摘要
多孔无机材料在催化、药物缓释以及能源存储等领域都表现出了极大的应用潜力。研究多孔无机材料的合成，同时开发与多孔材料相对应的功能是一件非常有意义的工作。其中，微孔分子筛以其独特的孔道结构、稳定的骨架组成和优异的性能，受到各国科研工作者的青睐。目前，将分子筛作为主体，引入各种客体材料，对其进行功能化研究是多孔材料发展的一个重要方向。
本文以微孔分子筛材料作为研究对象，利用真空化学气相反应法，将分子筛分别与锌蒸汽和钠蒸汽反应，制备出了富电子分子筛多孔材料以及多孔硅材料，并且对这两类材料进行了详细和深入的研究工作。论文的研究课题主要包括新型富电子分子筛的制备与材料中锌的化学环境的探索，富电子分子筛材料分解二氧化碳气体的研究，分子筛的钠热还原法制备多孔硅材料及其储能研究三个部分。通过对基于分子筛的无机多孔材料的制备、表征和功能化的研究，我们发掘出这些材料的内在特点，从而拓宽它们的应用。本论文主要得到了以下的结果和结论。
1.采用化学气-固相反应法，在真空条件下，使金属锌蒸汽与质子化的H-Y分子筛相互作用，成功地将锌引入到分子筛的孔道中，制备出一种含有离域电子的新型锌-分子筛材料。金属锌蒸汽在与分子筛反应，在得到Zn2+离子的同时，还生成额外的电子，使锌-分子筛成为富电子的分子筛多孔材料。这种富电子分子筛多孔材料在低温下，呈现出了明显的顺磁性。
2.探讨富电子锌-分子筛材料中锌的化学环境。基于上海光源同步辐射BL14W1线站的XAFS技术研究表明，在富电子分子筛材料中锌主要以Zn2+离子的形式存在，在部分的Zn2+离子附近，一些多余的电子离域在分子筛骨架上。Zn2+离子主要以三或者四配位的形式与分子筛骨架的氧原子配位，平均的Zn-O键长为1.98。在水分子的存在下，富电子分子筛材料中锌的配位环境会发生明显的改变，Zn2+离子转变为以六配位的形式与分子筛骨架的氧原子配位，平均的Zn-O键长增长至2.04。
3.电子顺磁共振（EPR）技术发现，在同步辐射X-射线的辐照下，富电子锌-分子筛内部会产生有趣的电子转移现象。离域在骨架上的多余的电子会从骨架转移到Zn2+离子的4s空轨道中，生成特殊价态的一价锌（Zn+）离子。用普通的X-射线辐照激发，也可以得到这种特殊价态的Zn+离子，这无疑为我们提供了一种快速制备一价锌（Zn+）离子的方法。
4.这种有趣的电子转移不仅仅是在分子筛材料内部进行，与引入的客体气体分子之间也能够发生电子转移。利用这种材料的电子转移特性，可以将它作为活化剂，活化热力学上非常稳定的CO2气体分子，使之分解成为碳和氧气。该发现提供了在密闭的生命体系中，实现CO2气体和O2气相互转换的一种新的可能性。
5.通过同步辐射XAFS和EPR技术的结合应用，探讨了电子转移的路径，阐释了CO2活化的反应机理。离域在分子筛多孔材料骨架上的额外电子在分解CO2反应中扮演着一个重要的作用。密闭环境中，离域在Zn2+离子附近的电子可以转移到CO2分子上，使之分解成碳的同时还形成超氧自由基（O-2），在相对高温的条件下，这种超氧自由基最终可释放出氧气分子。在对富电子锌-分子筛多孔材料在经过一系列的真空操作之后，骨架上的额外电子仍然具有良好的电子转移性能。
6.开发出一种钠热还原分子筛制备多孔硅的方法。钠热法还原分子筛时，能够生成多种无机副产物，这些副产物起到了填充孔道物的作用，形成具有多级孔结构的多孔硅材料。与以往的镁热还原法制备多孔硅技术相比，钠热还原法进行了方法的全面改进和提升。它克服了分子筛硅源只能用纯硅沸石的局限，将硅源扩大到硅铝酸盐沸石分子筛，反应温度也更低。
7.钠热还原法制备的多孔硅具有高比表面积的优势，达到570m2/g以上，远远超过有关文献中关于对多孔硅比表面积的报道。将这种多孔硅作为储能材料应用于超级电容器中，发现它表现出良好的双电层电容行为。以1.0mol/L的H2SO4溶液作为电解液，在1.0mV/s的扫描速率下，这种多孔硅最大可达到194F/g的比容量，同时具有好的充放电性能和良好的循环稳定性等特点。
Porous materials have shown great application potential in a variety of areas such ascatalysis, drug delivery and energy storage. The design, preparation and functionalizationof the porous materials are of great significance to the fundamental research and practicalapplication. Among all the porous materials, the inorganic porous materials represented bymolecular sieves are of particularly importance due to their rich diversities in porousstructures, framework elements and compositions. New properties are expected to begenerated through the introduction of guest species into the pores of the inorganic porousmaterials, leading to the formation of host-guest materials. Nowadays, increasing attentionhas been paid to the investigation on the host-guest materials based on microporousmolecular sieves.
In this dissertation, we focus on synthesis, characterization and function ofelectron-rich zeolite material and amorphous porous silicon material based on microporouszeolites. Zinc-incorporated electron-rich zeolite material has been prepared via a vacuumchemical vapor-solid reaction route. Over the electron-rich zinc-incorporated zeolite, CO2can be decomposed into carbon and oxygen under relatively mild condition. Asodiothermic reduction method has been developed for the preparation of amorphousporous silicon with high specific area by using aluminosilicate zeolites as precursors. Theamorphous porous silicon shows distinctive supercapacitive behavior in a three electrode system using1.0mol/L H2SO4as electrolyte.
1. Preparation and characterization of zinc-incorpored electron-rich zeolite. A novelzinc-incorporated zeolite has been successfully prepared through a vapor-solid reactionbetween a dehydrated HY zeolite and metallic zinc vapor. One is that each zinc atomreduces one isolated proton to form a Zn2+cation. This electron-rich zeolite shows aparamagnetic behavior at low temperatures.
2. The chemical environment of the zinc species in the electron-rich zeolite has beenelucidated on the basis of XAFS spectroscopy. The zinc cations are three orfour-coordinated with the zeolite framework oxygen atoms with an average Zn-O bondlength of approximately1.98in the zinc-incorporated electron-rich material. After theas-prepared material is reacted with water molecules, the coordination number of the Zn2+species increases to six, and the Zn-O distance to2.04
3. The formation of univalent zinc (Zn+) within the electron-rich zeolite was observedupon the irradiation of X-ray from either a synchrontron radiation source or a conventionalX-ray diffractomer. It is demonstrated that divalent zinc cations partly accompanied byextra electrons delocalized over the zeolite framework in their vicinity exit in the obtainedzinc-incorporated zeolite. The X-ray irradiation initiated the electron transfer from theelectron-rich framework of zeolite Y to the nearby Zn2+cations, generating Zn+species.
4. Decomposition of CO2to C and O2under mild conditions over the electron-richzinc-incorporated zeolite. Electron-rich zinc-incorporated zeolite Y material showsubstantial activity for the decomposition of CO2to carbon with the release of O2at about300oC. It is found that the zeolite material functions as an efficient activator for thedecomposition reaction. The generation of O2molecules and carbon via the decompositionof molecular CO2is of significance in both theoretical and practical aspects.
5. It is elucidated that electrons delocalized in the vicinity of zinc cations in the zeolite material play an essential role in the decomposition reaction. The in situ EPR and XAFStechniques have been employed to pinpoint the mechanism for the decomposition reaction.At elevated temperatures, the electrons delocalized within the electron-rich zeolite materialare transferred to CO2molecules, generating carbon species and O-2radicals associatedwith zeolite material. These O-2radicals can generate O2molecules and leave electrons tothe zeolite framework.
6. A sodiothermic reduction method has been developed for the preparation of poroussilicon using aluminosilicate zeolite NaY as a precursor. The sodiothermic reductionmethod is promising for the preparation of porous silicons through a wide variety of siliconsources, such as silicates and aluminosilicates. By comparing with magnesiothermicreduction method, the advantages of the sodiothermic reduction method are thesignificantly lower reaction temperature and the possibility to use various siliconprecursors.
7. The specific surface area of the porous silicon via sodiothermic reduction method is571m2/g, much higher than those of the porous silicons prepared via magnesiothermicreduction and etching of silicon wafer. To the best of our knowledge, the sample preparedin this work has the highest specific surface area among the porous silicon materials. Whenused as an electrode material, a large specific capacitance of approximately194F/g isachieved for this porous silicon at the scanning rate of1.0mV/s. This porous silicon alsoshows high rate capability and good cycling stability. The high supercapacitiveperformance is attributed to its unique porous structure and high specific surface area ofthe porous silicon.
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