Study On Construction Of Bismuth Based Nanomaterials And Removal Of Harmful Heavy Metals And Microorganisms In Food

In recent years,China's food industry has developed rapidly,but the ensuing food safety problems are becoming more and more serious.Food may be affected by various pollutants in the stages of raw material,production,processing,transportation and storage.Foodborne diseases have become the most harmful diseases to human health.Effective removal of contaminants in food has become a major and urgent task.However,the traditional pollutant removal technology gradually can not meet the production needs of producers due to the high cost of equipment,high energy consumption or poor effect and other reasons.It is of great significance to research and develop low-cost,efficient and environmentally friendly new technology to deal with food contaminants to achieve sustainable development.In recent years,nanotechnology has developed rapidly.Due to the large specific surface area and high surface activity,nanomaterials show obvious properties superior to their corresponding traditional materials,which brings opportunities for the innovation of food contaminant removal technology.Bismuth-based nanomaterials have many excellent properties such as stability,adsorption capacity,photothermal conversion capacity and catalytic activity because of their adjustable chemical form,which are very suitable for the removal of major pollutants in the food industry.Based on this,a series of bismuth-based functional nanomaterials with unique performance were developed in this thesis according to the characteristics of main contaminants in food.Combined with the excellent adsorption performance and optical properties of the developed nanomaterials,the efficient removal of heavy metals and microorganisms in food contaminants was experimentally conducted.The main research contents and results of this thesis are as follows:(1)Preparation of sea urchin-like bismuth sulfide(Bi₂S₃)hollow nano-adsorbent and its adsorption technology for heavy metalsHigh quality sea urchin-like Bi₂S₃ hollow nano-adsorbent was prepared by simple hard template combined with polyol technology.Firstly,various characterization techniques were used to confirm the successful synthesis of sea urchin-like Bi₂S₃ hollow nanoparticles.Then,the adsorption kinetics,equilibrium isotherm and adsorption thermodynamics of the adsorption process were evaluated by batch experiments to study the adsorption of Ag⁺with time,solution p H,temperature and initial concentration of Ag⁺.The change of the structure composition of the adsorbent during the removal process was studied to clarify its adsorption mechanism.Results showed that the preparation of sea urchin-like Bi₂S₃ hollow nano-adsorbent has good specific surface area,chemical stability and adsorption,high adsorption rate,larger adsorption capacity(1172.25 mg/g)and the advantage of p H widely used(0.4?8).It can quickly and effectively remove heavy metal Ag⁺from liquid food without affecting other beneficial ions,showing great potential in the control of heavy metal pollutants in food.(2)Construction and study of slow and controlled release antimicrobial system of Linalool/Bi₂S₃ composite nanometer and its bactericidal propertiesUsing the inner cavity of sea urchin-like Bi₂S₃ hollow nanoparticles,natural antimicrobial agent(Linalool)was loaded into the cavity by using the thermal sensitive phase change material tetraethyl alcohol to construct a precisely controlled antimicrobial nanoplatform(TD/Linalool@Bi₂S₃ composite nano-antibacterial agent).A variety of characterization methods were used to prove the success of the construction of the composite nano-antibacterial system.Then,the photothermal properties,photothermal conversion efficiency,release of antibacterial agent at different temperatures and responsiveness of the antibacterial agent were evaluated respectively.Two kinds of food-borne bacteria,Gram-negative Escherichia coli(E.coli)and Gram-positive Staphylococcus aureus(S.aureus),were used as representative models to measure the minimum inhibitory concentration(MIC)and minimum bactericidal concentration(MBC)of TD/Linalool@Bi₂S₃,respectively.The germicidal efficiency of TD/Linalool@Bi₂S₃was studied by gradient dilution method and coating plate method and the state changes of bacteria before and after treatment were observed.The results showed that under the near-infrared(NIR)light,TD/Linalool@Bi₂S₃ composite nano-antibacterial agent can effectively convert NIR energy into heat energy and effectively release Linalool,which has a fast and effective in vitro killing effect on food-borne bacteria.When the concentration were 320?g/m L and 360?g/m L,it could kill E.coli and S.aureus 100%.In addition,the antimicrobial agent has low cytotoxicity and good biosafety,which can safely and quickly kill S.aureus in liquid food,and the bactericide rate can reach92.87±5.67%.The research and development of TD/Linalool@Bi₂S₃ composite nano-antibacterial agent can lay a foundation for the subsequent development of new nano-antibacterial agent and its application in the field of microbial contamination of food.(3)Preparation and bactericidal performance of gold nanorods(Au)@Bi₂S₃ core-shell nano-antibacterial agentThe Au@Bi₂S₃ core-shell nano-antibacterial agent was prepared by the method of hard template combined with polyols by the middle layer transformation strategy and its successful preparation was proved by various characterization methods.The photothermal properties and photothermal conversion efficiency of Au@Bi₂S₃ core-shell nano-antibacterial agent were measured,and the reactive oxygen species(ROS)were evaluated by using a variety of probes.Then the MIC and MBC of Au@Bi₂S₃ against E.coli and S.aureus were determined,respectively.The bactericidal efficiency of Au@Bi₂S₃ core-shell nano-antibacterial agent was studied by gradient dilution method and coating plate method.The results showed that it has good photothermal conversion performance under the NIR light drive.At the same time,this typical Schottky structure can improve the separation efficiency of electron-hole pairs triggered by near-infrared light,and generate considerable ROS.It has synergistic PTA/PDA antibacterial activity against E.coli and S.aureus,and can be completely inactivated at concentrations of 140?g/m L and 120?g/m L.In addition,the in vitro cell test and in vivo mouse test proved that the nano-antibacterial agent has low toxicity and good biosafety.It can quickly and effectively kill foodborne bacteria in liquid food,and the bactericidal rate reaches98.34±6.74%,which provides a new idea and means for solving the problem of food contaminants.