Study On Functional Materials For Adsorption Of Ruthenium At Room Temperature

The radioactive xenon istopes are applied to monitor nuclear test and nuclear reactor safty. The radioactive xenon need to be enriched by adsorption and separation from the air. Since its concentration is low in the air and its chemical properties are extremely unlively, it is very difficult to adsorb and separate xenon from air.As noble gas, Xenon has stable physical and chemical properties. At room temperature, the adsorption of xenon is mainly physical adsorption, which is not easy because physical adsorption is highly related to temperature. This dissertation is focused on how to get the high selective xenon adsorption materials at room temperature. First, combining calculation and experiatal results, we proved that materials with high selectivity need suitable aperture size for the xenon adsorption and separation. Second, we confirmed that highly adsorptive separating materials also need metal ions or functional groups with polarization effect. Xenon atom is too big to constrain electrons at outer orbital. These electrons could be attracted by other atoms through weak van der Waals force, which is called as polarization effect. Thus, such effect could enhance the adsorpting performance.Based on the first principles, we used the local density approximation (LDA) method and density functional theory after dispersion correction (DFT-D) to calculate the adsorption energy of xenon with silicon aluminate. The ion of silicaon aluminate was substituted with Ag+, Na+and K+, respectively. The results showed that silver alumino-silicate(silver-exchanged zeolite) has strong adsorpting ability for Xe. The adsorption energy of xenon with Ag+ is 76.568 kJ/mol, which is much higher than that of Na+and K+. We also found that the polarization effect ofinternal electric field in silver alumino-silicate led charge density distribution transiting from spherto triangle. Compared to other typies of rare gases, xenon atom has a larger number of electrons involved in the van der Walls disperstion and higher value of minimum charge density. Therefore, Ag+has the strongest coulomb polarization effect to xenon atom, with polarization charger surrounded in the maximum range. This could explain why the silver alumino-silicate has the strongest adsorption with xenon atoms. According to the theoretical calculation, ETS-10(one of zeolite)was chose to prepare Ag-ETS-10 by substituting with different proportions of Ag+. The results of gas adsorption and separation experiment shows that the Ag-ETS-10 has a better adsorption ability of xenon than the ETS-lOat room temperature. The results also shows that the proportion of Ag+ has a great influence on the adsorption performance. Interestingly, Ag-ETS-10with a large amount of Ag+shows adsorption capacity of xenon increases as temperature rises, which is on the contrary of common adsorption law. We hypothesize that numerous Ag+produces strong polarization effect to boost the adsorption of xenon. This needs further study.Using the computational chemistry simulation methods, a combination of theoretical calculation and experimental results could guide synthesis of functional materials. Nowadays, Metal-organic frameworks (MOFs) and covalent-organic materials (COMs) have been developing rapidly. Due to their characteristics of ultra-high specific surface area, tunable structures and multifunctions, they have been widely used in gas storage, adsorption and separation, Considering a large variation of MOFs and COMs structures, not only time-consuming repeated experiments but computational chemistry simulation are indispensible to develop high-performance materials. The computational chemistry simulation reveals that materials with small pore size (such as Cu-BTC) have high xenon adsorption quantity under low pressure and good separation effect as well. By studying the microstructure and microscopic density distribution in the process of adsorption with xenon, we found that xenon tend to be adsorbed on the open metal bits of framework materials. As metal bits is saturated, xenon becomes adsorbed onligands of the framework material.Three kinds of materials:Cu-BTC, ZIF-8 and COP-4, were synthesized by the hydrothermal solution method, and their structure properties were characterized. Cu-BTC, ZIF-8 and COP-4 belong to the microporous materials, with suitable pore size for xenon adsorption. To study the adsorption performance, a type of activated carbon was selected for comparison. Static adsorption, dynamic adsorption, low concentration breaktrough, chromatography were used to study the adsorption and separation properties of these materials. The static and dynamic adsorption results showed that Cu-BTC performs excellent adsorption property of xenon at room temperature due to open metal sites, high specific surface area and appropriate pore size (about lnm). The breakthrough curves of low concentration demonstrated that Cu-BTC can effectively separate Xe with Kr, N2, and O2. The chromatographic separation experiments revealed that Cu-BTC can effectively separate Xe with CO2even if their concentration is close. We first decrease the CO2 concentration and then select appropriate temperature and flow rate to isolate Xe.The theoretical calculation and experimental research show that the size effect and the polarization effects of materials increase both the adsorption capacity and the selectivity of xenon. Thus, in this dissertation we proposed that functional materials for highly selective adsorption of xenon at room temperature need to provide size effect and polarization effect.The functional materials with high adsorpting selectivity at room temperature can be used in monitoring technology of radioactive xenon, which could simplify the monitoring process. Applying new functional materials, the monitoring system will be smaller and lighter. So, study of highly selective functional material adsorbing xenon at room temperature has importment implications for monitoring radioactive xenon technology.