Study On Preparation Of A Novel Magnetic MOFs/Polymeric-iron And Its Coagulation For Dissolved Organic Matter(DOM)

Dissolved organic matter?DOM?in surface source water can be divided into dissolved carbon/nitrogen?DOC/DON?.DOM is a precursor of disinfection by-products,which causes problems such as eutrophication of water bodies and membrane fouling,which seriously affects the safety of water supply.Coagulation-flocculation process is one of important operation units in water treatment,which has profound influence on the subsequent water operational units in water plants.But the existing flocculation technology has a limited effect on processing the DOM.At present,the optimal design of the preparation of coagulant is the key element and core link to improve the coagulation-flocculation efficiency.The important direction is towards obtaining a highly efficient coagulant.The research on preparation of composite coagulants is very extensively needed,which provides a powerful way for environmentally-friendly and cost-effective coagulants.Preparing a magnetic coagulant is an emerging research hotspot by mainly introducing superparamagnetic and biosafety magnetic nanoparticles into a coagulant system.In this study,magnetic metal-organic frameworks?MMOFs?were prepared by loading MOFs on surface of core-shell magnetic nanoparticles?MNPs?,with was characterized by rich structure,easy-adjustment,high surface-active sites,high adsorption capacity and large specific surface area.The preparation and structural characteristics of a novel magnetic MOFs/polymeric-iron?PFS-MMOFs?by introducing the MMOFs into a polyferric sulfate?PFS?system were investigated in removal of dissolved organic matter?DOM?.The main conclusions obtained in this study were as follows:?1?The stable crystal structure and superparamagnetic Fe₃O₄ based on solvothermal method was synthesized.The surface of SiO₂ shell of Fe₃O₄ was modified by used Stober method to increase its dispersibility,oxidation resistance and acid resistance;In-situ growth method is used to grow UiO-66-2COOH layer on the surface of Fe₃O₄@SiO₂;PFS-MMOFs by copolymerization of MMOFs and PFS was synthesized.The control level of each factor was obtained by single factor experiment.The optimal level of each factor was synthesized by using response surface design:the mass ratio of MNPs to MOFs(m_MNPs/m_MOFs)was 2,the mass ratio of MMOFs to effective Fe components(m_MMOFs)/m _Fe)was 0.2,the synthesis temperature was 40°C,and the degree of alkalinity(n_OH/n _Fe molar ratio)was 0.16.?2?Fe-Ferron time-lapse complex colorimetry?Ferron method?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,Fourier transform infrared spectroscopy?FTIR?,X-ray diffraction?XRD?The vibrating sample magnetometer?VSM?and Zeta potential were used to analyze the physical and chemical structures of Fe₃O₄,MNPs,MOFs,MMOFs and PFS-MMOFs.The results show that MMOFs can redistribute the iron hydrolyzed form of PFS,and the intermediate complex morphology?Fe_b?increases significantly.The obtained Fe₃O₄ particle size is 300⁴00 nm spherical,and the wrapped SiO₂shell is about 10 nm.The stacked MOFs were successfully grown on the surface of Fe₃O₄@SiO₂,and finally formed MMOFs.The study successfully introduced MMOFs into the polyferric sulfate system to form PFS-MMOFs,and the resulting flocs have recyclable magnetism.MOFs was able to enhance the electrical neutralization of PFS and increase the ability to potentially adsorb negatively charged organics under alkaline conditions.?3?The effects of PFS-MMOFs dosage,pH and hydraulic conditions on the coagulation performance were investigated.The effects of MMOFs on PFS removal of water environmental pollutants were compared.The three-dimensional fluorescence spectroscopy and molecular weight cut were explored.The effect of PFS-MMOFs flocculation water environmental pollutants has obtained the applicability of its water environment.The results showed that PFS-MMOFs were able to obtain the best removal effect of turbidity,UV₂₅₄ and DOC at pH=9 and speculative amount of 22 mg/L.The PFS-MMOFs doped with MMOFs were better than PFS.The effect of removing UV₂₅₄ and DOC is good,but the removal mechanism of UV₂₅₄ and DOC is inconsistent;the optimal hydraulic conditions are:fast stirring for 90 s,slow stirring for 20 min,fast stirring speed 210 r/min,slow stirring speed 80r/min,static precipitation 30 min;PFS-MMOFs have a good removal effect on micro-polluted source water,which showing the directionality of removal of water-like proteins?I,II?and soluble microbial metabolites?IV?.