Preparation Of Three-dimensional Composite Filter Column By Immobilizing ZnO NPs On Corn Straw And Discussion On Its Antibacterial Mechanism

Air,water,medical apparatus,and implantable devices of bacterial contamination is one of the major problems for human health and the environment.Therefore,the research for developing safe and effective antibacterial materials has an importantly practical significance.The inorganic antibacterial agent based on Zn O possesses such advantages as high stability,prominently antibacterial effect,and good biocompatibility.Selection of a suitable carrier to load Zn O can enhance its microbial effect and achieve great economic value.Corn stalk core（CSC）is a kind of low cost and sustainable biomass resources,and it contains abundant macromolecular components such as cellulose,hemicellulose and lignin,which are conductive to adsorb zinc ions and in-situ growth of Zn O.Parenchyma cells with high reaction accessibility provide good places for immobilizing Zn O nanoparticles（Zn O NPs）,and CSC has naturally three-dimensional and abundantly porous structure,in favor of the fluid diffusion and flow.Based on this investigation,corn stalk core,one of rich resources,was chosen as a carrier to grow in-situ support Zn O NPs,which provided an experimental and theoretical basis for expanding the functional application of agricultural waste stalks.Meanwhile,based on the uniquely porous structure,CSC would be used as a three-dimensional filtration device to explore the killing effect of Zn O NPs against Escherichia coli（E.coli）and Staphylococcus aureus（S.aureus）,thus offering an economical and effective way for the efficient disinfection of water.The research not only made up for the vacancy for carrier utilization of CSC,and improved the full utilization efficiency of stalk resources,but also solved the problems about easy agglomeration and difficult recovery of Zn O NPs,leading to the effective enhancement on the bacteriostatic effect of Zn O NPs.This work chose two kinds of CSCs with and without the defatted treatment as raw materials.And zinc nitrate,zinc chloride,zinc acetate and zinc sulfate were applied as zinc sources.CSC/Zn O NPs composite filter was prepared by the facile method of in-situ chemical precipitation.The crystal structure,chemical composition,pore configuration and internal morphology of the composites were analyzed thoroughly.And the results were shown as follows:Nano Zn O was successfully loaded on the surface of CSC cells;The cellulose crystal types in the composites were cellulose I,and Zn O NPs were the hexagonal type of wurtzite;The loading amount and micro-scaled morphology of Zn O NPs were dependent on the types of zinc salts,which led to the corresponding differences in porous structure of the composite;And the defatted treatment could increase the porosity and specific surface area of CSC,resulting in the improvement of Zn O NPs-loaded content.In order to construct the filtration system of the composite antibacterial column,E.coli and S.aureus were selected as experimental strains,and the antibacterial effect of the filter column was detected by plate-coating method.The results were showed that the composite filter column on the basis of the defatted CSC as a raw material and zinc acetate as a zinc source displayed the best antibacterial effects.That is,when the filtration time was 5min,the antibacterial rates could reach 99.2%for E.coli and 95.4%for S.aureus.Therefore,the defatted CSC（B-CSC）and zinc acetate were selected as the raw material and zinc source,respectively,for the subsequent experiments.During the optimization of the hybrid process,three factors which had great influence on the antibacterial effect of the filter column,namely zinc ion concentration,zinc-salt adsorption time and temperature,were studied by the single-factor experiment.The optimal process conditions for preparing the filter column were determined by measuring the antibacterial property of the products.Experimental results were revealed that B-CSC/Zn O NPs composite column with the optimized antibacterial effect was prepared under the conditions of zinc ion concentration of 1.00mol/L and zinc-salt adsorption temperature of 40℃for 30 h.Simple filtration via the as-obtained composite for 2 min and 5 min could kill more than 99%of E.coli and S.aureus in water.The antibacterial mechanism of B-CSC/Zn O NPs composite was analyzed by such techniques as fluorescence staining,scanning electron microscopy（SEM）,inductively coupled plasma atomic emission spectrometry（ICP）,electron paramagnetic resonance spectroscopy（EPR）,antioxidant enzyme detection and agarose gel electrophoresis.The model of interaction between microparticles and porous media was utilized to evaluate the retention of bacteria via the filter column.The outcomes were presented that based on its hierarchically and highly porous structure,CSC had a high retention of bacteria,because Zn O NPs physically rubbed with germs during the filtration process,causing by mechanical damage;The loaded Zn O NPs and their dissolved Zn²⁺were adsorbed and deposited on the cell surface due to the coulomb force,which would destroy the structure and function of cell membrane;This alteration of cell membrane made Zn O NPs along with Zn²⁺act on and inactivate antioxidant enzymes,leading to non-elimination of ROS produced in bacteria.Excessive ROS caused oxidative damage to bacteria,consequently broke and degraded DNA,which would severely affect the normal growth and reproduction of microbes,and eventually bring about their death.