Fabrication And Application Of Bifunctional Micro/Nanomotors For Colorimetric Detection And Degradation

The environmental pollution caused by the large-scale emission of hard-to-degrade organic pollutants has attracted sustained attention from many countries.In order to achieve efficient restoration of polluted water bodies,micro-nano materials with catalytic activity are combined with self-propelled motors to form local micro-mixing through the continuous movement of micro-nano motors,accelerate mass transfer,improve the effective contact between pollutants and active materials,and construct a catalytic platform with dual functions of visualization detection and dynamic degradation,which can greatly improve the detection sensitivity and degradation removal rate of pollutants.This paper mainly focuses on the weakness of the single function of micro-nano motors in the field of environmental restoration,and uses the high dispersibility and controllability of active metal sites（Co,Cu,Mn,Ni）in the derived materials of metal-organic framework materials（MOFs）and layered double hydroxide materials（LDHs）,and functionalized assembly of materials with excellent nano-enzyme activity and Fenton-like catalytic activity,to sequentially prepare micro-nano motors with excellent enzyme-like activity based on Co-N/C,Co-O/C-LDHs,CuAl-LDHs/C and NiMn-CLDHs,respectively,and to carry out specific surface modification and functionalization,and innovatively construct multiple dual platforms that can achieve visualization detection and dynamic degradation of water pollutants.Firstly,a Co-N/C-based magnetic micro/nano motor was constructed using high-hollow akund fiber as a biological template,with ZIF-67-derived（nitrogen）magnetic Co-N/C nanoenzyme as the detection and degradation dual functional unit and Mn O₂ nanoplates as the micro motor driving fuel catalytic unit.Based on the chemical bonding between-COOH in citric acid（CA）and-NH₂ in aniline,the Co-N/C-based magnetic micro/nano motor was surface-modified with CA,and a dual-functional platform for aniline colorimetric detection and dynamic degradation was successfully constructed.By using H₂O₂ as fuel,the motor’s continuous motion was achieved through a chemical propulsion mechanism,and its movement speed increased with the concentration of H₂O₂,reaching up to 398.88μm/s at 7wt%H₂O₂.Its inherent strong magnetism enabled the micro/nano motor to be precisely direction-controlled under an external magnetic field.The enzyme-like activity experiment confirmed that CA-Mn O₂@Co-N/C exhibited excellent peroxidase-like activity,and a visual detection platform for aniline mediated by CA-Mn O₂@Co-N/C was constructed,with a detection limit of 0.185μM.The chemical bonding between-COOH in CA and-NH₂ in aniline,as well as the excellent Fenton-like catalytic activity of Mn O₂ and Co-N/C,enabled dynamic catalytic degradation of aniline in water,with a removal rate of 83%at p H 5.0.The autonomous motion of the multi-layered structure of the CA-Mn O₂@Co-N/C micro/nano motor and the synergistic effect among the components improved the probability of molecular collisions and mass transfer efficiency,greatly enhancing the detection and degradation performance of pollutants.The secondly,using ZIF-67-derived（air）Co-O/C nanoenzymes as the three-functional unit for detection,degradation,and propulsion,and using magnesium-aluminum layered double hydroxide（Mg Al-LDHs）flower-like microsphere as a carrier,a Janus micro-motor with exposed nanoenzyme activity sites of Co-O/C-LDHs spheres was constructed.The micro-motor was functionalized with natural laccase（Lac）to create a dual-functional platform with both nanoenzyme and natural enzyme catalytic activity for colorimetric detection and catalytic degradation of catechol.The asymmetrical distribution of Co-O/C activated H₂O₂,which propelled the micro-motor through bubble recoil.The micro-motor had a speed of 171.83μm/s at 7 wt%H₂O₂.The Co-O/C in ZIF-67 has high dispersion of Co sites,exhibiting high peroxidase-like activity that can effectively catalyze the decomposition of H₂O₂to produce·OH to oxidize the substrate TMB,achieving sensitive detection of catechol with a detection limit of 0.24μM.The synergistic effect of laccase catalytic activity and Co-O/C’s Fenton-like catalytic activity continuously decomposes catechol molecules,ultimately mineralizing them into CO₂ and H₂O.At p H 5.0,the removal rate of catechol was95.9%.The synergistic effect between the peroxidase-like activity of Lac-Co-O/C-Mg Al-CLDHs micro-motor,laccase catalytic oxidation activity,Fenton-like catalytic activity,and self-propulsion performance enhanced the diffusion and mass transfer of reactant solutions,accelerating the visual detection and dynamic degradation of catechol.Then,based on the high peroxidase-like activity of Cu sites in copper-aluminum layered double hydroxides（CuAl-LDHs）,porous CuAl-LDHs-based tubular micromotors with high surface area were prepared using the platanus fruits fibers as templates.Combining their excellent nanoenzyme activity and Fenton-like catalytic activity,a dual-functional platform for colorimetric detection and catalytic degradation of malathion was constructed.The inner layer of Mn O₂ acted as a fuel catalyst to decompose H₂O₂,producing a large number of bubbles to drive the motor’s motion.The location of bubble generation and detachment was not fixed,leading to uneven forces acting on the micromotor in different directions and exhibiting different motion trajectories.Cu sites in CuAl-LDHs exhibited excellent peroxidase-like activity in weakly acidic environments.However,after co-incubation with malathion,the nanoenzyme activity was inhibited due to the formation of a coordination complex between Cu active centers and sulfur-containing groups,establishing a colorimetric sensor for malathion detection with a detection limit of 0.061 mg/L（0.186μM）.Based on the Fenton-like catalytic activity of CuAl-LDHs,dynamic degradation of malathion in water was achieved,with 82.4%degradation at p H 6.0.The excellent detection and degradation performance of CuAl-LDHs@Mn O₂/C micromotors was the result of the synergistic effects of each component,as well as the self-propelled motion of the micromotor,which enhanced mass transfer in the degradation system.Finally,based on the synergistic enhancement of nano-enzyme activity from the Ni and Mn bimetallics in nickel-manganese layered double hydroxide derivatives（NiMn-CLDHs）,as well as the heterogeneity,tunable surface groups,and high chemical stability of the natural mineral halloysite（HNTs）,a HNTs-supported,nanoscale NiMn-CLDHs motor with silver nanoparticles as fuel catalyst and ascorbic acid（AA）modification was designed and prepared.The results show that surface modification with AA significantly enhances the nano-enzyme activity and Fenton-like catalytic activity of the nanomotor,enabling sensitive visual detection and dynamic rapid degradation of phenol in water.The synergistic catalytic effect of nano-Ag and NiMn-CLDHs drives the nanomotor in a clearly directional motion trajectory in high-concentration H₂O₂.The highly exposed Ni and Mn active centers of the NiMn-CLDHs nanosheets,along with the self-propelled motion process,accelerate the effective contact between phenol molecules and active centers,achieving sensitive visual detection and efficient dynamic degradation of phenol with a detection limit as low as 0.225μM and a96.51%removal rate of phenol within 90 min.The surface functionalization with AA,combined with the motility of the nanomotor and its rich pore structure advantages,further enhances the catalytic activity and achieves rapid phenol treatment.