Study On The Adsorption Performance Of Metal Organic Framework Materials For Microcystins

Microcystins（MCs）,as secondary metabolites produced during algal blooms,are potentially threatening ecosystems and human health.Therefore,it is of great significance to develop new and efficient adsorption materials to remove MCs from water.In this paper,the structural characteristics,types,and preparation and modification methods of metal organic framework materials（MOFs）are reviewed.Aiming at the problem of MCs pollution in water,based on the typical material ZIF-8 in metal organic framework materials,Fe-ZIF-8 and Fe₃O₄@ZIF-8 were prepared by metal doping modification and magnetic loading modification,respectively.The morphology and structural properties of the adsorbent were observed by scanning electron microscopy,transmission electron microscopy,X-ray powder diffraction,Raman spectroscopy,nitrogen adsorption-desorption isotherms,hysteresis regression curves,and thermogravimetric analysis.The effects of single factor conditions on the adsorption of microcystin-RR（MC-RR）by the adsorbent were investigated,and a kinetic model and an adsorption isotherm model were established,the adsorption mechanism was elucidated through characterization methods such as Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy,providing a basic basis for subsequent research on MOFs materials in the treatment of MCs pollution.The main results of this article are as follows:（1）Using zinc nitrate hexahydrate,ferrous sulfate heptahydrate,and 2-methylimidazole as raw materials,using methanol as an organic solvent,composite materials with Fe²⁺:Zn²⁺ratios of 0:10,1:9,2:8,and 3:7 were prepared using a stirring synthesis method.They were sequentially named ZIF-8,Fe ZIF-8-10%,Fe ZIF-8-20%,and Fe ZIF-8-30%.The adsorption properties of the above materials for MC-RR were compared,and the results showed that the adsorption capacity of the composite materials for MC-RR showed a trend of first increasing and then decreasing with the increase of the metal Fe doping amount,and it had the strongest adsorption capacity for MC-RR when the Fe doping amount was 10%.The adsorption kinetics conformed to quasi second order kinetics.SEM analysis results showed that ZIF-8 has a clear rhombic dodecahedral structure,which remained after incorporation of iron metal,but the crystal surface became rough.The XRD analysis results also showed that the doping of Fe element was destructive to the crystal form integrity of ZIF-8,and the greater the doping amount of Fe element,the greater the degree of crystal form destruction.The adsorption mechanism analysis results showed that the adsorption mechanism mainly involves complexation.（2）Fe₃O₄magnetic nanoparticles were prepared by hydrothermal method using ferric chloride hexahydrate,anhydrous sodium acetate and ethylene glycol as raw materials.Then took methanol as organic solvent,added zinc nitrate hexahydrate and 2-methylimidazole to generate ZIF-8 on the surface of Fe₃O₄magnetic nanoparticles,and finally successfully prepared composite materials Fe₃O₄@ZIF-8.The results showed that the adsorption rate was fast,and the theoretical maximum adsorption capacity of MC-RR could reach 6.055 mg·g^-1.The adsorption conformed to the quasi-second order kinetic model,indicating that the adsorption process was mainly multilayer adsorption.The adsorption isotherm curve conformed to the Freundlich adsorption isotherm model,indicating that the adsorption process was dominated by chemical adsorption.The adsorption process was less affected by anions and actual water samples.Fe₃O₄@ZIF-8 still had high adsorption capacity after three cycles of use and could realize rapid recovery under the action of magnetic field.The adsorption mechanism showed that the adsorption process included surface complexation,π-πinteraction.