Preparation Of Silver-Based Antibacterial Materials And Investigation Of Their Performance

The worsening living environment broke the harmony symbiosis between natural microorganisms and human beings.Antibiotic abuse has led to formation of drug-resistant bacteria,meanwhile emission of industrial refuse and household waste accelerates the spread of pathogenic microorganisms.Conventional sterilization method includes ultraviolet irradiation,chlorination and ozone treatment,which are time-consuming with secondary pollution.It is necessary to develop new antibacterial agents without toxicity and pollution.Nano silver can achieve broad-spectrum disinfection performance in biomedical field,industrial water treatment and civilian clothes.The application of single nano silver antibacterial agent is still limited by many disadvantages.Hence,the antibacterial agents with multifunctional synergy are being developed to remedy the shortcomings of single antibacterial agent,so as to improve the antibacterial efficiency with less environmental pollution and provide promising strategies for highly efficient and accurate disinfection.In this thesis,three types of Ag NPs-based multifunction-collaborative antibacterial agents are fabricated for bactericidal effect.The gelatin/Ag nanoparticle antibacterial agents with gelatin molecules surrounded Ag NPs are prepared in the gelatin crude extract from fresh pig skin with in-situ reduction by heating.The ultraviolet-visible absorption spectra are used to monitor the formation of Ag NPs.The influence of reactant concentrations,reaction time and heating temperatures on the Ag NPs formation are systematically studied.FT-IR and XPS are carried out to confirm the functions of gelatin molecules.TEM images and continuous ultraviolet-visible absorption spectra for 16 d are used to explore the morphology,size and stability of Ag NPs.The standard curve between the characteristic absorption peak intensity and Ag contents is established for studying the minimal inhibitory concentration(MIC)of gelatin/Ag nanoparticles against E.coli.With the MIC of 9.8 mg/L,the inactivation rate can be 98.9%within 480 min.The optical density at 600 nm(OD₆₀₀)of E.coli with and without gelatin/Ag nanoparticles are recorded for dynamic growth curves.Finally,the SEM and TEM images are used to observe the morphology changes of bacteria,indicating that gelatin/Ag nanoparticle can effectively destroy the cell membranes and result in the cytosol leakage.The gelatin/Ag NPs composite sponge is prepared via vacuum freeze drying for convenient water treatment as a point-of-use filter.Graphite C₃N₄(g-C₃N₄)prepared by thermal polycondensation method is used as the supporter to fabricate the Ag NPs loaded g-C₃N₄ for photocatalytic disinfection.Ag ions are evenly anchored onto the g-C₃N₄ sheets via electrostatic adsorption,followed by the in-situ UV lamp irradiation to form Ag NPs.Fundamental characteristics are conducted to study the structure,morphology and silver chemical state of Ag/g-C₃N₄.The influences of Ag NPs loading contents on optical properties and photocatalytic activities are systematically investigated by diffuse reflection spectrum(DRS),fluorescence spectra and photoelectrochemical characteristics such as steady-state surface photovoltage spectra and photo current curves under visible light irradiation.The results showed that the surface plasmon resonance(SPR)effect of Ag NPs can enhance the photo-response among visible light spectra and facilitate the separation and migration of photo electrons and holes as well as th e inhibition of electrons and holes recombination.Among all the Ag loading contents,3%Ag loading exhibits the optimal photocatalytic properties.The Ag/g-C₃N₄ is applied to treat E.coli under visible light ilustration.The 99.8%antibacterial efficiency can be achieved within 75 min by collaborative attack of photo-generrated h⁺produced by photocatalyst and released Ag ions from Ag NPs.Pomegranate Fe₃O₄ nanoparticles prepared by a hydrothermal method are used as the supporter,followed by the second hydrothermal method to vertically fabricate S-vacancy Mo S₂ nanosheets wrapped Fe₃O₄ nanoparticles.The molar ratios of sulfur and molybdenum resources are adjusted to obtain the optimal condition for fully and densely wrapping.Ag ions are anchored onto the Mo S₂ nanosheets via electrostatic adsorption,followed by the in-situ UV lamp irradiation to reduce Ag ions and form Fe₃O₄@Mo S₂-Ag nanozyme.The Mo S₂ nanosheets modify the surface topological structures,thus enhancing the adhesion to bacteria through physical contact and chemical bonds.The peroxidase-like property,p H-dependent and temperature-dependent activities and enzyme kinetics are well studied with TMB as the substrate.In the meantime,Fe₃O₄@Mo S₂-Ag nanozyme exhibited excellent absorbance during near-infrared(NIR)spectra and good photothermal conversion performance under808 nm NIR laser irradiation by reaching 50.7?within 15 min.During E.coli treatment,adhesive ability of Fe₃O₄@Mo S₂-Ag to bacteria is combined with hyperthermia under NIR irradiation,ROS produced by peroxidase-like property and released Ag ions to realize highly efficient and accurate?100%disinfection within15 min.Moreover,this method shows abroad-spectrum antibacterial properties against gram-negative bacteria,gram-positive bacteria,drug-resistant bacteria and fugal.