Catalytic mechanism of yavapaiite confined in interlayer space of graphite oxide in heterogeneous electro-Fenton oxidation.

Conventional iron-based catalysts are prone to aggregation and deactivation in the heterogeneous electro-Fenton (hetero-EF) process resulting in electrocatalytic activity reduction. Herein, a simple one-pot strategy using potassium ferrate (K2FeO4) as both oxidant and iron source was developed to synthesize a novel yavapaiite confined in graphite oxide (KFe(SO4)2-in-GO) nano-electrocatalyst. GO with spatial confinement effect and surface negativity could in-situ incorporate KFe(SO4)2 nanoparticles inside the interlayer space and inhibit the agglomeration. Three dimensional hetero-EF system with KFe(SO4)2-in-GO showed more than 97 % removals of organic pollutants (sulfamethoxazole, bisphenol A and 2,4-dichlorophenol) owing to synergistic effects of layered structure of GO and the matching crystal structure of KFe(SO4)2 and electric field, and exhibited high efficacy in removing rhodamine B (RhB) at a wide pH range of 3∼9 in the presence of various coexisting inorganic ions and humic acid. The specific energy consumption per unit COD mass of KFe(SO4)2-in-GO hetero-EF system was only 0.08163 kWh/gCOD. Compared with Fe3O4-in-GO, KFe(SO4)2-in-GO increased degradation reaction rate of RhB by 2.62 times due to its uniformly dispersed iron sites, which activated electro-generated H2O2 to convert to •OH by high charge transfer efficiency. Quenching experiments and electron paramagnetic resonance spectroscopy tests revealed that the surface-bound •OH dominated RhB degradation. Moreover, the adsorption energy and electron transfer process of H2O2 on KFe(SO4)2-in-GO were calculated via Density Functional Theory, which demonstrated that the surface-bound •OH generated on active iron sites could effectively react with RhB in confined space of GO interlayer. The covalent skeleton and spatial confinement effect of GO was confirmed to enhance the stability of KFe(SO4)2-in-GO. This study gives insights into the simple design of high-efficient confined electrocatalysts for the treatment of wastewater containing organic pollutants.