Hematite facet confined ferrous ions as high efficient Fenton catalysts to degrade organic contaminants by lowering H2O2 decomposition energetic span

In this study, we demonstrate that ferrous ions confined on the hematite facets can significantly promote the H 2 O 2 decomposition to produce •OH for more efficient organic contaminants degradation than the unconfined counterparts, while hematite nanorods with exposed {0   0   1} and {1   1   0} facets exhibit better confining effect than nanoplates with exposed {0   0   1} facets. Experimental results revealed that the H 2 O 2 decomposition efficiency of hematite facet confined ferrous ions was affected by the amount of surface confined ferrous ions, and also governed by the binding mode of ferrous ions on the hematite facets. We interestingly found that the polar {1   1   0} facets could confine ferrous ions of higher density with a five-coordination binding mode and thus lower the H 2 O 2 decomposition energetic span more efficiently than the nonpolar {0   0   1} facets, which confined ferrous ions with a six-coordination binding mode. The specific surface area normalized •OH formation rate constants were, respectively, 5.50   ×   10 −3 and 1.04   ×   10 −2   s −1 for hematite nanoplates and nanorods confined ferrous ions, which were 1.2 and 2.2 times that (4.75   ×   10 −3   s −1 ) of the unconfined counterpart. Moreover, rhodamine B could be efficiently degraded in the presence of hematite (0.4   g   L −1 ), Fe 2+ (5.0   ×   10 −5   mol   L −1 ) and H 2 O 2 (5.0   ×   10 −5   mol   L −1 ) at pH 4.7, along with 23.6% and 72.5% of H 2 O 2 consumption efficiencies for hematite nanoplates and nanorods, respectively. Meanwhile, 6.6% and 11.8% of nitrogen in rhodamine B were converted to NO 3 − in the hematite nanoplates and nanorods confined ferrous ions Fenton systems, respectively. It was found that N -deethylation, destruction of chromophores, opening-ring and mineralization occurred during the confined ferrous Fenton rhodamine B oxidation process. This study can deepen our understanding on the enhanced reactivity of ferrous ions bound on the surface of iron oxides, and also shed light on the design of high efficient heterogeneous Fenton catalysts.