3-methylaminopropylamine as a templating agent in the synthesis of phosphate-based inorganic polymers

Abstract

3-(Methylamino)propylamine (MPA) was studied as a structuredirecting agent (template) in the synthesis of open-framework phosphate-based materials. The influence of temperature, mole ratio of reactants, crystallization time and presence of fluoride ions on the crystallization of aluminophosphate, transition metal-substituted aluminophosphate (transition metal -Mn(II), Cr(III) and Co(II)) and zincophosphate was also investigated. MPA exhibited a templating role and in all the as-synthesized crystalline products, it is entrapped in an inorganic lattice interacting with the framework via hydrogen or/and electrostatic interactions. According to detailed thermal analysis, the type of interactions seems to be crucial for the thermal behavior of MPA and for the thermal stability of the organic-inorganic crystal system. Structural analysis suggested that the formed crystalline structures had no mutual structural analogy. This indicates that the precise role of the organic (guest) component in nucleation process for the open-framework phosphates (host) is very complex as is the nucleation process itself.Available online at shd.org.rs/JSCS/ 1894 JEVTIĆ, RAJIĆ and KAUČIČ late). Usually, different amines and/or quaternary ammonium cations exhibit template ability in the synthesis of metallophosphates. 1 It should be added that the relationship between the template and the crystal type of the formed metallophosphate has not yet been well established. 1 It is known that the organic template itself is not the sole factor involved in the structure-directing role. Namely, various other parameters also influence the crystallization process, such as the source of the inorganic components, pH, conditions of crystallization, etc. However, the presence of organic species in the crystallization process is crucial. Without the organics, a metallophosphate cannot be formed.The template species remain after crystallization in the lattice pores and their removal from the channels and cages is necessary in order to achieve lattice porosity. 2 The removal of the template is performed by a thermal treatment (calcination), usually in an air atmosphere at about 500 °C. The calcined product usually possesses molecular sieving, catalytic and/or adsorptive properties. 3,4 Moreover, in order to obtain novel materials with catalytic properties for specific reaction systems, as well as to obtain materials of desired selectivity, various investigations were directed towards transition metal substituted aluminophosphates. 5 Incorporation of transition metal cations in an aluminophosphate lattice at the aluminum or phosphorous crystallographic sites brings a charge into neutral aluminophosphate skeleton and greatly affects its catalytic and adsorptive properties. In addition, the use of fluoride ions in the synthesis of porous aluminophosphates led to the emergence of novel and zeolite-like aluminophosphate structures. As an example, an open-framework aluminophosphate with a chabazite structure can be obtained only if fluoride ions are present in the re...