Preparation Of ZIF-8-based Nano-core Shell Materials And Their Adsorption Properties Research

Water pollution is a global issue of considerable concern,and heavy metal ion/dye wastewater pollution bears the brunt.Generally,the treatment of heavy metal ion/dye in wastewater could be classified into chemical precipitation,ion exchange,membrane separation,biological and adsorption.Among above-mentioned methods,adsorption is cost-effective and operates simply.Based on the typical MOFs（ZIF-8）,the Fe3O4@ZIF-8magnetic core-shell material and porous hollow carbon sphere（PHCS）@ZIF-8 novel core-shell adsorption nanomaterial were prepared by a simple method.The physical and chemical structures of the above materials were characterized.The adsorption properties of two adsorbent materials on heavy metal ions and dyes in wastewater were investigated.The factors affecting the adsorption performance and the dynamic adsorption process of the fixed bed were also studied.The following are the main research contents and results:（1）The core-shell nanospheres based on Fe3O4 and ZIF-8 were successfully prepared by a facile method.The method uses an anionic polyelectrolyte to pretreat Fe3O4 to change the surface charge of the particles and adsorb Zn²⁺to initiate nucleation,and then grow a thin ZIF-8 layer on the surface of Fe3O4.SEM characterization confirmed that the ZIF-8shell was continuous with a thickness of 80-100 nm.Fe3O4@ZIF-8 was used to remove Cu²⁺and crystal violet（CV）dye from wastewater.The effects of p H,contact time and concentration on the adsorption process were investigated.The adsorption kinetics and mechanism were discussed systematically.The adsorption data better followed the Langmuir isotherm and the pseudo-second-order model,and the maximum adsorption capacity was 164.74 and 46.4 mg g^-1,respectively.The adsorbent can be quickly separated and recovered by a magnetic field,avoiding secondary pollution and having good recycling performance,which is superior to the original parent material.（2）A PHCS with a particle size of 300 nm was successfully prepared by the St?ber method.By adjusting the content of PHCS,a novel porous core-shell nano-adsorbent PHCS-15@ZIF-8 with ZIF-8 nanoparticles uniformly coated with PHCS core was obtained by a facile method.The characterization results indicated that the obtained PHCS-15@ZIF-8 nanophere has an average thickness of 100 nm,with porous structure,high specific surface area(1140 m²g^-1)and numerous oxygen-containing functional groups.Compared with the parent material ZIF-8,PHCS-15@ZIF-8 showed better dispersibility and enhanced adsorption,and the maximum adsorption capacity for Pb²⁺reached up to462.9 mg g^-1.The adsorption data better followed with Freundlich isotherm and pseudo-second-order model.The effects of PHCS content,initial concentration,solution p H and competing ions on the sorption performance were discussed in detail.The possible sorption mechanism was also systematically analyzed by zeta potential,FT-IR,AAS and XPS studies.In addition,desorption and regeneration studies showed that PHCS-15@ZIF-8still remained over 90%recycling efficiency after four cycles.（3）The dynamic adsorption process of Pb²⁺in PHCS-15@ZIF-8 fixed bed was studied.The effects of flow rate,initial concentration of Pb²⁺solution and adsorption dose on the characteristics of breakthrough curve were explored.Results indicated that the breakthrough time and equilibrium time were positively correlated with the amount of adsorbent,while it was negatively correlated with the inlet flow rate and the initial concentration of the solution.The Thomas model and Yoon-Nelson model were used to fit the dynamic adsorption breakthrough curves under different conditions.The dynamic adsorption process of Pb²⁺adsorbed by PHCS-15@ZIF-8 fixed bed was theoretically analyzed,and the effect of different solvents on PHCS-15@ZIF-8 desorption was explored.