【作者】 李立硕；

【导师】 冯庆革；

【作者基本信息】 广西大学 ， 化学工艺， 2013， 博士

【摘要】 碳酸锶(SrCO3)作为一种重要的化工原料,广泛应用在显像管玻壳、小型磁性电机、荧光材料等生产中。超细碳酸锶尤其是纳米级高纯SrCO3是一种现代电子元器件的基础材料之一,具有良好的发展前景。离子液体(ILs)是一种潜在的绿色溶剂,常被用于化工反应、分离及纳米材料制备中。本文的主要目的是采用ILs作为模板剂和反应介质来控制合成不同形貌的纳米SrCO3,研究SrCO3形貌与性能之间的关系,并从ILs对纳米SrCO3的成核动力学影响规律解释纳米SrCO3制备的机理问题。主要研究成果如下：(1)利用不同ILs对纳米SrCO3的形貌控制作用,在ILs-水体系中制备出了纳米晶须,纳米梭、纳米棒、海葵状聚集体等纳米SrCO3晶体。研究发现：功能性离子液体1-(2-羟基乙基)-3-甲基咪唑双(三氟甲磺酰基)亚胺盐([HOEmim]NTf2)因能与CO2发生化学反应而增加了溶液中CO2的浓度,体系成核速率大,获得的SrCO3晶体颗粒小。改变体系中1-丁基-3-甲基咪唑六氟磷酸盐([C4mim]PF6)离子液体的浓度可实现不同形貌纳米SrCO3的可控制备。采用1-丁基-3-甲基咪唑氯盐([C4mim]Cl)为反应介质,考察不同时间间隔SrCO3的形貌演化过程,提出了“晶核-纳米梭-棒形-花束形聚集体-海葵状聚集体”的SrCO3晶体形貌演化模型。不同形貌的SrCO3在紫外-可见光范围内都表现出吸收现象,粒径越小,比表面积越大,对紫外-可见光的吸收越强。(2)以ILs-甲醇混合液作为CO2+Sr(OH)2的碳化反应介质,分别制备出了纳米晶须、纳米梭形、椭球体、球形聚集体、纳米球、棒形聚集体等SrCO3晶体,产品的均匀性和分散性好,纳米球的直径仅为80nm。甲醇在体系中起到了增加Sr(OH)2溶解度的作用,因而制备出的纳米SrCO3的形貌及均匀性比ILs-水中好。不同浓度的[C4mim]Cl可实现对SrCO3不同形貌和粒径的调控。反应温度高有利于减小产品的粒径。不同形貌的纳米SrCO3,其开始分解的温度不同,粒径越小,表面越粗糙,开始分解温度越低。实验结果表明,纳米球和纳米晶须的分解温度最低为938℃,而不定形SrCO3分解温度最高为1000℃。(3)在甲醇-水体系中成功合成出椭球形、棒形、哑铃形纳米SrCO3多级结构。纯甲醇中制备的纳米SrCO3晶体结晶度低,反应温度低有利于多孔结构SrCO3的形成。水-甲醇体系中反应得到了高结晶度和高长径比的棒形碳酸锶。红外分析表明,甲醇通过氢键作用影响碳酸锶晶体的表面自由能,从而改变SrCO3的形貌。N2等温吸附-脱附分析表明,哑铃型碳酸锶的比表面积为14.9m2·g-1,具有中孔结构,孔径分布为12-32nm。(4)采用溶剂热法在ILs-水体系中制备出具有特殊形貌的花状聚集体、高长径比纳米棒、六面体结构椭球体、纳米球和空心微球等特殊形貌纳米SrCO3晶体。研究表明,疏水型离子液体通过微乳液影响产品SrCO3的形貌,亲水型离子液体通过晶面吸附改变晶体的形态。熟化温度高,产品的晶粒小,延长熟化时间SrCO3晶体发展越完全。通过对ILs中合成的SrCO3:1%Eu3+的荧光性质研究发现,产品在325nm激发光下激发的荧光发光光谱以5Do-7F2跃迁激发的614nnl红光为主。三种掺杂了铕离子的不同形貌碳酸锶荧光强度顺序为：花状聚集体>纳米球>空心微球。(5)通过扫描电子显微分析技术(SEM)和原子吸收分光光度技术(AAS),研究了添加1-辛基-3-甲基咪唑溴盐([C8mim]Br)离子液体对Sr(OH)2-CO2-H2O碳化体系成核动力学的影响。在cSr(OH)20=0.lmol·dm-3时,[C8mim]Br添加量的不同直接影响到碳化速率的演化过程,[C8inim]Br添加量越大,碳化速率越慢。在碳化开始的很短时间内,SrCO3成核速率快,体系中Sr(OH)2主要消耗于SrCO3的成核。SrCO3的成核速率J随反应进程逐渐变小。添加72.7mmol [C8mim]Br下,反应进行到20s时,SrCO3的成核速率达84.9×1017number·m-3·s-1,而晶体的线生长速率为0.63nm·s-1。随着[C8mim]Br添加量的增大,SrCO3的成核速率增大,[Cgmim]Br的添加促进了碳化结晶过程中SrCO3的非均相成核。更多还原

【Abstract】 Strontium carbonate (SrCO3) is one of the basic chemical reagents, and it has been widely used in the producing of glass for color television tubes, ferrite magnets for small DC motors and fluorescence materials etc. Superfine SrCO3with high purity is one of basic material in modern manufacturing electronic units and has bright use potential. Ionic liquids (ILs) has been regarded as one of green solvents and been used in chemical reaction, separation process and nanomaterials preparation. The main goals of this article is to use ILs as template agents and reaction media to synthesis nanostructure SrCO3with different morphology and try to explain the mechanism of how ILs effect the nucleation kinetics when prepare nanostructure SrCO3in ILs. The performances of the different morphology nanostructure SrCO3have also been investigated. The main results are as follow.(1) By used the different ILs, we successfully prepared nano SrCO3with special morphology such as nanowhisker, nanospindle, nanorod, seaflower-like aggregate etc. and it is found that SrCO3synthesis in ILs with special task groups [HOEmim]NTf2gain smaller particle; different concentration of [C4mim]PF6can modulate suitable reaction environment, and it lead the auto assembling nano SrCO3with special morphology. When [C4mim]Cl was taken into account as reaction media, by recording the morphology of SrCO3in different time interval using SEM techniques, we propose the model of "nucleus-nanospindle-rodlike-flower bundles aggregate-seaflower aggregate" morphology evolution. The different morphology nano SrCO3shows good UV-Vis absorption phenomena, and the smaller particle, the stronger UV-Vis absorption it revealed.(2) In ILs-methanol bi-system, nano SrCO3with special morphology such as nanowhisker, nanospindle, ellipsoidal, sphere aggregate, nanosphere, rodlike aggregate, etc. have been obtained. The as-synthesized product show good uniformity and monodisperse, the diameter of nanosphere is about80nm. Methanol can enhance the solubility of Sr(OH)2in the system, and the morphology and uniformity of nano SrCO3obtained better than that obtained in ILs-water system. However, when the higher reaction temperature was presented the smaller diameter of the product it has. Different diameters of nano SrCO3show different initial decomposing temperature. The smaller grain and the rougher surface, the lower decomposing temperature it has. The experimental results indicate that nanosphere and nanowhisker showed the lowest decomposition temperature of938℃, and the irregular shape SrCO3showed the decomposition temperature as high as1000℃(3) In water-methanol system, nano SrCO3with dumbbell like, ellipsoidal and high length to diameter ratio of rodlike have been obtained. Nanometer SrCO3crystal prepared in pure methanol shows low crystallinity, low reaction temperature is beneficial to the formation of the porous structure. FTIR analysis show that the hydrogen bond was found in the product indicate the methanol’s absorption can low down the surface free energy of strontium carbonate crystal nucleus, thereby change the morphology of SrCO3, N2isothermal adsorption-desorption analysis showed that the dumbbell strontium carbonate surface area is14.9m2·-g-1, and its pore size distribution is range from12nm to32nm.(4)By using solvothermal method, nanostructure of SrCO3with morphology of flower-like aggregate, nanorod, hexahedral ellipsoids, nanosphere, hollow microsphere etc. has been obtained. Study results revealed that hydrophobic ionic liquids can affect SrCO3morphology by microemulsion while hydrophilic ionic liquids can change the crystal morphology by absorbing certain crystal plane. The higher the solvothermal temperature, the smaller grain size the product it has; by prolong the solvothermal time, the strontium carbonate crystal development more completely. By studying the fluorescence properties of SrCO3:1%Eu3+with different morphology synthesis in ILs, it is found that under325nm light excitation, the spectra of the luminous intensity central around614nm and it belongs to red light region, which is due to the electron transition of5D0-7F2. The order of the intensity of fluorescence prepared from three different morphology of strontium carbonate is:flowerlike aggregate> nanosphere> hollow microsphere.(5) By using the technology of scanning electron microscope (SEM) and atomic absorption spectrophotometer (AAS), we studied the effect of the present of [Cgmim] Br to the nucleation kinetics in Sr (OH)2-CO2-H2O carbonation system. With a starting concentration of cSr(OH)20=0.1mol·dm-3, the relationship between the heterogeneity nucleation rate J and time reveals that in the starting period of nucleation, nucleation took place rapidly, the Sr(OH)2in the system were mainly supplied the nucleation of SrCO3crystallization, and the nucleation speed decreased as the crystallization proceeding. Higher concentration [C8mim]Br resulted in lower carbonation speed. At20s after reaction, the present of72.7mmol [C8min]Br can reach a nucleation rate of84.9×1017number·m-3·s-1and a growth speed of0.63nm·s-1. High concentration [C8mim]Br can speed up the nucleation rate. The presented of [C8mim]Br can promote the heterogeneity nucleation.更多还原