CHARACTERIZATION OF CERTAIN PHYSICAL PROPERTIES ON MODIFIED KAOLINITE-COUPLED CATALYSTS PREPARED WITH AG AND ZN IONS

Abstract

This study used kaolinite clay as a carrier and exchanged Ag+ and Zn2+ onto the kaolinite via ion exchange. The coupled kaolinite-Ag/Zn catalysts at the nanolevel were formed after surface modification. Various physicochemical experiments, such as Fourier-transform infrared spectroscopy (FT-IR) analysis, x-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) analysis, thermal analysis, and potentiometric titration analysis were conducted to further discuss the physicochemical properties of the kaolinite-Ag/Zn catalysts. 
 First, a function group analysis on the kaolinite clay conducted using a Fourier-transform infrared spectrometer showed many significant and complex wave crests in the following wavenumber sections of the fingerprint area: 415~600 cm-1 and 750~1170 cm-1; these represent strong bonds between impure silicates (Si-O) and silicates (O-Si-O) within the silicate mineral. The mineral structures of the kaolinite-Ag/Zn catalysts remained intact after being sintered at 350oC. In terms of the x-ray diffraction analysis, following high-temperature sintering a dehydration reaction occurred in the kaolinite-Ag/Zn catalysts. The spacing of layers was thereby narrowed to 0.7170 nm. Moreover, a TEM observation of the kaolinite-Ag/Zn catalysts after high-temperature sintering showed that the sizes of Ag+ and Zn2+ on the kaolinite-Ag/Zn catalysts were between 25 and 60 nm, respectively. This proves that with ion exchange, the kaolinite-Ag/Zn catalysts are at the nanolevel. Regarding thermal analysis, the kaolinite-Ag/Zn catalysts had endothermic peaks at 464oC, 527oC and 888oC, respectively and exothermic peaks at 585oC and 921oC, respectively. As for TGA weight loss, two pyrolysis temperatures were found: The first pyrolysis occurred at 464oC, where the weight loss was caused by oxidative pyrolysis. The second pyrolysis occurred at 775oC, where the TGA weight loss resulted from decomposition of the remaining organic (carbon-containing) compounds. Lastly, regarding potentiometric titration, there were two end points of the titration for the kaolinite-Ag/Zn catalysts, indicating that there are two different acidic function groups. The titration curves of these said end points were obviously affected by two ions, and these two end points of the titration were quite obvious. The intensities of the two acidic function groups were similar; consequently, there is an obvious two-stage dissociation in the titration curves.