【作者】 王海霞；

【导师】 刘世权；

【作者基本信息】 济南大学 ， 材料学， 2011， 硕士

【摘要】 球形纳米孔SiO₂材料中存在大量纳米孔,具有比表面积大、孔容高、流动性好和表面易功能化等特点,在吸附分离、催化剂载体、色谱分析、阻热、光子晶体和药物可控释放等方面具有广阔的应用前景。实验采用溶胶-凝胶法,结合喷雾干燥、自组装途径制备了结构和孔特性不同的球形纳米孔SiO₂材料。采用扫描电子显微镜、红外光谱、差热-热重分析、N₂等温吸附和小角X-射线衍射等实验手段研究了所得样品的形貌、结构和性能,重点研究了不同球形纳米孔SiO₂材料对罗丹明6G（R6G）、甲基蓝、金属离子以及焦亚硫酸钠的吸附特性。实验首先考察了正硅酸乙酯-乙醇-氨水-水-十六烷基三甲基溴化铵（CTAB）体系中水硅比变化对所得产物形貌的影响。当反应体系无外加水时,TEOS在氨水中发生水解缩聚反应,所得SiO₂微球中只存在少量的无序微孔;水硅比为124 : 1时,表面活性剂形成的胶束与TEOS水解缩聚的产物进行自组装,产物干燥煅烧后最终得到有序介孔SiO₂微球。若增加反应体系水硅比增至248 : 1时,样品逐渐变为球形和棒状的混合物。水硅比超过372 : 1时,样品为多孔纳米棒。随着水硅比的增大,SiO₂纳米棒的长度和长径比减小,孔径增大,且孔的有序性降低。纳米棒的形成是由于CTAB位阻效应凸现所致。以稳定的复合纳米棒悬浮液喷雾干燥、煅烧制得纳米孔球形SiO₂颗粒。所得球形纳米孔SiO2颗粒尺寸为1μm左右,其比表面积、孔容、孔径均比对应的多孔纳米棒小。在上述体系随着CTAB用量增多,所得多孔SiO₂微球的相貌和尺寸变化较小,孔径减小,但比表面积增大。不同孔径微球混合物的N2吸附等温线在毛细管凝聚阶段无分离特征,但孔径分布曲线呈现双峰,两峰的相对面积随混合物中不同孔径微球所占比例变化而变化。研究表明,低浓度的前驱体溶液、高吸附质含量的条件下有利于多孔SiO₂微球对Ce²⁺、Cu²⁺离子的吸附。染料分子吸附实验结果显示,由于水和CTAB用量不同时制得的SiO₂微球中纳米孔的孔径均大于R6G的分子直径,纳米孔SiO₂微球吸附R6G的速率和最终吸附量均随着样品比表面积的增大而提高;而多孔纳米棒吸附R6G的速率及吸附量随棒尺寸的减小而降低;喷雾干燥制得的球形纳米孔SiO₂颗粒吸附R6G的量均比对应的多孔纳米棒小。所有样品对染料的吸附过程均符合准二级动力学吸附模型。实验还分别考察了壳上具有纳米孔的厚壁中空SiO₂微球和薄壁中空SiO₂微球对R6G、甲基蓝以及焦亚硫酸钠的吸附行为。结果表明,厚壁中空SiO₂微球的孔径、染料分子的直径影响中空SiO₂微球对染料的吸附特性。当样品的孔径均大于染料分子直径时,孔径增大,吸附量增加。薄壁中空SiO₂微球中,样品孔径、球壳厚度均对样品吸附R6G的性能产生影响。样品孔径增大,球壳厚度增加,吸附R6G的速率和平衡吸附量增大。中空微球对R6G的吸附过程均符合准二级动力学模型。此外,实验发现随着薄壁中空SiO₂微球球壳厚度的增加,其吸附焦亚硫酸钠的量依次增加,分别为51%、63%和72%。更多还原

【Abstract】 Spherical nanoporousSiO₂ materials possess abundant nanopores, high surface area, large pore volume, good fluidity and ease of surface functionalization etc. They may find potential applications in the fields of adsorption and separation, catalysis, chromatographic analysis, heat resistance, photonic crystal, controlled drug delivery and release. In this work, spherical nanoporous SiO₂ materials with different structures and pore features were prepared using sol-gel technique combined with spraying-dry and self-assembly approach. SEM, FT-IR, DTA-TG, N2-sorption, small angle XRD were used to charcterize the morphology, structure and properties of the obtained samples. The adsorption of Rodamine 6G （R6G）, methyl blue, metal ions and Na₂S₂O₅ by the prepared spherical nanoporous SiO₂ materials were studied in detail.The influence of water to silica ratio on the morphology of the products in tetraethylorthosilicate （TEOS） - EtOH - ammonia - water - cetyltrimethylammonium bromide （CTAB） system was first investigated. When no extra water was added, hydrolysis and condensation of TEOS occurred in the ammonia solution. SiO₂ microspheres with disordered micropores were formed. When the water to silica ratio of the system was 124: 1, surfactant and the silica species from the hydrolysis and condensation of TEOS self-assembled, resulting in ordered mesoporous SiO₂ microspheres. When the water to silica ratio of the system was doubled to 248: 1, the sample consisted of spherical and rod-like particles. When the water to silica ratio of the system was more than 372: 1, porous nanorods were obtained. The results show that the length and aspect ratio as well as the pore ordering of the nanorods decrease with increasing the water to silica ratio of the system. However, the pore diameter increases. The steric effect of CTAB is responsible for the formation of the naorods. Spray-drying stable suspensions containing the silica-CTAB nanorods generated spherical nanoporous SiO₂ particles sized about 1μm. The surface area, pore volume and pore diameter of the spray-dried spherical particles were smaller than those of the correspondent nanorods. Also, increase in the amount of CTAB in above system had little effect on the morphology and size of the obtained porous SiO₂ spheres. However, the pore diameter decreased while the surface area increased. N₂-sorption isotherms of mixed silica spheres with different pore diameters do not show distinct break in the capillary condensation stages. In contrast, that pore size distribution curves of mixed samples exhibit double peaks whose relative areas change with the proportion in the mixture of microspheres with different pore diameters.Adsorption studies indicate that the precursor solutions with low concentration, high dosage of absorbent are favorable for the adsorption of Ce²⁺, Cu²⁺ ions in the nanoporus silica microspheres. Since the size of nanopores inside the SiO₂ microspheres synthesized with different water and CTAB additions is larger than the diameter of R6G molecules, it is demonstrated that the adsorption rate and final adsorbance of R6G in nanoporous SiO₂ spheres are improved mainly due to the increase in the surface area of silica microspheres. The adsorption rate and final adsorbance of R6G in the porous nanorods decreases as the rods become shortened. The adsorbance of R6G in spray-dried nanoporous SiO₂ particles is less than that in the correspondnet porous nanorods. All the above samples show the pseudo-second-order adsorption process of R6G. The adsorption of Rhodamine 6G, methyl blue and Na2S2O5 by nanoporous hollow SiO₂ microspheres with thick and thin shells was also investigated. The results indicate that the pore size of nanopores in the thick-walled hollow silica microspheres and the diameter of dye molecules affect the adsorption of dyes in hollow SiO₂ microspheres. When nanopores are larger the dye molecules, the adsorbance increases with the pore diameter. However, in the case of hollow silica microspheres with thin shells, the pore diameter and shell thickness have effects on the adsorption of R6G.The adsorption rate and equilibrium adsorption capacity of R6G in thin-walled hollow silica microspheres increased with the pore diameter and shell thickness. All the adsorption process of R6G in hollow silica microspheres are also pseudo-second-order. In addition, the adsorbance of Na₂S₂O₅ in the thin-walled hollow silica microspheres is found to be increased from 51% to 63%and 72% with the increases in shell thickness.更多还原