Preparation Of Magnetic MOFs Nanomaterials And Research On Algae Removal Characteristics

With the continuous development of society and ever-increasing exploitation of water resources by human,water eutrophication and water bloom have become common phenomenon,resulting in many serious problems,such as:seriously damaged aquatic ecosystems,algal toxins,and unhealthy human beings,animals and aquatic organisms.The structural characteristics of algae make the treatment of algae-containing water a tough issue,which requires immediate attention and dedication of researchers in the field of water pollution treatment.As an emergency algae removal method,adsorptive flocculation has attracted more and more attention due to its advantages of high efficiency,no secondary pollution and ease of practical application.The environment-friendly and energy-saving magnetic MOFs nanomaterial is one of the new solutions for algae removal.The following innovative progresses were achieved in paper:1)The magnetic nanoparticles of Fe₃O₄ was prepared using the solvothermal method and the structure and properties of Fe3O4 were characterized by X-ray diffraction?XRD?,fourier-transform infrared spectroscopy?FT-IR?,transmission electron microscopy?TEM?,scanning electron microscopy?SEM?,vibrating sample magnetometer?VSM?and thermogravimetric analysis?TGA?.2)The metal-organic framework material ZIF-8 was coated on the surface of the prepared magnetic nanoparticles Fe3O4 by polyelectrolyte?PSS?modification method,then the magnetic core shell MOFs material of Fe3O4@ZIF-8 was prepared.It can be separated by magnetism,which gives the algae-removing material an excellent performance for recycling.And the structure and properties of the magnetic MOFs nanomaterial of Fe3O4@ZIF-8 were characterized by X-ray diffraction?XRD?,fourier-transform infrared spectroscopy?FT-IR?,transmission electron microscopy?TEM?,scanning electron microscopy?SEM?,vibrating sample magnetometer?VSM?,N₂adsorption desorption?BET?and thermogravimetric analysis?TGA?.3)The BG-11 medium was used to cultivate Microcystis aeruginosa?FACHB-942?.In addition,the effect of magnetic core-shell MOFs material of Fe3O4@ZIF-8 on the removal of Microcystis aeruginosa was studied.The content of chlorophyll a was used to calculate the algae removal rate.The effects of concentration of Fe3O4@ZIF-8,reaction time,pH value,temperature and ionic strength of water on algae removal were studied,and the best conditions for algal removal were determined.At the same time,the recycling effect of the algae-removing material of Fe3O4@ZIF-8 was studied,and the algae removal rate of different recovery times was explored.4)The morphology and structure of algae cells and flocs before and after algae removal by Fe3O4@ZIF-8 were characterized and analyzed by X-ray diffraction,infrared spectroscopy,Zeta analyzer and various microscopes,thus the mechanism of algae removal by Fe3O4@ZIF-8 was determined.The kinetics of adsorptive flocculation of microcystis aeruginosa was studied by using the quasi-first and quasi-second order kinetic models.The Langmuir and Freundlich adsorption isotherm equations were used to fit the adsorption equilibrium experimental data and the adsorption isotherm model was determined.The research shows that the prepared magnetic MOFs material of Fe3O4@ZIF-8 has obvious core-shell structure and uniform particle size about 600 nm.In addition,it still maintains high magnetic properties?54.8 emg/g?,which enables its excellent recyclability.After four adsorptions and desorption,the algae removal rate remains at around 70%.The adsorption amount of Fe3O4@ZIF-8 was 0.58124 mg/g.The optimal material concentration was 0.8 g/L and the optimal reaction time was 30 min.By exploring the mechanism of algae removal,it was found that the algae-removing material of Fe3O4@ZIF-8 adsorbed and flocculated algal cells through charge neutralization.The adsorption behavior accords with the two-stage reaction kinetics and the Langmuir adsorption isotherm model through the data fitting.Therefore,the use of magnetic MOFs materials for algae collection and removal is a rapid and efficient process.