The Preparation Of Nano-MgO And Their Antibacterial Performance And Kinetics Of Formation Of Mg?OH?₂ Crystal

Magnesium oxide?Mg O? is considered as an ideal antibacterial material and has various potential applications due to their advantages such as rich abundance, resistance to color change, unlit restriction, low requirements in antibacterial conditions and nontoxicity. However, the antibacterial performance of Mg O still does not meet the requirements for practical application and thus it is vital to improve the performance. In this work, nano-Mg O with different morphologies was prepared using a microwave hydrothermal method and an electrospinning method to improve the antibacterial performance. The crystallization kinetics of the precursor of Mg O, magnesium hydroxide?Mg?OH?₂?, were investigated by measuring the conductivity of the solution, which provides fundamental data and theory for the control of the morphology and size of the nano-Mg O. The performance of the as-prepared nano-Mg O was tested using the inhibition zone method and the 24 h sterilization rate.1. In this thesis, nano-Mg O with different morphologies, including particles, monolith and rod-like shape was synthesized by a microwave hydrothermal method using magnesium acetate and urea as the raw materials. The effects of microwave power, microwave temperature and calcination temperature on the morphologies, microstructure and antibacterial performance of the nano-Mg O were investigated. The structures and morphologies were characterized using scanning electron microscopy?SEM?, X-ray diffraction?XRD?, thermogravimetric-differential thermal analysis?TG-DTA? and antibacterial performance tests. It was found that the best performance can be obtained using a microwave power of 900 W, microwave temperature of 90 °C, and a calcination temperature of 600 °C. Specifically, the 24 h sterilization rate for Escherichia coli?E. coli? was 86% using the nano-Mg O, whereas this value was 78% for Staphylococcus aureus?S. aureus?. Therefore, gram-negative bacteria?E. coli? is more severely affected by Mg O than that for gram-positive bacteria?S. aureus?.2. Mg?OH?₂ was synthesized using sodium hydroxide, magnesium chloride, magnesium acetate, magnesium sulfate and magnesium nitrate as the raw materials. The crystallization kinetics were investigated by measuring the conductivity at different reaction times, through which the mechanism of the reaction was revealed. The crystallization process was also monitored using SEM. It was found that both the nucleation growth rate?K1? and the grain growth rate?K2? of Mg?OH?₂ can be described by the first order reaction rate equation, and K1 is significantly higher than K2. This suggests the nucleation occurs much faster than the grain growth, and the nucleation of Mg?OH?₂ only occurs through a rapid process, which prevents the growth of crystallites.3. Composite nanofibers containing Mg O and polylactic acid?Mg O/PLA? were fabricated by an electrospinning method using nano-Mg O and PLA as the raw materials. The processing conditions including the loading of Mg O, the rotating rate of the collector, working voltage, stirring time and collection distance were adjusted. The effects of these conditions on the diameters, the dispersion state of Mg O and the antibacterial performance of the resultant nanofibers were studied. It was found that the best performance was achieved using the following conditions: the loading of Mg O is 0.4 g, a rotating rate of 600 r/min, a working voltage of 12 k V, a stirring time of 12 h, a collection distance of 13 cm. It might be due to that fibers with suitable diameters in which Mg O nanoparticles were dispersed uniformly were obtained through the aforementioned conditions.