Green Construction And Application Of Corn Stalk-based Immobilized AgNPs Antibacterial Composites

Corn stalk,as a biomass resource with rich sources,low cost and renewable,has been widely used in packaging,transportation and furniture field.However,the corn stalk itself has no antibacterial activity,which limits its application.Silver nanoparticles（AgNPs）are broad-spectrum antibacterial agent with good antibacterial effect and no drug resistance.While AgNPs also have the problems of accumulative toxicity caused by too fast release,and the preparation also needs chemical reducing agents and stabilizer.In this research,corn stalk was used as reducing agent and stabilizer to green synthesize AgNPs,hydrothermal carbon spheres,graphene oxide and chitin were used as composite carriers with the help of physics and chemistry methods,followed by preparing safe and non-toxic corn stalk-based immobilized AgNPs composite antibacterial materials.Meanwhile,the antibacterial mechanism and application were also explored.The main contents of this work are as follows:（1）Preparation and application of corn stalk-based antibacterial paper with AgNPs@CS on keeping strawberry freshCarbon spheres immobilized silver nanoparticles（AgNPs@CS）was synthesized by using corn stalk as the reducing agent and carbon source under the one-step hydrothermal method.Furthermore,the antibacterial composite paper（CNF/AgNPs@CS）was prepared by compositing AgNPs@CS and cellulose nanofibers under the dispersion-mixing-filtration method.The results showed that the composite paper exhibited excellent antibacterial properties against E.coli and S.aureus.Due to the dual anchoring effect of the hydrothermal carbon spheres and cellulose nanofibers,the release rate of AgNPs was controlled,and the final release amount was safe,which could effectively solve the problem of cumulative toxicity and achieve durable antibacterial.In addition,the adding AgNPs@CS could improve the compactness of the composite paper,resulting in the improving of mechanical and barrier properties.Fresh-keeping experiments showed that the composite paper could keep strawberries fresh for up to 9 days without decay and deterioration.（2）Preparation and properties of sandwich-like chitosan/reducing graphene oxide immobilized AgNPs antibacterial nanocomposite filmReducing graphene oxide immobilized AgNPs（rGO@AgNPs）was prepared by using corn stalk as the reducing agent and graphene oxide（GO）as the template under the microwave-assisted one-step method.Further,a sandwich-like CS/r GO@AgNPs composite film was prepared by electrostatic self-assembly of r GO@AgNPs and chitosan（CS）solution with a solvent evaporation method.The results showed that the sandwich-like structure effectively reduced the release rate of AgNPs,which was only 1.9%after 14 days.The composite film still had good antibacterial activity against E.coli and S.aureus.At the same time,the reduction of corn stalk makes GO partially reduced to r GO.Compared with pure chitosan film,the synergistic effect of r GO and AgNPs also improved the mechanical and barrier properties of film,which can be used in the field of food packaging.（3）Green synthesis and immobilization of AgNPs by lumpy corn stalk for durable antibacterialAn efficient and durable antibacterial filling material（CS@AgNPs）was developed by using lumpy corn stalk as reducing agent and immobilizing agent.Through the honeycomb structure and reducing properties of lumpy corn stalks,AgNPs was in situ synthesized and immobilized for preventing bacterial growth.The results showed that the maximum release amount of AgNPs was only 0.011 mg/L after 12 days,which was within a safe range,and the CS@AgNPs had excellent and durable antibacterial ability against E.coli and S.aureus.The main reason was that the released AgNPs from corn stalk could penetrate cell membranes,destroy cell integrity,leak cell contents and suffocate bacteria to achieve a sterilization effect.This research provides a novel approach for biomass-based in situ synthesizing and immobilizing AgNPs antibacterial materials,which can prevent the growth of bacteria for a long time,and has a huge application potential in the fields of food packaging and home decoration field.（4）Lumpy corn stalk with improved fire retardancy and antibacterial activity prepared by montmorillonite and AgNPs immobilizationLumpy corn stalk with antibacterial and fire-resistant properties（DLCS/MMT/AgNPs）was prepared by using massive corn stalk of delignification as reducing agent and immobilizing agent after delignification treatment.During the process,AgNPs was in situ reduced and immobilized on the honeycomb structure,followed by immobilizing montmorillonite particles（MMT）in tracheids and vascular bundles of corn stalk by vacuum filtration.The results showed that the lumpy composite corn stalk still retained 65.8%and 61%of its original mass after being burned in a nitrogen and air atmosphere at a high temperature of 800^oC,while the untreated sample was almost burnt out.Under the simulated conditions,the composite corn stalk could keep its morphology basically unchanged within 5 s,while the untreated sample begun to burn and gradually turned into coke within 1 s.In addition,the antibacterial properties of composite corn stalk were analyzed by the method of inhibition zone,inhibition rate and OD₆₀₀ values,which showed that it had good and durable antibacterial activity.Therefore,the DLCS/MMT/AgNPs is suitable for application in food packaging and home decoration field.（5）Preparation and application of corn stalk/AgNPs/chitin antibacterial and hemostatic composite spongeThe porous compressible composite sponge（CH/CS/AgNPs）was developed by using corn stalk and AgNPs to improve the physical structure,hemostatic and antibacterial properties of pure chitin sponge.The results showed that the blood adsorption rate of composite sponge was 2.4 times and 2.7 times than that of pure chitin sponge and commercial polyvinyl formal sponge（PVF）.The in vitro blood clotting index（19%）of the composite sponge was also much lower than that of pure chitin sponge（45%）and PVF sponge（65%）,indicating its good hemostatic performance.The cytotoxicity and hemolysis rate（3.18%）also proved the biocompatibility and safety of the composite sponge.The rat liver hemorrhage model proved that the composite sponge had good hemostatic ability and efficiency,and wound not cause wound inflammation.Due to the immobilization of AgNPs,the composite sponge also exhibited good antibacterial activity against E.coli and S.aureus,which could reduce the risk of wound infection during hemostasis and promote wound healing.