Synthesize Of Novel Adsorbent Based On Metal Organic Framework ZIF-8 And Their Adsorption Properties On Liquid Phase

With the development of material science,compared with traditional adsorbents,the research and development of new adsorbents has become one of the hot research directions.As a new material,metal organic framework has attracted wide attention due to its advantages of large specific surface area,adjustable pore size and abundant adsorption sites,and has been applied in the field of gas adsorption and liquid adsorption.ZIFs,as one of the metal organic frameworks,has the greatest advantages of well-developed pore structure,large specific surface area and strong hydrothermal stability.Therefore,the metal organic framework ZIF-8 and magnetic composite Fe₃O₄@ZIF-8were prepared and used as new adsorbents to study the adsorption properties of anionic dye Congo Red.In this paper,ZIF-8 was successfully prepared by mechanical stirring at room temperature,and a new magnetic adsorption material Fe₃O₄@ZIF-8 was prepared by combining Fe₃O₄ and ZIF-8.The morphology,structure and composition of ZIF-8 and magnetic composite Fe₃O₄@ZIF-8 were characterized by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,Fourier transform infrared spectroscopy?FTIR?,X-ray diffraction?XRD?,thermogravimetric analysis?TG?and magnetic properties analysis?VSM?.Through static adsorption experiments,the effects of different factors on the removal of Congo Red dyes by adsorbents were investigated.In addition,the adsorption kinetics,adsorption isotherm and thermodynamic model were used to analyze the adsorption process,and the adsorption mechanism was preliminarily explored.At the same time,the selective adsorption properties of new adsorbents ZIF-8and Fe₃O₄@ZIF-8 and their competitive adsorption properties in mixed dyes were systematically studied.The cyclic regeneration properties of the adsorbents ZIF-8 and Fe₃O₄@ZIF-8 were investigated.Finally,the adsorption effects of ZIF-8,Fe₃O₄@ZIF-8,Fe₃O₄ and activated carbon on Congo Red dyes were compared.The main achievements of this paper are as follows:?1?The metal organic framework ZIF-8 was successfully synthesized by mechanical stirring at room temperature.The material was confirmed by XRD and FTIR characterization.SEM analysis showed that the synthesized ZIF-8 had polyhedral structure,uniform morphology and particle size,and its particle size was about 100 nm.TG analysis showed that ZIF-8 had excellent thermal stability.?2?Based on the synthesis of ZIF-8,a new magnetic adsorption material Fe₃O₄@ZIF-8 was successfully prepared by adding magnetic nanoparticles Fe₃O₄.XRD and FTIR analysis showed that Fe₃O₄ had been successfully combined with ZIF-8.SEM and TEM characterizations showed that Fe₃O₄@ZIF-8 had a typical core-shell structure with rough surface and stacked particles to form many channels.Magnetic properties?VSM?analysis showed that Fe₃O₄@ZIF-8 had good magnetic properties and could be rapidly separated from solution by applying magnetic field?3?The selective and competitive adsorption properties of ZIF-8 and Fe₃O₄@ZIF-8adsorbents for dyes were investigated.It was found that both ZIF-8 and Fe₃O₄@ZIF-8adsorbents have selective adsorption properties for Congo Red,an anionic azo dye.Their adsorption removal rates were Congo Red>Direct Blue 86>Methyl Orange>Methylene Blue.Moreover,both ZIF-8 and Fe₃O₄@ZIF-8 preferentially adsorb Congo Red dyes in mixed dyes?Congo Red+Direct Blue 86?,indicating that Congo Red dyes occupy an advantage in competitive adsorption.However,the removal rates of Congo Red and Direct Blue 86 in mixed dyes were lower than those in single system,and the removal rates of Congo Red decreased with the increase of the concentration of Direct Blue 86.?4?The adsorption mechanism of ZIF-8 and Fe₃O₄@ZIF-8 was preliminarily discussed.The adsorption kinetics of the two adsorbents accorded with the second-order kinetic model,and the adsorption isotherms accorded with the Langmuir model.Thermodynamics showed that the adsorption process was spontaneous endothermic reaction.The whole adsorption process is the coexistence of physical adsorption and chemical adsorption.The adsorption mechanism is mainly electrostatic attraction.The unsaturated skeleton metal Zn²⁺in ZIF-8 and Fe₃O₄@ZIF-8 and—SO₃ in Congo Red dyes have electrostatic attraction.At the same time,the imidazole rings in ZIF-8 and Fe₃O₄@ZIF-8 materials also have pi-pi bonding with benzene rings in Congo Red molecules.?5?Comparing the removal effects of ZIF-8,Fe₃O₄@ZIF-8,Fe₃O₄ and activated carbon?AC?on Congo Red,it was found that the unit adsorption capacity of adsorbent was ZIF-8>Fe₃O₄@ZIF-8>activated carbon>Fe₃O₄,but the magnetic adsorbent Fe₃O₄@ZIF-8 still maintained a high removal efficiency for Congo Red,and could be recycled efficiently by adding external magnetic field.ZIF-8 and Fe₃O₄@ZIF-8 have excellent cyclic adsorption properties.After five cycles,the removal rate of Congo Red remains above 90%.