Synthesis, Properties And Application Of Porous Composite Materials

With the advance of science and technology, the limited performance provided by the single-component system can not meet the needs of practical applications. Composite materials which are investigated extensively in the past two decades, always demonstrate superior performances and novel features showing well prospects for development. Among all the inorganic hosts, the porous materials represented by zeolite molecular sieves are particularly ideal host materials due to their versatile structures and stable performance. The zeolite based composite materials have shown great application potential in a variety of areas such as catalysis, drug delivery and energy storage. Therefore, the studies on the assembly of the inorganic porous materials and the functional development of the composite materials have great significance to the scientific research and practical application.In this thesis,we focus on the preparation of composite materials on the basis of porous host materials through various synthetic approaches. All the prepared composite materials exhibit either enhanced sensing property or superior catalysis performance. And this thesis is divided into five parts.In the introduction of Chapter One, we briefly review the current development status and prospect of the porous materials-based host-guest composite materials. In particular, the assembly of metal ions or metal ion clusters with special valence confined in the microporous molecular sieves, the application of porous materials in sensing realm, and the state of the art of porous composite catalyst are introduced in detail. Also the significance and achievement of this thesis is summarized.In Chapter Two, elemental sulfur is introduced into microporous silicoaluminophosphate molecular sieves SAPO-CHA which consist of univalent zinc in its microporous through chemical vapor deposition route. As is known, the unstable univalent zinc displays strongly reductive, due to the tendency of losing its single electron in the 4s orbital to become the stable Zn²⁺. After introduced into the Zn⁺-containing microporous SAPO-CHA, the elemental sulfur is reduced, while Zn⁺ is oxidized to Zn²⁺. In this process, the single electron transfers from the univalent zinc to elemental sulfur, resulting in the microporous SAPO-CHA with occluded zinc and trisulfur anionic radicals (·S₃^-) composite system. The signals in the ESR and Raman spectra confirm the presence of the chromogenic·S₃^-, which show an intense blue color, in accordance with the UV/vis spectrum. This·S₃^--containing composite material displays unusual sensing performance to trace amounts of water either in air or in an organic solvent. When the composite material is exposed to water, its color changes obviously from ultramarine blue to primrose yellow according to the water contents. Moreover, this color variation can be observed on the basis of visualization without the need of specialized equipments. Under appropriate thermal and vacuum conditions, the used composite materials are able to be recycled by the extraction of adsorbed water molecules. The high sensitivity, broad detection range, excellent selectivity and superior recyclability render the composite material an ideal sensing material for detecting trace amounts of water.In Chapter Three, we use several kinds of small molecules, such as O₂, H₂O and CO, as probe molecules introduced into the Zn⁺-containing microporous SAPO-CHA through chemical vapor diffusion to further study the special property of the univalent zinc. The mechanism of the reaction between the univalent zinc and small molecules and the relevant functions are investigated in detail. The Zn⁺-containing microporous SAPO-CHA is exposed to the oxygen atmosphere. The ESR spectrum indicates that the single electron in the 4s orbital of univalent zinc tends to transfer to the anti-bonding orbital of oxygen molecules, resulting in a relatively stable O₂- ion which is the necessary intermediate in many catalytic reactions. In addition, this electron transfer process is reversible, that is, the single electron is able to move back to the zinc atom under appropriate thermal and vacuum conditions for the release of the oxygen molecules from the molecular sieves. When exposure to water, the Zn⁺-containing microporous SAPO-CHA reacts with water immediately under ambient conditions with the release of H₂. In the comparative experiments, whether the pristine or the Zn²⁺ ion-exchanged SAPO-CHA has no reactivity with water. Therefore, the univalent zinc is considered to be responsible for the moderate reactivity of the composite materials. In a coexistent atmosphere of both water vapor and oxygen, the Zn⁺-containing microporous SAPO-CHA shows interesting catalytic performance for the oxidation of carbon monoxide. At a relatively low temperature, carbon monoxide is able to be converted to carbon dioxide by this composited material.In Chapter Four, a series of mesoporous semiconductor metal oxide are prepared using the mesoporous molecular sieves as the template through an inverse duplication approach, and their sensing performance are investigated detailedly. Using the mesoporous silica SBA-15, we prepared the pristine and Au loaded In₂O₃ with different loadings. The X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy have been performed, and the results indicate that the prepared materials consist of periodically ordered, uniformly mesoporous structures with crystalline pore walls, and the Au nanocrystals successfully dispersed in the mesopores. The gas-sensing properties of the mesoporous Au-In₂O₃ to triethylamine are investigated for the first time. Comparing with the pristine mesoporous In₂O₃, the Au loaded composite materials hold enhanced sensing properties. The sensor based on the 0.5 wt.% Au-loaded In₂O₃ shows a sensitivity of 31 to 20 ppm triethylamine, four times higher than that of the pristine In₂O₃, at 140 oC. Furthermore, the mesoporous ZnO is prepared through the inverse duplication of the template mesoporous carbon CMK-3 by the incipient wetness technique and the gas-sensing performance is investigated. Unlike the reported ZnO sensor previously, the mesoporous ZnO we prepared shows the highest sensitivity to methanol but not ethanol. At the optimized temperature of 120 oC, the sensitivity of the sensor fabricated from the mesoporous ZnO to methanol is 3.5 times higher than that to ethanol. Therefore, the sensor presents successful discrimination between methanol and ethanol.Due to their low cost of manufacture, anionic surfactant shows great application potential in the preparation of novel mesoporous catalysts through a templating route. In chapter five, a new kind of metal ions functionalized and anionic-surfactant-templated mesoporous silica is prepared through a one-step approach. The sodium dodecyl sulfate and ferric nitrate are used as the template and iron source, respectively. Through the one-step route, the Fe3+ ions were introduced into the mesoporous framework and highly dispersed in the mesopores. The prepared composite material has a twisted hexagonal rod-like morphology. And the catalytic performance is assessed through Friedel-Crafts benzylation of benzene by benzyl chloride. Under an optimized reaction condition, the catalyst with 20 wt.% Fe₂O₃ loading showed a 100% yield and selectivity of diphenylmethane within 90 s, which is superior to that of the analogous Fe-mesoporous catalyst.