Controllable Construction Of Bifunctional Molecule/ion Recognitional Materials And Their Application In Enhancement Of Heavy Metal Pollutant Removal

With the rapidly growth of economy and industry,the consumption and discharge of various kinds of metal increase day by day,which usually bring serious metal pollutants in the same time.Due to their hard degradation,bioaccumulation and toxicity,the heavy metals pose a huge threat to the environmental safety and human health.Among them,the copper,lead and uranium are typical types of heavy metal pollutants,which wildly exist in industrial wastewater such as mining,electronics,energy and chemical industries.Thus,how to efficiently separate and recover heavy metals is one of the important research tasks in the field of environmental engineering.Ion-recognitional adsorbents play an important role in the treatment of heavy metal pollution owing to their flexible design,high selectivity,and good separation effect.This paper selected the construction of bifunctional ion-recognitional adsorbents for enhanced selective decontamination as research object by designing and selecting highly specific functional monomers and combining with ion imprinting technology.Meanwhile,on the basis of analyzing the pollution sources,existing forms and properties of heavy metal ions,there are still some shortcomings that exist in current ion-recognitional adsorbents:（1）The research regarding to simultaneous adsorption of heavy metal ions and their composite pollutants is relatively few,（2）The selective adsorption kinetic can be further improved,（3）The controllable regulation and enhancement of the selective adsorption process of heavy metal pollutants is weak.Therefore,this paper prepared three types of ion-recognitional composite adsorbents with excellent adsorption performance towards Cu（Ⅱ）,Pb（Ⅱ）,and U（VI）.The adsorption performance and specific binding mechanism were comprehensively investigated,and the influence of self-propelled technology,external field regulation and droplet microreactor on adsorption thermodynamics/kinetics as well as the mechanism of enhancing the adsorption process were elucidated,which provided reference for design and application of the multifunctional adsorbents for selective separation of heavy metal pollutants.The main research contents of this thesis are as follows:1.Construction of bispecific recognition site adsorbent based on droplet microreactor and its application for simultaneously removal of heavy metal ions and their compound pollutants（1）Smart absorbents with high affinity to specific toxicant,especially with multi-affinity to both metal ions and organic pollutants,are very appealing for the treatment of heavy metal and organic co-contaminated water.A versatile strategy based on Pickering high internal phase emulsions（HIPEs）and controllable pore-filled technique was reported to fabricate molecule and ion dual-imprinted polymer adsorbent（M/I-DIPA）.2-Bromoisobutyryl bromide（BIBB）-modified silica nanoparticles（MSPs）were firstly employed to form Pickering HIPEs template,and then it was used to prepareλ-cyhalothrin（LC）-imprinted polymer foam（MIPA）.Secondly,surface-initiated atom transfer radical polymerization（SI-ATRP）was adopted to controllably produce Cu（Ⅱ）-imprinted adsorbent onto the MSPs which firmly“locked”in the MIPA shell.As-prepared M/I-DIPA effectively avoids the burying of recognition sites in a secondary imprinting process,and possesses highly permeable macroporous morphology.In batch mode experiments,M/I-DIPA exhibits fast binding kinetics（i.e.60 min）,and the maximum monolayer adsorption amount from Langmuir model for LC and Cu（Ⅱ）are 120.8μmol/g and 101.7μmol/g at 35°C,respectively,indicating this strategy makes the defined imprinted cavities well protected in twice imprinting steps.Moreover,LC and Cu（Ⅱ）have both higher imprinting factorα（about two times）than the other structural analogues,and the excellent selectivity coefficientβin multi solute system also demonstrates the preferential affinity to templates（i.e.LC and Cu（Ⅱ））due to a good imprinting effect.The loss in adsorption amounts of M/I-DIPA for LC and Cu（Ⅱ）at 120 min after four regeneration cycles are 7.295%and 13.05%,respectively,illustrating good retention of the activity of M/I-DIPA.（2）Inspired by the Suzhou bifacial embroidery,whereby the Janus-like planar structure allows different compositions compartmentalized onto two distinct surfaces,Janus silica nanosheets partitioning bispecific artificial receptors（i.e.molecular imprinted sites and thiol groups）onto distinct recognition surfaces（J-MIPs/cys）are designed to independently uptake 2,6-dichlorophenol（DCP）and Pb（Ⅱ）.For J-MIPs/cys,the thiol groups are expected to capture Pb（Ⅱ）via chelating action and molecularly imprinted cavities act as the high specific recognition sites for DCP.J-MIPs/cys possessed uniform cross-sectional dimension and thickness（～25.3 nm）,and particle-like surface imprinted layer（～21.8 nm）.In the monocomponent system,J-MIPs/cys displayed fast binding kinetics（60 min and 45 min）,large monolayer adsorption capacity（129.4mg/g and 82.95 mg/g）,high affinity,and excellent regeneration after five reuse cycles（9.134%and 12.16%loss in adsorption amounts）for DCP and Pb（Ⅱ）,respectively.Additional,spontaneous and endothermic adsorption process was also confirmed.In binary system,the presence of Pb（Ⅱ）produced a prominent increase in DCP adsorption at high initial concentration and a decrease at low initial concentration,owing to the partial complexation of Pb（Ⅱ）with excess DCP and occupation of imprinted sites by Pb（Ⅱ）.However,the uptake of Pb（Ⅱ）was inhibited over the whole range of concentration in the presence of DCP due to the competitive adsorption onto thiol groups.2.Liquid/liquid and liquid/solid interface-induced synthesis of micro/nano-motor adsorbents and their application in enhancement of selectively adsorption of Pb（Ⅱ）or U（VI）（1）A water/n-amyl alcohol droplet microreactor was constructed for the preparation of anisotropic bullet-like imprinted nanomotor adsorbents.Typically,Janus bullet-like hollow silica particles（JSNBs）were fabricated by anisotropic sol-gel process of three kinds of saline（TEOS,APTES and CPTES）at droplet interface.Then,the internal and external surface of JSNBs was respectively medicated with Ag nanoparticles and Pb（Ⅱ）IIPs to obtain the JSNMs@IIPs.The static adsorption results show that the JSNMs@IIPs can reach the adsorption equilibrium within90 min,and the maximum adsorption capacity is 130.5 mg/g at 25°C.In addition,JSNMs@IIPs exhibit enhanced adsorption performance when immersed into H₂O₂ environment.The self-propelled speed of JSNMs@IIPs increases with increased H₂O₂concentration,and reach 23μm/s at 20 wt%H₂O₂.Besides,the adsorption kinetics are greatly improved to approximately 3.2 times（10 wt%H₂O₂）,which shorten the time needed for contaminants removal.Moreover,JSNMs@IIPs also exhibit high Pb（Ⅱ）selectivity,with selectivity coefficients of 16.8,61.3,31.8,and 47.8 for Pb/Cu,Pb/Ni,Pb/Cd,and Pb/Fe,respectively.（2）We proposed an amidoxime-functionalized polydopamine tubular nanomotor adsorbent and demonstrated its application for rapid selectively adsorption of U（VI）in water phase.The nanotubes were firstly obtained by self-polymerization of dopamine on the surface of curcumin crystal template induced by its solid/liquid interface,and Mn O₂ nanoparticles and amidoxime functional groups were subsequently introduced on the wall to construct amidoxime-functionalized tubular nanomotor adsorbent（DNBMs-AO）,which featured with high yield and low cost.Besides,the distribution and amount of Mn O₂ nanoparticles and amidoxime functional groups can be simply controlled by varying the reaction time.The obtained DNBMs-AO are actuated and propelled by microbubbles generated by Mn O₂-triggered catalytic decomposition of H₂O₂,with the highest self-propelled speed at 215.45μm/s（8.6 body length per second）.The static adsorption results indicate that the adsorption of U（VI）onto DNBMs-AO can be better described by Langmuir model with the maximum adsorption capacity of 170.2 mg/g.Moreover,the motion of DNBMs-AO can efficiently improve the U（VI）diffusion under low H₂O₂concentration,and enhance the adsorption kinetics to 1.6 times（5 wt%H₂O₂）and 2.9 times（10 wt%H₂O₂）,respectively.DNBMs-AO also exhibit high selectivity towards U（VI）and excellent performance stability,endowing its potential application in environmental engineering field.3.The fabrication of stimuli-responsive ion recognitional adsorbents and their application in enchantment of selective removal of Pb（Ⅱ）or U（VI）（1）In this work,an oil-in-water-in-oil（O₁/W/O₂）droplet microreactor was designed as the polymerization carrier to prepare a crescent-shaped polydopamine-coated Pb（Ⅱ）imprinted microgel adsorbent（DMHIIPs）with near-infrared responsive ability,where the solution containing Pb（Ⅱ）,isopropylacrylamide and N-methylol acrylamide was selected as inner water phase.Then,the polydopamine shell was grown on the surface of the microgel particles,which endows the thermosensitive microgel with photothermal conversion ability.Due to the crescent-shaped asymmetric structure and excellent photothermal conversion performance,DMHIIPs can achieve reversible phase transition under 808 nm near-infrared irradiation,thereby precisely controlling and enhancing the selectively adsorption process of Pb（Ⅱ）.Static adsorption experiments show that DMHIIPs can reach adsorption equilibrium within 60 min at 20℃,with a maximum adsorption capacity of 128.0 mg/g.In addition,DMHIIPs have high photothermal conversion efficiency and stability.The temperature of DMHIIPs dispersion（0.5 mg/L）can be quickly heated to above 50℃ under NIR（808 nm,1W/cm²）irradiation for 10 min.It is worth noting that the DMHNIPs exhibits a unique step-up adsorption behavior under NIR irradiation,and the adsorption capacity and adsorption rate are both significantly enhanced.What’s more,the adsorption process of DMHIIPs can be precisely controlled by adjusting the NIR light field intensity and irradiation time,which further improves the selective adsorption rate and desorption effect of DMHIIPs.（2）We proposed a strategy that integrate the nanochain stirrer and emulsion microreactor to enhance the U（VI）selectively adsorption performance.In this work,one-dimensional（1D）magnetic nanochains are rationally synthesized through a controlled magnetic-induced interface co-assembly approach.Then,the polydopamine shells were grown on the surface of nanoclusters through heterointerfaces to obtain polydopamine-coated magnetic nanochains.The amidoxime functional group was further modified on the surface of the nanochain by the Schiff base reaction with polydopamine as the anchor point to obtain the amidoxime-functionalized magnetic stirring bar adsorbent（MSB-AO）.MSB-AO exhibits excellent structural stability,water dispersibility and magnetic responsive ability.The static adsorption results show that MSB-AO can reach the adsorption equilibrium within 60 min,and the adsorption process can be described by Langmuir isotherm adsorption model,and the maximum adsorption capacity is 140.3 mg/g at 25°C.In addition,MSB-AO can rotate in the solution with the magnetic field,which accelerates the mass transfer and diffusion,thereby increasing the U（VI）adsorption rate by about 17.2%（within 30min）.After trapping the adsorption process of MSB-AO within the confined-space of emulsion microreactor,the structure-activity relationship between the vortex effect of MSB-AO and the adsorption microvolume is further explored.The adsorption rate of MSB-AO is negatively correlated with the droplet diameter,and the smaller the adsorption space is beneficial to improve the eddy current diffusion efficiency.Compared with the ordinary stirring process,the adsorption efficiency of MSB-AO in the confinement of the droplet microreactor was improved by 10.1%.In addition,MSB-AO also shows high U（VI）adsorption selectivity and resistance to ionic strength interference,and able to maintain high selective adsorption performance after multiple adsorption/desorption cycles.