Design,Preparation And Application Of Three-dimensional Hierarchical Micromotors For Detection And Removal Of Contaminants In Water

Micro/nanomotor is a category of artificially synthesized intelligent materials or devices.Under the stimulation,micro/nano motors are able to convert chemical energy or other forms of energy into kinetic energy.Owing to the characteristics of miniaturization and auto-movement,micro/nanomotors can actively contact the target molecules to achieve the improvement of time efficiency and space distance movement.Micro/nanomotors can not only realize drug delivery and disease diagnosis,but also dynamically detect and degrade pollutants in environmental remediation.Therefore,these micro/nano materials or devices are expected to be widely used in biomedical and environmental remediation fields.In view of the increasingly serious water pollution problems,from the mode of degradation,the type of raw materials,intelligent detection and dynamic degradation,innovatively combining of functional organic groups,natural enzyme,enzyme and micro/nanomotor’s voluntary movement,the author designed and prepared multifunctional multi-layered structure of micro/nanomotors as the goal.Orderly assembly of structural units on micro and nanometer scales,precise construction of novel structure and diverse functions of micro/nanomotors with multiple functional units,were able to achieve dynamic intelligent detection,efficient removal and degradation of pollutants in environmental water.The specific research contents are as follows:1.In view of the disadvantage of secondary pollution of H₂O₂ for the chemical bubble driven micromotor in the water environment,this paper designed and prepared3D hierarchical,double-channel endogenous H₂O₂ Janus micromotor using glucose solution as fuel,and used for the detection of tetrabromobisphenol A（TBBPA）.NH₂-MIL-101（Fe）immobilized natural glucosaccharide oxidase（GOx）and reasonably matched heterojunction structure were able to produce H₂O₂.Therefore,the produced H₂O₂ can be used for peroxidase detection of TBBPA and to drive micromotor movement.Firstly,WO₃ microspheres composed of hollow nanosheets were prepared by hydrothermal,impregnation-calcination method.Then,semi-coating and light reduction method were used to uniformly load Ag nanoparticles onto the surface of WO₃ nanosheets.Finally,NH₂-MIL-101（Fe）immobilized GOx was grown onto the surface of microspheres by one-step co-precipitation method.In this way,the immobilized enzyme Janus micromotor（GOx@MIL-101（Fe）/Ag/WO₃）capable of endogenous H₂O₂ was prepared.NH₂-MIL-101（Fe）enables the micromotor to have nanozyme activity and provides active sites for subsequent TBBPA adsorption.The micromotor presents a 3D hierarchical micro-nano structure with large specific surface area and highly exposed active sites,improving detection capabilities.The GOx@MIL-101（Fe）/Ag/WO₃ micromotor presented linear and circular motion in 0.1 M glucose solution,and its motion speed is about 61.6μm·s^-1.The effective motion of the micromotor provides a premise for the subsequent dynamic detection of TBBPA.Based on the inhibitory effect of TBBPA on TMB color rendering,a colorimetric detection method for TBBPA by micromotor was established.The detection limit of TBBPA was0.05μM.The synergistic effect among components of GOx@MIL-101（Fe）/Ag/WO₃micromotor,the improvement of molecular collision and mass transfer efficiency caused by motor movement,and the unique three-dimensional structure of micro/nano composite layer greatly improve the performance of detection for TBBPA.2.Mesoporous silica core-shell microspheres coated with Fe₂O₃ nanoparticles were synthesized by hydrothermal calcination.After that,the magnetic particle was-NH₂ functionalized through chemically modifing.Finally,the bubble drivenγ-Fe₂O₃@Ag-m SiO₂-NH₂ Janus magnetic micromotor was prepared by the method of evaporation,which loaded half of the particles with nano-sized Ag particles.The micromotor moves at a speed of 203.06±10.6μm s^-1(approximately 253.8 body length S^-1)in 10%H₂O₂ solution.Due to the synergistic effect of self-propulsion,γ-Fe₂O₃@Ag-m SiO₂-NH₂ magnetic Janus micromotor showed higher adsorption removal capacity for Cu²⁺(15.59 mg·g^-1)and tetracycline(31.45 mg·g^-1).Under the same conditions,the removal capacity of micromotors was 1.53 times and 1.44 times that of non-micromotors and non-amino functionalized materials.In addition,the magneticγ-Fe₂O₃ magnetic core can realize the remote control of the motion direction and the recovery in water.3.Three-dimensional hierarchical Fe-MOF immobilized laccase magnetic micromotor（laccase@Fe-BTC/Ni Fe₂O₄/Mn O₂）acting as an active self-propelled micromachine for dynamic adsorption and degradation of methylene（MB）from water were successfully prepared by hydrothermal,impregnation-calcination and one-step co-precipitation using naturally-hollow kapok as biotemplate.The micromotor retains the hollow tubular structure of kapok and its unique micro-nano composite hierarchical structure has a large specific surface area,which can expose more active sites and improve the adsorption and degradation capacity.At 30℃,p H=3.0,the activity of immobilized enzyme micromotor was 8.6 times that of free laccase.In addition,the speed,drag force and mechanical efficiency（η）of the micromotor increase with the increase of H₂O₂ concentration.In 5%H₂O₂,the kinetic velocity is 300±27.5μm·s^-1,the drag force is 1.73±0.31×10^-9 N,and theηis（50.1±19.6）×10^-8.The pollutant MB was selected as the object for dynamic degradation.Under the condition of 30℃,p H=3.0,5%H₂O₂ concentration,MB can be completely degraded within 20 min.The dynamic degradation effect is better than that of non-motor material mechanical agitation,because the motor movement is irregular and disorderly,and the fluid of mechanical agitation moves in a certain direction,and the independent movement effectively increases the contact frequency of pollutants and active molecules.Besides,Fe-MOF with high specific surface area has certain adsorption capacity for pollutants,which increases the degradation effect.4.The MIL-100（Fe）immobilized horseradish peroxidase（HRP）magnetic micromotor（MIL-100（Fe）@Ti O₂@Fe₃O₄）was prepared by hydrothermal calcination/one-step co-precipitation methods.The micromotor could be used as a novel intelligent active platform to simultaneously detect and degrade pollutants in water.In the presence of H₂O₂,three kinds of motion trajectories,linear,curved and circular were observed for Janus micromotors,and the average speed of the micromotor can reach 140±7.0μm·s^-1 in 5%H₂O₂,which provides a basis for the subsequent dynamic detection and degradation.Free radical capture experiments confirmed the existence of hydroxyl radical（·OH）and superoxide radical（·O₂^-）in the catalytic process,indicating that HRP-MIL-100（Fe）@Ti O₂@Fe₃O₄ micromotor has the activity of oxidase-like and peroxidase-like.Under the same conditions,the maximum reaction rate constants V_m and Michaelis--Menten constant K_m were 23.6 n M·s^-1 and 0.131 m M,which confirmed that the micromotor had strong catalytic activity.Based on the activity of micromotor peroxidase,a colorimetric detection method was established for inhibiting TMB color rendering by hydroquinone（HQ）.The limit of detection for HQ was as low as 1.84μM,the detection range was 2-240μM,and it was not affected by allotrope,common organic pollutants and metal ions.In addition,micromotors could also be used for colorimetric detection of HQ in actual water samples.In the light condition,with the unique three-dimensional hierarchical structure and highly exposed active sites,micromotor was able to dynamicly degrade HQ in wastewater.The dynamic degradation of HRP-MIL-100（Fe）@Ti O₂@Fe₃O₄ micromotor is superior to that of non-dynamic traditional static degradation due to the active self-propulsion motion,high activity of similar peroxidase,and bandgap matching heterojunction.Nearly 91%HQ can be degraded within 70 minutes at 30℃,p H=5.0,5%H₂O₂.Besides,due to the high stability of the immobilized enzyme,the micromotor still has high degradation activity over a wide p H range（4-7）.Combined with the characteristics of magnetic recovery,the intelligent micromotor has a broad application prospect in environmental remediation.