Synthesis And Characterization Of ZSM-5 Crystal(Host)-Metal Oxide(Guest) Materials

In the field of material chemistry, research and development (R&D) of zeolite related materials are still in burgeoning in the latest few decades. Zeolite and related molecular sieves are widely used in adsorption, heterogeneous catalysis, gas separation, ion exchange and so on, due to its unique channel structure and fantastic thermal stability. Recently, the applications of zeolite are not confined in the traditional adsorption and separation field but in nonlinear optical materials, zeolitic cells, zeolitic chemical sensors, etc. In this dissertation, the ZSM-5 crystals are employed as a good host material for several metal oxides'encapsulation with different preparation methods. A series of methods have been introduced to characterize the so-obtained materials from several points of view, such as the crystal phase, images, contents of oxides and pore structures. Based on the features of the material, the photoluminescence (PL) properties have been investigated. Furthermore, the mechanisms of the PL spectra of two most-studied materials after small molecule adsorbed have also been deduced. The main results are as follows.1. The ZSM-5 crystals have been synthesized successfully and stably with pure chemical reagents, by adding sodium ethylenediamine tetracetate (EDTA-Na2) as a mineraliser to alter the crystallization manner of ZSM-5 molecular sieves. The pore structures have been analyzed by nitrogen adsorption methods. Besides, the crystals have been characterized intensively by different ways, such as, scanning electron microscopy (SEM), optical microscopy, infrared spectra (IR) etc. Generally, the crystals possess outstanding properties to be applied as a host material, and pave the way for the following works.2. By making the as-synthesized ZSM-5 crystals as the host material, a thermal diffusion method has been employed for the guests'encapsulation, and three host-guest materials have been obtained, i.e., ZnO/ZSM-5, SnO2/ZSM-5 and CdO/ZSM-5. Separately, the crystal images, crystal phases, pore structures and photoluminescence properties have been tested and studied. Take a global view of the thermal-diffusion-prepared materials, some commonness have been found and stated as follows.(a) The contents of guests in the materials are closely related with the thermal diffusion temperatures. The higher the temperature takes in the experiment, the higher the guest's content holds. This is because the vapor pressure gets high at a relative high temperature, which thereby increases the partial pressure of guest source within the reactors, thus, the metal species diffusing into the host turn more.(b) The thermal diffusion temperature affects the integrity of crystals. Some cracks or crystal defects appear as the temperature arising. Therefore, the selection of reaction temperatures is critical to the thermal diffusion process. (c) The characteristic features of materials preparing by this method is that the guests'content is low, resulting in the unfulfilled pore spaces of ZSM-5. Most guests could be dispersed in the pores of the host, (d) As a result of the oxygen-poor environment within the reactor, the so-synthesized material always possesses oxygen vacancies.At the same time, each material has its own characteristics, (ⅰ) ZnO/ZSM-5 exhibits two photoluminescence peaks at 350 & 440 nm individually, when induced by a beam of ultraviolet light. It is deduced that the emission peak at 350 nm is ascribed to the defects of zinc oxide clusters, whereas the peak at 440 nm, it is generated by oxygen defects in the material, (ⅱ) SnO2/ZSM-5 possesses good optical transmittance properties when prepared at 750℃, and the SnO2 clusters are not occupy the channels of zeolite sweepingly, which has a good potential in being used as optical device-based material. When the diffusion temperature rising to 850℃, the pore structures are occupied even blocked by guest particles, therefore, it is not appropriate to be applied in optical devices. SnO2/ZSM-5 undergoes good photoluminescence properties, of which the emission center locates at 451 nm. The emission phenomenon is assigned to the semiconductor defects caused by oxygen vacancy, (ⅲ) CdO/ZSM-5 material shows good optical transmittance. CdO nanoparticles locate in the pores of ZSM-5 but not block the channels, when the content of CdO is low. As for the content of CdO turns higher, the pores of zeolite are jammed, as a result, the related pore parameters change accordingly.3. Employing microwave assistant and common water bath heating method, titania is encapsulated into the channels of ZSM-5 crystals by using adsorption-hydrolyzation method. The so-obtained TiO2/ZSM-5 material is bright and clean on the surfaces. The TiO2 clusters are distributed into the zeolite but not standing on the surface of zeolite crystals. It is inferred that the crystal phase of TiO2 is anatase. The different heating methods affect the loading content of TiO2 in the material, even from the same initial titanium species dosing amount. TiO2/ZSM-5 material performs good photoluminescence behaviors, of which the emission center is focused at 436 nm, resulting from the defect sites on the surface generated from the cleavage of the bridging oxygen atom. The nanosized titania clusters are standing in the external surface of the host material. Only a little guest locates at the microstructures, and the pore structure has not been altered evidently.4. In a general consideration of the materials as-synthesized, two with outstanding combination properties which are prepared by different methods have been selected, i.e., TiO2/ZSM-5 & ZnO/ZSM-5. Primary investigations to their applications have been carried out. Due to the fantastic optical transmittance feature of them, besides, the crystal size is relatively big, these materials are apt to be used in optical sensing fields. Therefore, the photoluminescence spectra have been collected after the materials adsorbing small molecule gases statically. The mechanisms of the variation in the emission spectra are also analyzed and investigated, which supplies the follow-up researches with the original data and theoretical foundation.