Fabrication Of Magnetic Micro-Nanocomposites And Study The Removal Performance Toward Polycyclic Aromatic Hydrocarbons(Phenanthrene And9-Phenanthrol)from Wastewater

In recent years,with the development of urbanisation and industrialisation,the problem of water pollution has become a serious challenge to the development of human society.As one class of persistent organic pollutants in the water environment,polycyclic aromatic hydrocarbons（PAHs）,which have the characteristics of variable environmental mobility,carcinogenicity,mutagenicity and teratogenicity,could cause serious environmental hazards and endangering human life and health.Adsorption technology possessed with simple,high-efficiency and widely used characteristics,which could be used to remediate PAHs pollution,but the subsequent recovery of traditional micro-nanocomposites was difficult and may lead to secondary environmental pollution.Some studies have used catalytic and microbial degradation method to treat PAH contaminants,which may cause secondary contamination.In addition,most studies in the field of adsorption lack studies on the micro-environmental mechanisms of pollutants in the adsorption reaction system.The development of new micro-nanocomposits that are green,inexpensive,easily recyclable and possessed with excellent removal performance towards PAHs contaminants is of great environmental importance.In this work,a series of new magnetic micro-nanocomposites with excellent removal performance towards phenanthrene and 9-phenanthrol were designed by encapsulation and grafting techniques using nano-iron tetroxide as the matrix material,the tricyclic low molecular weight PAHs pollutant-phenanthrene and its toxic degradation intermediate 9-phenanthrol were used as the target pollutants.This work explored the environmental microscopic behaviour of pollutants,clarified the micro-environmental relationship between adsorbent and adsorbate,provided insight into the potential adsorption reaction mechanism and expanded the strategy for the synthesis of novel magnetic micro-nanomaterials which could be used in environmental remediation.The main studies of this work are as follows.（1）Fe₃O₄ nanoparticles were used as the initial matrix material,the Si O₂ layer was used to connect the magnetic oxides and provide hydroxyl groups for the subsequent silane coupling reaction,the aromatic ring of dimethoxydiphenylsilane could provide active sites for the adsorption of phenanthrene viaπ-πinteraction.The Fe₃O₄-dimethoxydiphenylsilane（Fe₃O₄-Si O₂-DMDPS）magnetic nanocomposite was fabricated,which not only exhibited excellent removal performance towards phenanthrene,but also maintaining 75.97%adsorption capacity after four regeneration cycles.Homogeneous adsorption played a crucial role in the overall adsorption process,while film diffusion was the important mechanism to control the adsorption reaction rate.Theoretical calculations suggested the most favourable binding mode between Fe₃O₄-Si O₂-2DMDPS and phenanthrene molecular,confirming theπ-πinteractions were effective,which were usually existed in the form of parallel displacement.This work may contribute to the development of effective modification strategies towards Fe₃O₄ nanoparticles and expand their application in the PAHs removing field.（2）The Fe₃O₄-benzhydrylamine（Fe₃O₄-1.5BENZHY）magnetic nanocomposite with excellent removal performance towards phenanthrene was successfully fabricated via silane coupling reaction and Schiff base substitution reaction.The aromatic rings of benzhydrylamine could formπ-πinteractions with phenanthrene molecular,which could facilitate the adsorption performance towards phenanthrene.The loading amount of diphenylmethylamine and the synthesis strategy both could affect the adsorption performance of the synthesized magnetic nanocomposites towards phenanthrene to some extent.The DFT calculations combined with the characterization of the used adsorbent not only verified that theπ-πinteractions between Fe₃O₄-1.5BENZHY and phenanthrene molecular usually existed in the form of offset parallel stacking,but also contributed to deeply analysis the bonding mechanism at the microscopic level.In addition,the stability and adsorption energy values of all the different bonding modes were calculated,and LUMO-HOMO energy gap values(E_GAP)and electron distribution were evaluated.In general,Fe₃O₄-1.5BENZHY possessed with homogeneous outer-surface,the phenanthrene molecules were adsorbed as monolayer form.The adsorption performance of Fe₃O₄-1.5BENZHY（26.07 mg/g）was significantly improved compared to that of original Fe₃O₄ nanoparticles（13.28 mg/g）.This work helps broaden insight on the molecular binding mechanism of the adsorbent/adsorbate system and expands the modification strategies based on magnetic oxide,for achieving high-efficiency adsorption of hazardous PAHs.（3）Fe₃O₄-4,4’-biphenyldicarboxaldehyde（Fe₃O₄-0.75BIPHENY）with core-shell structure was synthesized via silane coupling reaction and condensation reaction,the Fe₃O₄-0.75BIPHENY could be used for high-efficient removing 9-phenanthrol.Magnetic oxides offered the possibility for the rapidly separation and recovery,and the aromatic carbon of 4,4’-biphenyldicarboxaldehyde improved the adsorption performance towards 9-phenanthrol by formingπ-πinteractions.The loading amount of 4,4’-biphenyldicarboxaldehyde,the initial concentration of 9-phenanthrol and the p H values all affected the removal performance of the magnetic nanocomposites towards 9-phenanthrol to some extent.It is noteworthy that Fe₃O₄-0.75BIPHENY not only exhibited excellent adsorption performance towards 9-phenanthrol,but also possessed with excellent regeneration performance.The DFT calculations explored the different bonding modes between Fe₃O₄-0.75BIPHENY and 9-phenanthrol,and the visualised the electrostatic potential and energy orbital distribution analyzed the effectiveness of the adsorption reaction and the stability of specific configurations.This study provided new guidance for designing novel magnetic nanocomposites to alleviate traditional and secondary pollution caused by PAHs.（4）4,4’-biphenyldicarboxaldehyde m-phenylenediamine magnetic Schiff base polymer（magnetic BIPH-PHEN）was successfully fabricated via Schiff base condensation reaction and subsequent one-pot embedded method.The mutual aromatic nucleus of BIPH-PHEN polymer and phenanthrene and 9-phenanthrol could formπ–πinteraction.The removal efficiency of magnetic BIPH-PHEN towards phenanthrene and 9-phenanthrol was 85.65%and 98.52%,respectively（Initial concentration:8 mg/L;Adsorbent:0.2 g/L）.The DFT calculations including energy calculations,electrostatic potential distribution and molecular orbitals analyzed the different bonding modes and proposed the most favorable bonding mode in all adsorption system.Monolayer adsorption occured on the homogeneous surfaces of magnetic BIPH-PHEN,simultaneously the chemisorption was dominant.This work proposed new insights on assembling magnetic Schiff base polymer for the remediation of conventional and secondary PAHs contamination.