【作者】 张鹏曲；

【导师】 蔡炳新； 詹拥共；

【作者基本信息】 湖南大学 ， 物理化学， 2010， 硕士

【摘要】 本文以MnSO4为锰源,尿素为沉淀剂和十六烷基三甲基溴化铵(Cetyltrimethylammonium bromide, CTAB)为结构导向剂,通过控制合成参数,制备一系列具有不同形貌的MnOx微纳结构材料；同时,用所合成的Mn3O4八面体纳米单晶对亚甲基蓝溶液催化降解性能进行系统研究。借助SEM图、TEM图、XRD曲线、]Raman曲线、FT-IR曲线、N2吸附-脱附和TG-DSC等表征手段,研究了MnOx微纳结构材料的晶体形貌和结构、晶型、比表面积、孔径分布和热稳定性。微纳米晶体的尺寸和形貌可通过改变实验参数轻易控制。结果表明：水体积在200 mL时,主体是Mn3O4八面体纳米材料,其平均尺寸与反应时间有关,反应时间在8h、16h和24 h其对应的平均尺寸为151.5：nm、238.3 nm和390 nm；升高温度(150℃)和使用CTAB/PVP混合表面活性剂能相应改善八面体分散程度,而单独使用P123时,晶体结构转换成球形；改变锰源,其形貌由八面体向多面体及纳米棒形貌转变；在600℃焙烧4 h,晶体由Mn3O4转变成Mn2O3；此体系下,缺点是产率较低。水体积在180mL-190 mL时,特别是在180 mL体积水时,在85℃条件下反应,八面体产率接近100%。然而,水体积在50：mL-150 mL时,在120℃条件下反应,其形貌几乎为Mn2O3立方体微米结构。以Mn3O4八面体纳米晶体做催化剂,以H2O2为氧化剂,催化降解亚甲基蓝(MB)溶液。系统考察了反应温度、MB初始浓度、H2O2质量分数、催化剂用量和不同形貌Mn3O4对MB降解率的影响。结果表明,反应温度、H2O2质量分数和不同形貌Mn3O4影响最为明显,且在最佳实验条件下其降解率达到99.68%,而MB初始浓度和催化剂用量对其影响并不显著；同时,通过对反应后溶液离子色谱分析可知MB基本上转化成无机盐(SO42-和NH4+离子浓度分别为2.13μmol·L-1和6.94μmol·L-1),FT-IR曲线分析可断定亚甲基蓝中的苯环结构消失。反应结束,将体系溶液与Mn304催化剂分离,对体系溶液蒸干后固体产物的XRD曲线、EDX和SEM图分析,可知此产物为含Mn、P、O、H元素的无机盐,且其形貌随溶液pH不同发生改变。此外,多次循环使用后催化剂仍保持很高的催化活性,其降解率仍达到90%以上,并推测出其可能反应机理。通过对MnOx微纳米结构的系统研究,为验证这种方法的普遍性,以相同的方法对其他过渡金属氧化物纳米结构的合成进行了一系列探索性研究。在200 mL溶液体系中,以尿素为沉淀剂,CTAB为结构导向剂,加入金属盐(Co(NO3)2·6H2O,CdCl2·2.5H2O,Cu(NO3)2·3H2O),在85℃下晶化1d,并在一定温度下焙烧获得相应的纳米结构金属氧化物(Co3O4、CdO、CuO),此体系也可以用于FePO4纳米材料的合成；与此同时,采用金属离子与有机物形成金属有机配合物,再将此化合物400℃焙烧得到相应的过渡金属氧化物。更多还原

【Abstract】 In this thesis, using surfactants as structure-directing agents, urea as precipitator, and manganese sulfate (MnSO4·H2O) as the source of manganese, a serials of micro-and nano-MnOx crystals with different morphologies and structures had been successfully synthesized by controlling synthetic parameters. At the same time, the obtained octahedral Mn3O4 nanocrystals were investigated systematically on the catalytic degradation of methylene blue (MB).Scanning electron microscope(SEM), transmission electron microscopy(TEM), X-ray scattering techniques(XRD), Raman, Fourier transform infrared spectroscopy (FT-IR), N2 adsorption-desorption and DSC-TG were used to investigate the structures and morphologies of the synthesized samples, such as crystalline, surface area, pore size distribution and thermal stability. The size and shape of the micro- and nano- crystals were easily controlled by varying the synthetic parameters. The results indicate that the average crystallite size of octahedral Mn3O4 nanocrystals is related to the reaction time in the system of 200 mL water volume, which increased from 151.5 nm to 238.3 nm and to 390 nm corresponded to the reaction times of 8 h,16, and 24 h, respectively. The octahedral Mn3O4 nanocrystals could be gradually dispersed very well by increasing reaction temperature (from 80℃to 150℃) and using CTAB/PVP as a mixture surfactant, while in the presence of P123, the nanocrystals were transformed from octahedron to sphere-like shapes. When the manganese source was changed, the octahedral nanocrystals were altered to polyhedron and nano-rods. The crystals were transformed from Mn3O4 to Mn2O3 by calcinations at 600℃for 4 h, and in our opinion, the defects of the this system is the lower morphology yield. And in the system of 180 mL, the yield of octahedral shapes was almost 100% at 85℃. However, the shapes were almost Mn2O3 micro-cubic structure at 120℃.It was presented that octahedral Mn3O4 was H2O2-assisted catalytic degradation of MB, which was synthesized in extremely dilute solution by soft template self-assembly. The influence on degradation of MB at reaction temperature, the initial concentration of MB, H2O2 content, catalytic loading, and different morphologies of Mn3O4 was investigated systematically. The results indicated that the most important factions involved reaction temperature, H2O2 content, and different Mn3O4 morphology. The degradation of MB was 99.68% under the optimum experiment condition, however, the initial concentration of MB and catalyst contents had no obviously influenced on the degradation. Meanwhile, the degradation products of MB dye were analyzed by ion chromatography, which contained 2.13μmol·L-1 SO42- and 6.94μmol·L-1 NH4+, and the benzene structure of MB vanished in the analysis of FT-IR. After separating the catalyst from the solution, the analysis of XRD, EDX, and SEM on solid product coming from the evaporation of reaction solution showed that it contained Mn, P,O and H, and the shapes were changed along with different pH. Moreover, the catalytic activity was still high after multiple circulation use, whose degradation was still above 90%.Through the system investigation of MnOx micro- and nano-structure, in order to prove the universality of the method, we have performed a series of explorative research for other transition metal oxides nanostructure in the same sys. In the sys of 200 mL water volume, we used urea as precipitator and surfactants as structure-directing agents, added some metallic salts (Co(NO3)2·6H2O, CdCl2·2.5H2O, Cu(NO3)2·3H2O), reacted at 85℃for 1 d, and obtained conresponded transition metal oxides (Co3O4, CdO, CuO) after a certain calcinations perature, which was suitable for the synthesis of FePO4 nanomaterials. Meanwhile, we used metal ions and organic materials as forming metal-organic ligands, which were calcinated at 400℃in the result of conresponded transition metal oxides.更多还原