Study On The Adsorption Of Metal Ions In Wastewater By Zeolitic Imidazolate Framework Hybrid Membrane

In this study,the main content is the preparation and characterization of Zeolitic Imidazolate Framework-8(ZIF-8)and its hybrid membrane.As well as the research on the adsorption mechanism and performance of Pb²⁺,Cu²⁺and Cr³⁺on the hybrid membrane.In this experiment,ZIF-8 material was prepared by ordinary solution method.Mix Zn(NO₃)₂·6H₂O and 2-Methylimidazole into methanol and stir at room temperature.After the reaction was complete,the precursor of ZIF-8 could be obtained by centrifugation,cleaning with methanol and drying in the oven.The membrane solution was prepared by stirring poly(vinylidene fluoride)and polyvinyl alcohol at 95?with dimethyl sulfoxide as the solvent.Zif-8 materials of different qualities were weighed and added into dimethyl sulfoxide for ultrasonic dispersion.After being dispersed into uniform colloidal solution,the materials were poured into the membrane solution and blended and stirred at room temperature.After the stirring,they were put into the vacuum box for degassing and ultrasonic dispersion in the ultrasonic instrument.After completion,the membrane solution is poured on the smooth glass plate and the hybrid film is made by phase transformation method.The ZIF-8 material and its hybrid membrane were characterized by XRD,FTIR,TGA,SEM and EDS.Zeolite imidazolium ester skeleton material ZIF-8 and hybrid membrane material A?F were characterized by X-ray diffraction,and the diffraction characteristic peak of ZIF-8 could be seen,namely,(011),(002),(112),(022),(013),(222),(114),(233),(134).The diffraction characteristic peaks of zeolite imidazolium ester framework material ZIF-8 can also be seen in hybrid film materials A?F.The infrared spectrum analysis was used to characterize the zeolite imidazolium ester framework material ZIF-8 and hybrid film material A?F.The infrared absorption peaks of ZIF-8 were observed near 3135 cm^-1,2930 cm^-1,1583 cm^-1,1456 cm^-1and 1423cm^-1,corresponding to C-H bond stretching vibration peak and the C=N bond stretching vibration peak.In addition to the ZIF-8 infrared absorption peak,the infrared absorption peaks of hybrid membrane A?F are located near 3333 cm^-1,2923cm^-1,1402 cm^-1,1173 cm^-1,1073 cm^-1and 875 cm^-1.Corresponding to O-H stretching vibration peak,-CH₂asymmetric stretching vibration peak,C-F bond stretching vibration peak and-CF₂characteristic band.According to thermogravimetric analysis,ZIF-8 material begins to lose weight rapidly at about 576.7?and loses about 10%at616?.The decomposition of hybrid membranes can be roughly divided into four stages.The first stage is less weight loss at room temperature to 281?.In the second stage,thermal decomposition gradually occurs at the accessory temperature from281?to 359?.In the third stage,thermal decomposition occurs at the accessory temperature of 359?to 523?.In the fourth stage,the weight decline trend of each hybrid film material slows down.The appearance structure of ZIF-8 material and hybrid membrane materials was observed by scanning electron microscope,and energy spectrum analysis showed that the hybrid membrane did have adsorption effect on metal ions.It is proved that ZIF-8 material is indeed introduced into hybrid membrane material in the experimental process,and has a certain adsorption effect.The optimum p H values for Pb²⁺,Cu²⁺and Cr³⁺adsorption are 5,4 and 5,respectively.F membrane has the best adsorption effect in Pb²⁺,Cu²⁺and Cr³⁺ionic solutions at room temperature,with adsorption capacity of 62.40mg/g,18.36mg/g and 20.43mg/g,respectively.The kinetic model showed that the adsorption of Pb²⁺and Cu²⁺by hybrid membrane was more consistent with chemisorption,and the adsorption of Cr³⁺was partly physical adsorption and partly chemical adsorption.The intra-particle diffusion model and Elovich kinetic model were used to show that the rate-limiting step is only one factor and the heterogeneous adsorption reaction was not the main process of the adsorption reaction.The fitting results of isothermal adsorption model show that the adsorption process is simple monolayer adsorption.The(35)G,(35)S,(35)H of the hybrid membrane A?F for each ion adsorption reaction can be known that the adsorption reaction can be spontaneous,and when the adsorption reaches equilibrium,it is an endothermic irreversible reaction.In the case of multi-ion mixed adsorption,each ion has interference,and its adsorption capacity is lower than that of single ion adsorption.Using hydrochloric acid,nitric acid and ethylenediamine tetraacetic acid disodium solution for desorption of membrane materials,after 5 cycles,the adsorption capacity decreased by 62.62%?98.97%.