Research On The Adsorption Of ZIF-8

Zeolitic Imidazolate Frameworks (ZIFs), with high thermal stability, large Langmuir surface area, and volume, flexible structure, rich functional. ZIF-8 is a sodalite model of ZIFs with microporous structure material, which has a large specific surface area, pore size controllable and good hydrothermal stability etc. This research is on the study of the adsorption performance of ZIF-8 which is one of the zeolite imidazole ester structure material of metal organic framework.This paper studies the influence on the adsorption properties at different temperature over ZIF-8, the Langmuir adsorption isotherm show that:the adsorption amount was increased along with the increase of temperature, the adsorption process was an endothermic adsorption process. The effect of concentration on the adsorption properties, the conclusion is that, BTEXs with small pore volume can be more adsorbed on the adsorbent; The effect of adsorption time and the adsorption kinetics, the adsorption speed is much faster at the beginning of the contact time, then reached a balance, which may be attributed to the adsorption at the beginning has a large number of available adsorption activity sites, but with the increase of the adsorption time, the adsorption activity was reduced and the adsorption activity sites reached saturation. The pseudo-second-order model can explain the adsorptive dynamics with the change of adsorption time, the adsorption kinetic constants (k2) and correlation coefficient (r2) show that the kinetic constants of BTEXs integrated afore-mentioned available, the shape and size of BTEXs molecular also has an important influence on the adsorption; This paper also study the effect of PH on the adsorption, the experimental data shows that, the adsorption amount into a decreasing trend with the increase of pH, which may be attributed to the electrostatic interaction mechanism is not the mainly effect of the adsorption over ZIF-8, the aromatic imidazole ester functional groups on benzene ring, and π-π bond interaction should be the main mechanism. The shape and structure effect on the adsorption of ZIF-8 has been studied, the experimental data shows that the BTEXs with small molecular diameter such as benzene, toluene, ethylbenzene, p-xylene has higher adsorption capacity than the large molecular structure and o-xylene and m-xylene.This paper also makes a dynamic research on the adsorption of hydrocarbon gases over ZIF-8 and ST-ZIF-8 at different pressure and temperature conditions, the adsorption amount of methane, ethane, ethylene, propane, propylene. The dynamic adsorption experiment show that the dead volume void and sample within the pore system of the excess adsorption accumulation within the system has small influence on the accurate calculation, so it can be ignored, but, through experiments, the hydrocarbon gases accumulation of dead volume pipe valve within a larger amount of influence on the adsorption amount, must be ruled out. The adsorption capacity on ST-ZIF-8 less than ZIF-8 shows that the auxiliaries of the structure in the forming process may lead to the pore blockage. The experiments show that the adsorption of propylene was greater than that of ethylene, which shows that it is physical adsorption between the olefin and the adsorbent.This paper also carried on the adsorption of ammonia nitrogen of water pollutant over ZIF-8, the experiment proves that ZIF-8 is suitable for the adsorption of low concentration of NH4+, consider the follow-up was applied to the treatment of ammonia nitrogen in water pollutants.