Preparation And Properties Of ZIF-67 Derived Cageshaped Micromotors

Nanozyme-based micro/nano motors are small dynamic catalytic reaction platforms that can move autonomously.Nanozymes have activities similar to natural enzymes,which are widely used in the colorimetric detection and degradation of pollutants.In recent years,researchers have found that the rapid movement ability of micromotors can effectively promote the collision probability between various reactants,thus improving the reaction efficiency.The combination of the nanozyme and the micromotors can effectively improve the sensitivity of pollutant detection and degradation efficiency,which is better than the traditional static nanomaterials.In this paper,ZIF-67,a cobalt-based MOF material with high specific surface area and porosity,was used as a precursor for the synthesis of micromotors.By combining ZIF-67-derived nanozymes with micromotors,different types of micromotors were prepared to achieve efficient degradation of phenolic pollutants.Especially,in the second system,we used the nanozyme micromotors as the immobilization platform for laccase,and realized the innovation of using the nanozyme micromotors as the carrier of the natural enzyme.The specific work content is as follows.1.Preparation of Co₃O₄-CeO₂ nanocage micromotor and its colorimetric detection and removal of hydroquinone:In this work,we used ZIF-67 as a precursor to synthesize a novel ZIF-67-derived Co₃O₄-CeO₂cage micromotor with a variety of enzyme activities through the ingenious combination of template sacrifice and calcination method.The micromotor was characterized by SEM,TEM,EDS,BET and other characterization methods.It was found that the micromotor was composed of a novel hollow porous Co₃O₄-C skeleton and embedded CeO₂ nanoparticles.Its specific surface area was 109.9 m² g^-1,showing a typical mesoporous structure.ZIF-67-derived Co₃O₄-C has catalase activity,which enabled it to catalyze the decomposition of H₂O₂ to produce O₂bubbles to drive the micromotor at speed up to 122.33±10.14μm s^-1.Considering that Co₃O₄-CeO₂ had peroxide-like and oxide-like activities,which can produce·OH and·O₂^-in the presence of H₂O₂,the colorimetric detection and degradation performance of hydroquinone（HQ）by this kind of micromotor was explored.In the colorimetric detection experiment,the limit of detection for HQ is up to 0.789μM,and the linear range was 2-200μM.Besides,this colorimetric detection method had high selectivity and anti-interference,and also had good reproducibility in actual water samples.In the degradation experiment,the degradation performance of HQ reached 98.21%in 210 minutes due to the high-speed motion performance of the micromotor and the ability of Co₃O₄-CeO₂ to generate a variety of reactive oxygen species stimulated by xenon lamp.At the same time,the micromotor also had good chemical stability and regeneration performance.After 5 cycles,the degradation rate of HQ was still over70%.2.Self-actuated"urchin-shaped"NiO/NiCo₂O₄@Mn O₂-Laccase Janus micromotor for colorimetric detection and removal of catechol:In this work,we used ZIF-67 as a self-sacrificing template,and synthesized a NiO/NiCo₂O₄@Mn O₂ micromotor with an urchin-shaped morphology through ultrasonic growth,calcination,and seed-mediated method.This micromotor showed a hollow-broken Janus structure,with a specific surface area of 158.99 m² g^-1 and the average pore diameter is2.059 nm,which was demonstrated to have a typical mesoporous structure.The large specific surface area and appropriate aperture range provided the basis for laccase loading.Therefore,we immobilized laccase on it by cross-linking method to obtain NiO/NiCo₂O₄@Mn O₂-Laccase micromotor,which made the micromotor serve as the carrier of natural enzyme and nanozyme to further improve the catalytic activity of the micromotor.The motor can move at a speed of81.03±13.34μm s^-1 in 5%H₂O₂.Therefore,based on the catalytic properties of nanozyme and laccase,as well as the improved mass transfer efficiency brought by the self-driving capability of the micromotor,we realized the highly selective and highly sensitive colorimetric detection of catechol.The detection limit of the final calculation was 0.4846μM,and the detection linear range was 1-130μM.Besides,in the presence of H₂O₂ and xenon lamp excitation,the micromotor can realize the efficient catalytic degradation of catechol with the help of the motor motion capacity,the photo-assisted reactive oxygen capacity of nanozyme and the REDOX capacity of immobilized laccase.The degradation rate was up to 97.79%.Meanwhile,in the cyclic degradation experiment,the micromotor showed good cyclic stability and chemical stability.