【作者】 王维；

【导师】 乔学亮；

【作者基本信息】 华中科技大学 ， 材料学， 2008， 博士

【摘要】 纳米氧化镁(MgO)作为一种新型的多功能无机材料,在许多领域有着广阔应用前景,尤其是在与人类生存和健康密切相关的环境净化和抗菌方面显示了独特的优势。在氧化物的晶格中掺入外来元素会产生空位、间隙原子、置换原子和位错等晶格缺陷,而这些缺陷的产生可以在一定程度上促进母体氧化物的物理和化学性能。本文正是基于这一点,选用与Mg2+离子半径相近的Ti4+、Zn2+和Li+三种不同价态的金属离子作掺杂剂,拟通过掺杂来提高纳米MgO的吸附和抗菌性能。首先简要概述了MgO在环境净化和抗菌方面的研究进展以及纳米MgO的制备方法和掺杂改性的研究。然后采用修饰沉淀法或溶胶-凝胶法分别制备了纳米MgO和掺杂纳米MgO粉体,研究了制备工艺参数及掺杂对粉体结构、形貌的影响。最后,研究了三种不同离子掺杂对纳米MgO粉体的吸附和抗菌性能的影响,在此基础上初步探讨掺杂促进性能的机理。主要包括以下几方面:以聚乙二醇(PEG)为分散剂,采用直接化学沉淀法制备了纳米MgO粉体。正交实验结果显示:反应温度对晶粒影响最大,其它影响因素依次为PEG用量、反应时间、氨水用量和Mg2+浓度;就收率而言,氨水用量影响最大,PEG用量和反应时间次之,反应温度的影响更次之,Mg2+浓度的影响最小。确定纳米MgO的制备工艺条件为:氨水用量8mL,Mg2+浓度0.5mol/L,PEG用量8mL,反应温度50℃,反应时间1.5h,煅烧温度500℃。PEG对粉体颗粒的形状和大小有影响,在Mg(OH)2成核数少时,形成了片状形貌;随着成核数的增加,形成了细小颗粒密堆的“网络”状形貌。以冰乙酸作修饰剂,不仅可以避免了直接沉淀法中局部沉淀剂浓度过高,发生不均匀沉淀的现象,还可以促进前驱体Mg(OH)2晶体在(001)面的取向生长,降低由氢氧化物到氧化物热分解温度,有利于氧化物的晶化。直接沉淀法制备的掺钛纳米MgO,得到的粉体颗粒尺寸随着掺钛量的增加而显著增大,硬团聚严重;而修饰沉淀法制备的样品颗粒尺寸随着掺钛量的增加而减小,且团聚少,分散性好。制得的前躯体在500℃下煅烧后,所有样品均只有MgO相,而经800℃煅烧,掺钛量大于1mol%的样品中有含钛的杂相析出,因而可以确认钛在MgO晶格中固溶度为1mol%左右。随着掺钛量的增加,MgO的结晶性能降低,晶粒变小。在修饰沉淀法制备了掺锌纳米MgO中,研究发现锌含量的增加对衍射峰的强度和晶粒及颗粒大小基本上没有影响。与未加冰乙酸制备的样品相比,使用冰乙酸制得的粉体晶粒尺寸大,结晶性能好。说明冰乙酸在此制备过程中的促进了由氢氧化物到氧化物的转变,有利于产物的晶化,这与修饰沉淀法制备纳米MgO中的结论是一致的。采用廉价的无机溶胶-凝胶法制备了纳米MgO及掺锂纳米MgO。在制备纳米MgO过程中,溶剂用量、反应温度和柠檬酸用量对凝胶时间和晶粒都有不同程度的影响。干凝胶的热处理采用了在低温下分步预处理一段时间,然后在600℃下煅烧2h,可以制得白色的高纯纳米MgO。掺锂后干凝胶的热分解温度向高温方向偏移。600℃煅烧后,0.5% Li和1% Li样品中只有MgO相,而掺锂量高的样品中均有杂相。随着掺锂量的增加,衍射峰强度变强,晶粒和颗粒尺寸都变大,形貌也由粒状变成了薄片状。经800℃煅烧,所有掺锂样品中都有杂相存在,衍射峰更尖锐,强度更强。以甲基橙和大肠杆菌为模型来研究所制备粉体的吸附性能和抗菌性能。纳米MgO的吸附性能随着晶粒的变小,对甲基橙的吸附量变大,吸附速率也变快。随着处理温度的升高,达到吸附平衡时的吸附量略有增加,但吸附速率变慢。掺钛MgO对甲基橙的吸附性能都较纯MgO的好,其中1% Ti样品的吸附性能最好;掺锌MgO的吸附性能开始随着掺锌量的增大而减弱,但当掺锌量达到15mol%时,吸附速率虽减慢,但平衡时的吸附量反而增大;掺锂MgO的吸附性能随着掺锂量的增加而逐渐减弱。对大肠杆菌实验表明,掺钛MgO的抗菌性能均较纯MgO的差;掺锌MgO样品中,5% Zn和10% Zn具有良好的杀菌性能,而1% Zn几乎没有抗菌作用;1% Li和5% Li的抑菌性能与纯MgO基本相当,而10% Li的抑菌效果稍好一些。掺锂MgO的杀菌率均达99%以上,显示了优良的杀菌性能。更多还原

【Abstract】 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.更多还原