The Role of Hydroxyl Surface Groups on the Dechlorination Activity of Iron Bearing Nanoparticles

Dechlorination of groundwater contaminants by nano zero valent iron (nZVI) has been successfully utilized for a wide range of halogenated hydrocarbons. At the same time incorporation of noble metals such as Pd to nZVI has shown to result in a catalytic effect in the dechlorination reaction. Despite the extensive research to improve nZVI reactivity, 1,2-DCA remains recalcitrant to dechlorination by nZVI. These dechlorination processes are known to occur as a surface mediated reactions. However, a complete understanding of the surface composition and the role of the species present on the nZVI surface in the dechlorination adsorption/reaction mechanisms still needs to be achieved. -FeOOH, -Fe2O3, Fe2O3 are the most frequently observed species present in the surface of the nZVI particles. In this thesis, the mechanisms through which 1,2-DCA and TCE interact with these iron species are studied by means of in situ spectroscopic techniques. Experimental results demonstrate that surface hydroxyl groups play a critical role in the adsorption processes and that interaction of both 1,2 DCA and TCE with these hydroxyl groups results in the formation of an ethoxide surface complex. From temperature program experiments it was found that surface morphology, crystalline structure and surface speciation can lead to the existence of nonequivalent adsorption sites, with different chemical environments. This surface heterogeneity has a direct effect in the adsorption/reaction mechanisms, resulting in the formation of different observed desorption products. A reaction mechanism is proposed to rationalize all these observations