Fotokatalytický rozklad oxidu dusného v přítomnosti nanočástic ZnS imobilizovaných na montmorillonitu

Abstract

Diploma thesis is aimed on photocatalytic decomposition of nitrous oxide in presence of ZnS catalyst immobilized on montmorillonite (ZnS-MMT). The purpose of photocatalytic decomposition of nitrous oxide, one of the greenhouse gases, is his transformation to oxygen and nitrogen; both are natural compounds in the atmosphere. Nanoparticles of ZnS were prepared by precipitation in presence of cationactive surfactant and the nanosuspension was deposited on clay mineral montmorillonite. Prepared catalyst was characterized by atomic absorption spectroscopy, transmission electron microscopy and by measuring UV-Vis spectra. Photocatalytic decomposition of nitrous oxide was carried out in stirred batch reactor in presence of powder catalyst ZnS-MMT. 8 W Hg lamp with wavelength 254 nm was used and the lamp was placed into quartz glass tube. Optimal amount of used catalyst ZnS-MMT was experimentally determined from maximal conversion of N2O point of view. This amount (0.1 g catalyst) was used in all kinetic experiments. Conversion 78.8% after 24 hours of irradiation was reached during experimental study of photocatalytic decomposition of N2O in presence of nanoparticles of ZnS-MMT. Also influence of presence of water vapor and oxygen on photocatalytic decomposition of N2O was investigated. Presence of water vapor significantly decreased conversion of N2O (only 57.2%), which could be caused by its adsorption on catalyst’s surface and hence blocking active sites for adsorption of N2O. Adsorption of water can also lower penetration of light and hence lower efficiency of photocatalytic decomposition of N2O. On the other side presence of oxygen had positive influence on photocatalytic decomposition of N2O. Oxygen most likely reacted with evolved holes and formed radical •O- which reacted with N2O and formed nitrogen and oxygen. Evaluation of kinetic data confirmed assumption that photocatalytic decomposition of N2O corresponds to first order of reaction rate.