Investigation Of Mass Changes In The Surface Of Metal Organic Frameworks Films By A Piezoelectric Sensor

Metal–organic frameworks (MOFs), a new class of hybrid porous solids, aresynthesized by coupling inorganic clusters with organic “linker” groups, yielding rigidbut open frameworks that can accommodate guest molecules. Various structures ofMOFs materials are a rapidly developing with immense potential in the areas of gasstorage, molecular separation, catalysis, and sensing, among many others. The cagestructure in MOFs can capture and store gases selectively and effectively. Theadsprption characteristics of MOFs to gases is an active research area.Quartz crystal microbalance (QCM) sensors are sensitive to mass change at thesensing surface. They allow on-line and direct detection of label-free adsorbates, thussaving time and providing the opportunity to study the kinetics of the adsorptionprocess. In this thesis，the adsorption kinetics of volatile organic compounds over twoCu-MOFs a films were investigated by a QCM technique. Details are listed below.1. Determination the adsorption characteristics of metal-organic framework filmby piezoelectric sensor methodThe adsorption kinetics of chloroform over a metal-organic framework film of[Cu(C24H22N4O3)]·CH2Cl2(Cu-MOFs) was investigated by a QCM technique. Thechange in the mass of Cu-MOFs film during the adsorption and desorption processeswas monitored in real time by the frequency shift of QCM. The adsorption processfollows closely the pseudo-second-order kinetic model. The adsorption rates at vaporpressure of chloroform are1.4-2.1times of that in the presence of N2at atmosphericpressure. More than half of chloroform adsorbed over Cu-MOFs film is reversiblewith respect to the dilution of chloroform concentration in gas phase. The adsorptionisotherms are fitted well by the Langmuir model. For chloroform adsorbed at its vaporpressure and in N2of1atm over Cu-MOFs film with thickness of0.337m (25C), the adsorption equilibrium constants are6.47and3.93L/g, the maximum adsorptioncapacities are27.2and24.7g/cm2.2. A quartz crystal microbalance study of the adsorption of1,2-dichloroethaneon metal organic frameworks [Cu(C24H22N4O3)]·CH2Cl2film.The adsorption kinetics of1,2-dichloroethane (DCE) on Cu-MOF film weremonitored in real time by a QCM technique. It is shown that the adsorption processfollows closely the pseudo-second-order kinetic model. With increasing amount ofDCE added, the adsorption rate constant decreases while the initial adsorption rateincreases. More than half of DCE adsorbed on Cu-MOF film is reversible with respectto the concentration dilution in gas phase. The adsorption isotherms are fitted well bythe Langmuir model. The pre-adsorbed N2at atmospheric pressure on Cu-MOF filmreduces slightly the adsorption rate constant, equilibrium constant and capacity ofDCE. The adsorption rates at vapor pressure of DCE are1.2–1.8times of those in thepresence of N2at atmospheric pressure. With increasing film thickness, the adsorptionrate constant and mass adsorbed per unit film mass decreased. For DCE adsorbed atits vapor pressure (25°C) on Cu-MOF film with thickness of0.169,0.564and1.12μm, the adsorption equilibrium constants are716.5,695.5and649.2L/mol, and thesaturation adsorption capacities are6.537,5.742and5.193mmol/g, respectively. Withincreasing temperature, the adsorption rate constant increases, but the mass of DCEadsorbed on the adsorption equilibrium constant and capacity decreases.3. Monitor the grow process of ZIF-8film and adsorption process of DCM andn-hexane on the film.By using a solution assembly of coordination method, a MOFs film ofZIF-8was grown on the surface of QCM sensor from the mixture of Zn(NO3)2and2-methylimidazole. The grow kinetics of ZIF-8film and adsorption process of DCMand N-hexane on the film were monitored in real time by a QCM technique. Theinfluence of solvent, concentration and temperature on the film and film adsorptionperformance was investigated. The assembly rate of ZIF-8film in the solvent is inthe order of methanol> ethanol>water and decreased with the time. The duration of assembly in the solvent is in the order of water> ethanol> methanol. The ZIF-8filmfabricated in the solvent of methanol shows higher adsorption capacity to n-hexaneand DCE than the films fabricated in the solvent of ethanol or water. Under theexperimental conditions used, the adsorption kinetics of n-hexane and DCE onto ZIF-8film were well described by a pseudo-second-order kinetic model. The initialadsorption rate of DCM is higher than that of n-hexane. Their adsorption isothermfollow the Langmuir model with the adsorption equilibrium constants of8.36104and4.67104L/mol, and the saturation adsorption capacities of171.1and364.3mg/m2for n-hexane and DCE, respectively(h=0.708m). For the adsorption in the mixture ofn-hexane and DCE, part of DCE adsorbed previously onto ZIF-8film was desorbed byn-hexane in a competitive adsorption mechanism.