Synthesis Of Core-Shell Ag@SiO₂ Nanoparticles And The Studies Of Its Antibacterial, Anticorrosion, And Application Properties

Fouling caused by marine organisms is a critical problem when the human develop and utilize the ocean. Using marine antifouling coatings is a more economical and effective method, and biocides are one of key components which determine the coatings antifouling effect. Traditional biocides achieve the goal by poisoning the fouling organisms, and some are so likely to enter food chain as to pose a threat to the human health and ecological safety. So, novel, efficient and environment-friendly biocides are a hot problem studying currently. For this purpose, Ag@SiO2 core-shell nanoparticles (NPs) were designed and assembled in view of superior bactericidal properties of silver NPs and porous structure of silica NPs in this paper. The bactericidal kinetics, mechanism of killing bacteria, and anticorrosion properties of Ag@SiO2 NPs were studied deeply. Then a feasible formula of antifouling coating was tried to develop. The main contents and conclusions of this paper are induced as follows:Firstly, the monodisperse Ag@SiO2 core-shell NPs which the morphology is even and controllable had been successfully prepared. A series steps, such as the reaction between silver nitrate and hydrazine hydrate, hydrolysis and polycondensation of TEOS, and lastly the coating of silica NPs on silver NPs, were conducted in the presence of CTAB. Through studying the effects of the addition time of TEOS and the added quantity of TEOS, CTAB, ammonia and ethanol on the microstructure of the specimens, the optimal preparation condition of Ag@SiO2 NPs below to 70 nm in diameter with a 15～20 nm silver core encapsulated within a 20～25 nm thick silica shell was gained. The results showed that it is suitable for preparation of Ag@SiO2 NPs that TEOS is added at 7～10 min after the reaction of silver nitrate and hydrazine hydrate with the quantity meeting 2.5 ratio of silica to silver. CTAB plays a positive role in dispersing silver NPs and directing silica NPs and its added quantity should be appropriate. Similarly, the right amount of ammonia takes effect in formation of silica microspheres, and adding the volume ratio of ethanol to water attributes to its smooth surface. Secondly, the bactericidal properties of as-synthesized Ag@SiO2 NPs against both Gram-negative strain (E. coli) and Gram-positive strain (S. aureus) had been deeply studied. The bactericidal kinetics test showed extraordinary antibacterial properties, and when the concentration of Ag@SiO2 NPs was 18.17 mg/L, the time needed for destruction total approximate 7 log S. aureus was about 39 min, whereas the inactivation time was shortened to 25 min for E. coli. TEM measurement confirmed the cells were destructed upon treatment, with a leakage of the intracellular substances or the rupture of the cell wall. Because reactive oxygen species (ROS), such as·OH and·O2-, were not found in the Ag@SiO2 NPs system using electron spin resonance (ESR) spin-trap technique, and there was an obvious decrease of Ag+ in the suspension, it could be concluded that inactivation of the bacterial was not due to ROS in the case, but probably owing to Ag+ eluted from Ag@SiO2. The above three experiments confirmed E. coli were found to be more susceptible to the biocidal activity of Ag@SiO2 NPs comparing to S. aureus because of its thinner cell wall.Thirdly, the influences of Ag@SiO2 NPs additive with different P/B ratios on the corrosion resistance of the epoxy coatings in different media were further investigated. Electrochemical impedance spectroscopy (EIS) of the epoxy coatings pigmented with Ag@SiO2 NPs with P/B=0,0.1% and 0.3% before and after 110 h immersion in E. coli and S. aureus solution, respectively, and corresponding equivalent circuits for the coatings were proposed and analysed. Meanwhile, the surface microstructure of the coatings was observed by atomic force microscope (AFM) before immersion in bacterial solution, and the surface topography of the coatings was compared before and 850h immersion in bacterial solution. The results showed that the resistances of the coatings with P/B=0 were decreased by 96% after immersion in E. coli solution and 94% in S. aureus solution, while that of the coatings with P/B=0.3% were 73% and 96%. The obvious rusty spots were found in the surfaces of above two coatings. However, there was little change in both resistance and topography of the coating with P/B=0.1%.The results of electrochemical noise (EN) also showed that Ag@SiO2 NPs additive improves inorganic salt corrosion resistance of its epoxy coatings to a 88-99% degree, and microbiological corrosion resistance goes up by above 80%.Finally, on the basis of traditionally cuprous oxide antifouling paint formula, the author tried to find a new antifouling paint formula using Ag@SiO2 NP as biocides. The main idea is that firstly cuprous oxide is replaced with Ag@SiO2 NP, and other alternative fillers. Secondly, according to the physical and chemical properties of the paint film, the proportion of biocides, resins, oils, fillers, various solvents, and additives are further adjusted and optimized. In the end, the antifouling paint formula is determined. A basic paint formula was given by different processes and repeated experiments, in which adding 2.5% Ag@SiO2 NPs as the antifouling agent,40% acrylic resin, appropriate proportion of pigment, filler and mixed solvent. The physical performance test results showed that the paint film posesses the appearance of smooth, adhesion to 4, pencil hardness HB, bad strength and flexibility. So the antifouling paint formula will be further optimized and improved.