Study On The Antibacterial Activity Of Mg (OH)₂ Nanoparticles

The study on the antibacterial agents with high efficiency and no toxicity is of great importance for the healthy development of society to control the growth of microorganism and the spread and infection of bacteria. The existing researches on the inorganic antibacterial agents are mainly focused on the metals and metal oxides, as well as novel engineered nanomaterials. The major antibacterial mechanisms reported in the literature fall into three general views, including the release of metal ions, generation of reactive oxygen species of semiconductor materials, and contact of nanoparticles with microorganisms. In this thesis, the antibacterial activity of Mg(OH)2 has been explored, and a novel antibacterial mechanism has been proposed. The Mg(OH)2 nanoparticles have been mixed into the fibers and Poly(vinylidene fluoride) (PVDF) to prepare antibacterial paper and hybrid membrane respectively, which extends the applications of the Mg(OH)2 nanoparticles. In addition, the multiple headspace extraction (MHE) technique for monitoring the growth of bacteria has been established in order to improve the existing headspace gas chromatography (HS-GC) method which gives a larger data scattering and causes larger errors.Firstly, the antibacterial activity of Mg(OH)2 nanoparticles was investigated and the Escherichia coli(E.coli), Staphyloccocus aureus, Burkholderia phenazinium were used as testing bacteria. The antibacterial efficiencies of different nanomaterials were also compared. Results indicate that Mg(OH)2 nanoparticles have a broad antibacterial spectrum, and the antibacterial efficiency of Mg(OH)2 against G- bacteria is almost the same as CuO, while a little lower for G+ bacteria, suggesting that Mg(OH)2 nanoparticles have an excellent potential application as antibacterial agents. Meanwhile, the MHE-GC technique for monitoring the growth of bacteria was established, and the growth curve of E.coli was obtained. The comparisons among the results from MHE-GC, turbidity measurement and viable cell counts indicate that the present method is very simple, sensitive and safe, which can easily perform an automatic measurement for bacteria growth at various desired incubation conditions.Secondly, the factors affecting antibacterial efficiency of Mg(OH)2 nanoparticles were investigated, including the ions in the suspension, UV and visible irradiation, the contact mode of nanoparticles and cells, the size and shape of Mg(OH)2. Results indicate that OH-and Mg2+ in Mg(OH)2 suspension can not kill E.coli; the antibacterial activity of Mg(OH)2 depends on its size rather than the shape; Mg(OH)2 nanoparticles can kill E.coli in the dark, suggesting its potential wide application. A novel antibacterial mechanism has been proposed that Mg(OH)2 nanoparticles can penetrate into the cells by endocytosis and release large amount of OH-, which will increase the pH value of the inter cells and cause the protein denaturation, leading to the cell death of bacterial.Finally, the Mg(OH)2 antibacterial paper and hybrid membrane were prepared, which extends the applications of the Mg(OH)2 nanoparticles. The retention rate of Mg(OH)2 and the antibacterial activity of the paper sheet were investigated. Results indicate that the retention rate of Mg(OH)2 in the paper sheet is above 75%, which reaches the standard of the industrial production. In our experiment, the paper sheet with 3% Mg(OH)2 nanoparticles performed a 100% antibacterial ratio in 18 h, suggesting an excellent potential application for Mg(OH)2 nanoparticles. In addition, the PVDF/Mg(OH)2 hybrid membrane was prepared by phase inversion method. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) measurements were performed, and the ultrasonic stability, porosity, hydrophilicity, permeation and bovine serum albumin (BSA) and E. coli adsorption of the membrane were investigated. Results indicate that the addition of Mg(OH)2 alters the pore structures and hydrophilicity of the modified membrane, and the relative flux of membrane to pure water has been improved by more than 1.5 times with 10 wt% Mg(OH)2 added, suggesting it will be very effective in preventing flux losses caused by biofilm formation.