Exploring Catalytic Traits of so4 2--Functionalized Iron Oxides Exploited to Decompose Aqueous Recalcitrant Pollutants

Abstract

Iron oxides are considered as ubiquitous yet valuable carriers of surface Fe2+ activators to excite H2O2, which results in the production of •OH used to decompose refractory contaminants present in H2O. To exploit catalytic nature provided by surface Fe2+ species, Fe2+ species can experience their modification by S to form S-doped iron oxide, Fe3S4, and Fe7S8, etc.1,2 For instance, we have synthesized Fe2O3 and have functionalized its surface using S species.2 The resulting S-doped Fe2O3 has manifested itself as an intriguing catalytic solid for H2O2 activation. This was because of its several benefits including 1) the incorporation of large amount of surface Fe2+ species used to cleave H2O2 via heterogeneous catalysis, 2) meso-porosity allowing for improved accessibility of H2O2 into surface Fe2+ species, and 3) chemical rigidity leading to minimized loss of Fe2+ species during H2O2 scission reactions.2 Nonetheless, surface of S-doped Fe2O3 isn't disclosed in two particular aspects of 1) H2O2 scission mechanism on S-modified Fe2+ species and 2) their catalytic functions. To answer these questions, we strategized the functionalization of Fe2O3 (pristine) surface with SO4 2- species at 300-600 °C to generate S300-S600 and investigated their surface properties using chemi-sorption/spectroscopy techniques. We then performed reaction runs under regulated environments, while using phenol as a model compound of recalcitrant compounds. Apparently, phenol degradation was directed by the characters of SO4 2- functionalities dispersed on Fe2O3 surface, whose features were markedly varied upon the change in the temperatures utilized to modify Fe2O3 surface with SO4 2- functionalities. 500 °C was required to degrade phenol in the most efficient manner among all SO4 2- functionalization temperatures studied, as showcased below. (XPHENOL and kAPP denote conversion of phenol and reaction rate constant, respectively.) In this presentation, we will address the answers to pivotal questions detailed above. In addition, we will also highlight our efforts for clarifying catalytic roles of surface SO4 2- functionalities via a series of kinetic assessment.