| As a new type multifunction inorganic material, nano-MgO has wide application prospect in many fields, especially in environment purification and antibacterial materials which are closely correlated with the survival and health of human beings. Doping other ion into oxide matrix, could cause lattice defects such as vacancies, interstitials and antisites, which play an important role in modifying the physical and chemical properties of mother oxide at a certain extent. Based on this point, this paper aims to improve the adsorption and antibacterial properties of nano-MgO through doping with three different value state metal ions of Ti4+ ion, Zn2+ ion and Li+ ion, the ion radius of whose are close to Mg2+ ion. Firstly, the research progress of MgO in environment purification and antibacterial materials, and the studies of nano-MgO preparation and doping modification were introduced in brief. Subsequently, undoped and doped MgO nano-powders were synthesized by modified precipitation or sol-gel method. The influences of preparation technology and doping on the structure and morphology of nano-powders were also investigated. Finally, the adsorption and antibacterial properties of three different ions doped nano-MgO powders were studied in detail. On the basis of experimental results, the mechanism for doping to improve properties of nano-MgO was primarily discussed. This work mainly includes the following aspects:Nano-MgO powders were prepared by direct chemical precipitation using polyethylene glycol (PEG) as dispersing agent. The results of orthogonal experiment showed that the most important effect factor on crystalline size was reaction temperature, and then amount of PEG, reaction time, amount of ammonia and concentration of Mg2+ ion, as for product yield, the effect order was in turn amount of ammonia, amount of PEG, reaction time, reaction temperature and concentration of Mg2+ ion. The technological conditions for nano-MgO preparation were 8mL NH3·H2O, 0.5mol/L Mg2+ ions, 8mL PEG, reaction at 50℃, reaction time 1.5h and calcination at 500℃. The influence of PEG on the morphology of nano-particles was investigated. The results show that PEG may be adsorbed preferably on the (001) crystal plane of Mg(OH)2, and the growth along this facet is therefore considerably restricted to produce plates. With the increase of the nuclei, the selective adsorption is weakened, and the nuclei are mainly wrapped with PEG, which inhibit the nuclei growth to form a network-like shape. Glacial acetic acid used as a modifier not only avoids a high local concentration of precipitant, which could result in the phenomenon of inhomogeneous precipitation, but also enhances the crystal growth of the precursor Mg(OH)2 in (001) orientation, and significantly lowers the transition temperature from Mg(OH)2 to MgO in favor of the crystallization of MgO.Ti-doped MgO powders prepared by direct precipitation showed serious hard-agglomeration, and the particle size increasing with Ti content. However the powders prepared by modified precipitation showed a clear decrease in particle size and improved particle dispersion with the increase of Ti content. When the obtained precursors were calcinated at 500℃, all of the samples have only MgO phase. However, new phases containing titanium present besides magnesia phase in 2mol% and more Ti-doped samples calcined at 800℃, which indicated the solid solubility limit of Ti into MgO crystal lattice was about 1mol%. In addition, Ti doping has the effect of inhibiting crystallization of MgO, and the crystallite size gradually decreased with the increase of titanium content. During the preparation of Zn-doped nano-MgO by modified precipitation, it was found that Zn content has no effect on crystallization, crystallite size and particle size. Compared to the samples without using glacial acetic acid, the powders using glacial acetic acid showed big crystallite size and good crystallization. It was demonstrated that glacial acetic acid could promote the transition from hydroxide to oxide and enhance the crystallization of product, which is consistent with the results in nano-MgO preparation by modified precipitation.The pure and Li-doped nano-MgO were prepared by sol-gel method using low-cost inorganic salts as starting materials. In the process of MgO preparation, the amount of solvent, reaction temperature and the amount of citric acid have varying effects on gel time and crystallite size. To obtain white high-purity nano-MgO, xerogel was pretreated by the stepped temperature heat treatment at low temperature, and then calcined at 600℃for 2h. The decomposition temperature of Li-doped xerogel was shift to high temperature with increasing Li content. After calcination at 600℃, 0.5%Li and 1%Li samples only have MgO phase,and other Li-doped samples have the presence of other phases beside MgO phase. With the increase of Li content, the intensity of diffraction peak was much strong, the crystalline size and particle size were much large, and the morphology changed from granular to thin sheet-like. All of Li-doped samples calcined at 800℃have the presence of other phases beside MgO phase (including 0.5% Li sample). The diffraction peaks were much sharper, and the intensity of peaks was much stronger.Methyl orange and E. coli were selected as models to investigate the adsorption and antibacterial properties of the as-synthesized powders. With decreasing crystalline size of powders, the adsorption capacity of methyl orange on nano-MgO increased, and the adsorption rate was also improved. As the heat treatment temperature increased, the equilibrium adsorption capacity increased slightly, and the adsorption rate was slower. The adsorption properties of Ti-doped MgO were better than that of pure MgO, and the 1% Ti sample's adsorption performance is the best one. The adsorption properties of Zn-doped MgO start to weaken with Zn content. When Zn content achieves 15mol%, although the adsorption rate reduces, the equilibrium adsorption capacity instead increases. The adsorption properties of Li-doped MgO weaken gradually with the increase of Li content. The antibacterial experiments on E. coli indicated that the antibacterial properties of Ti-doped MgO were poorer than pure MgO. In the Zn-doped samples, 5% Zn and 10% Zn have the good sterilization performance, but 1% Zn shows hardly any antibacterial function. The antibacterial properties of 1% Li and 5% Li is almost similar to that of pure MgO, but the bacteriostatic effect of 10% Li is slightly better. The bactericidal rate of Li-doped samples reach above 99%, which demonstrates the excellent sterilization performance.
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