT-IR?,scanning electron microscope?SEM?,energy dispersive X-ray spectroscopy?EDS?,X-ray photoelectron spectroscopy?XPS?,and specific surface area test?BET?and other methods are used to characterize the microstructure,functional groups and elemental composition of MOFs.The effects of initial p H,catalyst concentration,hydraulic retention time?HIT?and temperature on the efficiency of MOFs on succinonitrile degradation were investigated.The orthogonal experiment was used to analyze the influence of each factor on the catalytic oxidation.COMSOL software was used to analyze the concentration field distribution of each substance during the reaction under the actual control boundary conditions.The results show that in the process of ozone liquid-phase catalytic oxidation,gas-phase ozone is dissolved into liquid-phase ozone before it can be further utilized.The stability,specific surface area and content of catalytic sites of the catalyst are the core factors of the catalytic efficiency of heterogeneous catalysts.Among various MOFs photocatalysts,T2-MOF?a Fe???-MOFs synthesized from ferric ions and tartaric acid?has good catalytic effect,and the COD removal rate of succinonitrile can reach to 73.1%.T2-MOF belongs to a monoclinic system with multiple dominant growth directions.It is a quadrangular prism with uniform grains and a length of about 1?m.The CH₂ absorption peak in the FT-IR spectrum was red-shifted,which may be due to the influence of the electron-withdrawing characteristics of Fe-O-C.T2-MOF is composed of C,O and Fe elements,and is uniformly distributed.The change in the binding energy of different chemical bonds in XPS proves that trivalent iron has effects on different chemical bonds.The specific surface area,total pore volume and pore size of T2-MOF are 24.9m²/g,0.070cm³/g and 14.2nm,respectively,indicating that T2-MOF is a typical mesoporous material.The results of single factor experiments and orthogonal experiments show that T2-MOF can stably catalyze in a wide p H range?3.0?7.0?.The optimum reaction conditions are as follows:gas phase ozone concentration is 20?25mg/L,the dosage of catalyst is 30 mg/L,p H is about 7,temperature is about 22°C and hydraulic retention time is 180 min.Compared with other parameter,HRT has greatest influence on the catalytic oxidation effect.The reaction mechanism shows that CO₃^2-and Cl^-inhibite the oxidation of succinonitrile obviously,but SO₄^2-has almost no effect.Treatment of succinonitrile by MOFs catalytic ozonation process followes a pseudo-first-order reaction.The reaction rate constant is7.75×10^-3min^-1,the activation energy is 7.36 KJ/mol,and the pre-factor is 0.15.COMSOL software calculates that ozone is mainly concentrated near the aeration port during the oxidation of succinonitrile;organic matter is uniformly dispersed in the reaction chamber,and has a low concentration only in the parts that contacts with the ozone;the oxidation products are distributed in the aeration flow path of the ozone.