| Pharmaceuticals are closely related to human life with numerous varieties and massive consumption.In recent years,the ubiquitous occurrence of pharmaceuticals in the environment has raised wide concern.Despite the low concentrations(?g/Lto ng/L),pharmaceuticals could bioaccumulate through the food chain,posing potential hazards or risks to ecological system and human health.Especially,the wide application of antibiotics can induce anti-resistance genes in the microorganism,directly threatening human health.Conventional water treatment processes can not sufficiently eliminate pharmaceuticals.Advanced treatment techniques like adsorption,advanced oxidation and membrane separation should be incorporated to improve their removal.Activated carbon adsorption is one of the most common techniques for the removal of micropollutants including pharmaceuticals.However,the adsorption of pollutants by activated carbon is positively related to the hydrophobicity.Pharmaceuticals generally contain a lot of hydrophilic functional groups like hydroxyl,carboxyl,carbonyl,amine groups,etc.and certain pharmaceuticals will ionize in water.Therefore,activated carbon shows low removal capability for hydrophilic and ionizable pharmaceuticals.Besides,the disadvantages of low mechanical strength,difficulty to regenerate and high operational cost limit the application of activated carbon.Synthetic resins have the advantages of adjustable structure,large adsorption capacity and ease of regeneration.But conventional resins have large particle size(0.3-1.2mm),which can only be utilized in fixed bed or moving bed reactor.The low adsorption rate,the high investment and the high operational cost limit their wide application.Recently,the development of magnetic resins conquers this flaw.The particle size of magnetic resins is reduced to below 150 ?m,which largely increases the adsorption rate.Magnetic resins can be applied in completely mixed reactors,and can be separated from the aqueous phase after adsorption.The water treatment volume is increased greatly and the operational cost is significantly reduced.Current magnetic resins include magnetic anion exchange resins(MIEX??NDMP),magnetic hypercrosslinked resins(Q100),magnetic amine modified hypercrosslinked resins(GMA30).Magnetic anion exchange resins are only capable of the removal of pollutants by anion exchange,which show little effect on the removal of cationic and non-ionic pharmaceuticals.The hydrophobic backbone of Q100 leads to the lowered removal of hydrophilic pharmaceuticals.GMA30 can remove anionic pollutants as well as neutral contaminants,but its performance is seriously inhibited by anionic natural organic matter at high concentrations in practical application.There are no studies about the development of magnetic resins for the removal of cationic pharmaceuticals yet.Based on the above background,a novel magnetic carboxyl modified hypercrosslinked resin was developed for the removal of cationic and neutral pharmaceuticals.The main research contents and conclusions are as follows.(1)By comparing different coating agent including oleic acid and silanes,the double layer coating method by TEOS and VETO was determined as the suitable method for the preparation of the magnetic resins.After coating,the magnetic Fe3O4 particles showed high acid resistance.Besides,the vinyl group introduced by VETO renders that the coated particles can be dispersed in the monomers.With DVB and MA as the monomer,after copolymerization with the coated Fe3O4 particles,hydrolysis,and post crosslinking,the magnetic carboxyl modified hypercrosslinked resin were successfully prepared.The obtained resin possessed high specific area as well as high cation exchange capacity.By adjusting the ratio of DVB and MA,a series of magnetic carboxyl modified hypercrosslinked resins were prepared.The particle size of the resins was around 50 ?m with dominant mesopores.The average pore size was in the range of 5.25-7.20 nm.The specific area of the magnetic resins were positively correlated to the DVB content,while the cation exchange capacity was positively related to the MA content.The resins possessed super paramagnetism,which can be separated from water by virtue of an external magnetic field.(2)The removal of different pharmaceuticals by the magnetic carboxyl modified hypercrosslinked resins was studied.The adsorption kinetics,the adsorption isotherms and the effect of solution chemistry were investigated.The magnetic resins showed fast adsorption kinetics.The adsorbed amount of the basic pharmaceuticals atenolol(ATL)was positively related to the cation exchange capacity of the resins.The removal of the acidic pharmaceutical ibuprofen(IBF)and the neutral chloramphenicol(CP)was positively related to the specific area of the resins.MA-50 resin showed the highest removal of tetracycline(TC)among the studied resins.The electrostatic repulsion between the negative IBF and the negatively-charged resin surface reduced the adsorption rate of IBF.The increase of pH changed the form of ATL from cationic form to neutral from,leading to the transition of the adsorption mechanism from ion exchange to hydrophobic effect.Low pH conditions were suitable for the removal of IBF,while neutral pH values were preferred by TC.Inorganic salt posed high inhibition effect on the uptake of ATL.Under high concentrations of salt,the adsorbed amount of ATL increased as the specific area of the resins increased.Humic acid and tannic acid showed no significant effect on the removal of ATL,IBF,TC and CP.The magnetic resins also showed excellent regeneration property.(3)The adsorption mechanism of TC on the magnetic reins was explored.As the cation exchange capacity of the resins increased,the adsorption process of TC turned from an exothermic process to an endothermic process.The adsorption could spontaneously happen.The absolute value of the enthalpy change increased with the increase of cation exchange capacity,indicating that the contribution of ion exchange interaction to the adsorption process enlarged.By analyzing the increase of Na+during adsorption and shielding the carboxyl group,significant synergistic effect was observed during the adsorption of TC onto MA-50.The adsorbed amount of TC on MA-50 was a lot higher than the sum of the adsorbed amount by single ion exchange and single non-electrostatic effect.MA-50 resin showed high adsorption performance for two types of zwitterionic antibiotics,i.e.,tetracyclines and fluoroquinolones.The distance between the positively charged and negatively charged functional groups was larger for ciprofloxacin(CPX)than TC,which led to the faster adsorption kinetics and the larger adsorption amount of CPX.(4)The coremoval of TC and Cu2+by the magnetic carboxyl modified hypercrosslinked resin was investigated.The adsorption kinetics,isotherms in binary system were studied.Magnetic hypercrosslinked resin Q100 and magnetic cation exchange resin NDMC were selected as comparison to illuminate the complexing mechanism.In mixed solutions,the adsorbed amount of TC and Cu2+on MA-40 was larger than that in single substrate solutions,but the adsorption kinetics significantly decreased.In mixed solutions,the Langmuir constants KL of TC and Cu2+were almost two orders higher than those in single substrate solutions,demonstrating the higher binding affinity between the resin and the adsorbate.In binary system,Q100 and NDMC could both co-remove TC and Cu2+due to the formation of tertiary complex Q100-TC-Cu2+and NDMC-Cu2+-TC,respectively.As a result of the lower steric resistance,the complex ratio on Q100 was higher than that on NDMC.Possessing both functional groups,two tertiary complexes(MA-40-TC-Cu2+and MA-40-Cu2+-TC)and one quaternary complex(MA-40-Cu2+-TC-Cu2+)were formed on the surface,promoting the removal of TC and Cu2+.As the carboxyl groups on MA-40 were scatteredly distributed,the highest complex ratio was obtained for MA-40.MA-40 exhibited high regeneration performance in the coremoval,showing potential in practical applications. |
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