Synthesis, Characterization And Functionalization Of Porous Inorganic Materials Based On Molecular Sieves

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 to2.043. 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.