Font Size: a A A

Ionothermal Synthesis, Structure Control, And Properties Of Metal Phosphate Framework Materials

Posted on:2011-03-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:L LiuFull Text:PDF
GTID:1101360305473968Subject:Chemical Engineering and Technology
Abstract/Summary:PDF Full Text Request
Inorganic microporous crystal materials play important roles in the chemical industry as adsorption and catalytic materials. Their crystal structure, chemical composition, crystal size, and assembly are closely associated with their applied properties. To meet the need for excellent materials for industrial applications, the rational design and control of their crystal structure and physicochemical properties have become key topics in the fields of materials science and chemical engineering. The solvent and the organic template-agent are two important factors in the synthetic chemistry of inorganic porous materials. Given this, there is a strong need for designable solvents and controllable template-agents in the rational design and synthesis of novel inorganic porous materials.Ionic liquids as reaction media for green and clean technology and environment-friendly catalytic systems have received increasing attention in recent years. The species and structure of ionic liquids are very rich and dynamic; their properties can be adjusted by designing and changing the structure and component of the anions and cations. This is why ionic liquids are called designable solvents. In recent years, ionic liquids have been widely applied in organic reactions, and they have had promising applications in the synthesis of inorganic materials. The novel ionothermal synthesis, which uses ionic liquid as the solvent and template agent, has interesting features and potential advantages over the traditional solvothermal synthesis for the preparation of novel aluminophosphates. Ionic liquids with rich species and designable properties not only provide a new approach to synthesize novel inorganic microporous materials but also offer additional methods to adjust effectively the physicochemical properties of the target products.In this paper, a series of novel ionic liquids (ionic eutectic mixture) was selected and designed with the aim to synthesize novel metal phosphates. The ionic liquids were employed as solvent and source of the template or the structure-directing agent using an emerging ionothermal approach. The involved synthetic systems mainly included urea-based derivative-, carboxylic acid-, and alcohol-quaternary ammonium salt ionic liquids. Three synthetic systems and ionothermal synthetic processes were examined to discuss the solvent effect and template role of the ionic liquid. The synthetic route was also optimized and extended to investigate the effect of the addition of an organic base or inorganic cation to the initial reaction system on the resulting metal phosphate framework. The crystal structures and physicochemical properties of the obtained products were determined and characterized by single and powder diffraction technology and the modern instrument analytical method, respectively. The catalytic performance of transition metal phosphate materials in cyclohexane oxidation and the tribological properties of layered zirconium phosphate as a solid lubricant additive in miner oil were also studied. The main findings are as follows:1. The possibility of the synthesis of zirconium phosphate and zinc phosphate materials was explored in eutectic mixtures composed of urea and different quaternary ammonium salts. Urea-based components were found to undergo thermal decomposition easily during the reaction process. Decomposition products (ammonium) have a stronger template role, and quaternary ammonium cations do not affect the final products. The decomposition of urea-based compounds can be controlled, so a series of urea-based derivatives with symmetrical structure was designed, such as 1,3-dimethyl urea, 1,3-diethyl urea and ethylene urea as deep eutectic mixtures with quaternary ammonium halides. Many novel zirconium phosphate and zinc phosphate materials were successfully synthesized by utilizing the thermolysis products of urea-based compounds (methylamine, ethylamine, and ethylene diamine). The results show that template in situ generation results in a slow cumulative effect, which not only easily induces a novel structure but also contributes to the formation of a large single crystal. This crystal is beneficial to structure determination using single crystal diffraction data.2. Quaternary ammonium halide is an excellent template for inorganic pore materials. However, quaternary ammonium cation performs poorly in its template role in urea-based ionic liquid. In this paper, urea was replaced by carboxylic acid to form ionic liquid with quaternary ammonium salts, in which the carboxylic acid component cannot act as a template. This methodology addresses the template competition between the"byproduct"and quaternary ammonium cations, as well as facilitates the demonstration of the template role of quaternary ammonium cation. In carboxylic acid-based ionic liquids, several zirconium phosphates templated on quaternary ammonium cation were synthesized by changing various quaternary ammonium halides. Quaternary ammonium salts with a long alkyl chain (Cn, n≥3) cannot exhibit their template capability in the zirconium phosphate framework, thereby only leading to the layeredα-ZrP phase. Further, carboxylic acid-based ionic liquids are not suitable for the synthesis of alumino- or zincophosphates due to their strong acidity, with the resulting products being dense tridymite andα-hopeite phase, respectively.3. For ionic eutectic mixtures, in order for the template role of quaternary ammonium cations to be exhibited, the systems should have appropriate acid-base properties and should also avoid the introduction of extra thermolysis products as potential template for metal phosphate framework. In this paper, a class of novel ionic liquids composed of alcohol and quaternary ammonium halide were designed. They cannot contribute decomposition"byproducts"as templates to the reaction, and they also possess appropriate acid-base properties that do not need adjustment with the addition of organic amine. Thus, the template competition between the undesired organic amines and the quaternary ammonium cations can be eliminated. Therefore, the quaternary ammonium cation components in the eutectic mixtures can now be controlled to exhibit their structure directing effect. By designing the structure of the quaternary ammonium halides, five different aluminophosphates have been synthesized with the AFI, ZON, ERI, AWW, and CHA frameworks, respectively.4. In the case of urea-based derivative/quaternary ammonium salt ionic liquids, the introduction of a small amount of sodium ions can result in a co-template role with the in situ thermolysis product for metal phosphate frameworks. In this work, the first metal phosphate analogue of the zeolite Na-J (framework type JBW) was reported in a eutectic mixture with a small amount of sodium ions. This result cannot be achieved using conventional solvothermal synthesis. Interestingly, the sodium ions obviously improved the thermal stability of the framework structure, which is beneficial to their practical application as catalytic and adsorption materials.5. The ionic liquid analogue composed of oxalic acid and tetrapropylammonium bromide (TPABr) exhibit a unique solvent effect for the zinc phosphate framework. For the oxalic acid/TPABr solvent in the presence of triethanolamine (TEA), a novel layered zinc phosphate [N2C6H12]2[Zn7H3(HPO4-x)5(PO4)3]?H2O with unique 10-member ring ellipsoidal channels running perpendicular to its inorganic layers has been synthesized via in situ generation of 1,4-diazabicyclo[2.2.2] octane from TEA in an ionothermal reaction. Guanidine phosphate was again used as the template agent and phosphorus source in an oxalic/TPABr and water reaction medium, which produced two new zincophosphates with different structures. These results also proved the unique solvent effect of the oxalic acid/TPABr ionic liquid.6. Functional nitrogen containing heterocyclics cannot only produce novel zirconium phosphate structures but also deliver their functionality to the resulting target products as guest molecules. In this paper, two novel photoluminescent zirconium phosphate compounds, |(C9H8N)4(H2O)4|[Zr8 -P12O40(OH)8F8] and |(C9H8N)2|[Zr2P2O6(OH)4F4], have been hydrothermally synthesized using nitrogen containing the heterocyclics of quinoline fluorescent probes. Interestingly, the former has a unique layered structure, whereas the latter has a chain structure with an unusual Zr/P ratio of 1. The application of a novel technical method involving a charge-flipping algorithm successfully determined the crystal structure of the zirconium phosphate powder samples, which addressed the difficult structure determination process for a non-single crystal.7. The selective oxidation of cyclohexane to yield cyclohexanol (-ol), cyclohexanone (-one), and adipic acid has an important industrial significance in the production of Nylon-6 polymers. In this work, the catalytic performance of some transition metal ions substituted aluminophosphates and zirconium phosphates in cyclohexane oxidation was examined. For MeAPO-5 and MeAPO-11(Me=Co, Mn, Cr) containing the identical metal ion, compared with MeAPO-11 that has a small pore size (10-ring), MeAPO-5 molecular sieves with a large pore size (12-ring) exhibit better catalytic performance and selectivity for cyclohexanol and cyclohexanone (denoted as KA oil) but lower selectivity for adipic acid. Among MeAPO-n molecular sieves, CoAPO-5 is the best catalyst for the production of KA oil. The conversion ratio for cyclohexane at 120 oC for 15 h can reach 16.3%, and the selectivity for KA oil is 77.8%, with the ratio between -one and -ol at 3.25. Cyclohexane oxidation on MeAPO-n proceeds with a free radical mechanism. Notably, compared with MeAPO-n materials, microporous zirconium phosphate exhibits exceptional catalytic performance, with a cyclohexane conversion ratio of 32% and a selectivity of 90% for KA oil, with the ratio between -one and -ol at 11.9. The catalytic mecahnism of ZrPO material is still under investigation, so definitive conclusions cannot be made at this time.8. Solid lubricants as a class of important materials in high-technology fields (e.g., aerospace, nuclear energy, etc.) can effectively reduce the friction and wear in severe conditions such as ultra-high vacuum, strong radiation, and high load. Layered zirconium phosphates have an inorganic layered structure similar to conventional lubricant additives, so the tribological properties of layered zirconium phosphates as additives in lubricant oil were examined. Interestingly,α-ZrP and novel ZrPO-DES6 materials exhibit excellent friction behaviors with a higher load-carrying (PB) and anti-wear capacity compared with typical lubricant additives such as MoS2 and graphite. After 1.0 wt%α-ZrP was added to 100SN base oil, the PB value of the base oil was improved by 27.2%, and the wear scar diameter decreased from 0.58 to 0.33 mm.
Keywords/Search Tags:metal phosphate, ionothermal synthesis, ionic liquid, eutectic mixture, cyclohexane oxidation, lubricant additive
PDF Full Text Request
Related items