Application of Spectroscopy Techniques to Measure the Adsorption and Chemical Reaction of Molecule Between Liquid and Solid Phase

• Main Authors: Hsiu-Fang Fan, 范秀芳
• Other Authors: 林金全
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/09233429887689827105

博士 === 國立臺灣大學 === 化學研究所 === 94 === Part I (A) By using Fourier transform near infrared (NIR) absorption spectroscopy with the aid of a kinetic model, we have investigated the conversion of quadricyclane to norbornadiene as catalyzed by anhydrous CuSO4 and SnCl2 in chloroform. The reaction mixture is kept still to avoid the effect of sample heterogeneity. The NIR absorption spectra are acquired, at a position 2 mm above the catalyst surface, at 30-second intervals for a reaction period of 4 hours. The related concentrations of quadricyclane and norbornadiene in the temporal evolution are determined with the analysis of partial least squares. The evolution of quadricyclane, as numerically solved from the model, is expected to describe its behavior more accurately in the catalytic system than that obtained previously. In addition to the isomerization rate, the kinetic model takes into account the contribution of diffusion motion. The diffusion coefficients of quadricyclane can be explicitly determined to be 3.8x10-5 cm2s-1 in chloroform and 1.14 x10-5 and 2.85x10-6 cm2s-1 inside the CuSO4 and SnCl2 stacks, respectively. The diffusion motion is slowed down inside the solid stacks and thus the molecular mechanism cannot be suitable for this system. Given the diffusion coefficients, the pseudo-first order depletion rate constants are evaluated to be 3.7x10-3 and 3.8x10-3 s-1 for CuSO4 and SnCl2, respectively. The corresponding second-order depletion rate constant is determined to be 6.6x10-6 and 2.0x 10-6 s-1M-1 by considering the density and pore size of the catalyst; M denotes the total catalyst surface per unit effective volume of solvent. The reaction rates are found to be a factor of two slower as compared with others obtained in a continuously stirred solution. In the surface-mediated reaction, the catalytic isomerization is subjected to a one-site coordination (1:1 complex) between the reactant and the catalyst. Nevertheless, a two-site coordinated reaction cannot be justified unless a pore size dependence of the depletion rate is discerned. (B) The related concentrations of quadricyclane and norbornadiene in the temporal evolution are determined with the analysis of partial least squares. The concentration of quadricyclane, as numerically solved from the model, is expected to describe its behavior more accurately in the catalytic system than that obtained previously. In addition to the isomerization rate, the kinetic model takes into account the contribution of diffusion motion. In order to look into the motion inside the catalyst more accurately, the simulation model is developed into two-dimensional form. The branch model can describe the distribution of catalyst and solvent within catalyst layer. Under this model, the simulation result is as the same as that under one-dimensional model. In addition to branch model, another two-dimensional model that the distribution of catalyst and solvent within catalyst layer is at random is also built. Although the distribution within catalyst layer much conforms to the real condition, the problem of time and money consuming is much serious. Under these considerations, we adapt the branch model to simulate the experiment date in order to evaluate the diffusion coefficient, which is set the same both in solvent layer and catalyst layer. In the surface-mediated reaction, the catalytic isomerization is subjected to a one-site coordination (1:1 complex) between the reactant and the catalyst. Nevertheless, a two-site coordinated reaction cannot be justified unless a pore size dependence of the depletion rate is discerned. From the following experiments, we plot the pseudo-first order depletion rate constants vice the 6Wt/daVeff. The second-order depletion rate constant 8.47x10-6 s-1M-1 and third-order depletion rate constant2.19x10-8 s-1M-2 could be evaluated. When the ln(k) is plotted vice 1/RT, the slope is . Then the activation energy is acquired. The activation energy of one-site path is calculated to be 24.8 kJ/mol and that of two-site path is 286.2 kJ/mol. The value is assumed to be exact right because we get the almost the same value through another procedure. Part II (A) An evanescent wave cavity ring down absorption spectroscopy is designed to measure the thermodynamic properties on the surface adsorption. Neutral trans-4-[4-(dibutylamino)-styryl]-1-(3-sulfopropyl) -pyridinum(DP) and charged trans-4-[4-(dibutylamino)styryl]-1-methyl pyridinium iodide (DMP+I) as adsorbates are flowed through the CH3CN/fused silica interface. The surface density of adsorption at the interface is determined by measured absorbance. The concentration dependence of the surface density may be characterized with Langmuir isotherm model. The fit to the adsorption measurements at the interface yields saturated surface density, equilibrium constant and free energy of adsorption to be 7.0x10^13 cm-2, 1.3x10^4 M-1, and -23.5kJ/mol, respectively, for DP and 8.9x10^12cm-2,2.6x10^4 M-1, and -25.2kJ/mol for DMP+I. The DP is adsorbed to the SiOH sites by forming hydrogen bond, while the DMP+ cation is bound to the SiO- sites by electrostatic attraction. The force variety may be verified by addition of triethylamine(TEA), which is competitive with DP for the silanol site. (B) Combination of evanescent wave cavity ring down and dichroism absorption technique is a good way to probe the orientation of adsorbed molecule on interface. Crystal violet which has strong absorbance at 600nm is chosen to be measured in this experimental setup. The nearly flat structure and bulky size makes itself a good surface-geometry probe. The binding phenomenon of crystal violet on CH3CN/ fused silica interface could be defined into two types which could be approved by studying the adsorption plot. The fit to the adsorption measurements at the interface yields equilibrium constant and free energy of adsorption to be 1.7x10^5 M-1, and -30.1kJ/mol, respectively, for CV+ and type I silanol site and 1.2x10^3 M-1, and -17.9kJ/mol for CV+ and type II silanol site. By analyzing the tilt angle plot, the adsorption between CV+ and type I site could be said that the CV+ approach the type I SiO- freely and randomly because the average tilt angle reaches magic angle~35.3 degree. As the concentration increases, the tilt angle increases. It means that CV+ would get closer and closer to the surface as the surface density increases. This trend is seen both on CH3CN/fused silica and thin film/fused silica conditions. (C) Using Double layer model to acquire the adsorption phenomenon of R610 on water/fused silica surface has been done. The adsorption equilibrium constants are 1.3x104±8.4x102, 6.3x103±7.9x102 and 2.6x102±8.2x101 for R610 neutral form, R610+ charged form and Na+, irrespectively. By using double layer model, the information for both type of R610 molecule on the silica surface could be solved. Part III The FCS system is verified under our experimental setup by using R6G and Cy5. It is checked by acquired the FCS at fast time scale and slow time scale. The reasonable results have been acquired and compared with the theoretical value and the results from other literatures. In order to acquire high qualified FCS spectrum, the alignment and the excitation power should be optimized to prevent the misinterpretation. In our experimental setup with 532nm excitation light source, 1.25 oil objective and 63 um optical fiber and R6G as analyst, the optimized pump energy is about 60uW in order to get the best signal to noise ratio and better qualified FCS spectrum. The instrumental parameters under above experimental condition are 3.88 and 4.63 for 532nm and 630nm, irrespectively. For further experiment, the instrumental parameter should be fixed in order to acquire the diffusion time or bunching time of analyst for doing further studies.