Preparation Of Nanometer-sized Magnetic Porous Materials And Their Application In Metal Ions Adsorption

With the rapid development of industrialization,accidental and purposive dumping of metal ions into environmental water occurs regularly,which has contributed to serious water pollution and potential harm to the health of living organisms.Adsorption technique featuring with simple and fast separation,high efficiency and low-cost has been extensively used for water treatment.However,the low adsorption capacity and poor selectivity of conventional adsorbents limit its application to a great extent,and the development of novel adsorbents with plenty of selective adsorption sites for target metal ions has become the main orientation in adsorption field presently.Metal organic frameworks(MOFs),also known as porous coordination polymers,are a new kind of porous materials.Due to their large specific surface area,high stability,easy preparation and flexible structure,MOFs have been widely used as adsorbents for pollutants capture.However,they still suffer from the relative poor water stability in water treatment process;for the adsorption of interest metal ions,functionalization of MOFs is imperative to introduce selective adsorption sites.In addition,high-speed centrifugation or filtration is generally necessary for the recovery of MOFs after adsorption,which is inconvenient and tedious.The aim of the dissertation is to develop environmental friendly and cost-efficiency synthesis strategies;to prepare magnetic porous sorbents,including magnetic MOFs composites(MFCs),magnetic N-doped porous carbons(MNPCs)and magnetic porous organic polymers(MOPs),with good selectivity,high adsorption capacity and high stability;and to realize high efficient adsorption of interest metal ions from environmental water with the prepared porous adsorbents.The main research contents are described as follows:(1)MFCs were successfully prepared by a novel and green strategy through reasonable design.Nano Fe3O4@SiO2 core was firstly coated by a shell of Cu(OH)2 as the self-template,followed by a conversion of Cu(OH)2 into HKUST-1 at room temperature in water-ethanol mixture solvent,resulting in Fe3O4@SiO2@HKUST-1 with core-shell nanostructure.Based on it,Bi-I-functionalized magnetic HKUST-1 composite was prepared through a flexible coordination-based post-synthetic strategy.The adsorption of Hg2+ on Fe3O4@SiO2,Fe3O4@SiO2@HKUST-1 and Bi-I-functionaluized MFCs were investigated,and a good adsorption selectivity of Bi-I-functionalized MFCs towards Hg2+ was demonstrated with high adsorption capacity(264 mg g-1)and fast adsorption dynamics.(2)Amino-decorated Zr-based MFCs were prepared by a facile and efficient strategy.Nano-sized Fe3O4@SiO2 core(about 15 nm)was coated with a shell of Zr-MOFs(about 5 nm)by means of in-situ growth.Fe3O4@SiO2@UiO-66 and its amino derivatives(Fe3O4@SiO2@UiO-66-NH2 and Fe3O4@SiO2@UiO-66-Urea)were successfully prepared by using different precursors.The obtained Zr-MFCs were demonstrated to be efficient adsorbents for metal ions(Cu2+,Cr3+,pb2+ and Hg2+)adsorption from aqueous solution,with high adsorption capacity and fast adsorption kinetics.Amino-decorated MFCs exhibited higher adsorption capacity for interest metal ions than Fe3O4@SiO2@UiO-66,and Fe3O4@SiO2@UiO-66-NH2 exhibited the highest capacity for Pb2+(102 mg g-1),which can be remained unchanged after 6 adsorption-desorption recycles.(3)A facile preparation of MFCs with flexible mercapto group pendants in their pores was realized through solvent-assisted ligand exchange(SALE)under mild conditions in water,and terephthalate in UiO-66 was replaced with mercaptoacetic acid(MAA).After SALE process,the crystallinity,porosity,and superparamagnetism of the mercapto functionalized Zr-MFCs(MFC-S)were well maintained,and the obtained MFC-S exhibited higher adsorption capacity(282 mg g-1)for Hg2+ than that of the Zr-MFCs(MFC-O).Furthermore,the prepared MFC-S can be regenerated easily by liquid desorption after adsorption of metal ions and be reused more than 5 times without obvious decrease in adsorption performance.The proposed SALE method for the preparation of MFCs is easy-to-operate and low cost,providing a simple and efficient synthesis route for the preparation of functionalized MFCs which cannot be achieved through conventional approaches.(4)Magnetic MIL-53(Al)were prepared in water under room temperature by employing organic salts as anionic linker sources.Amino-functionalized MFCs(MFC-N)with different amino group content were successfully prepared by varying the ratio of disodium of 2-aminoterephthalic(NH2-Na2BDC)/terephthalic acid(Na2BDC).The prepared nano MFC-N-X(X represents the percentage of NH2-Na2BDC,i.e.X=0,50,100)showed high surface area,large pore volume,excellent magnetic response,as well as good water and thermal stability.Among these prepared MFC-N-X,MFC-N-100 exhibited the highest adsorption capacity of 71 mg g-1 for AsO43-due to its porous structure and abundant amino groups.The prepared MFC-N-100 exhibited high adsorption efficiency for AsO43-in different water samples(tap water,lake water and domestic sewage)with a rapid magnetic separation ability,demonstrating a great application potential of the prepared MFC-N-100 as a fascinating adsorbent for removal of metal ions from different water samples.(5)MNPCs with high special surface areas(688 m2 g-1)and rich nitrogen content(-16 wt%)was prepared by direct pyrolyzing the mixture of ZnO,2-methylimidazole(HmIm)and Fe3O4@SiO2 magnetic nanoparticles(MNPs)or Co(OH)2.During the carbonization process,ZnO NPs directly reacted with HmIm to yield porous ZIF-8,which acted as the self-temp late in subsequent high-temperature pyrolysis for fabricating MNPCs.The prepared MNPCs exhibited a superior adsorption performance for Hg2+ which is ascribed to the rich active groups of pyrrole-N and pyridinic-N in MNPCs.Furthermore,the prepared MNPCs exhibited good chemical stability and the adsorption capacity was maintained unchanged even after 10 adsorption-desorption cycles.The proposed method is easy operation and economic,providing an attractive way for manufacturing efficient MPC sorbents.(6)MOPs with abundant thiol groups were synthesized successfully in high yield through a temp late-free and catalyst-free diazo-coupling reaction.The reaction was conducted under mild conditions in aqueous solution,in which the introduction of magnetism and thiol-functionalization was realized simultaneously,avoiding the use of environment-unfriendly organic solvents.The MNPs were embedded into hierarchical porous network structures of porous organic polymers(POPs)physically and the magnetism of thiol-functionalized MOPs(MOP-SH)was easily controlled by varying the amount of spiked MNPs.The obtained MOP-SH exhibited high thermal stability and chemical stability within a wide pH(2-13),and good adsorption performance for Hg2+ over a wide pH range due to the abundant thiols in its hierarchical structure.After the adsorption process using MOP-SH,the concentration of Hg in the spiked domestic sewage(100 μg L-1)reached 1.1μg L-1,which is even lower than the acceptable limit of national standard for drinking water(2 μg L-1).Besides,the prepared MOP-SH exhibited high adsorption capacity,fast adsorption kinetics and easy-recycling behavior,providing a new avenue for the preparation of functionalized adsorbents with good performance for water decontamination.