Synthesis And Modification Of Microporous Materials And Study Of Their Cation Exchange Capability

Inorganic microporous materials with controlled pore-size distribution are very attractive for wide range of applications, such as cation exchange, catalysis and adsorption, etc. Zeolite is the most important family of microporous materials, which is being applied to more and more areas. However, the existing preparation technologies for zeolites with high cost and complicated process, can't meet the demand of social development. So wise use of the abundant natural zeolites has great practical meaning. In addition, the synthesis of organic templated metal phosphates with various open frameworks is also an active area of microporous materials.Nature zeolites mined are abundant in the world, but they are commercially low in price due to the exploitation mostly as raw materials. Generally, natural zeolite deposits have high Si/Al ratio and contain quite a few impurities. These factors greatly reduce their cation exchange capacity (CEC), and limit their application to some high-value areas, like environment protection. The conventional methods of pretreating natural zeolites are heat activation and cation exchange. But these methods can't remove the impurities or change the frameworks of materials, so the CEC is slightly increased.In this paper, for the first time, we transformed the low-grade Chinese natural clinoptilolite from Jinyun to high capacity cation exchangers by hydrothermal reaction with or without fusion with sodium hydroxide. The characteristics of the products depend greatly on the reaction conditions. By the direct hydrothermal treatment, a product with higher CEC (231 meq/100g) can be formed, in which zeolite Na-P coexists with quartz. However, the quartz can't be completely removed. By the hydrothermal treatment with fusion, high purity of Na-Y, Na-P or analcime is selectively synthesized. Both Na-Y and Na-P are high capacity cation exchangers, and their CEC are 275 and 355 meq/100g, respectively. These values are much higher than the CEC of natural clinoptilolite (97 meq/100g). The products have been identified by X-ray diffraction, and characterized by IR, SEM and ICP, etc.When the natural clinoptilolite was treated by fusion with NaOH prior to hydrothermal reaction, there was an interesting phenomenon of crystal transformation in the hydrothermal process. At first, Na-Y was formed, and then it changed to Na-P. However, the transformation didn't stop, and the products transformed between Na-Y and Na-P. Gradually, Na-Y appeared more and more rarely, and the final product was zeolite Na-P. It's a kind of direct crystal transformation, and the compositions in solution participate in the reaction course. The transformation indicates that Na-P is thermodynamically more stable.By the same treatment methods, the natural mordenite from Jinyun was also successfully changed to high purity of Na-P. However, Na-Y wasn't found in the products.Secondly, the uptakes of NH₄⁺ onto the natural clinoptilolite and modified zeolites (Na-Y and Na-P) have been investigated. The thermodynamic parameters showed that the exchange reactions were all exothermic and spontaneous processes with negative entropies. The equilibrium studies indicated that the Freundlich model provides a more consistent fit to the data compared with the Langmuir model.The results also showed that the ammonium exchange capability of modified zeolites was much higher than that of the natural zeolite. The two modified zeolites have faster exchange rate, higher exchange amounts and better regeneration ability. The ammonium removal efficiencies for the modified zeolites were above 90% at the ammonium initial concentrations less than 100 mg NH₄⁺/g. It seemed that they were fit for the further treatment of waters polluted with ammonium.In addition, the influence of other cations (K⁺, Ca²⁺ and Mg²⁺) present in water upon the ammonia uptake was also investigated. In each case, a significant reduction in ammonium removal could be observed. The effects suggest the orders of preference: K⁺ > Ca²⁺ > Mg²⁺ for natural clinoptilolite, and Ca²⁺> K⁺ > Mg²⁺ for the modified zeolites. These orders were determined by electrostatic free energy and cation-hydration free energy.Thirdly, a new zinc-cobalt phosphate, [NH(CH₂)₂NH₂(CH₂)₂NH₃]²⁺[Zn_5-xCo_x (PO₄)₄]^2-(x≈0.96), in which the structure-directing organic amine acts as a ligand, has been synthesized hydrothermally. It consists of a network of MO4, PO4 and MO₃N (M = Zn, Co) moieties, leading to formation of three-dimensional structure with a 10-membered channel along b axis.Finally, A new metal-organic coordination polymer [Zn₂ (C₂O₄)₂(C₃N₂H₄)₂]_n has been hydrothermally synthesized. The compound has a 2D network, which consists of infinite zinc (II) oxalate chains connected to each other by three-coordinated oxygen atoms. Furthermore, there are two coordination modes of oxalate to zinc ions: chelate bis-bidentate and chelate/bridging bis-bidentate in the compound, and the latter is rare among zinc oxalates.