Preparation Of ZIF-8-based Composites And Their Adsorption Performance On Cadmium And Tetracycline In Water

With the rapid growth of the industrial and agricultural sectors,a considerable volume of wastewater including heavy metals and antibiotics is released into the environment,posing environmental risks.The heavy metals cadmium（Cd）and tetracycline（TC）are important constituents in the industrial production sector and the pharmaceutical industry respectively,and are also common contaminants in water that can cause varying degrees of harm to life on earth.Because of their toxicity and difficulties in biodegradation,these two contaminants have gotten a lot of attention.Adsorption is a low-cost and effective method for removing pollutants from water,and the major goal is to improve the adsorption performance of materials for contaminants.In order to effectively remove these two substances from the aqueous environment,ZIF-8,a metal-organic skeleton with a high specific surface area,tunable pores,and stable structure,was selected for the removal of Cd（II）and TC from water after reasonable modification.In this study,Fe₃O₄ and multi-wall carbon nanotubes（MWCNTs）were selected as the modified materials.With the advantages of magnetic and chemical stability of Fe₃O₄ and the high specific surface area and structural stability of MWCNTs,Fe₃O₄/ZIF-8 was synthesized for the removal of Cd（II）composites and Fe-ZIF-8/MWCNTs composites for the removal of TC,which enable the materials to have magnetic separation properties and high specific surface area,respectively,to compensate for the defects of the original materials and enhance the adsorption capacity of the materials.The main elements of this study are as follows.1.Magnetic Fe₃O₄/ZIF-8（MFZ）composites were prepared by a simple precipitation method and characterized by SEM,FTIR,and VSM,showing that MFZ composites were successfully prepared and had certain magnetic separation properties,and solid-liquid separation was achieved after 20 s under the action of an external magnet.The results of static adsorption experiments showed that the adsorption of Cd（II）by MFZ was best at a solution p H of 7,with an adsorption equilibrium time of 3 h.The effects of possible co-existing ions in the environment such as Cl^-,SO₄^2-,Mg²⁺,Ba²⁺,Ca²⁺,CO₃^2-on the adsorption of Cd（II）were also investigated,and the results showed that only CO₃^2-had a facilitating effect on the adsorption of Cd（II）,while the rest had a negative effect on the adsorption effect.In addition,the adsorption process followed the proposed secondary kinetic model and the Langmuir isotherm model,indicating that the adsorption reaction was mainly chemisorbed and that the reaction occurred in a single molecular layer.The theoretical maximum saturation adsorption capacity fitted to the Langmuir model was 160.26 mg/g at a temperature of 298 K,which is better than most adsorbent materials.The adsorption thermodynamic results indicate that the adsorption of Cd（II）on MFZ is a heat-absorbing,spontaneous process,and the increase in temperature favors the adsorption reaction.Comparing FTIR and XPS before and after adsorption,the analysis showed that the adsorption mechanism of Cd（II）on MFZ mainly included ion exchange,coordination reaction,and electrostatic interaction.The response surface optimization experiments showed that the predicted adsorption capacity of Cd（II）was 103.97 mg/g at the optimum conditions of 141.39 mg/L dosage,p H 6.7,and 301.4 K,with a deviation of 2.41%from the actual value.In addition,MFZ is also well reusable,with the adsorption capacity of Cd（II）still reaching over 75mg/g after four cycles of regeneration,with a loss of approximately 25%.Production cost estimates yielded that the cost required to treat 40mg/L of Cd（II）containing wastewater was approximate CN￥55.76/m³,indicating that MFZ has some potential for Cd（II）removal.2.Fe-ZIF-8/MWCNTs（FZM）composites were synthesized by simple precipitation and solvothermal methods and characterized by SEM,XRD,and FTIR,showing that the composites were successfully prepared and had a chain-like structure.The results of static adsorption experiments showed that the adsorption of TC by FZM was best at a solution p H of 6,with an equilibrium time of 6 h.The effect of co-existing ions showed that the presence of Cl^-,SO₄^2-,Mg²⁺,and CO₃^2-inhibited the adsorption of TC on FZM,while the presence of Ca²⁺slightly promoted the adsorption of TC.The results of the adsorption model fitting showed that the adsorption of TC on FZM followed the proposed secondary kinetic and Freundlich isotherm models,indicating that chemisorption was the dominant factor in the adsorption of TC and that the adsorption reaction was multilayer adsorption,and the theoretical maximum saturation capacity of 1111.11 mg/g was fitted according to the Langmuir model,which was better than other adsorbents.The adsorption thermodynamic results showed that the adsorption process of TC on FZM is a heat-absorbing,spontaneous process,with the adsorption capacity increasing with increasing temperature.Comparison of FTIR before and after adsorption to explore the possible adsorption mechanism of TC on FZM showed that the adsorption mechanism mainly consisted of hydrogen bonding,surface complexation,π-πinteractions and electrostatic interactions between the FZM composites on the TC molecules.Response surface optimization experiments showed that the optimum adsorption conditions at p H 7.1,a temperature of 312.5 K and a dosage of 64.43 mg/L resulted in a predicted adsorption capacity of 599.78 mg/g of TC,with a deviation of 1.73%from the actual value.In addition,FZM has good reusability and after four cycles of experiments,the adsorption capacity of FZM for TC was still able to reach over 370 mg/g with a loss of approximately 15%.Production cost estimates yielded a cost of approximately CN￥32.29/m³ for the treatment of 100 mg/L of TC wastewater,indicating that FZM shows good promise for the removal of TC.Both composites,MFZ and FZM,showed good adsorption of Cd（II）and TC respectively,indicating that both composite adsorbents have potential for practical application.Through the study of ZIF-8 and its modified materials in wastewater treatment,this thesis explores the adsorption mechanism of ZIF-8-based composites on metal ions and antibiotics,as well as the regeneration effect of the adsorbents,providing some theoretical basis and direction for the future treatment of pollutants such as heavy metal ions and antibiotics remaining in wastewater and enhancing the reusability of the adsorbents themselves.