|
چکیده
|
Zeolites are hydrated aluminosilicates with channels and cages which are occupied by exchangeable active metal ions. Their unique properties such as uniform pore size, acidic properties, thermal stability, mobile extra cation, hydrophilicity and hydrophobicity lead to the use of these compounds as catalysts, water purifiers, absorbents and in agriculture. Review on the previous article researches give very good results in order to have targeted research on the structure of zeolites, which will be briefly presented in this poster [1]. Zeolite surface chemistry with using BET and BJH isotherms, and loop of hysteresis diagrams can possibly determine the surface area and volume pore and type of adsorption -desorption on the zeolite. Kinetic factors including time, temperature and pH of the solution have been investigated abundantly in the literature for different compounds, which show that absorption has direct relation with time, pH and opposite relation with temperature, while crystallization increases with increasing temperature and time in the hydrothermal process [2]. The study of the thermodynamic parameters including enthalpy, heat content, heat capacity, Gibbs energy and entropy also shows that the absorption process on the zeolite is exothermic or endothermic, and obtained higher activation energy is the sign of the stronger absorption of ions on the zeolite. In order to determining the surface energy, many models have been introduced like Doris and Gray's method. Various molecular models such as Kisliev, Vander Waals, Redlich Wang, etc., for measuring the acidic and basic characteristic of the zeolite have been carried out and the effect of solvent polarity on the acidic or amphoteric properties was investigated and acidic constant has been estimated. In order to separate the mixture of gases, especially the purification of gases in binary mixtures, several models have been introduced and the interaction between the adsorbed gases on the zeolite at different pressures has been investigated by using the Longmuir model, extended-Long Muir, Toth and Sip [3]. In all these cases, the combination of kinetics and thermodynamics of surface and Langmuir, Freundlich Isotherms and hysteresis diagrams and the multi-layer absorption process are determining the type and porosity of the zeolite [4]
|